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HomeMy Public PortalAbout4-9_HydrologyWaterQuality.pdf4.9 HYDROLOGY AND WATER QUALITY 4.9-1 A. Introduction This section addresses impacts of the proposed project on hydrology, water quality, and flooding within the site and its surroundings. The analysis con- tained within this section considers all short-term hydrologic impacts associ- ated with construction and long-term impacts associated with buildout of the Canyon Springs Subdivision, and addresses all factors contained within Ap- pendix G, Environmental Checklist, of the California Environmental Quality Act (CEQA) Guidelines. This analysis is based on review of available reports, regulatory documents, site-specific environmental investigations, and site re- connaissance conducted in August 2011. Based on this information, this sec- tion describes potential impacts that may result from the proposed project and identifies mitigation measures to reduce potential impacts to a less-than- significant level, if feasible. B. Regulatory Framework This section summarizes existing local, state, and federal laws, policies, and regulations that apply to potential hydrology, water quality, and flooding impacts associated with the proposed project. 1. Federal Laws and Regulations a. Clean Water Act Under the Clean Water Act (CWA) of 1977, the US Environmental Protec- tion Agency (EPA) seeks to restore and maintain the chemical, physical, and biological integrity of the nation’s waters. The statute employs a variety of regulatory and non-regulatory tools to reduce direct pollutant discharges into waterways, finance municipal wastewater treatment facilities, and manage polluted runoff. The CWA authorizes the EPA to implement water quality regulations. The National Pollutant Discharge Elimination System (NPDES) permit program under Section 402(p) of the CWA controls water pollution by regulating stormwater discharges into the waters of the United States. California has an approved state NPDES program. The EPA has delegated authority for water permitting to the State Water Resources Control Board TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-2 (SWRCB), which has nine regional boards. The Lahontan Regional Water Quality Control Board (RWQCB) regulates water quality in the project area. Sections 401 and 404 of the CWA are administered through the Regulatory Program of the U.S. Army Corps of Engineers (ACOE) and regulate the wa- ter quality of all discharges of fill or dredged material into waters of the Unit- ed States including wetlands and intermittent stream channels. Section 401, Title 33, Section 1341 of the CWA sets forth water-quality certification re- quirements for “any applicant applying for a federal license or permit to con- duct any activity including, but not limited to, the construction or operation of facilities, which may result in any discharge into the navigable waters.” Work associated with road/stream crossings in the proposed project area and other construction activities may require the acquisition of a permit from the ACOE under Section 404 of the CWA and water quality certification from the Lahontan RWQCB under Section 401 of the CWA. Section 401 certifica- tion is required from the Lahontan RWQCB prior to final issuance of Section 404 permits by the ACOE. i. Total Maximum Daily Load Section 303(d) of the CWA requires that each state identify water bodies or segments of water bodies that are “impaired” (i.e., not meeting one or more of the water quality standards established by the state). These waters are identi- fied in the Section 303(d) list as waters that are polluted and need further at- tention to support their beneficial uses. Once the water body or segment is listed, the state is required to establish Total Maximum Daily Load (TMDL) for the pollutant causing the conditions of impairment. TMDL is the maxi- mum amount of a pollutant that a water body can receive and still meet water quality standards. Typically, TMDL is the sum of the allowable loads of a single pollutant from all contributing point and non-point sources. The in- tent of the 303(d) list is to identify water bodies that require future develop- ment of a TMDL to maintain water quality. In accordance with Section 303(d), the RWQCB has identified impaired water bodies within its jurisdic- tion, and the pollutant or stressor responsible for impairing the water quality. The Middle Truckee River, which runoff from the project area ultimately TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-3 drains to, is listed for sediment. The primary sources of sediment identified in the TMDL are dirt roads, urban stormwater runoff, legacy erosion sites, and in some subwatersheds, graded ski runs. ii. Federal Emergency Management Agency The Town is a participant in the National Flood Insurance Program (NFIP), a federal program administered by the Federal Emergency Management Agency (FEMA). Participants in the NFIP must satisfy certain mandated floodplain management criteria. The National Flood Insurance Act of 1968 has adopted, as a desired level of protection, an expectation that development should be protected from floodwater damage produced by the Intermediate Regional Flood, defined as a flood that has an average frequency of occur- rence on the order of once in 100 years, although such a flood may occur in any given year. The Town has adopted a floodplain management ordinance as a part of their Development Code that exceeds the minimum requirements established by FEMA. The Town is occasionally audited by the California Department of Water Resources to ensure that proper implementation of FEMA floodplain management regulations is occurring. 2. State Laws and Regulations a. Porter-Cologne Water Quality Control Act In 1969, the California Legislature enacted the Porter-Cologne Water Quality Control Act to preserve, enhance, and restore the quality of the state’s water resources. The act established the SWRCB and nine RWQCBs as the princi- pal state agencies with the responsibility for controlling water quality in Cali- fornia. Under the act, water quality policy is established, water quality stand- ards are enforced for both surface water and groundwater, and the discharges of pollutants from point and non-point sources are regulated. The act author- izes the SWRCB to establish water quality principles and guidelines for long- range resource planning including groundwater and surface water manage- ment programs and control and use of recycled water. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-4 b. Water Quality Control Plan for the Lahontan Region (Basin Plan) Section 13240 of the Porter-Cologne Water Quality Control Act requires each RWQCB to formulate and adopt water quality control plans, or basin plans, for all areas within their region. The Porter-Cologne Act also requires each RWQCB to establish water quality objectives within the basin plans. Title 40, Code of Federal Regulations, Part 131 requires each state to adopt water quality standards by designating water uses to be protected and adopt- ing water quality criteria that protect the designated uses. In the State of Cali- fornia, the beneficial uses and water quality objectives are the State’s water quality standards. The project site is located within and regulated by the Lahontan Region Water Quality Control Plan. The project site ultimately drains to the Truckee River, and the Lahontan Region Water Quality Control Plan lists specific water quality objectives for the segment of the Truckee Riv- er below the confluence with Donner Creek. In addition, Chapter 4 of the Basin Plan prohibits the discharge or threatened discharge, attributable to human activities, of solid or liquid waste materials including soil, silt, clay, sand, and other organic and earthen materials to lands within the 100-year floodplain of the Truckee River or any tributary to the Truckee River. However, exemptions may be granted by the Lahontan RWQCB that fall within the following categories of new projects: ¤ Projects solely intended to reduce or mitigate existing sources of erosion or water pollution, or to restore the functional value to previously dis- turbed floodplain areas. ¤ Bridge abutments, approaches, or other essential transportation facilities identified in an approved General Plan. ¤ Projects necessary to protect public health or safety or to provide essen- tial public services. ¤ Projects necessary for public recreation. ¤ Projects that will provide outdoor public recreation within portions of the 100-year floodplain that have been substantially altered by grading and/or filing activities which occurred prior to June 26, 1975. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-5 c. Statewide National Pollutant Discharge Elimination System General Permit for Construction The SWRCB is responsible for implementing the CWA and issues the NPDES permits to cities and counties through RWQCBs. The project site is located in a portion of the state that is regulated by the Lahontan RWQCB. The SWRCB has issued a statewide General Permit (Water Quality Order No. 99-08-DWQ) for construction activities within the state. The Construc- tion General Permit (CGP) is implemented and enforced by the RWQCBs. The CGP applies to construction activity that disturbs 1 acre or more and requires the preparation and implementation of a stormwater pollution pre- vention plan (SWPPP) that identifies best management practices (BMPs) to minimize pollutants from discharging from the construction site to the max- imum extent practicable. On September 2, 2009, the SWRCB adopted a new CGP (Order No. 2009-0009-DWQ, as amended by Order No. 2010-0014- DWQ) that superseded the existing CGP on July 1, 2010. A summary of the differences between the prior CGP and the current CGP follows: ¤ Rainfall Erosivity Waiver. This General Permit includes the option al- lowing a small construction site (>1 and <5 acres) to self-certify if the rainfall erosivity value (R value) for their site’s given location and time frame computed to be less than or equal to 5. ¤ Technology-Based Numeric Action Levels. This General Permit in- cludes numeric action levels (NALs) for pH and turbidity. ¤ Technology-Based Numeric Effluent Limitations. This General Per- mit contains daily average numeric effluent limitations (NELs) for pH during any construction phase where there is a high risk of pH discharge and daily average NELs turbidity for all discharges in Risk Level 3. The daily average NEL for turbidity is set at 500 turbidity (NTU) to repre- sent the minimum technology that sites need to employ (to meet the tra- ditional Best Available Technology Economically Achievable (BAT)/Best Conventional Pollutant Control Technology (BCT) standard) and the traditional, numeric receiving water limitations for turbidity. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-6 ¤ Risk-Based Permitting Approach. This General Permit establishes three levels of risk possible for a construction site. Risk is calculated in two parts: (1) Project Sediment Risk, and (2) Receiving Water Risk. ¤ Minimum Requirements Specified. This General Permit imposes more minimum BMPs and requirements that were previously only required as elements of the SWPPP or were suggested by guidance. ¤ Project Site Soil Characteristics Monitoring and Reporting. This General Permit provides the option for dischargers to monitor and re- port the soil characteristics at their project location. The primary pur- pose of this requirement is to provide better risk determination and even- tually better program evaluation. ¤ Effluent Monitoring and Reporting. This General Permit requires ef- fluent monitoring and reporting for pH and turbidity in stormwater dis- charges. The purpose of this monitoring is to determine compliance with the NELs and evaluate whether NALs included in this General Permit are exceeded. ¤ Receiving Water Monitoring and Reporting. This General Permit re- quires some Risk Level 3 dischargers to monitor receiving waters and conduct bio-assessments. ¤ Post-Construction Stormwater Performance Standards. This General Permit specifies runoff reduction requirements for all sites not covered by a Phase I or Phase II MS4 NPDES permit, to avoid, minimize and/or mitigate post-construction stormwater runoff impacts. ¤ Rain Event Action Plan. This General Permit requires certain sites to develop and implement a Rain Event Action Plan (REAP) that must be designed to protect all exposed portions of the site within 48 hours prior to any likely precipitation event. ¤ Annual Reporting. This General Permit requires all projects that are enrolled for more than one continuous three-month period to submit in- formation and to annually certify that their site is in compliance with these requirements. The primary purpose of this requirement is to pro- TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-7 vide information needed for overall program evaluation and pubic in- formation. ¤ Certification/Training Requirements for Key Project Personnel. This General Permit requires that key personnel (e.g., SWPPP preparers, inspectors) have specific training or certifications to ensure their level of knowledge and skills are adequate to ensure their ability to design and evaluate project specifications that will comply with General Permit re- quirements. The Lahontan RWQCB has also established project guidelines for erosion control that include specific BMPs that are required to be incorporated into construction projects and has established waste discharge prohibitions and exception criteria for projects within the Truckee River Hydrologic Unit. Certain actions during construction may also need to conform to a General Permit (Water Quality Order No.5-00-175) which requires that a permit be acquired for dewatering and other low threat discharges to surface waters, provided that they do not contain significant quantities of pollutants and ei- ther (1) are four months or less in duration, or (2) the average dry weather discharge does not exceed 0.25 million gallons per day (mgd). Examples of activities that may require the acquisition of such a permit include well devel- opment water, construction dewatering, pump/well testing, pipeline/tank pressure testing, pipeline/tank flushing or dewatering, condensate discharges, water supply system discharges, and other miscellaneous dewatering/low threat discharges. However, the actions applicable to the proposed project may already be covered under the CGP, and therefore a separate permit may not be required. 3. Local Regulations and Policies a. National Pollutant Discharge Elimination System General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems The federal NPDES program is administered locally by the Lahontan RWQCB. The Lahontan RWQCB has delegated responsibility for imple- TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-8 mentation of stormwater regulations in the vicinity of the Plan Area to the Town. The General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems, Water Quality Order (WQO) No. 2003-0005-DWQ (Small MS4 General Permit), requires that Dischargers (such as the Town) to develop and implement a Stormwater Management Program (SWMP). The SWMP describes the BMPs, measurable goals, and time sched- ules for implementation as well as assigns responsibility for each task. The MS4 General Permit requires all permittees to develop and implement a SWMP designed to reduce the discharge of pollutants through their MS4s to the maximum extent practicable. A SWMP has been prepared by the Town and has been approved by the Wa- ter Board (Permit No.6A290712005). The SWMP describes the programs to be implemented in the Town to control stormwater pollutants. The SWMP includes guidance for new development and significant redevelopment pro- jects. The SWMP includes by reference Attachment 4 of the General Permit, which provide specific design standards applicable to the project based on the size and nature of the proposed project. As specified by the MS4 General Permit, all new development projects, regardless of size, should incorporate appropriate source control and site design measures that minimize storm- water pollutant discharges to the maximum extent practicable. The proposed project would be required to comply with the terms of the SWMP. This in- cludes (but is not limited to): ¤ Numeric Sizing Criteria for Pollutant Removal Treatment Systems. The project must include source controls, design measures, and treatment controls to minimize stormwater pollutant discharges. Treatment con- trols must be sized to treat a specific amount—about 85 percent—of aver- age annual runoff. ¤ Operation and Maintenance of Treatment Measures. Treatment con- trols often do not work unless adequately maintained. The permit re- quires an operations and maintenance (O&M) program, which includes: (1) identifying the properties with treatment controls, (2) developing agreements with private entities to maintain the controls, and (3) periodic inspection, maintenance (as needed), and reporting. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-9 ¤ Limitation on Increase of Peak Stormwater Runoff Discharge Rates. Urbanization creates impervious surfaces that reduce the landscape’s nat- ural ability to absorb water and release it slowly to creeks. These imper- vious surfaces increase peak flows in creeks and can cause erosion. Pro- jects must evaluate the potential for this to occur and provide mitigation as necessary. b. Town of Truckee 2025 General Plan The following goals from the Land Use, Conservation and Open Space, and Safety Elements of the Town of Truckee 2025 General Plan are applicable to hydrology and water quality (see Table 4.9-1) c. Town of Truckee Development Code The Town’s Development Code includes several chapters that address condi- tions and requirements associated with storm drainage. Chapter 18.34 (Flood Plain Management) addresses development and permitting requirements and restrictions associated with building within the regulatory floodplain (includ- ing the minimum requirements established by FEMA). Chapter 18.38 (Lake and River/Stream Corridor Development) addresses setback requirements along stream corridors. Chapter 18.30, Section 050 (Drainage and Storm- water Runoff) addresses requirements related to drainage and erosion control, runoff treatment, and ongoing maintenance. Section 5 of these standards de- scribes accepted methodologies for runoff calculations, design criteria, and standards for drainage facilities and structures, and requirements for the prep- aration and submittal of drainage reports. Section 8 of these standards de- scribes requirements for erosion and sediment control, including the require- ments for the preparation of erosion and sediment control plans. d. Town of Truckee Municipal Code – Stormwater Quality Ordinance The Town recently adopted a Stormwater Quality Ordinance (Article 11.01 of the Municipal Code) to enhance and protect the quality of waters of the State in Truckee by reducing pollutants in stormwater discharges to the max- imum extent practicable, control stormwater discharges to the storm drain system, and cause the use of best management practices by the Town and its TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-10 TABLE 4.9-1 TRUCKEE GENERAL PLAN GOALS AND POLICIES PERTAINING TO HYDROLOGY AND WATER QUALITY Policy or Goal No. Goals and Policies Goal LU-4 Coordinate land development with provision of services and infra- structure. LU-P4.5 Require new infrastructure and development to be designed and built to manage stormwater runoff and to minimize or eliminate harmful impacts to property prone to flooding, water quality, and riparian, wetland, and meadow habitats. When infrastruc- ture is replaced or retrofitted, require the upgrading of storm- water management systems to minimize or eliminate these im- pacts. Goal COS-11 Protect water quality and quantity in creeks, lakes, natural drainag- es, and groundwater basins. COS-P11.1 Minimize excessive paving that negatively impacts surface water runoff and groundwater recharge rates. COS-P11.2 Protect surface and groundwater resources from contamination from runoff containing pollutants and sediment, through imple- mentation of the Regional Water Quality Control Board’s Lahontan Region's, Best Management Practices. COS-P11.3 Cooperate with State and local agencies in efforts to identify and eliminate all sources of existing and potential point and non- point sources of pollution to ground and surface waters, includ- ing leaking fuel tanks, discharges from storm drains, auto dis- mantling, dump sites, sanitary waste systems, parking lots, road- ways, and logging and mining operations. COS-P11.5 Require new development projects that have the potential to impact local water quality through increased stormwater runoff or erosion to include analysis of water quality impacts as a com- ponent of project review and to integrate mitigation measures that would reduce identified impacts to an acceptable level. COS-P11.6 Utilize Low Impact Development and Best Management Practic- es established in the Regional Water Quality Control Board’s Truckee River Hydrologic Unit Project Guidelines for Erosion Control, and the State of California Stormwater Best Manage- ment Practices Handbooks, and other resources such as the Prac- tice of Low Impact Development (US Department of Housing and Urban Development) and Water Quality Model Code and Guidebook (State of Oregon, Department of Land Conservation and Development) as guidelines for water quality and erosion control measures required by the Town. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY TABLE 4.9-1 TRUCKEE GENERAL PLAN GOALS AND POLICIES PERTAINING TO HYDROLOGY AND WATER QUALITY (CONTINUED) 4.9-11 Policy or Goal No. Goals and Policies COS-P11.9 Recognize the importance of stormwater management in protect- ing all water resources in Truckee, for example, flood control, surface, and ground water quality, and river, stream and lake health. Goal COS-13 Reduce particulate matter pollution in Truckee to meet State and federal ambient air quality standards. COS-P13.1 Require multi-family residential, commercial, industrial, subdivi- sions and other discretionary development to maintain con- sistency with the goals, policies, and control strategies of the Town’s Particulate Matter Air Quality Management Plan. COS-P13.2 Existing non-paved roads within new development and subdivi- sion, and existing off-site non-paved roads that serve new devel- opment and subdivisions shall be paved to the extent necessary to offset emissions generated by the development and subdivision traffic to the degree feasible. New non-paved roads shall not be allowed for new development and subdivisions except for single family residences, secondary residential units, and duplexes on existing lots. New paving shall take into consideration the poli- cies under Goal COS-11 concerning minimization of impacts to water quality and groundwater recharge that may result from increases in paved areas. COS-P13.3 Require all construction projects to implement dust control measures to reduce particulate matter emissions due to disturb- ance of exposed top-soils. Such measures would include watering of active areas where disturbance occurs, covering haul loads, maintaining clean access roads, and cleaning the wheels of con- struction vehicles accessing disturbed areas of the site. Goal SAF-2 Reduce hazards associated with flooding. SAF-P2.1 Continue to work with appropriate local, State, and federal agen- cies (particularly FEMA) to maintain the most current flood hazard and floodplain information and use it as a basis for project review and to guide development in accordance with federal, State, and local standards. SAF-P2.2 Continue to participate in the National Flood Insurance Pro- gram (NFIP). SAF-P2.3 Incorporate stormwater drainage systems in development pro- jects to effectively control the rate and amount of runoff, so as to prevent increases in downstream flooding potential. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY TABLE 4.9-1 TRUCKEE GENERAL PLAN GOALS AND POLICIES PERTAINING TO HYDROLOGY AND WATER QUALITY (CONTINUED) 4.9-12 Policy or Goal No. Goals and Policies SAF-P2.4 Discourage development within the Truckee River floodplain and adjacent to other waterways to minimize risks associated with flooding. Source: Town of Truckee 2025 General Plan. citizens that will reduce the adverse effects of polluted runoff discharges to waters of the State. The ordinance seeks to promote these purposes by: ¤ Prohibiting illicit discharges to the storm drain system. ¤ Establishing authority to adopt requirements for stormwater manage- ment, including source control requirements to reduce pollution to the maximum extent practicable. ¤ Establishing authority to adopt requirements for municipal operations to reduce stormwater pollution and erosion to the maximum extent practi- cable. ¤ Establishing authority to adopt requirements for public and private de- velopment projects to reduce stormwater pollution and erosion both dur- ing construction and after the project is complete. ¤ Establishing authority that will enable the Town to implement and en- force the Stormwater Management Program (SWMP) adopted by the Town. e. Low-Impact Development The Town encourages the use of Low Impact Development (LID) methods to prevent erosion both during the construction project and for the long term. LID is a stormwater management and land development strategy that empha- sizes conservation and use of on-site natural features integrated with engi- neered, small-scale hydrologic controls to more closely mimic natural hydro- logic functions. It involves dispersing runoff water into vegetated areas for TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-13 infiltration. The type of hydrologic controls should be designed for the soil and subsurface conditions specific to the site. BMP plans should not concentrate runoff. Roof and driveway runoff should be dispersed to infiltration systems and landscaped areas capable of infiltrating runoff from impervious surfaces. General principles of LID include: ¤ Conservation: Conserve natural vegetation and soil. ¤ Site Design: Design site to minimize total impervious area. ¤ Direct runoff into or across vegetated areas to filter runoff and encourage groundwater recharge. ¤ Use integrated management practices to reduce runoff from impervious surfaces and retain pre-development time of concentration. C. Existing Conditions 1. Climate The Truckee-area climate is characterized by cold, wet winters and short, relatively mild summers. Annual precipitation has varied from 16 inches (1976) to 54.6 inches (1996), with a one-day high of 5.2 inches of precipitation on February 1, 1963. Typically, about 75 percent of the precipitation occurs during the winter and spring (December to May), predominantly as snowfall. Of this precipitation, the average annual snowfall amounts to 203.6 inches; with a high occurring in 1952 of 401.4 inches of snow. 2. Site Conditions The site topography generally slopes gently downward to the northwest along two ridges and varies in elevation from approximately 6,120 feet in the southeast to about 5,920 feet in the northwest. Ground surface elevations rise to 6,750 feet for watershed areas that influence the on-site drainage ways. Many on-site trails and unpaved roads traverse the site and are well-used by local residents. Most roads and trails are unimproved and many exhibit evi- dence of significant erosion near stream crossings. The vegetation communi- TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-14 ty is dominated by Jeffrey Pine and related understory shrubs such as bitter- brush, sagebrush, and rabbitbrush. Vegetation in wetland areas is dominated by sedges, rushes and other hydrophitic grasses and forbs. Most wetland- upland boundaries are marked by an abrupt shift from hydrophitic vegetation to upland vegetation. The site was likely logged in the past, removing many of the larger diameter trees. 3. Drainage Features and Hydrology The proposed project area is located in the Truckee River Hydrologic Unit. Several ephemeral drainages that include wetlands trend northeasterly through the northern, central, and southern portions of the site. All of the waters within the project site are considered Relatively Perennial Waters (RPWs) and are tributaries to the Truckee River. Field reconnaissance was not conducted during spring runoff. However, the hydrology of the ephem- eral drainages on-site is likely driven by surface water runoff during spring snowmelt periods and some portion of subsurface flow discharge later in the season. Some of this surface runoff likely originates from the network of highly compacted trails and roads on-site, many of which cross ephemeral drainages and wet meadows on the property. a. Stormwater Runoff, Erosion, and Sedimentation Water quality problems related to stormwater discharges, erosion, and sedi- mentation are among the most frequent and widespread water quality prob- lems. Eroded sediment is often carried to surface waters in stormwater. The term “stormwater” includes surface runoff resulting from rainfall and snow- melt. It is synonymous with “urban runoff,” “highway runoff,” and “surface runoff.” The project involves possible stormwater quality impacts that are both short-term associated with construction as well as long-term, permanent impacts associated with creation of impervious areas (e.g. paving, houses). This proposed project is subject to permitting and regulations as outlined in the Regulatory Framework section above. These short and long-term impacts are considered individually in Sections D and E below. Under natural conditions, most rainfall and snowmelt is absorbed by soils and taken up by vegetation, and very little surface runoff occurs. Creation of TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-15 large amounts of impervious surface (e.g. roads, parking lots, and buildings) can greatly increase the potential for surface runoff, reduce the potential for soil/vegetation treatment of chemicals in rain and snow, and add a large varie- ty of possible contaminants to the runoff discharge downstream. Urbaniza- tion of a watershed affects surface runoff quality by increasing intensity of peak discharges, runoff volume per storm, runoff velocity during the storm, and the frequency and severity of flooding. These changes can lead to in- creases in stream bedload transport and streambank erosion, and to conse- quent degradation of aquatic habitat. Erosion is a natural process, which tends to be accelerated by large-scale soil disturbance and concentrated human activity in a watershed. Sedimentation of surface waters affects beneficial uses by increasing turbidity and physically altering streambed habitat. Sediment can reduce the hydraulic capacity of stream channels, causing an increase in flood peaks and flood damage. Sediment can fill drainage channels, especially along roads, plug culverts, and storm drainage systems. b. Groundwater A site reconnaissance was conducted in June 2004 by Geocon Consultants, Inc. Surface water was observed in the northwestern portion of the northern most drainage, within the wetlands area. Groundwater was not observed flowing to the surface on-site, but a spring is depicted on the Martis Peak Quadrangle (photo updated 1969) as being near the south property boundary. One well was observed on the site during the field reconnaissance, the well appeared to be capped and not in service. According to the Phase I Environ- mental Site Assessment (ESA) performed for the site (Section 12.0, Reference 12), the well was drilled in 1983 to a total depth of 252 feet (see Appendix F of this Draft EIR). The static water level was at 190 feet below the ground sur- face at the time of drilling. Pump test results indicated a well yield of 10.5 gallons per-minute (gpm), which later improved to about 15 gpm. Water quality analysis results were within U.S. EPA standards, although iron and manganese were somewhat elevated. Arsenic was not included in the testing. According to the Phase I ESA, arsenic is known to occur in groundwater in the Glenshire area at concentrations above U.S. EPA maximum contaminant Level of 0.050 milligrams per liter. The water supply for the project would TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-16 be provided by Truckee Donner Public Utilities District (see Section 4.15, Utilities and Services Systems, of this Draft EIR) and would not rely on indi- vidual wells. c. Flood Mapping Figure 4.9-1 shows the mapped FEMA flood zones in the vicinity of the pro- posed project site. The 100-year FEMA flood zone is largely contained with- in the ravine of the Truckee River, which is several hundred feet below the elevation of the project site. For the two main ephemeral drainages on the project site, 100-year floodplain limits and 50-foot setbacks are shown on Figure 3-6. d. Proposed Drainage Plan The preliminary drainage plan for the proposed project site was completed in 2003.1 A revised site/drainage plan was prepared in April 2011, reflecting 37 fewer building lots than the original 2003 plan. A Final Hydrology and Hy- draulics Report is not planned to be prepared. Prior to initiation of construc- tion, the project proponent would need to demonstrate that the post- development design storm hydrograph leaving the project is not changed from pre-project conditions such that downstream drainage structures (cul- verts, bridges, etc.) remain adequate post-development. To this end, soil infil- tration rates, pond detention times, and other suggested revisions from the 2007 technical review by Geocon would also need to be incorporated into the construction plans to illustrate the feasibility of the proposed drainage design. The project site plan (see Figure 3-6) incorporates four floodplain road cross- ings. Pre-cast, concrete arch bridges are planned to span the width of the drainageways, and would be designed to accommodate a 100-year flood event. The project proponent has proposed a minimum 50-foot setback from 100- year floodplains for all drainages on the property. The project has been 1 CFA of Reno Nevada, October 3, 2003, Preliminary Hydrology and Hydrau- lics Report for Tahoe Boca, Appendix F of 2003 DEIR. FIGURE SAF-2 A R E A S S U B J E C T T O F L O O D I N G T O W N O F T R U C K E E 2 0 2 5 G E N E R A L P L A N 00.51Mile Source:FederalEmergencyManagementAgency,1998Note:Thisfigureincludesfloodhazard mapping for Nevada County only FEMAFLOODHAZARD ZO NES Zone A:Subject to 100-Year Flood.Base Elevation Undetermined. Annual probability of flooding of 1%or greater. Zone X500:Area between the limit of the 100-year and 500-year flood; orcertain areas subject to 100-year flood with average depths of less thanone fo ot.Annual Probablility of Flooding 0.2%to 1% Zone D:Unstudied Area:Flood Hazards Undetermined Zone X:Areas Outside of 500-year floodplain §¨¦80 §¨¦8 0 §¨¦8 0 §¨¦8 0 267 267 89 89 T r u c k e e R iv e r Truckee-Tahoe Airport Tahoe Donner Gle n s h i r e D riv e D o r c h esterWay DonnerLake P r o s s e r L a k e TruckeeTownLimits ProposedSphereofInfluence Project Site Creek or other Drainage FIGURE SAF-2 A R E A S S U B J E C T T O F L O O D I N G T O W N O F T R U C K E E 2 0 2 5 G E N E R A L P L A N 0 0.5 1 Mile Source:Federal Emergency Management Agency,1998 Note:This figure includes flood hazard mapping for Nevada County only FEMA FLOOD HAZARD ZONES Zone A:Subject to 100-Year Flood.Base Elevation Undetermined. Annual probability of flooding of 1%or greater. Zone X500:Area between the limit of the 100-year and 500-year flood; or certain areas subject to 100-year flood with average depths of less than one foot.Annual Probablility of Flooding 0.2%to 1% Zone D:Unstudied Area:Flood Hazards Undetermined Zone X:Areas Outside of 500-year floodplain §¨¦8 0 §¨¦8 0 §¨¦8 0 §¨¦8 0 267 267 89 89 T r u c k e e R iv e r Truckee-Tahoe Airport Tahoe Donner Glen s h i r e D riv e D o r c h esterWay D o n n e r L a k e P r o s s e r L a k e Truckee Town Limits Proposed Sphere of Influence Project Site Creek or other Drainage TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY Source: Federal Emergency Management Agency, 1998 Note: This figure includes flood hazard mapping for Nevada County only. FIGURE 4.9-1 FEMA FLOOD ZONES 10 2 MilesNORTH TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-18 configured to avoid these setback areas and, in most cases, provides an addi- tional 20-foot setback to any structure. The project would include construction of vegetated, earthen swales on both sides of the site’s crowned, paved roads to convey flows to decentralized treatment and infiltration facilities. Road runoff from asphalt during a 20- year event is anticipated to be collected, treated, and infiltrated within vege- tated swales and detention ponds. Peak drainage flow rates from the 20-year event are planned to be detained to that estimated for pre-development condi- tions. Flows in excess of the 20-year storm event would bypass these treat- ment/infiltration facilities via rock-armored outfalls or other energy dissipa- tion structures and discharge to the nearest drainage way. D. Standards of Significance The proposed project would have a significant impact with regard to hydrol- ogy and water quality if it would in the short-term (construction period) and long-term (post-project): ¤ 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 pro- duction 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, includ- ing 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, includ- ing through the alteration of the course of a stream or river, or substan- tially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-19 ¤ Create or contribute runoff water which would exceed the capacity of ex- isting or planned stormwater drainage systems or provide substantial ad- ditional sources of polluted runoff. ¤ Otherwise 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. ¤ Inundation by seiche, tsunami, or mudflow. ¤ Require or result in the construction of new stormwater drainage facili- ties or expansion of existing facilities, the construction of which could cause significant environmental effects. E. Impact Discussion 1. Project Impacts a. Violate any water quality standards or waste discharge requirements. During the construction period, the proposed project would involve grading, excavation, and potential cut and fill activity. Ground disturbance associated with these activities has the potential to cause erosion of exposed surfaces dur- ing rainfall events and snowmelt. Runoff has the potential to cause sedimen- tation of on-site and off-site watercourses. In the short-term, this is a poten- tially significant impact. Following project construction, creation of impervious surfaces (roads, hous- es) and slight changes of local topography has the potential to alter surface runoff rates and drainage patterns from the site. Impervious surfaces limit TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-20 infiltration rates, possible groundwater recharge and can increase surface run- off rates and drainage peak flows downstream. Increased runoff rates and concentrated flows associated with drainage of roadways can result in aggres- sive erosion and gully formation and transport of sediment to downstream drainage structures. Urban runoff from roadways, driveways, and parking lots may carry metals and petroleum-based contaminants to waterways. In the long-term, these are potentially significant impacts. b. 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 pro- duction 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). The water supply for the project would be provided by Truckee Donner Pub- lic Utilities District and would not rely on on-site wells. According to the 2011 Truckee Donner PUD Urban Water Management Plan, the District currently has 12 active wells in the Truckee area and 1 in the Hirschdale area that supply potable water to residents and customers. The Plan also states that local water resources are adequate to meet projected buildout conditions through the year 2023, and that the available production capacity is currently sufficient to meet existing demands. The District presently obtains its drink- ing water through the pumping of groundwater from the Martis Valley Groundwater Basin. No additional well-drilling is proposed for the proposed project, nor are any additional production wells proposed for the Canyon Springs project area in the foreseeable future. The two nearest wells to the Canyon Springs project area are the Glenshire Drive Well and the Martis Val- ley Well No. 1, which are both outside of the proposed project area.2 There is no pumping proposed for the Glenshire valley, which includes the Canyon Springs project area. Construction and full buildout (creation of roads, hous- es, etc.) would decrease localized infiltration capacity across individual parcels 2 Truckee Donner Public Utility District, 2011, 2011 Truckee Donner PUD Urban Water Management Plan, Figure 3-1 Location of Water Production Facilities, page 3-3. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-21 and roadways. However, net infiltration across the project area, hence poten- tial groundwater recharge would remain unchanged through the use of LID principles. These include such practices as water capture and infiltration of stormwater runoff in close proximity to the source (e.g. in roadside swales and detention ponds). Therefore the overall potential decrease in infiltration- driven groundwater recharge across the project area would likely be less than significant. c. Substantially alter the existing drainage pattern of the site or area, includ- ing 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. As discussed above and illustrated in the project site plan (Figure 3-6), the project does not propose to alter the main drainage features or topography of the site. Building setbacks and construction of roadways along existing paths/dirt roads are such that the existing site drainage ways remain un- altered. Localized erosion during construction is possible, though it would be unlikely to reach 303(d)-listed waterways or result in siltation off-site. This impact is less than significant. d. Substantially alter the existing drainage pattern of the site or area, includ- ing through the alteration of the course of a stream or river, or substan- tially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site. As discussed above and illustrated in the project site plan (Figure 3-6), the proposed project does not propose to alter the main drainage features or to- pography of the site. Creation of impervious surfaces across the project site may result in greater surface runoff rates and peak volumes, though net sur- face runoff volumes leaving the site are unlikely to change substantially as a result of deployment of infiltration swales and detention ponds along drain- age ways. No downstream flooding potential is anticipated. This impact is less than significant. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-22 e. 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. As discussed above and illustrated in the project site plan (Figure 3-6), the proposed project does not alter the main drainage features or topography of the site. Creation of impervious surfaces across the project site would result in greater surface runoff rates and peak volumes, though net surface runoff volumes leaving the site are unlikely to change substantially as a result of de- ployment of infiltration swales and detention ponds along drainage ways. Planned detention storage ponds would be designed to contain site drainage flows from 20-year runoff events such that downstream drainage systems are not impacted by the proposed development. Stormwater runoff from road- ways is expected to be treated through drainage way vegetated infiltration swales and settling in detention ponds such that downstream pollution poten- tial is minimized. This impact is less than significant. f. Otherwise substantially degrade water quality. See above items a, c, and e. g. 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. As discussed above and illustrated in the project site plan (Figure 3-6) and the FEMA floodplain map (Figure 4.9-1), the proposed project does not propose to construct structures within the NFIP-mapped 100-year floodplain of the Truckee River, nor in the 100-year floodplain delineation for the two primary drainages (blueline waterways) of the project site. The project area would be located completely outside of the 100-year floodplain of the Truckee River as mapped by FEMA. In addition, proposed bridges would be designed to span the entire width of the drainage way and would not create any disturbance within the 100-year floodplain as calculated by the project engineer. Any underground utilities that have to cross a stream would be constructed utiliz- ing a jack and bore method or would be mounted under the bridge deck in order to avoid stream disturbance. Finally, the project has designated all of TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-23 the drainage ways as open space areas where no development would occur and established a 100-foot buffer zone from the edge of the drainage ways. For these reasons, this impact is less than significant. h. Place within a 100-year flood hazard area structures which would impede or redirect flood flows. As discussed above and illustrated in the project site plan (Figure 3-6) and the FEMA floodplain map (Figure 4.9-1), the proposed project does not allow construction of structures within the NFIP mapped 100-yr floodplain of the Truckee River, nor in the 100-yr floodplain delineation for the two primary drainages of the project site. This impact is less than significant. i. 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. As discussed above and illustrated in the project site plan (Figure 3-6) and the FEMA floodplain map (Figure 4.9-1), the proposed project does not allow construction of structures within the NFIP mapped 100-year floodplain of the Truckee River, nor in the 100-yr floodplain delineation for the two pri- mary drainages of the project site. There are no dams or related impound- ment structures proposed for the site that pose a risk of flooding. This im- pact is less than significant. j. Inundation by seiche, tsunami, or mudflow. A seiche is a wave that oscillates in lakes, bays, or gulfs from a few minutes to a few hours as a result of seismic or atmospheric disturbances. A tsunami is a very large ocean wave caused by an underwater earthquake or volcanic erup- tion. Hazards associated with mudflow typically affect structures which are located at the base of slopes or within close proximity to the area of flow. The potential for mudflows to impact the project site are low because the project is not located at the base of a steep slope. The potential for seiches and tsunamis to impact the project site does not exist because there are no large bodies of water in close proximity to the site. Donner Lake is located approximately 8.5 miles to the southwest of the project site and Lake Tahoe is TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-24 located over 12 miles northwest of the project site. Reservoirs located near the site include the Boca Reservoir located approximately 2.5 miles to the northwest of the project site, Prosser Creek Reservoir located approximately 3.5 miles to the northwest of the project site, and the Stampede Reservoir located approximately 8 miles to the northwest of the project site. Therefore, impacts associated with seiches, tsunamis, or mudflows are less than significant and no mitigation measures are required. k. Require or result in the construction of new stormwater drainage facili- ties or expansion of existing facilities, the construction of which could cause significant environmental effects. As discussed above (items c, d, and e), the proposed project includes the crea- tion of impervious surfaces across the project site and construction of storm- water infiltration swales and detention ponds close to the sources of runoff. Planned detention storage ponds would be designed to contain site drainage flows from 20-year runoff events such that downstream drainage systems are not impacted by the proposed development. Stormwater runoff from road- ways is proposed to be treated through vegetated infiltration swales and set- tling in detention ponds close to the sources of runoff. No large-scale storm- water drainage facilities (such as concrete spillways or channels) are proposed. Therefore, this impact is less than significant. F. Cumulative Impacts In the short-term, land disturbance and potential for discharge of pollutants associated with construction has the potential to have a cumulative impact on the water quality of receiving waters, which eventually flow to the Truckee River. As noted above, the Truckee River is listed as impaired for sediment. Any addition of sediment could have a significant cumulative effect. Howev- er, as described in the Project Impacts section above, the project applicant would minimize the project impacts by complying with the applicable water quality regulations including preparing and implementing a SWPPP; comply- ing with the Town’s Municipal Code requirements; and installing BMPs and practicing water quality protection measures to manage and reduce erosion, TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-25 stormwater runoff, and sedimentation downstream. Creation of impervious surfaces across the project site may result in greater surface runoff rates and peak volumes; however, as discussed above and illustrated in the drainage plan, runoff would be captured and detained through use of vegetated swales and retention basins to minimize any potential on- or off-site flooding im- pacts that may result from construction activities. In the long term, imple- mentation of the proposed project could result in long-term impacts related to water quality, and flooding from increased impervious areas. Addition of impervious surfaces from the proposed project could reduce infiltration and increase storm runoff flows. The cumulative increase in impervious surfaces could cause a substantial increase in runoff, which if not controlled could re- sult in a significant flooding effect downstream. However, the proposed pro- ject would be required to comply with the stormwater flow and water quality performance standards listed in the MS4 permit (e.g. runoff rates from the project would be similar to pre-development rates and minimize stormwater pollutant to MEP), such that the long-term impact would be less-than- significant. Given the regulatory and permitting requirements that the pro- posed project would need to comply with, the project is unlikely to substan- tially contribute toward long-term flooding and cumulative water quality impacts. Therefore, this impact is less than significant. G. Impacts and Mitigation Measures Impact HYDRO-1: The proposed project would involve grading, excava- tion, and potential cut and fill activity. Ground disturbance associated with construction activities has the potential to cause erosion of exposed surfaces during rainfall events and snowmelt. Runoff has the potential to cause sedi- mentation of on-site and off-site watercourses. Mitigation Measures HYDRO-1a: Prior to approval of improvement plans, a grading plan shall be prepared for the project site that contains the following provisions: TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-26 ¤ Identify areas where topsoil is to be salvaged prior to grading for later reuse on-site. ¤ Identify and protect areas not planned to be disturbed to the greatest extent practicable using temporary fencing or other methods. ¤ Limit cuts and fills and balance cut and fill on-site. ¤ Limit grading to the smallest practical area of land. ¤ Limit exposure of disturbed soils to the shortest practical amount of time. The National Pollutant Discharge Elimination System (NPDES) permit requires that disturbed soils are temporarily stabi- lized within 14 days of disturbance. ¤ Establish a winterization plan such that all disturbed soil areas are sta- bilized by October 15th of each construction year (per NPDES re- quirements). ¤ Permanently stabilize graded/disturbed areas through soil loosening, application of salvaged topsoil, establishment of native vegetation and application of native mulch material. The State Water Resources Con- trol Board (SWRCB), “Sediment Source Control Handbook” provides field-tested guidelines for revegetating and permanently stabilizing dis- turbed soil areas in the Tahoe-Truckee area. ¤ Create grading contours that blend with the natural contours on-site or with contours on property immediately adjacent to the area of de- velopment. ¤ Locate and design roadways, parking areas, trails, and paths to blend in with the natural terrain. ¤ Limit development on steep slopes in order to minimize erosion. Mitigation Measures HYDRO-1b: Best Management Practices (BMPs) shall be applied during construction to minimize erosion and sedimenta- tion. A stormwater pollution prevention plan (SWPPP) shall be pre- pared and submitted prior to ground disturbing activities that specifies what specific measures will be implemented to protect water quality and TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-27 minimize erosion during construction. BMPs selected shall be in accord- ance with the California Stormwater Quality Association “Stormwater Best Management Practice Handbook” and the Lahontan Regional Water Quality Control Board (RWQCB) “Project Guidelines for Erosion Con- trol.” These guidelines include the following temporary construction BMPs: ¤ Surplus or waste materials shall not be placed in drainage ways or within the 100-year flood plain of surface waters. ¤ All loose piles of soil, silt, clay, sand, debris, or earthen materials shall be protected in a reasonable manner to prevent discharge of pollutants to waters of the State. Material stockpiles should be placed on the up- gradient side of excavation whenever possible. Stockpiles should be covered prior to forecasted rain events and sediment barriers should be installed around stockpiles at all times. ¤ Dewatering shall be done in a manner so as to prevent the discharge of pollutants, including earthen materials, from the site. The first option is to discharge dewatering waste to land. A separate permit may be required if, due to site constraints, dewatering waste must be dis- charged to surface waters. Contact the Regional Board for infor- mation on discharging to surface waters. ¤ All disturbed areas shall be temporarily or permanently stabilized by October 15 of each year. ¤ Any soil-disturbing work that is allowed to be performed (which re- quires a variance) between October 15 and May 1 of each year shall be conducted in such a manner that the project can be winterized within 48 hours. Winterized means implementing erosion and/or sediment controls that would prevent the discharge of earthen materials from the site and the controls would remain effective throughout the rainy/snow season without requiring maintenance. In general, this requires stabilizing bare disturbed soils with mulch, erosion protection blankets, or other suitable materials, and installing perimeter sediment TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-28 controls such as fiber logs or other similar materials that would remain effective during significant rain and snow events. ¤ After completion of a construction project, all surplus or waste earth- en material shall be removed from the site and deposited at a legal point of disposal. ¤ All non-construction areas (areas outside of the construction zone that would remain undisturbed) shall be protected by fencing or other means to prevent necessary encroachment outside the active construc- tion zone. ¤ During construction, temporary erosion control measures (e.g. im- permeable dikes, silt fences, wattles, etc.) shall be used as necessary to prevent discharge of earthen materials from the site during periods of precipitation or runoff. ¤ Control of run-on water from off-site areas shall be managed (protect- ed, diverted, treated, etc.) to prevent such water from encountering pollutants before it is discharged from the site. ¤ Where construction activities involve the crossing and/or alteration of a stream channel, such activities require a prior written agreement with the California Department of Fish and Game (CDFG) and shall be timed whenever possible to occur during the period in which stream flow is expected to be lowest for the year. Other control measures may be necessary to prevent adverse effects from work in or near surface waters. ¤ Revegetated areas shall be regularly and continually maintained in or- der to assure adequate vegetation growth and root development, mulch surface cover, and absence of any signs of erosion (rills, gullies, deposition). Revegetated areas shall be routinely inspected and main- tained as necessary to ensure continued erosion control effectiveness. The Sediment Source Control Handbook, a Sierra Business Council publication in collaboration with the Lahontan Regional Water Quali- ty Control Board, provides field-tested guidelines for revegetating and permanently stabilizing disturbed soil areas in the Tahoe-Truckee area. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-29 Mitigation Measure HYDRO-1c: Additional requirements for Truckee River hydrologic area: ¤ Except in the event of emergencies, land disturbance associated with project construction is prohibited between October 15th and May 1st of the following year. Exemptions may be granted by the Lahontan Ex- ecutive Officer on a case-by-case basis. ¤ The project’s SWPPP and erosion control plan shall specify what spe- cific measures will be implemented to protect water quality and min- imize erosion during construction per NPDES permit requirements and Town standards. The plan shall address storm drainage during construction and propose site-specific BMPs to prevent erosion and water quality degradation. All drainage and infiltration facilities shall be constructed to Town specifications. The plan shall also specify res- toration measures for graded areas including but not limited to land- scaping, revegetation, or other soil stabilization methods shown to be effective in the Truckee-Tahoe area. ¤ Low Impact Development (LID) techniques should be utilized during and after construction. On-site infiltration should be utilized wherev- er possible to minimize runoff. Such infiltration features may include wet ponds, detention ponds, infiltration swales, and/or rain gardens between the road surfaces and other paved areas. Roof downspouts should be directed towards on-site infiltration areas away from the building foundations. ¤ Earthen drainage facilities should be protected immediately following construction using rock riprap, erosion control fabric or other energy dissipation measures to prevent erosion of the soil surface. In addi- tion, cut slopes and drainage ways should be protected from direct ex- posure to water runoff immediately following grading activities. ¤ Cut and fill embankment slopes shall be protected from sheet, rill, and gully erosion and shall not exceed 2:1, horizontal to vertical. Run-on areas should be identified and managed as necessary to prevent concen- trated flow from eroding cut and fill slopes. TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-30 Significance after Mitigation: Less than significant. Impact HYDRO-2: Following project construction, creation of impervious surfaces (roads, houses) and slight changes of local topography has the poten- tial to alter surface runoff rates and drainage patterns from the site and in- crease surface runoff rates, peak flows, and sediment transport downstream. Urban runoff from roadways, driveways, and parking lots may carry metals and petroleum-based contaminants to waterways. Mitigation Measures HYDRO-2a: Prior to approval of improvement plans, a grading plan shall be prepared for the project site that contains the following provisions: ¤ Limit grading to the smallest practical area of land. ¤ Locate and design roadways, parking areas, trails, and paths to blend in with the natural terrain. ¤ Limit development on steep slopes in order to minimize erosion. ¤ Create grading contours that blend with the natural contours on-site or with contours on property immediately adjacent to the area of de- velopment. ¤ Permanently stabilize graded/disturbed areas through soil loosening, application of salvaged topsoil, establishment of native vegetation and application of native mulch material. The Water Board’s “Sediment Source Control Handbook” provides field-tested guidelines for revege- tating and permanently stabilizing disturbed soil areas in the Tahoe- Truckee area. Mitigation Measures HYDRO-2b: The following permanent BMPs shall be applied during construction to minimize alteration of surface runoff rates and prevent associated water quality and flooding impacts: ¤ Low Impact Development (LID) techniques shall be utilized during and after construction. On-site infiltration should be utilized wherev- er possible to minimize runoff. Such infiltration features may include TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-31 wet ponds, detention ponds, infiltration swales, and/or rain gardens between the road surfaces and other paved areas. Roof downspouts should be directed towards on-site infiltration areas away from the building foundations. Other control measures may be considered if site constraints are such that construction of infiltration features is not feasible. Additional specific design specifications are required by Lahontan RWQCB for the Truckee River Hydrologic Area (see spe- cific requirements below). ¤ Where possible, existing drainage patterns should not be significantly modified. ¤ Drainage swales should be stabilized with rock, riprap, erosion control fabric, and/or vegetation as appropriate to prevent erosion and scour- ing. ¤ Revegetated areas should be regularly and continually maintained in order to assure adequate vegetation growth and root development, mulch surface cover, and absence of any signs of erosion (rills, gullies, deposition). Revegetated areas shall be routinely inspected and main- tained as necessary to ensure continued erosion control effectiveness. The Water Board’s “Sediment Source Control Handbook” provides field-tested guidelines for revegetating and permanently stabilizing dis- turbed soil areas in the Tahoe-Truckee area. Mitigation Measure HYDO-2c: Additional requirements for Truckee River hydrologic area: ¤ Runoff from impervious surfaces shall be treated or contained on-site. For purposes of this requirement, the volume of water to be contained or treated is the 20-year, 1-hour storm, which is equal to 0.7 inches of rain. ¤ Design, construction, and maintenance techniques should ensure de- velopment near a creek would not cause or worsen natural hazards (such as erosion, sedimentation, flooding, or pollution) and would in- clude appropriate erosion and sediment control practices such as: (1) TOWN OF TRUCKEE CANYON SPRINGS DRAFT EIR HYDROLOGY AND WATER QUALITY 4.9-32 turbidity screens and other management practices, which shall be used as necessary to minimize siltation, sedimentation, and erosion, and shall be left in place until disturbed areas are stabilized with permanent vegetation that would prevent the transport of sediment off-site; and (2) temporary vegetation and/or mulch cover sufficient to stabilize disturbed areas. ¤ Post-project stormwater flows shall equal pre-project stormwater flows for the design year event. ¤ Prior to initiation of construction, the project proponent shall demon- strate that the post-development design storm hydrograph leaving the project is not changed from pre-project conditions such that down- stream drainage structures (culverts, bridges, etc.) remain adequate post-development. To this end, soil infiltration rates, stormwater pond capacities and detention times, and other suggested revisions from the 2007 technical review by Geocon shall be incorporated into the construction plans so that Lahontan RWQCB and the Town can fully evaluate the feasibility of the proposed drainage design. Significance after Mitigation: Less than significant.