4.9 Hydrology and Floodplain/Water Quality and Storm Water Runoff

Transcription

1 Storm Water Runoff This section describes the environmental and regulatory setting for hydrology, floodplains, water quality, and storm water runoff as it relates to the Project, the impacts that may result, and feasible and appropriate mitigation measures that would be required to reduce these impacts. Hydrology, floodplains, water quality, and storm water runoff information in this section is based on the Water Quality Assessment and the Location Hydraulic Study prepared for the Project, which is located in Appendix H Regulatory Setting The following federal, state, and local regulations and plans are relevant to the Project. For a detailed discussion of the regulatory setting, refer to Appendix E. Federal Clean Water Act (various sections) Executive Order Federal Emergency Management Agency (FEMA) National Flood Insurance Program (NFIP) California Porter-Cologne Water Quality Control Act California National Flood Insurance Program Municipal Separate Storm Sewer System (MS4) Construction General Permit Regional Water Quality Control Board Basin Plan (refer to Section 4.4, Biological Resources) Santa Clara County Flood Insurance Studies Environmental Setting/Affected Environment This section provides a discussion of the existing conditions related to hydrology, floodplains, water quality, and storm water runoff in the Project corridor and surrounding area Topography Santa Clara Valley is primarily in a flat alluvial plain that lies between the Santa Cruz Mountains and the Diablo Range. On the east and west sides of the valley are foothill areas that become steeper and graduate into the mountain ranges. The Salinas Valley is to the south, and San Francisco Bay is to the north. The elevations in the County range from approximately 0 feet to 4,370 feet above mean sea level; the slope of the land is toward the bay (Federal Emergency Management Agency 2009) Hydrology There are nine waterway crossings in the Project corridor: San Tomas Aquino Creek, Saratoga Creek, Calabazas Creek, Sunnyvale East Channel, Stevens Creek, Permanente 4.9-1

2 Creek, Adobe Creek, Barron Creek, and Matadero Creek. These water bodies eventually discharge into the Lower South San Francisco Bay. Although outside of the Project corridor, Los Gatos Creek could receive runoff from the Project corridor Regional Hydrology The Project is within the San Francisco Bay Delta Watershed. According to the Caltrans Water Quality Planning Tool, within the project limits, El Camino Real crosses both the Guadalupe River and Palo Alto hydrologic areas within the Santa Clara hydrologic unit (see Table 4.9-1). The Project corridor spans two unnamed planning watersheds, 1 which both lie within the Santa Clara Hydrologic Unit (see Figure 4.9-1). Table Hydrologic Areas within the Project Corridor Nearest Cross Streets Hydrologic Unit Hydrologic Area Hydrologic Subarea Number Planning Watershed S. Autumn Street in San José to Guadalupe Santa Clara Magnolia Avenue in San José River Undefined Magnolia Avenue in San José to University Avenue in Palo Alto Santa Clara Palo Alto Undefined Source: California Department of Transportation 2013d Local Hydrology Precipitation and Climate Santa Clara County is characterized by a Mediterranean climate with warm, dry summers and cool, moist winters. Periodically, summer temperatures may rise above 100 degrees Fahrenheit ( F). Although the winters are generally mild, temperatures may drop below 20 F for short periods of time. The variance in temperature in the northern portion of the county is relatively small as a result of the close distance to San Francisco Bay (Federal Emergency Management Agency 2009). Annual precipitation averages approximately 20 inches in the area; more than 35 inches has been recorded in some years. Most of the precipitation occurs from October through May. Violent snowfalls, thunderstorms, and other extreme weather conditions are rare. Surface Streams A cumulative list of Project receiving water bodies was determined using the Santa Clara Valley Urban Runoff Pollution Prevention Program Hydromodification Management Applicability Maps, FEMA maps, United States Geological Survey (USGS) topographic maps, and aerial maps. Table lists the Project receiving water bodies (see Figure for a map of approximate location of each creek and stream crossing). San Tomas Aquino Creek, Sunnyvale East Channel, Permanente Creek, and Barron Creek flow under El Camino Real through concrete box culverts, while the other water bodies are crossed by bridges. 1 Planning watersheds lie with in hydrologic sub-areas and are delineated for planning purposes rather than based on drainage surface area

3 NORTH Undefined NO SCALE Undefined Graphics ( ) Source: Caltrans. Figure Project Planning Watersheds

4 NORTH NO SCALE Graphics ( ) Source: USGS. Figure Creek Crossings

5 Table Project Receiving Water Bodies Stream Name El Camino Real (State Route 82) Post Mile Nearest Cross Street Crossing Type Length (feet) Bridge Dimensions b Width (feet) Los Gatos Creek a NA Delmas Avenue Bridge No. 37-C San Tomas Aquino Creek San Tomas Expressway Reinforced Concrete Box N/A Saratoga Creek Bowe Avenue Bridge No Number of Spans Calabazas Creek Calabazas Boulevard Bridge No Sunnyvale East Channel E. Remington Drive Reinforced Concrete Box N/A Stevens Creek SR 85 Bridge No Permanente Creek Mariposa Avenue Reinforced Concrete Box N/A Adobe Creek Monroe Drive Bridge No Barron Creek Los Robles Avenue Reinforced Concrete Box N/A Matadero Creek Fernando Avenue Bridge No Notes/Source: a Waterway crosses outside of the Project corridor, but the waterway has the potential to receive runoff from the Project corridor. b Bridge dimensions are from the California Log of Bridges on State Highways (California Department of Transportation 2013c) Groundwater Hydrology The Project corridor is within the Santa Clara Valley groundwater basin, Santa Clara groundwater sub-basin, which together are also known as Coyote Valley groundwater basin (San Francisco Bay Regional Water Quality Control Board 2013b). The depth to groundwater varies between approximately 5.6 and 59.6 feet below ground surface (bgs) in the Project corridor (see Table 4.9-3). The groundwater elevation gradually decreases from San José in the east to Palo Alto in the west. Table Water Table Information in the Project Area Project Area Depth to Water (feet bgs) Groundwater Elevation (feet above mean sea level) San José 5.6 to to 79.1 Santa Clara 6.4 to to 72.0 Sunnyvale 30.1 to to 75.0 Mountain View Palo Alto 18.1 to to 14.8 Source: State Water Resources Control Board Geology/Soils According to the Geologic Map of California (California Department of Conservation), the Project corridor is within Quaternary (Q) deposits and Quaternary older alluvial (Qoa) sedimentary deposits. Q deposits are from the Holocene epoch and are defined as alluvium, 4.9-3

6 lake, playa, and terrace deposits; unconsolidated and semi consolidated. Qoa deposits are from the Pleistocene epoch and are defined as older alluvium, lake, playa, and terrace deposits. Hydrologic Soil Group (HSG) C soils have low infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water and soils with moderately fine to fine texture. Areas of HSG C occur in San José, Santa Clara, and Palo Alto. HSG D soils have high runoff potential. They have very low infiltration rates when thoroughly wetted. Most of the Project corridor contains soils that are classified as HSG D. For a detailed description of the geology/soils at the Project site, refer to the Water Quality Assessment and Geotechnical Report in the Appendix H Soil Erosion Potential Erosion is the detachment and movement of soil material by natural processes, such as wind and water. The rate of soil erosion, which is dependent on the local landscape, climate, and soil properties, can be accelerated by human activities such as construction grading and excavation. In the Project vicinity, erosion from storm water runoff is the dominant natural erosion process. The susceptibility of soils to water erosion is described by the K factor derived for the Universal Soil Loss Equation. Soils with a moderate susceptibility to water erosion have K factors between 0.25 and 0.4, and soils with a high susceptibility to water erosion have K factors greater than 0.4. Based on K factors estimated by Caltrans Stormwater Design Application, all soils in the surface layer within the Project corridor have a K factor of 0.32, or moderate susceptibility to water erosion (California Department of Transportation 2013d) Water Quality and Water Quality Objectives/Standards and Beneficial Uses Surface Water The San Francisco Regional Water Quality Control Board s (RWQCB) Basin Plan identifies water quality objectives for the region. The general water quality objectives established for surface waters within the San Francisco Bay region address bacteria, bioaccumulation, biostimulatory substances, color, dissolved oxygen, floating material, oil and grease, population and community ecology, ph, radioactivity, salinity, sediment, settleable material, suspended material, sulfide, taste and odors, temperature, toxicity, turbidity, and un-ionized ammonia. The Basin Plan lists beneficial uses for several of the Project s receiving water bodies. Detailed descriptions of the individual beneficial uses are provided in the excerpts from Chapter 2 Beneficial Uses of the Basin Plan. Sunnyvale East Channel is the only Project receiving water body that does not have any existing or potential beneficial uses listed in the Basin Plan (2013). Groundwater The Basin Plan identifies groundwater objectives for the region. The Basin Plan states, At a minimum, groundwater shall not contain concentrations of bacteria, chemical constituents, 4.9-4

7 radioactivity, or substances producing taste and odor in excess of the groundwater quality objectives unless naturally occurring background concentrations are greater. The Coyote Valley groundwater basin has the existing beneficial uses of municipal and domestic water supply, industrial process and service water supply, and agricultural water supply. Groundwater sub-basins identified as having the existing groundwater beneficial use of municipal and domestic water supply are subject to further objectives regarding bacteria, organic and inorganic constituents, radioactivity, and taste and odor. Groundwater sub-basins identified as having the beneficial use of agricultural water supply are subject to additional objectives regarding organic and inorganic chemical constituents Existing Water Quality List of Impaired Waters Los Gatos Creek, Saratoga Creek, Stevens Creek, Permanente Creek, and Matadero Creek are Project receiving water bodies listed as impaired waters in the latest CWA Section 303(d) Integrated Report (State Water Resources Control Board 2010). This impairment is due to diazinon, trash, temperature, and toxicity. Groundwater Contamination The Initial Site Assessment for the Project (prepared in 2013, refer to Appendix H) revealed residual groundwater contamination from closed hazardous materials release sites in the Project vicinity. Based on the large quantity of closed release sites, residual groundwater contamination may likely be present beneath the Project corridor Floodplain Floodplains were defined using the FEMA Flood Insurance Rate Maps (FIRMs). The FIRMs show that the Project corridor crosses 13 floodplains with a 1% annual chance of flooding (also known as the 100-year flood) (refer to Figure for a map of the floodplains). The FIRMs can be found in Location Hydraulic Study (Appendix A) in Appendix H. As indicated in Table 4.9-4, there are several areas within the Project corridor that are inundated during a 1% annual chance flood. A flood could interrupt traffic on El Camino Real, forcing traffic onto other roads that are not flooded

8 Table Hydrologic and Hydraulic Information at Flooding Sources on El Camino Real Post Mile Flood Source At Creek Crossing FIRM Panel(s) SFHA a 1% Annual Chance Peak Discharge (cubic feet per seconds) Drainage Area (square miles) Water Surface Elevation or Flood Depth Upstream Downstream Approximate Roadway Elevation (feet) 8.42 N/A No 06085C0234H AO N/A N/A Depth 1 foot Yes R10.76 N/A No 06085C0231H AH N/A N/A Elevation 66 feet Yes R11.32 N/A No 06085C0227H AH N/A N/A Elevation 65 feet Yes San Tomas Aquino Creek Yes 06085C0227H, 06085C0226H AO/A H 3, Elevation 79 feet Depth 1 foot Yes Inundates El Camino Real b Saratoga Creek Yes 06085C0226H A 4, Contained c Contained c No c Calabazas Creek Yes 06085C0226H A 2, Contained c Contained c 89 No c N/A No 06085C0207H AO N/A N/A Depth 1.5 feet Yes Sunnyvale East Channel No 06085C0207H AO N/A N/A Depth 1.5 feet Yes Stevens Creek Yes 06085C0039H A N/A N/A N/A N/A Yes Permanente Creek Yes 06085C0039H AO 1, Depth 1 foot Yes Adobe Creek Yes 06085C0036H and 06085C0038H A 2, Contained d Contained d No d Barron Creek No 06085C0017H A Contained d Contained d 42 No d Matadero Creek Yes 06085C0017H A 2, Contained d Contained d 39 No d Source: Federal Emergency Management Agency Notes: a 1% Annual Chance Flood Hazard = Special Flood Hazard Area (SFHA), which can include Zones A, AO, AH, A1-30, AE, A99, AR, AR/A1-30, AR/AE, AR/AO, AR/AH, AR/A, VO, V1-30, VE, and V. Zone X = 0.2% annual chance flood hazard zone and Zone D = Areas of undetermined flood hazard zone. b Based on information shown on FIRMs. c To be verified. FEMA flood profile not available at this location. d Confirmed by available FEMA flood profile at this location

9 1% Annual Chance Flood Hazard 1 Zone X 2 Zone AH at PM R11.32 Zone D 3 Zone AO at PM Zone AH at PM R10.76 Zone AO at PM 8.42 Graphics ( ) Notes: 1. 1% Annual Chance Flood Hazard=Special Flood Hazard Areas, which can include Zones A, AO, AH, A1-30, AE, A99, AR, AR/A1-30, AR/AE, AR/AO, AR/AH, AR/A, VO, V1-30, VE, and V. 2. Zone X= 0.2% annual chance flood hazard zone. 3. Zone D= Areas of undetermined flood hazard zone. Legend 1% Annual Chance Flood Hazard 0.2% Annual Chance Flood Hazard Areas of undetermined flood hazard zone Source: FEMA, Figure FEMA Floodplains

10 4.9.3 Environmental Impact Analysis Criteria for Determining Significance The California Environmental Quality Act (CEQA) Guidelines Appendix G (14 California Code of Regulations et seq.) has identified significance criteria to be considered for determining whether a project could have significant impacts related to hydrology, floodplains, water quality and storm water runoff. The Project would have a significant impact if it would result in any of the following conditions. Violate any water quality standards or waste discharge requirements. Substantially deplete groundwater supplies or interfere substantially with groundwater recharge, resulting in 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 that would not support existing land uses or planned uses for which permits have been granted). 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 that would result in substantial erosion or siltation onsite or offsite, or flooding, onsite or offsite. 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 that would result in flooding onsite or offsite. Create or contribute runoff water that would exceed the capacity of existing or planned storm water drainage systems or provide substantial additional sources of polluted runoff. Otherwise substantially degrade water quality. Place within a 100-year flood hazard area structures that would impede or redirect flood flows. All other Appendix G significance criteria related to hydrology and water quality are described in Section 4.14, Other Environmental Considerations Methods The information derived for these impacts was taken from the Location Hydraulic Study and the Water Quality Assessment prepared for the Project, both of which are located in Appendix H Impacts Impact HYD-1: Violate any water quality standards or waste discharge requirements, or otherwise degrade water quality No Build Alternative (No impact) There would be no construction or changes to the existing transit corridor under the No Build Alternative. Therefore, there would be no impact on any water quality standards, waste 4.9-7

11 discharge requirements, or other potential adverse effect involving degradation of water quality. Build Alternatives (Less than significant) Construction Soil erosion or the introduction of suspended solids into waterways as a result of Project construction could impact or contribute to degradation of water quality. Each of the Build Alternatives would disturb at least 1 acre of soil. Therefore, all of the Build Alternatives would be required to comply with the National Pollutant Discharge Elimination System (NPDES) Construction General Permit (CGP), as described in Avoidance and Minimization Measure (AMM) HYD-A: Comply with the NPDES General Construction Permit and Caltrans MS4 Permit. As part of the permit application for the CGP, the Project contractor will prepare a Stormwater Pollution Prevention Plan (SWPPP) containing best management practices (BMPs) that will be implemented to prevent, or minimize the potential for, sedimentation and erosion. Adherence with the CGP and the BMPs listed in the SWPPP would keep sediment and suspended solids from entering the waterways and ensure that impacts on water quality during Project construction would be less than significant. No mitigation is required. AMM HYD-A: Comply with the NPDES General Construction Permit and Caltrans MS4 Permit Prior to Project construction, the Santa Clara Valley Transportation Authority (VTA) will ensure that the Project s contractor submits a SWPPP as part of the permit application for the CGP to the State Water Board. The SWPPP will be submitted by the Project contractor and approved by Caltrans prior to the start of construction. The Project contractor will implement the SWPPP during construction to comply with the conditions of Caltrans MS4 Permit and CGP. The SWPPP will include selected temporary BMPs to prevent or minimize the potential for sedimentation and erosion. The Project Planning and Design Guide (California Department of Transportation 2010c) describes approved erosion control BMPs. Temporary erosion control and water quality measures will be defined in detail in the Erosion Control and Water Pollution Control design sheets prepared for the Project. The proposed construction site BMPs will be reviewed and approved by Caltrans Construction Stormwater Coordinator during the design phase. Coverage under the CGP considers dewatered water as an authorized non-storm water discharge. However, if dewatering is necessary, the contractor will be required to comply with dewatering requirements of the San Francisco Bay Regional Water Quality Control Board. Groundwater extracted during dewatering will either be treated prior to discharge or disposed of at a publicly owned treatment work (POTW)

12 Operation Under any of the Build Alternatives, there would be minimal permanent impacts on water quality because there would be a net reduction in pervious area. Impacts on water quality would be proportional to the length of dedicated lanes constructed. For example, Alternative 4c would have the longest dedicated lane segment, and, thus, would have the most potential water quality impacts. Alternative 4c, which is the alternative with the longest dedicated lane, would create a total of 58.3 acres of new impervious surface. This total does not take into consideration any potential conversion of existing impervious surface to landscaping, which would benefit water quality. The Caltrans MS4 permit contains provisions to reduce pollutant loadings from the Project once construction is complete. The permit stipulates that Caltrans and non-caltrans projects within the Caltrans right-of-way that are new development or redevelopment will comply with the standard project planning and design requirements for new development and redevelopment. Permanent control measures located within Caltrans right-of-way reduce pollutants in storm water runoff from the roadway. These measures reduce the suspended particulate loads, and, thus, pollutants associated with the particles, from entering waterways. The measures would be incorporated into the final engineering design or landscape design of the Project and would take into account expected runoff from the roadway. In addition, the permit stipulates that an operation and maintenance program for permanent control measures must be implemented. None of the Build Alternatives would result in a net increase in impervious areas in the portion of the Project corridor within Caltrans right-of-way. Therefore, under the Caltrans MS4 permit, additional hydromodification management is not anticipated. VTA would coordinate with Caltrans during the Project design phase to verify requirements within Caltrans right-of-way. For the Project portion east of I-880, which is within the City of San José s right-of-way, the Project is not a regulated project and thus is exempt from treatment BMP and hydromodification management requirements. Section 4 of the Project Planning and Design Guide (California Department of Transportation 2010c) presents the methods used to determine whether a project is required to consider the use of treatment BMPs. The Project portion within Caltrans right-of-way is required to consider the use of treatment BMPs because this Project is not classified as an emergency project, directly discharges to surface waters, and results in the addition or replacement of at least 1 acre of impervious area under any of the Build Alternatives. AMM HYD-B contains provisions for implementing the BMPs that would provide permanent pollution prevention design that would address potential impacts on water quality during Project operation. Impacts on water quality during Project operation would be less than significant. No mitigation is required. AMM HYD-B: Implement permanent pollution prevention design measures The Project will comply with Caltrans MS4 Permit, including implementation of operational BMPs. Caltrans has an approved list of treatment BMPs that have been studied and verified to remove targeted design constituents and provide general pollutant 4.9-9

13 removal. The Caltrans approved treatment BMPs that may be applicable to the Project include biofiltration swales/strips, infiltration devices, detention devices, traction sand traps, media filters, and multi-chamber treatment trains. In addition, the potential provision of trash capture devices may be explored if requested by Caltrans as part of its strategy to meet the trash capture reduction provisions in Attachment V, Part 2 of the Caltrans MS4 permit for the San Francisco Bay region. Gross solids removal devices, which have been approved by Caltrans, and hydrodynamic separators, which are used in Santa Clara County as flow-through pre-treatment structures to remove sediment and trash, may be considered as viable trash capture devices for the Project. The feasibility and determination of preferred treatment BMPs should be coordinated with the Caltrans District 4 Office of Water Quality Stormwater Coordination Branch to ensure that both Caltrans and regional requirements are met. Impact HYD-2: Substantially deplete groundwater supplies or substantially interfere with groundwater recharge No Build Alternative (No impact) Under this alternative, there would be no construction of station improvements or dedicated lanes. Therefore, this alternative would have no potential adverse effect involving substantial depletion of groundwater supplies or substantial interference with groundwater recharge. Build Alternatives (Less than significant) Construction Construction of any of the Build Alternatives would not involve substantial excavations that would affect groundwater resources. Based on preliminary geotechnical information, the depth to groundwater varies from approximately 5.6 to 59.6 feet bgs. Construction of the Build Alternatives would involve storm drain trenching. Under all Build Alternatives, there would be excavation to a maximum depth of 18 feet bgs at one location near the Santa Clara Transit Center, in Santa Clara. At this location, the existing depth to water is between approximately 6.4 and 12.2 feet bgs. Therefore, dewatering would be anticipated for the Project at this location. Residual contaminated groundwater could be encountered during dewater activities. As described under AMM HYD-A, if dewatering is necessary, the Project contractor would be required to comply with dewatering requirements of the RWQCB. Groundwater extracted during dewatering activity would either be treated prior to discharge or disposed of at a wastewater treatment facility. Adherence to dewatering requirements of the RWQCB will ensure that impacts on groundwater would be less than significant. No mitigation is required. Operation As described under Impact HYD-1, implementation of any of the Build Alternatives would result in either no change or a net reduction in impervious area. An increase of pervious area could result in an increase in the volume or amount of water that recharges localized aquifers

14 and an increase in regional groundwater volumes. The reduction of impervious area would be minimal, ranging from 0.3 percent to 1.0 percent depending upon the Build Alternative that is implemented. Any impact on groundwater recharge would be less than significant. No mitigation is required. Impact HYD-3: Alter existing drainage patterns in a manner that would result in substantial erosion, siltation onsite or offsite, or flooding onsite or offsite No Build Alternative (No impact) There would be no construction of station improvements or dedicated lanes. Therefore, there would be no potential adverse effect involving substantial erosion, siltation onsite or offsite, or flooding onsite or offsite. Build Alternatives (Less than significant) Construction Construction activities, such as grading and excavation, could result in increased erosion. In addition, there would be minor modification to city street storm drains. However, these modifications would not include culvert widening or conversion of open channels to closed conduits and drainage patters would remain approximately the same. As described under AMM-HYD-A, which would require compliance with the NPDES CGP, preparation and implementation of a SWPPP that contains temporary construction site BMPs would occur. These BMPs would be implemented during construction to prevent, or minimize the potential for, erosion sedimentation, or flooding onsite or offsite. Because the Project would be required to comply with the conditions of the NPDES CGP, impacts related to erosion, siltation, and flooding would be less than significant. No mitigation is required. Operation Existing storm drains may be modified to accommodate Project construction work, but the existing drainage pattern is not expected to change. No stream or river would be altered. The drainage design would limit the design water surface elevations and velocities to no greater than the existing conditions or to what can be handled by the existing conditions within the Project area. The 13 floodplains that intersect the Project corridor would not be affected by any of the proposed BRT stations. However, under Build Alternatives 3 and 4, the Project would construct new landscaped and hardscaped medians associated with the dedicated lanes. Under these alternatives, the total areas of newly constructed landscaped median would be greater than the total areas of newly constructed hardscaped median and newly constructed pavement. Overall, the landscaped median construction would reduce the impervious area within the Project corridor. The reduction in impervious surface would increase the areas available for infiltration of storm water, resulting in a decrease in peak runoff. Because the change in impervious surfaces would be 0.01% compared with the overall watershed area draining to each creek, the Project does not pose a significant flooding

15 risk. Therefore, impacts related to erosion, siltation, and flooding during operation of any of the Build Alternatives would be less than significant. No mitigation is required. Impact HYD-4: Create or contribute to runoff water that would exceed the capacity of existing or planned storm water drainage systems or provide substantial additional sources of polluted runoff No Build Alternative (No impact) Under this alternative, there would be no construction of stations or dedicated lanes. Therefore, there would be no potential adverse effect involving creation of or contribution to runoff water. Build Alternatives (Less than significant) Construction The Project drainage design would maintain existing drainage patterns; however, temporary drainage facilities could be required to redirect runoff from work areas. The temporary drainage facilities would be sized according to city standards to avoid any exceedance to the capacity of existing or planned storm water drainage systems. Storm drain relocation work is proposed, which may require the need for groundwater dewatering at locations with a high water table. Residual contaminated groundwater may be encountered during dewatering activities. As described under AMM HYD-A, if dewatering is necessary, the Project contractor would be required to comply with dewatering requirements of the RWQCB. Groundwater extracted during dewatering activity would either be treated prior to discharge or disposed of at a wastewater treatment facility. Therefore, Project construction impacts would be less than significant. No mitigation is required. Operation The Build Alternatives would result in a net decrease in total impervious surface area within the Project corridor. Therefore, none of the Build Alternatives is expected to increase the volume of storm water runoff. Potential sources of pollutants from the Project s right-of-way are total suspended solids, nutrients, pesticides, particulate metals, dissolved metals, pathogens, litter, biochemical oxygen demand, and total dissolved solids. Existing drainage facilities within the Project limits may be modified as necessary to provide proper off-site and roadway drainage. Additionally, adherence to the Caltrans MS4 permit, as described under AMM-HYD-A, would ensure that the appropriate treatment BMPs are applied to the Project so that there would not be additional sources of polluted runoff. Therefore, Project operation impacts on runoff would be less than significant. No mitigation is required

16 Impact HYD-5: Place structures that would impede or redirect flood flows within a 100-year flood hazard area No Build Alternative (No Impact) No station improvements or dedicated lanes would be constructed. Therefore, this alternative would have no potential impact on flood flows within a 100-year flood hazard area. Build Alternatives (Less than significant) Under Build Alternatives 3 and 4, the proposed dedicated lanes would be at-grade, and, under all Build Alternatives, the locations of new BRT stations would not be within any floodplains. Under Alternatives 3 and 4, there would be some fill located within the floodplain related to construction of the landscaped medians. The overall change in land use due to median construction would be minimal. The fill and the change in impervious area would have minimal impact on the water surface elevation during a 100-year flood event. The proposed curb at the median would be approximately 6 inches high, which would not be tall enough to interrupt the flood flow pattern. Therefore, the Build Alternatives would not place structures that would impede or redirect floodflows within a 100-year flood hazard area, and impacts would be less than significant. No mitigation is required