4.F HYDROLOGY AND WATER QUALITY

Transcription

1 4.F HYDROLOGY AND WATER QUALITY 1. INTRODUCTION This section evaluates potential Project impacts on surface water hydrology and surface water quality. The analysis is primarily based on the Water Resources Technical Report prepared by KPFF Consulting Engineers 1 provided in Appendix I, the Geology and Soil Discipline Report prepared by Shannon & Wilson 2 provided in Appendix G, the Methane Report prepared by Geosyntec Consultants 3 provided in Appendix H 1, and the Phase I Report prepared by Citadel Environmental Services, Inc. 4 provided in Appendix H 2 of this Draft EIR. Additional discussion of groundwater and groundwater contamination is provided in Section 4.D, Geology and Soils and Section 4.E, Hazards and Hazardous Materials, of this Draft EIR. 2. ENVIRONMENTAL SETTING a. Existing Conditions (1) Surface Water Hydrology (a) Regional The Project Site is located within the nine mile long, 130 square mile Ballona Creek Watershed. The Ballona Creek Watershed is bounded by the Santa Monica Mountains on the north, the Harbor Freeway (SR 110) to the east, the Baldwin Hills on the south, and the City of Santa Monica to the west. The watershed is comprised of all or portions of the cities of Beverly Hills, Culver City, Inglewood, Los Angeles, Santa Monica, West Hollywood, and unincorporated Los Angeles County. 5 Stormwater that does not percolate into the ground is directed by storm drains into major tributaries including Centinela Creek, Sepulveda Canyon Channel, and Benedict Canyon Channel. The Ballona Creek Watershed generally flows southwest and eventually discharges into the Santa Monica Bay. During a 50 year storm event, the watershed is designed to discharge to Santa Monica Bay at approximately 71,400 cubic feet per second ( cfs ). (b) Local Underground storm drain facilities in the Project vicinity are owned and maintained by the City and County. A City owned 39 inch reinforced concrete storm drain runs beneath Fairfax Avenue and discharges to a County owned reinforced concrete box main line approximately 12 feet by 8.5 feet in size at Wilshire Boulevard and San Vicente Boulevard. Stormwater runoff from properties in the Project area is typically discharged into gutters and storm drains along Fairfax Avenue and Wilshire Boulevard and enters the KPFF Consulting Engineers, Water Resources Technical Report, July Shannon & Wilson, Inc., Geology and Soil Discipline Report, July Geosyntec Consultants, Methane Report Academy Museum of Motion Pictures, July Citadel Environmental Services, Inc., Phase I Environmental Site Assessment Report, July Los Angeles County Department of Public Works: Ballona Creek Watershed, Accessed June 22, F 1

2 4.F Hydrology and Water Quality August 2014 underground City or County storm drains through catch basins; stormwater is then conveyed through this underground network into Ballona Creek. (c) Project Site The existing Project Site is generally flat and developed with the May Company Building, a gravel area to the north historically used for parking, a loading dock, service driveways, and pedestrian walkways, on approximately 2.2 acres. Approximately 6 percent of the Project Site, including an area of lawn east of the Original Building and small areas of ornamental landscaping to the north, is currently pervious, and the remaining 94 percent is developed and impervious. Drainage from the portion of the Project Site north of the May Company Building is conveyed off site via sheet flow to the Fairfax Avenue gutter, where it is intercepted by a storm drain inlet and catch basin at the intersection of Fairfax Avenue and Wilshire Boulevard, and via a 15 inch underground lateral storm drain pipe located beneath the gravel area north of the Original Building, which discharges directly to the storm drain beneath Fairfax Avenue. Runoff is also conveyed via the May Company Building s roof drains to curb drains along Fairfax Avenue and Wilshire Boulevard, where flows are intercepted by storm drain inlets for the catch basin at the intersection of Fairfax Avenue and Wilshire Boulevard and discharged to the storm drains beneath those roadways. 6 As shown on Figure 4.F 1, Existing Project Site Drainage Areas, and listed in Table 4.F 1, Existing 50 Year Storm Event Flow Rate, the Project Site is divided into two drainage subareas, Drainage Area A1 and Drainage Area A2. To estimate the existing runoff rates from the Project Site, hydrology calculations were performed in accordance with the Los Angeles County Department of Public Works ( County Department of Public Works ) 2006 Hydrology Manual. Drainage Area A1 drains south into Wilshire Boulevard and Drainage Area A2 flows west into Fairfax Avenue. As indicated in Table 4.F 1, during a 50 year storm event the existing runoff rate at the Project Site is approximately 3.73 cfs for Drainage Area A1 and 3.00 cfs for Drainage Area A2. There are no known deficiencies in the on site storm drain system or the City or County storm drain network serving the Project Site. Drainage Area Table 4.F 1 Existing 50 Year Storm Event Flow Rate Area (Acres) Existing Flow Rate (cfs) A A Total Source: KPFF Consulting Engineers, July Communication with Oscar Gonzalez, KPFF Consulting Engineers, July 11, F 2

3 PCR N Exis ng Project Site Drainage Areas Academy Museum of Mo on Pictures Project Source: KPFF Consul ng Engineers, FIGURE 4.F-1

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5 August F Hydrology and Water Quality (2) Surface Water Quality (a) Regional The Project Site lies within the Los Angeles Basin ( Basin ) as designated by the Los Angeles Regional Water Quality Control Board ( LARWQCB ). The Basin consists of the coastal areas of the County, the area south of the divide of the San Gabriel Mountains and Santa Susana Mountains, a small coastal portion of Ventura County, and the area south of the divide of the Santa Monica Mountains. The Basin is drained by seven watersheds: Ventura River, Santa Clara River, Calleguas Creek, Malibu Creek, Ballona Creek, Los Angeles River, and San Gabriel River. 7 Numerous tributaries discharge into these watersheds, most of which have intermittent flow. Most tributaries have been converted to flood control channels lined with concrete and stone rip rap. The Project Site is also located within the Santa Monica Bay Watershed Management Area of the Basin, which includes the City and Ballona Creek. The LARWQCB prepared a plan for the Basin ( LA Basin Plan ) to preserve and enhance water quality and protect the beneficial uses of all regional waters. The LA Basin Plan lists existing beneficial uses for Ballona Creek as non contact water recreation and wildlife habitat. 8 However, Ballona Creek does not meet the water quality standards for beneficial uses and is listed in the State Water Resources Control Board s ( SWRCB ) 2010 Integrated Report (Clean Water Act Section 303(d) List) as an impaired waterway. The following Total Maximum Daily Loads ( TMDL ) 9 for the pollutants that contribute to the impairment of Ballona Creek include cadmium (sediment); coliform bacteria; copper (dissolved); cyanide; lead; selenium; toxicity; trash; enteric viruses; and zinc. 10 The LA Basin Plan identifies environmental issues associated with the safety of consuming seafood from and swimming in the Santa Monica Bay. Regarding seafood, studies have shown that some local seafood species contain elevated concentrations of dichloro diphenyl trichloroethane ( DDT ) and polychlorinated biphenyls ( PCBs ). Regarding the safety of swimming in the Santa Monica Bay, some beaches are occasionally closed due to stormwater contaminated with minimally treated sewage overflows. The Clean Water Act, Section 303(d) List identifies Santa Monica Bay as impaired due to DDT (tissue and sediment), debris, fish consumption advisory, PCBs, and sediment toxicity California Regional Water Quality Control Board, Los Angeles Region (4), Water Quality Control Plan, Los Angeles Region, Basin Plan for the Coastal Watersheds of Los Angeles and Ventura Counties, /losangeles/water_issues/programs/basin_plan/basin_plan_documentation.shtml. Accessed June 24, California Regional Water Quality Control Board, Los Angeles Region (4), Water Quality Control Plan, Los Angeles Region, Basin Plan for the Coastal Watersheds of Los Angeles and Ventura Counties, /losangeles/water_issues/programs/basin_plan/basin_plan_documentation.shtml. Accessed June 24, The TMDL is an estimate of the total load of pollutants from point, non point, and natural sources that a water body may receive without exceeding applicable water quality standards (with a margin of safety included). California Environmental Protection Agency, State Water Resources Control Board, Water Issues, Impaired Water Bodies, 2010 Integrated Report, 303(D)Listed Waters (Web Based Interactive Map), tmdl/integrated2010.shtm. Accessed June 24, California Environmental Protection Agency, State Water Resources Control Board, Water Issues, Impaired Water Bodies, 2010 Integrated Report, 303(D)Listed Waters (Web Based Interactive Map), tmdl/integrated2010.shtm. Accessed June 24, F 5

6 4.F Hydrology and Water Quality August 2014 (b) Local Urban stormwater runoff generally occurs following precipitation events. The volume of runoff flowing into the regional drainage system depends on the intensity and duration of the rain event. Pollutants of concern from developed areas that have the potential to affect stormwater quality include trash, sediments, bacteria, metals, oil and grease, nutrients, organics and pesticides. The source of contaminants includes surface areas where precipitation falls, as well as the air it falls through. Contaminants on surfaces such as roads, maintenance areas, parking lots, and building, which are usually contained in dry weather conditions, may be carried by rainfall runoff into drainage systems. (c) Project Site The Project Site currently has no means of treatment for stormwater runoff. As previously described, drainage from the Project Site is conveyed off site via sheet flow and roof drains on the May Company Building into the gutters along Fairfax Avenue and Wilshire Boulevard, where flows are intercepted by storm drain inlets and enter underground storm drain facilities beneath those roadways, and runoff is also conveyed off site by an underground storm drain pipe in the northern portion of the Project Site that discharges directly to the storm drain beneath Fairfax Avenue. b. Regulatory Framework Summary The regulatory framework summarized below is described in detail in Appendix B, Regulatory Framework, Section 4.F, of this Draft EIR. There are numerous federal, State, and local regulations and plans that address surface water hydrology and surface water quality and are applicable to the Project. Key federal and State regulations include the federal Clean Water Act, which established the National Pollution Discharge Elimination System ( NPDES ) permit program, and the State s Porter Cologne Water Quality Control Act, which established the California Water Code that authorizes the SWRCB to implement the Clean Water Act through nine Regional Water Quality Control Boards. The County s NPDES Permit Program establishes stormwater control requirements through a variety of programs including the Storm Water Pollution Prevention Plan ( SWPPP ), which defines Best Management Practices ( BMPs ) that would prohibit pollutants from being discharged into the public storm drain system during construction; the Waste Discharge Requirements for Discharges of Groundwater from Construction and Project Dewatering, which would require testing and treatment of groundwater prior to discharge to the storm drain system; and the Standard Urban Stormwater Mitigation Plan ( SUSMP ) which ensures that stormwater is addressed through BMPs that are applicable during the operational life of the Project. The City has adopted the County Department of Public Works Hydrology Manual to govern the design of storm drain facilities and limit allowable discharge into existing storm drains. The Municipal Code and Low Impact Development ( LID ) Ordinance (Ordinance No. 181,899) governs stormwater retention and treatment. 4.F 6

7 August F Hydrology and Water Quality 3. ENVIRONMENTAL IMPACTS a. Methodology The analysis of potential impacts to surface water hydrology and surface water quality is based primarily on the Water Resources Technical Report prepared by KPFF Consulting Engineers, the Geology and Soil Discipline Report prepared by Shannon & Wilson, the Methane Report prepared by Geosyntec Consultants, and the Phase I Report prepared by Citadel Environmental Services, Inc. (included in Appendices I, G, H 1, and H 2 respectively, of this Draft EIR). (1) Surface Water Hydrology As noted above and discussed in detail in Appendix B, Section 4.F, of this Draft EIR, the City has adopted the County Department of Public Works Hydrology Manual as its basis of design for storm drain facilities. The County Department of Public Works Hydrology Manual requires new facilities to be designed for a 25 year storm event and meet the Urban Flood level of protection, which is defined as runoff from a 25 year frequency design storm falling on a saturated watershed. 12 As discussed below, the L.A. CEQA Threshold Guide establishes the more intense 50 year frequency design storm event as the threshold for evaluation of potential project impacts on surface water hydrology. Therefore, to provide a more conservative analysis, the Water Resources Technical Report used the 50 year frequency design storm event. Potential impacts to the storm drain system were analyzed by comparing the calculated pre Project stormwater runoff rates to the calculated post Project runoff rates. Additional discussion of the runoff calculation methodology is provided in the Water Resources Technical Report included in Appendix I of this Draft EIR. (2) Surface Water Quality Water quality impacts were assessed by considering the types of pollutants and effects on water quality likely to be associated with construction and operation of the Project, as identified in the Water Resources Technical Report, Geology and Soil Discipline Report, Methane Report, and Phase I Report; compliance with applicable regulatory requirements for the treatment of contaminants; and Project Design Features to implement a dewatering program during construction and control nitrates in stormwater runoff during operation. Project consistency with relevant regulatory requirements, including BMPs and applicable plans, is evaluated to demonstrate how compliance would ensure that the Project would not significantly degrade existing water quality. b. Thresholds of Significance Appendix G of the State CEQA Guidelines provides a set of screening questions that address impacts with regard to hydrology and water quality. These questions are as follows: Would the project: Violate any water quality standards or waste discharge requirements? 12 A 25 year frequency design storm has a 1 in 25 probability of being equaled or exceeded in any given year. 4.F 7

8 4.F Hydrology and Water Quality August 2014 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 onor 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 that 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? Otherwise substantially degrade water quality? Place housing within a 100 year flood plain as mapped on federal Flood Hazard Boundary or Flood Insurance Rate Maps or other flood hazard delineation maps? 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? As discussed in the Initial Study, provided in Appendix A of this Draft EIR, and in Chapter 6.0, Section F, Effects Found Not to be Significant, the Project would have a less than significant impact or no impact with respect to depletion of groundwater supplies; alteration of the existing drainage pattern which would result in flooding; placing housing within a 100 year flood hazard area; placing structures within a 100 year flood hazard area; exposing people or structures to risk due to dam failure; and inundation by seiche, tsunami, or mudflow. As such, no further analysis of these topics in this section is necessary. (1) Surface Water Hydrology According to the L.A. CEQA Thresholds Guide, a project would normally have a significant impact on surface water hydrology if it would: Cause flooding during the projected 50 year developed storm event, which would have the potential to harm people or damage property or sensitive biological resources; Substantially reduce or increase the amount of surface water in a water body; or Result in a permanent, adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow. Based on these factors, the Project would have a significant impact on surface water hydrology if it would: WQ 1 Cause flooding during the 50 year projected storm event, which would have the potential to harm people or damage property; 4.F 8

9 August F Hydrology and Water Quality WQ 2 Substantially reduce or increase the amount of surface water in a water body; or WQ 3 Result in a permanent, adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow. (2) Surface Water Quality According to the L.A. CEQA Thresholds Guide, a project would normally have a significant impact on surface water quality if it would: Result in discharges that would create pollution, contamination or nuisance as defined in Section of the California Water Code or that cause regulatory standards to be violated, as defined in the applicable NPDES stormwater permit or Water Quality Control Plan for the receiving water body. Based on these factors, the Project would have a significant impact on surface water quality if it would: WQ 4 Cause pollution, contamination, or nuisance as defined in Section of the California Water Code or that cause regulatory standards to be violated, as defined in the applicable NPDES stormwater permit or Water Quality Control Plan for the receiving water body. WQ 5 Result in discharges from dewatering that create pollution, contamination or nuisance as defined in Section of the California Water Code, or that cause regulatory standards to be violated as defined in the applicable NPDES stormwater permit or Water Quality Control Plan for the receiving water body. c. Project Characteristics and Project Design Features (1) Project Characteristics The amount of pervious area on the Project Site would increase from approximately 6 percent under current conditions, to approximately 15 percent of the Project Site s area. Among other BMPs to be proposed for LID compliance, at grade stormwater flow through planters are planned to cover approximately 5 percent of this pervious area and would collect runoff from building roof drains and hardscape areas. Given that there are currently no stormwater runoff treatment systems on the Project Site, the BMPs incorporated into the Project would improve water quality compared to existing conditions. On site storm drain improvements, including new underground storm drain pipes, would collect and convey runoff from the Project Site north of the Original Building and New Wing to the existing off site storm drain system. Roof drains would continue to collect and convey runoff from the roof of the Original Building to curb drains along Fairfax Avenue and Wilshire Boulevard. The State Water Resources Control Board s ( SWRCB s ) GeoTracker Groundwater Monitoring and Assessment Program website indicates that the depth to groundwater is variable in the Project vicinity but typically ranges between 10 and 15 feet below grade. Groundwater monitoring wells installed in conjunction with construction of the Broad Contemporary Art Museum on the LACMA Campus indicated that groundwater was at a depth of approximately 10 feet below grade between August and October of Geology and Soil Discipline Report, page 9, provided in Appendix G of this Draft EIR. 4.F 9

10 4.F Hydrology and Water Quality August 2014 Readings taken in June 2011 from monitoring wells installed the Metro Westside Subway Extension within Wilshire Boulevard, approximately 300 feet west and slightly south of the Project Site, encountered groundwater at depths of approximately 13.5 feet and 17.5 feet, respectively. 14 As stated in the Geology and Soil Discipline Report provided in Appendix G of this Draft EIR, the variations in reported estimates and monitored depth to groundwater may be attributed to seasonal fluctuations, rainfall levels, and boring well distance from the Project Site. Groundwater flow directions range from southwesterly to southeasterly. 15 A design groundwater depth of approximately 10 feet below grade (approximately 157 feet above mean sea level) was conservatively assumed by the Project geotechnical engineers at the Project Site, to reflect the historically shallowest groundwater depth encountered at the Project Site during prior monitoring and reported for the Project area by the California Geological Survey and the State Water Resources Control Board. 16 Construction activities are therefore expected to encounter limited groundwater during deeper excavations for the shear wall foundations, elevator pits, and underground utility corridor, as well as installation of micropiles, augercast piles, and the Gas Mitigation and Monitoring System, and therefore temporary dewatering would be required. Drainage of small quantities of groundwater may be necessary in association with the operation of the Gas Mitigation and Monitoring System. (2) Project Design Features To following Project Design Feature would be implemented during construction to address the treatment and disposal of potentially contaminated groundwater that could be encountered during dewatering: PDF WQ 1, Construction Dewatering Discharge Analysis and Treatment. Groundwater is expected to be encountered during deeper excavations for the shear wall foundations, elevator pits, installation of micropiles and augercastpiles, underground utility corridor, and installation of the Gas Mitigation and Monitoring System which would require dewatering. The extracted groundwater is anticipated to contain dissolved methane and hydrogen sulfide gases, Total Recoverable Petroleum Hydrocarbons ( TRPH ), Total Petroleum Hydrocarbons ( TPH ), Metals, and volatile organic compounds ( VOCs ) which exceed water quality standards. 17 In addition, vapor encroachment caused by the release of vapors from contaminated groundwater due to previous uses of hazardous materials in the basement of the May Company Building may occur. Therefore groundwater vapors would be monitored and extracted groundwater would require treatment prior to discharge into the storm drain system. Dewatering, treatment, and disposal of groundwater would be conducted in accordance with the LARWQCB s Waste Discharge Requirements for Discharges of Groundwater from Construction and Project Dewatering to Surface Waters in Coastal Watersheds of Los Angeles and Ventura Counties. The dewatering program for the Project is expected to implement the following: Geology and Soil Discipline Report, page 10, provided in Appendix G of this Draft EIR. Geology and Soil Discipline Report, page 10, July 2014, provided in Appendix G of this Draft EIR. Geology and Soil Discipline Report, page 10, July 2014, provided in Appendix G of this Draft EIR. Jim Osborne, Sales Manager, Pure Effect Incorporated, letter dated April 17, 2009 and included in Appendix C of the Geology and Soils Discipline Report (see Appendix G of this Draft EIR). 4.F 10

11 August F Hydrology and Water Quality Dewatering would include one or two dewatering wells or well points to lower groundwater level at each excavation site. Each dewatering well would extend at least 20 feet into the tar sand stratum or approximately 40 feet below the concrete basement topping slab. Each dewatering well would be capable of operating continuously and be equipped with controls to avoid the well running dry. Dewatering wells would be designed to reduce the potential for plugging from tar. The proposed groundwater treatment system for dewatering would consist of a frac tank, a bag filter and two carbon filter units. Compliance with LARWQCB permit requirements require treatment of effluent prior to discharge and implementation of a monitoring and reporting program to ensure that effluent limitations are not exceeded. In addition, sumps and/or trenches could also be used for dewatering smaller excavation areas. The following Project Design Features would reduce the amount of nitrates in stormwater runoff during Project operation: PDF WQ 2, Nitrate Control. As the majority of pollutants of concern for stormwater runoff are captured and filtered out by soils, except for nitrates often used in landscaping fertilizers, the Applicant would voluntarily control nitrates through the selection of native plants and minimal use of nitrogen based fertilizers for landscape maintenance. The following Project Design Features presented in Section 4.E, Hazards and Hazardous Materials are applicable to address elevated levels of subsurface gases that may be present in groundwater, manage contaminated soil, and treat groundwater that may be encountered during operation of the Gas Mitigation and Monitoring System. PDF HAZ 1, Health and Safety Plan. Given the Project s susceptibility to naturally occurring methane and hydrogen sulfide gas, a Health and Safety Plan would be prepared in compliance with OSHA Safety and Health Standards (29 Code of Federal Regulations ) and Cal/OSHA requirements (CCR Title 8, General Industry Safety Orders and California Labor Code, Division 5, Part 1, Sections ) and submitted for review by the Department of Building and Safety. The Health and Safety Plan would address, as appropriate, safety requirements that would serve to avoid significant impacts or risks to workers or the public in the event that elevated levels of subsurface gases are encountered during grading and construction. The Health and Safety Plan would also address potential vapor encroachment from the possible contamination of soil and groundwater due to past storage and use of hazardous materials within the basement of the May Company Building. Gas monitoring devices would be in place to alert workers in the event elevated gas or other vapor concentrations occur when basement slab demolition or soil excavation is being performed. Contingency procedures would be in place in the event elevated gas concentrations are detected, such as the mandatory use of personal protective equipment, evacuation of the area, and/or increasing ventilation within the immediate work area. Workers would be trained to identify exposure symptoms and implement alarm response. Areas of soil and groundwater that are exposed during excavation would be minimized by staggering exposed demolition areas 4.F 11

12 4.F Hydrology and Water Quality August 2014 to reduce to potential for off gassing or other vapor encroachment. Construction fencing would be installed to limit public access to the Project Site and provide additional distance between the public and excavation activities to allow for gas and vapor dilution. The Health and Safety Plan would have emergency contact numbers, maps to the nearest hospital, gas monitoring action levels, gas response actions, allowable worker exposure times, and mandatory personal protective equipment requirements. The Health and Safety Plan would be signed by all workers on site to demonstrate their understanding of the construction risks. PDF HAZ 2, Soil Management Plan. Due to the high potential for excavated soil to contain methane and hydrogen sulfide gases, tar sands, and other contaminants that may result in vapor encroachment conditions, a Soil Management Plan would be prepared. Excavated soils would be sampled and tested for disposal in a timely manner. The Soil Management Plan would specify the testing parameters and sampling frequency. Anticipated testing includes TPH and TPH diesel, VOCs, vapor encroachment conditions, and certain metals. If such metals are elevated, additional testing may be required. If soil is stockpiled prior to disposal, it will be managed in accordance with the Project s Storm Water Pollution Prevention Plan. All impacted soils would be properly treated and disposed of in accordance with applicable SCAQMD, DTSC, and LARWQCB requirements. PDF HAZ 3, Gas Mitigation and Monitoring System. Given the Project s susceptibility to naturallyoccurring methane and hydrogen sulfide gases, a Gas Mitigation and Monitoring System would be installed and maintained as part of the Project to ensure subsurface gases do not pose a significant health or safety risk. Design and construction of the Gas Mitigation and Monitoring System would be subject to review and approval by the Department of Building and Safety, the Fire Department, and the Bureau of Sanitation, Watershed Protection Division, and would meet requirements set forth in the Methane Code, Building Code Sections , , and Fire Prevention Bureau Requirement No. 71. The Gas Mitigation and Monitoring System would be integrated into the architectural and landscape designs for the Project and would include a combination of passive and active systems. Per Methane Code Site Design Level V requirements, the Original Building (including the remaining below grade portions) and underground utility corridor are required to have the following: Dewatering system (unless a waiver is granted by the Department of Building and Safety) Passive system Impervious membrane Sub slab vent system Perforated horizontal pipe within a gravel trench Gravel blanket Vent Risers Active system Sub slab vent system: mechanical extraction Lowest occupied space: Gas detection system 4.F 12

13 August F Hydrology and Water Quality d. Project Impacts (1) Surface Water Hydrology Mechanical ventilation Alarm system Control panel Miscellaneous components Trench dam Conduit or cable seal fitting Threshold WQ 1: The Project would result in a significant impact on surface water hydrology if it causes flooding during the 50 year projected storm event, which would have the potential to harm people or damage property. Impact Statement WQ 1: The Project would have a less than significant impact related to flooding during a 50 year storm event with compliance with applicable regulatory requirements, including an at grade stormwater flow through planter to collect and control runoff and implementation of the required SWPPP and SUSMP and corresponding BMPs. These regulatory requirements would ensure no increase in surface water runoff volumes compared to existing conditions. As previously described, under existing conditions approximately 6 percent of the Project Site is pervious and 94 percent of the Project Site is impervious. Implementation of the Project would involve the demolition of the 1946 Addition and the construction of the New Wing generally within the same building footprint area. The Project would also include landscaping, the Piazza, and pedestrian paths. Overall, the Project would increase the amount of pervious area to 15 percent and decrease the amount of impervious area to 85 percent. As presented in Table 4.F 2, Post Project 50 Year Storm Event Flow Rate, a comparison between existing and proposed conditions indicates that the Project would not increase stormwater runoff flows and therefore would not cause flooding during a 50 year storm event. As shown on Figure 4.F 2, Proposed Project Drainage Areas, although there would be a slight change to the drainage areas, runoff from the Project Site would follow the same discharge paths and drain to the same storm drain facilities as under existing conditions. In addition, as a Project Characteristic and LID BMP, approximately 5 percent of the planned pervious landscape area on Site would be developed with at grade stormwater flow through planters, which would contribute to controlling stormwater runoff. Additional SUSMP and LID BMPs would be implemented throughout the operational life of the Project to ensure that, at a minimum, no increase in flows would result from Project development compared to existing conditions. LID BMPs proposed for the Project include capture and use, and biofiltration, since the presence of tar sands and shallow groundwater precludes the use of infiltration BMPs. Therefore, compliance with regulatory requirements would ensure that the Project would not cause flooding during a 50 year storm event and impacts would be less than significant. Threshold WQ 2: The Project would result in a significant impact on surface water hydrology if it substantially reduces or increases the amount of surface water in a water body. Impact Statement WQ 2: The Project would have a less than significant impact related to a substantial reduction or increase in the amount of surface water in a water body, due to the increase in pervious 4.F 13

14 4.F Hydrology and Water Quality August 2014 Drainage Area Table 4.F 2 Post Project 50 Year Storm Event Flow Rate Area (Acres) Proposed Flow Rate (cfs) Incremental Decrease from Existing to Proposed Condition a A A Total % a Although there is a slight decrease in impervious surface area compared to existing conditions, the corresponding decrease in flow rate is negligible and has been rounded to zero. Source: KPFF Consulting Engineers, July area on the Project Site and compliance with regulatory requirements which would ensure there is no increase in stormwater runoff volumes, including groundwater discharge from construction dewatering activities, compared to existing conditions. (a) Construction Project construction activities would temporarily disturb portions of the Project Site during demolition, grading and excavation, stockpiling of soils, and construction of new Project components. Such activities have the potential to disrupt existing surface drainage. The Applicant would be required to address stormwater runoff during construction at the Project Site through the preparation and implementation of a Site specific SWPPP, which would specify BMPs to minimize the amount of impervious area on Site and control stormwater and nonstormwater discharges during construction. As discussed in Project Design Feature PDF WQ 1, the Applicant would also be required to comply with NPDES regulations governing the discharge of groundwater from dewatering operations during construction. For these reasons, Project construction would have a less than significant impact related to a substantial increase or decrease in the amount of surface water in a water body. (b) Operation Project buildout would increase the amount of pervious area on Site over existing conditions. Although the New Wing and Piazza would occupy the current locations of the existing 1946 Addition and otherwise impervious hardscape, additional landscape areas would be provided. Approximately 15 percent of the Project Site would therefore be pervious following Project buildout, an increase of 7 percent over existing conditions. In addition, SUSMP and LID BMPs implemented for the Project would ensure that, at a minimum, there would be no increase in stormwater flows discharged off site compared to current conditions. Project operation would have a less than significant impact related to a substantial increase or decrease in the amount of surface water in a water body. Threshold WQ 3: The Project would result in a significant impact on surface water hydrology if it results in a permanent, adverse change to the movement of surface water sufficient to produce a substantial change in the current or direction of water flow. 4.F 14

15 N Proposed Project Drainage Areas Academy Museum of MoƟon Pictures Project PCR Source: KPFF ConsulƟng Engineers, FIGURE 4.F-2

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17 August F Hydrology and Water Quality Impact Statement WQ 3: The Project would not substantially change the current or direction of surface water flows, due to compliance with regulatory requirements which would ensure there is no increase in stormwater runoff volumes compared to existing conditions; planned on site storm drain improvements that would capture, convey, and discharge surface water runoff to off site City and County storm drain facilities; and the existence of adequate capacity in City and County facilities to serve the Project at buildout. Impacts would be less than significant. (a) Construction Project construction activities would include demolition of the 1946 Addition, grading and excavation, construction of the New Wing, and paving and landscaping. It is anticipated that approximately 5,862 cubic yards of soil would be excavated and require export to construct the Project. Such activities have potential to temporarily alter existing drainage patterns and flows by exposing the underlying soils and making the Project Site temporarily more permeable. During construction a SWPPP and associated BMPs would be implemented to provide for temporary stormwater management and prevent construction activities from adversely affecting the amount or direction of flow of surface water. In addition, the Project would be required to comply with all applicable City grading permit regulations that require necessary measures, plans, and inspections to reduce sedimentation and erosion. Therefore, with preparation of a SWPPP and implementation of the associated BMPs, and compliance with applicable City grading regulations, the Project would not result in a permanent, adverse change to the movement of surface water. As such, constructionrelated impacts to surface water hydrology would be less than significant. (b) Operation As previously stated, the areas of pervious surface would increase and impervious surface would decrease on the Project Site compared to existing conditions and approximately 5 percent of the pervious area would be developed with stormwater flow through planters to collect runoff from building roof drains and hardscape areas. Furthermore, development of the Project Site would not increase stormwater runoff flows during a 50 year storm event and runoff from the Project Site would follow the same discharge paths to the same storm drain facilities as under existing conditions. Therefore, the Project would not substantially reduce or increase the amount of surface water in a water body or result in a permanent adverse change to the movement of surface water, and operational impacts to surface water hydrology would be less than significant. (2) Surface Water Quality Threshold WQ 4: The Project would result in a significant impact on surface water quality if it causes pollution, contamination or nuisance as defined in Section of the California Water Code or that causes regulatory standards to be violated, as defined in the applicable NPDES stormwater permit or Water Quality Control Plan for the receiving water body. Impact Statement WQ 4: Project construction and operation would result in less than significant impacts on surface water quality related to pollution, contamination, or nuisance or violation of regulatory standards, due to Project Design Features and regulatory requirements that include preparation of a Soil Management Plan, implementation of SWPPP BMPs, SUSMP BMPs, and LID BMPs; compliance with City grading regulations; and control of nitrate in stormwater runoff to protect surface water quality. 4.F 17

18 4.F Hydrology and Water Quality August 2014 (a) Construction Construction activities such as earth moving, maintenance and operation of construction equipment, and handling, storage, and disposal of materials could contribute to pollutant loading in stormwater runoff. However, construction contractors disturbing more than one acre of soil would be required to obtain coverage under the NPDES General Construction Activity Permit (SWRCB Order No DWQ). In accordance with the requirements of the permit, the Applicant would prepare and implement a site specific SWPPP that would specify BMPs to be used during construction. BMPs would include but not limited to erosion control, sediment control, and non stormwater management and materials management BMPs. With implementation of these BMPs, the Project would reduce or eliminate the discharge of pollutants in stormwater runoff to the maximum extent practicable. As described in Section 4.E, Hazards and Hazardous Materials, soils that are stockpiled during grading and excavation may contain methane and hydrogen sulfide gases, tar sands, and other contaminants due to previous uses within the basement of the Original Building which could contribute to pollutant loading in stormwater runoff. Therefore, Project Design Feature PDF HAZ 2 would require the preparation of a Soil Management Plan to ensure that all impacted soils are would be properly treated and disposed of in accordance with applicable LARWQCB, DTSC, and SCAQMD requirements. In addition, the Applicant would be required to comply with City grading permit regulations, which include standard measures, plans (including a wet weather erosion control plan if construction occurs during the rainy season), and inspections to reduce sedimentation and erosion. Through compliance with NPDES requirements, implementation of a Soil Management Plan, and compliance with City grading regulations, construction of the Project would not result in discharge that would cause: (1) pollution which would alter the quality of the waters of the State (i.e., Ballona Creek) to a degree which unreasonably affects beneficial uses of the waters; (2) contamination of the quality of the waters of the State to a degree which creates a hazard to the public health through poisoning or through the spread of diseases; or (3) nuisance that would be injurious to health; affect an entire community, neighborhood, or any considerable number of persons; or occurs during or as a result of the treatment or disposal of wastes. Furthermore, Project construction would not result in discharges that would violate regulatory standards in Ballona Creek. Therefore, constructionrelated, short term impacts on surface water quality would be less than significant. (b) Operation Stormwater runoff from the Project Site has the potential to introduce pollutants into the municipal storm drain system. Anticipated and potential pollutants that could be generated by different types of land uses associated with the Project are presented in Table 4.F 3, Pollutants of Concern Generated by On Site Land Uses. The Project is subject to NPDES and SUSMP requirements because it proposes 100,000 square feet or more of impervious surface area and restaurant uses. Therefore, the Applicant would be required to prepare and implement SUSMP and LID requirements through the operational life of the Project. Stormwater BMPs to address water quality would include source control and treatment control BMPs. Source control BMPs would be used to prevent pollutants from entering into stormwater discharge and may include effective site design and landscape planning; storm drain signage; properly managed storage areas, loading docks, and trash storage areas; and proper maintenance of structural and treatment control BMPs. Treatment control BMPs remove pollutants from stormwater discharges and may include vegetative systems, vortex/hydrodynamic systems, catch basin systems, infiltration/retention, pervious pavement, and media 4.F 18

19 August F Hydrology and Water Quality Table 4.F 3 Pollutants of Concern Generated by On Site Land Uses Project Pollutant Sources Lawns, Landscaping, and Parks Parking Lots and Driveways Roads and Highways Food Related Commercial Animal Related Commercial Auto Related Commercial Industrial Pollutants of Concern Sediment (coarse and fine) Nutrients (dissolved and particulate) Pesticides, pathogens, trash and debris Sediment (fine) Metals (dissolved and particulate) TPH, trash Sediment (coarse and fine) Metals (dissolved and particulate) TPH, PAH, trash and debris Pathogens, oil and grease Pathogens Metals (dissolved and particulate) TPH, PAH, surfactants Sediment (coarse and fine) Metals (dissolved and particulate) TPH, PAH, PCB, ph, surfactants Source: KPFF Consultant Engineers, July filtration. LID BMPs use these methods to address infiltration, capture and use, and biofiltration of stormwater runoff. Project Design Feature PDF WQ 2 proposes the use of native plants and minimal use of fertilizers containing nitrogen to reduce generation of nitrates on site. As shown on Table 4.F 4, Efficiency of Treatment Control BMPs and Target Pollutants, different types of treatment control BMPs target different pollutants and have different removal efficiencies. Table 4.F 4 Efficiency of Treatment Control BMPs and Target Pollutants a BMP Sediments Nutrients Trash Metals Bacteria Oil/Grease Organics Vegetated Swale Medium Low Low Medium Low Medium Medium Vegetated Buffer Strip High Low Medium High Low High Medium Vortex/Hydrodynamic Medium Low Unknown Low Unknown Unknown Unknown System b Catch Basins System b Unknown Unknown Unknown Unknown Unknown Unknown Unknown Infiltration/Retention High High High High High High High Media Filtration High Low High High Medium High High a b Low, Medium, and High indicate how efficient a BMP is at reducing the targeted pollutant. Performance of system varies per manufacturer and model. Source: KPFF Consulting Engineers, July F 19

20 4.F Hydrology and Water Quality August 2014 The Project would implement BMPs for managing stormwater runoff in accordance with current SUSMP and LID requirements. However, the Project Site is not suitable for the use of infiltration as a stormwater BMP due to the presence of shallow ground water and asphalt tar sands. Horizontal and vertical migration of asphalt tar can clog underground infiltration systems causing failure and contamination of stormwater overflow from infiltration BMP s during an intense storm event. Therefore, stormwater capture and reuse is planned as a potential post construction BMP. In addition, the Project would increase the percentage of impervious surfaces compared to existing conditions with approximately 15 percent or 0.46 acres of landscape area. Approximately 5 percent of the landscaped area would include at grade stormwater flowthrough planters and runoff would now be directed into planting media where pollutants are filtered, absorbed, and biodegraded by the soil and plants, prior to discharge. In addition, as stated in Project Design Feature PDF WQ 2, nitrates often used in landscaping fertilizers would be controlled through the selection of native plants and minimal use of nitrogen based fertilizers for landscape maintenance. Therefore, the Project would reduce or eliminate the discharge of potential pollutants from stormwater runoff to the maximum extent practicable and would result in a net reduction of pollutants compared to existing conditions. As such, operation of the Project would not result in discharges that would cause: (1) pollution which would alter the quality of the waters of the State (i.e., Ballona Creek) to a degree which unreasonably affects beneficial uses of the waters; (2) contamination of the quality of the waters of the State by waste to a degree which creates a hazard to the public health through poisoning or through the spread of diseases; or (3) nuisance that would be injurious to health; affect an entire community or neighborhood, or any considerable number of persons; or occurs during or as a result of the treatment or disposal of wastes. Furthermore, operation of the Project would not result in discharges that would cause regulatory standards to be violated in Ballona Creek but rather is anticipated to improve water quality with implementation of SWPPP and LID BMPs. Therefore, operational impacts on surface water quality would be less than significant. Threshold WQ 5: The Project would result in a significant impact on surface water quality if it results in discharges from dewatering that create pollution, contamination or nuisance as defined in Section of the California Water Code, or that causes regulatory standards to be violated as defined in the applicable NPDES stormwater permit or Water Quality Control Plan for the receiving water body. Impact Statement WQ 5: Project construction would result in a less than significant impact on surface water quality resulting from discharges from dewatering due to Project Design Features and regulatory compliance which would require analysis and treatment of the effluent prior to discharge to protect surface water quality. (a) Construction Groundwater is expected to be encountered during deeper excavations for the shear wall foundations, elevator pits, and installation of micropiles and augercast piles, underground utility corridor, and Gas Mitigation and Monitoring System. Such excavations would require dewatering. The extracted groundwater is anticipated to contain dissolved methane and hydrogen sulfide gases, TRPH, TPH, Metals, and VOCs which exceed water quality standards. 18 In addition, vapor encroachment from contaminated groundwater due to previous uses of hazardous materials in the basement of the Original Building may occur. Therefore, 18 Jim Osborne, Sales Manager, Pure Effect Incorporated, letter dated April 17, 2009 and included in Appendix C of the Geology and Soil Discipline Report (see Appendix G of this Draft EIR). 4.F 20