Hoover Powerplant Modification Environmental Impact Statement

HOOVER POWERPLANT MODIFICATION ENVIRONMENTAL IMPACT STATEMENT

Department of the Interior Bureau of Reclamation

OCT 2 9 MID o U.& FISH & WILDLIFE SERVICE ES FIELD OFFICE. PHOENIX, AZ Surge Tank A8 .4 A9 Replacement 500 -MW Underground Powerhouse

500 - MW Surface Powerhouse •

Aerial photograph of the location of the proposed alternatives for the Hoover Powerplant Modification Project, Hoover Dam and Powerplant, Arizona-Nevada.

DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION LOWER COLORADO REGION

DRAFT ENVIRONMENTAL IMPACT STATEMENT

HOOVER POWERPLANT MODIFICATION - CLARK COUNTY, NEVADA MOHAVE COUNTY, ARIZONA

ABSTRACT

The Bureau of Reclamation proposes to increase the generating capacity of the Hoover Dam and Powerplant by installing additional generators. The powerplant would be increased by either 260 or 500 megawatts for a total plant capacity of 2,060 or 2,300 megawatts. The environmental impacts associated with the proposed project are primarily due to increases in water velocity, which could reduce algae production, and increases in the weekly water level fluctuations on Lake Mohave, which could reduce the fishery. No endangered or threatened species would be jeopardized. There will be no cumulative or synergistic effects to the Colorado River Basin.

This environmental impact statement is intended to serve environmental review and consultation requirement pursuant to:

Executive Order 11988 (Floodplain Management) Executive Order 11990 (Wetlands Protection) Clean Water Act of 1977 (Section 404 r) Rivers and Habors Act of 1899 (Section 10)

For Further Information Contact: Mr. Gary L. Bryant (Environmental) P.O. Box 427 Boulder City, Nevada 89005 Phone: (702) 293-8609

Mr. Martin P. Einert (Engineering) Same Address Phone: (702) 293-8510

Comments should be received by: AUG 04 1983 Statement Number: TNT 1)-eg 83 -

Filing Date: MAY G 4 19,';3--

SUMMARY

This summarizes the environmental effects and impacts of increasing the peaking capacity of Hoover Dam and Powerplant by constructing additional generating units. The location of the project and the general layout are shown in the frontispiece location map and photograph.

Coordination as required by the Endangered Species Act and the Fish and Wildlife Coordination Act was completed on December 30, 1980, and April 1981, respectively. However, developments in the engineering and economic aspects of the project changed the plant operation from that which was originally proposed and on which the coordination was based. We, therefore, reinitiated coordination under the above two acts on October 16, 1981. Coordination on the new developments was completed April 1, 1982 for the Endangered Species Act and April 7, 1982 for the Fish and Wildlife Coordination Act. Discussions relative to the above acts can be found in Chapter III.B.7. and Attachment B, respectively.

The Federal Water Pollution Control Act Amendments of 1972 (P.L. 92-500) require a Corps of Engineers permit, under Section 404 of the act, for the discharge of dredged or fill material into navigable waters. The Clean Water Act of 1977 amended Section 404 by adding subsection (r) which provides a procedure by which Federal water projects may be exempted from securing a Corps of Engineers permit. Accordingly, it is intended that this environmental impact statement be used to qualify for exemption to the 404 permit process under Section 404 (r), of P.L. 92-E00, as amended. Impact discussions relative to the permit are found in Chapters II.B.1.a. and b. (Cofferdam), III.B.4. (Geology), III.C.4 (Geology), III.C.5.g.(2) (Lake Mohave), and Attachment E.

This project would have no cumulative or synergistic effects on the Colorado River Basin (see Chapter III.C.14.; D.14.; E.13.; and F.12).

Background

Hoover Dam and Powerplant were designed and constructed by the Bureau of Reclamation (Bureau) pursuant to the Boulder Canyon Project Act of December 21, 1928. The dam was constructed to protect the low lying valleys of Arizona and southern California from the yearly threat of flood, to store annual spring runoff needed for later use, and to generate power. The construction of the dam began in 1931 and was completed in 1935 with the first commercial energy generated in 1937.

In addition to the Nation's largest manmade lake, Lake Mead, Hoover Dam has one of the largest hydroelectric powerplants in the world with an installed capacity of about 1,340 megawatts (MW) provided by 17 generating units and two station service units. When the water stored in Lake Mead is released, it passes through Hoover's turbines and generates low-cost hydroelectric energy, which Western Area Power Administration (Western) markets. Hoover Dam energy is SUMMARY

sold to both public and private agencies under contracts and is presently allocated to the States of Arizona and Nevada, and in California to the Metropolitan Water District of Southern California, City of Burbank, City of Glendale, City of Pasadena, City of Los Angeles, and Southern California Edison Company.

The Bureau, as part of a routine replacement and maintenance program, is in the process of overhauling and replacing worn generator windings and turbine runners for 14 of the 17 units. This replacement or uprating of the generating units is scheduled to be completed in the late-1980's. Due to improved technology and materials, each of the uprated units will be capable of generating between 30 and 50 MW of additional capacity. This will increase the present nameplate capacity of Hoover Powerplant from 1,340 MW to about 1,800 MW (at rated head of 490 feet). The increase in peaking capacity addressed in this document is in addition to the replacement and maintenance (uprating) program previously mentioned.

Purpose and Need

On December 16, 1975, Public Law 94-156 authorized the Secretary of the Interior to engage in feasibility investigations of 12 potential water and/or energy resource projects including the modification of the existing Hoover Powerplant. The purpose of this investigation is to determine the optimum amount of peaking capacity that can be added to Hoover Powerplant within the constraints imposed by water operations, environmental, recreational, and marketing considerations. The extent and method of modification are governed by the availability of water and agreement among downstream water users.

The need for the project is reflected in the population growth rate in the Southwest, one of the fastest in the Nation. Arizona and Nevada rank first and third, respectively, in the continental United States in population growth. Utility companies serving these areas must find new sources of electrical energy for both baseload and peakload power to meet the needs of the ever increasing population.

The Western Systems Coordinating Council, a group of 43 inter- connected Western utilities, has estimated that the various utility companies in the Southwest will need an additional 3,200 MW of peaking capacity by 1986 to meet peakload requirements.

On a broader scale, the region presently obtains over half of its generating capacity from gas and oil, nonrenewable resources whose cost is increasing. To meet needs for additional generating capacity and energy, it is projected that by 1988 substantial increases in coal and nuclear generating stations will be needed, with lesser increases in gas and oil generation for peaking loads. Any contribution that increased hydrogeneration at Hoover Powerplant can make to meeting the future needs will help to reduce the amount of oil and gas generation.

The amount of available water for release, power system operations, physical limitations, power marketing, and environmental

11 SUMMARY

effects were major factors in the amount of capacity that could be added at Hoover Dam and Powerplant.

Alternatives

In accordance with Federal planning guidelines, a range of alternatives was examined. Included among them were methods for reducing power demands as well as various nonstructural and structural alternatives for meeting increased power demands. Alternatives that were studied under this investigation are shown in Table 1. The three alternatives and the no action (future without the project) alternative identified as not eliminated are described, by features, in Table 2.

The first alternative (proposed action) for the Hoover Powerplant Modification is the construction of a surface powerhouse about 50 feet downstream from the present Arizona powerhouse on an extended transformer deck. This alternative, as with all the alternatives, requires the construction of a concrete surge tank, 40 feet of which would be exposed. The powerhouse would contain two 250-MW generators which would increase the nameplate capacity of the plant 500 MW. The 500 MW would be added to the uprated capacity of 1,800 MW, for a total plant capacity of 2,300 MW.

The second alternative consists of removing two small existing generating units, with a combined capacity of 90 MW, and replacing them with one large unit (350 MW). This alternative would be 240 MW short of the potential 500-MW capacity. The physical changes, with the exception of the surge tank, would be within the present powerhouse with no noticeable outside change. The 260 MW would be added to the uprated capacity of 1,800 MW, for a total plant capacity of 2,060 MW.

The third alternative is similar to the first alternative except the units are built within the canyon wall with no external structures, other than a surge tank, being present. The total plant capacity would be 2,300 MW.

A fourth alternative is no action (future without the project). No action would be taken to increase the generating capacity of Hoover Dam. Current replacement and maintenance (uprating) programs (discussed in Chapter I, Background) would continue. As a consequence of improved technology and materials since the original construction of the generators at Hoover Powerplant, the replacement and maintenance program will allow the Bureau to increase the powerplant's present nameplate capacity from 1,340 MW to about 1,800 MW.

Description of Environment

This brief description of the project area is followed by a description of those components of the existing environment which may be impacted by the project. The environmental impacts of each of the three alternatives and the no action (future without the project) alternative are analyzed and presented in Table 3. Table 1 ALTERNATIVES CONSIDERED Hoover Powerplant Modification Project

Capacity Maximum Releases Alternative (MW) (ft3 /s) Notes

Existing Powerplant Present Capacity 1,340+ 40,000 Occasionally runs as high as 1,500+MW. Nominal Capacity After Uprating Program (No Action-Future 1,800 49,000 Rewinding generators and replacing turbine Without the Project) runners are necessary and will uprate the capacity. Alternatives Not Eliminated 500-MW Surface Powerplant 2,300 62,000 Provides sufficient peaking capacity. Optimizes use of a penstock. Adds another visible powerhouse. Replace Units A8 and A9 with 2,060 56,000 Less than sufficient peaking capacity. with a 350-MW unit Space and construction dust problems in existing powerhouse. 500-MW Underground Powerplant 2,300 62,000 Provides sufficient peaking power. Optimizes use of a penstock. Powerhouse is concealed from view. No Action 1,800 49,000 No action is the same as the existing powerplant after uprating.

Nonstructural Alternatives Eliminated Modify reservoir operations Would not provide additional capacity. Energy conservation Utilities are already conducting this program. Load management Utilities are already conducting this program. Interruption of loads Publically not acceptable. Time-of-day rates Utilities are planning this program, but additional peaking capacity will be needed. Voltage reduction Publically not acceptable.

Structural Alternatives Eliminated Nuclear powerplant Economically inefficient as a peaking resource. Coal-fired powerplant Economically inefficient as a peaking resource. Combustion turbine Uses costly oil or natural gas. Combined-cycle plant Unsuitable for peaking. 500-MW powerplant with Economically unviable. present operation Pumped storage Pumping energy unavailable. Environmental problems. Geothermal power Sufficient generating capacity not presently available. Hualapai Dam Engineeringly feasible, but more expensive than modifying Hoover. Other mainstem dams Severely limited by sites and operation. Solar and wind Large scale technology not proven. Not feasible in planning time frame. Thermoclines Large scale technology not proven. Not feasible in planning time frame. Hydrogen power Large scale technology not proven. Not feasible in planning time frame. Table 2 COMPARISON OF ALTERNATIVES Hoover Powerplant Modification Project

Surface Powerhouse Replacement of A8/A9 Underground Powerhouse Features Alternative 1 Alternative 2 Alternative 3

Powerhouse Construct new powerhouse Replace existing units Construct new powerhouse (222'X90X110') downstream inside Arizona (Az.) along lower Az. penstock. from Az. powerhouse. powerhouse.

Tailrace Deck Extension Widen 28 for access to Widen 28' for access to Widen 28' for access to construction site. construction site. construction site.

Generators 2/250-MW units, 55' dia.ea. 1/350-MW unit, 65' dia. 2/250 units, 55' dia.ea. Increased Capacity 500 MW 260 MW 500 MW 3 Discharge w/490' Head 13,000 ft Is 7,000 ft3 Is 13,000 ft /s

Draft Tube Discharge Into river channel Into tailrace of Into river channel immediately below existing powerhouse. through Arizona Stoney Gate. existing powerhouse.

Transformer Deck Extend Arizona deck Replace six Underground transformer 338'X132, along river. transformers with vault constructed 110'X72.

Transformers Six transformers and one three transformers and Six transformers and one spare (16'X18'X22'). one spare (18'X20'X26'). spare.

Surge Tank 80' dia. X230' high extend 80'dia. X230' high extend 80' dia. X230' high extend from lower Az. penstock from upper Az. penstock from lower Az. penstock (25' dia. riser between). (25' dia. riser between). (25' dia. riser between).

Penstocks Construct 2/18'dia. branches Replace existing 13' dia. Extend existing 25' dia. in 2/26' dia, tunnels to penstock with 19' dia. penstock with two new 21' dia. connect new turbines to penstock. penstocks. existing 25' dia. penstock. Penstock Bulkhead Install hemispherical or Install in upper Az. pen- Install hemispherical or (Temporary Effects) elliptical head in lower stock (outage for 45 days elliptical head in Az. pen- Az. penstock (outage for installation and 36 days stock (outage for 45 days 45 days installation and removal). installation and 36 days 36 days removal). removal).

Cofferdam Construct cofferdam Construct cofferdam No construction. Existing (Temporary Effects) 120'X510' in river channel 125'XI30' in river Arizona Stoney Gate used (excavate 20' of channel). channel (excavate 20' as cofferdam. of channel). 3 W/releases @ 49,000 ft /s Tailrace Surface Elevation Rise 2.6 feet 2.6 feet None Head Loss 2.6 feet 2.6 feet None Loss in MW 9.2 MW 9.2 MW None 2/ Water Velocity (Maximum) 8.2 mph 1, 8.2 mph 1, 4.7 mph Dia. of Stable Material 12 inches— 12 inches— Same as present

Construction Costs $302,000,000 $232,000,000 $286,000,000 Period 5 years 41 years. 5 years Capacity Loss (MW) 9.2 99.2 MW-/ Workers 420 315 420

Benefit-Cost Ratio 1.73:1 1.16:1 1.82:1

1/ Diameter of bottom material in tailrace area which will remain stable (armored) when flows are increased as a result of cofferdam. 2/ Tailrace flow which is expected without the construction of a cofferdam. 7/ Due to the two units (A8 and A9) being taken out of service during construction.

V Table 3 ENVIRONMENTAL IMPACTS OF THE ALTERNATIVES Hoover Powerplant Modification Project

At Completion Alternatives of Unit Uprating Surface Underground Environmental Existing (No Action) Powerhouse Replace A8-A9 Powerhouse Parameters Condition (Future Without Projectj (500 MW) (350 MW) (500 4W) 1/ l Air Quality Good No impact. Exhaust fume increase.'. Exhaust fume increase- . Exhaust fume increasel .

Esthetics No impact. New powerhouse and surge New surge tank. New surge tank. tank built to blend harmo- niously with existing structures.

Minimum Flow (ft3/s) 0-2000 0-2000 0-2000 0-2000 0-2000

Maximum Flow (ft3/s) 40,000 49,000 62,000 56,000 62,000

Minimum Average Velocity (mph) ( Hoover Dam to River Mile 18) 0.1 0.1 0.1 0.1 0.1

Maximum Average Velocity (mph) (Hoover Dam to River Mile 18) 2.5 2.9 3.6 3.4 3.6 2/ 11 2/ 11 11 Maximum Velocity Cofferdam Area (mph) 3.0 3.4- 8.2 8.2 3.4-

Maximum Daily River Fluctuation at Dam (in feet) 17 20 24 22 24

Maximum Daily River Fluctuation at Willow Beach (in feet) 2.5 3.5 6 5 6

Average Weekly Lake Mohave Fluctuation (ft) 1-2 1-2 2-3 2-3 2-3

Maximum Daily Temperature ° ° Fluctuation (°F) 0 0 3 3° 3

Aquatic Plant Impacts Slight periphyton Slight periphyton Possible increased Slight possibility of Possible increased disturbance. disturbance. periphyton disturbance increased periphyton periphyton disturbance for 6 months. disturbance for 6 months. for 6 months.

Aquatic Animal Impacts None. None. Possible small loss of Slight possibility of Possible small loss of food organisms for 6 small loss of food food organisms for 6 months. Reduction in organisms for 6 months. months. Reduction in Lake Mohave fishery. Reduction in Lake Mohave Lake Mohave fishery. fishery.

Terrestrial Plant Impacts None. None. Loss of 34 acres of Loss of 8 acres of desert Loss of 5 acres of desert wash habitat. wash habitat. desert wash habitat.

Terrestrial Animal Impacts None. None. Corresponding loss of Corresponding loss of Corresponding loss of animals inhabiting wash. animals inhabiting wash. animals inhabiting wash.

Special Status Species None. None. Possible reduction in Possible reduction in Possible reduction in razorback sucker spawning razorback sucker spawning razorback sucker spawning success. No endangered success. No endangered success. No endangered or threatened species or threatened species or threatened species impacted. impacted. impacted.

I mpacts on Fish Hatchery Pumping problems. Increased possi- Increased possibility Increased possibility of Increased possibility of Never draw warm bility of occasion- of occasionally drawing occasionally drawing occasionally drawing warm water into hatchery. ally drawing warm warm water into hatchery. warm water into hatchery. water into hatchery. water into hatchery.

Archeological Impacts Erosion of site. Slight increase in Slight increase in Slight increase in Slight increase In erosion of site. erosion of site. erosion of site. erosion of site.

Socioeconomic Impacts None. Population of Clark Population of Clark Population of Clark Population of Clark County increased by County increased by County increased by County increased by 967 at peak of 1,935 at peak of 967 at peak of 1,935 at peak of construction, construction. construction. construction.

Recreational Impacts Slight navigational Slight increase in Increase in Increase in Increase in problems. navigation problems. navigation problems. navigation problems. navigation problems. Possible reduced fishing Possible reduced fishing Possible reduced fishing access. access. access.

Cost Comparison (Construction) 0 5302,000,000 $232,000,000 5286,000,00bl

Power Capacity 1,340 141 1,800 MW 2,300 MW 2,060 MW 2,300 MW Power Capacity Loss Due to 1/ Construction 0 0 9.2 MW- 99.2 0

1/ Indicates impact would occur during construction period only. 7/ The tailrace flow is that which is presently experienced or expected to be experienced without a cofferdam. -N/ 90 MW lost due to removal of units A8 and A9 and 9.2 MW lost due to decrease in head.

vi SUMMARY

The Hoover Powerplant is located at Hoover Dam in the Black Canyon of the Colorado River on the Arizona-Nevada border, 25 miles southeast of Las Vegas, and 7 miles northeast of Boulder City, Nevada. (See frontispiece location map and photograph of the area.) The area surrounding Black Canyon is typical Mojave Desert with its associated plants and animals. However, the actual affected environment lies primarily within the high canyon walls of Black Canyon.

The massive volcanic walls of Black Canyon are approximately 500 feet apart and rise nearly vertically 700 feet above the riverbed. The 20 miles of Black Canyon below Hoover Dam are considered the upper portion of Lake Mohave formed by Davis Dam. This portion of the lake can be characterized as a river with a flow that varies from fast to slow depending on water levels in Lake Mohave and releases from Hoover Dam. Black Canyon extends three-fourths of a mile above Hoover Dam into Lake Mead. Lake Mead, at maximum elevation, extends 110 miles upstream from Hoover Dam and forms, by capacity, the largest reservoir in the country (28.5 million acre-feet of storage). There are no impacts associated with this project below Lake Mohave (Davis Dam) nor above Lake Mead (Grand Canyon, Arizona).

Impacts and Proposed Mitigation

The following discussion summarizes the environmental impacts and the proposed mitigations for the three alternatives and the no action (future without the project) alternative on Table 2.

Alternative 1 - Construction of a 500-MW Surface Powerhouse

Summary of Impacts. This alternative is the Bureau's proposed action based on project objective, engineering, and economic considerations. If Alternative 1 were implemented, the following impacts to the environment could be expected:

1. Emissions from construction vehicles and airborne particulates from construction activities would cause a slight deterioration in air quality around Hoover Dam. The deterioration would not be enough to affect visibility, human health, vegetation, or wildlife.

2. The new powerhouse and surge tank would slightly change the visual appearance of Hoover Dam.

3. Traffic congestion at the dam would be increased during the 5-year construction period.

4. During the construction period, increased velocities due to placement of a cofferdam around the proposed new Arizona powerhouse location could reduce primary productivity (algae growth) through a 500- to 800-foot section of river immediately below the dam.

5. Once the project is operational, scouring and bottom instability due to increased water velocities are expected to cause an initial decline in periphyton productivity in a 3-mile section of river immediately below Hoover Dam. Restabilization should occur in

vii SUMMARY

approximately 6 months after the proposed project is fully operational. The restabilized area may experience: increased, the same as presently exists, or decreased productivity. There should be no appreciable change in the Black Canyon fishery if the productivity increases or remains the same. If the productivity decreases, there may be a redistribution of fish within Black Canyon (i.e., they would move downstream toward Lake Mohave). Fish species primarily affected would be trout, carp, and the razorback sucker. The bonytail chub, an endangered species, would not be impacted in the Black Canyon area.

6. The temperature of the river below Hoover Dam, presently a near constant 54°F, would fluctuate between 54-57°F. This fluctuation is not expected to have a discernible affect on aquatic organisms in the river.

7. A reduction in the recreational opportunities in the Willow Beach area is expected, particularly in fishing.

8. Vertical mixing, and hence phytoplankton productivity, would be slightly increased in Black Canyon above Hoover Dam. The effect would be unnoticeable without sensitive measuring equipment and is expected to have no impact on the overall aquatic system.

9. Possibly during a few days in the summer, the warm/cold water interface in Lake Mohave would move far enough upstream to allow warm water to be drawn into the Willow Beach National Fish Hatchery. This could result in the loss of some or all of the hatchery fish. Debris would be brought up with the interface which could become a nuisance to the hatchery and marina.

10. Materials required for construction would result in 34 out of 242 surface acres of desert wash vegetation being destroyed. Reestablishment of vegetation would be slow and this habitat would be lost to wildlife, probably in excess of 10 years.

11. Lake Mohave would increase in weekly fluctuations. This may reduce the productivity of several fish species including largemouth bass, and other sunfish, razorback sucker, and threadfin shad. This could result in a reduction in the largemouth bass/sunfish fishery in Lake Mohave. Razorback suckers, which spawn in shallow water, might also experience a reduction in spawning success. Trout would not be impacted.

12. Except for increases in traffic congestion, no significant social or economic impacts to nearby communities resulting from the project are anticipated.

13. Increased water depth during high releases may increase the erosion of an archeological site (Willow Beach No. 2).

14. Navigational hazards and inconvenience to recreationists would increase on the river above Willow Beach due to the

viii SUMMARY

increased water velocities and fluctuations. A decrease in recreational use for this portion of river is anticipated.

15. During construction, 9.2 MW of capacity would be lost because of the decreased head (2.6 feet) caused by the cofferdam.

Proposed Verification Studies and Mitigation. See Attach- ment B to this document.

Alternative 2 - Replacement of Generating Units A8 and A9 with a 350-MW Unit

Summary of Impacts. If this alternative were implemented the environmental impacts would be similar but slightly less than Alternative 1 with the following exceptions:

1. There would be no change in the appearance of Hoover Dam except for the addition of a surge tank.

2. Materials needed for construction would result in 8 out of 242 surface acres of desert wash vegetation being destroyed. Reestablishment of vegetation would be slow and this habitat would be lost to wildlife, probably in excess of 10 years.

3. This alternative is 240 MW short of the potential 500 MW.

4. During construction 99.2 MW of capacity would be lost due to the removal of units A8 and A9 and the 2.6 feet of head loss due to the cofferdam.

Proposed Verification Studies and Mitigation. See Attach- ment B to this document.

Alternative 3 - Construction of a 500-MW Underground Powerhouse

Summary of Impacts. This alternative would have the same capacity and operation as Alternative 1. Thus, environmental impacts would be the same as Alternative 1 with the following exceptions:

1. There would be no change in the appearance of Hoover Dam except for the addition of a surge tank.

2. No cofferdam is required for construction, thus, there would be no capacity loss due to a 2.6 feet head differential, and no loss in primary production due to increased velocities caused by a cofferdam.

3. Materials needed for construction would result in 5 out of 242 surface acres of desert wash vegetation being destroyed.

Proposed Verification Studies and Mitigation. See Attach- ment B to this document.

i x SUMMARY

Alternative 4 - No Action (Future Without the Project)

Summary of Impacts. If the no action alternative was implemented, the environment of the project area would remain essentially as presently experienced with the following exceptions:

I. A scheduled uprating program for the existing generating units will increase the maximum releases from Hoover Dam to 49,000 cubic feet per second. This is likely to cause some initial substrate instability and temporary loss in primary productivity in the first few miles below the dam. The instability and loss in primary production should be short term, 6 months or less.

2. A new visitor facility planned for Hoover Dam is expected to alleviate some of the traffic congestion which often occurs at the dam. This facility could be constructed with or without the proposed project.

x TABLE OF CONTENTS

Page

LOCATION MAP AND PHOTOGRAPH ...... Frontispiec

ABSTRACT ......

SUMMARY ......

I. PURPOSE AND NEED ...... 1

A. Background ...... 1

1. Existing Powerhouse and Facilities ...... 1 2. Uprating Existing Units 2

B. Purpose and Need ...... 2

1. Power Needs ...... 3 2. Projected Needs ...... 4

II. ALTERNATIVES INCLUDING THE PROPOSED ACTION ...... 5

A. Alternatives Eliminated ...... 5

1. Nonstructural Alternatives ...... 5

a. Modifying River Operations ...... 5 b. Energy Conservation ...... 5 c. Load Management ...... 6 d. Interruption of Loads ...... 6 e. Time-of-Day Rates ...... 6 f. Voltage Reduction ...... 6

2. Structural Alternatives ...... 7

a. Nuclear Plants ...... 7 b. Solar and Wind Energy 7 c. Coal Plants ...... 7 d. Combustion Turbines 8 e. Combined-Cycle Plants ...... 8 f. Hoover Powerplant Modification (500 MW) with Present Operation ...... 9 g. Pumped Storage (1,000 MW) at Hoover Dam . . 9 h. Offstream Pumped Storage ...... 9 i. Geothermal Energy ...... 10 j. Hydrogen Energy ...... 10 k. Colorado River Resources ...... 10

xi TABLE OF CONTENTS (Continued)

Page

B. Alternatives Not Eliminated ...... 11

1. Alternatives ...... 11 a. Surface Powerhouse (500 MW) - Alternative 1 12 b. Replacement of Generating Units A8 and A9 - Alternative 2 14 c. Underground Powerhouse (500 MW) - Alternative 3 15 d. No Action (Future Without the Project) - Alternative 4 .....16

2. Construction of Alternatives ...... 16 3. Operation of Alternatives ...... 17

III. AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES . • • 21

A. Introduction ...... 21

B. Affected Environment ...... 21 1. Hoover Dam 21 2. Climate and Air Quality ...... 21 3. Seismicity ...... 22 4. Geology ...... 22 5. Hydrologic and Aquatic Environment ...... 22

a. Background - Hoover Dam/Powerplant Operations 22 b. Water Level and Velocity Fluctuations . . 23 c. Substrate Stability and Primary Productivity (Algae Growth) ...... 26 d. Temperature Fluctuations ...... 27 e. Temperature Instability Versus Productivity ...... 28 f. Warm/Cold Water Interface ...... 29 g. Interface Versus Fish Hatchery ...... 29 h. Fishery Resources ...... 29

(1) Lake Mead ...... 29 (2) Lake Mohave ...... 32'

6. Terrestrial Environment ...... 33

a. Black Canyon ...... 33

(1) Vegetation ...... 33 (2) Wildlife ...... 35

xii TABLE OF CONTENTS (Continued)

Page

b. White Rock Canyon ...... 35

(1) Vegetation ...... 36 (2) Wildlife ...... 36

7. Special Status Species ...... 36

a. Peregrine Falcon ...... 37 b. Bald Eagle ...... 37 c. Yuma Clapper Rail ...... 38 d. Devil's Hole Pupfish .....39 e. Bonytail Chub ...... 39 f. Razorback Sucker ...... 42

8. Recreation 43 9. Archeological and Historical Sites 47 10. Socioeconomic Environment ...... 48

C. Environmental Consequences of a 500-MW Surface Powerhouse (Alternative 1) .. 48

1. Hoover Dam ...48 2. Climate and Air Quality ...49 3. Seismicity ...... 49 4. Geology ...49 5. Hydrologic and Aquatic Environment ...50

a. Hoover Dam/Powerplant Operations ... 50 b. Water Level and Velocity Fluctuations . . . .. 50 c. Substrate Stability and Primary Productivity ... 51 d. Temperature Fluctuations ... 52 e. Temperature Instability Versus Productivity ... 53 f. Interface Versus Fish Hatchery ...53 g. Fishery Resources ... 54

(1) Lake Mead ...54 (2) Lake Mohave ...54

6. Terrestrial Environment ... 57

a. Black Canyon ... 57

(1) Vegetation ...... 57 (2) Wildlife ...... 57

b. White Rock Canyon ...57

(1) Vegetation ...... 57 (2) Wildlife ...... 57

TABLE OF CONTENTS (Continued)

Page

c. Spoil Sites 58

7. Special Status Species ... 58 8. Recreation ...... 58 9. Archeological and Historical Sites ... 59 10. Socioeconomic Environment ...60 11. Capacity Loss ...63 12. Cumulative Impacts ...63 13. Summary of Impacts ...65 14. Proposed Verification Studies and Mitigation . 67

D. Environmental Consequences of Replacing Generating Units A8 and A9 with a 350-MW Unit (Alternative 2) . . 67

1. Hoover Dam ...67 2. Climate and Air Quality ...67 3. Seismicity ...... 67 4. Geology ...67 5. Hydrologic and Aquatic Environment ...67

a. Hoover Dam/Powerplant Operations ...67 b. Water Level and Velocity Fluctuations ...... 67 c. Substrate Stability and Primary Productivity ...68 d. Temperature Fluctuations 68 e. Temperature Instability Versus Productivity . 68 f. Interface Versus Fish Hatchery ...68 g. Fishery Resources ...68

6. Terrestrial Environment ...69

a. Black Canyon ...69

(1) Vegetation ...... 69 (2) Wildlife ...... 69

b. White Rock Canyon 69 c. Spoil Sites ... 69

7. Special Status Species ...69 8. Recreation ...... 69 9. Archeological and Historical Sites ...69 10. Socioeconomic Environment ...69 11. Capacity Loss ...69 12. Cumulative Impacts ...69 13. Summary of Impacts ...69 14. Proposed Verification Studies and Mitigation . 70

xiv TABLE OF CONTENTS (Continued)

Page

E. Environmental Consequences of a 500-MW Underground Powerhouse (Alternative 3) ...... 70

1. Hoover Dam ...... 70 2. Climate and Air Quality ...... 70 3. Seismicity ...... 70 4. Geology ...... 70 5. Hydrologic and Aquatic Environment ...... 70 6. Terrestrial Environment ...... 70

a. Black Canyon ...... 70 b. White Rock Canyon ...... 70 c. Spoil Sites ...... 70

7. Special Status Species ...... 70 8. Recreation ...... 70 9. Archeological and Historical Sites ...... 71 10. Socioeconomic Environment ...... 71 11. Cumulative Impacts ...... 71 12. Summary of Impacts ...... 71 13. Proposed Verification Studies and Mitigation . 71

F. Environmental Consequences of No Action/Future Without the Project (Alternative 4) ...... 71

1. Hoover Dam ...... 71 2. Climate and Air Quality ...... 71 3. Seismicity ...... 71 4. Geology ...... 71 5. Hydrologic and Aquatic Environment ...... 71

a. Hoover Dam/Powerplant Operations ...... 71 b. Water Level and Velocity Fluctuations • • • • 72 c. Substrate Stability and Primary Productivity . 72 d. Temperature Fluctuations ...... 72 e. Temperature Instability Versus Productivity . 72 f. Interface Versus Fish Hatchery ...... 72 g. Fishery Resources ...... 72

(1) Lake Mead 72 (2) Lake Mohave 73

6. Terrestrial Environment ...... 73 7. Special Status Species ...... 73 8. Recreation ...... 73 9. Archeological and Historical Sites ...... 73 10. Socioeconomic Environment ...... 73 11. Cumulative Impacts ...... 73 12. Summary of Impacts ...... 73

XV TABLE OF CONTENTS (Continued)

Page

G. Relationship to Other Projects and Actions ... 73

1. Reregulation of Lake Mohave ... 73 2. Hoover Dam Visitor Center ... 74 3. Floodplain Management ... 74 4. Permits, Licenses, and Other Entitlements ... 74

IV. CONSULTATION AND COORDINATION ... 75

A. Coordination Groups ... 75

1. Planning Team ... 75 2. Interagency Group ... 76 3. Power Group ... 76

B. Major Participants in Planning Process ... 77

1. Federal ... 77 2. State of Nevada ... 77 3. State of Arizona ... 77 4. Local Municipalities ... 78 5. Private ... 78 6. Utilities ... 78

C. Public Meetings ...78

V. LIST OF PREPARERS ...80

LIST OF TABLES

No. Page

1 Alternatives Considered for Hoover Powerplant Modification Project ...... iv

2 Comparison of Alternatives ..... v

3 Environmental Impacts of the Alternatives .... vi

4 Construction Manpower Requirements .... 18

5 Mover-Nonmover Allocation of Manpower .... 19

6 Daily Fluctuations in Water Levels Due to Hoover Dam Releases .... 24

xvi TABLE OF CONTENTS (continued)

LIST OF TABLES (continued)

Page

7 Actual and Predicted Mean and Maximum Water Velocities in Black Canyon ...... 25

8 Relationship Between Warm/Cold Water Interface in Lake Mohave, Daily Releases From Hoover Dam, and Lake Mohave Elevation ...... 30

9 List of Fish Species Found in Lake Mead and Lake Mohave and Status ...... 31

10 Monthly Elevation Ranges of Lake Mohave, 1977-81 ...... 34

11 Number of Visitors to Lake Mohave - 1979 and 1980 ...... 44

12 Lake Mohave Visitor Use 1979 ...... 45

13 Water Related Visitor Statistics for Willow Beach - 1979 and 1980 ...... 46

14 Direct Population Influx Due to Construction Workers and Their Families ...... 60

15 Community Allocation of Total Population Impact Due to the Proposed Modification of Hoover Powerplant 61

16 Relative Gravity of Impacts on Services and Facilities in Henderson and Boulder City ...... 62

17 A Composite Evaluation of Community Services from Boulder City and Henderson Key Informants ...... 64

LIST OF FIGURES

Following No. Page

1 Typical Weekly Power Use ...... 4

2 Photo of Existing Hoover Dam and Powerplant ...... 12

3 Photo of Artist's Conception of Proposed 500-MW Surface Powerhouse Alternative ...... 12

4 Diagram of Cofferdam for Alternative 1 Located in the River Channel 13

xvii TABLE OF CONTENTS (Continued)

LIST OF FIGURES (Continued)

Following Page

5 Photo of Generating Units A8 and A9 Inside Powerhouse . 14

6 Photo of Arizona Side of Black Canyon With Either Potential Underground Powerhouse or A8 and A9 Replacement Alternative ...... 15

7 Hoover Modification Study - Weekly Load Curve - Winter . . 19

8 Hoover Modification Study - Weekly Load Curve - Spring . . 19

9 Hoover Modification Study - Weekly Load Curve - Summer . . 19

10 Hoover Modification Study - Weekly Load Curve - Fall . 19

11 Colorado River Water Surface Profiles for Lake Mohave-- Elevation 647 ...... 20

12 Colorado River Water Surface Profiles for Lake Mohave-- Elevation 630 ...... 20

13 Projected Effects of Modified Hoover Powerplant Releases upon Lake Mohave Elevations ...... 26

14 Diagram of Theoretical Withdrawal Layer ...... 28

15 Schematic of Lake Mohave Interface ...... 29

16 Photo of Willow Beach Fish Hatchery on Lake Mohave . . • • 30

17 Map of Recreation Use on Lake Mohave from Hoover Dam to Davis Dam ...... 44

18 Map of Regional Impact Area for Hoover Modification Socioeconomic Assessment ...... 48

19 Photo of Public Involvement Display ...... 78 TABLE OF CONTENTS (Continued)

ATTACHMENTS

Page

ATTACHMENT A DISTRIBUTION LIST ..... A-1

ATTACHMENT B ENVIRONMENTAL COMMITMENTS MADE IN THIS STATEMENT .....B-1

ATTACHMENT C PUBLIC IDENTIFIED CONCERNS ..... C-1

ATTACHMENT D RATIONALE FOR PREDICTING HATCHING SUCCESS REDUCTION DUE TO PROJECT ..... 0-1

ATTACHMENT E APPLICATION FOR CORPS OF ENGINEERS 404 (r) EXEMPTION . . . E-1

ATTACHMENT F LITERATURE CITED .....F-1

ATTACHMENT G GLOSSARY OF TERMS .... G-1

ATTACHMENT H ARCHEOLOGICAL CONSULTATION LETTERS .... H-1

ATTACHMENT I INDEX ..... 1-1

xix

CHAPTER I

PURPOSE AND NEED

CHAPTER I

PURPOSE AND NEED

This document presents the environmental effects of increasing the generating capacity of Hoover Powerplant by constructing additional generating units. The location of the project and general layout are shown in the frontispiece location map and photograph.

Coordination as required by the Endangered Species Act and the Fish and Wildlife Coordination Act was completed on December 30, 1980, and April 1981, respectively. However, developments in the engineering and economic aspects of the project changed the plant operation from that which was originally proposed and on which the coordination was based. We, therefore, reinitiated coordination under the above two acts on October 16, 1981. Coordination on the new developments was completed April 1, 1982 for the Endangered Species Act and April 7, 1982 for the Fish and Wildlife Coordination Act. Discussions relative to the above acts can be found in Chapter III.B.7. and Attachment B, respectively.

The Federal Water Pollution Control Act Amendments of 1972 (P.L. 92-500) require a Corps of Engineers permit, under Section 404 of the act, for the discharge of dredged or fill material into navigable waters. The Clean Water Act of 1977 amended Section 404 by adding subsection Cr) which provides a procedure by which Federal water projects may be exempted from securing a Corps of Engineers permit. Accordingly, it is intended that this environmental impact statement be used to qualify for exemption to the 404 permit process under Section 404 (r), of P.L. 92-500, amended. Impact discussions relative to the permit are found in Chapters II.B.1.a. and b. (Cofferdam), III.B.4. (Geology), III.C.4. (Geology), III.C.5.g.(2) (Lake Mohave), and Attachment E.

This project would have no cumulative or synergistic effects on the Colorado River Basin (see Chapter III.C.14.; D.14.; E.13; and F.12).

A. Background

Hoover Dam and Powerplant were designed and constructed by the Bureau of Reclamation (Bureau) pursuant to the Boulder Canyon Project Act of December 21, 1928. The dam was constructed to protect the low lying valleys of Arizona and southern California from the yearly threat of flood, to store annual spring runoff needed later for irrigation, and municipal and industrial use, and to generate power. The construction of the dam began in 1931 and was completed in 1935 with the first commercial energy generated in 1937.

1. Existing Powerhouse and Facilities. In addition to creating Lake Mead, the Nation's largest manmade lake, Hoover Dam has one of the largest hYdroelectric powerplants in the world with an installed 1 CHAPTER I PURPOSE AND NEED

capacity of about 1,340 megawatts (MW). When the water stored in Lake Mead is released, it passes through Hoover's 17 turbines and generates low-cost hydroelectric energy. The Western Area Power Administration (Western), Department of Energy, is responsible for marketing the energy from Hoover Dam. This energy is sold to both public and private agencies under contracts and is presently allocated to the States of Arizona and Nevada, and in California to the Metropolitan Water District of Southern California, City of Burbank, City of Glendale, City of Pasadena, City of Los Angeles, and Southern California Edison Company. These contracts, which expire May 31, 1987, are presently being renegotiated, and Western will decide the distribution of the power contracts by 1987.

Sixteen high-voltage transmission lines connect Hoover Dam with its power market area; southern California, southern Nevada, and Arizona.

Today, the average annual net generation for Hoover Powerplant is about 4 billion kilowatthours (kWh) of hydroelectric energy. This amount of energy is estimated to save the country about 10 million barrels of oil annually that otherwise would have to be used for the generation of electrical energy.

2. Uprating Existing Units. This is part of the no action (future without the project) alternative which is discussed in Chapters II and III. The present generating units at the powerplant are nearing the end of their economic life. The Bureau, as part of a routine replacement and maintenance program, is in the process of overhauling and replacing worn generator windings and turbine runners for 14 of the 17 units. This replacement or uprating of the generating units which began in 1979 is scheduled to be completed in the late-1980's. Due to improved technology and materials, each of the uprated units will be capable of generating between 30 and 50 MW of additional capacity. This will increase the present nameplate capacity of the Hoover Powerplant from 1,340 MW to about 1,800 MW (at rated head of 490 feet). The uprated units would operate in essentially the same manner as presently experienced, with the excgption of infrequent discharges up to 49,000 cubic feet per second (ft Is) (1,800 MW). The uprating program was described in a Special Report (Water and Power Resources Service, 1980). The uprating program was evaluated and it was determined that the program met criteria for a categorical exclusion under Section 9.4(d) of Appendix 9 to the Department of the Interior's Policy and Procedures for compliance with the National Environmental Policy Act (516 DM 6).

B. Purpose and Need

On December 16, 1975, Public Law 94-156 authorized the Secretary of the Interior to engage in a feasibility investigation of 12 potential water and/or energy resource projects including the modification of the existing Hoover Powerplant. The purpose of this investigation is to determine the optimum amount of peaking capacity that can be

2 CHAPTER I PURPOSE AND NEED

added to Hoover Powerplant within the constraints imposed by water operations, environmental, recreational, and marketing considerations. No additional energy will be produced by this proposed project.

The distinction between electrical peaking capacity and increased electrical energy is a subtle but important distinction which must be understood to fully realize the purpose of modifying Hoover Power- plant. The following analogy should be helpful in understanding the difference.

Imagine the energy produced by Hoover Powerplant as the water in a 5-gallon bucket. The only way to release the energy (5 gallons worth) is to open a 1-inch spigot located at the bottom of the bucket. If we open the spigot half way, the water (energy) will run out at a certain rate, say 1 gallon/hour. This is comparable to producing energy at 100 kWh. Now suppose we release the 5 gallons of water through the spigot in the following manner. Most of the time the spigot is open only half way (1 gallon/hour) but occasionally it is opened all the way (2 gallons/hour) for short periods (peakload) to meet some increased requirement. The 2 gallons/hour is the peakin capacity for that spigot. It does not change the amount (5 gallons of water (energy) available in the bucket, it only allows us to use the water at a faster rate. If we replace the 1-inch spigot with a 2-inch spigot (Hoover Powerplant Modification), we have increased our peaking capacity up to say 4 gallons/hour but still have only 5 gallons of water (energy) to use.

This analogy is applicable to Hoover Powerplant Modification because the amount of water released through the powerplant for energy production is limited by downstream water demands. The present powerplant (1-inch spigot) is capable of meeting downstream water demands, but is presently not capable of meeting predicted electrical peaking capacity demands. By installing additional units, (2-inch spigot), the Bureau will be able to meet predicted peaking capacity demands as well as continue to satisfy the downstream water requirements.

1. Power Needs. There is an increasing need for additional peaking capacity in the Southwest. To understand this need, a short explanation of the role hydroelectric powerplants play in the scheme of energy production will be helpful. Nuclear, coal- and oil-fired powerplants are designed to deliver a steady source of power to its users. Unfortunately in most, if not all areas of the country, the daily requirement for power is not steady. During the late evening hours offices and homes need little power but during the daylight hours they require a substantial amount of power. This daily increase and decrease in demand (peakload) for power can be depicted as a series of peaks and valleys throughout a week's time (see Figure 1). The steady requirement for electrical energy by 24-hour factories, all night businesses, etc., makes up the baseload energy requirement (Figure 1) which is easily fulfilled by the steady generation of nuclear, coal- and oil-fired plants. Hydroelectric powerplants, such as Hoover Powerplant, and gas turbine generators produce the power to accommodate the daily peakloads. This division of power sources works well because the major daily, weekly, or monthly requirement for power

3 CHAPTER I PURPOSE AND NEED

can be accommodated by a steady (baseload) nuclear, coal- or oil-fired powerplant. The relatively small amount of power needed for the daily peaks, when compared to the total amount required (Figure 1), can be quickly obtained from the fast responding hydroelectric and gas turbine powerplants.

2. Projected Needs. The Western Systems Coordination Council, a group of 43 western utilities, issued a Loads and Resources Report in 1979 that stated the average annual compound peakload growth rate for the Southwest from 1979-88 was forecasted in 1978 to be 4.1 percent. This will increase the 1978 peakload requirement of 28,067 MW to an estimated 1988 peakload requirement of 42,024 MW.

In 1977, the Bureau conducted a peaking capacity needs survey of all utilities and power vendors in the Hoover Powerplant marketing area to determine the magnitude of its peaking capacity requirements. Out of 42 responses to the survey, 15 entities expressed a need for potential peaking capacity at Hoover. Their combined needs that could be provided from a resource like Hoover Powerplant by 1990 amounted to a total of 5,813 MW. This is much more than could be provided at Hoover because of the limited amount of water available.

Through an analysis of projected peaking capacity needs of the present Hoover power allottees, recognizing the available water supply and penstock capacity, the maximum practicable generating capacity at Hoover Powerplant from an engineering viewpoint was determined to be 2,300 MW. Since the powerplant would have a capacity of 1,800 MW after uprating, the potential for addition of more capacity is 500 MW, which became the capacity of the proposed new powerhouse.

4 TYPICAL WEEKLY POWER USE SOUTHWEST AREA

Nuclear, coal-and oil- fired plants typically produce the baselood energy depicted in the graph. The peak loads ore usually supplied by gas turbines or hydroelectric powerplants. El PEAKLOAD NOTE Most of the energy produced during BASELOAD any one day is baselood. ni _ CHAPTER IE

ALTERNATIVES INCLUDING THE PROPOSED ACTION

CHAPTER II

ALTERNATIVES INCLUDING THE PROPOSED ACTION

Three alternative methods of increasing capacity at Hoover Powerplant were identified for detailed investigation. Tables 1, 2, and 3 of the Summary present a comparison of these alternatives and the environmental impacts summary. The proposed alternative is identified. Included in the comparison,is the alternative of no action (future without the project).

Several additional alternatives were considered but eliminated from detailed study. Section A of this chapter briefly discusses these alternatives and the reasons they were eliminated. Section B describes in detail the proposed action and viable alternatives.

A. Alternatives Eliminated

In accordance with Federal planning guidelines, a range of alternatives was examined, most of which were dropped from further consideration as explained below. Included among them were methods for reducing power demands as well as various nonstructural and structural alternatives for meeting increased power demands.

Alternatives that were eliminated from further study under this investigation are discussed below:

1. Nonstructural Alternatives

a. Modifying River Operations. Modifying river operations to increase generating head would provide more generating capacity. Physically, this could be achieved by keeping Lake Mead at maximum storage level. Projections of future river operations show that Lake Mead will be at that level only a small percentage of the time after 1990. The available water supply in the river is not sufficient to keep Lake Mead at a maximum conservation elevation regularly. More- over, the Boulder Canyon Project Act and a Supreme Court Decree state that Hoover Dam will be operated in order of priority for: (1) flood control and river regulation; (2) irrigation and domestic uses, and (3) power generation. Thus, the reservoirs and the river cannot be operated to maximize power to a greater extent than at present.

b. Energy Conservation. It is quite difficult for utilities to assess the impacts of energy conservation on their systems. Energy conservation does reduce future energy growth, and this reduction is incorporated in their estimates of load growth. Most of the utilities in the service area have quite extensive energy conservation programs. The programs include dissiminating conservation measures to both industrial and residential customers by use of newspapers, television, radio, and other forms of education to encourage energy conservation and efficient energy use by customers. Since energy conservation is voluntary and the responsibility of the energy consumer, many utilities feel that conservation is not a reliable alternative to adding generation capacity. Energy conservation does

5 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION reduce or delay the need for constructing additional generation capacity, but most utilities have taken this into consideration in planning future generation facilities.

c. Load Management. Load management (i.e., running dish- washers at midnight instead of noon) shifts energy requirements from times of high energy demand to times of low energy demand thus reduc- ina the peak demands of a utility system by spreading the energy requirements over the entire day. This again is primarily a voluntary program which must be the responsibility of the customers. A reduction of generating capacity can be realized through load management, however, no energy is saved since energy is only displaced from onpeak to offpeak periods. This allows utilities to meet energy demands with more economical baseload plants such as nuclear, and coal plants, and reducing the reliance on oil or natural gas which is the fuel used to meet peakloads. For the near future obtaining significant savings through load management is uncertain. Most utilities are pursuing some kind of program to encourage voluntary load management. Even with load management there is still a need for additional generating capacity.

d. Interruption of Loads. To decrease demand during emergency periods, prearranged power interruptions to customers (rolling blackouts) have been used successfully by many utilities.

Another type of load interruption is voluntary customer shutoffs, primarily industrial customers, although some private individuals are being asked to participate on an experimental basis, especially those which have large enough loads to be effective in reducing demands on utility systems during periods when capacity is inadequate. The acceptability of interruptible loads is related to the savings resulting from the reduced rate of interruptible power versus the potential economic loss resulting from unannounced electrical interruptions. If the installed capacity of a utility system is so insufficient that the interruptions are frequent or of long duration, then the industrial customer may elect to discontinue the interrupted service. This method is only in its experimental stages and since it is strictly voluntary it cannot be considered a viable alternative.

e. Time-of-Day Rates. Time-of-day rates (increasing the cost of power during the high demand peak periods) are designed to reduce peakload requirements, by inducing customers to defer energy consumption from costly onpeak to less costly offpeak periods. Thus, the need for new peaking generation facilities could be reduced. Time-of-day rates are being tried on an experimental basis by some utilities, but even with their potential contribution, there is still a need for generating capacity.

f. Voltage Reduction. Voltage reduction (brownouts) is another method to reduce peak energy demands on a utility system during periods when generation capacity is inadequate. Voltage levels may be reduced 3 to 5 percent and in extreme emergencies 8-percent

6 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

reduction may be required. However, this method is not well received by customers and is usually used during emergency periods only. It is, therefore, not a viable alternative.

2. Structural Alternatives. Many types of generation resources are available to meet future load growth. The majority of these facilities use nonrenewable resources (coal, oil, etc.) as the fuel source for the generation of electricity. Although a number of methods of increasing generating capacity were identified, only those that were reasonable from an engineering, environmental, and economic standpoint received detailed study and are included in this statement. Those structural methods that were eliminated from further study are listed and briefly discussed below:

a. Nuclear Plants. Nuclear thermal-electric plants utilize the heat liberated in a nuclear reactor to generate steam. The capital costs of nuclear plants dictate large capacity units 1,000 MW or greater. Even though operation costs are low, nuclear units are not suitable for rapid changes in operation. Therefore, these units are used for baseload generation. The operation of nuclear reactors is interrupted for refueling once a year. During this period, all routine maintenance operations are performed. Since nuclear generation plants provide baseload energy as opposed to the peaking generation proposed by the modification of Hoover Powerplant, they are not considered as an alternative.

b. Solar and Wind Energy. Solar and wind energy production are expected to increase as conventional fuel costs continue to rise. Development of wind energy resources, as an important source for power generation, will depend on continued research of the resource. Both solar and wind power were found to be infeasible for peaking needs, since they provide little dependable capacity. A cloudy or calm day would reduce or eliminate power generation.

The difference in temperature between a lake's upper and lower levels, especially in the summer (thermoclines), was a solar thermal energy resource alternative suggested at a public involvement meeting. The top layer of water in Lake Mead is heated by the sun and, therefore, contains thermal energy which could be converted to power. This is a relatively new concept which is in the research stage and has not been proven technically and economically feasible. Until the commercial and technical feasibility of this alternative is proven, it will not be considered as a viable alternative to modifying Hoover.

c. Coal Plants. New coal-fired thermal electric plants are commonly designed for 500-MW units. They are less expensive to construct than nuclear plants, but are more expensive to operate, especially if the coal source is not nearby. They are limited in their ability to change energy production rapidly; however, they have some flexibility and can operate at a near constant rate as low as about 50 percent of capacity. Coal plants operate most efficiently at a steady output because it takes a relatively long period to build up steam to drive the turbines to meet the demands. For a thermal plant

7 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION to meet peaking demands, generators must be online running with no load, which uses scarce fossil energy, whereas the hydro turbines can be quickly and easily brought online in response to the load with no appreciable waste of water. Coal-fired plants require shutdown for annual maintenance for a period of several weeks or months. Coal plants are usually alternatives to nuclear plants and vice versa for the production of electricity. However, they also generally are a baseload resource and would not normally be considered as an alternative.

d. Combustion Turbines. Combustion turbines are internal combustion engines that burn liquified natural gas, residual oil, or distillate oil. Combustion turbines are compact, relatively low in capital cost, fast starting, easy to operate, and reliable. Turbines do not require cooling water or large amounts of land, only about 75 acres for a 750-MW plant. Since turbine units are relatively small in size, they can be remotely located at substations or near other powerplants and linked with existing electrical distribution systems. However, combustion turbines have several disadvantages, such as, environmental problems related to air emissions and noise levels, and the consumption of nonrenewable fossil fuels (oil or gas). From an economic standpoint, combustion turbines have high fuel costs and high fuel consumption. Combustion turbines are best suited for short duration peaking or emergency reserve service. This is the alternative that would need to be constructed by local interests in lieu of Hoover Powerplant Modification. This alternative was used to evaluate project benefits. Turbine units used to provide peaking capacity are normally less expensive to construct, but are expensive to operate because they use scarce natural gas and oil which are nonrenewable resources. Thus, cost of a combustion turbine is to be avoided by building Hoover Modification. For this reason, this type of generating unit is not a viable alternative to modifying Hoover Powerplant.

e. Combined-Cycle Plants. Combined-cycle plants are basically combustion turbine plants with heat recovery steam generators added to utilize the 1,000-degree exhaust from combustion turbines. The combined-cycle portion increases total plant output 30 to 40 percent by using the waste heat to power low-pressure turbines and generators. Combined-cycle plants provide flexibility due to their ability to function either as a combustion turbine for intermittent use or as a combined turbine-steam system for prolonged use. Relatively low initial cost, low manpower requirements, and high thermal efficiency are other advantages of the combined cycle. Since combined-cycle plants lend themselves to urban siting, transmission costs are minimal and units can be located close to load for added system reliability. Environmental problems with the combined-cycle plants are relatively few. The problems of waste heat rejection can be resolved by the use of dry cooling towers. Noise in the combined- cycle operating mode is rather low because the turbines exhaust into waste heat boilers. Air pollution problems are minimal because of the high efficiency of the combined cycle. Unlike combustion turbines which can be "online" and operating in 10 to 12 minutes, combined-cycle plants startup time is from about 1 to 4 hours,

8 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION depending on whether or not the units are hot. From an economic standpoint, combined-cycle plants are more expensive to build than combustion turbine plants, but are cheaper to operate. The long startup time makes this alternative not viable as a peaking plant.

f. Hoover Powerplant Modification (500 MW) with Present Operation. This alternative has the same structural plan as the proposed action. The operation of this plan is similar to the operation which is presently experienced, wyh the exception of infrequent high peaks up to 2,300 MW (62,000 ft /s). Analysis shows that a plant operated in this fashion would produce an estimated plant factor of less than 1 percent. A plant factor of less than 1 percent results in a benefit-cost ratio of less than unity and makes the plant unjusti- fied economically.

This alternative would have had impacts similar to those alternatives not eliminated with the following exception: Lake Mohave fishery would not be impacted.

g. Pumped Storage (1,000 MW) at Hoover Dam. This alternative would involve construction of a new powerhouse at Hoover Dam in which reversible generating units would be used to pump water from Lake Mohave to Lake Mead at night and generate (release water) during the day. At night, when the power demand is lower and the cost cheaper, power to pump the water back into Lake Mead would be obtained from baseload plants that operate continuously, such as coal or nuclear. The extra water provided by pumping back, would support more capacity in a new powerhouse; about 1,000 MW, which would boost the overall powerplant capacity to 2,800 MW. The alternative of pumped storage would require that capacity be secured from a low cost source of power for pumping, such as coal or nuclear. The effectiveness of pumped storage depends in part on the efficiency of pumping and energy conversion. A drawback to a pumped-storage operation is that it is a net consumer of energy, using 3 kWh for every 2 kWh produced. How- ever, the unit cost of the pumping energy is lower than that of the onpeak energy generated, which is why pumped storage becomes economically feasible.

This alternative was not considered a viable alternative at Hoover Powerplant for several reasons. The necessary low cost baseload energy needed to pump the water back is not available; utilities in the Southwest are in need of more baseload energy themselves. The extreme variations in flows in Black Canyon would be a detriment to recreation and the fishery in Black Canyon. Pumped-storage operation would require either that Lake Mohave be kept near the top of its operating range, or that a large amount of dredging be done to deepen the channel downstream from Hoover Powerplant. Controlling Lake Mohave in this manner is contradictory to the purposes for which it was built, and dredging is economically and environmentally undesir- able.

h. Offstream Pumped Storage. Consideration is being given to the development of a large offstream pumped-storage project

9 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

1/ (2,000-3,000-MW range) under another investigation by the Bureau.- Such a project would draw water from Lake Mead, Lake Mohave, or Lake Havasu and pump it up to a new offstream reservoir, from which power releases could be made. In scope and size, such a project attempts to address peak power needs farther in the future than the investigation reported in this environmental impact statement (EIS). A source of low cost baseload energy for pumping is not presently available.

i. Geothermal Energy. Many utilities are exploring the use of geothermal resources; however, significant amounts of geothermal generation will not be available until after 1990. The technology for economic production of geothermal power appears well developed, but in many geothermal reservoirs it is believed that the temperature is not high enough to produce fluids that may be used with existing technology to produce economical bulk electricity. Geothermal developments would operate essentially as thermal plants, supplying baseload requirements and would thus be a nonviable alternative for supplying peaking capacity.

j. Hydrogen Energy. Hydrogen power, a relatively new technology still in the research stage, was also suggested at a public involvement meeting. This process splits the water molecule into its two elements of hydrogen and oxygen, and the hydrogen could be converted to power. Since this process is still in the research stage with no large scale production models in operation to prove feasibility, it is not a viable alternative to this project at the present time.

k. Colorado River Resources. The resources of the Colorado River, including the proposed Hualapai (Bridge Canyon) Dam, Glen Canyon Dam, Davis Dam, and the Parker Dam, were studied as possibilities for increased peaking capacity.

The Hualapai (Bridge Canyon) Dam Project was proposed by the Arizona Power Authority and authorized as part of the Central Arizona Project proposal. The proposal was for the construction of a dam and powerplant 237.5 river miles below Lee Ferry Gage on the Colorado River. The powerplant would have an installed capacity of 1,500 MW in six units. After much environmental opposition, the Colorado River Basin Project Act of 1968 deferred further Federal consideration of the project until some future time. Consideration of this project would require congressional authorization.

The Upper Colorado Region evaluated the environmental, economic, and engineering feasibility of increasing the present 1,000-MW capacity of Glen Canyon Powerplant by about 250 MW. The project lacked local public support and is no longer being studied.

1/ Reclamation and Energy Resources, LMNRA Wilderness Designation, Spring Canyon Pumped-Storage Project, Arizona, and Rifle Range Pumped-Storage Project, Nevada.

10 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

If modifying Glen Canyon Dam had been acceptable, the power would have been used primarily in the Upper Colorado River Basin and would thus be of no benefit to the Lower Basin.

Davis Dam contains five generators which have recently been rewound to have a total capacity of 240 MW. Downstream channel capacity and operational parameters could permit the addition of no more than one 40-MW unit. Any increase as small as that would have a greater cost per megawatt than an additional powerhouse at Hoover Dam, and would be of little help in comparison with regional power needs. Consequently, installation of additional generation at Davis Dam cannot be considered a viable alternative.

Parker Dam presently contains four 30-MW generators, with an installed capacity of 120 MW. The downstream river channel can carry little additional releases before flood damages occur, which virtually precludes adding more generating capacity. This, together with high unit cost and institutional restrictions, rules out additional generating capacity.

B. Alternatives Not Eliminated

Viable alternatives for increasing the total capacity of Hoover Powerplant include replacing existing generating units A8 and A9 (present combined capacity of 90 MW) with a single larger (350-MW) unit for a net capacity increase of 260 MW, or constructing an additional 500-MW surface or underground powerhouse on the Arizona side. The principal factors considered in determining maximum powerplant size were marketability of the additional capacity (this project produces no additional energy), and the maximum hydraulic capacity of an existing penstock lateral. The most critical was the maximum hydraulic capacity of existing penstocks. Based on these factors, a 500-MW powerhouse addition is proposed, which indicates that the maximum size powerplant that would be practicable is about 2,300 MW. For a detailed discussion of engineering and economic aspects of the alternatives, see Chapter VI of the accompanying Hoover Powerplant Modification Feasibility Report.

1. Alternatives. The three alternatives that have been determined to be viable from an engineering, environmental, and economic standpoint along with the no action alternative are discussed below and summarized in Tables 2 and 3. The three alternatives are:

Alternative 1 - Surface Powerhouse - 500 MW Alternative 2 - Replacement of Units A8 and A9 - 350 MW (net 260 MW) Alternative 3 - Underground Powerhouse - 500 MW

A decision on which alternative to construct has not been made. Preliminary analyses indicated that Alternative 1 would be most cost

11 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

effective, and it was selected for feasibility- 1 grade design and estimate. As the studies progressed, however, the underground alternative appeared to be most cost effective. But because the designs and estimates for the underground powerplant are only at appraisal—' grade, the level of confidence in the estimate is not as great as for Alternative 1. Consequently, Alternative 1 is being used in the feasibility report to demonstrate project feasibility. If advance planning studies prior to construction confirm that Alternative 3 is more cost effective, it would probably be selected for construction. Enough construction information was available so that environmental studies for all three alternatives could be conducted at feasibility grade.

a. Surface Powerhouse (500 MW) - Alternative 1. The proposed action is a new powerhouse which would be constructed at the downstream end of the present Arizona powerhouse. It would begin about 38 feet from the portal of the access tunnel to the tunnel plug outlet woks and would extend 222 feet downstream. About 80,000 cubic yards (yd ) of material would need to be excavated for the powerplant and taken to an existing dump site. The desired capacity of the powerhouse is 500 MW to be produced by two 250-MW generating units. This capacity is the maximum that can be added to the lower penstock lateral without causing excessive flow velocity. The architectural style of the new powerhouse and the layout of the transformers in its exterior would be harmonious with the existing powerhouse. (See Figures 2 and 3.) The construction cost of this alternative would be approximately $302 million.

Penstocks. The new generating units would be served through the existing 25-foot-diameter lower Arizona penstock, which is contained in the 50-foot-diameter lower Arizona penstock tunnel. The centerline of the lower penstock is at about elevation 647 and the centerline of the turbines would be at about elevation 623. The new powerhouse would require that an 18-foot-diameter branch penstock contained in a 26-foot-diameter penstock tunnel be constructed to each new turbine from the existing 25-foot-diameter penstock lateral.

Surge Tank. A concrete-lined surge tank would be needed to protect the penstocks from excess pressures that may occur with the new units. The tank would be 230 feet in height, 80 feet in diameter with a top elevation of 1270 and bottom elevation of 1040, and a 25-foot-diameter connecting tunnel to the header. The surge tank would be located at the east edge of the employees' parking lot on the Arizona side and would be underground except for 40 feet of exposed surface on one side.

A 25-foot-diameter connecting conduit (riser) would extend 440 feet on an incline from the 25-foot-diameter penstock to the surge tank. The riser would be connected to the penstock lateral at the intersection of the penstock tunnel and the lower construction access tunnel.

1/ See Attachment G for definition.

12 Figure 2. Photograph (looking north) of the existing Hoover Dam and Powerplant in Black Canyon of the Colorado River.

Figure 3. Photograph (looking north) of artist's conception of the proposed additional 500-MW surface powerhouse immediately downstream from the Arizona transformer deck. (Note: Surge tank in upper right corner).

CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

Construction activities include excavation for surge tank shaft, and tunneling for th riser from existing penstock to bottom of the shaft. About 55,000 yd of excavation material would be hauled to an existing disposal site about 1 mile southeast of the dam.

Transformer Deck. Any construction project on the Arizona side of Hoover Dam and Powerplant would require the widening of the transformer deck to allow for the large vehicles and equipment that would be required. The present construction access is down the lower portal road, along the Nevada transformer deck, through the machine shop of the powerhouse, and then down the Arizona transformer deck. This access interrupts the tours and the daily use of the machine shop facilities.

The existing wall on the transformer deck on the downstream side of the central portion outside of the powerhouse would be removed. The present deck would be extended downstream about 28 feet and another concrete wall 2-foot thick would be constructed. This would allow the construction vehicles and equipment access to the construction site without disturbing normal activities of the powerhouse or daily tours, and possibly would eliminate safety and traffic hazards to employees and tourists.

Transformer Circuits. In order to convey the power from the two new generators to the switchyards on the Nevada side, two additional transformer circuits would be constructed. One row of double circuit transmission towers would carry the two circuits across the river (between the cableway and existing Circuit No. 8) and then into the Arizona-Nevada switchyard. The tieline between the Arizona-Nevada switchyard and the Metropolitan Water District switchyard would be reconductored to handle the additional capacity.

Transmission Capability. The capacity of this alternative exceeds the available carrying capacity of existing transmission lines to some load centers in the region. However, the specific short- comings will not be definitely known until the post-1987 allocation of Hoover Modification capacity is made. Transmission lines which are presently being planned by utilities, and for which the Allen-Warner Valley Energy System Environmental Impact Statement (Bureau of Land Management, December 1980) has been prepared, will be designed to transmit the incremental portion of capacity generated by Hoover Modification. No separate powerline will be built from Hoover Switchyard specifically and solely for Hoover Powerplant Modification capacity.

Cofferdam. This alternative would require the construction of a temporary cofferdam (Figure 4), 120 feet wide, to divert water from the powerhouse construction site during the construction process. Sheet pilings, positioned in a cloverleaf design, with a top elevation of 666 feet would be driven into the alluvial deposits in the river channel about 50 feet from the proposed powerhouse. The cofferdam would be about 510 feet long and would require continuous pumping to offset leakage. The water will be returned to the river. The quality of the river water is not expected to be affected. About 20 feet of

13 SURGE TANK

f LOWER PENSTOCK PLUG OUTLET WORKS

II _ , \ \ Ht1N4; ENSTOC KS STONEY GATE STRUCTURE I 4‘ \ • \ N\ ‘4 , \ \ \\ \ \

CANYON WA LL TRAIL TO STONEY GATE I 1I OUTLET WORKS .11111111111' ARIZONA POWERPLANT ONGITUDINA L EA ADDITIONAL UNITS ADDITIONAL ARIZONA SURFACE POWERPLANT Lake Mead gg TAILRACE DECK _ TENS ION EL 673 0' Biller COFFERDA Colorado CABLEWAY

Figure 4. Diagram of cofferdam for Alternative I located in the river channel. Cofferdam for Alternative 2 would consist of only one of the cloverleaf structures. It would be located at the end of the existing Arizona powerhouse. Alternative 3 requires no cofferdam. CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

3 material (45,000 yd ) would be excavated from the channel bottom in the cofferdam area and hauled to an existing disposal site about 1 mile southeast of the dam. 3 About 215,000 yd of sand and gravel for the cofferdam would be obtained from a borrow area located at White Rock Canyon, about 3.7 miles southeast of Hoover Dam. This fill material would be lowered to the construction site by use of the overhead cableway and would be put inside the sheet pilings to act as a ballast. At completion of construction, the cofferdam fill material would be removed to an existing disposal site about 1 mile southeast of Hoover Dam. 3 During maximum turbine releases of 49,000 ft /s, with the uprating completed, the water surface elevation in the powerplant area would be about 2.6 feet higher under the influence of the cofferdam. Loss in head of 2.6 feet through 17 generators at maximum current output results in a reduction of about 0.39 percent of rat#d power output or a loss of 9.2 MW. For a release of 49,000 ft Is, the maximum velocity through the cofferdam area would be 8.2 miles per hour (mph). The estimated diameter of erodible material that would remain stable under this velocity is 12 inches.

b. Replacement of Generating Units A8 and A9 - Alternative 2. The Arizona wing of the Hoover Powerplant contains two small generating units with a combined capacity of 90 MW (Figure 5). These two units could be removed and replaced with one larger unit. The space available after the removal of the units limits the size of such a new unit to not more than 350 MW (making the net gain in capacity 260 MW). This alternative would be 240 MW short of the potential 500-MW capacity. The physical changes would be within the powerhouse with no noticeable changes outside. The present units, A8 and A9, along with the concrete partitions in the lower levels, would be removed from the powerhouse, causing the loss of their 904W capacity for the 4-1/2-year construction period. About 5,000 ye of material would be excavated and taken to an existing dump site. A new containment would be constructed for a single unit in the former location of A8 and A9. The construction cost of this alternative would be approximately $232 million.

Penstocks. The 13-foot-diameter penstock lateral No. 8 that serves units A8 and A9 would be replaced with a larger bifurcated penstock with an inside diameter of 19 feet. This would also require the removal of the concrete lining, and enlargement of the existing 18-foot-diameter tunnel to accommodate the larger penstock. A bulkhead would be installed in the 30-foot-diameter upper Arizona penstock, a short distance upstream from penstock No. 8, which would remain in place during the construction period.

Surge Tank. Protection of the generating unit would be provided by a concrete-lined surge tank. The tank would be 80 feet in diameter inside with a top elevation of 1270 and bottom elevation of 1040 with the top 40 feet exposed on one side. The tank would be located at the east edge of the employees' parking lot on the Arizona

14 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION side. A 25-foot-diameter riser would extend from the 30-foot-diameter upper Arizona penstock to the surge tank on an incline.

Construction activities include excavation for surge tank shaft, and tunneling for riser 3from existing penstocks to the bottom of the shaft. About 55,000 yd of materials would be excavated and hauled to an existing disposal site about 1 mile southeast of the dam.

Transformer Deck. Same as Alternative 1.

Transformer Circuits. Additional transformer circuits are not required.

Transmission Capability. Existing lines are capable of transmitting the power from this alternative.

Cofferdam. This alternative would require the construction of a temporary cofferdam, 130 feet in length, to divert water from the powerhouse construction site during the construction process. Sheet pilings, positioned in a circular design, with a top elevation of 666 would be driven into the alluvial deposits in the river channel about 50 feet from the existing powerhouse. The cofferdam would be about 125 feet wide and would require continuous pumping to offset leakage. The water would be returned to the river. The quality of the river water is 9ot expected to be affected. About 20 feet of material (12,000 ye) would be excavated from the channel bottom in the cofferdam area.

The sand and gravel for the cofferdam would be obtained from a borrow area located at White3 Rock Canyon, about 3.7 miles southeast of the dam. About 47,000 yd of material would be lowered to the construction site by conveyor system and fill the sheet piles. At completion of construction, the cofferdam fill material would be removed to an existing disposal site about 1 mile southeast of Hoover Dam. 3 During maximum turbine releases of 49,000 ft /s, with uprating completed, the water surface elevation in the powerplant area would be about 2.6 feet higher under the influence of the cofferdam. Loss in head of 2.6 feet though 17 generators at maximum current output results in a reduction of about 0.39 percent of ratfd power output or a loss of 9.2 MW. For a release of 49,000 ft /s, the maximum velocity through the cofferdam area would be about 8.2 mph. The estimated diameter of erodible material that would remain stable under this velocity is about 12 inches.

c. Underground Powerhouse (500 MW) - Alternative 3. An underground powerhouse (Figure 6) in the canyon wall on the Arizona side of the canyon would use some space in the existing underground gate chambers and tunnels.

Both the Arizona and Nevada sides of the river were closely studied for geological structure, since tunneling would be necessary for any underground construction. The geology on the Arizona side was found to be extremely sound, and provided better construction access

15 Figure 5. Photograph of generating units A8 and A9 on the Arizona side of the existing Arizona powerhouse of the Hoover Powerplant.

Figure 6. Photograph of the Arizona side of Black Canyon as it would look with either Alternative 2 (replacement of A8 and A9) or Alternative 3 (500-MW underground powerhouse). The only difference in appearance from present is the addition of the surge tank.

CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

for a surge tank than the Nevada side. Consequently, the Arizona side was selected as the favored site for the location of an underground alternative. The powerhouse would be constructed in a chamber in the canyon wall (abutment) behind the location of the suggested 500-MW surface powerhouse. The desired capacity of the powerhouse is 500 MW to be produced by two 250-MW generating units. This capacity is the maximum that can be added to the lower penstock lateral without causing excessive flow velocity. Since the construction would be underground, there would be no change in the present appearance of Hoover Dam and Powerplant. No cofferdam would be constructed, the Arizona Stoney Gate would be used as the dewatering structure. In other respects, such as penstocks, surge tank, transmission facilities, operation, riverflows, and velocities, this alternative woul4 be similar to the surface powerhouse alternative. T4e 120,000 ye of material removed from the tunnel and the 55,000 ye removed for the surge tank would be taken to the existing dump site discussed under Alternative 1. The construction costs of this alternative would be about $286 million.

d. No ATOon (Future Without the Project) - Alternative 4. Since the uprating—' program is underway, the capacity of Hoover Powerplant will be increased to about 1,800 MW, as discussed in Chapter I. Thus, if no action is taken as the result of this investigation, there will nevertheless be a 460-MW increase in the generating capacity over the present 1,340 MW. However, more than 500 MW of capacity are still required to meet the future demands and needs of the ever growing Southwest which would have to be supplied by other sources.

After uprating, the maximum releases frqm the powerplant3are expected to increase from the present 40,000 ft /s to 49,000 ft /s. All of the alternatives discussed in this document have assumed the uprating program would be completed before the construction of the Hoover Powerplant Modification Project begins.

2. Construction of Alternatives. All alternatives except no action (future without the project) would require blasting, excavating, and tunneling for construction. Replacing A8 and A9 would take about 4-1/2 years and the surface or underground powerhouse would take about 5 years each. For planning purposes, construction would be from 1987 through 1991. The process would occur in five stages: surveying and layout, building the temporary cofferdam, blasting and excavating, constructing the powerhouse, and installing the generators and other electrical equipment.

The blasting would be done using small charges and controlled blasting procedures, to protect existing generating equipment, and to protect tourists and employees. Most of the blasting would be done in

1/ Hoover Powerplant Uprating Special Report, May 1980, U.S. Department of the Interior, Water and Power Resources Service. Copies may be obtained by writing Bureau of Reclamation, Attention: LC-600, P.O. Box 427, Boulder City, Nevada 89005.

16 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

the canyon walls above the water level, but some would be in the canyon walls below water level. For Alternative 1 the estimated volume of material t be removed 3for the powerplapt, surge tank, and cofferdam (80,0003 yd , 55,000 yd , and 45,000 yd , respectively) is about 1803 000 yd . Alteratives 2 and 3 would require a total of 72,000 yd and 175,000 yd , respectively. The material would most likely be deposited at an existing Bureau dumpsite on the Arizona side of the dam. (See Frontispiece Map.) Two alternate dumpsites are located along the lower portal road (Bureau property) one is an existing dumpsite and the other, because of the sparsely vegetated nature of the area, could easily qualify as a dumpsite.

All alternatives3 would require large quantities (30,000- 80,000 yd ) of concrete, and a batch plant would need to be erected. The recommended site is on the Arizona abutment at the existing dump site. Sand and gravel for the concrete would be taken from existing commercial pits in Henderson, Nevada or from a 1.5-mile area just east of the Highway 93 bridge in White Roy< Canyon, Asizona. Alternatives 1, 2, and 3 would require 80,000 yd , 30,000 yd , and 50,000 yd of sand and gravel, respectively.

In order to convey the cofferdam fill material from White Rock Canyon to the construction site, it is anticipated that trucks would do the hauling at night to minimize traffic impacts at the dam and along U.S. Highway 93 in Arizona. Assuming this work would be done during a 90-day period, and that semitrailer haul units would be used, it is estimated that the traffic would amount to one truck every 7 minutes during a 12-hour night shift.

Table 4 indicates the manpower requirements for the construction of the modification of Hoover Powerplant by types of workers. The construction activities for both the surface and underground alternatives would require about 420 people to be working at the peak of the activities in 1989. After the construction is completed about 20 people would be needed to operate the plant. The alternative of replacing generating units A8 and A9 would require the same contractors but only about one-half the number of people.

Table 5 shows the probable breakdown between movers and nonmovers among the entire workforce necessary to undertake the proposed modification to Hoover Powerplant. A mover is defined as a worker who relocates residence into the area of the project in order to work. A nonmover is defined as a worker who returns daily to the same residence occupied prior to beginning work on the powerplant modification.

3. Operation of Alternatives. In order for the project to be economically feasible, the operation of the powerplant would have to be modified to allow for longer periods of high generating capacity. Since the water released through the powerhouse to generate power is dependent upon downstream water requirements, (i.e., no water is released for the sole purpose of generating power) only a certain amount of water per week or month is released. The powerplant operators must thus save as much water, by extremely low releases (0-2,000 ft Is) during certain portions of the day or week in order to make the high releases which emphasize peak power demands. This differs from the present operation as compared in Figures 7 through 10.

17 CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

Table 4 ! 1/ 1 CONSTRUCTION MANPOWER REQUIREMENTS- ,1 Hoover Powerplant Modification Project

Peak Item 1987 1988 1989 1990 1991

Bureau Forces 30 45 70 55 40

Contractor Forces

Engineering and Administrative 22 39 54 42 24 Pipefitter 2 4 3 2 Plumber 4 6 5 2 Sheet Metal Worker 4 6 4 1 Mechanic 3 13 19 16 3 Millwright -- 7 12 10 4 Carpenter 15 22 32 22 6 Cement Mason 5 5 17 10 3 Iron Worker 7 7 15 4 2 Welder 4 8 15 3 2 Driller 2 4 2 Miner 5 8 4 Teamster 5 8 25 10 7 Laborer 15 30 60 35 20 Heavy Equipment Operator 13 20 40 20 12 Oiler 2 6 9 6 2 Electrician 2 15 15 14 8 Lineman 8 15 6 2

Contractor Subtotal 100 210 350 210 100

Combined Total 130 255 420 265 140

1/ Figures presented are estimates for Alternatives 1 and 3. — Alternative 2 would require the same contractor forces but only about one-half the number of people. CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

Table 5 MOVER-NONMOVER ALLOCATION OF MANPOWER-11 Hoover Powerplant Modification Project

Peak 1987 1988 1989 1990 1991

Movers

Bureau Forces

Technical 16 24 38 30 22 Clerical 0 0 0 0 0

Contractor Forces

Management

Technical 14 23 32 26 14 Clerical 0 0 0 0 0

Labor 16 34 59 34 15

Subtotal Movers 46 81 129 90 51

Nonmovers

Bureau Forces

Technical 4 6 9 7 5 Clerical 10 15 23 18 13

Contractor Forces

Management

Technical 3 6 8 6 4 Clerical 5 10 14 10 6

Labor 62 137 237 134 61

Subtotal Nonmovers 84 174 291 175 89

Total Manpower 130 255 420 265 140

1/ Figures are for Alternatives 1 and 3. Alternative 2 would require — the same contractor forces but only about one-half the number of people.

19 HOOVER MODIFICATION STUDY - WEEKLY LOAD CURVE LEGEND Revised Operation PRESENT GENERATION Typical Week — Winter - - -PROJECTED GENERATION Fourth Week of December 2400 64,320 I I I I I I

2200 58,960

2000 53,600

1800 ^ 48,240

en -4- '4- 1600 42,880 ri Ust 1400 37,520 0 L4.1

1200 32,160 Li) a-

MEGAWATTS 1000 26,800 1.1a 6.4.)

800 21,440

C) 600 16,080

111 10,720 400 1 I 1 1 71:11 1 I 1 i I 5,360 200 I I 1 s I I I I i I IL — —I I — I I SUN MON TUE WED THU FRI SAT HOOVER MODIFICATION STUDY - WEEKLY LOAD CURVE LEGEND

PRESENT GENERATION PROJECTED GENERATION Revised Operation Typical Week - Spring Third Week of March 2400 64,320 I 1 2200 i- i58,960 20004— 53,600

1800 -- A 48240 r ---1 I \i'l I ....VA I ogi , I 1600— I 42,880 t I I I I I cn 1400 — I 37,520 i— I I t— I a 1 3 I 200 — I 32,160 a co La 2 10000--- 26,800 i'T 1 21,440

16,080

10,720

5,360 -----1

0 r 0 SUN MON WED

6 MOH

MEGAWATTS eri œ 0 R). .; 0 0 0 0 0 0 0 0 0 0 0 8 8 8 00 0 0 1

.1•1■11

ow N. =I alF

L 4

—4 I. X ...."1.11naa• C

...... 31.1.6100•••••■ 4

JrLISIMIAMONme...

J.0

1 1 1 1 I I IV IV t.+1 to 4L. E> F - P - - 4 - -4 oCi . C, cow IV PO 4, -47) RV 0 0 0 0 § 0 0 0 0 CUBIC FEET PER SECOND (ft s/s) HOOVER MODIFICATION STUDY - WEEKLY LOAD CURVE LEGEND

PRESENT GENERATION PROJECTED GENERATION Revised Operation Fall Typical Week — First Week of October 2400 64,320

2200 — — 58,960

2000 — — 53,600

1800 L v — 48,240 7.;.... 0,4- 1600 — V — 42,880 clz u) 1400 — — 37,520 8 - Li.,L.,, 1200 — —32,160 cr CD a.w 1- . 2 WOO — — 26,800 LLLA) Li_ 800 — —21,440 (--) m D C.) 600 — — 16,080

400 — 10,720 I I I I 200 I II I I 5,360 I I I _J _ J 1 cLj 0 SUN MON T UE WED THU FR I SAT CHAPTER II ALTERNATIVES INCLUDING THE PROPOSED ACTION

They were produced by optimization of peaking energy production under the conditions of average projected water supply, and are regarded as the maximum peaking attainable. Normal operation would probably involve slightly less peaking.

The operation of the plant would vary from month to month during a yearly cycle. From November through January3 the maximum generation would be approximately 1,500 MW (40,000 ft /s) as illustrated by Figure 7, representing the fourth week of December. In3 February the generating peak increases to up to 1,800 MW (49,000 ft /s) and continues at that level through March, as shown on Figure 8, representing thq third week of March. In April, the peaks rise to 2,100 MW (56,000 ft /s) nearly every weekday and continue at that level through July. This pattern is illustrated by Figure 9, representing the fourth week in July. Occasionally generation would rise above 2,100 MW toward 2,300 MW as the reserve capacity is needed to cover system emergencies.

Peak generation would decline to 1,800 MW (49,000 ft3/s) during part of August, but would generally continue at 2,100 MW thr2ugh September. In October, peaks would decline to 1,700 MW (45,500 ft /s) as shown on Figure 10, representing the first week of October. It would attain that level intermittently until November, when the peak would drop to about 1,200 MW.

On a weekly basis, the operation would consist of minimal generation on Saturday and Sunday. Each weekday the generation would begin to rise at about 8 a.m., and when peaks of about 2,100 MW occurred, they would be reached shortly after noon. Generation would drop back to a minimal value in the evening hours, and reach minimum by about 10 p.m.

The minimum generation shown on Figur9 7, 8, 9, and 10 represents an assumed minimum release of 2,000 ft /s, which would assure a live stream below the dam even when Lake Mohave levels are low. However, it is anticipated that in actual operation the nighttime releases would fluctuate somewhat to meet power system regulation needs rather than be as steady as shown. When Lake Mohave is high, the generation would drop to zero at times.

Figures 11 and 12 show the Colorado River Water Surface Profiles with Lake Mohave at elevations 647 (maximum) and 630 (minimum). Each profile shows the Colorado River bottom from Hoover Dam to just below the Willow Beach National Fish Hatchery and Resort. The present and projected alternative flows are represented on the profiles. The velocities of each release are for three specific areas of concern; the rapids at mile 2, Ringbolt Rapids, and the Willow Beach National Fish Hatchery.

Davis Dam, the dam which creates Lake Mohave, would be operated in the same manner as presently experienced. This is because the total amount of water released from Hoover Dam into Lake Mohave during any week, month, or year is totally dependent upon the amount of water required by downstream users and flood control considerations. No water is released for the sole purpose of generating power.

20 :6 3 a 62,000 ft /S ac. @CAC)EnD© ROWER WINER WMEPG0 PEOFEEZ 56,000 ft 3/s r 4, 4— 11=1 141011Mff L4111M4frail =',. t6T

.... AMIlla.._ Addition& 500 MW Powarlwaw (2,300 NW) wn 81 tt© " 144i55 — I G Z R aplaci ng AO and A9 (2,060 V CO 00 WW) 0 ft Upalindln 1,600 MW waft, 1 0 Currant maximum (1,340 MW) 0 =II tg0 — 3 current ILO 0'2.000 ft /s minimum MVO =g r

ft3/%„:.! cubic feet ;er second _

1 CO20 Ei o, M Va c= N N INTAKE PIPE L' (C© A A A

,,F30 clu NO 11,4 • Mr Lg ,=n N I IF IF VEL. VEL. VELi gt© imPhi. OK IMO). 4.5 - 3.4 RIVER BED 1.7 .2 L5 I.4 11 i 1.4 0.2 _0.1 0.7_ gEt% aa aa 2.43. RIO[L,NZ [31111,W 1100WEG3 LAW

Figure 11 Graphic representation of the rise in water level due to each of the proposed alternatives with Lake Mohave at elevation 647, the maximum lake level. Areas of possible concern are noted on the graph. The water velocity in miles per hour (mph) for each of the water surface profiles is shown for the areas of concern. (The velocities are listed in the same vertical order as the profiles). 43 ©CATBE&D© Oil WEE W1 @VILEZ 62,000 ft 5/S ... . . N 1 MEE RICAMEELEMVOCMf= CM 3 01 56,000 FT /6 *" , . W a) GT© . i A4d,tlunoI 500 Mai Raannhaam(2,500 w) 4- CO 49 0 0 00 f g I I M 3 an, IX 0 4 R•placing lie and A9 (2,060MW) -0 = 0,000 3C 3 cA & 11- tg 1 22, tg© Uprating co I $0051 Paq i=9 Co r r ani McKinnon (1,540 Mail UMMIMMW (::? 3 ft /s= cubic feet IIIIIirail (II get@ NOW

• -2 000 ft Current Minimum flow

IIII 0 co L. . i N rA 1!) INTAK E PIPE Il — @AO 11 A , A I T N I 1 R G A OR= A ,--0 g ©CI y -far ., V V I v E L. V E L V E L g g 0 (MPH) (M (MPH) 4. 8 29 4.5 3.7 RIVER BED 2.4 4.3 3.5 2.2 4.1 3.3 1.9 0 5 0.1

hiffilAg IbElaW li@OWEE2 CAW

Figure 12. Graphic representation of the rise in water level due to each of the proposed alternatives with Lake Mohave at elevation 630, the present minimum lake level. Areas of possible concern are noted on the graph. The water velocity in miles per hour (mph) for each of the water surface profiles is shown for the areas of concern. (The velocities are listed in the same vertical order as the profiles).

CHAPTER Z

AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

CHAPTER III AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

A. Introduction

This chapter presents a brief description of the project area followed by a more detailed description of those components of the existing environment which may be impacted by the project. The environmental impacts of each alternative are analyzed and discussed. This analysis forms the basis for the comparison of alternatives presented in Table 3.

The Hoover Powerplant is located at Hoover Dam in the Black Canyon of the Colorado River on the Arizona-Nevada border, 25 miles southeast of Las Vegas, and 7 miles northeast of Boulder City, Nevada. (See frontispiece location map and photograph of the area) The area surrounding Black Canyon is typical Mojave Desert with its associated plants and animals. However, the actual affected environment lies primarily within the high canyon walls of Black Canyon and in the main body of Lake Mohave.

The massive volcanic walls of Black Canyon are approximately 500 feet apart and rise nearly vertically 700 feet above the riverbed. The 20 miles of Black Canyon below Hoover Dam are considered the upper portion of Lake Mohave formed by Davis Dam. This portion of the lake can be characterized as a river with a flow that varies from fast to slow depending on water levels in Lake Mohave and releases from Hoover Dam. The remaining 47 miles of Lake Mohave become a large basin bounded by Eldorado, Painted, and Pyramid Canyons. This portion of the lake is wider and is a typical reservoir environment. Black Canyon extends three-fourths mile above Hoover Dam into Lake Mead. Lake Mead, at maximum elevation, extends 110 miles upstream from Hoover and forms, by capacity, the largest reservoir in the country (28.5 million acre-feet of storage).

B. Affected Environment

1. Hoover Dam. At the time of its construction, Hoover Dam was an engineering feat of unprecedented proportions. The American Society of Civil Engineers has designated it a modern engineering wonder. Approximately 700,000 people from around the country and the world visit the dam annually and over 20 million persons have taken the guided tours of the dam and powerplant since 1936. Almost 365 days per year the area is bustling with crowds of people enjoying and photographing the impressive structure with its symmetrical powerhouses and scenic canyon setting.

2. Climate and Air Quality. The area around Hoover Dam is one of the driest and warmest areas of the United States. This area is characterized by hot summers, mild winters, and wide fluctuations in the annual rainfall. Mean annual temperature is 67°F with a minimum of 3°F and a maximum of 118°F. The average annual rainfall is

21 CHAPTER III AFFECTED ENVIRONMENT

5.4 inches. The rainfall usually occurs as local showers or downpours in July and August, and in February and March. The runoff, when rain does occur, is high because of the steep gradients and general scar- city of vegetation. Strong winds are frequent with most of the higher winds occurring in the spring and fall. The average mean wind velocity during the year is 9 mph, with maximum velocities in excess of 50 mph. Air quality around Hoover Dam is generally good. An increasing population in the Las Vegas Valley, approximately 20 miles northwest of the dam, has resulted in a smog problem in the valley.

3. Seismicity. The active California-Western Nevada seismic zone is 120 miles west of Hoover Dam. Many earthquakes have been associated with this zone and still occur in that region. The general area of southern Nevada has experienced more than 10,000 earthquakes since Hoover Dam was built, none of which have caused any damage to the dam. In May 1939, an earthquake of magnitude 5 on the Richter Scale occurred near Boulder City. Subsequent aftershocks ranged between magnitude 3.5 and 4.0. Local seismic activity in the vicinity of Lake Mead has been fairly continuous since 1936, reaching a peak of activity in 1954. This activity appears to have been associated with the filling of Lake Mead. Another source of earth movement in the vicinity has been the underground detonations of nuclear devices at the Nevada Test Site, about 100 miles northwest of Hoover Dam.

4. Geology. Hoover Dam is bordered by two discontinuous mountain ranges and broad alluvium-filled valleys. It is bounded by the Black Mountains on the east and the Eldorado Mountains on the west. These mountains were formed by volcanoes that erupted around the Eocene Epoch period (55 million years ago). During this period there were three major eruptive events that are now known as the Patsy Mine, the Golden Door, and the Mt. Davis volcanics. There has been no volcanic activity here for millions of years. Nevertheless, the many hot springs in this area suggest that there are still nearby sections of rock that are hot at depth.

The material which must be excavated for the cofferdam required in project Alternatives 1 and 2 is principally bedrock material (con- glomerate) of volcanic origin.

Some sand, which is brought in by occasional flash flooding of tributary washes, also exists in the proposed cofferdam area. No silt, clay, mud, etc., deposits exist in the area partially because of the high releases from the dam.

5. Hydrologic and Aquatic Environment

a. Background - Hoover Dam/Powerplant Operations. The aquatic system in Lakes Mead and Mohave is influenced by the water released through the powerplant at Hoover Dam. As the water is released for downstream use, it produces electrical energy. Since monthly and weekly water requirements downstream can be met by several different patterns of releasing water, the operators at the powerhouse

22 CHAPTER III AFFECTED ENVIRONMENT

can schedule water releases, within certain restrictions,- " to be most beneficial to energy needs. During periods of low energy demand, water is retained in Lake Mead for release during peria0 of higher demand. However, when Lake Mohave is below elevation 637±I a minimum release is maintained, so that "live stream" conditions can be maintained below the dam. For purposes of 8analysis, this release is assumed o average approximately 2,000 ft Is but flows of less than 2,000 ft Is occasionally and temporarily (1 to 4 hours) occur under present operations.

Water releases from the dam follow a seasonal, weekly, and daily cycle. On a seasonal basis, releases are greatest during the spring and summer months and lowest during the winter months. On a weekly basis, releases are lowest on weekends but increase progres- sively to a maximum on Wednesday or Thursday. The typical daily release cycle fluctuates from a minimum flow in the early morning hours to peak flows in the late afternoon hours. The powerp;ant presently reaches its nameplate capacity of 1,340 MW (40,000 ft Is) only about 4 to 5 percent of the time during the year. The solid curves in Figures 7 through 10 show representative weekly releases from Hoover Dam for the four seasons.

The generation of electricity in the cyclic manner, described above, affects the aquatic biota above and below the dam by subjecting it to daily fluctuations in water velocity, temperature, and nutrient content.

b. Water Level and Velocity Fluctuations. The elevation and velocity of the water within the Black Canyon area below the dam depend on the elevation of Lake Mohave and the quantity of water released from the dam. Lake Mohave, when at elevation 647, acts as a buffer to the water released from Hoover Dam. As the daily power cycle increases and more water is released, the water level at the base of the dam rises. As generation decreases, the water level drops. The daily fluctuations in water level (Table 6 and Figure 11), approximately 10 feet at peak release, decrease downstream to less than one-half foot at Willow Beach. In concert with the rising and falling water is an increase ary decrease in flow velocity. The present peak releases (40,000 ft /s), vary in velocity through the canyon but average about 1.9 mph with a maximum velocity of 3.8 mph at a narrow3 section 1 mile below the dam (Table 7). Low releases of 2,000 ft /s, vary in velocity through the canyon but average about 0.1 mph. The maximum velocity of 0.3 mph during minimum releases occurs about 1 mile below the dam (Table 7, Column 1).

1/ The total amount of water released through Hoover Dam in any given month is determined by downstream water user requests and flood control requirements, not by energy requirements. No water is released from Hoover Dam for the sole purpose of developing energy.

2/ Elevation is in feet above mean sea level.

213ldVHD Table 6

DAILY FLUCTUATIONS IN WATER LEVELS DUE TO HOOVER DAM RELEASES III Hoover Powerplant Modification Project

Daily Daily Fluctuation Fluctuation . Peak please MinimuT Release at Dam Tailrace at Willow Beach Condition (ft /s) (ft /s) (feet) (feet)

Lake Mohave Elevation 647

Existing, / 40,000 '0-2,000 10 0.5 L prati 49,000 0-2,000 12 1.0

Hoover Powerplant Modification

Alternative 2 56,000 0-2,000 14 1.5 Alternatives 1 and 3 62,000 0-2,000 16 1.5

Lake Mohave Elevation 630

Existingi, 40,000 2,000 17 2.5 1 49,000 2,000 20 3.5 Uprating- in C) Hoover Powerplant Modification in

Alternative 2 56,000 2,000 22 5 Alternatives 1 and 3 62,000 2,000 24 6 iN3WN0dIAN3 I/ Future without the project. Table 7 ACTUAL AND PREDICTED MEAN AND MAXIMUM

WATER VELOCITIES IN BLACK CANYON Hoover Powerplant Modification Project

Unit: mph 2]131dVH)

Velocities Velocities with Velocities with III Due to Alternatives 1 Alternative 2 1/ Uprating- of or 3 (new 500- (Replacement Generators Difference MW powerhouse) Difference of Units A8-A9) Difference Existing (No Action Columns and Columns and Columns Velocities Alternative) 1 and 2 Uprating 1 and 4 Uprating 1 and 6 Conditions (1) (2) (3) (4) (5) (6) (7) Lake Mohave Elevation 647

Peak Release Mean Velocity 1.9 2.4 +0.5 2.8 +0.9 2.6 +0.7 Maximum Velocity 3.8 4.2 +0.4 4.5 +0.7 4.3 +0.5

Minimum Release* Mean Velocity 0.1 0.1 0.0 0.1 0.0 0.1 0.0 Maximum Velocity 0.3 0.3 0.0 0.3 0.0 0.3 0.0 Lake Mohave Elevation 630

Peak Release Mean Velocity 2.5 2.9 +0.4 3.6 +1.1 3.4 0.9 Maximum Velocity 4.1 4.7 +0.6 5.1 +1.0 4.7 0.6 Minimum Release* Mean Velocity 0.5 0.5 0.0 0.5 0.0 0.5 0.0 Maximum Velocity 3.0 3.0 0.0 3.0 0.0 3.0 0.0 3 *Minimum Release - 2,000 ft /s

1/ Future without the project. CHAPTER III AFFECTED ENVIRONMENT

At elevation 630 Lake Mohave continues to buffer the releases from Hoover Dam but to a lesser extent. This equates to a greater fluctuation (17 feet) in water levels (Table 6 and Figure 12) at the base of the dam during peak releases. Fluctuations decrease downstream to 2.5 feet at Willow Beach. Lower lake levels also mean that the low and maximum release velocities will increase. During a peak release, the mean velocity is 2.5 mph whilel the maximum velocity is 4.1 mph 1 mile below the dam. At a 2,000 ft Is release, the mean velocity is 0.5 mph while the maximum velocity is 3 mph 1 mile below the dam (Table 7, Column 1).

Figure 13 depicts the cyclic manner in which Lake Mohave is presently operated. The normal schedule line depicts the ideal level at which the Bureau would like to operate Lake Mohave throughout the year. Increased or decreased water demands, localized rainstorms, cropping patterns, power requirements, etc., usually prevent the Bureau from meeting the normal schedule can be seen by the line depicting the 1978 actual water elevations—' . Water level fluctuations on Lake Mohave of 1 or 2 feet during the week are considered normal with fluctuations in excess of 3 feet occurring rarely.

c. Substrate Stability and Primary Productivity (Algae Growth). Under present conditions, the first 3 miles below the dam are probably the most productive section of river (Paulson, et al., 1980d) between Hoover Dam and the warm/cold water interface (see Section f. that follows). This condition persists because of three factors: light penetration, water velocity, and substrate type (Paulson, et al., 1980d). The shallow, rocky nature of the 3-mile section below the dam enhances attached algae (periphyton) and invertebrate production. The river below this section is deeper, (30-90 feet), becomes more channelized, and has a predominantly sand and gravel substrate which is unsuitable for attached algae growth. Although the substrate below the dam is basically stable, additional aggregate is introduced into the system from the many washes in the Black Canyon area. Under presentl conditions, short periods of high releases (greater than 30,000 ft /s) are sufficient to shift sand, gravel, and smaller introduced materials downstream. This action maintains some of the substrate in an armored rocky condition that favors algae growth by providing a substrate that has large rocks used by plants to anchor themselves. Without these currents, sand would accumulate and periphyton growth would decline. When peak discharges are reached, smaller shifting substrate (that may contain periphyton grown at lower velocities) may move, causing some periphyton to break off. Higher velocities also tear or break loose the large filaments of algae. This action decreases the biomass of algae (Paulson, et al., 1980d) during peak flows, but the community reestablishes during the seasons when flows are low. Substrate material which has armored or is greater than 3-5 inches remains fairly stable and productive.

1/ The Lake Mohave 1978 water year, when compared to the last 5 years, is considered to be the most typical of past operations.

26 ■•••■••■••

655

650

DAVIS DAM SPILLWAY CREST

615

/VV.\

635

630

The Lake Mohave water elevations are ideally scheduled to meet the "Normal NORMAL SCHEDULED MOHAVE ELEV. Scheduled Mohave Elevations" line. However, varying situations, increased — • — AVERAGE FUTURE YEAR (1996) or decreased water demands, rainstorms, power requirements, etc., prevent the Bureau from exactly following the normal schedule line as shown by the ------HISTORIC ELEVATIONS 625 1978 "1978 Historic flevations" line. The "Average Future Year (1996)" line takes the 1978 historic line and projects what the Lake Mohave elevation would look like when based on the proposed Hoover Powerplant Modification operation.

620 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

CALENDAR YEAR (MONTHS)

Figure 13. Projected effects of modified Hoover Powerplant releases upon Lake Mohave elevations. CHAPTER III AFFECTED ENVIRONMENT

Species diversity is greatly limited by the cold water releases from the hypolimnion of Hoover Dam. The rocky substrate affords stable anchoring for attached algae (Cladophora glomerata). Cladophora makes up the largest vegetative biomass in the area and is predominant in the upper 3-mile section. Diatoms (Diatoma vulgare and Melosira varians) make up the other dominant algae of the area.

The diversity of benthic invertebrates in the first 8 miles below Hoover Dam is very low and overwhelmingly dominated by the amphipod (Hyalella) and chironomid larvae. The periphyton of the upper section is vital for sustaining herbivorous invertebrates such as Hyalella (Paulson, et al., 1980d). Further downstream (past 8 miles), the predominant invertebrates are oligochaetes. The decline of Hyalella may be linked to the decrease of periphyton productivity downstream.

The above species are utilized by fish in the area. The Nevada Department of Wildlife examined stomach contents from rainbow trout caught by anglers at Willow Beach during 1971-76 (Lake Mohave Progress Report, Nevada Department of Wildlife, 1971-76). The findings indicated that 60 percent of the trout had consumed some algae and 57 percent of some invertebrates. This does not necessarily link these fish to the upper 3-mile section, but it does indicate an importance of algae and invertebrates as fish food items. Ongoing food habitat studies indicate that threadfin shad and chironomids are the most important food items (Allan, 1978, page 20).

Periphyton in the river undergoes daily as well as seasonal exposure to the air. This is due to the daily release cycles from Hoover Dam and the seasonal fluctuations in Lake Mohave. This exposure reduces the overall abundance of periphyton and invertebrates available to the aquatic species, however, some terrestrial species, birds, mammals, etc., probably utilize the resource.

d. Temperature Fluctuations. Lake Mead, as with most water impoundments over a few feet deep in temperate latitudes, is thermally stratified during the warmer months of the year. The warm (up to ±80°F) upper layers of water overlie a colder deeper layer of water. The deeper water temperature remains a fairly constant 54°F all year round while the upper warmer layer responds readily to local atmospheric changes in temperature. During the cooler months of the year the water in Lake Mead is fairly uniform in temperature from top to bottom.

Hoover Dam has four intake towers, one for each penstock. Each tower has two 9-foot high cylinder gates located at elevations 1045 and 895. During the summer, if the lake is low (1120), warm water withdrawn by the upper gate will enter the penstock and be released downstream. Conversely, if water is drawn from the lower gate, located at elevation 895 feet, cold water is released downstream. When both gates are open, a mixture of the two temperatures is released downstream resulting in an intermediate water temperature being released in the summer months.

27 CHAPTER III AFFECTED ENVIRONMENT

Since the early 1950's only the lower gates have been used, except in the summers of 1977-81, to release water downstream. The lower gates were used primarily to insure that the cold water requirements of the Willow Beach National Fish Hatchery, located below Hoover Dam at Willow Beach, Arizona, were satisfied. During the past few summers, the Bureau has been able to use both the upper and lower gates simultaneously. This was possible because of the high lake elevations (1180+) during 1977-81 which kept the warmer surface water from entering the penstocks.

A funnel-like withdrawal area is formed at the intake gates of the penstocks as they draw water from Lake Mead for release to Lake Mohave (Figure 14). The current velocity is maximum at the intake depth, and decreases above and below the penstock intake gates. The depth (dl) of the withdrawal layer (Figure 14) varies in relation to the rate of release, and the distance (d2) that it extends uplake, (Figure 14) depends on the duration of the release cycle. The withdrawal layer is further influenced, however, by the thermal stratification of Lake Mead which occurs in the spring and summer months.

The strength of the density gradient that exists during thermal stratification can dictate the upper limit of the withdrawal layer. Warm water is less dense (more buoyant) than cold water, and therefore, as lake surface temperatures increase, it becomes progres- sively more difficult to draw replacement water into the penstocks from the surface strata (epilimnion). Consequently, on a prolonged power cycle, water is drawn from the cooler, denser lake water (hypolimnion) at successively greater distances uplake from the dam (dl is decreased, d2 is increased). The temperature of the release water from Hoover Dam rarely exceeds 54.5°F, indicating that replacement water is currently drawn primarily from the cold hypolimnion uplake from the dam.

e. Temperature Instability Versus Productivity. As releases decrease at the end of a power cycle, the Lake Mead temperature isotherms immediately above the dam start to return to normal position due to the natural tendency of warm water to rise. However, as the hypolimnion water mass that was set in motion on the power cycle collides with the dam, the temperature isotherms are displaced toward the surface. The daily alternation of high and low release creates some temperature instability, similar to the rocking motion produced by a wind induced seiche. The effect is not apparent without the use of instruments.

The extent of this temperature instability is a function of the duration of the power cycle. Uplake from Kingman Wash, in Boulder Basin, the volume increases significantly and buffers the effects of the daily power cycles from Hoover Dam. The temperature and current patterns in Boulder Basin may be slightly influenced by releases from Hoover Dam only after prolonged release in the summer.

28 Lake Surface

Intake Tower

Minimum Predicted Lake Surface El. 1120.0 ---■

Upper Intake Gate E1.1045.0

Lower Intake Gate El. 895.0 di

•••••... NIP d2

Figure 14. Diagram of theoretical withdrawal layer created by Lake Mead releases from Hoover Dam. Elevations are in feet above mean sea level. The depth of the withdrawal layer (dl) varies with the rate of release, while the distance (d2) the withdrawal layer extends uplake varies with the duration of the release cycle. (Modified from Paulson, et al., 1980a). Note: The minimum predicted lake surface elevation shown was an assumed elevation for the purpose of the water temperature study. The minimum may be lower under future conditions of water supply. CHAPTER III AFFECTED ENVIRONMENT

The vertical mixing above the dam resulting from Hoover Dam releases influences the distribution of nutrients and phytoplankton productivity in the summer. Nitrate is depleted in the euphotic zone (depth to which 1 percent of sunlight can penetrate a body of water) but remains high in the metalimnion and hypolimnion in the summer. The vertical mixing near the dam increases the availability of nitrate and phosphorus to plants within the euphotic zone, thus increasing the phytoplankton and zooplankton productivity.

f. Warm/Cold Water Interface. An evident interface develops in Lake Mohave during the summer when cold water (54.5°F) released from Hoover Dam underflows the warm surface water (60-80°F) of Lake Mohave (Figure 15). The river water is relatively high in nitrogen and phosphorus and mixing at the interface produces high phytoplankton productivity during the summer. Thus, during the summer, a marked color difference is created between the river and lake water which provides a means of monitoring the location of the interface.

The location of the warm/cold water interface changes in relation to releases from Hoover Dam and water elevation in Lake Mohave. The interface is pushed downstream during high releases from Hoover Dam, but moves upstream during low releases. The movement upstream is more pronounced when Lake Mohave elevation is high. During limnological investigations (Paulson, et al., 1980a), the interface location (Table 8) varied from just below Willow Beach (mile 12.5) to Eldorado Canyon (mile 24).

This movement is caused by the fluctuation of daily and weekly releases from Hoover Dam and seasonal fluctuations in the water level in Lake Mohave. Typically, the interface extends farthest upstream on weekends when the releases from Hoover Dam are low.

g. Interface Versus Fish Hatchery. The location of the interface is important to the Willow Beach National Fish Hatchery, located 12 miles below Hoover Dam (Figure 16). The hatchery and the cold water trout fishery rely almost entirely on cold river water (54.5°F). If the interface moves past the hatchery's intake pipe (Figures 11 and 12) at elevation 610, large daily fluctuations of water temperature (54-80°F) would impair the operation of the hatchery and perhaps require that other sources of water be provided to satisfy its requirements. Under present conditions the warm/cold water interface never reaches the hatchery. The closest it has been observed in the past 18 years (personal communique with Lyle Miller, 1982) is 0.5 mile below Willow Beach Resort; about a mile below the hatchery's intake.

h. Fishery Resources. A list of all known fish occurrences and their present status in Lake Mead and Lake Mohave is given in Table 9.

(1) Lake Mead. Prior to construction of Hoover Dam and formation of Lake Mead, fish species present in this area of the Colorado River included the native Colorado River squawfish, humpback

SCHEMATIC OF LAKE MOHAVE INTERFACE

• PREVAILING WINDS South North • surface surface

cold water 111 ::: 31

-Al ■IM 3 3 3 3 3 3

bottom bottom

Figure 15. Hypothetical schematic representation of warm/cold water interface. Vertical mixing occurs where cold ('^54°F) water released from Hoover Dam underflows the warmer surface water of Lake Mohave. This occurs only during the summer months when Lake Mohave is stratified. (Priscu, 1978). CHAPTER III AFFECTED ENVIRONMENT

Table 8 RELATIONSHIP BETWEEN WARM/COLD WATER INTERFACE IN LAKE MOHAVE, DAILY RELEASES FROM HOOVER DAM, AND LAKE MOHAVE ELEVATION Hoover Powerplant Modification Project (From Paulsonl et al., 1980a)

Interface Location Average Daily Lake Mohave (Miles below Rele4ses Elevation Date Hoover Dam) ( ft Is) (ft)

May 4, 1977 24 18,200 645.7 May 11, 1977 24 14,100 645.8 May 29, 1977 18 6,390 645.2 June 14. 1977 19 13,6Go 642.5 ,uiv 4, 1977 July 5, 1977 15 11,700 July 6, 1977 23 18,500 635.5 July 28, 1977 20.5 16,700 633.3 July 29, 1977 21 21,000 633.6 August 8, 1977 17.8 17,800 632.1 August 10, 1977 21.5 17,200 632.4 August 25, 1977 19 13,200 638.8 September 17, 1977 12.5 3,150 635.7 July 10, 1978 21.5 15,700 632.8 July 16, 1978 18.6 7,120 632.0

Empirical formula developed by Dr. Paulson to predict the location of the interface under varying releases and lake elevations. -4 1 L = 4.63205D x 10 + 20399.2- - 19.6726

Where: L = interface location (miles below Hoover D = mean daily releases from Hoover Dam (fe/s-') E = Lake Mohave elevation (feet above mean sea level)

Willow Beach National Fish Hatchery is located 12 mi1,23 blow the cam.

30 Table 9 LIST OF SPECIES FOUND IN LAKE TEAD AND LAKE MOHAVE AND STATUS -= Hoover Powerplant Modification Project

FAMILY AND SPECIES STATUS

ANGUILLIDAE, freshwater eels Freshwater eel (Anguilla rostrata) Rare; only two adult individuals reported in 1972 from Lake Mead.

CLUPEIDAE, herring and shad Threadfin shad (Dorosoma Petenense) Abundant in Lake Mead and Lake Mohave.

SALMONIDAE. trout and salmon Coho (Silver) salmon (Oncorhynchus kisutch) No longer found in Lake Mead or Lake Mohave.

Sockeye (Kokanee) salmon (Oncorhynchus nerka) No longer found in Lake Mohave.

Cutthroat trout (Salmo clarki) Uncommon in Lake Mead and Lake Mohave.

Brown trout (Salmo trutta) Rare; to be stocked in Lake Mead in the future.

Rainbow trout (Salmo gairdneri) Uncommon (once common) in Lake Mead; abundant in Lake Mohave.

Hybrid bowcutt (Salmo qairdneri X S. clarki) Rare in Lake Mead.

Brook trout (Salvelinus fontinalis) Rare in Lake Mohave.

CYPRINIDAE, minnows *Colorado River squawfish (Ptychocheilus lucius) Considered extinct in Lake Mead and Lake Mohave.

*Bonytail chub (Gila elegans) Considered extinct in Lake Mead and endangered in Lake Mohave.

*Humpback chub (Gila cypha) Considered extinct in Lake Mead and Lake Mohave.

Carp (Cyprinus carpio) Abundant in Lake Mead and Lake Mohave.

Golden shiner (Notemigonus crysoleucas) Uncommon in Lake Mead and Lake Mohave.

Fathead minnow (Pimephales promelas) Uncommon in Lake Mead and Lake Mohave.

Red shiner (Notropis lutrensis) Common in Lake Mead; rare in Lake Mohave.

Goldfish (Carassius auratus) Rare in Lake Mead.

CATOSTOMIDAE, suckers *Humpback (razorback) sucker (Xyrauchen texanus) Uncommon in Lake Mead; common in Lake Mohave.

*Flannelmouth sucker (Catostomus latipinnis) Status unknown.

Gila mountain sucker (Catostomus clarki) Status unknown.

ICTALURIDAE, catfishes Channel catfish (Ictalurus punctatus) Abundant in Lake Mead and Lake Mohave.

Black bullhead (Ictalurus melas) Rare in Lake Mead (common in Overton area).

CLARIIDAE, clariid catfishes Walking catfish (Clarias batrachus) Two individuals taken from Rogers Spring in 1971.

POECILIIDAE, livebearers Mosquitofish (Gambusia affinis) Common only in and around some tributary streams of Lake Mead.

PERCICHTHYIDAE, temperate basses Common in Lake Mead. Rare in Lake Mohave, Striped bass (Morone saxatilis) but may be increasing.

CENTRARCHIDAE, sunfishes Largemouth bass (Micropterus salmoides) Common in Lake Mead and abundant in Lake Mohave. Black crappie (Pomoxis nigromaculatus) Abundant in Lake Mead and Lake Mohave.

Green sunfish (Lepomis cyanellus) Common in Lake Mead and Lake Mohave.

Bluegill (Lepomis macrochirus) Abundant in Lake Mead and Lake Mohave. PERCIDAE, perches Walleye (Stizostedion vitreum) Rare in Lake Mead.

1/ From Nevada Department of Wildlife 1978. Base Fisheries Data, Phase I, Boulder Canyon to Davis Dam.

*Native fishes 31 ARIZONA

FISH HATCHERY IN rit KE WILLOW BEACH FISH HATCHERY -

, r A' WILLOW BEACH RESORT 01P . 41,k- A.-qt,tV:1 : Al r

Figure 16. Photograph of the Willow Beach Fish Hatchery and Resort on Lake Mohave.

CHAPTER III AFFECTED ENVIRONMENT

chub, bonytail chub, and humpback sucker. Channel catfish and carp were also present. The formation of Lake Mead created good potential for game fish and during the years 1935-42, largemouth bass, black crappie, bluegill, and green sunfish were stocked into the lake. Lake Mead soon gained national fame as a prime warm water fishery and until 1969 was managed exclusively as a warm water fishery. Threadfin shad were introduced in 1954 as a forage fish for the game species. In the mid-1960's it became apparent that the renown largemouth bass fishery of Lake Mead was declining in quality.

Prior to 1969, rainbow and brown trout were occasionally caught by fishermen in Lake Mead. These fish were apparently downstream migrants from the Colorado River. In 1969, in an effort to enhance the declining fishery, cold water species such as rainbow, cutthroat, and hybrid bowcutt trout, and silver salmon were stocked into the lake. Major stocking of the salmonids, continued until 1979. Also in 1969, introductions of striped bass into Lake Mead began. Stocking of this species continued through 1972 until reproducing population of striped bass became established.

(2) Lake Mohave. Following completion of Hoover Dam, the part of the Colorado River later to become Lake Mohave changed from a warm, silt-laden river into a cold, clear, swift-flowing stream. In 1935, the "new" Colorado River was first stocked with rainbow trout. Between 1935 and 1951, a total of 3,714,054 rainbow trout was stocked into the river. With the filling of Lake Mohave in 1951, the 67-mile section of river was considerably modified and formed a warm water and a cold water fishery. The upper portion below Hoover Dam and the deeper portions of the rest of the reservoir remained ideal for trout and have developed into an excellent trout fishery. The upper, warmer strata of lower Lake Mohave developed into an excellent warm water fishery for largemouth bass, black crappie, channel catfish, and other sunfish. In recent years (Allan, et al., 1978) total angler harvests have roughly averaged 60 percent cold water and 40 percent warm water fishes by number. Warm water species became established in the new reservoir from small preimpoundment populations. In 1955, threadfin shad were introduced as a forage species for the game fish. Stocking of rainbow trout has continued regularly to maintain the fishery since natural reproduction does not occur. The majority of stocking is accomplished from the Willow Beach National Fish Hatchery. Experimental releases of other salmonids (sockeye and silver salmon, cutthroat and brook trout) have also been made. Striped bass have never been planted in Lake Mohave, There are, however, frequent reports (Robert Allan, Nevada Department of Wildlife, personal communique) of stripers being taken from Lake Mohave. The fish may have been accidentally or intentionally introduced by fishermen or entered the lake through the Hoover Powerplant turbines. If stripers become a large viable population in Lake Mohave, their aggressive predator tendencies, which have been documented in Lake Mead, may impact other fish populations especially smaller fish (i.e., shad, trout).

32 CHAPTER III AFFECTED ENVIRONMENT

A 5-year Bureau study of Lake Mead's largemouth bass population has been conducted for the past 4 years. Since the lakes are adjacent to each other and no data were available on Lake Mohave, the Lake Mead data were extrapolated to Lake Mohave. The study on Lake Mead shows that about 50-58 percent of all bass nests are successful (i.e., the eggs, hatch) (letter from Sue A. Morgenson, Arizona Game and Fish, September 22, 1981). The data also showed that in general nests built 0-1 foot below the surface were not successful, only 25 percent of the nests built 1-2 feet below the surface were successful and approximately 57 percent of the nests were successful if built below 2 feet. The above information was used to assess the long-term impacts on the Lake Mohave fishery due to the proposed project.

6. Terrestrial Environment. Terrestrial areas affected by the project would be confined to the shoreline of Black Canyon downstream to approximately river mile 18 (Figures 11 and 12), the construction area around Hoover Dam, and borrow and spoil dump areas.

a. Black Canyon

(1) Vegetation. Development of vegetation along the river in Black Canyon is limited by the steep topography of the canyon and fluctuating river levels. Through a large portion of the canyon the rock walls rise almost vertically from the water level. In these areas, riparian vegetation is nonexistent or consists of occasional individual or stands of salt cedar (Tamarix sp.) that have developed on shelves or cracks in the rock walls near the high waterline. In areas where the canyon slopes gently to the river level, soil material has been deposited by high flows prior to construction of Hoover Dam and by runoff from the numerous washes that enter the canyon. In these areas, dense stands of vegetation have developed consisting predominantly of salt cedar, but also including arrowweed (Pluchea sericea), saltbush (Atriplex spp.), saltgrass (Distichlis stricta), willow (Salix sp.), seepwillow (Bacharis sp.), catclaw (Acacia sp.), mesquite—(P715sopis sp.), and others. These stands of vegetation range in size from about 100 square feet or less up to about an acre. In total, there is estimated to be about 8 acres of riparian vegetation between Hoover Dam and the Willow Beach National Fish Hatchery.

As discussed previously, the river level fluctuates seasonally with Lake Mohave elevations and daily with releases from Hoover Dam. Lake Mohave has, in recent years, been operated between elevations 630 and 647. A review of past records, however, shows that these extremes rarely occur in actual operation. In the past 5 years, Lake Mohave reached a maximum elevation of 646 for only 5 days in May 1977. Likewise the minimum elevations are reached only occasionally and for relatively brief.periods of time (Table 10).

In addition to the seasonal fluctuations, there are daily fluctuations in the river level resulting from releases from Hoover Dam. As shown in Figures 11 and 12, the maximum effect of releases is at the dam and the effect diminishes downstream and is negligible beyond mile 18. The current maximum release of

33 Table 10 MONTHLY ELEVATION RANGES OF LAKE MOHAVE 1977-81 Hoover Powerplant Modification Project

81 80 79 78 77 Max Min Max Min Max Min Max Min Max Min

Jan 642 638 645 640 644 641 642 640 645 642

Feb 644 642 645 642 645 639 643 639 642 641

Mar 645 642 641 637 642 641 644 640 643 642

Apr 644 641 641 636 641 636 640 638 645 639 li May 645 643 645 637 641 636 644 641 646 644

June 645 640 644 638 642 639 643 636 644 638

July 641 634 639 635 639 633 not available 639 633

Aug 633 631 638 636 634 632 633 630 638 631

Sept 634 632 637 632 635 632 634 631 636 633

Oct 636 633 635 633 632 630 638 634 635 633

Nov 637 633 637 635 636 632 640 638 635 632

Dec 639 637 639 636 640 636 not available 640 635

1/ This elevation reached on 5 days during the month.

34 CHAPTER III AFFECTED ENVIRONMENT

3 40,000 ft /s raises the river elevation at Hoover Dam to 654 with Lake Mohave elpation at 630. At Mohave elevation 647, a release of 40,000 ft Is raises the river elevation at Hoover Dam to 657. How- ever, since Lake Mohave rarely approaches maximum elevation (Table 10) and high releases occur for relatively brief periods during spring and summer months, the river rarely reaches the maximum possible levels. Thus, actual fluctuations in river level are less than the possible range. Existing vegetation in the canyon is rarely subjected to extreme conditions.

Vegetation, other than annuals, below maximum river elevations is almost exclusively salt cedar. Mature stands were found growing at elevations of approximately 646 within one-half mile from the dam to approximately elevation 643 in the Willow Beach area. A previously discussed, development of vegetation at these elevations is probably a reflection of the operating levels of the river over the past few years. Apparently salt cedar is able to withstand some periods of inundation and the line at which it becomes established advances and retreats depending on the operation of Lake Mohave over a period of years. Perennial plants other than salt cedar do not become established in this zone of fluctuating water levels.

The construction area around Hoover Dam has almost no vegetation. This is a highly modified area consisting of concrete, sheer rock faces, and a high level of human activity.

(2) Wildlife. Coots, cormorants, grebes, several species of ducks, and great blue herons are among the birds commonly seen on the river in Black Canyon, particularly during the winter months. In addition, several passerine species including black-tailed gnatcatcher, loggerhead shrike, canyon wren, phoebes, and sparrows are often seen around the mouths of washes and other vegetated areas. A group of approximately 15 pairs of double-crested cormorants have been observed nesting on cliff ledges about 100 yards downstream from the dam on the Nevada side. Bighorn sheep are often seen in the canyon, particularly in the summer months. Bighorn sheep are also known to frequent the sewage treatment ponds near Hoover Dam on the Arizona side.

b. White Rock Canyon. Construction material would be excavated from White Rock Canyon in Arizona (see frontispiece map). White Rock Canyon is a dry desert wash that originates at Wilson Ridge and runs some 8 miles to enter the Colorado River at Ringbolt Rapids. It crosses U.S. Highway 93 about 2.5 miles up from the river ana about 3.7 miles on the highway from Hoover Dam.

The borrow site would be located somewhere between the Highway 93 bridge and a point 1.5 miles up the wash. White Rock Canyon is a relatively large wash and is accessible to vehicular traffic from U.S. Highway 93. Gravel piles in the canyon give evidence the wash has been used in the past for construction activities. At the location of the borrow area, the canyon consists

35 CHAPTER III AFFECTED ENVIRONMENT

of a relatively straight, flat-bottom wash varying in width from 250 to 550 feet. The entire wash contains about 242 acres (250 feet by 8 miles).

(1) Vegetation. Desert washes are important elements of the Mojave Desert, in that vegetative cover tends to be greater than the surrounding desert, and several wildlife species common to the desert reach their greatest abundance in the washes. Descriptions of the floral and faunal communities characteristic of the project area can be found in two publications: The Biotic Communities of Southern Nevada by W. Glen Bradley and James F. Deacon, available from the University of Nevada, Las Vegas, and Biota of Lake Mead National Recreation Area available from the Department of the Interior, National Park Service (NPS).

Vegetative composition in White Rock Canyon is typical of desert washes described in the previous publications. Plants characteristic of the surrounding creosotebush community such as creosotebush (Larrea tridentata), burrobush (Ambrosia dumosa), ratany (KramerfTi-157, brittlebush (Encelia farinosa), and buckwheats (Eriogonum sp.) occur in the wash. In addition to these, are plants which are commonly found only in washes. Cheeseweed (Hymenoclea salsoW is abundant in the borrow area. Also present are bladder-sage (Salazaria mexicana), snakeweed (Gutierrezia sp.), indigobush (Dalea fremontii), and golden weed (Haplopappus sp.). Several catclaw trees, many containing clumps of mistletoe (Phoradendron californicum), are present in the upper portions of the wash.

(2) Wildlife. Small mammal trapping in White Rock Canyon during July 1980 revealed a relatively dense population of small mammals in the wash (67 animals per acre). Pocket mice (Perognathus formosus and P. longimembris) comprised 73 percent of the animals captured. Other species encountered were the Merriam kangaroo rat (Dipodomys merriami), desert woodrat (Neotoma lepida), Yuma antelope squirrel (Ammospermophilus harrisi), and cactus mouse (Peromyscus eremicus). On separate occasions a red-tail hawk and a Swainson's hawk were observed and coyote droppings were found in the wash. These and other predators often hunt along washes - an indication of the more abundant food supply found there relative to the surrounding desert.

7. Special Status Species. In accordance with the Endangered Species Act Amendment of 1978, the U.S. Fish and Wildlife Service (FWS) identified five endangered species which might occur in the project area. These were the peregrine falcon (Falco peregrinus), bald eagle (Haliaeetus leucocephalus), Yuma clapper rail (Rallus longirostris yumanensis), Devil's Hole pupfish (Cyprinodon dTEETITs), and the bonytail chub (Gila elegans). In addition, the FWS identified two species which were proposed for listing as threatened. These were the Trelease's beavertail prickly-pear cactus (Opuntia basilaris var. treleasei), and the razorback sucker (Xyrauchen texanus). Trelease's beavertail prickly-pear cactus has not been found in any of the areas potentially affected by the project. Subsequently, the proposal to

36 CHAPTER III AFFECTED ENVIRONMENT

list these two species has been withdrawn. An evaluation of project impacts to the listed species was conducted and it was determined that the bonytail chub could be impacted. The Bureau entered into informal consultation with the FWS on December 30, 1980 and March 6, 1981. Formal consultation on the endangered bonytail chub, as called for under Section 7 of the Endangered Species Act, was initiated on October 16, 1981. The FWS responded with an opinion, dated April 1, 1982, that the species would not be jeopardized by the project. Each consultation was initiated as a result of new information on the species or changes in project features. The following is a condensed version, by species, of the evaluation presented to the FWS.

a. Peregrine Falcon. The peregrine falcon is considered a rare transient and winter resident in the project area (Blake, 1978). Recorded sightings in the area have been few (a total of eight observation records on file at NPS in Boulder City and Nevada Department of Wildlife, Las Vegas). Sightings have been mostly in the fall and spring months indicating birds occur here primarily as transients.

Peregrines normally nest in a shallow scrape on cliff ledges (Bent, 1938). Cliff ledges are numerous in the project area but there are no indications from the literature or observation records that peregrines do, or ever have, nested in the area.

The peregrine falcon preys primarily on birds, often waterfowl (Blake, 1978). A large number of waterfowl occur on the lakes in winter and would appear to offer peregrines an abundant food supply.

Little information regarding peregrine falcons in the project area is available. It appears that peregrines occur here only rarely and as transients.

Implementation of the Hoover Powerplant Modification Project is not expected to alter the availability of nest or perch sites, nor affect the food supply of peregrines. Therefore, no impact is expected.

b. Bald Eagle. The bald eagle is considered a rare to uncommon winter resident in the Lake Mead National Recreation Area (Blake, 1978). Observation records on file at the Nevada Department of Wildlife in Las Vegas and the NPS in Boulder City show an average of about six bald eagle sightings per year in the Lakes Mead and Mohave areas in recent years. The earliest sighting on file is in late September and the latest in May; the majority of sightings occur during the winter months. During the National Wildlife Federation's 1979 Midwinter Bald Eagle Survey, a total of four bald eagles were recorded near Lake Mead and one near Lake Mohave (NPS files, Boulder City). The majority of sightings for Lake Mead are in the upper portions of the lake (Temple Bar to Pierce Ferry) and the Lake Mohave sightings are generally below the Cottonwood Cove area.

There are no indications from the literature or the observation records that bald eagles breed in the area. The only recorded nesting activity in Nevada was near Pyramid Lake in 1867 (Ohmart and

37 CHAPTER III AFFECTED ENVIRONMENT

Sell, 1979). The only known nest site along the Lower Colorado River is in the Topock Marsh area in the Lake Havasu National Wildlife Refuge. An artificial nest structure was provided at this site and a pair of adult eagles have appeared at the site every year since 1975. Although courtship and nesting activities have been observed, apparently no eggs have been laid. The reason is unknown.

The diet of bald eagles varies widely with both region and season (Steenhoff, 1978). In the Southwest, fish, especially carp (Cyprinus carpio) and catfish (Ictalurus punctatus), are the primary food items during the breeding season (Rubink and Pedborny, 1976; and Ohmart and Sell, 1979). Wintering birds reportedly make greater use of waterfowl, mammals, and carrion (Ohmart and Sell, 1979). One observation record for Lake Mead reports an adult eagle capturing an American coot (Fulica americana) (NPS files, Boulder City, Nevada).

Little information is available on bald eagles in the Lake Mead/Lake Mohave area. Observation records are as much a reflection of the number and location of observers in the field as they are of the number and location of birds present. The records indicate, however, that at least a small number of wintering eagles occur in the Lake Mohave area and as many or more occur around Lake Mead.

Although little is known of eagles in the area, an analysis of project impacts leads to the conclusion that the Hoover Powerplant Modification would have no foreseeable impact on bald eagles. Project implementation would not result in direct mortality or displacement of eagles, and possible perch sites, nest sites, or foraging areas would neither be created nor destroyed. The only conceivable impact to prey of the bald eagle would be to fish in the first 12 miles below Hoover Dam. Impacts to fish in the river, and especially impacts to carp and catfish, are expected to be minor to nonexistent. Assuming, for discussion, severe impacts to the fishery below the dam, the effect on bald eagles would still be negligible since abundant food sources exist above and below this reach of river.

c. Yuma Clapper Rail. The original range of the Yuma clapper rail was confined to the Colorado River delta but the range has been extending northward during the past 60 years (Ohmart and Smith, 1973).

There is no evidence that the Yuma clapper rail existed north of the Colorado River delta prior to 1921. From descriptions of the Lower Colorado River made by Grinnell (1914), suitable habitat for this rail was not available along the river. Construction of dams and subsequent river management and control have created suitable Yuma clapper rail habitat to the north of the original range. The first specimens taken north of the Colorado River delta were secured in 1921 by Huey and Canfield (Dickey, 1923) in the vicinity of Laguna Dam. The first recorded presence of clapper rails north of Laguna Dam follows a few years after the beginning of operation of Parker, Imperial, and Headgate Rock Dams which were 1938, 1939, and 1942,

38 CHAPTER III AFFECTED ENVIRONMENT

respectively (Ohmart and Smith, 1973). In 1966, Yuma clapper rails were first recorded in Topock Marsh (Welch, 1966). This is the northern most record of the Yuma clapper rail to date.

Bennett and Ohmart (1978) studied the habitat requirements of the Yuma clapper rail in the Imperial Valley of California. Rails used fresh water marsh areas containing mature stands of cattail (Typha domingensis) and bulrush (Scirpus californicus). Water level variation was found to influence the permanence of territories and the breeding effort. Marsh areas with permanent shallow water through the breeding season contained the highest rail densities. Crayfish (Procambarus sp. and Orconectes sp.) formed a major portion of the clapper rail diet.

The Yuma clapper rail is not known to exist along the Colorado River north of Topock Marsh. However, the northward expansion of rails that has apparently occurred in recent times might be expected to continue and the range of the Yuma clapper rail could conceivable extend as far north as the project area in the future. Surveys (by taped calls) were conducted by Bureau biologists in 1976 in marsh habitat in Las Vegas Wash, about 14 airline miles north of Hoover Dam. The results were negative. There are no areas of suitable habitat as described by Bennett and Ohmart (1978) between Davis Dam and Las Vegas Wash.

The Hoover Powerplant Modification Project would have no impact on the Yuma clapper rail since no rails exist in the area and no marsh habitat would be created or destroyed by project implementation.

d. Devil's Hole Pupfish. An artificial refugium for the Devil's Hole pupfish was created in 1972 about 650 feet below Hoover Dam on the Nevada side of the river above the river level. Water is supplied from a naturally occurring hot spring and temperature is controlled by adjusting the flow of water through the refugium. After an initial population boom soon after initial stocking the pupfish population has stabilized at about 60 fish in the refugium.

The Hoover Powerplant Modification Project would have no effect on the pupfish refugium. The refugium operates independently of Colorado River operations. Construction activities would be on the opposite side of the river more than one-fourth mile upstream. Construction activities, including blasting, have occurred much closer to the refugium without affecting the pupfish.

e. Bonytail Chub. The status of the bonytail like many native species is not fully known. The bonytail 's range has greatly declined to a point where the species is only represented by the Lake Mohave and Upper Colorado River (Green River), Utah populations. The Gila complex which includes the species G. elegans, G. robusta and G. cypha has been an area of controversy among experts. Apparently G. cypha and G. elegans interbreed (Holden, 1968) causing additional taxonomic difficulties to a genus whose species closely resemble one another. As a result, some icthyologists question the genetic purity

39 CHAPTER III AFFECTED ENVIRONMENT

of the Upper Basin population since the three species interbreed in that area. This is not the case with the Lake Mohave population where the other two Gila sp. are apparently absent.

Past collections of the bonytail in the Upper Colorado River indicate that optimum habitat for the species consists of a river environment with a shifting sand substrate, water depths of 3 to 4 feet and relatively constant, moderately swift current (Behnke and Benson, 1980). These conditions, coupilled with the correct teperature regime, are not found in Black Canyon-1 or Lake Mohave proper—

There is concern that the bonytail is at the point of extinction in Lake Mohave because the species is apparently not reproducing. The last documented collections of bonytail young from Lake Mohave were collected at Cottonwood Landing, Nevada, June 15, 1950 (Sigler and Miller, 1963). The frequency of bonytail observations has greatly declined, even though people are actively looking, since the closing of Davis Dam in 1951. Today the species is considered extremely rare. However, in November 1981, the FWS introduced 42,500 young (3 to 4 inches) bonytail chubs from the Dexter National Fish Hatchery into Lake Mohave. The introduction was part of a recovery effort to establish a viable population. The results of that introduction have not been determined.

The capture of ripe bonytails in Lake Mohave and their successful spawning in hatchery facilities suggests that spawning can take place, but no evidence has been found which indicates that it is taking place. There is no evidence of successful hatching or development of fry in Lake Mohave. It has been speculated by fishery biologists that bonytail recruitment is either extremely limited or spawning is not successful at all with the population represented by only old fish (20 years plus).

Lake Mohave, as explained in previous sections, is really two separate and distinct systems. The first is Black Canyon which is a cold (54°F) deep, swift river section about 18 miles in length, and Lake Mohave proper which is a wide basin with typical lake characteristics. Observation and literature research indicate that the Black Canyon section at Lake Mohave probably does not contain bonytail chub and if it did they would have no reproductive success because of the cold water. This conclusion, which was concurred with by the FWS, is based on the following:

1/ The river through the Black Canyon area is deep, cold, and swift. — It extends from just below Hoover Dam downstream for approximately 18 miles.

2/ Lake Mohave proper is that area of Lake Mohave starting approximately 18 miles below Hoover Dam and continuing to Davis Dam. It is a wide basin with typical lake-like features.

40 CHAPTER III AFFECTED ENVIRONMENT

- The last bonytails taken from the Black Canyon area were collected 20 years ago (1961) at Willow Beach. Biologists from the Bureau and the University of Nevada at Las Vegas have done extensive scuba diving throughout Black Canyon and have never observed the bonytail.

- Bonytail chubs and other native Colorado River fish species evolved exhibiting unique body characteristics. The bonytail's sleek body suggests a swift mainstream niche. The bonytail chubs are found in canyon habitats in the Green River, but they have only been collected in eddies and back waters, which is also the reported habitat of its young. Vanicek and Kramer (1969) stressed this habitat preference for the chub in the Green River, Utah.

- Eddies and pool habitat are extremely limited in Black Canyon especially above Willow Beach (mile 12). The canyon presently forms a channel which is relatively deep (30-90 feet) with uniform current velocities and very few back eddies with suitable bottom habitat.

- It can be deduced that Black Canyon does not support reproduction. The temperature regime has completely changed from predam days and temperature experiments by FWS personnel stationed at the Willow Beach National Fish Hatchery (Toney, 1974) show that the daily discharge water temperatures are too cold to support egg development. If bonytails existed in Black Canyon and spawning did occur, successful egg incubation is highly unlikely because of cold releases from Hoover Dam.

Lake Mohave proper does contain bonytail chubs. Ripe bonytails have been collected throughout Lake Mohave but the only recorded spawning observations were made by Jonez and Sumner (1954). They reported an aggregate of 500 individuals spawning over a gravel shelf 10 miles below Eldorado Canyon (36 miles below Hoover Dam). This is also the approximate area where ripe bonytails have recently been taken (Minckley, personal communique) and successully spawned in hatchery facilities. Although no successful recruitment has been observed, viable reproducing adults do exist making it possible that spawning occurs. However, the substrate of the lake does not appear to be suitable habitat and there is not a moderately swift, or any current along the shore. However, the temperatures of Lake Mohave are about right for spawning. The species inability to successfully sustain its population level may be due to a lack of spawning habitat or to predation by introduced game and exotic fish species.

Bonytail chubs feed primarily on the surface for terrestrial insects and plant debris (Vanicek, 1967). During the inundation of Lake Mohave, bonytails were observed feeding on algae and midge larvae among the submerged tree tops around the perimeter of the new reservoir (Jonez and Sumner, 1954). Bonytails taken in recent years by a cooperative effort of state, private, and Federal concerns were also collected near the surface using tramel nets.

41 CHAPTER III AFFECTED ENVIRONMENT

The observed feeding behavior and diet items suggest that the bonytail forages near the surface or upper water column. The possibility of bottom movement and flushing in the upper section of Black Canyon would not limit food availability for the bonytail; to the contrary it may enhance its availability. A limited amount of flushing may suspend benthic organism and make them available food items.

In conclusion, the Bureau and FWS feel that no bonytails are present in the cold water (54°F) areas of Black Canyon and that if they did exist, the cold water coupled with unsuitable habitat would make reproduction and a viable population impossible. The changes to Black Canyon brought about by the proposed project would not jeopardize the further existence of the bonytail chub in Black Canyon.

Considering the lack of evidence of bonytail recruitment in Lake Mohave, and that the proposed project would have no affect on the already unsuitable environment of Lake Mohave, it is the Bureau's and FWS's opinion that the project would not jeopardize the continued existence of the species.

f. Razorback Sucker. The razorback sucker, (Xyrauchen texanus), although not a special status species, will be discussed since the species is of interest to resource agencies within Arizona, California, and Nevada.

The razorback was present throughout the Lower Colorado River prior to 1955 with some populations considered abundant. Presently, they are rarely taken below Parker Dam but are reported to be fairly abundant in Lakes Havasu, Mohave, and Mead. In Lake Mohave, they are found in abundance both in Black Canyon and in Lake Mohave proper. Only adult fish have been taken in recent surveys indicating poor recruitment. Smaller razorbacks (12.3 to 14.9 inches) have been taken in the Parker, Arizona (Mike Donahoo, FWS, Parker, Arizona, personal communique) area and observed in Lake Mohave (Paulson, et al., 1980d). A post larval fish was taken from the area below the Hoover Dam tailrace and has tentively been identified as a razorback (Minckley, personal communique). Expected egg mortality within Black Canyon would be high as confirmed by the Willow Beach National Fish Hatchery incubation experiments. They showed 100 percent egg mortality when the eggs were incubated in the 54°F river water (Toney, 1974).

Although adult razorbacks have adapted in reservoirs, reproduction has not maintained their population densities. Except for an occasional isolated incident, no spawning has been observed in Black Canyon of Lake Mohave. Spawning usually occurs in late winter through early summer when water temperatures reach the 54° to 68°F range (Behnke and Benson, 1980). Spawning individuals congregate in 1 to 20 feet of water over gravel substrate along shorelines or in bays. Spawning activities in Lake Mohave are annually observed in Arizona Cove and Cottonwood Cove (Kraig Beckstrand, Nevada Department of Wildlife, personal communications). Large numbers (200-300) of fish are observed during these sitings.

42 CHAPTER III AFFECTED ENVIRONMENT

Although razorbacks are observed spawning in Lake Mohave, evidence of successful recruitment is not apparent. Razorback fry were observed (Minckley and Paulson, personal communique), however, in 1981 and 1982. This was the first sighting in several years of young razorback fry in Lake Mohave.

The razorback sucker is basically a substrate grazer feeding on such benthic organisms as insect larvae, algae, and plant debris. Diets may change seasonally due to food availability trends. The abundance of razorbacks found in the upper section of Black Canyon is believed to be due to food availability. The periphyton community below Hoover Dam (first 3 miles) represents the primary food production of Black Canyon (Paulson, et al., 1980d).

Although scouring and flushing may temporarily reduce food production in Black Canyon, it is speculated that the area maintains a sufficient carrying capacity for the razorback population until the periphyton and invertebrate communities reestablish themselves during the low release seasons.

The habitats of the razorback sucker have changed greatly since the predam era. These native species evolved in an extreme environment of fluctuating flow, velocity, and seasonal temperature cycles all of which have been greatly modified by the introductions of dams and reservoirs to the Colorado River drainage. The inundation of natural habitats and the introduction of exotic species are undoubt- edly the major contributers to the decline of the species. Catfish, carp, sunfish, and other exotics have been observed feeding on razorback eggs and fry (Jonez and Sumner, 1954; Laudermilk, California Department of Fish and Game, personal communique). Apparently exotic fish can effectively suppress successful reproduction by predation on the eggs and young of both species (Minckley, 1979; Behnke, 1980).

8. Recreation. Recreation on Lake Mead would not be impacted by this project and is not discussed. Water-based recreation, especially fishing, on Lake Mohave would be impacted in the area between Willow Beach, Arizona and Hoover Dam during Hoover's peaking phase (weekdays - 10 a.m. to 4 p.m.). Land-based recreation on Lake Mohave is not expected to be impacted and is, therefore, discussed only in the most general terms.

Recreational information is taken from two sources, the NPS Monthly Public Use Form (1980) and two contracted studies by Dr. Greey, et al. (1980 oh) of Arizona State University (ASU). A disparity exists between the reports in the total numbers of people using Lake Mohave. The NPS estimates for total use on Lake Mohave are nearly twice that of ASU's estimates. The principal reason for this disparity is the NPS places automatic road counters across the access roads to the resort. The counter counts everyone; residents, service trucks, etc., entering the area. The ASU counted only the people on the water or within 50 to 100 feet of the water's edge. However, estimates for the Willow Beach area are in general agreement and close enough to give the reader an idea of the recreational activity of the area.

43 CHAPTER III AFFECTED ENVIRONMENT

Recreation management on Lake Mohave is administered by the NPS. Recreation use (camping, shore fishing, hiking, boating, boat fishing, swimming, water skiing, etc.) is dispersed along the river beginning at a cable located about 4,000 feet below Hoover Dam and extending some 67 miles south to Davis Dam.

The Willow Beach area (sections 9-13 on Figure 17) receives about 12 to 20 percent of the total visitor use for Lake Mohave as can be computed from Tables 11 and 12.

Table 11 NUMBER OF VISITORS TO LAKE MOHAVE - 1979 and 1980 Hoover Powerplant Modification Project

Visitors Location 1979 1980

Willow Beach Access Road 238,543 198,175 Cottonwood Cove Access Road 291,639 244,392 Katherine Access Road 772,260 950,467 Miscellaneous Access to Lake Mohave 522,052 259,080

TOTAL 1,824,494 1,652,114

Source: National Park Service Statistics, 1980.

Most of the recreation use is concentrated around three marina access points: Willow Beach, Cottonwood Cove, and Katherine Landing (Figure 17). Several other land access points allow smaller amounts of use over the lake. To aid in the reporting of these data, Lake Mohave was divided into 13 separate sections (Figure 17). This discussion will concentrate primarily on the water-based uses of sections 9-13. The land-based uses should not be impacted.

Table 12 provides a breakdown by section of land-based use (camping, shore fishing, hiking, etc.) and water-based use (boating, fishing, water skiing, etc.) of the entire Lake Mohave. It should be noted that actual visitor-use days are derived only from land-based data. All water-based participants have already been counted in the land-based inventory. Table 13 gives specific water-based use by month for sections 9-13.

Under the present fluctuations of Lake Mohave from elevation 647 to 630, and variation in releases from Hoover Powsrplant from a minimum of no release to a maximum of about 40,000 ft /s, the narrow upper reaches of Lake Mohave are almost always navigable by small boats, with minor caution needed at higher flows or low lake levels. Extreme conditions of Lake Mohave elevation and Hoover Dam releases currently have an adverse effect on recreational use of Lake Mohave, as described below.

44 Lake N Mead

Boulder Cit HOOVER 13 DAM * 1

I .Willow Beach # 1 1 t Nevada Arizona 'A(

Cottonwood Cove # TA * , 3 mohajLe

- t # 1 kt Katherine Landing DAVIS * - SECTION NUMBER DAM

Figure 17. Map of recreation use on Lake Mohave from Hoover Dam to Davis Dam. CHAPTER III AFFECTED ENVIRONMENT

Table 12 LAKE MOHAVE VISITOR USE - 1979 Hoover Powerplant Modification Project

Land-Based Use 2, Sect i on1/ Water-Based Use (Visitor-Use Days)-2 Katherine Landing to Cottonwood Cove

1 78,180 382,722 2 46,629 8,538 3 29,338 13,654

Subtotal 154,147 404,914

Cottonwood Cove to Willow Beach

4 39,951 182,392 5 26,503 1,641 6 16,260 0 7 11,986 4,290 8 11,409 2,156

Subtotal 106,109 190,479

Willow Beach to Hoover Dam

9 10,084 0 10 14,322 0 11 14,704 151,029 12 9,806 809 13 6,887 0

Subtotal 55,803 151,838

TOTAL 316,059 747,231

1/ Refer to Figure 17 for section. Source: Dr. Greey, et al., Arizona State University, 1980a.

Visitor-use days are derived from land-based data. All water- based participants have already been counted in the land-based inventory.

45 Table 13 WATER RELATED VISITOR STATISTICS FOR WILLOW BEACH 1979 and 1980 Hoover Powerplant Modification Project

Total Number Engaged , Number of Visitors Number Engaging in in Water Percent Use Factor-' at Willow Beach Activities Related Mo/Yr Swimming Boating Fishing During the Month Swimming Boating Fishing Activities

Jan 80 .007 2.2 7.0 10,134 1 223 709 79 .007 2.2 7.0 15,533 1 342 1,087

Feb 80 .03 2.9 9.4 12,953 39 376 1,218 79 .03 2.9 9.4 21,822 65 633 2,051

March 80 .12 2.9 11.8 15,467 19 448 1,825 79 .12 2.9 11.8 26,515 32 769 3,129

April 80 3.2 4.0 18.5 18,331 587 733 3,391 79 3.2 4.0 18.5 32,792 1,049 1,312 6,066

May 80 3.8 4.4 17.2 18,906 718 832 3,252 79 3.8 4.4 17.2 22,367 850 984 3,947

June 80 32.3 7.5 16.7 19,690 6,360 1,477 3,288 79 32.3 7.5 16.7 23,780 7,681 1,783 3,971

July 80 31.4 10.8 13.0 20,513 6,441 2,215 3,667 79 31.4 10.8 13.0 17,823 5,596 1,925 2,317

Aug 80 25.7 4.4 13.2 18,890 4,855 831 2,493 79 25.7 4.4 13.2 13,094 3,365 576 1,728

Sept 80 3.4 5.9 16.9 18,160 617 1,071 3,069 79 3.4 5.9 16.9 24,565 835 1,449 4,151

Oct 80 3.4 5.9 16.9 17,820 606 1,051 3,012 79 3.4 5.9 16.9 15,239 518 899 2,575

Nov 80 .3 4.2 14.9 18,417 55 773 2,744 79 .3 4.2 14.9 15,404 46 647 2,295

Dec 80 .002 2.5 10.7 8,894 0 222 952 79 .002 2.5 10.7 9,609 0 240 1,028

Total 80 197,815 20,298 10,252 28,620 59,170

Total 79 238,543 20,038 11,559 34,245 65,842

Source: National Park Service, Statistics, (1979, 1980)

1/ Percent Use factor is multiplied by the number of Willow Beach visitors during the month to arrive at the number engaging in each activity. Land based activities are not computed.

46 CHAPTER III AFFECTED ENVIRONMENT

When Lake Mohave is near a maximum elevation of 647, variations in releases from Hoover Dam cause the water level to fluctuate (Table 6) from about 10 feet at the dam to about one-half foot at Willow Beach. Such variations have a minor effect on recreation (as when navigational hazards that are submerged at high flows appear unexpectedly, or when water covers hazards normally exposed). When Lake Mohave is near elevation 630, the water level fluctuations are greater, about 17 feet at Hoover Dam and 2.5 feet at Willow Beach. At maximum flows, the increased velocity is an impediment to upstream navigation, and tends to reduce recreation in section 13 by about 40 percent (Greey, et al., 1980a) of the most favorable conditions with Lake Mohave full (elevation 647). Section 12 experiences a decline of 10 percent in water use. 3 Releases of 0 to 2,000 ft /s at lake level 647 causes some minor inconvenience to boat campers and creates some additional navigation hazards (exposed rocks). However, the low flow rate at this lake level reduces boat safety problems on the upper sections of Lake Mohave. The lake is sufficiently deep to navigate even at this low flow rate. Canoes and small watercraft easily travel upstream as well as down. 3 The reduced water flow with releases of 2,000 ft /s at lake level 630 makes the rapids in sections 12 and 13 become navigational hazards for most large boats. However, kayaking and canoeing become more interesting and challenging. Water-based use is reduced by about 70 percent in these two sections (Greey, et al., 1980a) when compared to the most favorable conditions with Lake Mohave full.

Out of the 150,000 to 240,000 people driving to Willow Beach in the last 2 years, depending on which survey is used, 55,000 to 65,000 engaged in water activities in sections 9-13. Of these, 20,000 went swimming, 10,000 to 12,000 went boating, and 28,000 to 34,000 went fishing. Willow Beach is 12 miles upstream of the no water skiing limit so water skiing in sections 9-13 (Figure 17) was considered to be zero.

9. Archeological and Historical Sites. Hoover Dam is on the National Register of Historic Places. Any modification to the structure and/or to the immediate environment will require, by law, a consultation process with the Arizona and Nevada State Historic Preservation Officers (SHPO), as well as with the Advisory Council on Historic Preservation (ACHP).

An intense historic and prehistoric Class III Survey of the area from Hoover Dam to Willow Beach was conducted by the Nevada Archaeo- logical Survey (NAS) of the University of Nevada, Las Vegas (Brooks, et al., 1977) in February-March 1977, in compliance with Executive Order 11593, 36 CFR Part 800, and 43 CFR 422. The NAS identified four archeological sites. The archeological content of two sites was meager, with no indication of midden depth. The other two sites, Cholla Rock Shelter and Willow Beach No. 2, are considered to have archeological research potential and may meet the criteria for inclusion on the National Register of Historic Places.

47 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

One site, Willow Beach No. 2, is located on a sandbar about 1 mile upstream from the Willow Beach National Fish Hatchery. This site is currently being subject to erosion caused by the fluctuation of the river's water level. In addition, the sandbar receives heavy recreational (picnicking and camping) use from boaters.

The other site, the Cholla Rock Shelter, is located about 6.5 miles below Hoover Dam on the Arizona side. The rock shelter is located approximately 15-20 feet above the river's high water mark.

10. Socioeconomic Environment. Two impact areas were defined, a regional impact area, and a local impact area. The regional impact area was defined as Clark County, Nevada. Because of the role of Las Vegas as the trade and service center for the region, any significant economic consequences of the Hoover Modification can be expected to occur within Clark County. The local impact area was defined as Henderson and Boulder City, Nevada, the communities of Clark County that could possibly receive significant demographic or social impacts from the proposed action. Figure 18 shows the location of these communities, the dam, and the highway network in the area.

Las Vegas is one of the prime gaming, resort, and convention centers in the United States. Henderson is a smaller city with an emphasis upon industry and manufacturing. Boulder City is a still smaller community which serves as a headquarters for several Federal agencies. Tourism is an integral part of the economy of each of these three communities. The magnitude of the tourist industry in Clark County can be indicated by the fact that resort activities employed approximately 47,000 workers serving 9.1 million vacationers in 1975.

In recent years, all of these communities have been growing rapidly. For instance, between 1970 and 1980, the population of the county increased by 69 percent. The 1980 advance population reports of the Bureau of the Census for these entities were as follows:

Clark County 461,816 Las Vegas 164,674 North Las Vegas 42,739 Henderson 24,291 Boulder City 9,590 Unincorporated Clark County 220,522

C. Environmental Consequences of a 500-MW Surface Powerhouse (Alternative 1)

The construction of Alternative 1 on the Arizona side is identified as the proposed action.

1. Hoover Dam. During construction, congestion and noise at the dam would be increased, perhaps adversely affecting the enjoyment some visitors might otherwise derive from a visit to the dam. On the

48 10 0 10 20 30 40 50

SCALE OF MILES

Figure 18. Map of regional impact area for Hoover Modification socioeconomic assessment. (Mountain West Research, Inc., Tempe, Arizona). CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

other hand, the chance to observe the construction activities might enhance the experience of some visitors. Some areas presently accessible to visitors might be restricted due to safety considerations. These restrictions would be minimal and guided tours of the dam would continue to be conducted. Significant adverse impacts to visitor use and enjoyment of the dam are not anticipated.

The greatest inconvenience during construction would occur to through traffic on U.S. Highway 93 which crosses Hoover Dam en route between Arizona and Nevada. An already congested traffic situation would be worsened by the construction activity especially during movement of heavy equipment when delays up to 45 minutes could be anticipated.

Alternative 1 would affect the esthetics of Hoover Dam by alter- ing the symmetry of the Arizona and Nevada powerhouses. The new powerhouse and surge tank would be built to blend in and be harmonious with existing structures. Because of the eight existing transformer circuits spanning the river at the dam and powerplant, the addition of two more circuits for the project would not cause a significant visual change. Figures 2 and 3 illustrate the change in appearance that would occur under this alternative.

2. Climate and Air Quality. Some increase in pollutants in the Boulder City and Hoover Dam area would result from exhaust fumes from construction and private vehicles, and from fugitive dust from construction activities such as blasting, hauling fill and excavation material, and sand and gravel screening.

The majority of emissions would be dispersed along a 4-mile section between the project site and the borrow area (White Rock Canyon). The emissions may raise the concentration of pollutants around the project area but are not expected to be of enough consequence to cause smog (photochemical reactions) or reduce visibility. Little deterioration of air quality and no change in climate are expected as a result of the proposed project. No impacts are expected to humans, vegetation, or animals due to the emissions.

3. Seismicity. Seismic activity comparable to that experienced in the past can be reasonably expected in the future. The project would not increase seismic activity in the area.

4. Geology. The geology presents no major obstacles to the project. The geologic formations of the area would not be impacted by the construction of the proposed project other than the removal of some of the rock for the powerhouse foundation and cofferdam.

The process of removing material would release no heavy metals or toxic substances into the stream although localized and highly temporary turbidity may result. The turbidity would be much less than experienced during seasonal flash floods and would not impact recreation or aquatic life.

49 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

5. Hydrologic and Aquatic Environment

a. Hoover Dam/Powerplant Operations. With the addition of the 500-MW powerhouse and the scheduled uprating program for the existing generators (see Chapter I, and the no action alternative in Chapters II and III.), Hoover Dam would have a total plant capacity of 2,300 MW (62,000 ft Is). The operational pattern discu9ed in Chapter II.B.3. would be releasing flows in excess of 49,000 ft Is during the summer season. The fall, winter, alpd spring releases would usually be less Oan 1,800 MW (49,000 ft /s). A flow of approximately 2,000 ft /s, equivalent to 70 MW, would continue to be the average minimum release when the level of Lake Mohave is below elevation 637.

b. Water Level and Velocity Fluctuations. During the 5-year construction period the cofferdam would increase the average cross-section velocity of 1.9 mph to 8.2 mph through a section of river about 500 to 800 feet in length immediately downstream from the present Arizona transformer deck. Hydrologic analysis indicates that the effect of the cofferdam on river velocities would be confined to the area immediately below the dam. The cofferdam would be removed after the construction activities are completed. Materials used to fill the cofferdam would be hauled to an existing dump site and would not be released into the river.

Upon completion lof construction, Hoover Dam would have releases of up to 62,000 ft /s durin45/ summer weekdays. Weekends would range from zero to about 2,0001 ft s depending on the lake level. Hoover Dam releases of 62,000 ft /s with Lake Mohave at lake elevation 647 could be expected to cause daily water level fluctuations of about 16 feet at the base of the dam (Table 6). Fluctuations would decrease downstream to about 1.5 feet at Willow Beach an less than one-half foot at river mile 14. Releases of 62,000 ft Is would cause the following velocities to occur in Black Canyon below the dam (Tables 6 and 7): 3 Peak Releases (62,000 ft /s, Mohave at 647) Mean Velocity (Hoover Dam to mile 18) = 2.8 mph Maximum Velocity (1 mile below dam) = 4.5 mph With Lake Mohave at lake elevation 630 and releases of 62,000 ft 3/s, the river level at the base of the dam could fluctuate approximately 24 feet in a 24-hour period. Fluctuations would decrease downstream to about 6 feet at Willow Beach and less than one-half foot at river mile 21 (Table 6). The following velocities would probably occur during peak releases (Table 7): 3 Peak Releases (62,000 ft /s, Mohave at 630) Mean Velocity (Hoover Dam to mile 18) = 3.6 mph Maximum Velocity (14 miles below dam) = 5.1 mph

The low release fluctuations and velocities would remain the same as those presently experienced (Tables 6 and 7).

50 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

Figure 13 depicts the cyclic manner in which Lake Mohave would be operated in the future with the Hoover Powerplant Modification. The "normal schedule" line is the lake elevation which the Bureau would ideally like to meet. This line would not change with or without Hoover Powerplant Modification. The average future year is the 1978 water year projected out into the future with the projected operational changes due to the Hoover Powerplant Modification (Alternative 1). The lake is expected to rise approximately 3 feet from Monday through Friday and decrease approximately 2 feet over the weekend. This would occur the first half of the year when the lake is rising. The opposite, 2-foot rise and 3-foot drop, is expected the second half of the year. This constant weekly fluctuation of Lake Mohave is expected to increase bank erosion slightly and impact the spawning activities of certain Lake Mohave fish. The fishery impacts will be discussed in the following Section g. of this chapter.

Recreational impacts due to water velocity and fluctuation increases are discussed in the following Section 8. of this chapter.

c. Substrate Stability and Primary Productivity. The high velocities created by the cofferdam would cause shifting of loose sand, gravel, cobbles, and small boulders (Hoover Powerplant Modification Feasibility Report). This could cause an increase in turbidity due to the resuspension of sand. This turbid condition, if it does occur, should be short term and not approach the magnitude of naturally occurring turbidity from side canyon flash floods. Periphyton would be disturbed and food production could be reduced by an unknown percentage. However, as indicated above, this increased instability due to the cofferdam would be limited to a relatively small section of the river (500 to 800 feet) immediately below the dam. The effect of any reduction in biomass in this section over the construction period is uncertain, but would probably be minor relative to the entire Black Canyon system.

The increased vejocities and fluctuations due to operational releases up to 62,000 ft Is would cause some immediate impacts on aquatic life located above Willow Beach, Arizona. Increased flows and their related velocities and fluctuations would tear loose filamentous algae and cause substrate scouring. Increased turbidity due to increased velocities is expected at extremely high discharges. The bottom, even at high discharges, should become stable (none or little turbidity) within 6 months. 3These conditions presently exist on releases greater than 30,000 ft /s, reducing the periphyton biomass by some unknown percentage. This condition can be expected to increase as flows and fluctuations increase. Because of the complexity of the . river system, it is difficult to make an accurate assessment without extensive quantitative investigations. From research that has been completed in Black Canyon thus far by the Bureau and others (Paulson, et al., 1980d), along with similar studies done elsewhere (Matter, et al., 1980), it has been determined there are three possible long-term impacts that the increased flows and fluctuations could have on the aquatic life above Willow Beach, Arizona. These possibilities are listed and discussed below in their order of probability:

51 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

First - Since proposed velocities are not expected to exceed the tolerance limits of the periphyton, increased velocities could enhance periphyton growth and its associated invertebrates. This would occur by reducing accumulated sand and making available substrate (cobbles, gravel, and boulders) that could support organism attachment. Under present conditions, the most productive periphyton are located in shallow (less than 15 feet) armored sections of the riverbed that experience the highest water velocities. A hydrological study of the substrate, along with similar investigations (Blanton, 1979), indicates that projected maximum velocities (5.1 mph) would scour the substrate until the particle size reaches 5 inches or greater. Under present conditions, the minimum size in those areas is between 3 and 5 inches. Smaller exposed gravel and rock debris would be washed downstream. The exposure of a larger area of rocky substrate would be expected to enhance algae attachment and promote growth. These substrate conditions could spread to areas that presently experience lesser velocities and are unproductive due to an accumulation of sand.

The reestablishment of the armoring is expected to take one high release season, about 6 months. Fluctuations in release rate are expected to continue the present process of breaking filamentous algae loose. Seasonal and daily fluctuations in water level would continue to expose periphyton along the bank areas in the same manner as presently experienced.

Second - Increased velocities could result in no noticeable change in the biomoss of periphyton or invertebrates. The degradation and enhancement of the environment would balance and closely maintain present productivity. The increase velocities would reduce periphyton growth in areas that experience maximum velocities and enhance growth in sandy areas by scouring them to a rocky substrate. The communities may reestablish themselves in areas that maintain the present river conditions. Periphyton exposure due to fluctuating river and Lake Mohave levels would remain the same as presently experienced.

Third - Increased velocities could reduce the primary productivity of Black Canyon by some unknown percentage. Scouring of unstable substrate and the additional force from water abrasion on algae anchored to stable armoring may reduce the total biomass presently experienced in the first 3 miles of the canyon. Scouring and substrate instability would persist indefinitely and be aggravated by the infrequent influx of materials washed into the canyon by rains. Even with the maximum amount of disruption, it is highly unlikely that the periphyton community would be completely eliminated but it could be reduced. Periphyton exposure due to fluctuating river and Lake Mohave levels would remain the same as presently experienced.

d. Temperature Fluctuations. The Bureau intends to continue releasing water in such a manner that downstream temperatures do not fluctuate more than 3°F (54-57°F). The 3°F temperature fluctuation was determined by calculating the temperature fluctuation of the most stringent operational conditions under which Hoover Powerplant

52 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

Modification could still be made to work. This was the condition of using lower gates on all but the tower serving the proposed project. Both upper and lower gates 3would have to be used on that tower. With a release level of 62,000 ft /s, a lake elevation of 1120 and with four lower and one upper penstock gates open, the maximum temperature would be 57°F. The lowest temperature would be the same as presently experienced (54°F). Thus, the maximum daily fluctuation would be between 54-57°F.

A daily temperature fluctuation of 3°F and a maximum temperature of 57°F would have no effect on the fishery within the Black Canyon nor the Willow Beach National Fish Hatchery located 12 miles downstream. The worst case condition would be if the modified penstock, which draws from both the upper and lower gates, is used without the other penstocks being used. The temperature would vary between 54-61°F for a daily fluctuation of 7°F. This situation is not expected to occur, but is presented to illustrate that even under the most extreme conditions of water temperature and release the temperature fluctuations would have little effect on the fishery.

e. Temperature Instability Versus Productivity. The increased releases under this alternative would further increase the temperature instability immediately above Hoover Dam. Since there would be no appreciable change in total weekly or monthly releases with the modification, the temperature and current patterns in Boulder Basin and elsewhere in Lake Mead should not change significantly.

The incremental increase in release may slightly accelerate vertical mixing above the dam, which in turn would influence the distribution of nutrients and phytoplankton productivity in the summer. There would be a slight increase in phytoplankton and zooplankton productivity; however, this change is not expected to be perceptible without the aid of limnological monitoring equipment (i.e., no nuisance algae blooms).

Lowering Lake Mead level to 1120 should not alter the impact of the proposed modification on plankton productivity over that discussed in the previous paragraph. Even though the rate of mixing, and hence nutrient recycling, would intensify at lower lake levels, it is likely that increases in productivity, beyond that which occurs at higher lake levels, would be limited by factors other than nutrient availability (e.g., light).

f. Interface Versus Fish Hatchery. The interface moves farthest upstream when Lake Mohave elevations are high and Hoover' Dam releases are low. Under Alternative 1, the mid-week releases from the dam would be greater and the weekend releases would be less than currently experienced. Calculations were made using a formula developed by Paulson, et al., 1980a to predict the location of the interface (Table 8).

The proposed Hoover Powerplant Modification may allow the Lake Mohave interface to move far enough upstream to impact the Willow Beach National Fish Hatchery on weekends. The typical weekly load

53 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE curves for the Hover Modification show the lowest mean daily release to be 0-2,000 ft Is occurring on a summer weekend. Extrapolating the data using Paulson's formula and a Lake Mohave elevation of 647 feet above mean sei level (a worst case condition), the mean daily release of 0-2,000 ft Is would cause the interface to be located around 11.9 to 12.6 miles below Hoover Dam. Since the Willow Beach National Fish Hatchery is 12 miles below Hoover Dam, the interface may interfere with its operation on one to four weekends in May or June. This could result in the loss of some or all of the hatchery fish depending on the length of time the fish are exposed to the warmer water. However, since the formula is empirical, the hatchery's intake water temperature would be monitored to ascertain if the interface does become a problem. If it does appear that there would be interference with the hatchery, actions, such as relocating the intake pipe to an area not affected by the interface or installing a water cooling device, would be initiated to alleviate the problem.

The interface, if it does move up to the Willow Beach area, usually carries debris with it. This could interfere with the hatchery's intake and cause a general nuisance problem in the Willow Beach Resort area.

g. Fishery Resources

(1) Lake Mead. The fishery of Lake Mead is not expected to be affected by Alternative 1. The only fish which could possibly be impacted is the striped bass. Striped bass have been observed spawning near the Arizona spillway. With water being drawn into the upper intake gate, there is a remote possibility that striped bass eggs and fry could be drawn into the upper gate. The upper intake gate is 80 to 150 feet (depending upon lake elevation) below the surface of Lake Mead near the dam. With the depth, distance from major spawning areas and low intake velocities insignificant numbers of eggs or fry are expected to be entrained. In addition, this is only one of many striped bass spawning areas in Lake Mead and if entrainment did occur it would not be expected to decrease the striped bass population in Lake Mead.

(2) Lake Mohave. As partially discussed in Section C.5.b.,c.,d., of this chapter, impacts in Black Canyon are expected to be minor and cause no long-term problems for the fishery. The increased velocities and fluctuations in Black Canyon should pose no direct problems.

Temperature fluctuations and increases of 3°F are not expected to negatively impact the trout fishery or aquatic community. A remote possibility exists that an increase in seasonal water temperatures may favor the reestablishment of some aquatic invertebrates which could not tolerate the uniform cold water regime which currently exists. This could increase the available forage base for the fish (trout, razorback suckers) found in Black Canyon.

54 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

Increased velocities below Hoover Dam are initially expected to scour and then rearmor the area immediately below Hoover Dam to a larger more stable substrate size. During this period, which is expected to take 6 months, the fish population (trout, razorback suckers) immediately below the dam is expected to thin, as fish move downstream to more suitable less disturbed habitat. The long-term conditions expected after rearmoring could be (listed in order of probability); (1) increased periphyton biomass resulting from more stable and larger substrate, (2) similar periphyton biomass reestablished, or (3) a decrease in periphyton biomass because of continual state of substrate scour. Conditions (1) and (2) would have no negative impacts, with (1) possibly enhancing the productivity of the river reach. If condition (3) occurred, which is considered the most remote, fish population densities (trout, razorback suckers) would be reduced in the area immediately (3 miles) below Hoover Dam because of more extreme physical conditions (scour, turbidity) and a reduction in the food (periphyton) base. Fish would generally remain in the lower reaches of Black Canyon and Lake Mohave where habitat and forage conditions would be more favorable. Currently, trout and razorback sucker are found throughout the main body of Lake Mohave, a condition which is expected to continue even under condition (3). Trout are restricted to the deep hypolimnic (cold) zone of the lake which is secure from the ramifications of the project. The impact of condition (3) on the overall trout and razorback sucker population would be limited to reducing or displacing a small percentage of the total fish that are presently supported by the 3-mile section below Hoover Dam. This is considered insignificant when compared to the total Lake Mohave fishery. The trout population .density in Lake Mohave and the lower portions of Black Canyon would continue to be maintained artificially by stocking. The impacts to razorback sucker reproduction in Lake Mohave proper are discussed in the Special Status Species section.

Lake fluctuations (Figure 13), however, within the main body of Lake Mohave may cause two basic impacts to fishes inhabiting the warmer surface layers which would result in a decrease in fishery productivity: (1) egg exposure and dehydration, and (2) physical disturbance from wave action.

Egg exposure could occur if fish spawn in water depths less than weekly lake fluctuations. It has been reported (Kramer, 1 961; Miller and Kramer, 1971) that wave action resulting from 17 mph plus winds over a 2-day period can destroy fish nests in less than 5 feet of water. Largemouth bass fry, found in shallow water, can be stressed by wave and wind action which increases mortality rates (Summerfelt, 1975; Von Geldern, 1971).

Since bass eggs and fry are susceptible to wave action, other fish species with similar habitat and reproductive requirements could be susceptible to wave action. This includes largemouth bass, green sunfish, crappie, threadfin shad, and razorback sucker, all of which are known to spawn in shallow water. In addition, the bonytail chub may also be impacted. The razorback sucker and bonytail chub will be discussed later in the Special Status Species section.

55 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

Largemouth bass, green sunfish, and crappie spawn from about March to June. Their nests are found in fairly shallow water (1-12 feet) with the greatest number of nests between 3 and 7 feet. Since wave action can disturb nests 5 feet below the surface, the maximum weekly spring and summer fluctuations with Hoover Modification of up 3 feet and down 2 feet in elevation could disturb as much as 7 feet of spawning habitat every 7 days. The significance of this disruption from year to year and spawning area to spawning area is highly variable and difficult to determine but based on Lake Mead studies and using the approach in Attachment 0 to this document, it appears that this could result in a 24-percent reduction in Lake Mohave productivity. The reduction would be expected to reduce the number of catchable bass and sunfish beginning about 2 years after the operation depicted on Figure 13 commences.

There is also the possibility that increased water level fluctuations could impact plankton production and cover availability for younger fish, thus decreasing the fish's survival chances.

Threadfin shad, a forage fish, utilized by largemouth bass, may also be impacted. Unlike the other fish species mentioned, shad do not construct nests but rather broadcast their eggs in shallow water ranging from 2 to 10 inches in depth. Weekly fluctuations could impact this spawning effort. A reduction in the recruitment of shad would directly affect largemouth bass production since shad are a major food source.

Indirect impacts on Lake Mohave could occur, if food resources in Black Canyon are reduced due to a decline, either short or long term, in primary productivity (see this chapter in previous Section C.5.c.). Primary production in the first 3 miles below the dam may provide the majority of the food base for the entire river downstream to the interface. A long- or short-term reduction in primary productivity during the restabilization of the substrate could cause a redistribution of the fish in Black Canyon during the reestablishment of the periphyton community. This is not expected to cause a reduction in fish populations within Lake Mohave as a whole, since no known fish populations are entirely dependent on Black Canyon for their existence.

Excavation of river bottom material for the cofferdam is not expected to impact the fishery. The area of excavation is bedrock or stabilized sandbars. Excavation, although it would increase the turbidity, is expected to be short term and intermittent. No clogging of gills or reduction in food resources would occur. The turbidity and movement of material during excavation would not approach the magnitude of naturally occurring turbidity in the canyon brought about by spring thunderstorms. It would, however, occur intermittently over a longer period. No toxic substances or increased biochemical oxidation demand would occur.

56 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

Material stirred up by increased water velocities would be short term and have essentially the same impacts as presently experienced during high discharges.

6. Terrestrial Environment

a. Black Canyon 3 (1) Vegetation. Releases of 62,000 ft /s would increase the maximum river elevation at the dam by 6 feet at elevation 647 and 7 feet at Lake Mohave elevation 630 (Table 6). Approximately 2 acres of vegetation (primarily salt cedar) could be subjected to increased inundation and erosion due to the higher releases. However, as discussed earlier, maximum elevations are rarely attained and present conditions suggest that the operating level of Lake Mohave is the primary factor controlling vegetation development and extended periods of inundation are required to inhibit salt cedar growth. The increased releases are not expected to cause a significant change in the quantity or quality of the vegetation in Black Canyon.

(2) Wildlife. Nesting cormorants might be displaced by the increased noise and activity associated with construction around Hoover Dam. Cliff faces with ledges similar to the present nest sites are available downstream and, if disturbed, the birds would presumably move elsewhere. Construction activities are not expected to affect bighorn sheep utilizing sewage treatment ponds near the dam. Upon completion of construction, conditions would be the same as presently exist. No other impacts to wildlife in Black Canyon are anticipated from construction or operation of Alternative 1.

b. White Rock Canyon

(1) Vegetation. Construction of the cofferdam and possible excavation lof sand and gravel for concrete would require an estimated 295,000 ye of material. Plans call for excavating material in White Rock Canyon to an average depth of 6 feet. This means that vegetation on about 34 out of 242 surface acres in White Rock Canyon would be destroyed. Impacts would extend well beyond the construction period. Although the borrow area could be expected to revegetate in time, the process would probably take, at least, in excess of 10 years. After construction, the borrow site would be contoured to reflect the natural terrain. Access through the borrow site to the upper canyon area would be maintained during construction.

(2) Wildlife. As stated earlier, desert washes are important to several wildlife species because of the abundant food and cover they provide relative to the surrounding desert. Excavation in White Rock Canyon would result in the direct loss of some wildlife and the displacement of other more mobile animals. Similar habitat exists above and below the excavation area and there are other washes in the general area. Displaced animals would likely move to these areas creating overcrowded conditions and probably exceeding the capacity of the areas to support them. No special status species would be impacted.

57 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

c. Spoil Sites. Areas for dumping spoils (see frontispiece map)lfrom construction have been identified. All or part of the 180,000 ye of material could be dumped in an existing dump site along U.S. Highway 93 on the Arizona rim of the canyon (Arizona abutment). A cleared landing adjacent to the highway and overlooking the site already exists. No significant impact to vegetation or wildlife is expected from dumping at this site since it is sparsely vegetated and provides little habitat to wildlife. Other areas suggested for dump sites include a ravine along a restricted use road leading to the Nevada powerhouse (Lower Portal Road) and an old dump site on the Nevada side that was used during dam construction. All dump sites are on Bureau property. Significant impacts to vegetation or wildlife would not be expected at either of these sites because they are sparsely vegetated and provide little habitat to wildlife.

7. Special Status Species. No threatened or endangered species would be affected as a result of the proposed project. This prediction was concurred with by the FWS in both formal (April 1, 1982) and informal Section 7 consultations.

The razorback sucker, a fish which may be listed as threatened sometime in the future, would be impacted by weekly lake fluctuations of 2 to 3 feet. The same impacts as those described for black bass and other sunfish in this chapter, the following Section F.5.g.(2) would be expected to occur. Razorback suckers are known to spawn in shallow water (1 to 20 feet) and swimup fry have been observed along a shallow shoreline in Lake Mohave (1981-82). Bureau studies indicate that the project would increase lake fluctuations by 1 foot per week which could expose as much as 30 percent of the razorback spawning effort (eggs).

8. Recreation. With Alternative 1, the daily fluctuation in water levels below Hoover Dam would be greater than at present, as shown on Table 6 and Figures 11 and 12. When Lake Mohave is at or near its maximum elevation (647), the daily fluctuation would vary from about 16 feet at Hoover Dam to about 1.5 feet at Willow Beach. Maximum flow velocity would be greater, possibly hampering upstream travel of smaller in@ter craft. At the extreme lake level (647) and releases (62,000 fe/s), an 80-percent reduction for section 13 and a 40-percent reduction for section 12 (Greey, et al., 1980a) in current recreation use would probably occur (Figure 17). The majority of the water-based users would be expected to redistribute over more appealing sections of the lake.

When Lake Mohave is at or near elevation 630, the water level would fluctuate from about 24 feet at Hoover Dam to about 6 feet at Willow Beach, as shown on Table 6 and Figure 12. When maximum Hoover releases occur, mean velocities would be greater by about 1.1 mph and special emphasis by the NPS on boating safety would be needed to avoid potential problems. Maximum flow velocity would be greater, hampering upstream travel of small water craft. Marinas and boat ramps would probably need some remodeling to accommodate the lake level and high flow velocity. Use in sections 12 and 13 would be reduced by 80 to 90 percent, respectively. This is 50 to 70 percent more reduction in

58 CHAPTER III ENVIRONNENTAL CONSEQUENCES SURFACE POWERHOUSE

use than is presently experienced. Reductions in the use of sectigns 9-11 would be minimal. Conditions with low releases of 2,000 ft Is would be the same as at present (see this chapter, previous Section B.8.).

The reductions and redistribution are approximately 1 to 2 percent of the total use of Lake Mohave, but are a fairly substantial reduction in the Willow Beach area, especially during the summer months. Lake Mohave is easily capable of handling the redistribution of recreationists.

The greater range of water level fluctuation creates a greater possibility of stranding the unwary boat camper or picnicker. The NPS would make special efforts (see Attachment B) to inform recreationists of this hazard.

The project would not have a significant effect on recreation use for the portion of Lake Mohave downstream from Willow Beach with the exception of bass fishing. If the bass fishery is reduced due to the fluctuations of Lake Mohave (see this chapter, previous Section 5.g.(2)) the catch/hour can be expected to decline over the years. This could result in a loss of enjoyment to the fishermen and a loss in revenue to the concessionaires if the number of fishermen using Lake Mohave declined.

9. Archeological and Historical Sites. No construction of the proposed modification would occur in the areas of the archeological sites. The change in riverflows would be the only modification from the present operation. The change in the maximum elevation (about an additional I or 2 feet) would have an impact on the archeological site, Willow Beach No. 2, by hastening the erosional process. There would be no impact from this action on the other archeological site, Cholla Rock Shelter.

Both the Arizona and Nevada State Historic Preservation Officers have been informed of the proposed project (see Attachment H). Consultation on effects as required by 36 CFR 800 and 43 CFR 422 has been ongoing since the earliest stages of project planning.

Hoover Dam is on the National Register of Historic Places. The site may be impacted by the proposed modification. If the alternative of a new powerhouse is selected, the architecture of the new structure would be designed to maintaih the architectural integrity of the dam. The same is true for the surge tank required by this and the other alternatives. Because of the eight existing transformer circuits spanning the river at the dam and powerplant, the addition of two more circuits for the project would not cause a significant visual change.

59 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

The Bureau is requesting a determination of "no adverse effect" for Hoover Dam based on the exterior architecture of the proposed powerplant being compatible with the existing architecture. A determination of "no adverse effect" for Williow Beach No. 2 is being requested based on a data recovery program.

With concurrence of the two state SHPOs on the above "no adverse effect" determinations, the Bureau will go to the ACHP for comments and concurrence. With this concurrence the Bureau will complete the "data recovery" program on Willow Beach No. 2 prior to construction. The Bureau will allow continuing review of the architectural plans for the proposed powerplant with the SHPOs and the ACHP.

10. Socioeconomic Environment. At the peak of construction in 1989, it is estimated that Alternative 1 would employ 420 employees. Of these 420 employees, it is estimated that 129 would relocate to either the regional or the local impact area. The 129 relocating employees would be accompanied by 164 family members. This represents a direct population influx of a total of 293 people in 1989. Table 14 shows where these workers and their families are expected to relocate.

Table 14 DIRECT POPULATION INFLUX DUE TO CONSTRUCTION WORKERS AND THEIR FAMILIES Hoover Powerplant Modification Project

1987 1988 1989 1990 1991

Las Vegas Valley 1/ 27 46 73 51 28

Henderson 53 93 147 103 57

Boulder City 26 46 73 51 29

TOTAL 106 185 293 205 114

Source: Mountain West Research, Inc., April 1980.

1/ Includes Las Vegas, North Las Vegas, and the unincorporated — portions of Clark County.

60 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

Table 15 represents the total population impact associated both directly and indirectly with the proposed action. Indirect or nonbasic population gains are due to services and support activities from nonconstruction workers and their families.

Table 15 COMMUNITY ALLOCATION OF TOTAL POPULATION IMPACT DUE TO THE PROPOSED MODIFICATION OF HOOVER POWERPLANT Hoover Powerplant Modification Project

1987 1988 1989 1990 1991

Henderson Construction 53 93 147 103 57 Nonbasic 114 233 399 235 118 167 326 546 338 175

Boulder City Construction 26 46 73 51 29 Nonbasic 13 26 44 26 13 39 72 117 77 42

Remainder of Clark County Construction 27 46 73 51 28 Nonbasic 342 700 1,199 707 355 369 746 1,272 778- 383

Clark County 575 1,144 1,935 1,173 600

Source: Mountain West Research, Inc., April 1980.

Another important measure is the project's effect on services and facilities in the communities of Henderson and Boulder City. It was found that the most significant impact was apt to occur in the transportation category. The major traffic artery, U.S. Highway 93, (also known as Boulder Highway), is currently critically congested between Hoover Dam and Las Vegas. The additional traffic volume generated by the project in terms of workers and large trucks would exacerbate this situation. This congestion potential is further compounded by several other major projects which are expected to occur in the local impact area during the late-1980's. These major projects include the construction of high-rise hotels, new industry, housing developments, commercial enterprises in Henderson, and a visitor center at Hoover Dam.

The construction of a temporary cofferdam woyld take about 90 days. The cofferdam would require about 215,000 yd of material be hauled by truck from White Rock Canyon in Arizona, which crosses U.S. Highway 93 about 3.7 miles from the Arizona abutment of Hoover Dam to the employees' parking lot on the Arizona side. To lower the material

61 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE to the construction area, a temporary bucket conveyor would be constructed from the employees' parking lot to the Arizona transformer deck.

Each truckload would contain about 22 yd of material, requiring 9,733 truckloads be hauled. These truck trips would only occur during a 12-hour night shift which amounts to 109 truckloads or a truck every 7 minutes.

The present night traffic on U.S. Highway 93 across the dam to Arizona is minimal. The additional truck traffic needed for construction may accelerate the deterioration of those parts of U.S. Highway 93 used. If the deterioration is significant, the Bureau would assist in the remedial measures.

Other less significant impacts were forecasted in the provisions of police protection, fire protection, recreation, and library facilities for both Henderson and Boulder City. These services are at their maximum capacity and would require additional staffing and resources to accommodate any further growth. It was not expected that the small increase in population generated by the Hoover Modification Project would affect education, health care facilities, solid waste disposal, wastewater treatment, or the water supply in either Henderson or Boulder City. Table 16 shows the relative gravity of impacts on these services and facilities.

Table 16 RELATIVE GRAVITY OF IMPACTS ON SERVICES AND FACILITIES IN HENDERSON AND BOULDER CITY Hoover Powerplant Modification Project

No Impact Minimum Impact Significant Impact

School systems Police protection Transportation Health care facilities Fire protection (during construction Solid waste disposal Recreation only) Wastewater treatment Library facilities Water supply

Additionally, 14 community leaders from both Henderson and Boulder City were thoroughly briefed on the economic and demographic effects of the proposed project. Each person was given a handout which included such essential data as a description of the proposed project, the expected manpower breakdown by year, the allocation of movers and nonmovers, a breakdown of anticipated population influx by city and year, and an estimation of the percentage of population change that would accrue to each city as a result of the project. The community leaders included the mayors, the city managers, five city councilpersons, and five city department directors. After they were

62 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE familiar with the quantifiable impacts of the project, they were asked to indicate whether or not these impacts represented a predominantly adverse or a predominantly beneficial effect on their community. Table 17 shows the composite evaluations of both the Henderson and Boulder City key informants. The table readily displays a prevailing frequency of neutral responses.

In conclusion, the key informants expressed little hesitancy about the desirability of the project. They judged that their communities would be beneficially affected in terms of employment and economic stimulation. Even in categories that received most of the adverse evaluations, such as roads, traffic, and police services, there was no indication that the magnitude of these impacts was so large as to affect the desirability of the project. Instead, there were several sincere observations from the key informants that their prevalent neutral responses not be construed to mean that they had any reservations about the project. Therefore, it can be stated with assurance that both these collective responses and the economic- demographic data mutually support and confirm the conclusion that the economic and social consequences of the Hoover Powerplant Modification Project would have a neutral effect on the futures of Boulder City and Henderson.

11. Capacity Loss. During construction 9.2 MW of capacity would be lost, due to cofferdam construction, for about 4-1/2 years. This capacity loss would be absorbed within the network of power generators and be unnoticed. There would be no loss or degradation of service to the public.

12. Cumulative Impacts. In compliance with the National Environmental Policy Act Regulations and in response to the settlement agreement between the Environmental Defense Fund, Trout Unlimited, Wilderness Society (Plaintiffs); and Robert N. Broadbent, Commissioner of Reclamation and James G. Watt, Secretary of the Interior (Federal defendants), the Bureau reviewed all of the impacts associated with this project to determine if they had cumulative or synergistic impacts. No impact of a cumulative or synergistic nature was identified. The impacts associated with this project are discrete and independent of other actions of a similar nature in the Colorado River Basin. Direct impacts which were evaluated and considered to have the most potential of becoming cumulative in nature are discussed below.

Water Quantity and Quality: No additional water is being released, diverted, or consumed as a result of this project. The quantity of water released from the powerplant during any one day or week would not be different from that presently experienced. The method of release, i.e., higher velocities and sustained high and low releases would be different (Figures 7-10) but not cumulative or synergistic.

Salinity and other water quality parameters would not be cumulative or synergistic due to this project. No additional evapor- ation, depletions, point sources or other actions which exacerbate the

63 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

Table 17 A COMPOSITE EVALUATION OF COMMUNITY SERVICES EFFECTS-1/ FROM BOULDER CITY AND HENDERSON KEY INFORMANTS DUE TO THE HOOVER POWERPLANT MODIFICATION PROJECT I. Construction Impact on 0 ++ A. Housing Availability 1 5 7 1 B. Health and Hospital Services 10 3 1 C. Police Services 4 5 5 D. Wastewater Services 2 5 7 E. Educational System 1 11 1 1 F. Employment 1 13 G. Governmental Services 1 12 1 H. Environmental Appearance 1 12 1 I. Roads and Traffic 8 6 J. Other 2 1

II. Levels of Impact on the 0 ++

A. Average Individual 1 12 1 B. Community's Economy 2 12 C. Community's Population 1 9 4 D. Regional Area (Clark County) 8 6

III. Time of Impact 0 ++

A. Preconstruction Impact 14 B. During Construction Impact 3 6 5 C. Long-Term Post-Construction Impact 10 3 1

IV. Conclusions: Impact on 0 ++

A. Overall Quality of Life (General Life Satisfaction) 8 6 B. Overall Social Well-Being (Stability of the Community) 9 5

1 / The above numbers refer to the 14 people who responded to each category. The symbols should be interpreted as follows:

(--) a large adverse impact is probable (-) a small adverse impact is probable (o) a neutral impact is probable (+) a small beneficial impact is probable (++) a large beneficial impact is probable

64 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE salinity problem would occur. Project water quality concerns are restricted to the increased mixing of Lakes Mead and Mohave in the summer months. The increased mixing is a result of the higher water releases (III.C.5.e.) from the dam. The change in water quality would be reflected in increased primary productivity due to the availability of hypolimnic nutrients. It is a highly localized occurrence and is in no way cumulative or synergistic to the Colorado River Basin.

Increases in velocity, temperature, scouring, etc., are discrete occurrences and are not cumulative or synergistic.

Primary Productivity/Fishery: Primary productivity is not expected to decrease, but if it did the effects would be discrete, localized in Lake Mohave and not be cumulative or synergistic to the Colorado River Basin. The same is true for any reduction in the fishery.

Terrestrial Vegetation: Terrestrial vegetation and wildlife impacts associated with the project are confined to White Rock Canyon and the 12-mile area below the dam. This again is highly localized and discrete to the area. No cumulative or synergistic impacts to the Colorado River Basin would occur. This included consideration of possible reductions in riverine communities in the lower reaches of the Colorado River.

Recreation: Recreation fishing opportunities may be reduced or displaced in Black Canyon and on Lake Mohave but the actual number of recreationists should continue at the same level or increase as it has in the past. This again is a highly localized and site specific impact which has no cumulative or synergistic impact on the rest of the Colorado River Basin.

Socioeconomic: The socioeconomic impacts associated with this project are almost nonexistent and would have no cumulative or synergistic impact on the Colorado River Basin.

13. Summary of Impacts. This is the Bureau's proposed action alternative. If Alternative 1 were implemented, the following impacts to the environment could be expected:

- Emissions from construction vehicles and airborne particulates from construction activities would cause a slight deterioration in air quality around Hoover Dam. The deterioration would not be enough to affect visibility, human health, vegetation, or wildlife.

- The new powerhouse and surge tank would slightly change the visual appearance of Hoover Dam.

- Traffic congestion at the dam would be increased during the 5-year construction period.

- During the construction period, increased velocities due to placement of a cofferdam around the proposed new Arizona powerhouse location could reduce primary productivity (algae growth) through a 500- to 800-foot section of river immediately below the dam.

65 CHAPTER III ENVIRONMENTAL CONSEQUENCES SURFACE POWERHOUSE

- Once the project is operational, scouring and bottom instability due to increased water velocities are expected to cause an initial decline in periphyton productivity in a 3-mile section of river immediately below Hoover Dam. Restabilization should occur in approximately 6 months after the proposed project is fully operational. The restabilized area may experience: increased, the same as presently exists, or decreased productivity. There should be no appreciable change in the Black Canyon fishery if the productivity increases or remains the same. If the productivity decreases, there may be a redistribution of fish within Black Canyon (i.e., they would move downstream toward Lake Mohave). Fish species primarily affected would be trout, carp, and the razorback sucker. The bonytail chub, an endangered species, would not be impacted in the Black Canyon area.

- The temperature of the river below Hoover Dam, presently a near constant 54°F, would fluctuate between 54-57°F. This fluctuation is not expected to have a discernible affect on aquatic organisms in the river.

- A reduction in the recreational opportunities in the Willow Beach area is expected, particularly in fishing.

- Vertical mixing, and hence phytoplankton productivity, would be slightly increased in Black Canyon above Hoover Dam. The effect would be unnoticeable without sensitive measuring equipment and would have no impact on the overall aquatic system.

- Possibly a few days during the summer the warm/cold water interface in Lake Mohave would move far enough upstream to allow warm water to be drawn into the Willow Beach National Fish Hatchery. This could result in the loss of some or all of the hatchery fish. Debris would be brought up with the interface which could become a nuisance to the hatchery and marina.

- Materials required for construction would result in 34 out of 242 surface acres of desert wash vegetation being destroyed. Reestablishment of vegetation would be slow and this habitat would be lost to wildlife, probably in excess of 10 years.

- Lake Mohave would increase in weekly fluctuations. This may reduce the productivity of several fish species including largemouth bass, and other sunfish, razorback sucker, and threadfin shad. This could result in a reduction in the largemouth bass/sunfish fishery in Lake Mohave. Razorback suckers, which spawn in shallow water, might also experience a reduction in spawning success. Trout would not be impacted.

- Except for increases in traffic congestion, no significant social or economic impacts to nearby communities resulting from the project are anticipated.

- Increased water depth during high releases would increase the erosion of an archeological site (Willow Beach No. 2).

66 CHAPTER III ENVIRONMENTAL CONSEQUENCES REPLACEMENT OF A8/A9

- Navigational hazards and inconvenience to recreationists would increase on the river above Willow Beach due to the increased water velocities and fluctuations. A decrease in recreational use for this portion of river is anticipated.

- During construction 9.2 MW of capacity would be lost because of the decreased head (2.6 feet) caused by the cofferdam.

14. Proposed Verification Studies and Mitigation. See Attach- ment B to this document.

D. Environmental Consequences of Replacing Generating Units A8 and A9 With a 350-MW Unit (Alternative 2)

This alternative, because of the reduced size of the unit (350 MW) and associated reduced water velocities, probably woula have slightly less downstream impacts. The reduction in impacts would be of such a subtle nature that attempting to quantify them is not realistic. Therefore, most impacts have been expressed as being the same as Alternative 1 with a mention of the expected slight reduction.

1. Hoover Dam. Like Alternative I, construction of Alternative 2 would increase noise and congestion at Hoover Dam. However, since fewer workers and less truck traffic would be required (Chapter II), the impact would be somewhat less than Alternative 1. Much of the construction activity would occur inside the Arizona powerhouse out of view. Tours would continue to be conducted with minimal adjustments due to safety considerations.

Alternative 2 would cause no change in the appearance of Hoover Dam except for the addition of the surge tank.

2. Climate and Air Quality. As with Alternative I, little change in air quality and no change in climate are expected. No impact to humans, vegetation, or animals from the emissions is expected.

3. Seismicity. Same as Alternative I.

4. Geology. Same as Alternative I.

5. Hydrologic and Aquatic Environment

a. Hoover Dam/Powerplant Operations. The total powerplant capacity with Alternatiite 2 and the scheduled uprating program would be 2,060 MW (56,000 ft /s). Powerplant operation would otherwise be the same as described for Alternative I.

b. Water Level and Velocity Fluctuations. Alternative 2 would require a smaller cofferdam than Alternative I (Chapter II). The cofferdam required for construction of this alternative would increase the water level in the tailbay by 2.6 feet and increase the velocity to a maximum of 8.2 mph. The impacts would be the same as discussed under Alternative I.

67 CHAPTER III ENVIRONMENTAL CONSEQUENCES REPLACEMENT OF A8/A9

Upon completion 9f construction, Hoover Dam would have releases of tp to 56,000 ft Is about 7 percent of the days. Releases of 56,000 ft Is with Lake Mohave elevation at 647 would cause daily water level fluctuations of about 14 feet at the base of the dam (Table 6). Fluctuations would decrease downstream to about 1.5 feet at Willow Beach and, less than one-half foot at river mile 14. Releases of 56,000 ft Is would cause the following velocities to occur in Black Canyon below the dam:

Peak Releases (56,000 ft3/s - Mohave at 647) Mean Velocity (Hoover Dam to mile 18) = 2.6 mph Maximum Velocity (1 mile below dam) = 4.3 mph

With Lake Mohave at elevation 630 and peak releases of 56,000 ft Is, the river level at the base of the dam would fluctuate approximately 22 feet in a 24-hour period. Fluctuations would decrease downstream to about 5 feet at Willow Beach and less than one-half foot at river mile 21 (Table 6). The following velocities would occur during peak releases: 3 Peak Releases (56,000 ft /s - Mohave at 630) Mean Velocity (Hoover Dam to mile 18) = 3.4 mph Maximum Velocity (14 miles below dam) = 4.7 mph

The low release fluctuations and velocities would remain the same as those presently experienced (Tables 6 and 7).

c. Substrate Stability and Primary Productivity. As shown on Table 7, river velocities occurring under Alternative 2 would be about 0.2 to 0.4 mph less than those occurring under Alternative 1. A decrease in velocities would cause less scouring and reduce the size of rock needed to stabilize the substrate. Because of the present condition and size of armor, it is unlikely that there would be a measurable difference between the effects of Alternatives 1 and 2 on substrate stability.

d. Temperature Fluctuations. Alternative 2 would, like Alternative 1, require the use of the upper gate on the modified penstock. Thus, temperature fluctuations in the river in Black Canyon would be essentially the same (54-57°) as discussed under Alternative 1.

e. Temperature Instability Versus Productivity. Same as Alternative 1.

f. Interface Versus Fish Hatchery. Same as Alternative 1.

g. Fishery Resources. Same as Alternative 1.

68 CHAPTER III ENVIRONMENTAL CONSEQUENCES REPLACEMENT OF A8/A9

6. Terrestrial Environment

a. Black Canyon

(1) Vegetation. River level fluctuations would be slightly less, but the effects would be essentially the same as Alternative 1.

(2) Wildlife. Same as Alternative 1.

b. White Rock Canyon. Construction of the cofferdam and possible excavation3 of sand and gravel for concrete would require an estimated 77,000 yd of material. Plans call for excavating material in White Rock Canyon to an average depth of 6 feet. This means that vegetation on about 8 out of about 242 surface acres in White Rock Canyon would be destroyed. Impacts would be similar to those discussed under Alternative 1.

c. Spoil Sites. Same as Alternative 1, except the amount of material to be dumped would be 72,000 ye.

7. Special Status Species. Same as Alternative 1.

8. Recreation. Fluctuations and velocities would be slightly less, but the effects would be essentially the same as Alternative 1.

9. Archeological and Historical Sites. Same as Alternative 1, except there would be no extension of the Arizona wing of the powerplant.

10. Socioeconomic Environment. Approximately one-half the number of workers would be required than for Alternative 1 (Chapter II). Thus, impacts to community services, etc., would be proportionately less under this alternative. Traffic congestion would be similar to that described under Alternative 1.

11. Capacity Loss. During construction the 90 MW of capacity available from units A8 and A9 would be lost for about 4-1/2 years. This capacity would be needed about 5 months of the year, so the Bureau would replace it from other sources at an estimated cost of $6.6 million. Operating units at Hoover could be run for a longer period to replace the energy. The cofferdam would cause an additional 9.2-MW capacity loss during construction.

12. Cumulative Impacts. Same as Alternative 1.

13. Summary of Impacts. If Alternative 2 were implemented, the environmental impacts would be similar but slightly less than Alter- native 1 with the following exceptions:

- No change in the appearance of Hoover Dam would occur except for the addition of a surge tank.

69 CHAPTER III ENVIRONMENTAL CONSEQUENCES UNDERGROUND POWERHOUSE

- Materials needed for construction would result in 8 out of 242 surface acres of desert wash vegetation being destroyed. Reestablish- ment of vegetation would be slow and this habitat would be lost to wildlife, probably in excess of 10 years.

- This alternative is 240 MW short of the potential 500 MW.

- During construction, 99.2 MW of capacity would be lost due to the removal of units A8 and A9 and the 2.6 feet of head loss due to the cofferdam.

14. Proposed Verification Studies and Mitigation. Same as for Alternative 1.

E. Environmental Consequences of a 500-MW Underground Powerhouse (Alternative 3)

1. Hoover Dam. Construction impacts would be essentially the same as discussed under Alternative 1. Since the new powerhouse would be underground, there would be no change in the appearance of Hoover Dam except for the addition of the surge tank.

2. Climate and Air Quality. Same as Alternative 1.

3. Seismicity. Same as Alternative 1.

4. Geology. Same as Alternative 1.

5. Hydrologic and Aquatic Environment. Upon completion of construction, the total capacity and operation of Hoover Powerplant would be the same as Alternative 1. Thus, the impact to the hydrologic and aquatic environment would be the same as discussed under Alternative 1, except no cofferdam would be required in the river channel with this alternative.

6. Terrestrial Environment

a. Black Canyon. Same as Alternative 1.

b. White Rock Canyon. Borrow material for cofferdam fill would not be required under this alternative. Sand and gravel for concrete may be required from White Rock Canyon for thi§ alternative. The amount of material would be approximately 50,000 ye. This would destroy vegetation on about 5 out of 242 surface acres in White Rock Canyon. The impacts would be similar but less than those discussed for Alternative 1.

c. Spoil Sites. Same as Alternative 1, except tha,t the volume of material to be disposed of would be about 175,000 ye. No increase in impacts is expected.

7. Special Status Species. Same as Alternative 1.

8. Recreation. Same as Alternative 1. 70 CHAPTER III ENVIRONMENTAL CONSEQUENCES NO ACTION

9. Archeological and Historical Sites. Same as Alternative 1, except there would be no extension of the Arizona wing of the powerplant.

10. Socioeconomic Environment. Same as Alternative 1, except traffic congestion impacts would be reduced since no cofferdam would be built.

11. Cumulative Impacts. Same as Alternative 1.

12. Summary of Impacts. This alternative would have the same capacity and operation as Alternative 1. Thus, environmental impacts would be the same as Alternative 1 with the following exceptions:

- There would be no change in the appearance of Hoover Dam except for the addition of a surge tank.

- No cofferdam is required for construction, thus, there would be no capacity loss and no loss in primary productivity within the tailrace area.

- Materials needed for construction would result in 5 out of 242 surface acres of desert wash vegetation being destroyed.

13. Proposed Verification Studies and Mitigation. Same as for Alternative 1. See Attachment B.

F. Environmental Consequences of No Action/Future Without the Project (Alternative 41

1. Hoover Dam. The Bureau plans to build a new visitor center and parking facilities at Hoover Dam within the next decade. This should alleviate some of the congestion which presently exists at the dam during high visitor use. All other conditions should remain as presently experienced.

2. Climate and Air Quality. With no action, the air quality around the dam would be expected to degrade as a result of normal population growth in the surrounding areas.

3. Seismicity. Seismic activity would be expected to continue in the future as it has in the past.

4. Geology. No change.

5. Hydrologic and Aquatic Environment

a. Hoover Dam/Powerplant Operations. When the present uprating program for the existing generators is completed, Hoove Dam will have a total plant capacity of about 1,800 MW (49,000 fe/s). Operation of the powerplant is expected to be the same as presently experienced.

71 CHAPTER III ENVIRONMENTAL CONSEQUENCES NO ACTION

b. Water Level and Velocity Fluctuations. After the upr4t- ing is completed, Hoover Dam would have releases up to 49,000 ft3/s for up to about 4 to 5 percent of the days. Releases of 49,000 ft /s with Lake Mohave at elevation 647 can be expected to cause daily water level fluctuations of about 12 feet at the base of the dam (Table 6). Fluctuations would decrease dpwnstream to less than 1 foot at Willow Beach. Releases of 49,000 ft /s would cause the following velocities to occur in Black Canyon below the dam: 3 Peak Releases (49,000 ft /s - Mohave at 647) Mean Velocity (Hoover Dam to mile 18) = 2.4 mph Maximum Velocity (1 mile below dam) = 4.2 mph 3 Lake Mohave at elevation 630, releases of 49,000 ftrt3/s /s would cause daily fluctuations of about 20 feet at the base of the dam. Fluctuations would decrease downstream to about 3.5 feet at Willow Beach and less than one-half foot at river mile 20 (Table 6). The following velocities would occur during peak releases: 3 Peak Releases (49,000 ft /s - Mohave at 630) Mean Velocity (Hoover Dam to mile 18) = 2.9 mph Maximum Velocity (1 mile below dam) = 4.7 mph

The low release fluctuations and velocities would remain the same as those presently experienced (Tables 6 and 7).

c. Substrate Stability and Primary Productivity. The 0.3 to 0.4 mph increase in velocities (Table 7) is not expected to have a discernible effect on primary productivity. The river is expected to stabilize at a new equilibrium with slightly more productivity than under present conditions. Any increase in turbidity due to the increase in velocity would be short term and probably unmeasurable.

d. Temperature Fluctuations. With the no action alternative, the Bureau has made a commitment to release water in such a manner that the water temperature would remain as at present, around 54.5°F.

e. Temperature Instability Versus Productivity. The increased releases (up to 49,000 ft /s) due to uprating would cause some slight increase in vertical mixing above the dam compared to present conditions. The resulting increase in phytoplankton productivity would be undetectable.

f. Interface Versus Fish Hatchery. The warm/cold water interface, even after uprating, is not expected to interfere with the Willow Beach National Fish Hatchery.

g. Fishery Resources

(1) Lake Mead. The no action alternative would have no effect on the fishery of Lake Mead.

72 CHAPTER III ENVIRONMENTAL CONSEQUENCES

(2) Lake Mohave. The fishery of Lake Mohave would be expected to remain essentially the same as under present conditions.

Recent collections of striped bass in Lake Mohave have led to speculation that this large predator may affect other fish populations especially the trout fishery. Further data are needed to determine if striped bass would successfully reproduce in Lake Mohave.

6. Terrestrial Environment. With the no action alternative, terrestrial vegetation and wildlife are expected to remain the same as under present conditions.

7. Special Status Species. The no action alternative is not expected to affect any special status species.

8. Recreation. The small increase in water level fluctuations and velocities after uprating are not expected to change the recreational use of Lake Mohave or Black Canyon.

9. Archeological and Historical Sites. The present status and condition of archeological and historical sites would remain the same as presently experienced under the no action alternative.

10. Socioeconomic Environment. The uprating program scheduled for Hoover Powerplant should have no detectable socioeconomic impacts. The uprating would involve about 20 workers for about 6 months per unit. The uprating would be done intermittently over a period of about 10 years. Thus, the no action alternative, which includes uprating, would cause no noticeable impact to the socioeconomic environment.

11. Cumulative Impacts. None.

12. Summary of Impacts. If the no action alternative was implemented, the environment of the project area would remain essentially as presently experienced with the following exceptions:

- A scheduled uprating program for the existing generaiors would increase the maximum releases from Hoover Dam to 49,000 ft /s. This is likely to cause some initial substrate instability and temporary loss in primary productivity in the first few miles below the dam.

- A new visitor facility planned for Hoover Dam should alleviate some of the traffic congestion which often occurs at the dam. This facility could be constructed with or without the proposed project.

G. Relationship to Other Projects and Actions

1. Reregulation of Lake Mohave. Lake Mohave has traditionally been operated between elevations 630 and 647. The lower limit has more or less evolved over time, although the operating criteria call for operating Mohave between elevations 570 and 647. Reregulating

73 CHAPTER III ENVIRONMENTAL CONSEQUENCES

Lake Mohave below 630 has an advantage to power operators, in that lower Lake Mohave levels would allow greater flexibility and capacity for power generation in the spring months.

Preliminary investigations indicate that, regardless of whether or not the Hoover Powerplant Modification Project were implemented, lowering Lake Mohave below elevation 630 would impact the fishery and recreational uses of Lake Mohave (Paulson, et al., 1980d). Because the lake has been operated to a minimum elevation of about 630 for many years, a thorough environmental analysis would be made before deciding to reregulate it to a lower level. The higher velocities resulting from implementation of any of the Hoover Modification alternatives would tend to increase the severity of impacts that would be associated with reregulation. However, implementation of any of the Hoover Modification alternatives is not expected to increase or decrease the likelihood of reregulation occurring.

2. Hoover Dam Visitor Center. Plans are underway for the construction of new visitor facilities at Hoover Dam. If the Hoover Powerplant Modification Project is authorized, the timing of these two projects may overlap. This would compound traffic congestion at Hoover Dam.

3. Floodplain Management. Executive Orders 11988 and 11990 require, that among other things, any Federal action involving a flood plain or Wetlands area should reduce the risk of flood loss, avoid long- and short-term adverse impacts to flood plains and wetlands, and evaluate alternatives to locating in the flood plain or disturbing the wetlands. The flood control function of Hoover Dam would not be affected by the proposed project or alternatives. Structural and nonstructural alternatives to locating the action in a flood plain are presented in Chapter II and the alternatives were presented at public meetings as discussed in Chapter IV. The reasons these alternatives were eliminated from further analysis are discussed in Chapter II. The alternatives considered in detail in this report would all be located in the flood plain but not on wetlands. The character of the flood plain and wetlands would not change in the Hoover Dam area due to the proposed project. The project is in compliance with the requirements and overall mandate of Executive Orders 11988 and 11990.

4. Permits, Licenses, and Other Entitlements. Three permits are required before construction activities can begin. In compliance with the Federal Water Pollution Control Act, Public Law 92-500, a Section 402 Permit from the Environmental Protection Agency, and 404 Permit from the Corps of Engineers, must be obtained. It is intended that this EIS be used to qualify for exemption to the 404 permit process under section 404 (0 of P.L. 92-500, as amended. In addition, a permit under Section 10 of Rivers and Harbors Act of 1899 must be obtained to bring powerlines from the Arizona side to the Nevada side of the Dam. This EIS is intended to satisfy the environmental requirements of that permit.

CHAPTER EZ

CONSULTATION AND COORDINATION

CHAPTER IV

CONSULTATION AND COORDINATION

A project plan for the Hoover Powerplant Modification was developed with the close consultation, coordination, and cooperation of several organizations and Government agencies.

To develop awareness and understanding of this project, a public involvement program with five phases was conducted by the Bureau of Reclamation. In accordance with the concepts of the multiobjective planning process, a wide range of viewpoints has been sought representing local, state, regional, and national interest groups. Direct input from private citizens and state utilities, city governments, and special interest groups has been vigorously pursued through public meetings, field trips, voluntary response forms, information programs, and citizens' committees.

More specifically, the four-phase program began in September 1977. The first phase was the introduction of the project to the public. This introductory session was conducted in Boulder City and Las Vegas, Nevada; Kingman, Bullhead City, Lake Havasu City, and Phoenix, Arizona; and Los Angeles, California. The public identified a number of problems and needs associated with the project and expressed public support of the need for increased peaking. The major items identified are presented in Attachment C to this document.

The second phase was the discussion of project alternatives and their effects or impacts. This session was conducted in Boulder city and Las Vegas, Nevada, and Bullhead City, Arizona. Special meetings were also held with the Boulder City Council, Henderson Chamber of Commerce, and the public utilities in the Los Angeles area. Three additional alternatives were brought up for our consideration in these meetings. They were the use of thermocline solar energy, hydrogen energy, and the construction of Hualapai (Bridge Canyon) Dam. These alternatives are described in Chapter II of this EIS.

The third phase was the scoping session for the draft outline for the EIS. This session was held in Boulder City, Nevada, and Bullhead City, Arizona, in October 1979, with a special presentation at the Southern Nevada Conservation Council in Las Vegas, Nevada. The comments from these meetings culminated into the final outline which are presented in Attachment C to this document.

The fourth phase is the distribution of the final draft EIS to interested groups or individuals.

A. Coordination Groups

1. Planning Team. The planning team, which was established in November 1976, is a working level group composed of specialists in the Bureau and other Federal agencies in various disciplines who provide

75 CHAPTER IV CONSULTATION AND COORDINATION their expertise to assure a plan of development that best uses the resources of the area. The people who served on the planning team are listed below:

BUREAU BUREAU (continued)

John D. Brown, Environment Mark Bird, Sociology Gary L. Bryant, Environment Davie Branstetter, Geology William I. Butler, Environment Robert T. Littleton, Geology Wayne 0. Deason, Environment Keith A. Barrick, Engineering Adrian O. Hutchens, Economics Kenneth Vick, Engineering Alan P. Kleinman, Economics Michael S. Cowan, Engineering and Design Benedict R. Radecki, Power Burton Simpson, Engineering and Design Michael J. Roluti, Power Virgil Frederiksen, Water Scheduling OTHER AGENCIES Robert V. Barton, Hydrology David J. Sobek, Hydrology Frank M. Baucom, Fish and Wildlife Service Russell Thomas, Hydrology Don Metz, Fish and Wildlife Service Martin P. Einert, Planning William Burke, National Park Service Wayne F. Fernelius, Planning Richard F. Brown, Western Dean F. Johanson, Planning John S. Forman, Western Deanna J. Miller, Planning Don Martin, Western

2. Interagency Group. The interagency group is composed of specialists from state and local agencies and private organizations and individuals. The group was involved primarily with the environmental and physical construction aspects, by providing counsel in identifying problems and needs of the study area, providing input, reviewing evaluation criteria, helping to formulate plans, and providing critiques of draft reports.

3. Power Group. Meetings were held with present and potential customers of Hoover power to evaluate the need for additional peak period capacity in the area served by Hoover Powerplant, and how such additional capacity could be utilized in their individual power systems. The meetings were supplemented with response forms on power needs and power system operations. Those people who were in the Power Group are listed below:

Alden Briggs, Bureau of Reclamation John D. Brown, Bureau of Reclamation Gordon B. Freeny, Bureau of Reclamation Gerald Moore, Bureau of Reclamation Benedict R. Radecki, Bureau of Reclamation Michael J. Roluti, Bureau of Reclamation William J. Williams, Bureau of Reclamation Tina Goeser, Western Area Power Administration Gordon N. Boyer, Federal Power Commission John F. Sullivan, Salt River Project Dean K. Yee, Salt River Project Frank Salas, Los Angeles Department of Water and Power Thomas T. Uechi, Los Angeles Department of Water and Power Wes Williams, Southern California Edison Company

76 CHAPTER IV CONSULTATION AND COORDINATION

Jack Young, Southern California Edison Company Bill Fell, City of Glendale Bill Hall, City of Glendale George Edwards, City of Anaheim Don Campbell, City of Riverside Alex E. Koutras, Pasadena Water and Power R. W. Schempp, Metropolitan Water District

Byron L. Miller, Nevada Power Company John C. Gibbs, Nevada Power Company Lee Bernstein, Colorado River Commission Duane R. Sudweeks, Colorado River Commission

H. A. Paine, Basic Industries of Henderson Les Ormsby, Arizona Power Authority Thomas Sawyer, Arizona Power Authority Leslie L. Daviet, II, Arizona Public Service Company Bill Murphy, Arizona Public Service Company Michael A. Curtis, Arizona Municipal Power Users' Association David T. Larsen, Arizona Electric Power Cooperative David Chapman, Valley Electric Association Elmer G. Vandas, R. W. Beck and Associates Victor B. Uehling, private concern of Boulder City, Nevada

B. Major Participants in Planning Process

The major participants in the planning process are Federal, State, and local governments, municipalities and contractors. Those entities participating are listed below:

I. Federal

Bureau of Reclamation Western Area Power Administration National Park Service Fish and Wildlife Service Federal Power Commission Upper Colorado River Commission

2. State of Nevada

Nevada Department of Wildlife University of Nevada, Las Vegas Nevada State Historic Preservation Office Colorado River Commission

3. State of Arizona

Arizona Game and Fish Arizona State University Arizona State Historic Preservation Office Mohave County Board of Supervisors

77 CHAPTER IV CONSULTATION AND COORDINATION

4. Local Municipalities

City of Boulder City City of Henderson Henderson Chamber of Commerce

5. Private

R. W. Beck and Associates Facilitators, Inc. Mountain West Research, Inc.

6. Utilities

Nevada Power Company, Nevada Department of Water and Power, The City of Los Angeles Southern California Edison Company, California Metropolitan Water District, California

C. Public Meetings

Public meetings and workshops, including question and answer sessions, were held periodically in the local area and in Phoenix, Kingman, Bullhead City, and Lake Havasu City, Arizona; Boulder City, Henderson, and Las Vegas, Nevada; and Los Angeles, California. Detailed discussions were conducted at these meetings covering plan formulation, input data on studies, evaluation procedures, content of environmental impact statement, and interim findings of the investigations. Although attendance by the general public was usually light, the meetings were frequently attended and reported by the press.

Interviews with the local news media resulted in several news- paper articles on the modification of Hoover Powerplant. Articles have been published in the "Henderson Home News and Boulder City News," the "Las Vegas Review-Journal," the "Las Vegas Sun," and the "Lake Havasu City Herald."

In addition to the scheduled public involvement meetings, representatives of the Bureau presented numerous slide/talk presentations to local organizations and special interest groups. The Fish and Wildlife Service, Regional Environmental Office, Mountain West Research, Inc., and other interested groups and individuals participated in field excursions and tours of the project area and down river to Katherine Landing, Willow Beach, and Cottonwood Cove recreation areas.

An illustrated pamphlet was prepared and distributed at formal public involvement meetings along with the presentation of a colorful display that was set up at each meeting (see Figure 19). A social assessment in Boulder City and Henderson was conducted to interpret opinions of community leaders on social impacts of the project.

78 Figure 19. The colorful display presented at the public involvement meetings for Hoover Powerplant Modification Investigation.

CHAPTER IV CONSULTATION AND COORDINATION

Public participation throughout the planning process has been beneficial, especially in respect to identifying the concerns for power supply and for potential disturbance to the fishery and recreation in the area of the Colorado River from Hoover Dam to Davis Dam.

A notice of the proposed preparation of an EIS for the Hoover Powerplant Modification was published in the Federal Register on September 26, 1979. Public meetings were held to discuss the draft outline of the EIS. Valuable additions, deletions, and corrections were made by those in attendance. After revisions were made, the outline was printed and distributed to all interested parties.

The citizens of the area have provided ideas and suggestions which have helped eliminate proposals which are not feasible more rapidly than if their input had not been used. On the other hand, their suggestions have given the Bureau ideas which might be very instrumental in future decisions in respect to the project. As studies continue, the public will be kept informed and their input utilized in the formulation and evaluation of project alternatives.

Throughout the planning process, an open-door policy has been maintained, with many conferences being held, press releases being printed, and telephone calls being received. State, regional, and local governments have conducted studies which have been most useful in the Hoover Powerplant Modification investigation and planning process. Close coordination with all parties has resulted in avoid- ance of duplication and a close spirit of mutual cooperation.

The Bureau of Reclamation gratefully acknowledges the assistance provided by the public and various organized entities toward the formulation of a project plan for the Hoover Powerplant Modification Feasibility Investigation.

CHAPTER 3E

LIST OF PREPARERS

CHAPTER V

LIST OF PREPARERS

This environmental statement was prepared by the Lower Colorado Region, Bureau of Reclamation, P. O. Box 427, Boulder City, Nevada 89005. A list of persons who prepared various sections of the statement or participated to a significant degree in preparing the statement is presented below:

NAME QUALIFICATIONS PARTICIPATION

BUREAU OF RECLAMATION (Bureau)

Joe Bailey B.S. Geology; Engineering Geology. Geologist, Corps of Engineers, 2 years; Bureau, 5 years.

Mark J. Bird M.A. Sociology; Social Social Assessment. Factors Analyst, Bureau, 3 years.

Gary L. Bryant B.S. Zoology; M.A. Biology; EIS Coordinator, Environmental Specialist, Quality Control Bureau, 9 years. Aquatic Evaluation.

M. A. Caves A.A. Civil Engineering; Plans and Estimates. Engineering Technician, Bureau, 11 years.

Michael L. Delamore B.S. Wildlife Management; Vegetation and Raptor Research, Forest Wildlife Evaluation. Service, 1 year; Wildlife Biologist, Bureau, 2 years.

Martin P. Einert B.S. Civil Engineering; Team Leader, Plan Civil Engineer, Bureau, Formulation. 21 years.

Donald J. Esgar B.S. Electrical Engineering; Power. Electrical Engineer, Bureau, 19 years.

Richard A. Groesbeck Illustrating and Selling Public Involvement for Private Industry, Design and Display, 16 years; Illustrator Cover. Bureau, 17 years.

Deanna J. Miller Technical Publications Writer, Feasibility Report and BLM, 3 years; Bureau, 16 years. EIS; Writing and Editing.

80 CHAPTER V LIST OF PREPARERS

NAME QUALIFICATIONS PARTICIPATION

Gordon Mueller B.S./M.S. Biology; River Aquatic Evaluation. Studies, NPS, 3 years; Aquatic Biologist, Bureau, 2 years.

Robin Rodgers Lead Cartographic Technician, Graphics. Bureau, 17 years.

David J. Sobek B.S. Civil Engineering; Hydrology. Engineering Consultant, 1 year; Hydrologist, Bureau, 2 years.

CONSULTANTS

Arizona State University, Tempe, Arizona

Glenn W. Cheatham B.S./M.S./PhD. Recreation; Recreation Survey Professor and Chairman, Report. Dept. of Leisure Studies, 5 years; Assistant Professor, 7 years; Community Center Director, 5 years.

George W. Greey B.S. Physical Education; Recreation Survey M.S. Industrial Education; Report. PhD. Education; Chairman, Dept. of Leisure Studies, 7 years; Professor of Recreation, 9 years.

Randy J. Virden B.S./M.S. Outdoor Recreation; Recreation Survey Faculty Research Associate, Report. 3 years; Park Ranger, 2 years; Instructor, 1 year.

University of Nevada at Las Vegas, (UNLV)

John R. Baker B.S./M.S. Biology; Research Limnological Survey Associate, Limnological of Lake Mead and Research on Lake Mead, 6 years. Lake Mohave Report.

James E. Deacon B.S. Biology; PhD. Teaching Limnological Survey and Icthyology 20 years; of Lake Mead and Chairman Dept. of Biological Lake Mohave Report. Sciences, 5 years.

Larry J. Paulson B.S. Biology; M.S. Aquatic Limnological Survey Biology; PhD. Ecology/ of Lake Mead and Limnology; Director Lake Mead Lake Mohave Report. Limnological Research Center, 9 years.

81 CHAPTER V LIST OF PREPARERS

NAME QUALIFICATIONS PARTICIPATION

CONSULTANTS (cont.)

Nevada Archaeological Survey, UNLV

Richard H. Brooks PhD. Archaeology; Teaching Cultural Resources and Archaeology, 22 years. Inventory Report.

Arnie L. Cunningham B.A. Archaeology; Ethno- Cultural Resources botonist/Archaeologist, UNLV Inventory Report. Survey, 2 years.

David Ferraro Student; Archaeologist, Cultural Resources UNLV, Survey, 4 years. Inventory Report.

Daniel Larson M.A. Archaeology: Cultural Resources Archaeologist, UNLV, Inventory Report. Survey, 5 years.

Kathryne Olson B.A. Archaeology; UNLV, Cultural Resources Survey, 4 years. Inventory Report.

Mountain West Research, Inc., Tempe, Arizona

James A. Chalmers PhD. Economics; Chief Economic/Demographic Economist, Private Consultant Analysis Report. for Assessment Economic and Regional Development, 10 years.

Nancy Post B.A. Regional Sciences; Economic/Demographic Teaching, 2 years; Consultant, Analysis Report. Private Consultants, 4 years.

Nevada Department of Wildlife, Las Vegas, Nevada

Robert C. Allan B.S. Zoology; Nevada Dept. Lake Mead and Lake of Wildlife, 20 years Mohave Fishery Report.

Dennis Roden B.S. Wildlife Management; Lake Mead and Lake Seasonal Aid, 2 years; Mohave Fishery Report. Nevada Dept. of Wildlife, 1 year.

ATTACHMENTS

ATTACHMENT A

DISTRIBUTION LIST

Hoover Modification Draft Environmental Statement

Statements to be distributed by the Commissioner, Bureau of Reclamation

Department of the Interior:

Fish and Wildlife Service, Washington, D.C.

National Park Service, Washington, D.C.

Bureau of Indian Affairs, Washington, D.C.

Geological Survey, Washington, D.C.

Bureau of Mines, Washington, D.C.

Bureau of Land Management, Washington, D.C.

Department of State, Washington, D.C.

Department of Agriculture, Washington, D.C.

Department of Energy, Washington, D.C.

Advisor on Environmental Quality, Federal Energy Regulatory Commission, Washington, D.C.

Department of Transportation, Washington, D.C.

Nuclear Regulatory Commission, Washington, D.C.

Department of Health and Human Services, Washington, D.C.

Department of Labor, Washington, D.C.

Department of Air Force, Washington, D.C.

Interstate Commerce Commission, Washington, D.C.

Department of Army, Civil Works, Washington, D.C.

Advisory Council on Historic Preservation, Denver, Colorado

A-1 Regional Director, Department of Housing and Urban Development, San Francisco, California

Regional Administrator, Environmental Protection Agency, San Francisco, California

Department of the Army, Environmental Planning Section, Corps of Engineers, Los Angeles, California

Statements to be distributed by the Commissioner, Bureau of Reclamation, for information only:

Honorable Howard W. Cannon, United States Senate, Washington, D.C.

Honorable Paul Laxalt, United States Senate, Washington, D.C.

Honorable James D. Santini, Member, U.S. House of Representatives, Washington, D.C.

Honorable Alan Cranston, United States Senate, Washington, D.C.

Honorable S.I. (Sam) Hayakawa, United States Senate, Washington, D.C.

Honorable Bobbi Fiedler, Member, United States House of Representatives, Washington, D.C.

Honorable Carlos J. Moorhead, Member, United States House of Representatives, Washington, D.C.

Honorable Anthony C. Beilenson, Member, United States House of Representatives, Washington, D.C.

Honorable Edward R. Roybal, Member, United States House of Representatives, Washington, D.C.

Honorable Julian Dixon, Member, United States House of Representatives, Washington, D.C.

Honorable Dennis DeConcini, United States Senate, Washington, D.C.

Honorable Barry M. Goldwater, United States Senate, Washington, D.C.

John J. Rhodes, Member, United States House of Representatives, Washington, D.C.

Bob Stump, Member, United States House of Representatives, Washington, D.C.

Eldon Rudd, Member, United States House of Representatives, Washington, D.C.

Morris K. Udall, Member, United States House of Representatives, Washington, D.C.

A-2 Statements to be distributed by the Regional Director, Lower Colorado Regional Office, Boulder City, Nevada for information only:

Department of the Interior

Regional Director, Fish and Wildlife Service, Albuquerque, New Mexico

Field Supervisor, Ecological Services, Fish and Wildlife Service, Phoenix, Arizona

District Chief, Water Resource Division, U.S. Geological Survey, Tucson, Arizona

District Hydraulic Engineer, Conservation Division, Geological Survey, Sacramento, California

Field Solicitor, Phoenix, Arizona

Coordinator, Fort McDowell Office, Scottsdale, Arizona

State Director, Bureau of Land Management, Phoenix, Arizona

State Director, Bureau of Land Management, Reno, Nevada

District Manager, Bureau of Land Management, Phoenix, Arizona

District Manager, Bureau of Land Management, Las Vegas, Nevada

Chief, Bureau of Mines, Denver, Colorado

Regional Environmental Officer, Office of the Secretary, Department of the Interior, San Francisco, California

Regional Director, National Park Service, San Francisco, California

Chief, Western Office, Review and Compliance, Advisory Council on Historic Preservation, Denver, Colorado

Superintendent, Lake Mead National Recreation Area, Boulder City, Nevada

Department of the Army

District Engineer, Corps of Engineers, Los Angeles, California

Department of Transportation

Commander, 9th District, U.S. Coast Guard, Los Angeles, California

A-3 Environmental Protection Agency

Nevada Branch, San Francisco, California

Interstate Commerce Commission

Regional Manager, San Francisco, California

Department of Energy

Administrator, Western Area Power Administration, Golden, Colorado

Area Manager, Western Area Power Administration, Boulder City, Nevada

James L. Kahan, representative of Senator Dennis DeConcini, Phoenix, Arizona

Thomas Dunlavey, representative of Senator Barry M. Goldwater, Phoenix, Arizona

Robert Scanlan, representative of Congressman John J. Rhodes, Phoenix, Arizona

Edna H. McDonald, representative of Congressman Bob Stump, Phoenix, Arizona

Michael J. Stubler, representative of Congressman Eldon Rudd, Phoenix, Arizona

Prior Pray, representative of Congressman Morris K. Udall, Tucson, Arizona

The Arizona Republic Phoenix, Arizona

The Phoenix Gazette Phoenix, Arizona

Boulder City News Boulder City, Nevada

Desert Star Needles, California

Associated Press Las Vegas, Nevada

Las Vegas Review-Journal Las Vegas, Nevada

A-4 Las Vegas Sun Las Vegas, Nevada

Lake Havasu City Herald Lake Havasu City, Arizona

Mohave County Miner Kingman, Arizona

United Press International Las Vegas, Nevada

Statements or summary descriptions to be distributed by the Regional Director inviting comments:

State of Arizona

Office of the Governor, Phoenix, Arizona

State Clearinghouse, Phoenix, Arizona

Department of Transportation, Phoenix, Arizona Highway Division

Game and Fish Department, Phoenix, Arizona

State Land Department, Phoenix, Arizona

Outdoor Recreation Coordinating Commission, Phoenix, Arizona

Department of Water Resources, Phoenix, Arizona

Department of Economic Security, Phoenix, Arizona

Bureau of Geology and Mineral Technology, Phoenix, Arizona

State Historic Preservation Officer, Phoenix, Arizona

Advisory Commission on Arizona Environment, Phoenix, Arizona

Department of Public Safety, Phoenix, Arizona

State of California

Office of the Governor, Sacramento, California

State Clearinghouse, Sacramento, California

Department of Water Resources, Sacramento, California

Colorado River Board of California, Los Angeles, California

A-5 State of Colorado

Office of the Governor, Denver, Colorado

State Clearinghouse, Denver, Colorado

State of Nevada

Office of the Governor, Carson City, Nevada

State Clearinghouse, Carson City, Nevada

Department of Conservation and Natural Resources, Division of Water Resources, Carson City, Nevada

Colorado River Commission, Las Vegas, Nevada

Department of Conservation and Natural Resources, District Office, Las Vegas, Nevada

Nevada Archaeological Survey, Southern Division, Las Vegas, Nevada

State of New Mexico

Office of the Governor, Santa Fe, New Mexico

State Clearinghouse, Santa Fe, New Mexico

State of Utah

Office of the Governor, Salt Lake City, Utah

State Clearinghouse, Salt Lake City, Utah

State of Wyoming

Office of the Governor, Cheyenne, Wyoming

State Clearinghouse, Cheyenne, Wyoming

Clark County, Nevada

Board of Supervisors, Las Vegas

Highway Department, Las Vegas

Department of Parks and Recreation, Las Vegas

Planning Department, Las Vegas

A-6 Mohave County, Arizona

Board of Supervisors, Kingman

Highway Department, Kingman

Planning Department, Kingman

Others

Mr. John Clonts, Western Archeological Center, National Park Service, Tucson, Arizona

Center for Environmental Studies, Arizona State University, Tempe, Arizona

Bob Glassburn Bait and Tackle, Henderson, Nevada

Linda Smiraglia, San Diego, California

Mr. Jerry McClain, MWD, Los Angeles, California

Mr. J. D. Woodburn, City of Burbank, Burbank, California

Mr. John H. Lauten, MWD, Los Angeles, California

Sierra Club, Las Vegas, Nevada

Sportsman's Bait and Lounge, Las Vegas, Nevada

Arizona Public Service Company

Blake's Holiday Marine, Henderson, Nevada

Desert Research Institute, Boulder City, Nevada

Chamber of Commerce, Bullhead City, Arizona

Robert Anderson, Cottonwood Cove, Nevada

E.H. Pratt, Bullhead City, Arizona

James A. Chalmers, Tempe, Arizona

Mrs. Virginia Morrison, Boulder City, Nevada

Director, Public Information on the Environment

Lake Mead Limnological Center, UNLV, Las Vegas, Nevada

Environmental Defense Fund, Western Land and Water Resources Program, Denver, Colorado

A-7 City of Boulder City, Nevada City of Henderson, Nevada City of Las Vegas, Nevada City of Bullhead City, Arizona City of Kingman, Arizona Arizona Public Service Company, Phoenix, Arizona

Museum of Northern Arizona, Flagstaff, Arizona

Arizona Water Sports Council, Phoenix, Arizona

National Wildlife Federation, Washington, D.C.

Sierra Club, Las Vegas, Nevada

Southern Nevada Recreation Council

Statements or summary descriptions to be distributed by the Regional Director for public access:

Kingman City-Mohave Co. Library, Kingman, Arizona

Phoenix Public Library, Phoenix, Arizona

Law Center Library, University of Southern California, Los Angeles, California

Los Angeles County Library, Los Angeles, California

Water Resources Archives, University of Californfa at Los Angeles, Los Angeles, California

University of Nevada - Las Vegas Library, Las Vegas, Nevada

Boulder City Library, Boulder City, Nevada

Bullhead City Library, Bullhead City, Nevada

Clark County Public Library, Las Vegas, Nevada

Henderson Public Library, Henderson, Nevada

A-8 ATTACHMENT B

ENVIRONMENTAL COMMITMENTS MADE IN THIS STATEMENT

The Bureau considers the greatest potential impacts to be to the aquatic environment below Hoover Dam. Because uncertainties are inherent in any prediction, the Bureau intends to carry out the listed actions to verify predicted impacts and avoid or mitigate adverse impacts.

The environmental commitments made in this EIS have taken into consideration the recommendations of the Fish and Wildlife Service (FWS) presented in the Fish and Wildlife Coordination Act (FWCA) Report dated April 7, 1982. The recommendations of the FWS incorporate commitments made by the Bureau in the EIS. The FWS's recommendations are quoted below and are accompanied by the Bureau's (BR) response. All recommendations were adopted except for No. 8 which would have affected the economic viability of the project.

FWS Recommendation No. 1 - "We recommend all fill material from White Rock Canyon should be taken from an area between Highway 93 and 1.5 miles upstream (northeasterly). Sides of the borrow pit should be sloped and permanent access be provided to Wilson Ridge around excavation activities."

BR Response - The recommendation is reasonable and does not impair the economic or engineering viability of the project. The White Rock Canyon borrow site will be confined to the.dry wash area between the Highway 93 bridge (on the Arizona side of the dam) and a point 1.5 miles upstream (northeasterly). After construction, the borrow site will be sloped and contoured to resemble the surrounding wash topography. Access through the site to Wilson Ridge will be maintained during construction.

FWS Recommendation No. 2 - "We recommend that revegetation of the upper reaches of the Black Canyon be tested to determine its practicability. Costs are approximated at $1,500 for the initial 50 tree test. Depending on availability of sites and success, another 400 trees or 1 acre would cost approximately $4,000."

BR Response - Although the destruction and accelerated erosion of riparian habitat within Black Canyon are not anticipated, the Bureau will monitor pre- and post-project conditions with aerial photographs. The flights will be flown within 2 years before construction begins and within 2 years after the project is operational. If a net loss in riparian habitat occurs, the Bureau will determine the practicability of revegetating the area by planting trees in selected areas and monitoring their response. If the experimental plantings are successful, additional trees would be planted to mitigate for those lost due to the project.

B-1 Study/Mitigation Description

Aerial Photography (Black Canyon)

Pre-Project Study: 2 years (approximately) prior to construction. Photographs to be taken in July or August. Scale 1-2,000.

Post-Project Study: 2 years (approximately) after powerplant is operational. Photographs to be taken in July or August. Scale 1-2,000.

Revegetation Study (inhouse) of selected Black Canyon areas, study will last 2 years and will commence approximately 2 years after the powerplant is operational.

Purchase trees/shrubs for the study and for mitigation if revegetation proves successful.

FWS Recommendation No. 3 - "We recommend that if there are other alternatives that will accomplish the purpose of the project, a surface powerhouse not be selected as an alternative."

BR Response - Further consideration will be given to the underground powerhouse. If it is more cost effective, it can be substituted for the surface powerhouse.

FWS Recommendation No. 4 - "We recommend that the productivity of the periphyton/invertebrate communities and the associated fish populations be studied during advance planning so as to establish baseline conditions from which to compare project impacts quantified in a subsequent follow-up report. Design of best mitigation structures or measures should be carried out during advance planning. Study design could be similar to many of the items in one of your previous proposals, Solicitation No. 30-V0153 (November 4, 1980).

"Cost of the productivity, associated fish, and mitigation design study could range from $150,000 to $300,000. The follow-up study is estimated at $100,000. Construction costs of rock reefs will be deferred to your engineering and construction expertise."

BR Response - The Bureau recognizes that the recommended area of study has the most potential for adverse impacts as a result of this project. Even though we have conducted extensive baseline studies, additional quantification is necessary to clearly verify the impacts. Therefore, the Bureau will conduct pre- and post-project studies to verify the predicted impacts on; (a) the food base in Black Canyon, (b) selected fish species that spawn in shallow water in Lake Mohave, and (c) the Willow Beach National Fish Hatchery (WBNFH).

B-2 The studies will be designed to establish the appropriate amount, type, and effectiveness of mitigation for each of the three areas of concern. Mitigation could include:

a. Introduction of boulders/artificial reefs into Black Canyon.

b. Improving the spawning habitat in the shallow areas of Lake Mohave by planting trees or other appropriate foliage in selected areas or by manipulating the substrate.

c. Placing water chillers or a suitable alternative at the WBNFH to prevent warm water from interfering with hatchery operations.

Study/Mitigation Description

Pre-Project Studies: Food Base Study in Black Canyon. Sampling would begin 3 years prior to project construction. The 2-year study would quantify the amount of periphyton and invertebrates presently existing in Black Canyon using a random sample method.

Lake Mohave Fishery. Sampling would begin 3 years prior to powerplant construction. The study would last 2.5 years. Emphasis would be placed on quantifying the existing habitat required for shallow water spawning. This would be related to existing reservoir operations.

Post-Project Studies: Food Base Study in Black Canyon. Sampling would begin within 2 years after proposed project is operational. The study would last 2 years, be designed to replicate the pre-project study and verify the impacts predicted in the EIS. Appropriate mitigation, if necessary, would be developed during the study.

Lake Mohave Study. Sampling would begin within 2 years after the proposed project is operational. The study would last 2.5 years, be designed to replicate the pre-project study and verify the impacts predicted in the EIS. Appropriate mitigation, if necessary, would be developed during the study.

Post-Project Mitigation: Possible mitigation measures have been suggested and are displayed below. Artificial reefs could be added to Black Canyon to increase the stable substrate for periphyton/invertebrate growth.

Improve spawning habitat by the use of planted vegetation or substrate manipulation in Lake Mohave to mitigate for the possible reduction of spawning activity due to the operation of the proposed project.

Place water chillers at the WBNFH to mitigate possible warm water intrusion brought about by the operation of the proposed project.

B-3 FWS Recommendation No. 5 - "We recommend that a temperature study be conducted to model the Black Canyon reach of the Colorado River in order to precisely predict the interface location at various project releases and elevations of Lake Mohave."

BR Response - The Bureau initiated a temperature study in late 1981 to determine how often the warm/cold water interface reaches within 7 miles of the WBNFH and under what operating conditions this occurs. The study will continue for at least 3 years after the project is in operation. If the interface reaches the WBNFH at a greater frequency than experienced under pre-project conditions and the affect is significantly detrimental, mitigation as described under No. 4 will be provided.

FWS Recommendation No. 6 - "We recommend that if the temperature study reveals adverse changes, measures be employed to prevent fishery losses at the hatchery. Such measures could include the installation of water chillers, locating the water intake upstream of the interface, or modifying Hoover Dam operating criteria when conditions are probable for an interface problem. Costs of the water chillers have been estimated by your agency. We would appreciate your estimate of intake modification."

BR Response - See Response to Recommendations Nos. 4 and 5. Cost estimates for mitigation alternatives will be prepared during the design and construction phase of planning.

FWS Recommendation No. 7 - "We recommend that a detailed map/brochure be provided to boaters using the Black Canyon below Hoover Dam listing monthly or seasonally the range of water fluctuations (depth and velocity) expected at various locations in the canyon. It may also be necessary to step the peak increases on a more gradual basis on Monday mornings or the morning after a long weekend to alert recreationists to the change in flow regime."

BR Response - The increased variation in velocities and water surface elevations would necessitate an increased boater awareness program in the upper reaches of Lake Mohave. A program to include identification of navigational hazards and distribution of cautionary literature to all boaters would be developed during project design and construction and would be implemented by the National Park Service. The Bureau does not believe any special operating constraints are necessary (i.e., Monday morning gradual water releases) since the dams projected operation would not create a safety hazard, merely a nuisance (i.e., boats being stranded).

Study/Mitigation Description

The Bureau will request the National Park Service to develop a boater awareness program and pamphlets which will address the project's operation (i.e., water discharge patterns and increased water velocities).

B-4 FWS Recommendation No. 8 - "We recommend, because of the great adverse potential for impact, that peaking operations be limited to the regime evaluated in our 1981 FWCA report."

BR Response - This recommendation by the FWS could not be accepted. The economic viability of the project hinges on the Bureau being able to operate the project as described within the EIS and Feasibility Report.

FWS Recommendation No. 9 - "We recommend that any weekly fluctuation (in Lake Mohave) that must occur be reduced to less than 2 feet per week during the period March 15 to April 30 and that operational criteria be developed that will maintain the elevation in Lake Mohave above 642 from March 15 to June 15."

BR Response - The Bureau will continue to try to stabilize Lake Mohave fluctuations during the above periods. This, however, is difficult to do because of the regulations governing flood control, water use priorities, etc., which dictate our activities.

FWS Recommendation No. 10 - "We recommend that a plan be considered to revegetate the near shore zone in Lake Mohave below elevation 639 so as to determine the practicability of establishing woody vegetation such as Goodding's willow. If considered, a small scale test would help determine specific techniques and potential for success. Estimated cost for 600 trees set on staggered 6-foot centers (approximately 2,000 feet) is $2,000; however, soil type and development of technique would probably reduce that initially to 150 trees."

BR Response - See Response to Recommendation No. 4.

FWS Recommendation No. 11 - "We recommend that a test be conducted to determine the suitability of a variety of artifical reef structures in Lake Mohave for Centrarchid species and artificial spawning habitat for threadfin shad. If sufficient use is determined, a number of such structures should be placed in the lake to provide the necessary habitat.

"Cost may be quite variable relative to availability and type of material. Nine reef sites covering an area of 2.5 acres are estimated at $10,000, 100 acres of reefs at $40,000."

BR Response - See Response to Recommendation No. 4.

In addition to the recommendations made by the Fish and Wildlife Service, the Bureau will also take the following steps to protect the environment or mitigate the project effects:

1. The Bureau would design the new powerhouse and surge tank to blend in with the visual appearance of Hoover Dam.

B-5 2. The Bureau has agreed to keep water temperature fluctuations below Hoover Dam to a minimum (54-57°F). The only exception would be if this conflicted, which it is not expected to, with the legal or safe operation of the dam.

3. The Bureau will sponsor a data recovery program for Willow Beach No. 2, archeological site.

Study/Mitigation Description

During construction and before the proposed project is operational, the Willow Beach No. 2 archeological site would undergo a contracted data recovery program.

4. If determined to be necessary, the Bureau will upgrade the anchoring system for the floating marina at Willow Beach.

Study/Mitigation Description

The present anchoring system at the Willow Beach Marina may undergo additional stress due to increased water velocities. If it is determined that an upgraded anchoring system is required, it will be built during the construction of the project.

B-6 ATTACHMENT C

PUBLIC IDENTIFIED CONCERNS

The major items identified at public involvement meetings are listed below in order of their importance as concerns to the public:

PUBLIC IDENTIFIED PROBLEM - NEEDS - CONCERNS

1. Who will benefit from increased capacity (how will power be allocated)?

2. Need to increase hydro peaking to reduce dependence on oil and reduce cost to customers.

3. Discuss the impacts on Lake Mohave fishery and endangered species.

4. Discuss the impacts of pumped-back storage on the environment.

5. Discuss the problems for recreationists (boating, fishing, hot springs, etc.).

6. All potential users should be involved in all phases of the study (plan selection).

7. The Bureau of Reclamation should proceed immediately with the uprating program.

8. Where is the source of power for pumped-back storage?

9. What will be the effects of the Hoover Powerplant Modification Project on Lake Mead aquatic environment?

C-1 SPECIFIC QUESTIONS AND CONCERNS IDENTIFIED AT THE SCOPING MEETING FOR THE ENVIRONMENTAL IMPACT STATEMENT HOOVER POWERPLANT MODIFICATION STUDY

1. If the power need is only for 4 days a week, 4 months of the year--how does this infrequent need justify the cost of an additional powerhouse?

2. What would the impact be on the fish and on the Willow Beach Resort?

3. Will the increased velocity scour the river channel bottom?

4. Will the releases from Hoover Dam be increased in the fall and winter also?

5. Would the warm water in Lake Mohave, with pumped-back storage, cause any problems to the cold water trout fishery?

6. If the 500-MW surface powerhouse modification is authorized now, will the powerhouse be enlarged again, about 20 years from now?

7. What is the cost of each alternative versus the amount of power revenues that will be earned?

8. How can we decide what we want without knowing the cost of each alternative?

9. Dropping Lake Mohave elevation below 630 is of great concern, since adverse impacts affect both the recreation and the fishery.

10. Traffic problems created by Hoover Modification construction are a major concern.

A scoping session for the draft outline of the EIS was held. The specific concerns and questions that were answered, and those items that would not be addressed in the EIS were identified as follows:

C-2 ITEMS WITH LIMITED OR NO DISCUSSION IN EIS

1. Water rights will not be discussed.

0 Long lists of flora and fauna of the area will not be included, but impacts on plant and animal communities will be discussed.

3. Climate, soil, geology, and ground water will be discussed, only in enough detail to give the reader a general idea of the project area.

4. Landownership will be discussed only briefly and primarily in relation to recreation losses.

5. Ancient historic human use of the area will not be discussed.

C-3

ATTACHMENT D

RATIONALE FOR PREDICTING HATCHING SUCCESS REDUCTION DUE TO HOOVER MODIFICATION PROJECT

Introduction

The success of largemouth bass spawning, as with other species, depends upon many environmental factors such as lake elevation stability, water temperature, storms, wind and wave action, nest predation, and habitat availability. Although several factors affect fish spawning, the Hoover Powerplant Modification Project would impact the Lake Mohave fishery by increasing lake elevation fluctuations and possible nest destruction caused by wave action.

The project would cause weekly lake fluctuations ranging from 2 to 3 feet (Figure 1). Due to the scheduling of water releases, lake levels would rise during the week and drop during the weekend. These fluctuations during the spawning season (March-May) could impact the spawning success of such fish as the largemouth bass, threadfin shad, and other sunfish species.

No specific information was available on fish spawning in Lake Mohave to assess the impacts of this project. However, data were available on largemouth bass spawning in Lake Mead which was used to estimate the effects of Lake Mohave fluctuations caused by the project. Because of the close proximity of the fishery, the data regarding spawning depth and natural nesting mortality rates were assumed to be similar.

These fishery studies conducted on Lake Mead (1978-81) revealed that about 55 percent of all observed largemouth bass spawning attempts were successful, producing swimup fry (Morgensen, 1981). Individual spawning success varied greatly with depth. The highest rate of failure was in shallow water and the most successful rates were in water exceeding 2 feet in depth. Failure of shallow spawning attempts could be partially attributed to nest exposure by lake elevation fluctuations and the physical disruption of nests by wave action. This discussion does not take into account the abandonment of nests or the failure of bass to establish nests during receding water levels. Weekly fluctuations could also have an affect on shoreline vegetation and lessen survival of fry and fingerling.

Similar observations have been documented by other authors (Kramer, 1961; Miller and Kramer, 1971). They reported that wave action can disturb nesting attempts at depths of 5 feet when wind speed and direction are optimum. Data for 1981 indicate that the depth range of greatest nest vulnerability on Lake Mead was to a depth of 2 feet. Apparently the long-term influence of wave action in Lake Mead is not as significant because of the additional protection that the many coves afford spawners. These protective conditions also exist on Lake Mohave.

D-1 655

650

DAVIS DAM SPILLWAY CREST

645 Z 0 > • N.0 A A ./Iv > „, 640 z V <

I> 00 635

A I j V 1.rA 630 \A-V

NORMAL SCHEDULED MOHAVE ELEV. —•—•— AVERAGE FUTURE YEAR (1996) 625 1978 HISTORIC ELEVATIONS

620 1 1 1 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

CALENDAR YEAR (MONTHS)

Figure I Projected effects of modified Hoover Powerplant releases upon Lake Mohave elevations. Methods and Discussion

The optimum depth selected by spawning largemouth bass in Lake Mead varied from 3.0 to 5.5 feet during the 1978-81 spawning seasons (Table 1). Data for the following estimates are based on the 1981 spawning season which represented the shallowest average nest depth for any spawning season from 1978-81. Therefore, it represented the most vulnerable spawning season of data collected on Lake Mead (1978-81).

Table 1 SUMMARY OF LARGEMOUTH BASS NESTING SUCCESS AT VARIOUS NEST DEPTHS FOR WAGON TRAIL AND CRAPPIE COVES, LAKE MEAD (1981)

Percent Depth Range Successful Nests (ft.) (ft.) (Number) No. Percent of Total

1 1.0 0 (0) 1 1.7 1-2 1.5-2.0 25 (2) 8 13.3 2-3 2.2-3.0 52.2 (12) 23 38.3 3-4 3.5-4.0 60.0 (6) 10 16.7 4-5 4.5-5.0 40.0 (2) 5 8.3 5-6 5.5-6.0 60.0 (3) 5 8.3 6-7 6.5-7.0 100.00 (2) 2 3.3 7-8 7.5-8.0 66.7 (2) 3 5.0 8-9 -0- -0- 0 9-10 9.5-10.0 66.7 (2) 3 5.0

51.7 (31) 60 99.9

Median Depth Range Year (ft.) (cm) ft. (cm.)

1978 5.0' (152) 2'-12' (61-367) 1979 3.2' (100) 2'-7.8' (60-240) 1980 5.5' (168) 2'-13' (61-396) 1981 3.0' (91) 1.5-10' (46-305.)

From Sue A. Morgensen, Fishery Biologist, Arizona Game and Fish Department, September 22, 1981.

D-2 Estimations of daily spawning success (number of nests hatching) due to lake elevations can be computed using data from Table 1. Assuming that bass in Lake Mohave nest at the same depths as those recorded for Lake Mead, we can predict the percentage of total spawners nesting at different depths (1-foot increments) in Lake Mohave. Hatching success as observed on Lake Mead can then be assigned to those depths (Table 1) in Lake Mohave, assuming nesting mortality rates for both lakes are the same. Because of the limited number of nests below 3 feet, we have averaged the success rate to more typify the events that are happening and also to simplify the procedure (0 to 1 foot = 0 percent, 1 to 2 feet = 25 percent, 2 to 10 feet = 57 percent).

By multiplying the 1-foot-depth increments by the hatching success rate, we can predict the percentage of successful nests expected to hatch from that depth zone in regard to the total (all depths) success rate (Table 2). As an example (Table 2), if 38.3 percent of all bass are expected to spawn at depths 2 to 3 feet and their expected success rate is 57 percent, then (38.3 x .57 = 21.8) 21.8 percent of the total successful nesting effort would come from the 2- to 3-foot depth zone.

Table 2 PREDICTED NESTING SUCCESS RATE OF LARGEMOUTH BASS FOR LAKE ELEVATION DECLINES USING LAKE MEAD DATA

Depth Total Success Percentage of Successful Recruitment Predicted Zone Spawn Rate For Lake Declines (ft) of: (ft) (%) (%) 0 -1 ft -2 ft -3 ft -4 ft -5 ft

0-1 1.7 0 0 0 0 0 0 0 1-2 13.3 25 3.3 0 0 0 0 0 2-3 38.3 57 21.8 9.6 0 0 0 0 3-4 16.7 57 9.5 9.5 4.2 0 0 0 4-5 8.3 57 4.7 4.7 4.7 2.0 0 0 5-6 8.3 57 4.7 4.7 4.7 4.7 2.0 0 6-7 3.3 57 1.9 1.9 1.9 1.9 1.9 .8 7-8 5.0 57 2.8 2.9 2.8 2.8 2.8 2.8 8-10 5.0 57 2.8 2.9 2.8 2.8 2.8 2.8

Totals 99.9 51.5 51.5 36.2 21.1 14.2 9.5 6.4

D-3 Lake fluctuations would, of course, change this. As lake elevations decline, so would the expected success rate as more nests were subjected to vulnerable shallow water. The established hatching success rate for each depth would remain the same but decline with the lake's elevation. For example, if a bass spawns at a depth of 2.5 feet and lake elevations remained stable, the nests expected survival rate would be 57 percent. If lake elevations declined 2 feet during the early stages of egg and fry development, the expected survival rate would drop to 0 percent because of the nests increased susceptibility to wind and wave action (Figure 2).

INITIAL LAKE ELEVATION LOWEST LAKE ELEVATION EXPERIENCED DURING SPAWNING ONE WEEK AFTER SPAWNING

PREDICTED SUCCESS RATE

2' drop REVISED SUCCESS RATE THEN: 1 0% 2 25% 57%

Figure 2. An example of the relationship of hatching success rates to nest location and declining lake elevations.

This method only addresses impacts due to lake declines and not rises. Past research has indicated that lake declines are a major factor in spawning success and that lake elevation increases have little or no effect on spawning bass (Carlander, 1977).

D-4 Using the above methods were able to project a hatching success rate curve (Figure 3). This curve represents the total spawning

success (all depths) for 41 given day at different lake elevation (0 to 5 feet) reductions.

Figure 3. Hatching success rates (percent) in relation to lake level declines. The weekly cyclic fluctuations expected to occur on Lake Mohave during the spawning season are more complex than Figure 3 illustrates. Impacts to spawning success would be minimal on days when lake elevations increased but would be detrimental on days when elevations dropped below those experienced during initial spawning. We must then look at the possible success rate for each day since they vary and average the daily rates to determine the weekly nesting success rate.

It may be argued that the lowest lake elevations for a longer period, 2 to 3 weeks, should be used since egg and fry are still in early stages of development and generally nestoriented. This statement is true, but it must be noted that Lake Mohave elevations generally are increasing during the bass spawning season which makes the weekly lake elevation low. The lowest elevation would impact the spawners.

Since the weekly fluctuation patterns change because of water scheduling requirement§ for different months, four possibilities were examined: (1) up 1 foot, down 1 foot (1/1); (2) up 2 feet, down 2 feet (2/2); (3) up 3 feet, down 3 feet (3/3); and (4) up 3 feet, down 2 feet (3/2).

Assuming that largemouth bass and other species spawn evenly throughout the weekly cycle, we can then figure the maximum lake decline for nests spawned on each day. Figure 4 shows during a 1/1 (ft) fluctuation cycle that fish spawning on Friday would experience a - 1.0 foot lake decline by Sunday. On Thursday, however, the lake elevation would still be climbing and the weekly decline would only be .8 foot.

D-5 +3 ^

2.3

1.6

1.2 VARIANCE 1.3 0 1.2 1.1 1.0 1.0 1- LLI LIU + 1 )Cf LLJ 0.8 .. 0.7 •• . 0.6 0.6 , -4X •• 0.3 0.3 0.5 • • OA acsNe 4b. . 0.0 0.2

I -0.6 NO IMPACT ZONE

1 -1 I ; i I I I I MON TUES WED THURS FRI SAT SUN

WEEKLY LAKE FLUCTUATIONS INCREASES (FT)/DECREASES (FT)

i n ..... 0 2/2 - - - - Figure 4. Depth of lake decline impacting spawning success for specific days. (Initial spawning lake elevation - weekly elevation 3/2 a Sunday equals nest depth decrease impacting spawning success). 3/3 By determining the lake decline experienced from each spawning day to the lowest elevation during that cycle (Figure 4), we can then find the corresponding success rate on Figure 3. These daily rates are then averaged to predict changes in weekly or seasonal success rates (Table 3).

Table 3 ESTIMATED NESTING SUCCESS RATES DUE TO DIFFERENT WEEKLY LAKE FLUCTUATION PATTERNS

Weekly Fluctuation Total Pattern Mon Tues Wed Thur Fri Sat Sun Nesting Recruitment Up/down lake elevation decline Success Decline (ft) Nesting Success Rate (%) (%) 0* 51.5 51.5 51.5 51.5 51.5 51.5 51.5 = 51.5 0

1/1 .1 .3 .5 .8 1.0 .6 .2 51.0 46.5 44.0 40.0 36.2 42.0 48.2 = 42.5 17.5

3/2 .0 .0 .7 1.3 2.0 1.2 .4 51.0 51.0 41.5 31.0 21.1 32.0 46.0 = 39.2 23.9

2/2 .2 .7 1.1 1.6 2.0 1.2 .4 48.2 41.5 35.9 24.0 21.1 32.0 46.0 = 35.7 26.8

3/3 .3 1.0 1.7 2.3 3.0 1.8 .6 46.5 36.2 24.0 18.4 14.2 23.9 42.0 = 29.3 43.1

* Lake Mead Data (Morgensen, 1981).

The 3/2 fluctuation would be the most representative and the 3/3 the worst possible condition expected during the largemouth bass spawning period (March-May). Calculations using these techniques predict a decline of 23.9 percent of the total fry production (from 51.5 percent to 39.2 percent success) for Lake Mohave, experiencing a 3/2 cycle, and a 43.1 percent reduction (from 51.5 percent to 29.3 percent success) from a 3/3 cycle.

Summary and Conclusions

Based on the available data, there is no known method to assess the projects impacts on the spawning success of these fish without making the following assumptions:

1. The spawning depth preference of largemouth bass in Lake Mohave is similar to those observed in Lake Mead.

2. That factors determining spawning success rates are also similar.

D-6 3. That lake elevation declines are detrimental to spawning bass and lake elevation increases in water elevations are not detrimental (Carlander, 1977).

4. That spawning initiation is equally distributed throughout the fluctuation cycle (week).

5. That spawning habitat availability is similar in both lakes.

6. That egg and fry mortality rates are the same throughout development.

Based on these assumptions, a 43-percent reduction in total fry recruitment could be expected for a weekly fluctuation of 3/3 and 24-percent reduction from a 3/2 cycle, the most representative of the two.

These rates, however, do not predict impacts to the adult fishery, only hatching success rates. A decline in the number of successful nests may or may not reflect impacts to the number of fish reaching adulthood. A decrease in fry numbers may decrease peer competition for available food and cover which could increase juvenile survival rates. Declines in forage species (threadfin shad, bluegills) may have a more significant impact to the adult bass community. A reduction in these species would cause a reduction in numbers and possibly poor quality bass if a substitute forage base was not available.

• Literature Cited for Attachment D

Carlander, K. A.; 1977. Handbook of Freshwater Fishery Biology. Volume Two, the Iowa State University Press, Ames, Iowa.

Kramer, R. H.; 1961. The early life history of the largemouth bass. (Micropterus salmoides) (Lacipede) with special reference to factors influencing year class strength. Ph.D. Thesis. University of Minnesota, Minneapolis, 122 pp.

Miller, K. D. and R. H. Kramer; 1971. Spawning and early life history of largemouth bass (Micropterus salmoides) in Lake Powell, pages 73-84 in F.H. Hall Ed. Reservoir fisheries and limnology. American Fish Society Special Publication No. 8.

Morgensen, S. A.; Fisheries Biologist, Arizona Game and Fish Department, personnel communique. September 22, 1981.

D-7

ATTACHMENT E

APPLICATION FOR CORPS OF ENGINEERS 404 (r) EXEMPTION (Excavating Bottom Material for Project Cofferdam)

I. INTRODUCTION

Two of the four alternatives (Alternatives 1 and 2) for this project require the placement of a cloverleaf-cellular cofferdam made of steel sheet piles within Hoover Dam tailbay adjacent to the existing Arizona powerhouse. Washed sand and gravel material must be excavated from the tailbay to allow for the proper seating of the cofferdam. Sand and gravel from White Rock Canyon, a dry wash tributary to the Colorado River would be used to fill the cofferdam. White Rock Canyon is located about 3 miles from the dam. All sand and gravel placed within the cofferdam would be removed after construction and disposed of at an existing dump site near the dam. No sand or gravel would be intentionally released into the river, although some fugitive material is expected. This analysis addresses the material to be removed from the river bottom to insure the proper seating of the cofferdam and the fugitive material which would inadvertently be released into the Colorado River during cofferdam construction.

II. PROJECT DESCRIPTION (See Environmental Statement Chapter II.B.)

A. Description of the Proposed Discharge of Dredged or Fill Material

Alternative 1 - Construction of a 500-MW surface powerhouse would require a cofferdam 120 feet wide and 510 feet long. A total of 45,000 cubic yards of sand and gravel would be removed from the river bottom. The excavated material would be inert and would consist of washed quartzite and feldspar sand and gravel which has been deposited over the life of the project from adjacent dry washes during heavy rainstorms.

Alternative 2 - The same circumstances as described for Alternative 1 would occur when replacing generating units A8 and A9, except the cofferdam would be 125 feet wide and 130 feet long. A total of 12,000 cubic yards of material would be excavated from the river bottom if this alternative were constructed.

B. Description of the Proposed Disposal Site for Dredged or Fill Material

The excavated material would not be discharged into the Colorado River, but would be taken to an existing disposal site approximately 1 mile southeast of Hoover Dam (see frontispiece map to EIS). The disposal site would be at the head of a small dry wash. The wash itself cuts through volcanic material and is comprised of the same material that would be excavated. It may even have been the source of the material to be excavated--brought in by the infrequent but intense flash floods experienced in the area during the late summer months.

E-1 III. PHYSICAL EFFECTS

A. Effects on Wetlands

No wetlands exist in or near the tailbay (excavation area) of the dam, consequently; there would be no effects. The disposal site would be a dry wash.

1. Food Chain Production. Excavation would not affect wetlands food chain production. Periphyton and limited invertebrate growth exist in the area of excavation. However, the removal of 6,800 square yards (Alternative 1) or 1,806 square yards (Alternative 2) of bottom surface area would have an immeasurably small affect on the river's food chain.

2. General Habitat. See III.A.1. above.

3. Nestin , S awnin , Rearm', and Restins Sites for A uatic or Land Species. No such sites exist within the excavation area.

4. Wetlands Set Aside for Aquatic Environment Study or Sanctuaries Refuges. None.

5. Changes in Natural Drainages. None.

6. Sediment Patterns. No change.

7. Salinity Distribution. No change.

8. Flushing Patterns. No change.

9. Current Pattern. Excavation would not change the current pattern. The cofferdam, once installed, would increase the average cross-section velocity within the tailbay from 1.9 miles per hour (mph) to 8.2 mph. This would occur in about an 800-foot section of the river adjacent to the cofferdam. The velocity rapidly returns to normal as the channel widens to its normal width.

10. Storage Area for Storm and Floodwaters. No change.

11. Prime Natural Recharge Area. No change.

B. Impact on Water Column

1. Reduction in Light Transmission. As material is excavated some fugitive dredge material is expected to reduce light transmittance. Light transmittance reduction is expected to be of short duration and of small magnitude. No reduction in the periphyton/invertebrate community or fish populations would occur.

2. Esthetic Value. Short durations of turbid water may replace the normally clear water release from the dam. This may occur intermittently for approximately 1 to 2 months during dredging operations.

E-2 3. Direct Destruction Effects on Nektonic or Planktonic Populations. None.

C. Covering of Benthic Communities

None (See III.A.1. above).

D. Other Effects

1. Changes in Both Shape and Sediment Composition. The river bottom in the area of excavation would be deepened by approximately 20 feet. This would be due to the removal of the sand and gravel overlying the bedrock of the river bottom.

2. Water Circulation. No change.

3. Salinity Gradients. No change.

4. Exchange of Constituents Between Sediments and Overlying Water with Alterations of Biological Communities. None.

IV. CHEMICAL AND BIOLOGICAL INTERACTIVE EFFECTS

A. Does the Material Meet Exclusion Criteria

The material meets the exclusion criteria. The material being excavated is washed in from tributary dry washes during heavy rainstorms. The material is the erosion product of surrounding mountains. No silt particles exist, only washed sand and gravel. No sources of pollutants which could have contaminated the excavated material are present.

B. Water Column Effects of Chemical Constituents

None.

C. Effects of Chemical Constituent on Benthos

None.

V. DESCRIPTION OF SITE COMPOSITION

A. Total Sediment Analysis

The total sediment analysis is not required.

B. Biological Community Structure Analysis

The biological community structure analysis is not required since the fill material contains no toxic substance that would adversely affect the community structure.

E-3 VI. REVIEW APPLICABLE WATER QUALITY STANDARDS

A. Compare Constituent Concentrations

No change in constituent concentrations would occur. Temporary turbidity due to fugitive releases from dredging equipment would be minimal and not as great as the natural turbidity which occurs after a flash flood from one of the many dry washes tributary to the river. Constituents would meet applicable state and Federal Water Quality Standards.

B. Consider Mixing Zone

Not significant.

C. Objectives

Based on A above, the disposal operation would conform with applicable standards.

VII. SELECTION OF DISPOSAL SITE

A. Need for Proposed Site

See Sections I and II of this attachment. The proposed disposal site is an existing dump site at the head of a dry wash.

B. Alternatives Considered

None.

C. Objectives to be Considered in Discharge Determination

None.

D. Impact on Water Uses at the Proposed Disposal Site

None.

E. Consideration to Minimize Harmful Effects

There would be no harmful effects due to disposal.

VIII. STATEMENT AS TO CONTAMINATION OF FILL MATERIAL IF FROM A LAND SOURCE

Not Applicable.

IX. DETERMINE MIXING ZONE

Not significant. Only a small intermittent amount of fugitive material would be released into the river as the bottom material is excavated.

E-4 ATTACHMENT F

LITERATURE CITED

Allan, Robert C.; Roden, Dennis L.; Base Fisheries Data, Phase I - Boulder Canyon to Davis Dam, 1978, Nevada Department of Wildlife, Las Vegas, Nevada.

Behnke, R. J. and D.E. Benson; Endangered and Threatened Fishes of the Upper Colorado River Basin, 1980, Cooperative Extension Service, Colorado State University, Fort Collins, Colorado, Bulletin 503A.

Bennett, William W., and Ohmart, R.D.; Habitat Requirements and Population Characteristics of the Clapper Rail (Rallus longirostris yumanensis) in the Imperial Valley of California, 1978, University of California, Lawrence Livermore Laboratory.

Bent, A.C.; Life Histories of North American Birds of Prey, 1938, Part 2. U.S. National Museum Bulletin 170, Washington, D.C.

Blake, John G.; Birds of the Lake Mead National Recreation Area, 1978, LAME Technical Report No. 1. Cooperative National Park Resources, Park Resources Studies Unit. University of Nevada, Las Vegas, Nevada.

Blanton, J.0. III; Grand Coulee Third Powerplant Degradation Study, 1979, Division of Planning Technical Services, Bureau of Reclamation, Denver, Colorado.

Bradley, W.G., and J.E. Deacon; The Biotic Communities of Southern Nevada, 1967, Nevada State Museum Anthropological Papers Number 13, Part 4: 202-295.

Brooks, Richard H.; Ferraro, David; Larson, O.; Cunningham, Arnie L.; and Olson, Kathryne; An Archaeological Survey From Below Hoover Dam to Willow Beach, Arizona, May 1977, Nevada Archaeological Survey, University of Nevada, Las Vegas.

Bryant, Gary; Glen Canyon Dive Report, Unpublished, September 9, 1980, Bureau of Reclamation, Boulder City, Nevada.

Bureau of Reclamation; Draft Environmental Assessment Hoover Dam Visitor Center and Parking Facilities, September 1979, Bureau of Reclamation, Boulder City, Nevada.

Bureau of Reclamation; Draft Environmental Statement Preliminary Wilderness Proposal Lake Mead National Recreation Area, Arizona- Nevada, January 1979, Bureau of Reclamation, Boulder City, Nevada.

Bureau of Reclamation; Hoover Powerplant Modification Special Report, January 1978, Bureau of Reclamation, Boulder City, Nevada.

Bureau of Land Mangement; Allen-Warner Valley Energy System Environmental Impact Statement, Final, Volume 1; Text, December 1980, Government Printing Office, Washington, D.C.

F-1 Chalmers, J.A.; Post, Nancy; and Bird, Mark; Economic-Demographic and Social Assessment of the Proposed Modification to the Hoover Powerplant, April 1980, Mountain West Research, Inc., Tempe, Arizona.

Department of Energy; Hydroelectric Power Evaluation, August 1979, Federal Energy Regulatory Commission, Office of Electric Power Regulation.

Department of the Interior; General History and Description of Project, Boulder Canyon Project Final Reports, Part I--Introductory Bulletin 1, December 1948, U.S. Government Printing Office.

Department of the Interior; The Story of Hoover Dam, 1976, U.S. Government Printing Office, Washington D.C.

Dickey, D.R.; Description of a New Clapper Rail from the Colorado River Valley, 1923, Auk.40 (1): 90-94.

Federal Power Commission; The 1970 National Power Study, Part 1, December 1971, U.S. Government Printing Office.

Gosse, J. C.; Preliminary Investigations of Microhabitat Requirements For Plants, Macroinvertebrates, and Fish in the Colorado River Below Glen Canyon Dam with Regard to Peaking Power Proposal, 1981. Report to U.S. Fish and Wildlife Service, Phoenix, Arizona. Unpublished.

Greey, G. W.; Cheatham, G. W.; and Virden, Randy J.; Recreation Use - Hoover Modification, Preliminary Draft, February 1980a, Department of Leisure Studies, Arizona State University, Tempe, Arizona.

; Outdoor Recreation U.S. and Participation Inventory of the Lake Mead National Recreation Area, 1980b, Department of Leisure Studies, Arizona State University, Tempe, Arizona.

Grinnell, J.; An Account of the Mammals and Birds of the Lower Colorado Valley, 1914, University of California Publ. Zool., Vol. 12, pp. 51-294.

Gustafson, E. and W.L. Minckley; Studies of the Razorback Sucker, (Xyrauchen texanus,) in Lake Mohave, Arizona-Nevada, 1976, Report to U.S. Fish and Wildlife Service, Albuquerque, New Mexico. Unpublished.

Holden, P. B.; Systematic Studies of Genus Gila (cyprinidae) of the Colorado River, 1968, unpublished Masters Thesis. Utah State University, Logan, Utah. 68 pp.

Hynes, H. B. N.; The Ecology Running Waters, 1972, University Press, Toronto, 555 pp.

Jonez, A. and R.C. Sumner; Lakes Mead and Mohave Investigations, 1954, Nevada Fish and Game Commission, Carson City, Nevada (processed).

F-2 Kramer, R. H.; The Early Life History of the Largemouth Bass (Micropterus salmoides) (Lacipede) with special reference to factors influencing year class strength. Ph. D. Thesis; 1961. University of Minnesota, Minneapolis, 122 pp.

Lower Colorado Region State-Federal Interagency Group for the Pacific Southwest Interagency Committee; Lower Colorado Region Compre- hensive Framework Study, June 1971.

Martin, Bollman, Gum; Economic Value of the Lake Mead Fishery, 1980.

Matter, W.J., G.E. Saul, and J.M. Nestler; Scour and Transport of Benthic Invertebrates and Particuate Organic Material During Peak Power Release Regimes, 1980, Environmental and Water Quality Studies, U.S. Army Corp of Engineers Information Exchange Bulletin Vol. E80-5.

Miller, K. D. and R. H. Kramer; Spawning and Early Life History of Largemouth Bass (Micropterus salmoides) in Lake Powell; Pages 73-84 in G. H. Hall ed. Reservoir fisheries and limnology. 1971. American Fish Society Special Publication No. 8.

Minckley, W.L.; Fishes of Arizona, 1973, Arizona Game and Fish Depart- ment, Phoenix, Arizona. 293 pp.

Minckley, W.L.; Aquatic Habitats and Fish of the Lower Colorado River, Southwestern United States, 1979, Prepared for Bureau of Reclamation. Arizona State University, Tempe, Arizona. 478 pp.

Moffett, J.W.; A Fishery Survey of the Colorado River Below Boulder Dam, 1942, California Fish and Game, Vol. 28, pp 76-86.

National Park Service; Monthly Public Use Form for 1979 and 1980.

National Park Service; Biota of Lake Mead National Recreation Area, Nevada-Arizona, 1978, Lake Mead Project Technical Report Series.

National Park Service; Wildlife Sighting Records. On file at National Park Service Headquarters, Lake Mead National Recreation Area, Boulder City, Nevada.

Nevada Department of Wildlife, Wildlife Sighting Records. On file at Nevada Department of Wildlife, Las Vegas, Nevada.

Nevada Department of Wildlife, Lake Mohave Progress Report, 1971-76.

Ohmart, R. D., and Sell, R.; An Annotated Literature Survey on Bald Eagles With Special Emphasis on Arizona, 1979, Draft Report Submitted to Bureau of Reclamation, Boulder City, Nevada.

Ohmart, R. D., and Smith, R.W.; North American Clapper Rail (Rallus longirostris), 1973, Literature Survey with Special Consideration Being Given to the Past and Current Status of yumenensis. Report submitted to the Bureau of Reclamation, Boulder City, Nevada.

F-3 Paulson, Larry J.; Baker, John R.; and Deacon, James E.; The Limnological Status of Lake Mead and Lake Mohave Under Present and Future Powerplant Operations of Hoover Dam, January 1980a, University of Nevada, Las Vegas.

Paulson, Baker, and Deacon, Temperature Fluctuation in Lake Mohave Due to Hoover Modification, 1980b, University of Nevada, Las Vegas.

Paulson, Baker, and Deacon, Impacts of Reregulating Lake Mohave, 1980c, University of Nevada, Las Vegas.

Paulson, Larry J.; Miller, Theron G.; Keenan, C. L.; and Baker, John B.; Influence of Dredging and High Discharge on the Ecology of Black Canyon, 1980d, University of Nevada, Las Vegas.

Priscu, John Charles, Jr.; Primary Productivity and Related Limnological Factors in Lake Mohave (Colorado River), April 1978, University of Nevada, Las Vegas.

Rubink, D.M., and K. Podburny; The Southern Bald Eagle in Arizona (a status report), 1976, Endangered Species Report 1, U.S. Fish and Wildlife Service, Albuquerque, New Mexico. 32 pp.

Sigler and Miller; Fishes of Utah, 1963, Utah State Department of Fish and Game, Salt Lake City, Utah. 203 pp.

Steenhof, K.; Management of Wintering Bald Eagles, 1978, USDI, U.S. Fish and Wildlife Service, Washington, D.C. 59 pp.

Summerfelt, R. C.,; Relationship Between Weather and Year-Class Strength of Largemouth Bass, 1975, pages 166-174 in H. Clipper, ed. Black Bass Biology and Management Sport Fishing Institute, Washington, D.C.

Toney, D.P.; Observations on the Propagation and Bearing of Two Endangered Fish Species in a Hatchery Environment, 1974, Unpublished Progress Report, Willow Beach National Fish Hatchery.

U.S. Army Corps of Engineers; Environmental and Water Quality Operational Studies, 1980, Vol. E-80-5.

U.S. Fish and Wildlife Service; Aquatic Study, Special Report on Distribution and Abundance of Fishes of the Lower Colorado River, 1980, submitted to Water and Power Resources Service, Boulder City, Nevada.

Vanicek, C.D.; Ecological Studies of Native Green River Fishes Below Flaming Gorge Dam, 1964-1966, PND., dissertation, 1967, Utah State University, Logan, Utah. 124 pp.

Vanicek, C.D., and R.H. Kramer; Life History of the Colorado Squawfish (Ptychocheilus lucius), and the Colorado Chub, (Gila robusta), in the Green River in Dinosaur National Monument, 1964-1966, 1969, Transactions American Fisheries Society 49 (2): 193-208.

F-4 Von Geldern, C. E. Jr.; Abundance and Distribution of Fingerling Largemouth Bass (Micropterus salmoides); 1971a as determined by electrofishing at Lake Nacimiento, California. California Fish and Game 57 (4):228-245.

Water and Power Resources Service; Hoover Powerplant Uprating - Special Report, May 1980, Water and Power Resources Service, Boulder City, Nevada.

Water and Power Resources Service; Hoover Powerplant Modification - Feasibility Report, May 1981, Water and Power Resources Service, Boulder City, Nevada.

Welch, J.M.; South Region Audubon Field Notes, 1966, 20 (5):590.

Western Systems Coordinating Council; Loads and Resources Report, 1979.

F-5

ATTACHMENT G

GLOSSARY OF TERMS

ABUTMENT - A surface of mass provided to withstand thrust; for example, end supports of an arch or a bridge.

ADIT - An access tunnel used for excavation of the main tunnel.

ADVANCE PLANNING - A final planning study after project authorization to work out details of the project needed to prepare construction specifications.

APPRAISAL STUDY - A preliminary study to develop a project plan and to determine whether a project is likely to be feasible, and whether a feasibility study should be undertaken. Information for the study is taken primarily from existing information.

ARMOR - To protect with rock or other non-erodible material.

BASELOAD - The minimum constant amount of electric power used in a stated period.

BASELOAD PLANT - A powerplant which is normally operated to carry baseload, and which consequently operates essentially at a constant output.

BIOMASS - The dry weight of lining matter including stored food, present in a species population and expressed in terms of a given area or volume of the habitat.

BIOTA - Animal and plant life characterizing a given region.

CAPACITY - The constant maximum load which a generator is rated to supply.

COMBINED-CYCLE PLANT - Combination of a steam turbine and gas turbine in an electrical generation plant.

DEMAND - The rate at which electric energy is used, expressed in kilowatts, either at a given instant, or averaged over any designated period.

DEPENDABLE CAPACITY - The capacity, which for specified time interval, can be relied upon to carry system load, provide assured reserve, and meet firm power obligations, taking into account unit operating variables, hydrologic conditions, and seasonal or other characteristics of the load to be supplied.

DISPATCHING - The operating control of an integrated electric system.

G-1 DRAFT TUBE - The piping system for a reaction-type hydraulic turbine that allows the turbine to be set safely above tailwater and yet utilize the full head of the site from headrace to tailrace.

ELEVATION - The number of feet above mean sea level that an object is located.

ENERGY - That which does or is capable of doing work. It is measured in terms of the work it is capable of doing; electric energy is usually measured in kilowatthours.

EPILIMNION - A fresh-water zone of relatively warm water in which mixing occurs as a result of wind action and connection currents.

EUPHOTIC ZONE - The upper levels of the marine environment.

FEASIBILITY STUDY - A study done in sufficient detail to show whether a project is feasible and to determine the desirability of seeking Congressional authorization of construction. The study is more com- prehensive and detailed than an appraisal study. Studies to gather new information are usually initiated.

FIRM POWER - Power intended to have assured availability to the customer to meet his load requirements.

FORCED OUTAGE - The shutdown of a generating unit, or other facility, for an emergency.

FOSSIL-FUEL PLANT - An electric powerplant utilizing fossil fuel, coal, lignite, oil, or natural gas as its source of energy.

GENERATOR - A mechanism which converts mechanical energy to electrical.

HYDROELECTRIC PLANT -.An electric powerplant utilizing falling water as its source of energy.

HYPOLIMNION - The lower level of water in a stratified lake, characterized by a uniform temperature that is generally cooler than that of other strata in the lake.

INTERFACE - The region of water where an inflow enters and mixes with the reservoir.

INTERRUPTING OF LOAD - Temporary power outages on a rotating or selective basis, which reduces power load to amount of power - available.

ISOTHERMS - A curve or formula showing the relationship between two variables, such as pressure and volume, when the temperature is held constant.

LIMNOLOGY - The science of the life and conditions for life in lakes, ponds, and streams.

G-2 LOAD - The amount of power needed to be delivered at a given point on an electric system. The rate at which electric energy is delivered to or by a system or to a piece of equipment expressed in kilowatts, kilovolt-amperes, or other suitable unit at a given instant or average over any designated period.

LOAD CURVE - A curve showing power (kilowatts) supplied, plotted against time of occurrence, and illustrating the varying magnitude of the load during the period covered.

LOAD FACTOR - The ratio of average load supplied during a designated period to the maximum peakload occurring in the same period.

MEGAWATT (MW) - The electrical unit of power which equals 1,000,000 watts or 1,000 kilowatts.

MEGAWATTHOUR - A basic unit of electrical energy which equals I megawatt of power applied for 1 hour.

METALIMNION - A temperature gradient as in a layer of sea water, in which the temperature decrease with depth is greater than overlying and underlying water.

NAMEPLATE CAPACITY - Equipment rating as determined by manufacturer.

NONBASIC - Employment activity that is indirectly dependent upon a construction project for its origin.

NUCLEAR PLANT - An electric powerplant utilizing nuclear energy as its source of energy.

OFFPEAK ENERGY - Electric energy supplied during periods of relatively low system demand, such as early morning and weekends.

ONPEAK ENERGY - Electric energy supplied during periods of relatively high system demand, such as midmorning and midafternoon.

OUTAGE - The period during which a generating unit or other facility is out of service.

PEAK DEMAND - The greatest demand occurring within a specified period.

PEAKING CAPACITY - Generating equipment operated only to meet the highest daily, weekly, or seasonal loads.

PEAKLOAD PLANT - A powerplant which is normally operated to provide power during maximum load periods.

PERIPHYTON - A group of algae attached to rocks and other natural substrates.

PHYTOPLANKTON - A group of free-floating algae.

G-3 PLANKTON - Passively floating or weakly moving aquatic plants and animals.

PLANT FACTOR - The ratio of the average load to the rated capacity of a plant.

PRIMARY PRODUCTIVITY - The suns energy is converted by green plants into a form which is usable by other plants and animals as a food source (algae growth).

PUMPED-BACK STORAGE PLANT - A powerplant utilizing an arrangement whereby electric energy is generated for peakload use by utilizing water which has been pumped into a storage reservoir during offpeak periods.

RATED HEAD - The water column height at which a turbine at rated speed will deliver rated horsepower at specified gate opening.

RESERVE GENERATING CAPACITY - Extra generating capacity available to meet unanticipated demands for power, or to generate power in the event of loss of generation from scheduled or unscheduled outages of regularly used generating capacity.

RESERVE MARGIN - The difference between system capability and system peakload requirements. It is the margin of capability available to provide for scheduled outages, forced outages, system operating requirements including stability control and spinning reserves, and unforeseen loads.

RISER - A conduit that connects the surge tank with the penstock.

SCHEDULED OUTAGE - The shutdown of a generating unit, or other facility in accordance with an advance schedule.

SEICHE - An oscillation of the surface of the lake that varies in period from a few minutes to several hours.

SPINNING RESERVE - Generating capacity connected to the electric system and ready to take load. Also includes capacity available in generating units which are operating at less than their full capacity.

SURGE TANK - A storage reservoir at the downstream end of a closed aqueduct or feeder pipe, to absorb sudden rises of pressure and to furnish water quickly during a drop in pressure.

THERMAL STRATIFICATION - Horizontal layers of differing densities produced in a lake by temperature variations at different depths.

THERMOCLINE - The region of greatest change in vertical temperature structure of a lake or reservoir.

TIME-OF-DAY RATES - Rates imposing higher charges during those periods of the day when the higher costs to the utility are incurred.

G-4 TURBINE - A rotary engine activated by the reaction and/or impulse of a current of pressurized fluid (water, steam, liquid, metal, etc.) and usually made with a series of curved vanes on a central rotating spindle.

WITHDRAWAL LAYER - The region of the reservoir where water is drawn for release.

ZOOPLANKTON - Microscopic animals which move passively in aquatic ecosystems.

G-5

ATTACHMENT H

ARCHEOLOGICAL CONSULTATION LETTERS

United States Department of the Interior

BUREAU OF RECLAMATION LOWER COLORADO REGIONAL OFFICE P.O. BOX 427 BOULDER CITY, NEVADA 89005 IN REPLY REFER TO LC-158A SEP 1 4 1992 650.

Ms. Mimi Rodden State Historic Preservation Officer 201 South Fall Street Carson City, NV 89701

Dear Ms. Rodden:

This is to continue our consultation in accordance with 36 CFR 800 and 43 CFR 422 concerning the proposed Hoover Powerplant Modification. As you recall from our earlier correspondence dated May 7, 1980, the purpose of this project was to determine the optimum amount of power peaking capacity that could be added to Hoover Powerplant within the constraints imposed by water operations, environmental, and recreational considerations.

The alternatives remain those described in the initial letter of consultation (May 7, 1980). The alternatives are: 1) a new surface powerhouse; 2) replacing two small generating units; and 3) a new underground powerhouse. A description of each of the alternatives was included in the letter of May 7, 1980. A copy of this letter is enclosed.

The two alternatives: 1) replacing two small generators with one large generator; and 2) an underground powerhouse, will have no effect on Hoover Dam. The third alternative, a surface powerhouse, will not impair the integrity of the National Register Site, Hoover Dam.

Preliminary designs for the powerhouse indicate that the exterior architecture will be compatible with the existing powerhouses. While the symmetry of the powerhouse, would be altered the overall scale and appearance of the dam would not be appreciably changed. We believe that the qualities that make Hoover Dam eligible for the National Register of Historic Places would not be impaired by construction of the external powerhouse. We therefore believe that a determination of "no adverse effect" will be appropriate at the time that you and the (Nevada) (Arizona) State Historic Preservation Officer have jointly reviewed plans and specifications for the powerhouse.

As discussed in our earlier letter we believe that construction of either the underground powerhouse or replacement of the generator would have "no effect" on the National Register qualities. 2

For your information we are also seeking a determination of "no adverse effect" for the prehistoric archaeological site located on the Arizona side of Lake Mohave. This site is discussed in our May 7, 1980 letter.

We are seeking your comments with our determinations.

Sincerely yours,

1 1 1,11 AAA., K. M. Trompeter Regional Environmental Officer

Enclosure May 7, 1980

LC-158-A 770.

Ms. Mimi Rodden State Historic Preservation Officer Nevada Division of Historic Preservation and Archeology 201 South Fall Street Nye Building, Room 113 Carson City, NV 89710

Dear Ms. Mimi Rodden:

This letter is to initiate a consultation process with you in compliance with Executive Order 11593, and 36 CFR Part 800, in regard to the cultural resources located in the Black Canyon. Because the area involved is within the Lake Mead National Recreational Area and under the jurisdiction of the National Park Service, we are writing this letter in concurrence with the National Park Service, Western Archeological Center, Tucson, Arizona. This resource will be affected by the proposed Hoover Dam modification project.

On December 16, 1975, Public Law 94-156 authorized the Secretary of the Interior to engage in feasibility investigations of 12 potential water and/or energy resource projects. The modification of the existing Hoover Dam powerplant on the Colorado RiV,er, on the Arizona/Nevada border, was one of the projects authorized for study.

The purpose of this investigation was to determine the optimum amount of peaking capacity that can be added to Hoover powerplant within the constraints imposed by water operations, environmental, and recreational considerations.

The extent and method of modification would be limited by the availability of water and agreement among affected parties.

The alternatives being considered for this project are 1) a new surface powerhouse; 2) replacing generating units AS and A9; and 3) a new underground powerhouse.

The above alternatives will all have impact on an archeological site downstream from the dam. This letter of consultation is concerned only with the archeological resource that will be impacted by the alternatives. There are several features of historic significance near the river downstream from Hoover Dam. These features include ringbolts which were used to winch steamboats up the river prior to the construction of Hoover Dam. Uther features are the historic gauging station and catwalk, related to the construction of Hoover Dam, as well as scattered evidence Of historic mining activity.

These features will not be impacted by the proposed Hoover Powerplant Modification. A further evaluation will be implemented on these historic features in the future.

We will initiate a separate consultation on the Hoover Dam modification as described below, when additional design data is available.

Alternative No. 1 - Surface Powerhouse. A new powerhouse would be constructed at the downstream end of the present Arizona powerhouse and would extend about 290 feet from the existing end of the Arizona powerhouse.

The new generating units would be served through the existing. 25-foot-diameter lower Arizona penstocks header. A concrete-lined surge tank would be needed to protect the penstocks from excess pressures that may occur with the new units. The tank would be 200 feet in height and 80 feet in diameter with a top elevation of 1,270 and bottom elevation of 1,070 and a 25-foot connnecting tunnel to the header. The surge tank would be located at the east edge of the employee's parking lot on the Arizona side and would be underground except for 40 feet of exposed surface on one side.

Construction activities include excavation for surge tank shaft, and tunneling for the riser from existing penstock to the bottom of the shaft and the powerhouse addition.

Alternative No. 2 - Replacement of generating units AS and A9. The • physical changes would be within the powerhouse with no noticeable changes outside.

Protection of the generation unit would be provided by a concrete-lined surge tank. The tank would be 70-feet in diameter inside with a top elevation of 1,270 and bottom elevation of 1,070 with the top 40 feet exposed on one side. The tank would be located at the east edge of the employee's parking lot on the Arizona side.

Construction activities include excavation for surge tank shaft, and tunneling for the riser from existing penstocks to the bottom of the shaft.

Alternative No. 3 - Underground powerhouse. Both the Arizona and Nevada sides of the river were closely studied and sites on the Arizona side were chosen. 3

The powerhouse would be constructed in a chamber in the canyon wall (abutment) behind the location of the suggested 500-MW surface powerhouse. In other respects, such as penstocks, surge tank, operation flows and velocities, this alternative would be similar to the surface powerhouse alternative.

The increased generating capacity would permit the powerplant to generate more power during peak summer demand periods.

All the above three alternatives would require blasting, excavating, and tunneling for construction. The area to be affected by the direct construction are the canyon walls. No prehistoric sites are located in this area, so there will be no effect on the cultural resources curing the construction.

In compliance with Executive Order 11593, and 36 CFR Part 800, the Water and Power Resources Service (Water and Power) contracted with Nevada Archeological Survey, Las Vegas, Nevada, to conduct an archeological survey of the subject project area. As a result of this survey a total of four archeological sites were located. Of the four located sites, two of these were limited to surface finds with no indication of any midden depth. The other two sites, Cholla Rock Shelter and Willow Beach No. 2, are considered to have archeological research potential and in our opinion would meet the criteria for inclusion on the National Register of Historic Places.

The Cholla Rock Shelter is located approximately 6.5 miles downstream from the dam on the Arizona side. The rock shelter is located approximately 15-20 feet above the river's high water mark and will not be affected by the Hoover Dam alternatives.

Willow Beach No. 2 is located 9.75 miles downstream from the dam on the Arizona side. This site is located on a sandbar which is currently . being subject to erosion caused by the fluctuation of the river's water level. As a result of the modifications to Hoover powerpiant there will be a cyclic increase of tne water level as well as an increase in the extent of fluctuation. The erosional process will be speeded up to tne detrimental effect of the site. In addition the sand bar receives heavy recreational (Picnicing and camping) use from boaters.

We are concurrently seeking a determination of eligibility. Enclosed is a copy of the documentation for the determination, including the i evada Archeological Survey keport and map showing the location of the resources. These sites may have the potential for answering questions of regional interest.

The data collection methods would include mapping of all site features, controlled collection of surfacc matriuls and subsurface testiry.. In all instances it is assumed that data collection will oe carrieu out using field methods to the standards of the profession. It is also assumed that all data and material recovered will be analyzed to recover data to eliminate problems and questions pertaining to this area, and that artifacts will receive proper curation. 4

3.a. We believe that, because of the nature of the property, such as the absence of impressive architectural remains, and artifacts, which are readily identifiable by lay people, they would have minimal value as in-place exhibits for the public.

3.b. We are not aware of any specific ethnic or social group or community which attach special significance to the above properties beyond the scientific values described above.

3.c. We believe that the proposal for study of the resources demonstrates that current archeological methodology can extract significant data from properties.

If the above properties are determined eligible for inclusion on the National Register of Historic Places it will be through application of criteria "d" of 36 CFR Part 60.6. The significance would appear to be in the data which the property may produce rather than for exhibit or other purposes.

We therefore believe that the criteria in Part 1 of the Advisory Council on Historic Preservation "Guidelines for Making 'Adverse Effect' and 'No Adverse Effect' Determinations for Archeological Resources in accordance with 36 CFR Part 800," are met for the Willow Beach No. 2 site. Our analysis is as follows:

1. The Willow Beach No. 2 site is not a National Historic landmark, National Historic Site in private ownership, and although this property is in the National Park System, is not designated as having National Significance.

2. We believe that inplace preservation .of the property is not feasible due to the accessibility of the site and the subsequent vandalism caused by visitors to the site. We believe that the mitigation recommendations in the enclosed report by the Nevada Archeological Survey, Southern Division, supports such a determination.

The criteria for Part II of the subject guidelines (Supplementary Guidelines II) will be met by contract with an organization meeting the standard contracting procedures of the Water and Power Resources Service and Federal procurement procedures.

Should modifications of the project plans result in any changes in impacts upon the identified cultural resources - within the project area, Water and Power will consult with you.

In conclusion, we believe that the above plan will result in a situation of no adverse effect to the Willow Beach No. 2 site and a ruling of no effect to the Cholla Rock Shelter site within the Hoover Dam modification project area. We are seeking your comments and concurrence with our determination.

Sincerely,

K.M. TROMPETER K. M. Trompeter Acting Regional Environmental Officer

Enclosures cc: Western Archeological Center, P. O. Box 41058, Tucson, AZ 85717 (without enclosures)

I Arc...4-- rchntar. United States Department of the Interior

BUREAU OF RECLAMATION LOWER COLORADO REGIONAL OFFICE P.O. BOX 427 BOULDER CITY, NEVADA 89005 IN REPLY REFER TO: • LC-158A SEP 1 4 SaZ 650.

Ms. Ann Pritzlaff Arizona State Historic Preservation Officer 1688 West Adams Phoenix, AZ 85007

Dear Ms. Pritzlaff:

As discussed in our earlier letter we believe that construction of either the underground powerhouse or replacement of the generator would have "no effect" on the National Register qualities. 2

The prehistoric site, Willow Beach No. 2, is currently subject to erosion caused by the fluctuations of the river's water level. The proposed Hoover Dam modification will result in speeding up of the erosional process with detrimental effect to the site.

A copy of the documentation for the determination of eligibility, as well as the Nevada Archeological Survey Report and a map showing the location of the resource were included in the original letter of May 7, 1980.

We are requesting for Willow Beach No. 2 both a determination of eligibility for listing on the National Register of Historic Places under 36 CFR Part 63, and for a determination of "no adverse effect" under the provisions of 36 CFR Part 800, based the data recovery program proposed in our earlier letter.

We are seeking your comments with our determinations.

Sincerely yours,

K. M. Trompeter Regional Environmental Officer

Enclosure May 7, 1980 •

LC-158-A 770.

Ms. Mimi Rodden State Historic Preservation Officer Nevada Division of Historic Preservation and Archeology 201 South Fall Street Nye Building, Room 113 Carson City, NV 89710 •

Dear Ms. Mimi Rodden:

On December 16, 1975, Public Law 94-156 authorized the Secretary of the Interior to engage in feasibility investigations of 12 potential water and/or energy resource projects. The modification of the existing Hoover Dam powerplant on the Colorado River, on the Arizona/Nevada border, was one of the projects authorized for study.

The purpose of this investigation was to determine the optimum amount of peaking capacity that can be added to Hoover powerplant within tht constraints imposed by water operations, environmental, and recreational considerations.

The extent and method of modification would be limited by the availability of water and agreement among affected parties.

The alternatives being considered for this project are 1) a new surface powerhouse; 2) replacing generating units A8 and A9; and 3) a new underground powerhouse.

The above alternatives will all have impact on an archeological site downstream from the dam. This letter of consultation is concurred only with the archeological resource that will be impacted by the alternatives. There are several features of historic significance near the river downstream from Hoover Dam. These features include ringbolts which were used to winch steamboats up the river prior to the construction of Hoover Dam. Uther features are the historic gauging station and catwalk, related to the construction of Hoover Dam, as well as scattered evidence of historic mining activity.

These features will not be impacted by the proposed Hoover Powerplant Modification. A further evaluation will be implemented on these historic features in the future.

We will initiate a separate consultation on the Hoover Dam modification as described below, when additional design data is available.

Alternative No. 1 - Surface Powerhouse. Anew powerhouse would be constructed at the downstream end of the present Arizona powerhouse and would extend about 290 feet from the existing end of the Arizona powerhouse.

The new generating units would be served through the existing 25-foot-diameter lower Arizona penstocks header. A concrete-lined surge tank would be needed to protect the penstocks from excess pressures that may occur with the new units. The tank would be 200 feet in height and 80 feet in diameter with a top elevation of 1,270 and bottom elevation of 1,070 and a 25-foot connnecting tunnel to the header. The surge tank would be located at the east edge of the employee's parking lot on the Arizona side and would be underground except for 40 feet of exposed surface on one side.

Construction activities include excavation for surge tank shaft, and tunneling for the riser from existing penstock to the bottom of the shaft and the powerhouse addition.

Alternative No. 2 - Replacement of generating units A8 and A9. The physical changes would be within the powerhouse with no noticeable changes outside.

Construction activities include excavation for surge tank shaft, and tunneling for the riser from existing penstocks to the bottom of the shaft.

Alternative No. 3 - Underground powerhouse. Both the Arizona and Nevada sides of the river were close4 studied and sites on the Arizona side were chosen. 3

The increased generating capacity would permit the powerplant to generate more power during peak summer demand periods.

In compliance with Executive Order 11593, and 36 CFR Part 800,.the Water and Power Resources Service (Water and Power) contracted with Nevada Archeological Survey, Las Vegas, Nevada, to conduct an archeological survey of the subject project area. As a result of this survey a total of four archeological sites were located. Of the four located sites, two of these were limited to surface finds with no indication of any midden depth. The other two sites, Cholla Rock Shelter and Willow Beach No. 2, are considered to have archeological research potential and in our opinion would meet the criteria for inclusion on the National Register of Historic Places.

Willow Beach No. 2 is located 9.75 miles downstream from the dam on the Arizona side. This site is located on a sandbar which is currently being subject to erosion caused by the . fluctuation of the river's water level. As a result of the modifications to Hoover powerplant there will be a cyclic increase of the water level as well as an increase in the extent of fluctuation. The erosional process will be speeded up to the detrimental effect of the site. In addition the sand bar receives heavy recreational (Picnicing and camping) use from boaters.

We are concurrently seeking a determination of eligibility. Enclosed is a copy of the documentation for the determination, including the Nevada Archeological Survey Report and map showing the location of the resources. These sites may have the potential for answering questions of regional interest.

The data collection methods would include mapping of all site features, controlled collection of surface materials and subsurface testing. In all instances it is assumed that data collection will be carried out using field methods to *the standards of the profession. It is also assumed that all data and material recovered will be analyzed to recover data to eliminate problems and questions pertaining to this area, and that artifacts will receive proper curation. 4

3.b. We are not aware of any specific ethnic or social group or community which attach special significance to the above properties beyond the scientific values described above.

3.c. We believe that the proposal for study of the resources demonstrates that current archeological methodology can extract significant data from properties.

2. We believe that inplace preservation of the property is not feasible due to the accessibility of the site and the subsequent vandalism caused by visitors to the site. We believe that the mitigation recommendations in the enclosed report by the Nevada Archeological Survey, Southern Division, supports such a determination.

Should modifications of the project plans result in any changes in impacts upon the identified cultural resources within the project area, Water and Power will consult with you.

Sincerely,

KAA.TRoMPFIER

K. M. Trompeter Acting Regional Environmental Officer

Enclosures cc: Western Archeological Center, P. 0. Box 41058, Tucson, AZ 83717 (without enclosures) •

JUN 1 1 1980

LC-158 7/0.

,j,:t mes Ayres Arizona StrL!:e Historic PrecervatThn Officer Vest Adams noenix, Arizona 85007

Dear Mr. Ayres:

In our previous correspondence to you we •documented effects upon cultural resources located downstream from Hoover Dam that could take place as a result of the proposed construction and operation of the proposed Hoover Power Plant modification project, The possible affected properties are independent from the dam and appurtenant structures themselves.-

The power plant modification alternatives that will include installation of additional generators are still in a preliminary stage of design. It is, therefore, premature to discuss any specific impacts at this time. We will keep you informed as plans for the alternatives are developed.

Sincerely, James C. Maxon Acting Regional Environmental Officer

cc: Ms. Mimi Rodden, State Historic Preservation Officer, 201 South Fall Street, Carson City, Nevada 89701

bt: Project Manager, Boulder City, Nevada Chief, Environmental Affairs Office, E&R Center

bbc: Z06 150 150 Chrono

JMaxon:sp MAY 0 7 1980

LC-158A 770.

rr. laIALts .e.vres State l Astoric Presrvation (ffit:er 16E6 liest :=' dans Street , Pher.!nix, P riivna 7

Dear "r. Ayres::

- This lettm- is to initiat ,.: consultatir:q 1? ■1 in covolianee with Executive ( Her 11593, atld Pirt in , renard t Cie cultural resources !ocatel 1 Rocause the area involved is wiU, in the H9tit)ral - Recrcetinal nrea and under tPe. r H2 r.ervice, we are writinn this letter in c rrrtf.rr_Grp •,!ith Pational Park Service, western Archcolo 1 Tuc:sq. Arizona. This resource will he affected -Tonvpr noeification pro5ket.

On '!' clu'ber 16, 1975, Puhlic Lail '4-156 ,tc.it'—:rizt,1 ! er c , cf the !nt,!!rior to en;ae in feasitAlity inli sri-tiens of •P potential v)ater end/ør enemy resf!,lirce cation of the existing )ioover rowerplant thf.' Rivg,r, co the ArizOna/Newida hurder, was author1ze:1 for study.

The purpns of tHs invest1,7atIon ,gas to - aount of peakin9 capacity that can be ecdr7-: poverOdnt witnin the constraicts impt 1 iatcr ervirx-,- , nentAl, 4 ! recreational considernions.

The extent ant! method cf viedificetion tlot , availeility of *tater and agraeert

The alternativi:s being considered for this !,r- c.,:t lre 1) ti nee.? surface powerhouse; 2) replacin generatim : .:nitsi aim 3) a new uderTround powerhncse.

The above alternatives will all have impact an archf - olo.gical site dowrstreari from the dec. This letter cclisultation is concerned only with the archeolorlcal resource that will F IrapeCteri by the alternatives. There are several features of historic sicwiticahce near the river downstream from loover Dam. These feetorPc include rinn- rirr bolts which were used to vinc s+eanhoats t riv=r tfN the censtr.!ctical of ! ncv-r rt r * c:auOng station and catwall, , related to Hoover dS well as scattered evidence n' Ictoric activity.

These features will not te t-pacted by .;ower plant Modification. A further evaluation , ill !,c., these nistoric features in the future.

We will initiate a separate consultation on 1, Hpuv.,:r òv ficaticn as described bOov, when additinol is available.

Mernative 'f o. I - Surfact Powerhouse. , • ,,,.i rn(Jus4, be constructed at the downstream end of t;.;. ' rs ,:nt Arizona powerhouse and would extend about 290 feg..t t*o ew of the Arizona powerhouse.

The new jenerating units wouH te. served tr t. 2-f..,, ot-rliallt:ter lower .Arizona penstocks ,r. lined surge tank would be nended to protect t.,.; fr(p - excess pressures that may occur with the net' ;wits. Thr- tink , - would he 200 feet in height and 30 feet in n er wit a too , elevation of 1,270 and bottoo elevation of 1, an• a 2h-foot , connectinn tunnel to the header. The sur.tt ■ e iocat at the east edoe of the enployee's parkin sot nr, the :rizona side an -Jould be under.;round excent for V: r OF exrosirw surface oh one side.

Construction activities include nxcavation fn s-!rIle tank shafi., and tunneling for the riser frtr, existinq tr Notto. of tte shaft are thc pw.ver)ouse addition.

Alternative Al. 2 - Replacenlent of generatiF:y units fk and The physical changes would be within the 0-:7r-1,,,-se with no noticeable charges outside.

Protection of the creneratino unit would tw !;F:Jvi ir) tv a concre- MEd sure tank. The tank would be 70-fut in rii eter inside tifIr 1,G70 with a ton elevation of 1,270 and !)ottoi.1 elc , of the top 4U feet exposed on one side. The ould be lccated at the east edge of the tylployee's parkine liL Qr the rizuna side. Construction activities include excavation t'or sorqe tank sh;ift, and tunneling for the riser fror existing ponstoc'es tn the -,ottom of the shaft.

Alternative No. 3 - Underground oowerhouse., 'ot!; 'kriz')r.? i . Nevada sides of the river were closely st!! ii sit f?S (11 the Arizona side were chosen. f -The powerhouse would be constructed in a r in tho c.!In nn wall (abutnent) behind the location of the coo ted 5rn-'*!- surface powerhouse. In other respects, such isrocs, surc;. tank, operation flows and velocities, this FOte, rnative woolJ similar to the surface powerhouse alternative. The increased cenerating capacity would norIi toe poter;-:lant tc generate nore power during peak strincr de-eoi) All the above three altPrnatives would rerTire '!-Aastirii, excavating, and tunneling for construction. TilE 5ree to be effecter by the direct construction are the canyon 1 ,,,,.11s. o prehistoric sites are located in this area, so there i11 no effect or. the cultural resources during the construction. In compliance with Executive Order 11593, ao 7; Cr R Part c], the rater and Power Resources Service (!ater io0 rnwer) contracted with•Nevada Archeological Survey, Las VoH . ;evada, to conduct an archeological survey of the subject :.roject, area. As a result of this survey a total of four archcolo3ical sites were located. Of the four located sites, two of those were limited tn surface finds with no indication of any n1c10 th. The othcr two sites, Cholla Rock Shelter and Willow reeci) A). 2, are considered to have archeological research poteotial ani.i in °or opinion would meet the criteria for inclusien o:r. the National Register of Historic Places.

The Cholla Rock Shelter is located approxiPtoly 5.r; miles downstream from the dam on the Arizona side. rock shelter is located approximately 15-20 feet above thc riv:7r's high water mark ad will not be affected by the Hoover alternatives. Willow Beach Ne. 2 is located 9.75 niles downstrearl fron te dao on the Arizona side. This site is located or d sandhar vhicn is currently teing subject to erosion caused nj. t.10 fluctuation of the river's water level. As a result of the . *difications to Hoover powerplant there will be a cyclic increase of the water level as well as an increase in the extent of fluctuation. The erosional process will he speeded up to the, Oetrifcntal effect of the site. In addition the sand bar receivt s Fravy recreational (picnicing an: camping) use fro l heaters. 4

We are concurrently seeking a determinative ef elieihility. Enclosed is a copy of the documentation for tric deterrinaticn, Including the Nevada Archeological Survey eeeort a.n showin,r; the location of the resources. These sitce -av have the potential for answering nuestions of regional intere!.t.

The data collection methods would include of all site features, controlled collection of surface , et rials and suh- surface testing. In all instances it is aseeeed that data collection will be carried out using field reteoOs to the standards of the profession. It is also assuried that all ' ate and oateriel recovered will he analyzed to recover data to elioinate proOlens and questions pertaining to this area, an6 t!et artifacts eill receive proper curation. 3.a. Ve believe that, because of the neture of the property, such as the absence of impressive architectural remains, and artifacts, which are readily identifieele ey lav peoele, they would have minimal value as in-elaee exhiO'its for the public.

3.h. ‘,4 arc not aware of any specific ethnic or social qrcup or community which attach special sieeificance to the above properties beyond the scientific velves ,iescriOed above.

Lc. We believe that the proposal for stidy of the resources deoonstrates that current archeolneicel oethodoloey can extract significant data from propertiee. If the above properties are determined elieiele for inclusion on the liational Register of Historic Places it he throueh application of criteria "d" of 36 CFR Part The slept- ficance would appear to be in the data which the property eey produce rather than for exhibit or other por.(c,scs. We therefore believe that the criteria in Pert I of the folvisory Council on Historic Preservation "Guidelines for !:aking 'Adverse Effect' and 'No Adverse Effect' eterminatiees for Archeological Resources in accordance with 36 CFR Part tU," are oet for the Willow Beach No. 2 site. Our analysis is as felloos:

I. The Willow Beach No. 2 site is nct e ational Historic landmark, National Historic Site ie private ownership, and although this property is in Vle ational Park System, is not designated as haviee ational Sienifi- cance. 5

2. W believe that inplace preservatirJ, ef the pronerty is not feasible due to thp accessibilir.y 0 the site and the subsequent vandalivi caused ,isitors- to th,: site. e believe that the niti53ti recu dations in the enclosed report by the revnel rChLClOiCl Survey, !;outhern Division, supr,orts 5 dvtrr .1- don.

Tht. criteria for Part II of th (Supplementary Guidelines II) will t. by contract with an organization rectinq t contrdctino procedures of the iliter and Pover i!riources ':ervice an reddral procurement procedures.

Should modifications of the proThct !lans result in any chances in impacts upon the 1denti'ii culturdl resour- cts within the project area, atr rover will consult with you.

In conclusion, we believe that tt..: plan Oil result in a situation of no adversc ,ffect to 111low Beach to. 2 site and a rulini of no effect to the Cholla Rock Shelter site withir! Vie hoover nam modification project area.

We are seeking your conments and concurrencE Ht!7- (nr detr- mination.

Sincerel,

N6 eM. TRUMPLT0i, e-4 K. M. Trompeter Acting Regional Environmental Officer Enclosures ›, cc: Western Archeological Center, P. 0, Eex 11c, Tursoil, r.!'3717 (w/o enclosures)

17 e'-":;er ,4 tm: Chief, Environmental Affairs Offic., • s AttcTitionl Dr. ',;are! tJeakly • Pri)ict "anae,er, noulder City, :i!.tvtle (each w/o enclosures) • c cu • Identical letter seat to: MI. Mimi Roder r, o Suits Historic Frlstrvltion )9ficIr 211 fall Street Carson City, MtV.: 1 7:1;n1 APPENDIX I INDEX

Affected environment: 21-48 Archeological and historical site 47 Climate and air quality 21 Geology 22 Hoover Dam 22-26 Hydrologic and aquatic environment 22-33 Recreation 43-47 Seismicity 22 Socioeconomic environment 48 Special status species 36-43 Terrestrial environment 33-36 Air quality: Changes 49 Impact 49 Algae: Cladophora 27 Damage 26, 51-53 Diatoms 27 Growth 26, 28-29, 53-54 Alternative 1 - surface powerhouse: 12-14 Cofferdam 13 Construction costs 12 Penstock changes 12 Surge tank 12 Transformer circuits 13 Transformer deck 12 Transmission capability 13 Alternative 2 - replacement of A8 and A9: 14-15 Cofferdam 15 Construction costs 14 Penstock changes 14 Surge tank 14 Transformer circuits 14 Transformer deck 14 Transmission capability 15 Alternative 3 - underground powerhouse: 15 Cofferdam 15-16 Construction costs 16 Penstock changes 15 Surge tank 15 Transformer circuits 15 Transformer deck 15 Transmission capability 16 Alternative 4 - no action: 16 Generating capacity increase 16 Maximum releases 16

I-1 Alternatives: 5-22 Comparison of v Considered iv Construction of see Construction Eliminated 5-11 Environmental impacts vi Nonstructural 5-7 Not eliminated 11-20 Operation 17-20 Structural 7-16 Amphipod 27 Aquatic biota impact 26, 64, 65 Archeological consultation letters H Archeological sites: Cholla Rock Shelter 47 Willow Beach No. 2 47 Arizona: Geology 15 Population 4 Power authority 10 Arrowweed 33

Bald eagle 36 Baseload: Energy needed 9 Energy requirement 3 Generation 7 Powerplants 6 Resource 8 Birds: Bald eagle 37 Black-tailed gnatcatcher 36 Canyon wren 36 Coots 36 Cormorants 36, 58 Great blue heron 36 Grebes 36 Loggerhead shrike 36 Peregrine falcon 37 Phoebes 36 Red tail hawk 36 Sparrows 36 Swainson hawk 36 Yuma clapper rail 36, 38 Black Canyon: Aquatic life 53, 56 Description 21, 33 Impact 69 Productivity 53-57 Vegetation 33, 57, 69 Washes 26 Water level 26 Water velocity 26, 50, 68 Wildlife 58, 69

1-2 Black crappie 29, 31, 32 Black Mountains 22 Blackouts 6 Black-tailed gnatcatcher 36 Bladder sage 36 Bluegill 31 Boating safety 59 Bonytail chub 29, 31, 36, 39-41, 59 Boulder Canyon Project Act 1, 5 Boulder City: Description 48 Earthquakes 22 Impact 60-63 Power market 2 Reference point 21 Bowcutt trout 32 Bridge Canyon 10 Brittle bush 36 Brook trout 31-32 Brownouts 6 Brown trout 31 Buckwheats 36 Bureau of Reclamation 1-2, 47, 70 Burro-bush 36

Cactus mouse 36 Canyon: Black see Black Canyon Bridge 10 Eldorado 21, 29 Painted 21 Pyramid 21 White Rock see White Rock Canyon Canyon wren 36 Capacity loss 64, 69 Carp 31 Catclaw 33, 36 Central Arizona Project 10 Channel catfish 31 Cheeseweed 36 Chironomed 27 Cholla Rock Shelter: Impact 60 Location 48 City services impact 62, 69' Cladophora 27 Clark County: Impact 60-63 Population 48 Clean Water Act, 404(r) 1 Climate changes 49 Coal powerplants 7-8

1-3 Cofferdam: Impact 50, 67 Velocity changes 50-57, 67 Water level 15 Colorado River: Basin Project 10 Flow 51 Operations 5 Productivity 68 Resources 10 Surface profiles 20 Temperature 68 Velocities 23-26 Colorado River squawfish 29, 31 Combined-cycle powerplants 8 Combustion turbines 8 Community impact 60-63 Community leader evaluations 62 Construction: Affects 48-49 Permits 74 Construction of alternatives: Arizona abutement 16 Batch plant location 16 Blasting 16 Disposal of debris 58 Manpower requirements 18 Movers and nonmovers 17, 19 Stages 19 Time 19 Consultants 81-82 Coots 35 Cormorants 36, 58 Corps of Engineers Permit 404(r) El-E4 Cottonwood Cove 44-45 Creosotebush 36 Cumulative impacts 64-65, 69, 70, 73 Cutthroat trout 31-32

Dams: Davis 10-11 Glen Canyon 10-11 Hualapai 10 Parker 10-11 Davis Dam 10-11 Density gradient 28 Desert wash: Destruction 69, 71 Vegetation 36 Desert woodrat 36 Devil's Hole pupfish 36, 39 Diatoms 27 Diesel emissions 49, 67 Distribution list Al-A8

1-4 Dumping construction spoils 16, 68

Earthquakes 22 Economic impact 62, 69 Eldorado: Canyon 21 Mountains 22 Employee totals 60 Endangered species: Act 1, 36 Bald eagle 37 Bonytail chub see Bonytail chub Devil's Hole pupfish 36, 39 Peregrine falcon 37 Razorback sucker see Razorback sucker Trelease's beavertail prickly pear cactus 36 Yuma clapper rail 38 Energy: 3 Conservation 5 Demand 3-4, 23 Geothermal 10 Hydroelectric 1-2 Hydrogen 10 Solar 7 Thermal 7 Wind 7 Environmental commitments Bl-B6 Environmental consequences of alternative 1: 48-66 Archeological and historical sites 59 Climate and air quality 49 Cumulative impacts 63 Geology 49 Hoover Dam 48 Hydrologic and aquatic environment 50-57 Power loss 63 Proposed mitigation 67 Recreation 58-59 Seismicity 49 Socioeconomic environment 60-63 Special status species 58 Summary of impacts 65-66 Terrestrial environment 57-58 Environmental consequences of alternative 2: 66-70 Archeological and historical sites 69 Climate and air quality 67 Cumulative impacts 69 Geology 67 Hoover Dam 67 Hydrologic and aquatic environment 67-68 Power loss 69 Proposed mitigation 70 Recreation 69 Seismicity 67 Socioeconomic environment 69

1-5 Special status species 69 Summary of impacts 69 Terrestrial environment 69 Environmental consequences of alternative 3: 70-71 Archeological and historical sites 71 Climate and air quality 70 Cumulative impacts 71 Geology 70 Hoover Dam 70 Hydrologic and aquatic environment 70 Proposed mitigation 71 Recreation 70 Seismicity 70 Socioeconomic environment 71 Special status species 70 Summary of impacts 71 Terrestrial environment 70 Environmental consequences of alternative 4: 71-73 Archeological and historical sites 73 Climate and air quality 71 Cumulative impacts 73 Geology 71 Hoover Dam 71 Hydrologic and aquatic environment 71-72 Recreation 73 Seismicity 71 Socioeconomic environment 73 Special status species 73 Summary of impacts 73 Terrestrial environment 73 Environmental impacts vi, 21-73 Epilimnion 28 Exemption from 404 permit El-E4

Feasibility investigation 2 Federal Water Pollution Control Act 74 Fish: Black crappie 29, 31, 32 Bluegill 31 Bonytail chub see Bonytail chub Bowcutt trout 36 Brook trout 31, 32 Brown trout 31 Carp 31 Channel catfish 31 Colorado River squawfish 31 Cutthroat trout 31, 32 Devil's Hole pupfish 36, 39 Green sunfish 31 Humpback chub 29, 31 Humpback sucker 29, 31 Largemouth bass 29, 31, 32 Rainbow trout see Rainbow trout Razorback sucker see Razorback sucker

1-6 Silver salmon 31, 32 Sockeye salmon 31, 32 Status 31 Striped bass 31, 32, 54 Threadfin shad 31, 32, 56

Fish and Wildlife Coordination Act Report 1, Bl-B6 Fishery resources 29, 54, 72-73 Flood control 5, 74 Future without the project vi, 2, 16, 71

Gas turbine generators 3 Generating units 2 Geothermal energy 10 Glen Canyon Dam 10-11 Glendale, City of 2 Glossary of terms Gl-G4 Golden door volcano 22 Golden weed 36 Great blue heron 36 Grebes 36 Green sunfish 31

Hatching success Dl-D7 Henderson description 48 Hoover Dam: Appearance 48, 67, 71 Description 21-22 Earthquakes 22 Existing facilities 1 Flood control 74 Historic: Impact 60 Value 47 Hypolimnion 28 Impact 50, 70, 73 Influence 23 Intake towers 27 Operation 5, 50, 67 Penstocks 28 Releases: Present 23, 30, 44 Proposed 50-51, 71 Seasonal 23 Temperature 27-28, 53 Velocities 50 Vegetation 33 Vertical mixing 28 Visitor center 74 Water withdrawal funnel 28 Hoover Powerplant: Alternatives 5 Capacity 4 Location 21

1-7 Marketing area 4 Modification 2-3 Operating patterns 20, 67 Releases 17, 50 Resource 4 Uprating special report 16 Hualapai Dam 10 Humpback chub 29, 31 Humpback sucker 29, 31 Hyalella 27 Hydroelectric: Energy 1-2 Powerplants 3 Hydrogen energy 10 Hypolimnion 28

Impact area 48 Impacts: Air quality 49 Black Canyon 69 Boulder City 60-62 Cholla Rock Shelter 60 City services 61-62, 69 Clark County 60-63 Cofferdam vi, 65, 70 Community 60-63 Cumulative 63, 69, 71, 73 Demographic 62 Economic 62, 69 Environmental 21-74 Fish 55, 68 Hoover Dam 48-49, 67, 71, 73 Summary 65, 71, 73 Traffic 49, 67 Uprating 79 White Rock Canyon 58, 69, 70 Willow Beach No. 2 60 Indigo bush 36 Interface: Extension 29, 54 Versus fish hatchery 29, 54, 72, 78 Warm/cold water 29 Invertebrates: Amphipod 27 Chironomed 27 Hyalella 27 Oligochaetes 27

Katherine Landing 44 Kingman Wash 28

Lake Mead: Description 21 Earthquakes 22

1-8 Elevation 51 Fishery 54 Fish species 29 History 1 Pumped water 9-10 Storage 5 Temperature 27, 53 Thermal energy 7 Thermal stratification 28 Lake Mohave: Buffer 23, 26 Description 21 Elevation: 20, 23, 33-34, 44, 50, 59 Reregulation 73 Fishery 32, 55-56 Fish species 31, 54-56 Interface 29 Navigation 44-47 Power generation 73 Pumped water 9-10 Vegetation 55 Visitors 43-47 Largemouth bass 29, 31, 32 Las Vegas: Description 48 Reference point 21 Smog 22 Lee Ferry Gage 10 Licenses 74 Limnological investigations 29 Literature cited Fl-F5 Load: Interruption 6 Management 6 Loggerhead shrike 36 Los Angeles 2

Mammals: Cactus mouse 36 Desert woodrat 36 Merriam kangaroo rat 36 Pocket mouse 36 Yuma antelope squirrel 36 Merriam kangaroo rat 36 Mesquite 33 Metropolitan Water District 2 Mistletoe 36 Mitigation 67, 70, 71, B1 -B6 Mountains: Black 22 Eldorado 22 Mt. Davis Volcano 22

1-9 National Environmental Policy Act 2 National Park Service 43 Nevada: Archaeological Survey 47 Department of Wildlife 27 Population 4 Test Site 22 Nonrenewable fossil fuels 8 Nonstructural alternatives 5-7 Nuclear powerplants 3, 7

Oil powerplants 3 Oligochaetes 27 Operation of alternatives 17-20

Painted Canyon 21 Parker Dam 10-11 Pasadena, City of 2 Patsy Mine Volcano 22 Peak: Capacity 2-4 Flows 23, 50, 68 Load 3 Projection 4 Reduction 6 Peregrine falcon 36, 37 Periphyton: Growth 26, 52, 55 Losses 26, 55 Reestablishment 55 Permits 74 Phoebes 36 Phytoplankton 29, 53 Planning team 75 Plants: Arrowweed 33 Bladder sage 36 Brittle bush 36 Buckwheats 36 Burro-bush 36 Catclaw 32, 36 Cheeseweed 36 Creosotebush 36 Golden weed 36 Indigo bush 36 Mesquite 36 Mistletoe 33 Ratany 36 Salt-bush 33 Salt-cedar 33 Salt-grass 33 Seepwil low 33 Snakeweed 36 Trelease's beavertail prickly pear cactus 36 Willow 33 Pocket mouse 36 Power: Cycle 28 Generation 1, 3, 6 Power group 76 Powerplants: Coal 3, 7-8 Combined cycle 8 Hydroelectric 3 Nuclear 3, 7 Oil 3 Preparers 80 Private agencies: Burbank, City of 2 Glendale, City of 2 Los Angeles 2 Metropolitan Water District 2 Pasadena, City of 2 Southern California Edison Company 2 Public involvement 78 Public Law: 94-156 2 92-500 74 Pumped storage: 9 Offstream 9 Pyramid Canyon 21

Rainbow trout: Impacts 31, 32, 55 Stocking 27 Stomach contents 27 Ratany 36 Razorback sucker: 31, 42, 36, 58 Impact 55 Population 42 Recreation 43, 58, 69, 70, 73 Red tail hawk 36 Relationship to other projects and actions 73 Releases: Daily cycle 23 Low 23 Peak see Peak Rates 17-20 Seasonal 24 Ringbolt Rapids 20

Salt-bush 33 Salt-cedar 33 Salt-grass 33 Section 7 consultation 36 Seepwillow 33 Silver salmon 31, 32 Smog 22 Snakeweed 36 Socioeconomic 48, 60-63, 69, 70, 73 Sockeye salmon 31, 32 Solar energy 7 Southern California Edison Company 2 Sparrows 35 Spawning habitat 56 Spoil sites 58, 69, 70 Striped bass 31, 32, 54 Structural alternatives 7-16 Studies see Mitigation Substrate stability and primary productivity 26-27, 51 Summary i-ix Supreme Court Decree 5 Surface profiles of Colorado River 20 Swainson hawk 36

Temperature: Fluctuations 27, 53, 72 Instability 28, 53, 72 Threadfin shad 31, 32, 56 Thermal energy 7 Thermoclines 7 Time-of-day rates 6 Tourism economy 48 Traffic impact 61, 67 Transmission lines 2 Trelease's beavertail prickly pear cactus 36

Upper Colorado Region 10 Uprating 2 U.S. Fish and Wildlife Service 36, 59 U.S. Highway 93 35, 58, 61

Velocity: Fluctuations 23, 50, 67, 71 Influence 26 Volcanoes: Golden Door 22 Mt. Davis 22 Patsy Mine 22 Voltage reduction 6

Water: Current 23-26 Layers 28 Level fluctuations 23, 24, 50, 67, 71 Pollution Control Act 1 Requirements 23 Uses 5 Velocity 23-26 Western Area Power Administration 2

1-12 Western Systems Coordination Council 4 White Rock Canyon: Description 13, 16, 35 Fill material 13, 15 Impact 58, 69, 70 Vegetation 36, 58 Wildlife 36, 58 Wildlife: 36, 57, 58 In desert washes 36 Willow 33 Willow Beach: Vegetation 33 Visitors 45-46 Water level 59, 72, 77 Willow Beach No. 2: Impact 60 Location 47 Willow Beach National Fish Hatchery: Cooling device 54 Interface 29, 54 Profile 20 Temperature 29, 54 Wind energy 7

Yuma antelope squirrel 36 Yuma clapper rail 36, 38, 78

Zooplankton 29, 53

1-13

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T 215 T 215 NevoCa CITY OF LOS ANGELES Spillway SWITCHYARD F.re House •—WO" r Ton loy House

M.W.D. HOOVER Boulder SWITCHYARD Beach Henderson T 31 el DAM Temple TAILRACE DECK T 30 N I Bar Intake EXTENSION Towers T 225

5.C.E SWITCHYARD Ringbolt Rapids

Sloan NEVADA-ARIZONA SWITCHYARD

-- T 23-S. -- Truckers broke Check oreo

Willow Beach

Dump Area

ALTERNATIVES NO. I AND 3

Eldorado Substation (S.C.S.) 'T 25

Dump Area

400. T 22 S M D VICINITY MAP

T 275

Dump Area

EXPLANATION T1 ALTERNATIVE — 500 hov Surface powerplant. T 24N. OREGON : .. ____ _ IDAHO ALTERNATIVE *2 — 350 mw Generator replacing 48 and A9. (260-mw Net Increase) ALTERNATIVE *3 — 500 MW Underground powerplant. L I B k. 1""tieSALT CAS Sell CITY NEVADA • I He C\ 29 5 I Gr... Hopper UTAH 11\ ton fLY PRICE. nc SACAANIENTK C irr I

• RANCISCO T 23 N eCEPAR CALIFORNIA \ CITY eFRESIO i, LAS (Soi9,,r1 Hoover powerplant presently has o nameplate rating of 1, 340 MW. Work N V R. 17 E. .8.18 E. (SSULDEPI I to uprate the \\I plant to 1,800 MW is in progress. Hoover powerplant 305 1 esL AGSTAFF1 \ modification additional capacity would be added to that 1,80C MW SAN IrRNARDINO ARIZONA rating. UNITED STATES X OS ANGELES DEPARTMENT OF THE INTERIOR Ses/r onto:KNIT T 22 N A t BUREAU OF RECLAMATION PdCl;lC iti ITI i _LIMA •TUCSON: ! NT315 • \. HOOVER POWERPLANT i s-- .. U ..1 S, FAbuco MODIFICATION 0 I 1'1„ Katherine LOCATION MAP Landing KEY MAP DWG. NO. 45-300-487 \)ss VI$ 0 5 10 SCALE OF MILES 5 1 , T 325

R 65 F R 66 E lIwnd CitY R 21 W J 5720 W j R i9 W