ltl nru eX' 1506-00055
Hydrogeology and Simulated Effects of Urban Development on Water Resources of Spanish Springs Valley, Washoe County, West-Central Nevada
U.S. GEOLOGICAL SURVEY
Water- Resou rces I nvestigations Repo ft 96-4297
Prepared in cooperation with the NEVADA DIVISION OF WATER RESOURCES
1506-00055 Northeastward photographic views of irrigated lands in southern part of Spanish Springs Valley in (A) 1967 and (B) 1996. Orr Ditch is in foreground. Trailer park seen at left in 1967 view is hidden by trees thirty years later. ln 1996, urban development in the form of a subdivision coexists with irrigated lands. Hydrogeology and Simulated Effects of Urban Development on Water Resources of Spanish Springs Valley, Washoe County, West-Central Nevada By David L. Berger, Wyn C. Ross, Carl E. Thodal, and Armando R. Robledo
U.S. GEOLOGICAL SURVEY
Wate r- Reso u rces I nvesti gatio ns Report 96- 4297
Prepared in cooperation with the NEVADA DIVISION OF WATER RESOURCES
Carson City, Nevada 1997 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary
U.S. GEOLOGICAL SURVEY GORDON P. EATON, Director
Any use of trade names in this publication is for descriptive purposes only and does not constitute endorsement by the U.S. Government
For additional information Copies of this report can be write to: purchased from:
District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 333 West Nye Lane, Room 203 Box 25286 Carson City, NV 89706-0866 Denver. CO 80225-0286 email : [email protected] CONTENTS
Abstract......
Location and General Features of Study Area ...... 2
U.S. Geological Survey Site Designations ...... 4
Geologic Histor General Character of Hydrogeologic Units I 5
Areal Extent and Thickness ...... 2l Hydraulic Properties 2l 26 27 32 Sources and Movement of Ground Water ...... 34 Chemical Composition of Ground Water ...... 42 Ground-$/ater Recharge and Discharge ...... 42
Infltration
Evaluation of the Ground-Water Budget and Yield, 1994 ...... 50 5l 5l 52 Selection of Time Periods and Assigned Recharge and Discharge ...... 52 54 Initial Conditions and Aquifer Properties 58 Simulation of Transient Conditions, 1979-94 6l 6l Simulated Ground-Water Budget 65 68 Limitations of Flow Model 68 Simulation of Responses to Hypothetical Ground-Water Development Scenarios 69 69 70 70 References Cited 77
CONTENTS ill FIGURES
l-6. Maps of the Spanish Springs Valley area, west-central Nevada, showing: L Location and general features...... 3 2. Parceled land with public-water systems and domestic wells and general area of agricultural land use
3. Wells, precipitation stations, surface-water gages, and water-chemistry sampling sites ...... 7 4. Generalized geologic units, structural features, and seismic-refraction lines...... l6
6. Complete Bouguer gravity field...... 20 7 -9. Graphs showing profiles of measured and calculated total-intensity magnetic anomaly and complete Bouguer gravity anomaly, and generalized geologic section:
ll-12. Graphs showing: I l. Water levels for sites 72 and 73, November l993-September 1995..'...' 26 12. Annual precipitation and cumulative departure from average precipitation at Reno airport for 57-year period of record, 1938-94 28 13. Map showing precipitation stations and average annual precipitation 30 l4-16. Graphs showing: 14. Relation of average annual precipitation to altitude for 34 precipitation stations used in determining distribution of precipitation and relation of difference between predicted and measured precipiiation to predicted average precipitation 3l 15. Daily mean discharge of Orr Ditch and North Truckee Drain, May 1992-September 1994,and percent of average annual precipitation at Reno airport, 1992-94...... JJ | 6. Relation of deuterium to oxygen- I 8 in sampled ground water and imported surface water, Spanish Springs Valley and Truckee River...... '.... 34 17-19. Maps showing ground-water levels in basin fill:
20-21. Maps showing change in ground-water level in basin fill: 20. From December l992toMay 1994..... '..'..""""".'"" 39 21. From May 1994 to December 1994...... 40 22. Graph showing general chemical composition of sampled ground water...... '. 43 23. Sketch showing three-dimensional, schematic conceptualization of ground-water recharge and discharge
24. Map showing block-centered finite-difference grid used for ground-water-flow model 53 25-26. Graphs showing assigned monthly rates used as model input for transient simulations:
2i. Map showing cells with assigned ground-water pumpage for municipal, irrigation, and industrial use in annual stress periods representing 1979 and 1994 in model simulations...... 57 28-31. Maps showing: 28. Model cells in layer I used to simulate ground-water recharge in transient model ...... 59 29. Ground-water levels assumed to represent water-level conditions prior to large pumping stresses and used as initial heads in model simulations.' 60 30. Horizontal hydraulic conductivity in layer I used in calibrated transient simulations 62 31. Transmissivity in layer 2 used in calibrated transient simulations.. 63 lV Hydrogeology and Simulated Etfects of Urban Development on Water Resources ol Spanish Springs Valley' Nevada 32-33. Graphs showing: 32. Measured and simulated ground-water levels for selected cells, layer l, during transient simulations...... 64 33. Cumulative percentage of absolute difference between 27 measured and simulated hydraulic heads for monthly stress period representing December 1994 of model simulation. 65 34. Map showing simulated heads in layer I calculated from monthly stress period representing December 1994
3 5 . Cumulative change since I 979 in annual ground-water discharge, recharge, and storage from results of
36. Map showing cells with assigned ground-water pumpage for municipal, irrigation, and industrial use in hypothetical development scenarios 2 and 3 used in model simulations ...... 7 | 37-39. Maps showing model-computed water-level change at the end of 5, 10, and20 years since December 1994 for hypothetical development for simulation with and without flow in the Orr Ditch
40. Graphs showing simulated cumulative depletion in ground-water storage since December | 994 for hypothetical development scenarios l,2,and 3...... 75
TABLES
I . Site number, location, and type of data available for well, precipitation, and surface-water sites, Spanish Springs 8 2. Age,lithology, and generalhydrologic properties of principal hydrogeologic units...... l8 3. Physical properties for lithologic units in geologic section along geophysical profiles. 2l 29 5. Estimated average annual precipitation and ground-water recharge 32 6. Summary of flow for Orr Ditch and North Truckee Drain, 1976-94 JJ 7. Concentrations of chlorofluorocarbons and tritium in ground water and corresponding CFC-model recharge ages.... 4l 8. Concentration of chloride in ground water and precipitation at selected sites...... 46 9. Estimated disposition and budget of imported Truckee River water for 1994...... 47 10. Summary of population and estimated ground-water withdrawals, 1979-94...... 49 I l. Estimated and simulated components of ground-water recharge and discharge, 1994 conditions ...... 50 12. Summary of model-sensitivity simulations at end of 1994...... 68
CONTENTS CONVERSION FACTORS. VERTICAL DATUM, AND ABBREVIATED UNITS
Multiply By To obtain
acre 4,047 square meter acre-foot (acre-ft) 0.001233 cubic hectometer acre-foot per year (acre-fV^yr) 0.001233 cubic hectometer per year cubic foot per second (ft'/s) 0.02832 cubic meter per second foot (ft) 0.3048 meter foot per day (fVd) 0.3048 meter per day foot per mile (fVmi) 0. I 894 meter per kilometer foot squared per day (ft'ld) 0.09290 meter squared per day gallon per minute (gallmin) 0.06309 liter per second inch (in.) 25.40 millimeter mile (mi) 1.609 kilometer square mile (mi2) 2.590 square kilometer
Temperature: Degrees Celsius ("C) can be converted to d€grees Fahrenheit ('F) by using the formula 'F = [.8('C)]+32. Degrees Fahrenheit can be converted to degrees Celsius by using the formula'C = 0.556("F-32).
Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly called "Sea-Level Datum of 1929"), which is derived from a general adjustment of the firsrorder leveling networks of the United States and Canada.
Metric water4uality and geophysical units: g/cm3 (gram per cubic centimeter) mGal (milliGal) mg/L (milligram per liter) pm (micrometer) pS/cm (microsiemens per centimeter at 25" C) mL (milliliter) permil (part per thousand) nT (nanotesla) pCi/L (picocurie per liter) pgll- (picogram per liter)
Vl Hydrogeology and Slmulated Effects of Urban Development on Water Resources of Spanish Springs Valley, Nevada Hydrogeology and Simulated Effects of Urban Development on Water Resources of Spanish Springs Valley, Washoe County, West-Central Nevada
by David L. Berger, wyn c. Ross, carl E. Thodal, and Armando R. Robledo
ABSTRACT that, although recharge from imported surface water prevented water-level declines in the inigated area, Land-use changes and increased ground-water declines from 20 to 60 feet may be expected through- withdrawals are expected as a result of increased out much of the modeled area after 20 years of sim- urban development in Spanish Springs Valley, about ulated pumping. In model simulations without 5 miles northeast of Reno, Nevada. Currently (1994), recharge from imported surface water, 8 percent imported Truckee River water used for irrigation to nearly 20 percent of the basin-fill aquifer would makes up more than 50 percent of the total source of be dewatered after 20 years of hypothetical ground- ground-water recharge to the basin-fill aquifer. The water withdrawal, and water levels long-term estimate of ground-water recharge from would decline more than 60 feet in the precipitation is about 770 to 830 acre-feet per year. southeastern part of the valley. Ground-water withdrawals have increased from about 500 acre-feet in1979 to nearly 2,600 acre-feet in 1994. An estimated 300,000 to 600,000 acre-feet INTRODUCTION of recoverable water is stored in the upper 330 feet of saturated basin fill. Augmented yield of the basin-fill Increasing population in the Reno-Sparks area of aquifer in Spanish Springs Valley, determined for west-central Nevada has resulted in urban development 1994 conditions, was estimated to be about 2,400 in outlying areas. Spanish Springs Valley is undergoing acre-feet, including about 1,400 acre-feet ofsecond- rapid growth because of its proximity to the Reno- ary recharge from imported Truckee River water. Sparks area. To accommodate this additional growth, Estimates of ground-water recharge and dis- land-use changes (from agricultural to suburban) and charge to the basin-fill aquifer were made 1994 for increased ground-water withdrawals are anticipated. conditions on the basis of field and empirical tech- For more than a century, flow from the Truckee River niques and evaluated using a mathematical flow has been imported to Spanish Springs Valley by way of model. The flow model constructed during this study the Orr Ditch for agriculture. Transmission losses from was calibrated principally in accordance with the the On Ditch and infiltration of applied irrigation water hydrologic data observed and collected during 1979- are the largest components of ground-water recharge to 94 because few predevelopment data were available. the basin-fill aquifer in the valley. As ground-water An estimated difference between ground-water withdrawals increase to support urban development recharge and discharge of 1,700 to 2,200 acre-feet and are accompanied with decreases in agricultural in 1994 suggest that an imbalance was created by land use, the potential for ground-water overdraft has ground-water withdrawals. become a concern. As a result, the U.S. Geological Sur- The probable response to land-use changes vey (USGS), in cooperation with the Nevada Division and increased ground-water withdrawals is evaluated of Water Resources, began a 5-year study in 1992 to by simulating three hypothetical development sce- improve the understanding of the water resources in narios. Simulated responses to the scenarios suggest Spanish Springs Valley.
ABSTRACT Purpose and Scope north. The drainage area of the valley floor is about 34 mi" including a small internally drained area in the The purposes of this report are to describe and north part of the valley. analyze the ground-water flow system in Spanish Spanish Springs Valley is bounded on the east by Springs Valley and to evaluate and refine estimates of the Pah Rah Range, whose highest summit, Spanish budget and yield of the basin-fill aquifer. The the water Springs Peak, is about 7,400 ft. Hungry Ridge and its ground-water budget and yield, estimated from field unnamed southern extension make up the western techniques, were determined for data and empirical boundary with summits approaching 6,000 ft. The The report also discusses 1994 hydrologic conditions. northem boundary separating Spanish Springs Valley of a ground-water flow model used to simu- the results from Warm Springs Valley is a narrow (less than 0.5 for a l6-year period late transient-flow conditions mi) topographic divide lying between bedrock out- (1979-94) and for several hypothetical development crops of the Hungry Ridge and the Pah Rah Range. The were designed to scenarios. The selected scenarios southem boundary is bedrock and includes a low allu- the removal of imported surface water and simulate vial divide where an irrigation ditch and drain enter and projected increases in ground-water withdrawal. In exit the study area. scope, the study includes Spanish Springs Valley and parts of the surrounding mountainous area. Hydrologic Agricultural land generally has been restricted to is data, including water levels, ground-water withdraw- the southern part of the valley that encompassed by Valley Ditch, als, precipitation, surface-water discharge, and water- the On Extension of the Spanish Springs (fig. chemistry analyses, were considered in this study. hereafter referred to as the On Ditch l). Water Geochemical techniques were used to determine diverted from the Truckee River for inigation has been (Nevada sources and relative ages of ground water. Geophysical delivered by way of the On Ditch since 1878 return Spanish methods were used to help define the geologic frame- State Journal, 1879). Irrigation flow in North Truckee Drain work and describe the general character ofthe hydro- Springs Valley is collected in the geologic units. and returned to the Truckee River downstream from the City of Sparks. Within the area encompassed by the On Work began in the spring of 1992. Principal work Ditch are several storage ponds where water from the included ( I reviewing published information elements ) ditch is impounded. Excluding the North Truckee well-construction, water-level, and and compiling Drain, no streams within the study area are perennial. pumpage data; (2) installing and maintaining two sur- face-water gages; (3) establishing a well-monitoring Spanish Springs Valley and Spanish Springs Peak network; (4) drilling several observation wells; (5) were named by Alces Blum after several springs on the installing nine precipitation stations and constructing valley floor; the springs were called Spanish Springs by an isohyetal map for the study area; (6) collecting early Mexican shepherds who wintered sheep there ground-water, precipitation, and surface-water samples (Carlson, 1974, p. 221). A land survey made on June for chemical analysis; and (7) constructing a ground- 24,1872, noted the spring area as being I chain long water flow model to test and refine the analysis of the (66 f0 and 50 links wide (33 ft), with numerous other ground-water system within the basin fill. small springs nearby (C.8. Hunter, written commun., 1980). Access to the study area from the Reno-Sparks metropolitan area, hereafter called the Truckee Mead- Location and General Features of Study Area ows, is provided by State Route 445 (Pyramid High- way), which passes through the south and north Spanish Springs Valley is a north-trending basin boundaries and continues north to Pvramid Lake. in west-central Nevada, about 5 mi northeast of Reno, and is tributary to the Truckee River (fig. I )' The study lFormal hydrographic areas in Nevada were delineated sys- area covers 80 mi2 including the Sp3nish Springs Val- tematically by the U.S. Geological Survey and Nevada Division of ley Hydrographic Arear and a 7 -mi' topographically Water Resources in the late l960's for scientific and administrative closed subbasin of the Tracy Segment Hydrographic purposes (Rush, 1968; Cardinalli and others, 1968). The official Area, hereafter called Dry Lakes. The valley floor is 3 hydrographic area names, numbers, and geographic boundaries to 4 mi wide, I I mi long, and the altitude ranges from continue to be used in Geological Survey scientific reports and 4,400 ft above sea level in the south to 4,600 ft in the Division of Water Resources administrative activities.
Hydrogeology and Simulated Etfects of Urban Development on Water Resources of Spanish Springs Valley, Nevada .t 19"45', 1 19'37',30',
39 37 30"
Base irom U S. Geo ogrcal Suruey dala. 1 r 1 00,000-scale, 1 980; O 1 2 3MILES Unrversal TrafsveTse Ny'ercalor projection, Zone 1 1 Shaded re iel base from 1:24.000-scale Digital Elevation l\,4odel |------# sun i iumrnal on lrom northwest al 30 degrees above horizon O 1 2 3KILOMETERS
Nevada EXPLANATION Study area ffi Pond
Basin boundary
Figure 1 . Location and general features of Spanish Springs Valley area, west-central Nevada. Dry Lakes, a subbasin of the Tracy Segment Hydrographic Area, is part of the study area.
INTRODUCTION Urban Development Previous Investigations
Many published and unpublished reports have Development in Spanish Springs Valley through been prepared on the hydrology and geology ofthe about 1960 was virtually non-existent, except for home- study area and vicinity. Descriptions of several reports the southern part the that were, steads within of valley pertaining to the hydrogeology of Spanish Springs and still are, associated with agriculture. Comparison Valley follow. among aerial photographs taken in 1956, 1977, and The first investigation, which described the gen- 1994, and parcel data, showed that general agricultural eral geology and hydrologic properties ofthe rocks and land use within the area serviced by the On Ditch for the the occurrence and quality of ground water, was made most part has remained unchanged, although some addi- by Robinson and Phoenix (1948). Wells within the val- tional acreage has been developed in the southwestern ley were inventoried and chemical analyses of ground- water samples from part. Growth and urban development proceeded at a selected wells were made. ln 1964, W.F. Guyton and Associates prepared a report for fairly slow pace until the late 1970's when a second Sierra Pacific Power Company to determine the feasi- mobile home park was established and the first of five bility of developing ground water to supply proposed subdivisions was started. Population within Spanish urban development in the northern part of Spanish Springs Valley has increased sharply from less than 800 Springs Valley. This study increased the general in 1979 to more than 4.000 in 1990 (U.S. Bureau ofthe knowledge of the distribution and properties of hydro- Census, written commun., 1995). Population in 1994 geologic units in the study area. Rush and Glancy was projected to be about 9,300 (Washoe County (1967), in appraising water resources of the Warm Department of Comprehensive Planning, written com- Springs-Lemmon Valley area, included a reconnais- They presented a mun., 1995). Most subdivisions have been constructed sance of Spanish Springs Valley. ground-water budget for Spanish Springs Valley under around the northern perimeter of the On Ditch, with natural conditions and conditions that incorporated the subdivisions in the southern part of the valley. smaller effects of imported surface water. Hadiaris (1988) generally In contrast, individual home sites are scattered describes the results of a two-dimensional mathemati- in the northern part ofthe basin, in and adjacent to the cal model used to simulate steady-state conditions of surrounding mountains. ground-water flow in Spanish Springs Valley. As of 1994, more than 3,000 houses associated with subdivisions had water supplied by a public utility; U.S. Geological Survey Site Designations however, nearly 1,000 of these are permitted to receive Each U.S. Geological Survey data-collection site water from outside the study area (Washoe County is assigned a unique identification on the basis of geo- Assessors Office, written conmun., 1995). Of the graphic location. Wells and precipitation and surface- public water supply, 1,600 had septic sys- houses with water sites are identified by a local (Nevada) system tems and about 1,400 were served by wastewater treat- and a standard latitude-longitude system. For conve- ment facilities outside the basin. Nearly 200 houses had nience, short site numbers (l to 89) also are used for domestic wells with septic systems. Land-use sumna- sites discussed in this report. ries as of l99l (Kennedy/Jenks/Chilton,1991, table 4- A local site designation is used in Nevada to iden- I ) indicate that 620 acres within the study area were tify a site by hydrographic area (Rush, 1968) and by the designated rural, 810 acres were suburban, and more official rectangular subdivision of the public lands ref- than 1,800 acres were agricultural. (Rural designations erenced to the Mount Diablo base line and meridian. Each site designation consists of four units. The first are defined as having I dwelling unit per 2.5 to l0 acres unit is the hydrographic area number. The second unit and suburban designations are defined as having I to 7 is the township, preceded by N to indicate location dwelling units per I -acre parcel.) More than 46,700 north of the base line. The third unit is the range, acres were classified as non-designated areas. Compar- preceded by E to indicate location east of the meridian. ison of land-use designations for 1979 and l99a $g2) The fourth unit consists of the section number and shows an increase in parceled land with municipal water letters designating the quarter section, quarter-quarter systems and domestic wells. section and so on (A, B, C, and D indicate the
Hydrogeology and Simulated Effects of Urban Development on Water Resources of Spanish Spilngs Valley, Nevada -xN =o- .9. oEv c O:U (5 -X! ao_ xo6 o,d E; I >o o-/ E o 96'.;E o) g Ni O)c l' 6C =Og; SE gE .=o o= oc E.3 32 OCD E> ;€ F E$E =90(E.= E*E 5(U .9(L a EHF bG' U 6.> >6 *atoc -- S (d9 IF t>lu (da96 l=IJ 6E "t 6lui E();io 8,i f' z EF '1- :o I O.q ruE -1_FN XE rrJ g -?i (U I o 50 olo o o .90 E o>\ ? ots ll ooEf tl .3 T Ec) ts 9A v> !o 4l KP r,o! nth EE -(d iEEO=tta 5= -00 6= 'i9oHbE AE .o(, Q(5 G'(!to -9d -oE EE tffit 3A=(5 9a>p 'Irbz aa 'FxEEB EE(U8 ;F E d)(,t Yda =(l) 9E F 3= - qtr E* JT- (L9 €v-C'O9 frE: e .,i E dd;j5N e3, .E'e LA
INTRODUCTION northeast, northwest, southwest, and southeast quar- hydrologic and geologic data and the application of sev- ters, respectively), followed by a number indicating the eral geochemical techniques and geophysical methods. sequence in which the site was recorded. For example, Mathematical models that describe the relation between site 85 N2l E20 26CDBDl is in Spanish Springs precipitation and altitude and that simulate ground- Valley (hydrographic area 85). It is the first site water flow in three dimensions also were used during recorded in the southeast quarter (D) of the northwest this study. General descriptions of the types of data quarter (B) of the southeast quarter (D) of the south- used, collection procedures, and data applications are west quarter (C) of section 26, Township 2l North, presented in the following paragraphs. Range 20 East, Mount Diablo base line and meridian. The standard site identification is based on the Collection of Hydrogeologic Data grid system of latitude and longitude. The number con- sists of l5 digits. The first six digits denote the degrees, Basic data collected consist of depth+o-water and minutes, and seconds of latitude; the next seven digits precipitation measurements; continuous measurements denote the degrees, minutes, and seconds of longitude; of surface-water discharge; and water-chemistry analy- and the last two digits (assigned sequentially) identify ses of ground-water, precipitation, and surface-water the sites within a l-second grid. For example, site samples. In addition, lithologic information was col- at 39"36'37" latitude and 393637119432901is lected during the installation of observation wells and 119"43'29" longitude, and it is the first site recorded from geologic mapping in the field. The site number, in that l-second grid. The assigned number is retained location, and type of data collected from sites used dur- as a perrnanent identifier even if a more precise latitude ing this study are listed in table l. Site numbers and are later determined. and longitude locations are shown in figure 3. Ground-water levels, precipitation, surface-water discharge, and general Acknowledgments water-chemistry data collected as part of this study were published by the U.S. Geological Survey in annual The authors express their appreciation to resi- water-data reports (Hess and others, 1993, p. 382-383, dents of Spanish Springs Valley for their cooperation p.444-447; Emett and others, 1994,p.387-390, p.552- in supplying data and permitting access to their wells. 567;Clary and others, 1995, p. 466-467,p.726-747; Further gratitude is expressed to the following individ- Bauer and others, 1996, p. 704-7 ll). observa- uals for allowing the installation of shallow Depth-to-water measurements were made at77 tion wells and collection of geophysical and hydrologic wells monthly from May 1992 through December 1994 David Kiley, data on their properties: Alan Oppio, and then quarterly through September 1995 (sites l-77, Grecian Iratcabal, and the Capurro family. Information table I ). These data were used to determine ground- Matthew Allen of the on the Orr Ditch was supplied by water flow directions and to characterize the effects of the Federal Orr Ditch Company and by the office of seasonal flows of imported surface water on the shal- were Water Master. Municipal water-supply data low ground-water system. Water levels in several wells furnished by Sky Ranch Utilities and by the Washoe County Department of Public Works, Utility Division. The drilling of several observation wells and collection EXPLANATION of borehole geophysical logs also were provided by the Washoe County Utility Division. Drillers' logs and lffi,tji,ffi Basln fill water-rights information were obtained from the consolldaled rock Nevada Division of Water Resources. I Basln boundary
Sites used in this study-Solid symbol METHODS USED IN THIS STUDY indicates water chemistry (except sites 52, 53, 75). Number corresponds to table 1 Several methods of investigation were used o76 Well (sites 1-77; site 77 is east of map area) during the course of this study to provide information o75 Well (chemistry only; sites 52, 53, and 75) needed to analyze the ground-water flow system and to evaluate the water budget and yield of the basin-fill o83 Precipitation station (siles 78-87) aquifer. These methods included the collection of t88 Surface-water gage site (sites 88 and 89)
Hydrogeology and Simulated Eflects of Urban Development on Water Resources of Spanish Springs Valley, Nevada 1 1 9"45', 1 19"37'30'
T. 22 N.
loe 07 oo T. 21 N. 19 610 \J'^tt ,Spanish Sprin Vallev ois df;,o' " ., 8 &d::?l'
39"37',30" 51 n Ps rf
T 20 N.
T. 19 N.
tructLe Meado*s 2Xu
R. 19 E. R.20 E R,21 E R.22E.
Bas€ from U.S. Gslogi€l Surusy data, O 1 2 3MILES Geology modified trom Bonham (1 969), 1 :100,000-scale, 1980: Universal Transversa Stewart (1980), Cordy (1985), and Mercator projection, Zon6 1 1 F--Lr---+------Bsll and Bonham (1987) O 1 2 3KILOMETERS
Figure 3. Wells, precipitation stations, surface-water gages, and water-chemistry sampling sites, Spanish Springs Valley, west-central Nevada. Site 77 is not shown because it is outside map area.
METHODS USED IN THIS STUDY Tabte 1. Site number, location, and type of data available for well, precipitation, and surface-water sites, Spanish Springs Valley area, west-central Nevada
[Available data: GL, geophysical logs; B precipitation; Q, dischargel QW, water chemistry: WL. ground-water levels. Data from Hessandothers(1993),WashoeCounty(1993),Emettandothers(1994),Claryandothers(1995),andBauerandothers(1996)l
U.S. Geological Survey site designations 1 Site Available Site name number Standard data Local identification (fis.3) identilicalion
Well sites I 84 N22 E2O 25DDCAI 394422119404901 Brown,D. WL 2 85 N2I E2O O2AAACI 394321119415101 O'Hair wL,QW 85 N2I E2O O2DDACI 394240119415001 SSP-9 WL,GL 4 85 N2I E2O IIDABAI 3942021194t5301 SSP-10 WL 5 85 N2I E2O I2DACDI 394154119405401 Wardrup WL 6 85 N21 E2O l3CAACI 3941091 l94l t50l ssP-7 WL 7 85 N2I E2O I4BDDAI 394n7r942t50t SSP-8 WL,GL 8 85 N2I E2O IsDABBI 394111119430301 Sha-Nevagravelpit WL 9 85 N2I E2O 22BADDI 394035119432901 Airport wL,QW l0 85 N2I E2O 23ADAAI 394032119414601 Donovan No. I WL ll 85 N2I E2O 23BCCDI 39402119424601 SSP-6 WL,GL t2 85 N2I E2O 24BDDAI 394023119412001 Donovan No. 2 wL,QW t3 85 N2I E2O 26CDBDI 393917119423601 AlyceTaylorSchool WL l4 85 N2I E2O 26DCCB2 393858119421301 SS-la WL l5 85 N2I E2O 2TCBDAI 39391711943440t SSP-5 WL,GL l6 85 N2I E2O 34CDADI 393813 I 19425301 Hawco monitoring WL l7 85 N2l 820 34DDCCl 393812119425701 Washoe Co. Utilities North WL t8 85 N2I E2O 35ADBDI 3938471 19415 l0l SS-3 WL l9 85 N2t E2035CCADl 393821I19423601 Golden West North WL 20 85 N2I E2O 35CCCDI 393812119424401 USGS-ParkObservation wL,QW 2l 85N2I E2O35DCBAI 3938191 19420501 55-6 wL,QW 22 85 N2l E2l ITCDCCI 394120119385601 Cole WL ZJ 85 N2I E2I 2OBBCBI 394040119392801 Cancilla WL .A 85 N2I E2I 3OABCCI 393944119400701 Armbruster WL 25 85 N2I E2I 3OCAAAI 393927119401301 Mack WL 26 85 N2l E21 3lADCCl 393839119394801 Sanders WL 27 85 N2I E2I 3IBABCI 393903119402001 Casale wL,QW 28 85 N2I E2I 3IBCBCl 393849119404001 Brown,W. wL,QW 29 85 N2r E2l 3rCACAl 393828119401601 May WL 30 85 N2l E2l 3lDDCCl 393812119394001 Colby wL,QW 3l 85 N2O E2O OIAADDl 393800119403601 Washoe Co. Countryside North WL tz 85 N2O E2O OICBABI 393743119413601 Huers WL 33 85 N2O E2O OIDABAI 3937431 l94l l50l Hon WL 34 85 N2O E2O OICACBl 393737119411501 Murray wL,QW 35 85 N2O E2O O2DBBAI 393743119420801 USGS-OppioObservation WL 36 85 N2O E2O O3ACDCI 393738119432101 Washoe Co. Utilities South WL JI 85 N2O E2O O3BCCCI 393744119435101 Falk WL 38 85 N2O E2O O3CDDCI 393720119432701 Springwood Utilities monitoring WL 39 85 N2O E2O O4BBADI 393804119443901 Sullivan wL,QW 40 85 N2O E2O O4CCBBI 393737119445201 Grube WL AI 85 N2O E2O O4DBDBI 393735119441701 Pace wL,QW qz 86 N2O E2O OSDBBC I 393643119453401 Kangas WL 43 85 N2O E2O IOAACB1 393713119430001 USGS-Lazy5aObservation wL,QW 44 85 N20 E20 I0AACB2 393713119430002 USGS-Lazy5bObservation WL 45 85 N2O E2O IOAACB3 393713119430003 USGS-Lazy5c Observation WL 46 85 N2O E2O IOCDABI 393637119432901 KileyNo. I WL 47 85 N2O E2O IODBBCI 393649119432301 KileyNo.2 WL 48 85 N2O E2O IODBBC2 393649119432302 Kiley No. 3 WL 49 85 N2O E2O l IBAAAI 393715119422801 Gaspari No. 2 WL 50 85 N2O E2O I IBDDAI 393655119421901 Gaspari No. I WL
Hydrogeology and Simulated Effects ot Urban Development on Water Resources of Spanish Springs Valley, Nevada Table 1. Site number, location, and type of data available for well, precipitation, and surface-water sites, Spanish Springs Valley area, west-central Nevad+Continued
U.S. Geological Survey I Site site designations number Site name Avallable (fig.3) Local identilication Standard data identification 51 85 N2O E2O I2AAAAI 3937t711940370t SSP-4 wL'Qwcr- 52 85 N2O E2O I2BDDAI 3937001l94ll20l Wingfield Ranch No. I Qw 53 85 N2O E2O I2CAABI 393651 I l94ll40l Wingfield Ranch No. 2 Qw 54 85 N20 E20 I2DBCCl 3936431194l0401 D'Anna wL,QW 55 85 N2O E2O I5DBBBI 393559119430801 KileyNo.4 WL 56 85 N2O E2O I5DBBA2 393559119431902 USGS-Kiley4aObservation wL,QW 57 85 N2O E2O I5DBBA3 393559119431903 USGS-KiL:y4bObservation wL,QW 58 85 N2O E2O I5DBBA4 393559119431904 USGS-Kiley4cObservation WL 59 85 N2O E2O 2IAAAAI 393527119435701 SpringcreekNorth WL 60 85 N2O E2O 21AABC1 393529119441601 BlueGem WL 6l 85 N2O E2O 2IADDAI 393515119435701 SpringcreekAbandoned wL,QW 62 85 N2O E2O 2IBDDAI 3935 l3 I 19443501 Bailey WL 63 85 N2O E2O Z2DBCAI 393459119432201 USGS-lratcabal2 Observation WL 64 85 N2O EzO22DCDCI 3934421 19431001 lratcabal No. I WL 65 85 N2O E2O 2TBBCAI 393434119435201 USGS-CapurroObservation WL 66 85 N2O E2O 2TCACAI 393405119433401 Bria wL,QW 67 85 N2O E2O ZTCCCBI 393400119435401 Brandsness WL 68 87 N2O E2O 34DABBI 3933221 19430801 Winners Corner Exxon WL 69 85 N2O E2I OTCBCBI 3936481 19403301 Sweger No. 2 WL 70 85 N2O E2I OTCCCCI 393631119403401 SwegerNo. I WL 7l 85 N20 E2l 0TDCCAl 393642119395601 TuckerNo.2 WL 72 85 N2O E2I O8BBCAI 3937t41 19393501 SSP-2 wL,QWGL 73 85 N2O E2I OSBBCA2 393714119393502 SSP-2a WL 74 85 N2O E2I I8DABDI 393558119395001 TuckerNo. I WL 75 85N20821 ISDAD I 3935521 19394501 Berry Qw 76 85 N2O E2I I8DADBI 393544119394701 Mills WL 2i7 83 N2O E22 2ICDDDI 39344611931 l70l Tracv WL Precipitation sites 78 84 N22 E2l 3lACABl 3944011 19395401 Bacon Rind Flat P 79 85 N2I E2I O9BACCI 394221119374901 CumowCanyon RQW 80 85 N2l 820 l5CCABl 394100119434801 Hungry Ridge North RQW 8l 85 N2I E2O 29DCDDI 393903119452501 Hungry Ridge South BQW 82 85 N2I E2I 34DBCDI 393903119423101 SpanishSpringsPeak P,QW 83 85 N2r E2035CCDAl 393824119363401 FireStation P 84 85 N2O E2O I4CDBBI 3935451 19423301 Msta P 85 85 N2O E2I 22BCBAI 393522119371901 DryLakes P 86 85 N2O E2O 21ACBCI 393515119443201 OasisTrailerPark P 87 85 N2O E2I 3ODAABI 393418119394101 CanoeHill BQW Surface-water sites3 88 85 N2O EzO 2TCACCI 3933581 19435 l0l On Ditch Q,QW 89 85 N2O EzO ?TCCADI 3934081 19433 l0l North Truckee Drain Q,QW I See report section titled "U.S. Geological Survey Site Designations."
2 Not rho*n in figure 3; outside map area. 3 USGS station numbers: 10348220,Orr Ditch at Spanish Springs Valley near Sparks, Nev.; 10348245, North Truckee Drain at Spanish Springs Road near Sparks, Nev.
METHODS USED IN THIS STUDY in adjacent basins were measured to provide water- Water-chemistry data were collected from 22 level information in areas of possible ground-water ground-water, 5 precipitation, and 2 surface-water movement from or to Spanish Springs Valley (sites l, sites. Ground-water and surface-water samples were 42,68, and77). analyzed for major ions, bromide, stable isotopes of hydrogen and oxygen, tritium, and selected species In cooperation with Washoe County Department of nitrogen and phosphorus. Samples from l9 ground- of Public Works, Utility Division, nine observation water sites were analyzed for chlorofluorocarbons wells were drilled in areas of the valley where geologic (CFC's). Precipitation samples were analyzed for and hydrologic information was sparse. The drilled selected species of phosphorus, bromide, and major depths ofthe observation wells (sites 3, 4, 6,7, I l, 15, anions. Results of the ground-water-chemistry analy- 51,72, and 73) ranged from 185 ft to 565 ft; differing ses, including the results from environmental tracer lengths of 2-inch slotted-steel pipe were installed for samples (stable isotopes, tritium, and CFC's), were sampling access. Lithologic and geophysical logs for used to support the conceptualization of the ground- these observation wells were described by Washoe water flow system determined from ground-water-level County ( 1993). In addition, several shallow holes (sites data. 20. 35. 43, 44, 45, 56, 57, 58,63, and 65) near the On Ditch and inigated fields were augered and 2-inch Field procedures for the collection of water sam- diameter pipe with 2-ft stainless steel screens was ples were similar to those described by U.S. Geological installed by the USGS. Survey (1977, chapters 1,2, and 5) and by Wood measured onsite Precipitation was measured monthly or as neces- (l 97 6). Water-quality variables included (l) temperature, by using a hand-held ther- sary at seven can-type collectors and quarterly at three to +0.5oC; (2) pH, by using a meter bulk-storage collectors (sites 78-87, table l). Each mometer, accurate with digital readout, accurate to +0.1 unit; (3) alkalinity collector contained a mixture of light oil and ethylene (reported as calcium carbonate, bicarbonate, and car- glycol to prevent freezingand evaporation. Most pre- by incremental-pH titration of 50-mL filtered cipitation sites were either on low hills or at higher alti- bonate), sample water with a field instrument, accurate to tudes in mountains that border the study area. Site 83, +l mg/L as CaCO3; (4) specific conductance, by using however, is on the valley floor (fig' 3) and is maintained a meter with digital readout, accurate to +l pS/cm; and by personnel at the Spanish Springs Valley Fire Station. (5) dissolved oxygen, by digital field instrument, accu- Precipitation data were used in developing a precipita- to 10.1 mg/L. Field instruments were calibrated tion-altitude relation for the study area. The period of rate before each use according to methods record for most precipitation data is luly 1992 through immediately described by Wood (1976). Except for alkalinity, September 1995. Bulk-precipitation (dry and wet fall) which is titrated, field measurements of surface-water collectors similar in design to those described by Lik- chemistry were made instream and measurements ens and others (1977 , p. l6) were installed at the pre- of ground-water chemistry were recorded using a flow- cipitation sites to collect samples for water-chemistry through cell. At each well, a minimum volume equiva- analyses. Results from the water-chemistry analysis lent to three times the volume of water in the well were used in a chloride-balance technique for estimat- allowed to discharge prior to sample collec- ing ground-water recharge from precipitation. casing was tion. Ground water was then pumped through the flow- stage-recording devices were used to Continuous through cell and field measurements of water tempera- on the basis of stage and channel compute discharge ture, electric conductivity, dissolved oxygen, and pH instantaneous or mean daily geometries where either were recorded to verify that these properties had stabi- be determined. Daily-mean discharge discharges could lized. Stable measurements were assumed to indicate (site 88) as it enters Spanish Springs of the Orr Ditch that the discharging ground water was representative of the North Truckee Drain (site 89) as it Valley and of water from the aquifer. Field-measurement techniques were computed from April 1992 to leaves the valley and instruments were quality-assured through annual miscellaneous discharge September 1995. In addition, participation in the U.S. Geological Survey National measurements using a standard USGS wading rod Field Quality Assurance program (Janzer, I 985)' and flow meter were made along the On Ditch as it traverses the valley floor. These measurements were Samples for determination of calcium, magne- made to estimate ground-water recharge by transmis- sium, sodium, potassium, sulfate, chloride, fluoride, sion losses from the On Ditch. silica, boron, bromide, orthophosphateo and selected
Hydrogeology and Simulated Elfects of Urban Development on Water Resources of Spanish Springs Valley' Nevada species of nitrogen (ammonia, nitrite, nitrate) were recharge water at the time when infiltrating water no passed through 0.45-pm pore-size capsule filters and longer is in contact with air. In general, pumps that collected in clean polyethylene bottles after rinsing might affect the pressure of sample water and contact with filtered sample water. Samples for cation analysis with most plastics, rubbers, greases, and oils were were collected in acid-washed polyethylene bottles and avoided. acidified with nitric acid to pH of about 2. Samples for determination of nitrogen and phosphorus were col- lected in opaque polyethylene bottles (to which mercu- Geochemical Techniques ric chloride was added as a biocide), immediately iced, and shipped to the laboratory within 5 days to minimize Water-chemistry characteristics, such as stable microbial degradation. Samples for determination of and radioactive isotopes, chloride ions, and CFC's, that major ions, boron, bromide, silica, and species of nitro- were determined as part of this study were used to eval- gen and phosphorus were shipped to the USGS uate infened recharge sources and volumes and National Water Quality Laboratory in Arvada, Colo., ground-water ages using documented geochemical for analyses (Fishman and Friedman, 1989). Quality- techniques described in this section. Appropriate data control procedures used in the laboratory are described for application of these geochemical techniques were by Friedman and Erdmann (1982) and Jones (1987). collected in Spanish Springs Valley during 1992-94. Unfiltered water was collected in 60-mL glass The stable isotopes evaluated were oxygen-18 bottles for stable-isotope analysis (oxygen- 18 relative l80/l60) relative to oxygen- l6'( and deuteriu- ltryO.o- to oxygen- l6 and deuterium relative to hydrogen- l ) gen-2) relative to hydrogen-l (D/tH). Each ratio is and in I -L high-density polyethylene bottles for tritium determined for a sampled water and is then related analysis. Polyseal caps were used on these bottles to mathematically to the comparable ratio for an intema- prevent evaporation of the sample. Stable-isotope anal- tional reference standard known as Vienna-Standard yses were done by the USGS isotope fractionation Mean Ocean Water (V-SMOW). By convention, the project in Reston, Va. Hydrogen-isotope ratios were computed results are expressed as delta oxygen- l8 determined using a hydrogen equilibration technique (6'oO) and delta deuterium (6D);the units of measure described by Coplen and others (1991) and oxygen- are parts per thousand (abbreviated "permil" or o/oo). isotope ratios were determined using the CO2 equili- The terms "isotopically heavier" and "isotopically bration technique described by Epstein and Mayeda lighter" are relative and are used for comparing the (1953). Samples collected for determination of tritium composition of water samples. A negative delta value (rH), the radioactive isotope of hydrogen, were ana- indicates that the sample water is isotopically lighter lyzedby the USGS Tritium Laboratory in Reston, Va. than the standard (that is, the sample has a smaller pro- Electrolytically enriched samples were analyzed by the portion of oxygen- l8 or deuterium relative to oxygen- liquid scintillation counting method (Thatcher and oth- l6 orhydrogen-l than the standard). Because SrdO and ers, 1977). 6D measure relative isotopic compositions of the two Samples for determination of chlorofl uorocarbon elements that constitute the water molecule (hydrogen concentrations were collected with an apparatus that and oxygen), they are ideal tracers of water movement excludes contact with air, and samples were flame- where the isotopic fractionation of both are usually sealed into borosilicate-glass ampules for transport and covariant. Isotopic fractionation results from physical, storage prior to analysis (Busenberg and Plummeq chemical, or biological processes, which cause the 1992,p.2257-2258). CFC analyses were done by the delta value of the stable isotopes of water to change. USGS Chlorofluorocarbon Laboratory in Reston, Va., For example, during the physical process of evapora- using a purge-and-trap gas chromatography procedure tion, 5'oO increases because 'oO is lighter and leaves with electron-capture detector (Busenberg and Plum- water at a faster rate than the heavier '60. Given two mer, 1992, p.2259-2260). Precautions were taken infened ground-water flowpaths composed of water regarding the type of pump used for ground-water sam- with different isotope compositions, the proportion of ple acquisition and types of material the sample water flow that each flowpath may have contributed to a might contact prior to its entry into the sampling appa- receiving flowpath can be evaluated on the basis of an ratus. These precautions were necessary because the isotopic mass balance. In addition, 6l80 and 5D com- use of CFC's as an age-dating tool is dependent on positions are useful for indicating ground-water source atmospheric concentrations and the temperature of areas.
METHODS USED IN THIS STUDY 11 Tritium is a radioactive isotope of hydrogen (5) atmospheric sources (both dry and wet fall; with an atomic mass of 3 and a half-life of 12.43 years Dettinger, 1989, p. 57). In Spanish Springs Valley, (Plummer and others, 1993, p.257). Tritium is pro- atmospheric sources of chloride are dominant and duced naturally at low levels in the atmosphere by runoff is negligible. Careful sample-site selection and interaction of cosmic rays with nitrogen and oxygen sample handling were used to avoid interference from (Drever, 1988, p. 379), but thermonuclear-weapons other sources. On the basis of the chloride-balance testing between 1952 and 1969 introduced amounts of method, the volume of recharge can be approximated tritium into the atmosphere that produced concentra- as follows: tions in precipitation as much as three orders of magni- R P(Clp/Clr) (1) tude greater than natural levels. This increased tritium = , serves as a marker of the timing of ther- concentration where, testing and thus provides a useful monuclear-weapons R is recharge, in acre-feet per year; indicator of the age (the time since the water has been P is total precipitation that falls in recharge- isolated from the atmosphere) of ground water. source area, in acre-feet per year; In 1993, mean levels of tritium in precipitation Cf is chloride concentration in bulk precipitation, were approaching the pretesting level of about in milligrams per liter; and 25 pCilL (Portland, Oreg., 16pCilL1, Albuquerque, C/, is chloride concentration of recharge water, in N. Mex., 37 pCilL; Robert L. Michel, U.S. Geological milligrams per liter. Survey, written commun., 1995). Tritium generated CFC's are relatively stable, volatile, organic com- prior to thermonuclear-weapons testing would have pounds that are present worldwide as a result of contin- decayed to levels of about I pCilL in 57 years. Samples uous releases to the atmosphere since the 1930's. No collected in 1993 from Spanish Springs Valley having natural sources of CFC's are known, which makes tritium concentrations less than I pCi/L are older than CFC's useful age-dating compounds for hydrologic 57 years; concentrations between I and l0 pCi/L rep- investigations (Plummer and others, 1993, p.268). resent ground water that is either a mixture of pre- and Dichlorodifl uoromethan e (CCI2F or CFC - I 2) was post-therrnonuclear weapons testing water or water 2 the first CFC compound manufactured. Production of that is about 38 to 57 years old; concentrations between trichlorofluoromethane (CCI3F or CFC-l l) began in l0 and 100 pCi/L represent water that is either a mix- the 1940's. These two compounds account for about 77 ture of pre- and post-thermonuclear weapons testing percent of the total CFC production. A third CFC com- water or water that is younger than 38 years; and con- pound--+richlorotrifl uoroethane (C2Cl3F3, or CFC- centrations greater than 100 pCi/L represent water I l3Fwent into production in the 1960's and accounts from 1958-59 or 1962-69 (Welch, 1994,p.16). for the remaining 23 percent of the global CFC market. The chloride-balance method was used in the All CFC's eventually are released to the atmosphere, present study as a reconnaissance effort to complement where they become partitioned into the hydrosphere by other techniques for estimating natural recharge. gas-liquid exchange equilibria. In 1990, atmospheric Because the concentration of chloride dissolved in volume fractions of CFC-12, CFC-ll, and CFC-ll3 ground water generally is not affected by sorption or were about 480, 285, and,77 parts per trillion, respec- ion-exchange processes, it has been used as a natural tively, and these levels have been increasing at an aver- tracer for estimating ground-water recharge from pre- age rate of about 3.7 percent annually (Plummer and cipitation, assuming that all sources of chloride are others, 1993, p.268). Low analytical reporting levels known (Dettinger, 1989; Claassen and others, 1989). (l pglL for CFC-12 and CFC-l l), relatively smooth, This method is based on the balance between total monotonic increase in atmospheric releases, resistance chloride concentration in bulk precipitation (dry and to degradation and transport retardation, and relative wet fall) that falls in recharge-source areas and chloride ease of reconstructing atmospheric concentrations concentration in ground water in and near recharge make CFC's useful as hydrologic tools for identifying areas. Potential chloride sources to ground water ground water that has recently received recharge and include (l) dissolution of evaporite minerals, (2) estimating the timing of recent ground-water recharge. weathering of nonevaporite minerals, (3) mixing Detection of as little as 0.01 percent modern water in with formation water, (4) anthropogenic sources a mixture with pre- 1940 ground water is possible (for example, road salt, wastewater leachate), and because of the low analytical reporting level.
Hydrogeology and Simulated Etlects ol Urban Development on Watel Resources ol Spanish Springs Valley, Nevada The presence of CFC-12 indicates that a portion of the of local industrial releases. Likewise, sewage effiuent sample water is composed of water that was recharged and (presumably) septic-system leachate can contain since 1940; CFC-l I indicates recharge since 1945; CFC concentrations that are orders of magnitude and CFC- I l3 indicates recharge as recent as 1966. greater than expected concentrations (Plummer and The age (time since infiltrating water recharged others, 1993, p. 272) due to domestic use of propellants an aquifer) of ground water may be estimated with a in aerosol cans. These sources of CFC's can result in precision of +l-2 years because the relatively smooth, CFC-model ages that are younger than the actual age of monotonic increase in atmospheric releases is known ground water. Relatively few CFC-discharging indus- (reconstructed from production records from 1940 to tries are based in northern Nevada and those that are 1975 and from atmospheric measurements since 1975; have a minimal effect on atmospheric levels. However, Busenberg and Plummer,1992). This "CFC model" of septic systems are relied on for disposal of domestic recharge age assumes that infiltrating water maintains waste and wastewater in some parts of Spanish Springs equilibrium with air in the unsaturated zone during Valley, representing a potential source of CFC intro- recharge-an application ofthe process ofgas solution, duction into ground water. based on Henry's law solubilities of CFC in water. The temperature at the base of the unsaturated zone is required to define the Henry's law solubility constant Geophysical Methods for nonstandard conditions. A recharge temperature of lOoC was assumed for deeper wells sampled for the In defining the ground-water flow regime of a Spanish Springs Valley investigation on the basis ofthe basin-fill aquifer system, the hydrogeologic framework long-term mean temperature for the weather station is described in terms of flow conditions at the bound- at the Reno-Tahoe International Airport (hereafter aries of the system, together with the hydrologic prop- referred to as the Reno airport). Shallow wells (less erties of the basin fill. Lateral boundaries lie along the than 45 ft below land surface) within irrigated areas periphery ofthe valley floor and the bedrock boundary were assigned a recharge temperature of l4oC to reflect lies beneath the basin fill. Because most wells within the temperature of infiltrating inigation water. The the study area do not penetrate through the basin fill to measured CFC concentration of a water sample can bedrock, geophysical methods were used to determine be converted to an equivalent air concentration at the thickness of the basin fill and to improve the knowl- appropriate recharge temperature by using the solubil- edge of the bedrock geometry. Geophysical methods ity of the compound. By comparing the equivalent air used for this study are gravity, magnetic, concentration to an atmospheric air-concentration and seismic refraction. Intrinsic differences in curve, the air concentration can be equated to a density, magnetic susceptibility, recharge date or age (Cook and others, 1995, p. 432). and seismic velocity are used by these Details of CFC-model age-dating are described by methods to define the contact between hydrogeologic Busenberg and Plummer (1992). units. Borehole-geophysical logs also were collected and used to characterizethe hydrogeologic units found Recent efforts to characterize transport properties during drilling of observation wells. of CFC's indicate thatCFC-12 was the most conserva- tive, CFC-l I shows degradation in an organic-rich Gravity and aeromagnetic data were evaluated by unsaturated zone and in anaerobic ground water, and qualitatively inspecting anomaly maps of the gravity CFC- I l3 shows retardation due to sorption (Cook and magnetic fields within the study area and by geo- and others, I 995, p. 432-433). Soil and aquifer charac- physical profile modeling. The anomaly map of the teristics in Spanish Springs Valley suggest that organic gravity data are the complete Bouguer anomaly, which content is relatively low, but some wells did have dis- have been corrected for latitude, elevation, and terrain. solved-oxygen concentrations of less than I mg/L. Rel- The magnetic data are presented as total magnetic ative agreement between CFC-model ages determined intensity or field strength. Anomalies within a gravity with CFC-12 and CFC-11 indicates that these com- or magnetic field are perturbations represented by pounds act conservatively. highs and lows in an otherwise uniform field. They pro- Water recharged in urban areas may contain con- vide information about the subsurface distribution and centrations of CFC's in excess of expected concentra- general geophysical character of hydrogeologic units. tions due to equilibrium with tropospheric air because Gravity data obtained during this study and in earlier
METHODS USED IN THIS STUDY 13 studies (Saltus, 1988) were used in combination with changes in relative grain size. These changes in grain aeromagnetic data (Hildenbrand and Kucks, 1988) to size may represent contacts between different hydro- create the anomaly maps. geologic units. Units composed of mostly coarse- grained deposits have a different response on the logs The gravity and aeromagnetic data also were used than fine-grained deposits. This allows a qualitative in an interactive geophysical profile modeling program estimate on the relative ability of different units to (Webring, 1985) that fits theoretical gravity and transmit water. Acoustic transit-time logs can be used magnetic responses from a geologic model to measured to provide information about lithology and porosity gravity and magnetic data. A mathematical representa- under a wide range of conditions. Transit times mea- tion of the geologic model includes locations of several sured by an acoustic log decrease with an increase in rock types as well as physical properties (bulk densities rock hardness and cementation. Caliper logs provide a and magnetic susceptibilities) of the rock. The geo- continuous measurement of diameter of uncased drill physical modeling during this study used three profiles, holes. Additional information on the application of across the northem, central, and southern parts of borehole geophysics to ground-water investigations is Spanish Springs Valley. The profiles were selected so presented by Keys (1990). that at least one well penetrating bedrock was inter- sected along the profile and used as a control point. Surficial geology at and near land surface and drill-hole Hydrologic Models information were used to constrain the model in terms of basin-fill thickness. Although the model results are To determine the distribution of precipitation in non-unique, additional constraints on the model were Spanish Springs Valley, precipitation data for 34 sta- provided by simultaneously using two geophysical tions, including 9 in the study area, were analyzed to methods--gravity and magnetics-that measure and develop a mathematical relation between precipitation respond to different properties ofthe subsurface geol- and altitude. Stations range in altitude from 3,900 ft to ogy. Once the adjusted modeled profiles coincided with 6,960 ft. Those stations outside the study area were the conceptualizationof the subsurface that was consis- selected because they lie in the rain shadow of the tent with available data, the profiles were used to guide Siena Nevada, as does Spanish Springs Valley. (Areas the development of a map showing basin-fill thickness. in a rain shadow lie on the lee side of a topographic Additional description of this type of gravity- and obstacle where the rainfall is noticeably less than on the magnetic-profile modeling is presented by Schaefer windward side.) The distribution of annual precipita- and Whitney (1992, p. 5). tion was used to estimate the potential for ground- water recharge from precipitation within the study area. Seismic refraction was used at two sites to pro- vide detailed information about the condition of the The U.S. Geological Survey modular finite- flow boundaries beneath the low alluvial divides at the difference model commonly called MODFLOW north and south ends of the valley. Determining the (McDonald and Harbaugh, 1988) was used to simulate thickness of basin fill beneath these areas aided in esti- ground-water flow through the basin-fill aquifer in mating the possible movement of ground water leaving Spanish Springs Valley. The digital model can simulate or entering the study area through basin fill. A third flow in three dimensions and was used to test the con- seismic refraction line was done to determine depth to ceptual model of ground-water flow developed during bedrock prior to installation of two observation wells this study and to estimate effects of hypothetical (sites 72 and 73). Additional information on the use of changes in land-use patterns and ground-water with- seismic refraction in water-resources investigations is drawal. General features of the ground-water flow presented by Haeni (1988). model of the basin-fill aquifer in Spanish Springs Valley are explained in the section "Simulation of Borehole-geophysical logs were collected in six Ground-Water Flow" observation wells drilled during this study (sites 3, 7, 1 l, 15, 51, and 72) and are presented in a report by Washoe County (1993). Borehole geophysics used in HYDROG EOLOGIC FRAMEWORK this study include caliper, natural-gamma, spontane- ous-potential, acoustic, and resistivity logs. In general, The geologic history of western Nevada and par- responses on natural-gamma, spontaneous-potential, ticularly the Spanish Springs Valley area is complex. and resistivity logs can be used, in part, to determine The area is situated in a transitional zone between the
14 Hydrogeology and Simulated Elfects of Urban Development on Water Resources of Spanish Springs Valley, Nevada Basin and Range and Sierra Nevada physiographic Valley is indicated by steep increases in basin-fill thick- provinces. Structural features associated with these ness near the contact between basin fill and consoli- provinces, in part, define the hydrogeologic framework dated rock along the west side of the study area. ofthe study area. Forpurposes ofthis report, five major Although extensional faulting is thought to have devel- geologic units identified in Spanish Springs Valley oped present-day topographic features, fault systems were divided into two general groups on the basis of associated with the Walker Lane also have created a their hydrogeologic properties: (1) consolidated rock, high degree of structural deformation. Faults that bor- which commonly have low porosity and permeability, der the Dry Lakes area and other faults in the southeast- except where fractured; and (2) basin fill, which gener- ern part ofthe study area that generally trend northeast ally has high porosity and transmits water readily. The (fig. 4) may be related to the Olinghouse Fault Zone, a areal distribution of the five geologic units is shown in left-lateral conjugate shear zone of the Walker Lane figure 4 and general hydrologic properties are pre- (Bell, 1981, p. 38). As a result of this combined defor- sented in table 2. mation, bedrock permeability has developed adjacent to and within highly fractured zones. In other places, Geologic History and Structural Setting faults may act as barriers to ground-water flow because ofcementation along fault surfaces within basin fill and Outcrops of rocks older than Mesozoic age are because of the offsetting of deposits with contrasting sparse in western Nevada and are not found within the permeabilities. study area. Consequently, geologic evidence from adjacent areas is used to describe the region during that General Character of Hydrogeologic Units time. Stewart (1980, p. 35-36) suggests that, during pre-Mesozoic time, western Nevada was the site of Fractured consolidated rock and the unconsoli- deep-water deposition with little tectonic activity. Dur- dated sediments that constitute the basin fill together ing most of the Mesozoic era, tectonic activity, which make up the ground-water reservoirs recognized within and thrustinE, may included compressional folding the study area. However, basin fill cunently forms the have been continuous. The oldest rocks exposed within principal water-bearing hydrogeologic unit. the study areaare metavolcanic and metasedimentary rocks of late to middle Mesozoic age (Triassic and Consolidated Rock Jurassic periods) that were regionally metamorphosed prior to intrusion by granitic plutons during the late Tertiary rocks make up most of the consolidated Mesozoic (Cretaceous period; Bonham, 1969, p. 42). rock exposed in the study area (fig. a); they are gener- A second period of deformation associated with exten- ally of volcanic origin and have intercalated lenses of sional faulting formed the present-day topographic sedimentary rocks. The Pah Rah Range consists almost features ofthe study area, including the structural entirely of Tertiary rocks, which can be characterized depressions underlying Spanish Springs Valley. This by high-amplitude magnetic anomalies (fig. 5). These period of deformation began during the middle to late rocks generally have little or no interstitial porosity, Tertiary period and has continued to the present (Bon- except where volcanic-flow units have abundant vesi- ham,1969,p.42). Tertiary volcanic rocks consisting of cles. Interbedded sedimentary rocks of the Tertiary unit several types of flows and tuffs interbedded with clastic consist mostly of fine-grained, partly consolidated sediments were extruded and deposited unconformably lacustrine deposits with low permeability, but may on the Mesozoic granitic and metamorphic rocks store a moderate amount of water. within the structural depressions. Most of the basin fill The complete Bouguer gravity field shown in fig- accumulated as a result of ongoing deposition of detri- ure 6 indicates that the volcanic rocks that compose tus from surrounding mountains bordering Spanish most of the Pah Rah Range are relatively less dense Springs Valley. (greater negative Bouguer values) than the intrusive The Spanish Springs Valley area lies between rocks that make up the western boundary and volcanic major tectonic structures of the Siena Nevada Frontal rocks ofthe southern boundary (fig. 4). This finding Fault Zone and the Walker Lane (Bell, 1981, p. 35). suggests that the northern and central parts ofthe Pah Range-front faulting associated with the formation of Rah Range are composed of a substantial amount of the structural depression beneath Spanish Springs low-density material. In addition, magnetic signatures
HYDROGEOLOGIC FRAMEWORK 15 , .t ir! tan tl l,!t lli tr rr :. I \..1. I I I !il r. I a' --jc -' B .rt !.1 rl a, '1r".-:\
nu Oircn
\= o :
\--Jo.ror Truckee Meadows ''t'ckee ''
Base trom U.S. Geological Survsy data, 0 1 2 3MILES Geology modified lrom Bonham (1969), 1 :100,00Gscale, 1980; Univereal Transveree Stewart (1980), Cordy (1985), and Memtor prciection, Zone 11 F-r--r-r---i------Bell and Bonham (1987) O 1 2 3KILOMETERS
Figure 4. Generalized geologic units, structural features, and seismic-refraction lines, Spanish Springs Valley, west-central Nevada.
16 Hydrogeology and Simulated Efiects of Urban Development on Water Resources of Spanish Springs Valley, Nevada of the Pah Rah Range indicate that the volcanic rocks As a result of structural deformation, secondary that compose the southern boundary may be a different permeability in the form of fractures has developed lithologic unit than those that compose the central and within the consolidated rock. In localized areas, con- northern parts. solidated rock may be capable of storing and transmit- The difference in geophysical responses of the ting large quantities of water. For example, wells in volcanic rocks can be seen on profiles shown in figures fractured volcanic rocks beneath the southeastern part 7 -9. On the basis of geophysical interpretations and of the valley reportedly have produced an average 300 information from drillers' logs, Tertiary rocks that to 400 gaUmin and as much as 1,500 gaVmin during a make up the Pah Rah Range were modeled as two sep- 5-day aquifer test (W.E. Nork, Inc., 1988a; site 70, fig. arate lithologic units (units 3 and 4 in figs. 7-9 and table 3 of this report). Anomalous spikes on the focused- 3) that extend beneath the eastern and southern parts of resistivity and acoustic logs collected by Washoe the valley. Lithologic unit 4, which represents volcanic County (1993, p. 5) at well7} suggest that the volcanic rock, was used to simulate measured magnetic and rock is highly fractured and that it may yield water in gravity highs on profiles B-B' and C-C centered at the interval between 180 and 315 ft. Below this inter- about the 4-mi mark along the profiles (figs. 8 and 9). val, the rock has considerably fewer fractures and pre- These measured highs are assumed to be caused by a sumably lower permeability. However, buried northern extension of volcanic rocks of the most con- solidated rock in the study area produce southern boundary and, as a result, are assumed to have about l0 to 40 gaVmin different geophysical properties than volcanic rocks and the probability of intercepting fractures represented by lithologic unit 3. The measured mag- within consolidated rock for developing high-yield netic and gravity lows along profile A-A'were simu- wells is low. lated by lithologic unit 3 (fig. 7). This interpretation of A relatively transmissive hydraulic connection two volcanic units is in agreement with the geologic between basin fill and volcanic rocks in the southeast- map of Bell and Bonham (1987), who differentiated the ern part of the basin was suggested by pumping effects Lousetown Formation of the Pah Rah Range from the on vertical gradients measured in nearby observation Alta Formation, which forms the southern boundary of wells. Hydrographs for November 1993 through Sep- the study area. Although detailed investigation of the tember 1994 from site72, which is a well screened in hydrologic character ofthese Tertiary volcanic rocks is fractured volcanic bedrock, and site 73, which is a well beyond the scope of this study, their hydrologic impor- screened within the overlying basin fill, are shown in tance at a regional scale may be significant. Cretaceous figure 11. These wells are next to each other about 0.5 intrusive rocks, which form the western and northern mi from the contact of the basin with rocks boundaries (fig. 4), and which were modeled to under- fill of the Pah Rah Range (fig. lie much of the study area, have virtually no interstitial 3).The upward vertical gradient measured between permeability. Thickness of the basin fill is presented in the two wells is interpreted as figure 10. ground-water recharge to the basin-fill aquifer gener- ated within the Pah Rah Range to the east. The gradi- ent, however, was reversed in response to ground- EXPLANATION water pumping in the springs area during the 1994 irri-
Younger alluvium (Holocene and Pleistocene) gation season (April through September). During 1995, no additional ground water was withdrawn in the Older alluvium (Pleistocene) springs area; consequently, the vertical gradient between sites 72 and73 returned upward. I Volcanic and sedimentary rocks (Tertlary) w Intrusive igneous rocks (Cretaceous) Basin Fill E Metavolcanic and metasedimentary rocks (Jurassic and Triassic) The structural depression occupied by Spanish Basin boundary Springs Valley is partly filled by interbedded deposits of sand, gravel, clay, and silt derived primarily from '---- Fault lines-Ball on downthrown side. Dashed adjacent where approximately located mountains. These deposits form the basin-fill aquifer, which is bounded and underlain by consoli- c- Selsmic-refraction line dated rock.
HYDROGEOLOGIC FRAMEWORK 17 o .c bF: ! ! o CL o CL sE c .9 EiaE Er o o It agggtgggEEaggiEigiie-9flesiEE: E a€; si$ (! p E E€!EegE* (! (! #gi o co z (to t caseOA a:rcrE$e i*EEaiH: FEEET EEi c o E !-q F^ q oP rB't E U'S a d'=;'i e E (Do35 9 b:- F F 9i:='a= g;r$=€i'g (U€-o0 EpF*, (Da af €g.g P: i'g rr E F I e E.9 ;= o 'j Et?;:sE: E5* i$sE$ oz (, :€ r H > ; E.e i -=a c Fj g;E g;{EE€tF EEtcE o *.EI:=E"E;#A PoEE EEg (,: e5 o L.; o €!E;EE€€ gEE g€aig 6E F€i€Fi;a€ a€EiE.€?€ _cg, ;H.E;: S16s rsj s::;: :( 'i >. >.'=- * = E q; .? (o6cbo E9g 9 F E F90- g!€g g€;E E E gB : E€ € .o: : € E6tr E iEE c6 =E= I! a oF -- cq 2- 9 E'H xe .F od E R'="" iER€E i iEd- o = ErEi;€Ei=EE.* sea (DE e G .= ;i (g o; s'a ao.Eflt= ?! *5'E - EiEIi€P€EEFEe =6xr 5E 6 3 l-u EEg -c ctt E 6 el Eb d -9 E FoE '66E o E I.e ,q 3 E'F g cv €€E!€E EEEgE EEg '= ,: = =g:8.Z 6H-:'o F E og cx= F:q+ v::g E; g,E E5" E}EE €{.e€ €; i qag E'*iEi''EiEgs*E o 6 g E€g E E ! E E i c; € s € €€s oo, E€gE3f Fgg .V
I b ,lza =c x 3 o F. OE .9 or.E E) !F o o d0) o o o0 FU a I C) bo >o o ? o s otV o o ..9 o ER o 60 6ta ct) I h o oF H# VE o tr o on(EA ,{.) (-) F=
18 Hydrogeology and Simulated Effects of Urban Development on Water Resources of Spanish Springs Valley, Nevada 1 1 9.45' 1 19.37',30',
;:,1^..$
j $ ,s\ !lj
i,'{ i lii r\fr-- \1\! I N/ wN\' "' \:i1.:::
\,..W\ 1\\\'q- :/.,t.1 ") ':.7:'i..:aiQ-;;--"-j ;22::---:::-:-,,-:..':ill* i,a.---* ffi)T 7'tr1(::-:', 1f'
Truckee Meadows
Base from U.S. Geological Surv6y data, O 1 2 3MILES Geology modified lrom Bonham (1969), '| :100,000-scale, 1980:Universal Transverse Stewarl ( 1 980), Cordy (1 985), and Mercator prcjection, Zone 1 1 F-r-Lr---+------Bsll and Bonham (1987) O -I 2 3KILOMETERS EXPLANATION
ffi.N Basln flll Llno ot egual magnstlc IntensltlFshows total-intensity magnetic lield of Earth relative rock I Consolidated to arbitrary datum (1,000 feet above land Basin boundary surface). Interval, in nanoleslas, is variable. Magnetic contouring by D.L. Berger, 1994; A-A' Location ol geologlc sectlon- based on data lrom Hildenbrand and See ligures 7, 8, and I Kucks (1988)
Figure 5. Total-intensity magnetic field, Spanish Springs Valley area, west-central Nevada.
HYDROGEOLOGIC FRAMEWORK 19 1 19"37',30',
u"#
39"37'30',
4Xuu Truckee Meadows
from Bonham (1969), Base trom U.S. G€ological Survey data, O 1 2 3MILES Geology modifi€d Stewart (1980), Cordy (1985), and 1 :'l 00,000-scale, 1 980;Universal Transverss Bell and Bonhaln ('1987) Mercator prcieclion, Zone 1 1 F--r-L-T--/------r O .I 2 3KILOMETERS
EXPLANATION
Basln flll /l:- Lines of equal Bougu€r gravlty anomaly- l?im -..1 Interval 1 millical, at density of 2.67 grams I Consolldated rock per cubic centimeter. Gravity contouring by D.L. Berger, 1994: based in part on data Basin boundary from Saltus (1988) A-A', T::?,il:3?:tn*oT"''*
Figure 6. Complete Bouguer gravity field, Spanish Springs Valley area, west-central Nevada'
20 Hydrogeology and Simulated Etlects of Urban Development on Waler Resources of Spanish Sprlngs Valley, Nevada Table 3. Physical properties for lithologic units in which transverses the northern part geologic section along geophysical profibs, Spanish of this feature, sug- Springs Valley area, west-central Nevada gest that the maximum thickness is at least 1,000 ft. In general, the basin fill is thickest beneath the western Denslty Magnetlc part of Spanish Springs Valley and thins toward the east. Body ilodeled (grams susceptlblllty Beneath the southem part of the valley, depth to bed- No. llthology percubic (centimeter{ram- centlmeter) second unlts) rock is less than 100 ft and becomes shallower toward the southem boundary. On the basis of data from an Proffle A-A'(ffgure 7) abandoned well in the Dry Lakes area, unsaturated I Granitic rocks 2.75 0.0009 basin fill is at least 350 ft thick and reportedly consists Basin fill l.9l .00001 2 almost entirely of clay. 3 Volcanic rocks 2.46 .0001 Proftle B-B'(ffgure 8) Hydraullc Properiles I Granitic rocks 2.71 0.0006 Two properties 2 Basin fill t.97 .00001 hydraulic used to express water- 3 Volcanic rocks 2.42 .0007 bearing characteristics ofaquifers are hydraulic con- 4 Volcanic rocks 2.75 .003 ductivity and storage. Hydraulic conductivity is a Profile C-C (figure 9) measure of the ability of an aquifer to transmit water. The term "storage coefficient" is used to describe the I Granitic rocks 2.71 0.001 2 Basin fill 1.90 .00001 water-storage capabilities of an aquifer. 3 Volcanic rocks 2.47 .0001 Typical values of hydraulic conductivity for Volcanic rocks 2.72 .003 4 coarse-grained deposits (sand and gravel) in other basins of Nevada range from 5 to more than 150 ff/d Area! Extent Thlckness and (Harrill, 1973, table 5; Berger, 1995, p. 2l). In fine- The areal extent of the basin-fill aquifer is approxi- grained deposits (clay, silt, and fine sand), the range mated by the contact between consolidated rock and is generally from 0.1 to 4 ft/d (Harrill, 1986, p. 10). basin fill along the periphery of the valley floor. Total sur- Hydraulic conductivity can be determined from esti- face area of basin fill is about 34 mi", almost 43 percent mates of transmissivity and aquifer thickness. Trans- of the total drainage area of Spanish Springs Valley. The missivity values determined from results of several basin fill is bounded on the east by the Pah Rah Range aquifer tests were used to calculate hydraulic conduc- and on the west by Hungry Ridge and its southern exten- tivities, which ranged from 0.5 to about 12 ftld (Shaw sion. On the north, an alluvial divide exists between Engineering, 1984, appendix; Guyton and Associates, Spanish Springs and Warm Springs Valleys. Results of a 1986, p. 6l; W.E. Nork,Inc., 1987, 1988b, 1989; seismic refraction survey (line A, fig.4) and drill-hole Washoe County, 1991). Data from these aquifer tests data indicate that this topographic divide is underlain by represent transmissivities of mixtures of coarse- and consolidated rock at shallow depths (less than 50 ft). At fine-grained deposits within the upper 330 ft of satu- the southern boundary ofthe study area, the saturated rated basin fill. basin fill in Spanish Springs Valley may be continuous Analysis of geophysical and lithologic logs and with saturated basin fill of Truckee Meadows. This grain-size distributions collected from some of the boundary which is not a topographic divide, is underlain observation wells drilled as part of this study (wells 7, by consolidated rock at depths of less than 20 ft. Basin fill ll, 15,51, and 72;Washoe County, 1993) provided also occupies the structurally controlled basins ofthe Dry qualitative estimates of the ability of the basin-fill aqui- Lakes area in the southeastern part ofthe study area. fer to transmit water. In general, basin fill that originates Wells drilled in Spanish Springs Valley range in in upland volcanic-rock tenains is predominantly com- depth from several tens of feet to more than 800 ft, with posed of finer grained deposits, resulting in an overall most completed in basin fill. Discrepancies in basin-fill lower hydraulic conductivity than basin fill derived thickness as reported on drillers' logs for several wells from granitic rocks, which is predominantly sands and limited the areal use of these logs as a tool to estimate gravels. Hydraulic conductivity beneath the deepest basin-fill thickness. The basin-fill-thickness map (fig. wells is unknown, but probably is lower than that of the l0), which was developed partly by geophysical meth- upper 330 ft due to additional compaction and indura- ods, indicates that basin fill is thickest along a northeast tion. The distribution of hydraulic conductivity within trending hough-like feature close to the mountain front the basin-fill aquifer was refined by using the ground- of Hungry Ridge. Results from profile A-A' (fi5.7\, water flow model.
HYDROGEOLOGIC FRAMEWORK A A' -1 00 I do ++++*+ iDdj . F5p -i.uzz=o Calculated *".^(), 361 9==- -400
-'t70 E -172 * .-- uJ> Measured -174
-176 ;;s< r.u -l -178 t4F>F>= Calculated i)z -1 80 =#=u(, -'t82
6,000
FJ TIJ I.IJ 5,000 r.! > tL uJ :< 4,000 HH tr>-) LlJ 3,000 F\J -J(D 2,000
1,000 1234 DISTANCE ALONG LINE OF SECTION, IN MILES
EXPLANATION
Well---Penetrates consolidated rock u nderlying basin fill 300 feet below land surface
Figure 7. Measured and calculated total-intensity magnetic anomaly and complete Bouguer gravity anomaly, and generalized geologic section A-A'showing distribution of lithologic units determined from geophysical modeling, Spanish Springs Valley, west-central Nevada. See figures 5 and 6 for section location and table 3 for physical properties of lithologic units.
22 Hydrogeology and Simulated Etfects ol Urban Development on Water Resources of Spanish Springs Valley, Nevada B B' 100
I cfo bdl Calculated F5-fi + zFo -1 00 -i.uz + + ++ =6'P1=- '\M"".rr"o
-'t70