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HomeMy WebLinkAbout4.H._Hydrology-Water_Quality IV. ENVIRONMENTAL IMPACT ANALYSIS H. HYDROLOGY /WATER QUALITY INTRODUCTION This section of the Draft EIR describes existing flood and inundation hazards, including creek overflow, dam and levee failure, and seismically-induced flooding, within the project area and describes whether implementation of the Precise Plan and subsequent phases of the Master Plan for the proposed project would cause a substantial change in the characteristics of local flood and inundation hazards. Surface water drainage, water quality, and other water resource issues, including flooding as a result of storm drain system deficiencies, are described in Utilities and Service Systems. Where appropriate, this section provides project level analysis for the Phase 1 Precise Plan, and program level analysis for the remainder of development proposed by the Gateway Business Park Master Plan. A regulatory framework is also provided in this section describing applicable agencies and regulations related to hydrology and water quality . Preparation of this section used data from various sources. These sources include (l) the City of South San Francisco General Plan update adopted in October 1999, (2) the East of 101 Area Plan adopted in July 1994; (3) Conceptual Project Plan by Ken Kay Associates; (4) Association of Bay Area Governments (ABAG) Hazard Maps; (5) Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRM) for the City of South San Francisco; (6) The Western Regional Climate Center web site at htto://www.wrcc.dri.edu/CLIMATEDATA.html; and (7) San Mateo County Local Agency Formation Commission. No comment letters related to flood and inundation hazards was received in response to the June 16,2007 Notice of Preparation (NOP) or the October 22, 2008 Revised NOP circulated for the project. The NOP and comment letters are included in Appendix A of this Draft EIR. Environmental Setting Climate and Topography The 22.7-acre project site is located at the southeast intersection of Gateway Boulevard and Oyster Point Boulevard in a northwest sloping area east of Highway 101 in the City of South San Francisco. The regional climate is typical of the San Francisco Bay Area and is characterized by dry, mild summers and moist, cool winters. About 80 percent of the total annual precipitation occurs during the months of November through March with an average annual precipitation of 20 inches. Average monthly temperatures range from a high of 74 degrees Fahrenheit in the summer to a low of 42 degrees Fahrenheit in the winter. 1 1 Western Regional Climate Center, 2007 Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-l City of South San Francisco October 2009 The project site and surrounding area are largely developed with light industrial, research and development, warehousing, retail, office, and hotel land uses. Over 90 percent of the 22.7-acre project area of work is currently covered in impervious surfaces. Four office buildings and associated parking areas currently occupy the site. Paved parking and office buildings are located on the west, north and east areas of the site, with a railroad right -of-way running along the southern boundary of the property. The San Francisco Bay shoreline is located approximately 850 feet north of the site. Elevations range from approximately 60 feet above Mean Sea Level (MSL) along the eastern boundary of the site to approximately 17 feet Oyster Point Boulevard in the north. The majority of working area of site is graded flat and slopes gently (less than one percent) to the north and west. Steeper landscaped slopes are located on the Oyster Point Boulevard and Gateway Boulevard in the north and west respectively, with bare slopes rising to the east at the old railroad right of way. Regional Hydrology The majority of the site drains to the Colma Creek watershed. The Colma Creek watershed includes portions of San Bruno Mountain as well as urbanized areas of Daly City, Colma, and South San Francisco. Most of this urbanized creek is channelized and/or conveyed underground to allow for urban development. The percent of impervious surface area in the Colma Creek watershed was previously estimated at 63 percent, the highest in the County? Colma Creek is a flood control channel maintained by the San Mateo County Department of Public Works that discharges into the San Francisco Bay just north of the San Francisco International Airport. Improvements and maintenance of the creek are funded by the Colma Creek Flood Control Zone, which contains the parcels that must contribute financially to the Zone's revenue and maintenance of flood control infrastructure. All but the northernmost portion of the project site is located within the designated boundaries of the Zone (Figure IV.H-l). Site Hvdrolo2:V More than approximately 70 percent of the 22.7-acre area of work at the project site is currently covered by impervious surfaces. Stormwater runoff from the project site begins as overland sheet flow and either infiltrates into site landscaping or is directed to numerous storm drain drop inlets in the parking areas. Existing storm drains convey storm water runoff westward to the stormwater network at East Grand Avenue. Stormwater is pumped southward along East Grand Avenue before discharging into the South Canal at Gateway Blvd and South Airport Blvd, and eventually into the San Francisco Bay. Groundwater The California Department of Water Resources (DWR) defines state groundwater basins based on geologic and hydrogeologic conditions. According to the DWR, the site is located across both the Westside and Visitacion Valley Groundwater Basins. These basins consist of bedrock and unconsolidated materials. Unconsolidated materials overlying the basin represent the primary water-bearing strata and comprise dune sands and the Colma Formation, which are overlain by a relatively impermeable clayey 2 City of Daly City Stormwater Pollution Prevention Program, 1998 Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-2 Figure IV.H-1 Calma Creek Flood Zone City of South San Francisco October 2009 formation of Bay Mud and fill materials. The Bay Mud layer in the east and Bedrock of the Franciscan Complex in the west underlie the water-bearing formations for the shallow groundwater layers. Groundwater is typically encountered within a few feet of the surface in the project area. While groundwater quality in the basins is generally in compliance with drinking water quality standards, some wells in the basin have experienced nitrate-nitrogen concentration in excess of the primary maximum contaminant levels. 34 Floodin2: The proj ect site is located outside of the 100-year flood hazard zone of Colma Creek as delineated by the current Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs) for the City of South San Francisco, CA, community panel number 065062 00002B, effective September 2, 1981. Stormwater generated by the project site would not contribute to the 100-year floodplain because it would be captured by stormdrains and redirected southward through the municipal stormwater network before discharging to the San Francisco Bay. Regulatory Setting The proposed project must be constructed in accordance with several regulatory programs, laws, and regulations that aim to protect surface water resources. In some cases, Federal laws are administered and enforced by state and local government. In other cases, state and local regulations in California are stricter than those imposed by Federal law. This section summarizes relevant regulatory programs, laws, and regulations with respect to hydrology and water quality and how they relate to the proposed project. Federal Clean Water Act The Clean Water Act (CW A) was enacted by Congress in 1972 and amended several times since inception. It is the primary federal law regulating water quality in the United States, and forms the basis for several state and local laws throughout the country. Its objective is to reduce or eliminate water pollution in the nation's rivers, streams, lakes, and coastal waters. The CW A prescribed the basic federal laws for regulating discharges of pollutants as well as set minimum water quality standards for all waters of the United States. Several mechanisms are employed to control domestic, industrial, and agricultural pollution under the CW A. At the Federal level, the CW A is administered by the U.S. Environmental Protection Agency (EP A). At the state and regional level, the CW A is administered and enforced by the State Water Resources Control Board (SWRCB) and the Regional Water Quality Control Boards (RWQCBs). The State of California has developed a number of water quality laws, rules, and regulations, 3 Phillips, Steven P., Scott N. Hamlin, Eugene B. Yates, 1993, Geohydrology, Water Quality, and Estimation of Ground-Water Recharge in San Francisco, California 1987-92. US Geological Survey Water-Resources Investigations Report 93-4019. 4 Department of Water Resources, 2003, California Department of Water Resources, California's Groundwater, Bulletin 118, Update 2003. Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-4 City of South San Francisco October 2009 III part to assist III the implementation of the CW A and related federally mandated water quality requirements. In many cases, the Federal requirements set minimum standards and policies and the laws, rules, and regulations adopted by the State and Regional Boards exceed the Federal requirements. National Flood Insurance Pro2:ram FEMA is responsible for determining flood elevations and floodplain boundaries based on US Army Corps of Engineers studies. FEMA is also responsible for distributing the FIRMs, which are used in the National Flood Insurance Program (NFIP). San Mateo County participates in the NFIP. FIRMs identify the locations of special flood hazard areas, including the 100-year and 500-year floodplain. Federal regulations governing development in a Zone A (lOO-year) floodplain are set forth in Title 44, Part 60 of the Code of Federal Regulations (CFR), which enables FEMA to require municipalities that participate in the NFIP to adopt certain flood hazard reduction standards for construction and development within floodplains. Mudflows are also covered under the NFIP in which San Mateo County participates. State Porter-Colo2:ne Water Quality Control Act The Porter-Cologne Water Quality Control Act establishes the SWRCB and the RWQCB as the principal state agencies having primary responsibility for coordinating and controlling water quality in California. The Porter-Cologne Act establishes the responsibility of the RWQCBs for adopting, implementing, and enforcing water quality control plans (Basin Plans), which set forth the state's water quality standards (i.e., beneficial uses of surface waters and groundwater) and the objectives or criteria necessary to protect those beneficial uses. The NPDES permit must be consistent with the Basin Plan for the site region. San Francisco Bay Water Quality Control Plan (Basin Plan) The San Francisco Bay RWQCB is responsible for the development, adoption, and implementation of the Water Quality Control Plan for the San Francisco Bay region. The Basin Plan is the master policy document that contains descriptions of the legal, technical, and programmatic bases of water quality regulation in the San Francisco Bay Region. The Basin Plan identifies beneficial uses of surface waters and groundwater within its region and specifies water quality objectives to maintain the continued beneficial uses of these waters. The proposed project is required to adhere to all water quality objectives identified in the Basin Plan. Beneficial Uses of Surface Waters and Groundwaters The Basin Plan defines beneficial uses for surface waters and groundwater in its corresponding jurisdiction. The beneficial uses of surface waters in Colma Creek include wildlife habitat, municipal and domestic supply, agricultural supply, and industrial supply. The beneficial uses of groundwater in the Westside Groundwater Basin (also referred to as the Merced Valley North Groundwater Basin) include municipal and domestic supply, industrial process supply, industrial supply, and agricultural supply. Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-5 City of South San Francisco October 2009 NPDES Permit Requirements The CW A has nationally regulated the discharge of pollutants to the waters of the U.S. from any point source since 1972. In 1987, amendments to the CWA added section 402(p), which established a framework for regulating nonpoint source (NPS) storm water discharges under the National Pollutant Elimination System (NPDES). The Phase I NPDES storm water program regulates storm water discharges from industrial facilities, large and medium-sized municipal separate storm sewer systems (those serving more than 100,000 persons), and construction sites that disturb five or more acres ofland. Under the program, the project applicant will be required to comply with two NPDES permit requirements. The NPDES General Construction Permit Requirements apply to clearing, grading, and disturbances to the ground such as excavation. The project applicant is required to submit a Notice of Intent (NO!) with the State Water Resource Control Board's (SWRCB) Division of Water Quality. The NO! includes general information on the types of construction activities that will occur on the site. The applicant will also be required to submit a site-specific plan called the Stormwater Pollution Prevention Plan (SWPPP) for construction activities. The SWPPP will include a description of Best Management Practices (BMPs) to minimize the discharge of pollutants from the site during construction. It is the responsibility of the property owner to obtain coverage under the permit prior to site construction. The NPDES General Industrial Permit Requirements apply to the discharge of storm water associated with industrial sites. The permit requires the implementation of management measures that will achieve the performance standard of best available technology (BAT) economically achievable and best conventional pollutant control technology (BCT). Under the statute, operators of new facilities must implement industrial BMPs in the project SWPPP and perform monitoring of storm water discharges and unauthorized non-storm water discharges. An annual report must be submitted to the RWQCB each July 1 st. Operators of new facilities must file an NOI at least 14 days prior to the beginning of operations. There are no state flood control regulations applicable to the proposed project. Local San Mateo Countywide Stormwater Pollution Prevention Pro2:ram To comply with the Clean Water Act, San Mateo County and the 20 cities and towns in the County formed the San Mateo Countywide Stormwater Pollution Prevention Program (STOPPP). STOPPP holds a joint municipal NPDES permit from the San Francisco Bay RWQCB. The permit includes a comprehensive plan to reduce the discharge of pollutants to creeks, San Francisco Bay, and the ocean to the maximum extent possible. San Mateo County Flood Control District The San Mateo County Flood Control District (SMCFCD) is a countywide special district that was created by state legislation in order to provide a mechanism to finance flood control projects. The Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-6 City of South San Francisco October 2009 legislation requires that a flood control zone be formed over an entire watershed and a proposed funding source is determined before a flood control project is undertaken. Recent changes in the California Constitution require an election if a flood control zone is to be financed with property assessments or taxes. There are currently three active flood control zones-Colma Creek, San Bruno Creek, and San Francisquito Creek-only one of which, Colma Creek, directly affects the project site. Colma Creek Flood Control District The Colma Creek Flood Control District (District) is administrated by the San Mateo County Department of Public Works. The District was created for the purpose of constructing flood control facilities along the Colma Creek channel and reducing flooding problems in the City of South San Francisco. The Colma Creek Flood Control Zone (Zone) extends over the entire watershed and contains the parcels that must contribute financially to the District's revenue and maintenance of the flood control facilities. Several channel improvements have been constructed since the District was created in 1964. All but the northern tip of the proposed project is located inside of the Zone boundary (Figure IV.H-l). Since the project is located inside of the Zone boundary, it would be required to contribute to funds for flood control improvements and maintenance. City of South San Francisco Water Quality Control Plant The City of South San Francisco Water Quality Control Plant requires Source Control Measures of Stormwater Pollutants for issuance of an NPDES permit, including methods for managing pollution sources. Applicable control measures include stormwater pollution prevention devices, management of refuse areas, reduced pesticide/fertilizer application for landscaping, use of treatment devices for interior level parking garage floor drains, and marking of on-site storm drains. City of South San Francisco General Plan The City's General Plan contains policies designed to protect people and development from damage associated with flooding. Policies applicable to the project are as follows. Oven Svace and Conservation Element: Water Oualitv 7.2-G-l Comply with the San Francisco Bay Regional Water Quality Control Board regulations and standards to maintain and improve the quality of both surface water and groundwater resources. 7.2-G-2 Enhance the quality of surface water resources and prevent their contamination. 7.2-G-3 Discourage the use of insecticides, herbicides, or toxic chemical substances within the city. Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-7 City of South San Francisco October 2009 Health and Safetv Element: Floodinf! 8.2-G-l Minimize the risk to life and property from flooding in South San Francisco. 8.2-1-2 Use the City's development review process to ensure that proposed development subject to the 100-year flood provides adequate protection from flood hazards, in areas identified in Figure 8-3. City of South San Francisco Municipal Code The purpose of Chapter 15.56 (Flood Damage Prevention) of the South San Francisco Municipal Code (SSFMC) is to promote the public health, safety and general welfare, and to minimize public and private losses due to flood conditions. To accomplish this purpose, this chapter includes methods and provisions to: . Restrict or prohibit uses which are dangerous to health, safety, and property due to water or erosion hazards, or which result in damaging increases in erosion or flood heights or velocities. . Require that uses vulnerable to floods, including facilities that serve such uses, be protected against flood damage at the time of initial construction. . Control the alteration of natural floodplain, stream channels, and natural protective barriers, which help accommodate or channel floodwaters. . Control filling, grading, dredging, and other development that may increase flood damage. . Prevent or regulate the construction of flood barriers which will unnaturally divert floodwaters or which may increase flood hazards in other areas. The provisions contained in SSFMC Chapter 15.56 are applicable only to development in special flood hazard areas as identified by FEMA. East of 101 Area Plan The project site is within the East of 101 Area, which is bounded by the San Francisco Bay on the east, US 101 and rail lines on the west, the City of Brisbane on the north, and San Francisco International Airport on the south. The East of 101 Area Plan, prepared in July 1994, is a policy document that guides land use, circulation, noise control, geotechnical safety, public facilities provision, design, recreation and natural resource enhancement, and financing in the East of 101 Area. With respect to hydrology and water quality, the plan aims to reduce flooding by evaluating specific development proposals to determine drainage and flood protection requirements, and to prevent the degradation of water quality by Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-8 City of South San Francisco October 2009 mInImIzmg erosIOn and sedimentation, and requmng that projects comply with NPDES permit requirements.5 The Public Facilities Element of the East of 101 Area Plan includes the following policy applicable to the project: Policy PF-8 Specific development proposals in the East of 101 Area shall be evaluated individually to determine drainage and flood protection requirements. ENVIRONMENTAL IMPACTS Thresholds of Significance The following thresholds of significance are based on Appendix G of the 2006 CEQA Guidelines. For purposes of this Draft EIR, implementation of the proposed project could result in potentially significant impacts on hydrology and water quality if the proposed project would result in any of the following: . Violate any water quality standards or waste discharge requirements. . 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) . . 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, which would result in substantial erosion or siltation on- or off-site. . 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, which would result in flooding on- or off-site. . Create or contribute runoff water, which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff. . Substantially degrade water quality. . Place 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. . Place within a 100-year flood hazard area structures which would impede or redirect flood flows. . Expose 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. 5 City of South San Francisco, East of 101 Area Plan, 1994. Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-9 City of South San Francisco October 2009 . Expose people or structures to inundation by seiche, tsunami, or mudflow. Project Impacts Impact IV.H-l: The proposed project would violate water quality standards or waste discharge requirements. The project will involve an intensification ofland-use through the gradual increase in development on the site through construction of the Precise Plan and subsequent phases of the Master Plan. Development of these phases would result in the incremental increase in floor area and number of occupants. This increased use may increase non-point source pollution to receiving waters. Non-point source pollutants (NPS) are washed by rainwater from roofs, landscape areas, and streets and parking areas into the drainage network. Typical industrial NPS pollutants for various industrial activities are listed in Table IV.H-l. Development of the proposed project would contribute to the levels ofNPS pollutants and litter entering downstream waters, including San Francisco Bay. An increase in NPS pollutants could have adverse effects on wildlife, vegetation, and human health. NPS pollutants could also infiltrate into groundwater and degrade the quality of potential groundwater drinking sources. Table IV.H-l shows potential NPS pollutants common to industrial activities. Table IV.H-1 Potential Pollutants from Industrial Activities Vehicle & Equipment Fueling X X X Vehicle & Equipment Washing X X X X X X Vehicle & Equipment Maintenance & Repair X X X Outdoor Loading & Unloading of Materials X X X X X X X Outdoor Container Storage of Liquids X X X X X X Outdoor Process Equipment Operations & Maintenance X X X X Outdoor Storage of Ray Materials, Products, & Byproducts X X X X X X X Waste Handling & Disposal X X X X X X Contaminated or Erodible Surface Areas X X X X X X X X uilding & Grounds Maintenance X X X X X X X uilding Repair, Remodeling, & Construction X X X X arking/Storage Area Maintenance X X X X ource: California Stormwater Quality Association, 2003. California Stormwater BMP Handbook, Industrial Commercial. Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-10 City of South San Francisco October 2009 Mitigation Measure IV.H-1.1 SWPPP Pursuant to NPDES requirements, the project applicant shall develop a SWPPP for the Precise Plan and each subsequent phase of the Master Plan to protect water quality during and after construction of each phase. The project SWPPP shall include, but is not limited, to the following mitigation measures for the construction period: . Erosion control/soil stabilization techniques such as straw mulching, erosion control blankets, erosion control matting, and hydro-seeding, shall be utilized, in accordance with the regulations outlined in the ABAG Manual of Standards for Erosion and Sediment Control Measures. Silt fences shall be installed down slope of all graded slopes. Hay bales shall be installed in the flow path of graded areas receiving concentrated flows and around storm drain inlets. . "Best management practices" (BMPs) for preventing the discharge of other construction- related NPDES pollutants beside sediment (i.e. paint, concrete, etc) to downstream waters. . After construction is completed, all drainage facilities shall be inspected for accumulated sediment, and these drainage structures shall be cleared of debris and sediment. Long-term mitigation measures to be included in the project SWPPP shall include, but are not limited to, the following: . Description of potential sources of erosion and sediment at the project site. Industrial activities and significant materials and chemicals that could be used at the proposed project site should be described. This will include a thorough assessment of existing and potential pollutant sources. . Identification of BMPs to be implemented at the project site based on identified industrial activities and potential pollutant sources. Emphasis shall be placed on source control BMPs, with treatment controls used as needed. . Development of a monitoring and implementation plan. Maintenance requirements and frequency shall be carefully described including vector control, clearing of clogged or obstructed inlet or outlet structures, vegetation/landscape maintenance, replacement of media filters, regular sweeping of parking lots and other paced areas, etc. Wastes removed from BMPs may be hazardous, therefore, maintenance costs should be budgeted to include disposal at a proper site. . The monitoring and maintenance program shall be conducted at the frequency agreed upon by the RWQCB and/or City of South San Francisco. Monitoring and maintenance shall be recorded and submitted annually to the SWRCB. The SWPPP shall be adjusted, as necessary, to address any inadequacies of the BMPs. . The applicant shall prepare informational literature and guidance on industrial and commercial BMPs to minimize pollutant contributions from the proposed development. This Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-ll City of South San Francisco October 2009 information shall be distributed to all employees at the project site. At a minimum the information shall cover: a) proper disposal of commercial cleaning chemicals; b) proper use of landscaping chemicals; c) clean-up and appropriate disposal of hazardous materials and chemicals; and d) prohibition of any washing and dumping of materials and chemicals into storm drains. Mitigation Measure IV.H-l. 2 Erosion Control Plans The applicant shall complete Erosion Control Plans to be submitted to the City of South San Francisco in conjunction with the Grading Permit Application for the Precise Plan and each subsequent phase of the Master Plan. The Erosion Control Plans shall include controls for winterization, dust, erosion, and pollution in accordance with the ABAG Manual of Standards for Erosion and Sediment Control Measures. The Plans shall also describe the BMPs to be used during and following construction to control pollution resulting from both storm and construction water runoff. The Plans shall include locations of vehicle and equipment staging, portable restrooms, mobilization areas, and planned access routes. Public works staff or representatives shall visit the site during grading and construction of the Precise Plan and all subsequent phases of the project to ensure compliance with the grading ordinance and plans, and note any violations, which shall be corrected immediately. Impact IV.H-2: The proposed project would not 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). More than approximately 70 percent of the project site is currently covered in impervious surfaces. Redevelopment of the site includes a number of strategies designed to decrease the amount of impervious surfaces. These strategies are shown on the conceptual site plan included in the Precise and Master Plans and include the following: replacement of ground level parking lots throughout the site with parking garages along the southeast portion of the site; replacement of wide, single story structures with multiple story buildings covering smaller footprints; and increased landscaping utilizing permeable drainage techniques. These strategies would result in the decrease the amount of impervious surfaces following construction of the Precise Plan and each subsequent phase of the Master Plan thereby increasing the potential groundwater recharge. Provided the site conceptual plans are followed, no impact due to depletion of supplies or interference with groundwater recharge would occur and no mitigation measures are required. Impact IV.H-3: The proposed project would not 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, which would result in substantial erosion or siltation on- or off-site. Stormwater runoff is currently handled by a series of stormdrains connecting to the City of South San Francisco stormdrain system. Proposed construction resulting from the Precise Plan and each subsequent Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-12 City of South San Francisco October 2009 phase of the project would also connect to the City stormdrain system. Therefore the existing drainage pattern would not be substantially altered in a manner that would result in substantial erosion or siltation either on- or off-site. Therefore this is a less than significant impact and no mitigation measures are required. Impact IV.H-4: The proposed project would not 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, which would result in flooding on- or off- site. The project would increase the percentage of area covered by pervious surfaces following construction of the Precise Plan and increasing with each subsequent phase of the project, thereby decreasing project site runoff. Therefore this is a less than significant impact and no mitigation measures are required. Impact IV.H-5: The proposed project would not place 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. The entirety of the project site is located outside of the 100-year flood zone as mapped by FEMA. Additionally the project development would consist of office and research facilities, with no housing planned. Therefore there is no impact associated with housing in a flood hazard area and no mitigation measures are required. Impact IV.H-6: The proposed project would not place within a 100-year flood hazard area structures which would impede or redirect flood flows. The entirety of the site is located outside of the 100-year flood zone. Therefore there is no impact and no mitigation measures are required. Impact IV.H-7: The proposed project would not expose 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. According to maps published by ABAG, the project is not subject to inundation due to failure of a dam, nor are there any levees near the project area. Therefore, there would be no inundation and no impact resulting from a dam or levee failure and no mitigation measures are required. Impact IV.H-8: The proposed project would not expose people or structures to inundation by seiche, tsunami, or mudflow. The proposed project is located over 2,000 feet from the San Francisco Bay, and over 5 miles from the Pacific Ocean. It is not located near an inland body of water, nor is it located adjacent to a soil slope susceptible to rapid mass wasting or mudflows. Therefore, there would be no impact due to inundation by seiche, tsunami or mudflow and no mitigation measures are required. Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-13 City of South San Francisco October 2009 CUMULATIVE IMPACTS Assuming concurrent implementation of the project with other reasonably foreseeable future projects in the vicinity, adverse cumulative effects on hydrology and water quality could include construction impacts related to increases in stormwater runoff and pollutant loading to Colma Creek and San Francisco Bay. The project and other future projects in the city would be required to comply with drainage and grading ordinances intended to control runoff and regulate water quality at each development site. New projects would be required to demonstrate that stormwater volumes could be managed by downstream conveyance facilities and would not increase flooding. Therefore, the impact of the project on water quality and hydrology, in combination with other foreseeable projects, would be less than significant. LEVEL OF SIGNIFICANCE AFTER MITIGATION Implementation of a SWPPP including BMPs to control erosion and siltation during the construction phase of the project will reduce erosion and siltation on and off the project site. The long-term mitigation measures in the SWPPP are important to mitigate the potentially increased non-point source pollution due to the intensified land-use. The short- and long-term mitigations and BMPs outlined above will serve to reduce the potentially significant impacts of increased non-point source pollution and increased sedimentation to receiving waters during construction activities to a level of less than significant. Gateway Business Park Master Plan Draft Environmental Impact Report IVH. Hydrology/Water Quality Page IVH-14