4.8 Hydrology and Water Quality

City of Azusa General Plan & Development Code 4.8 Hydrology & Water Quality Draft EIR

4.8 HYDROLOGY AND WATER QUALITY

SCOPE AND METHODOLOGY

This section examines the following issues: compliance with water quality standards and waste discharge requirements for groundwater supply and recharge, erosion, water runoff, water quality, flooding, and inundations. Impact assessments were performed based on criteria established by the CEQA Guidelines (discussed below under “Significance Criteria”). The following maps and documents were used for this section:

· City of Azusa, Analysis of Existing Conditions and Trends report, December 2001 · Federal Emergency Management Agency Flood Insurance Rate Maps · Los Angeles County Safety Element, 1990

ENVIRONMENTAL SETTING

Groundwater

Azusa lies within the San Gabriel Groundwater Basin, an extensive geolo gic feature from which 46 separate water departments, private water companies, and other water agencies draw approximately 200,000 acre-feet1 of water annually to meet potable water needs. The basin is replenished by stream runoff from the San Gabriel Mountains, rainfall onto the valley floor, subsurface inflow from the adjacent Raymond and Puente Basins, and percolation from urban water usage. In addition, imported water purchases from the Metropolitan Water District of Southern California (MWD) and the State Water Project (SWP) is used to recharge the basin.

The Los Angeles County Department of Public Works (LACDPW) artificially recharges the groundwater supply aquifers underlying the County by spreading imported water, local runoff (including the water impounded by the upstream dams during storms), and recycled water at their 27 spreading facilities. The Department of Public Works major spreading facilities are located downstream of the San Gabriel Canyon. The Metropolitan Water District (MWD) and the San Gabriel Valley Municipal Water District deliver imported water to the San Gabriel Canyon Spreading Grounds and to the San Gabriel River for spreading in cooperation with the Main San Gabriel Basin Watermaster. Imported and recycled water discharged into the channels and runoffs resulting from storm events are diverted into the spreading facilities. At the spreading facilities, the water percolates down to the water table. The water can then be pumped up to the surface for water supply purposes.

Groundwater levels vary naturally in response to seasonal rainfall patterns. They are also affected in complex ways by year-to-year climatic variations, local and regional groundwater pumping, volume and timing of artificial recharge, and storage levels in upstream reservoirs. Generally, groundwater south of Foothill Boulevard is greater than 100 feet deep and the depth decreases from north to south. This indicates that the regional water surface slopes southwest and south at an angle that is less than the topographic surface. Groundwater barriers upset this pattern between the Southern Pacific -Santa Fe right- of-way and Foothill Boulevard. Groundwater depths range from about 260 to 290 feet just south of Foothill Boulevard and from 180 to 270 feet from west to east along Arrow Highway.2

1One acre-foot equals 325,851 gallons and represents the amount of water a family of five consumes in one year. 2 City of Azusa, “Azusa General Plan Update: Analysis of Existing Conditions and Trends,” December 2001

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Drainage

The Flood Control Division of LACDPW is responsible for operating and maintaining major flood control facilities located throughout the County. The facilities include approximately 15 major dams, 450 miles of open channels, 2,500 miles of underground storm drains, 70,000 miles of street drains, 280 sediment entrapment basins, 218 concrete stream bed stabilization structures, 33 pumping plants, and other support facilities located throughout the County. The Flood Control Division only maintains those flood control facilities that are part of the County-maintained flood control system and provides no review, management, or on-going maintenance of private facilities.

The City of Azusa maintains and operates a limited number of drainage facilities in the City. The City of Azusa and the Flood Control Division’s local facilities are shown in Figure 4.8-1. The flood control channels in the City are shown in Figure 4.8-2. The existing storm drain and flood control systems contain most of the storm runoff within the system.

Dams

There are three dams that can potentially impact Azusa in the event of a dam failure: (1) San Gabriel Dam, (2) Cogswell Dam, and (3) Morris Dam. The San Gabriel and Morris dams are owned by the MWD and LACDPW Flood Control Division. The San Gabriel Dam is seven miles north of the Azusa city limits. Morris Dam is just south of the San Gabriel Dam, one mile north of the City limits, and the Cogswell Dam is in the West Fork of San Gabriel Canyon (Figure 4.8-3).

The San Gabriel Canyon recharge area is located next to the San Gabriel River, north of Interstate 210 and up the mouth of the San Gabriel Canyon. The recharge area holds water from the river and allows water to percolate into the water basin, recharging ground water sources. The water basin detains overflowing floodwaters of the San Gabriel River in the event of a major rainstorm.

Flooding

The Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRM) identify areas located with a 100-year flood boundary, which are termed “Special Flood Hazard Areas” (SFHAs). A 100-year flood does not refer to a flood that occurs every 100 years, but refers to a flood level with a one percent chance of being equaled or exceeded in any given year. The SFHAs is subdivided into insurance risk rate zones. Areas between the 100-year and 500-year flood boundaries are termed “moderate flood hazard areas.” The remaining areas are outside the 500-year flood boundary are termed “minimal flood hazard areas.” The northern part of the City along the San Gabriel River is within the 100-year flood zone (Figure 4.8-4).

Water Quality

The United States Environmental Protection Agency (USEPA), the State Department of Health Services (DHS), the Regional Water Quality Control Board - Los Angeles Region, and the Los Angeles County Health Department are responsible for monitoring and regulating groundwater in the San Gabriel Valley.

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Figure 4.8-1 (Drainage System)

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Figure 4.6-2 (Flood Control Channel)

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Figure 4.8-3 (Dams)

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Figure 4.8-4 (Flood Plains)

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The National Pollutant Discharge Elimination System (NPDES) is the primary regulation for storm water pollutant sources in the Los Angeles County and the cities within the County. NPDES permits are issued to Los Angeles County and the cities within the County by the USEPA. The Standard Urban Storm Water Mitigation Plan (SUSMP) was developed as part of the municipal storm water program to address storm water pollution from new development and redevelopment by the private sector. The SUSMP contains a list of minimum required Best Management Practices that must be used for a designated project.

SIGNIFICANCE CRITERIA

The proposed project would result in a significant adverse impact with regard to hydrology and water quality if it:

· Violates any water quality standards or waste discharge requirements; · Substantially degrades water quality; · Substantially depletes groundwater supplies or interferes substantially with groundwater recharge such that there would be a net deficit in aquifer volume or a lowering of the local ground water table level (e.g., the production rate of preexisting nearby wells would drop to a level which would not support existing land uses or planned uses for which permits have been granted.); · Substantially alters the existing drainage patterns of the site or area, including through the alteration of the course of a stream or river, in a manner which would result in substantial erosion or siltation on- or off-site; · Substantially alters the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, or substantially increases the rate or amount of surface runoff in a manner that would result in flooding on- or off-site; · Creates or contrib utes runoff water, which would exceed the capacity of the existing or planned stormwater drainage systems or provides substantial additional sources of polluted runoff; · Places housing within a 100-year flood hazard area as mapped on a Federal Flood Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation map; · Places within a 100-year flood hazard area structures that would impede or redirect flood flow; · Exposes people or structures to a significant risk of loss, injury or death involving flooding, including flooding as a result of the failure of a levee or dam; or · Exposes people or structures to inundation by seiche, tsunami, or mudflow.

ENVIRONMENTAL IMPACTS

Groundwater

The General Plan contains policies and programs that would protect groundwater supplies in the City. These water policies and programs are as follows:

2.6 Minimize water consumption through site design, use of efficient systems, and other techniques.

2.7 Continue the City’s water conservation efforts; review programs periodically and modify and/or expand them as appropriate and feasible.

2.8 Continue to require the incorporation of water conservation features in the design of all new construction and site development.

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2.10 Require the use of reclaimed water for landscaped irrigation, grading, and other non-contact uses in new developments, where available or expected to be available.

I7 Revise the City’s Development Code to require that new uses that consume very high levels of water or energy or discharge high levels of water be evaluated to determine the means by which these levels can be reduced.

The flooding and drainage policy that would protect groundwater supplies in the City is:

3.2 Where feasible given flood control requirements, maintain the natural condition of waterways and flood plains to ensure adequate groundwater recharge and water quality, preservation of habitat, and access to mineral resources.

The storm drainage policy that protects groundwater supplies is:

4.8 Require new developments to employ the most efficient drainage technology to increase ground percolation, control drainage, and minimize damage to environmentally sensitive areas.

The policies, above, would ensure that groundwater supplies would not deplete and that groundwater recharge would not be interfered such that there would be a net deficit in aquifer volume or a lowering of the local ground water table level. Thus, no significant impact is anticipated.

Drainage

One of the goals of the General Plan is to provide a flood control system that is able to support the permitted land uses while preserving public safety and to upgrade existing deficient systems. The General Plan contains policies to achieve this goal. These policies would:

· Where feasible given flood control requirements, maintain the natural condition of waterways and flood plains to ensure adequate groundwater recharge and water quality, preservation of habitat, and access to mineral resources (Flooding and Drainage 3.2); · Maintain existing public storm drains and flood control facilities, upgrade and expand storm drain and flood control facilities (Storm Drainage 4.1); · Coordinate with County agencies to improve the County’s facilities (Storm Drainage 4.3); · Monitor the demands and manage development to mitigate impacts and/or facilitate improvements to the storm drainage system (Storm Drainage 4.4); and · Designate, preserve, and acquire land, as necessary, for storm drainage and flood control facilities (Storm Drainage 4.5).

The following implementation programs provided in the General Plan would also maintain the existing drainage patterns in the City to prevent erosion, siltation, and flooding:

Geo12 Prepare a Master Drainage Plan for the Planning Area based on buildout of the General Plan to allow compilation of information from the San Gabriel River Master Plan, consultant flood and drainage studies, and projects associated with the San Gabriel River into an integrated whole.

Geo15 Implement stormwater facilities for improvement in priority areas as funding allows to accommodate the significant increase in stormwater flows expected as a result of development in the City’s current underdeveloped areas.

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Geo16 Reduce the effects of surface runoff in developing areas by the use of extensive landscaping with an emphasis on native and drought-resistant species, minimizing impervious surfaces, and providing for recharge.

The General Plan policies and implementation programs listed above would ensure that the existing drainage patterns of the City would not be substantially altered in a manner that would result in substantial erosion, siltation, or flooding. No significant impacts are anticipated.

Water Runoff

The General Plan policies and implementation programs (see “Drainage,” above) would maintain existing stormwater drainage facilities, as well as upgrade and expand storm drain and flood control facilities. The policies and implementation programs would also reduce impacts associated with water runoff. Thus, it is not likely that water runoff would exceed the capacity of the existing stormwater drainage facilities. No significant impacts are anticipated.

Flooding

As mentioned in the Environmental Setting above, the northern portions of the City adjacent to the San Gabriel River are within the 100-year flood zone. The proposed General Plan does not designate residential land uses in the 100-year flood zone and, moreover, the General Plan contains policies that would protect people and structures from loss, injury, or death related to such hazards. The storm drainage policy that would protect people and structures from flooding is:

4.6 During development review, determine if any structures meant for human habitation are constructed within the 100-year flood plain. If necessary, evaluate the structure’s flood safety, and require remedial actions.

The flooding and drainage policies that would protect people and structures from flooding are as follows:

3.4 Support the intent of the County of Los Angeles’ flood control policies as specified in the County General Plan. The County's detailed flood policies specify a range of protective measures, encourage coordination among jurisdictions, and acknowledge the need for a multi-use concept of streams and creeks.

The implementation programs of the General Plan that would mitigate flood flows in areas with people and structures are as follows:

Geo13 Prior to project approval in the vicinity of a waterway or drainage course, consult Flood Insurance Rate Maps on file with the Community Development Department to identify areas that have not been subject to detailed study; if the project falls within an area that has not been studied, require studies and, if necessary, require mitigation or restrictions on development.

Consider all proposed development within the 100-year flood plain of the San Gabr iel River drainage system on a case-by-case basis, to determine whether flood-related mitigation is to be required.

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Identify any critical facilities in flood hazard areas, and improve their level of protection, if necessary. Critical facilities include fire and emergency service facilities, utility lifeline facilities such as water, electricity, and gas supply, sewage disposal, communications, and transportation facilities.

Geo14 Work with the Los Angeles County Flood Control District to construct detention basins in the areas where inadequate 100-year flood protection along the San Gabriel Mountains exists to reduce or eliminate downstream flooding.

Geo17 Encourage timely FEMA map changes and annually incorporate mapped revisions to the 100- year flood zone into City hazards maps.

Although the General Plan would place housing within a 100-year flood hazard area, the General Plan policies would ensure that people would not be exposed to a significant risk of loss, injury or death involving flooding. Thus, a less-than-significant impact is anticipated.

Dam Failure Inundation

The City lies downstream from several dams and debris basins whose drainages ultimately flow into the San Gabriel River.3 The Cogswell Reservoir, San Gabriel Dam, and Morris Dam are shown as direct potential contributors to inundation in the City should they fail catastrophically. Cogswell Reservoir, San Gabriel, and Morris Dams lay in the foothills of the San Gabriel Mountains about 15, 6, and 3.5 miles north of the city, respectively. Together, they could impound about 102,000 cubic decameters, or about 82,691 acre-feet (over 27 million gallons).

Approximately 95 percent of the City lies within the inundation areas of one or more of these dams (Figure 4.8-5). The lowest areas of the City and those immediately along the San Gabriel River channel, would be the most susceptible to damages from rapidly flowing water and associated floating debris. Areas farthest from the channel would suffer more from sheet flow and rising water. Although a significant portion of the City is within the dam inundation area, the risk of loss, injury, or death involving dam failure already exists. The General Plan would not expose people or structures to any new risks associated with dam failures.

The following implementation programs provided by the General Plan would mitigate impacts of dam inundations.

Geo1 Development and building codes shall be amended for the dam failure inundation area to encourage discretionary approval of the Planning Commission and applicable review criteria for:

o The limited expansion of Critical Facilities. New construction of Critical Facilities in a potential dam failure inundation area shall be prohibited;

o Sensitive Facilities including: nursing homes, senior cit izen housing and other low- mobility uses, where rapid evacuation capabilities may be inhibited; and commercial and industrial facilities housing hazardous materials, or potentially hazardous operations requiring safe shutdown procedures; and

o High-Occupancy Facilities and all assembly occupancies of 100 or more occupants.

3 Table 3.11, Los Ange les County Safety Element, 1990.

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Figure 4.8-5 (Dam Inundation Area)

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The General Plan implementation programs listed above would mitigate impacts associated with dam inundation. Additionally, the General Plan would not expose people or structures to any new risks associated with dam failures. Thus, a less-than-significant impact is anticipated.

Inundations by Tsunami, Seiche, or Mudflow

Tsunamis. The tsunamis are usually caused by displacement of the ocean floor causing large waves. Tsunamis are typically generated by seismic activity. Tsunami hazard is not present for the City due to the elevation and distance from the ocean. Therefore, tsunamis and the inundation associated with tsunamis are not a potential hazard.

Seiche. A seiche is a standing wave in an enclosed or partly enclosed body of water. Seiches are normally caused by earthquake activity, and can affect harbors, bays, lakes, rivers, and canals. Seiche hazard could impact water impoundments within or immediately adjacent to the City, such as water storage tanks or reservoirs outside the City (e.g., Morris, San Gabriel, or Cogswell Dams) to the north, and could conceivably cause a dam to fail. Hazards associated with seiches already exist within the City and the General Plan would not expose people or structures to any new risks associated with seiches. Thus, no significant impact is anticipated.

Mudflow. A mudflow is a mixture of soil and water that runs like a river of mud down a hillside. It usually is generated by heavy rainfall. The discussion above under “Drainage” and “Dam Failure Inundation”, lists policies and implementation programs that would help prevent mudflows. Thus, no significant impacts are anticipated.

Water Quality

As discussed previously, the USEPA, DHS, the Regional Water Quality Control Board – Los Angeles Region, and the Los Angeles County Health Department are responsible for monitoring and regulating groundwater in the San Gabriel Valley. The NPDES permit is the primary regulation for storm water pollutant sources in the City of Azusa. Additionally, Los Angeles County provides storm water requirements in the SUSMP. The General Plan contains policies and programs that would ensure that the City would not violate these water quality standards or waste discharge requirements. The water policy that protects water quality is:

2.4 Require that new development and retrofit existing developments to contain safeguards and measures preventing water supply degradation.

The storm drainage policies that protect water quality are as follows:

4.6.1 Require new developments to employ the most efficient drainage technology to increase ground percolation, control drainage, and minimize damage to environmentally sensitive areas.

4.9 Conduct public education programs to discourage dumping of materials into the streets or into the stormwater collection facilities.

The General Plan program, I1, would development and implement pollutant runoff control programs. These programs include structural controls, non-structural controls, and best management practices. I1 would require all residential, commercial, and industrial sites and construction sites to implement pollution runoff controls. Additionally, the General Plan would expand the following programs: the NPDES, public education promoting resource conservation, and local, state, and federal requirements mandated by SCAQMD.

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In addition to I1, the General Plan program I8 would adopt and enforce a water pollution control ordinance protecting City’s surface waters and groundwater resources.

The General Plan policies and programs would ensure that the City would meet all applicable water quality and waste discharge requirements of the USEPA, DHS, the Regional Water Quality Control Board – Los Angeles Region, and the Los Angeles County Health Department. These policies and programs would also ensure that water quality in the City would not be degraded. Thus, the General Plan would not result in violations of any water quality standards or waste discharge requirements, and would protect water quality in the City. No significant impact associated with water quality standards, waste discharge requirements, and water quality is anticipated.

In consulting with the City of Glendora, it has been found that the City of Glendora owns four active wells in the vicinity of Azusa Greens Country Club. This area currently consists of residential uses and no changes in land use are proposed in this area or in the foothills in the immediate vicinity of the area. Thus, the amount or quality of urban runoff that could affect the City of Glendora’s water source is not anticipated to change. No impact is anticipated.

MITIGATION MEASURES

No significant impacts to hydrology and water quality are anticipated. Thus, no mitigation measures are required.

LEVEL OF IMPACT AFTER MITIGATION

As discussed, the General Plan provides policies and implementation programs that would minimize impacts associated with hydrology and water quality. Thus, no significant impacts are anticipated.

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