This section evaluates potential hydrology and water quality impacts associated with the project.

Transcription

1 Section 3.7 Hydrology and Water Quality This section evaluates potential hydrology and water quality impacts associated with the project Regulatory Framework Federal The U.S. EPA regulates water quality under the Clean Water Act (also known as the Federal Water Pollution Control Act). Enacted in 1972, and significantly amended in subsequent years, the Clean Water Act is designed to restore and maintain the chemical, physical, and biological integrity of waters in the U.S. The Clean Water Act provides the legal framework for several water quality regulations, including National Pollutant Discharge Elimination System (NPDES) permits, effluent limitations, water quality standards, pretreatment standards, anti-degradation policy, non-point source discharge regulation, and wetlands protection. The EPA has delegated the responsibility for administration of portions of the Clean Water Act to state and regional agencies. The Clean Water Act requires the states to adopt water quality standards for receiving water bodies and to have those standards approved by the EPA. Water quality standards consist of designated beneficial uses for a particular receiving water body (wildlife habitat, agricultural supply, fishing, etc.), along with water quality criteria necessary to support those uses. Water quality criteria are prescribed concentrations or levels of constituents, such as lead, suspended sediment, and fecal coliform bacteria, or they are narrative statements that represent the quality of water supporting a particular use. State The Porter Cologne Water Quality Control Act established the principal California legal and regulatory framework for water quality control and is embodied in the California Water Code. The Porter Cologne Act also provides for the development and periodic review of Water Quality Control Plans (Basin Plans) that designate beneficial uses of California s major rivers and groundwater basins and establish water quality objectives for those waters. The California Water Code authorizes the State Water Resource Control Board (SWRCB) to implement the provisions of the federal Clean Water Act. The SWCRB issues the Construction General Permit (CGP) for projects that involve one acre or more of soil disturbance. To receive the permit, the following must be met: Page 3.7-1

2 Local Notice of Intent (NOI) Risk Assessment Site Map Stormwater Pollution Prevention Plan (SWPPP) Annual Fee Signed Certification Statement The State Water Resource Control Board (SWRCB) is divided into nine regions governed by the Regional Water Quality Control Boards (RWQCBs) that implement and enforce provisions of the California Water Code and the Clean Water Act under the oversight of the SWRCB. The San Diego RWQCB (Region 9) has adopted a Basin Plan that outlines plans, policies, and provisions for water quality management in the region. Beneficial uses of major surface waters and their tributaries are identified and described in the Basin Plan. Under Section 303(d) of the federal Clean Water Act, states are required to identify surface water bodies that are polluted. States are required to compile these water bodies into a list, referred to as the "Clean Water Act Section 303(d) List of Water Quality Limited Segments." States must also prioritize the water bodies on the list and develop Total Maximum Daily Loads (TMDLs) to improve the water quality. Conformance with the federal Clean Water Act for projects within the City of San Diego is established through compliance with the requirements of the NPDES General Permit for the City of San Diego (Municipal Permit) and the CGP issued by the SWRCB. The NPDES Municipal Permit, issued in 2013 to the City of San Diego by the RWQCB, requires the development and implementation, to the maximum extent practicable, of measures to reduce storm water discharge, both during project construction and in the project s permanent design. The RWQCB regulates the discharge of water from construction sites if dewatering of excavated areas is necessary through its Waste Discharge Requirements for Groundwater Remediation and Dewatering Discharges Environmental Setting The San Diego region under the jurisdiction of the RWQCB contains 11 major drainage basins that encompass most of San Diego County and parts of Riverside and Orange counties. The project area is within the Los Peñasquitos Watershed Hydrologic Unit (HU; Basin Number ) and the Miramar Reservoir Hydrologic Area (HA; ). The project area drains westward to the Los Peñasquitos Lagoon, and ultimately the Pacific Ocean. This watershed drains a highly urbanized region located almost entirely west of I-15 in San Diego County. Los Peñasquitos Lagoon is sensitive to the effects of pollutants due to restricted or intermittent tidal flushing and is listed as impaired on the Page 3.7-2

3 California (d) list due to sedimentation/siltation. The beneficial uses of the Los Peñasquitos Lagoon are shown in Table TABLE BENEFICIAL USES OF RECEIVING WATERS FOR LOS PENASQUITOS LAGOON Beneficial Uses Definition Water Contact Recreation Water contact recreation waters, used for recreational activities (REC 1) involving body contact with water where ingestion of water is reasonably possible. Uses may include swimming, wading, water-skiing, skin and scuba diving, or fishing. Non-contact Water Recreation Waters are used for recreational activities involving proximity (REC 2) to water, but not normally involving body contact with water where ingestion of water would be reasonably possible. These uses may include, but are not limited to, picnicking, sunbathing, hiking, beachcombing, camping, sightseeing, and aesthetic enjoyment Commercial and Sport Fishing Includes the uses of water for commercial or recreational (COMM) collection of fish, shellfish, or other organisms including, but not limited to, uses involving organisms intended for human consumption or bait purposes. Preservation of Biological Includes uses of water that support designated areas or Habitats of Special Significance habitats, such as established refuges, parks, sanctuaries, (BIOL) ecological reserves, or Areas of Special Biological Significance (ASBS), where the preservation or enhancement of natural resources requires special protection. Estuarine Habitat (EST) Includes uses of water that support estuarine ecosystems including, but not limited to, preservation or enhancement of estuarine habitats, vegetation, fish, shellfish, or wildlife (e.g., estuarine mammals, waterfowl, shorebirds). Wildlife Habitat (WILD) Includes uses of water that support terrestrial ecosystems including, but not limited to, preservation and enhancement of terrestrial habitats, vegetation, wildlife (e.g., mammals, birds, reptiles, amphibians, invertebrates), or wildlife water and food sources. Marine Habitat (MAR) Includes uses of water that support marine ecosystems including, but not limited to, preservation or enhancement of marine habitats, vegetation such as kelp, fish, shellfish, or wildlife (e.g., marine mammals, shorebirds). Migration of Aquatic Organisms Includes uses of water that support habitats necessary for (MIGR) migration, acclimatization between fresh and salt water, or other temporary activities by aquatic organisms, such as anadromous fish. Spawning, Reproduction, or Includes uses of water that support high quality habitats Early Development (SPWN) suitable for reproduction, early development and sustenance of marine fish and/or cold freshwater fish. Shellfish Harvesting (SHELL) Includes uses of water that support habitats suitable for the collection of filter-feeding shellfish (e.g., clams, oysters and mussels) for human consumption, commercial, or sport purposes. SOURCE: Water Quality Control Plan for the San Diego Basin (State of California 2011b). Within the pipeline improvements area, drainage flows from east to west and slightly north to south, due to the relatively steep changes in topography. Within the access Page 3.7-3

4 road area, runoff flows into a narrow channel within the central portion of the alignment. This area also collects runoff from the earthen dam of the Miramar Reservoir. This runoff flows into the City s storm drain system, which then runs southwest underground towards the I-15. Within the southern part of the access road area, runoff flows south towards Scripps Lake Drive and the City s storm drain system Thresholds for Determining Significance Thresholds used to evaluate impacts to hydrology and water quality are based on applicable criteria in the state CEQA Guidelines (CCR ), Appendix G. A significant impact to hydrology and water quality would occur if the project would: 1) Violate any water quality standards or waste discharge requirements; 2) Substantially deplete groundwater supplies or interfere substantially with groundwater recharge such that there would be a net deficit in aquifer volume or a lowering of the local groundwater table level (e.g., the production rate of pre-existing nearby wells would drop to a level which would not support existing land uses or planned uses for which permits have been granted); 3) Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, in a manner in which would result in substantial erosion or siltation on- or off-site; 4) Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, or substantially increase the rate or amount of surface runoff in a manner in which would result in flooding on- or off-site; 5) Create or contribute runoff water, which would exceed the capacity of existing or planned storm water drainage systems or provide substantial additional sources of polluted runoff; 6) Otherwise substantially degrade water quality; 7) Expose people or structures to significant risk of loss, injury or death involving flooding, including flooding as a result of the failure of a levee or dam; or, 8) Result in inundation by seiche, tsunami, or mudflow Impact Analysis Due to overlap in the threshold issues and for clarity of analysis, the hydrology and water quality thresholds evaluated below are grouped into similar headings, where applicable. Page 3.7-4

5 Analysis of Project Effects Threshold 1: Water Quality Standards Would the project violate any water quality standards or waste discharge requirements? ALL PROJECT COMPONENTS Projects are required to control storm water runoff during construction and after construction (operation) in order to comply with federal, state, and local water quality standards. Compliance with the standards in existing regulations would ensure that construction and operation of the project would not violate water quality standards. Project construction activities have the potential to result in erosion, sedimentation downstream, and the discharge of construction debris. Clearing of vegetation for access and grading activities, for example, could lead to exposed or stockpiled soils susceptible to peak storm water runoff flows. The compaction of soils by heavy equipment could reduce the infiltration capacity of soils and increase surface runoff and erosion potential. Project construction activities would be required to comply with the CGP issued by the SWRCB. The Water Authority s contractor would prepare a SWPPP detailing the storm water management and erosion and sediment control BMPs that would be utilized on each construction site and the Water Authority would obtain coverage under the CGP. The SWPPP also includes a construction site monitoring program be prepared. Construction BMPs shall be required for the pipeline improvements, the access road, and the staging area, including (but not limited to): Perimeter protection BMPs; Sediment control and sediment control tracking BMPs; Prepare and implement a Rain Event Action Plan if there is a 50 percent (or more) chance for precipitation per the National Oceanic and Atmospheric Administration (NOAA) website; Designated and contained storage areas for materials and waste; Trash receptacles to be covered when not in use (i.e., at the end of each day); A storage, service, cleaning, and maintenance area for vehicles used during construction identification; On-site materials for spill control/containment; Non-storm water discharge eliminated or controlled; Page 3.7-5

6 Physical or vegetation erosion control BMPs; Limiting areas of exposed soil to an amount that can be adequately protected; Disturbed area not completed and not being actively graded must be fully protected if left for 14 or more calendar days; and, Erosion control plans with notes and locations of BMPs would be detailed on grading plans and/or within a project-specific SWPPP. Therefore, by obtaining a CGP through the SWRCB prior to construction activities, and implementing the SWPPP, construction-related water quality impacts would be less than significant. Operational components associated with the project would be limited to use of the access road for operation and maintenance. Pollutants such as sediments, heavy metals, organic compounds, oil and grease, and bacteria are associated with paved roads. However, these pollutants are typical of oft-traveled public roadways. After construction of the pipeline improvements is completed, the access road would be used on a weekly basis by Water Authority maintenance workers. The access road would require permanent post-construction measures in order to reduce pollutants from runoff entering natural areas. Low Impact Development (LID) Integrated Management Practices (IMPs) is an integrated site design technique that uses small-scale detention and retention to minimize pollutants conveyed by runoff and to mimic pre-project site hydrological conditions. This design integrates site planning and design measures with engineered, small-scale IMPs, such as bioretention. Bioretention basins are anticipated to serve as the primary means of filtering and detaining runoff from the access road. Bioretention detains runoff in a small surface basin, filters it through plant roots and a biologically active soil mix, and then infiltrates it into the ground. Where native soils are less permeable, an underdrain conveys treated runoff to storm drain or surface drainage. The design of the bioretention basins follows the County of San Diego Storm Water Standards (2012). Figure shows the typical cross-sections of an access road and an example of a typical bioretention area. Page 3.7-6

7 Map Source: SB & O, Inc Not to Scale FIGURE Conceptual Design of Access Road Cross-Sections and Bioretention Areas M:\JOBS4\6830\env\graphics\fig3.7-1.ai 02/05/14

8 The project has incorporated LID IMPs, including bioretention basins, in order to reduce the potential for pollutant discharge off-site, thus avoiding significant adverse water quality impacts following construction. The project would comply with all applicable federal, state, and local water quality standards through adherence to the City s Storm Water Standards and the General Construction Permit. Implementation of the construction BMPs and LID IMPs would reduce potential impacts to water quality to less than significant. Threshold 2: Groundwater Supplies Would the project substantially deplete groundwater supplies or interfere substantially with groundwater recharge such that there would be a net deficit in aquifer volume or a lowering of the local groundwater table level (e.g., the production rate of pre-existing nearby wells would drop to a level which would not support existing land uses or planned uses for which permits have been granted)? ALL PROJECT COMPONENTS The project would not require the use of groundwater and would not result in the substantial depletion of groundwater supplies, nor would it interfere with groundwater recharge such that it would lower the local groundwater table level. Although groundwater was not encountered during borings conducted for the preliminary geotechnical investigation, some groundwater could be trapped in low spots below the existing pipes and following a storm event. The quantity of water will be dependent on the size of the low spot, drainage, and the size and duration of the storm event. Thus, limited dewatering of the pipeline improvements area may be necessary. The quantity of water that could be discharged and the actual point of discharge as a result of dewatering operations are not known at this time, and cannot be accurately known until construction occurs. However, based on the results of geotechnical borings conducted for the project, it is not expected that a significant amount of groundwater would be encountered during construction. If a limited amount of groundwater were encountered (as defined by the RWQCB), a Waiver of Discharge Requirements would be obtained. However, if a significant amount of groundwater were to be encountered, the Water Authority s contractor would be required to comply with RWQCB s Waste Discharge Requirements for Groundwater Remediation and Dewatering Discharges. In the unlikely event that a significant amount of groundwater was encountered, adherence to the RWQCB s Waste Discharge Permit would ensure the project would not result in significant waste discharge. Impacts would be less than significant. Thresholds 3 and 4: Drainage Patterns Would the project substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, in a manner in which Page 3.7-9

9 would result in substantial erosion or siltation on or off site; or substantially increase the rate or amount of surface runoff in a manner in which would result in flooding on- or offsite? ALL PROJECT COMPONENTS Clearing, ground-disturbing activities, and construction staging associated with the project have the potential to temporarily alter drainage patterns. However, as previously described, BMPs would be installed and maintained throughout construction activities. The pipeline improvements area would be restored to its preexisting condition following construction. Temporary impacts would be less than significant. The access road has been designed in order to avoid alteration to existing drainage patterns. The preliminary access road grades follow the existing contours, thus minimizing the grading necessary and preserving the existing drainage patterns. The drainage basins then compensate for the impervious surfaces that run off at a higher rate. Within the northern portion of the access road area, runoff flows into a narrow channel. This area also collects runoff from the earthen dam of the Miramar Reservoir. Runoff currently flows into the City s storm drain system and is directed underground southwest towards I-15. Within the southern part of the access road area, runoff flows south towards Scripps Lake Drive and the City s storm drain system. Once constructed, surface runoff from the paved surface would also be slowed down through implementation of proposed bioretention areas. During rainfall events, flows would be directed down through the gutters to the bioretention areas. There would be bioretention areas in the central low point of the access road on either side of the road, just upstream of the low point these would either be piped together or connect to the existing storm drain system. The bioretention areas would filter the pollutants from the runoff before dissipating into the drain pipe, which connects to the storm drain. Riprap would also be installed in this area for flows which do not enter the bioretention areas and would also dissipate flows prior to entering the storm drain, located at the eastern edge of the road alignment. The LID IMPs at the southern portion of the access road would discharge to either the surface gutter of either the access road or to Scripps Lake Drive. Thus, the design of the access road and bioretention basins would ensure that drainage patterns are not substantially altered in a manner that would result in substantial erosion or sedimentation downstream to receiving waters. These features serve to slow down flows, similar to pre-existing conditions, such that the project would not result in a substantial increase in runoff that would result in flooding. Impacts would be less than significant. Page

10 Thresholds 5 and 6: Drainage Systems Would the project create or contribute runoff water, which would exceed the capacity of existing or planned storm water drainage systems; or provide substantial additional sources of polluted runoff, or otherwise substantially degrade water quality? ALL PROJECT COMPONENTS The project has the potential to contribute runoff water within the pipeline improvements area and access road area due to the removal of natural vegetation during construction. However, as previously described, BMPs would be installed and maintained throughout construction activities, including perimeter protection BMPs, sediment control BMPs, and physical or vegetation erosion control BMPs installed prior to the rainy season. The pipeline improvements area would be restored to its preexisting condition following construction. Temporary impacts associated with runoff would be less than significant. Paving associated with the access road and the loss of natural vegetation would create increased runoff water. However, as previously discussed under Thresholds 1, 3, and 4, the project incorporates LID IMPs that would ensure that runoff generated from the project is detained and treated to a level that is similar to the preexisting condition. Incorporation of bioretention areas along the access road, as described above, would ensure that runoff is similar to the preexisting condition, and thus would not exceed the capacity of the storm water drainage system. Impacts would be less than significant. Thresholds 7 and 8: Flooding Hazards Would the project expose people or structures to significant risk of loss, injury or death involving flooding, including flooding as a result of the failure of a levee or dam; or would the project result in inundation by seiche, tsunami, or mudflow? ALL PROJECT COMPONENTS The access road alignment is located within the dam inundation zone of the Miramar Reservoir, as mapped by the Federal Emergency Management Agency (FEMA). During construction of the access road and pipeline improvements, construction workers could be exposed to significant risk of loss, injury, or death involving flooding as a result of dam failure; but this risk is speculative as dam failure is unlikely to be caused by the project. Any such risk would be very small because of the short-term nature of construction of the project within the dam inundation zone. Furthermore, the project does not include construction of buildings or housing in the inundation area, and would not permanently expose people or structures to a significant risk from flooding. Impacts would be less than significant. Due to the distance between the project area and the coast, and the area s elevation above sea level, damage due to seismically induced waves (tsunamis) is not likely. Page

11 Although the project area is near Miramar Reservoir and may be susceptible to seiches and mudflow under extremely unusual seismic circumstances, the project does not involve the construction of structures that are susceptible to inundation (i.e., occupied or habitable structures). Following construction, any inundation of the project area would not affect the access road or the replacement pipelines. Impacts would be less than significant Analysis of Cumulative Effects Threshold 1: Water Quality Standards Construction and development of cumulative projects could contribute both point and non-point source pollutants to downstream receiving waters. However, development and construction proposed under the cumulative projects would be subject to regulations that require the inclusion of project design features ensuring compliance with water quality standards, including the CWA, Porter-Cologne Water Quality Control Act, NPDES, applicable basin plans, and local regulations and policies. Compliance with water quality standards would ensure that impacts to water quality standards are reduced and there is no increase in violations of water quality standards. As discussed above, the project would have a less than significant impact to water quality standards or waste discharge requirement violations due to its inclusion of project design features such as LID strategies and storm water BMPs. Therefore, the project would have a less than significant cumulative impact associated with water quality standards and requirements. Threshold 2: Groundwater Supplies The cumulative projects identified in the analysis would not be expected to utilize groundwater for water supply, as they are within the City of San Diego or MCAS Miramar with existing infrastructure to convey imported water supplies. These projects would also be subject to similar limits on withdrawal from groundwater aquifers, if necessary for construction activities, through the RWQCB s Dewatering Permit. Therefore, the project would have a less than significant cumulative impact associated with groundwater supplies. Thresholds 3 and 4: Drainage Patterns Cumulative projects identified in this analysis would result in developments that could potentially alter existing drainage patterns in a manner that could result in substantial erosion, siltation, or on- or off-site flooding in specific areas. Because several projects are proposed in close proximity to one another, it is reasonably foreseeable that some cumulative projects would occur simultaneously. While the cumulative projects could be expected to increase impervious surfaces within the area, each project would be Page

12 required to adhere to regulations and policies during and after construction to reduce each project s potential to alter drainage patterns or contribute polluted runoff. Additionally, each project would be required to maintain pre-development discharge rates and volumes of runoff. The project includes design features, including construction BMPs, storm water LID IMPs, and bioretention basins that would avoid potential erosion, siltation, and flooding impacts or reduce such impacts to less than significant. Therefore, the project would have a less than significant cumulative impact associated with erosion, siltation, and flooding on- and off-site. Thresholds 5 and 6: Drainage Systems Impermeable surfaces associated with the cumulative projects could contribute substantial quantities of runoff which could exceed the capacity of existing storm water drainage systems, while contributing to substantial additional sources of polluted runoff. However, these projects would be subject to CEQA review, and local regulations that require development to construct storm water drainage systems to address surface flows. Therefore, the project would not contribute to a significant cumulative impact associated with the capacity of storm water systems. Thresholds 7 and 8: Flooding Hazards The identified cumulative projects would be subject to CEQA review and, therefore, would be required to comply with existing regulations related to emergency evacuation procedures for dam inundation, tsunamis, and seiche or mudflow. Compliance with these regulations would be expected to avoid any potential cumulatively significant impacts. The project would not result in significant flooding hazard impacts. Therefore, the project would not contribute to a significant cumulative impact associated with flooding hazards, from dam inundation, tsunamis, seiche, or mudflows Mitigation Measures Impacts to hydrology and water quality would be less than significant. Therefore, no mitigation measures are required Significance after Mitigation Impacts would remain less than significant. Page