3.4 HYDROLOGY/WATER QUALITY

Transcription

1 3.4 HYDROLOGY/WATER QUALITY INTRODUCTION This subsection describes impacts to hydrology and water quality that could result from construction and operation of the proposed project. Topics addressed in this subsection include: drainage, flooding, water quality, and ground water ENVIRONMENTAL SETTING SURFACE WATER DRAINAGE The City of Lomita is drained by a man-made drainage system. The City s drainage system consists of gutters (in streets), catch basins, drainpipes, and other drainage facilities, which collect and transport storm water generally eastward into the regional drainage system that empties into San Pedro Bay. Drainage on the project site generally occurs as sheet flow, draining south to north following the site s topography. No discernable drainage courses exist onsite. The site s storm water is conveyed to a storm drain in Cypress Street, which empties into to an existing Los Angeles County Flood Control District (LACFCD) 60-inch storm drain approximately 400 feet north of the reservoir site. The existing 60-inch storm drain exists within an easement, parallel to, and south of, Pacific Coast Highway. In addition to storm water facilities, the project site contains a concrete retention basin designed to contain overflow water from the site s water supply facilities. This retention basin is an open top, overflow tank that is approximately 40 feet in diameter. FLOODPLAINS The City of Lomita is located in an area designated by the Federal Emergency Management Agency s (FEMA s) Flood Insurance Rate Maps (FIRMs) as Zone C, where minimal flood hazards exist. STORM WATER POLLUTION Section 402 of the Clean Water Act regulates the degradation of water quality. This regulation established the National Pollution Discharge Elimination System (NPDES), which is enforced in the project area by the Los Angeles Regional Water Quality Control Board (RWQCB). City of Lomita Cypress Street Reservoir Project

2 Section 402 prohibits the unauthorized discharge of pollutants from a point source (pipe ditch, well, etc.) to U.S. waters, including municipal, commercial, and industrial wastewater discharges and discharge from large animal feed operations. In addition to point source polluters, the NPDES manages non-point source pollutants by requiring local governments to obtain an NPDES Permit for municipal storm water and urban runoff discharges in their jurisdiction. The primary objectives of these permits are to: Effectively prohibit non-storm water discharges, and Reduce the discharge of pollutants from storm water conveyance systems to the Maximum Extent Practicable (MEP). In California (in accordance with the Porter-Cologne Act) the Regional Water Quality Control Boards (RWQCB) of the State Water Resources Control Board (SWRCB) administers NPDES Permits for municipal storm water, called Municipal Separate Storm Sewer Systems (MS4) permits. The City of Lomita is a co-permittee in a county-wide MS4 permit (Order no , NPDES Permit No. CAS004001, Waste Discharge Requirements for Municipal Storm Water and Urban Runoff Discharges within the County of Los Angeles, and the Incorporated Cities Therein, Except the City of Long Beach.). In accordance with this MS4 permit, Lomita is required to implement a Storm Water Quality Management Program (SQMP) that describes best management practices (BMPs), measurable goals, and timetables for implementation programs including: Public education and outreach, Illicit discharge detection and elimination, Inspections and monitoring; Public participation/involvement, Construction site runoff control/post-construction runoff control, and Pollution prevention/good housekeeping. The intent of the SQMP is to ensure that municipal storm water outflows do not cause their receiving waters to exceed water quality standards. Water quality standards consist of designated beneficial uses (such as drinking, swimming, or boating) and water quality objectives. Thus, the SQMP is designed to achieve compliance with the receiving water s limitations. On the project-level, the MS4 requires a Standard Urban Storm Water Mitigation Plan (SUSMP) and post-construction storm water treatment controls be implemented for the following Planning Priority Projects: a) Single-family hillside residential developments of one acre or more of surface area; b) Housing developments (includes single family homes, multifamily homes, condominiums, and apartments) of ten units or more; City of Lomita Cypress Street Reservoir Project

3 c) A 100,000 square feet or more impervious surface area industrial/commercial development; d) Automotive service facilities; e) Retail gasoline outlets; f) Restaurants; g) Parking lots 5,000 square feet or more of surface area or with 25 or more parking spaces; h) Projects located in, adjacent to, or discharging directly to an Environmentally Sensitive Area (ESA); and i) Redevelopment projects in subject categories that meet Redevelopment thresholds (generally includes land-disturbing activity that result in the creation or addition or replacement of 5,000 square feet or more of impervious surface area on an already developed site). GROUNDWATER GROUNDWATER RESOURCES Groundwater resources in Lomita consist of aquifers and aquicludes, as found in the Los Angeles groundwater basin within the Los Angeles coastal plain. The City of Lomita is located on the southern end of the Torrance plain, which is underlain by water-bearing sediments that form a complex system of interlayered aquifers and aquicludes. The City is within the West Coast groundwater basin, which is bounded by the Newport-Inglewood fault zone on the northeast. Groundwater resources in the West Coast basin generally consist of an upper layer of shallow, unconfined and semi-perched water; a principal body of fresh water underneath; and a salt water layer under the freshwater resources. Water movement is generally from points of recharge (percolation areas, spreading grounds, streams) to point discharge (groundwater wells, ocean, springs) because of differences in pressure between these points. WELL NO. 5 The project site includes the wellhead for the City s Well No. 5. This well was constructed in Its depth is 660 feet, and the well casing is 16 inches in diameter. This well is equipped with a 12- inch, 100-horsepower pump and has a pump capacity of 1,000 gallons per minute (gpm) at a pumping head of 300 feet. However, Well No. 5 has been shut down for many years because of poor water quality. In a report prepared by MacDonald-Stephens Engineers, Inc. in January 1993 for the Central Basin Municipal Water District, the water quality problems were identified to be high concentrations of iron, manganese, and color. The report also indicated that customers had complained about taste and odor in the water. Consequently, the use of Well No. 5 was discontinued THRESHOLDS OF SIGNIFICANCE For the purposes of this document, the project would result in a significant impact on hydrology or water quality if it would: Violate any water quality standards or waste discharge requirements; City of Lomita Cypress Street Reservoir Project

4 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; Result in providing water that does not meet drinking water standards to the constituents of the City of Lomita Water Department; Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river, in a manner which would result in substantial erosion or siltation on- or off-site; Substantially alter the drainage pattern of the site or area, including through the alteration of the course of a stream or river, or substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site; Create or contribute runoff water which would exceed the capacity of existing or planned storm water drainage systems or provides substantial additional 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; or Inundation by seiche, tsunami, or mudflow PROJECT IMPACTS TOPICS FOR WHICH THE PROJECT WOULD HAVE NO IMPACT PLACEMENT OF HOUSING WITHIN A 100-YEAR FLOOD HAZARD AREA The proposed project does not involve the development of residential land uses. Therefore, the proposed project would not place housing within a 100-year flood hazard area, and would have no associated impacts. PLACEMENT OF STRUCTURES WITHIN A 100-YEAR FLOOD HAZARD AREA The proposed project site is not located within a designated 100-year flood zone. The City of Lomita is located in an area designated by the Federal Emergency Management Agency s (FEMA s) City of Lomita Cypress Street Reservoir Project

5 Flood Insurance Rate Maps (FIRMs) as Zone C, where minimal flood hazards exist. Therefore, the project would not impact flood patterns and would not put people or structures at risk from natural flooding. INUNDATION BY SEICHE, TSUNAMI, OR MUDFLOW The City of Lomita is located inland from the Pacific Ocean and not within a tsunami flood zone. There are no major streams or rivers located in or near the City and the Pacific Ocean is three miles from the City at its closest point. Therefore the project would have no impact from seiche or tsunami. The project site would also not be impacted from mudflows. The most recent Seismic Hazards Maps, prepared by the State Division of Mines and Geology, indicate that landslide hazards in the project vicinity are confined to the sides of the adjacent quarry. As a result, no impact from landslides or mudslides would occur at the project site. POTENTIAL PROJECT IMPACTS Impact HYD-1: The proposed project would generate storm water pollutants during both construction and operation. However, compliance with the National Pollutant Discharge Elimination System (NPDES) would ensure the project-induced pollutants would not violate any water quality standards or exceed any waste discharge requirements. This impact is considered less-than-significant. The proposed project consists of replacing the exiting Cypress Street Reservoir and developing a water treatment facility for the City s Well No. 5. Neither the proposed reservoir nor the proposed water treatment plant would be a point source generator of water pollutants and, thus, no quantifiable water quality standards would apply to the project. However, as an urban development, the proposed project could add typical, urban, nonpoint-source pollutants to storm water runoff. These pollutants include sediment, household chemicals, trash, landscaping byproducts, and vehicle fluids. The potential storm water pollutants that could be generated from the proposed reservoir and water treatment facility would be reduced and controlled in accordance with the requirements of the countywide MS4 permit. The proposed project is considered a Planning Priority Project and, as such, is required to implement a SUSMP and post-construction storm water treatment controls. The SUSMP must include Best Management Practices (BMPs) to reduce storm water pollutants to the maximum extent practicable. Examples of BMPs and post-construction storm water treatment controls that could be implemented onsite include landscape buffers, catch basin inserts, sediment traps, oil/water separators, maintenance activities, etc. With the implementation of a SUSMP and post-construction storm water treatment controls, operation of the proposed project would not affect the beneficial uses of any receiving waters. The project also has the potential to generate water pollutants during construction. Grading and construction of the proposed project would temporarily expose unvegetated soils. Such exposed soils are prone to erosion during storm events. If a storm event occurs while soils are exposed, the project could increase the sediment load in onsite and downstream runoff. Another concern for City of Lomita Cypress Street Reservoir Project

6 water quality during construction is accidental spillage of vehicle or equipment fluids, which can contaminate receiving waters. The potential construction-induced pollutants that could be generated from the proposed project would be reduced and controlled in accordance with the requirements of the NPDES. The project size is greater than one (1) acre and, as such, is required to file a Notice of Intent (NOI) with the RWQCB to be covered under the state s NPDES General Construction Permit for discharges of storm water associated with construction activity. This NOI must include a Storm Water Pollution Prevention Plan (SWPPP) that identifies the BMPs that will be implemented during construction to reduce potential impacts to surface water quality. With the implementation of s SWPPP, construction of the proposed project would not affect the beneficial uses of any receiving waters. Since neither the operation nor the construction of the proposed project would affect the beneficial uses of receiving waters, the proposed project would not violate any water quality standards or exceed any waste discharge requirements. Therefore, the proposed project s impact on storm water quality is not significant. Impact HYD-2: The proposed project would result in the reactivation of Well No. 5 and, as such, would result in the withdraw of water from the underlying groundwater basin. However, the proposed withdrawal of groundwater is within the City s existing water rights and would not substantially deplete the groundwater basin. The project s impact on the groundwater basin is considered less-than-significant. Development of the proposed water treatment facility would lead to the use of the City s Well No. 5, which would extract water from the underlying groundwater. Well No. 5 is 680 feet deep and capable of producing approximately 1,000 gallons/minute. The reuse of this well would withdraw water from the West Coast Basin, a subbasin of the Coastal Plain of Los Angeles groundwater basin. The West Coast Basin underlies an approximately 101,000-acre area of land generally bounded by the Baldwin Hills to the northwest, the Newport-Inglewood fault zone to the northeast, Los Angeles/Long Beach Harbor to the southeast, the Palos Verdes Hills to the southwest, and Santa Monica Bay to the west 1. The City of Lomita owns 1,352 acre-feet per year (afy) of adjudicated water rights in the West Coast Basin, which it acquired from the Los Angeles County Waterworks District #13. With the proposed project, Lomita would have the capability to utilize their entire annual groundwater rights. However, even withdrawing up the City s maximum water rights would not substantially deplete the groundwater basin. Lomita s water rights comprise only 2% of the total 64,478 afy of water rights in the West Coast Basin 2. Regardless, groundwater withdraw from the West Coast Basin is governed by a court-determined adjudication of water rights (California Water Service Company, et al., v. City of Compton, et al., 1984), which is enforced by the California Department of Water Resources (DWR), Southern District (i.e., the Watermaster). Withdraw in accordance with the adjudicated water rights 1 California Water Service Company, et al., v. City of Compton, et al. (1984). Superior Court of the State of California for the County of Los Angeles No. 506,806. Amended Judgment (Declaring and Establishing Water Rights in the West Coast Basin, Imposing a Physical Solution Therein and Enjoining Extractions Therefrom in Excess of Specified Quantities.) 2 Ibid. City of Lomita Cypress Street Reservoir Project

7 ensures a balance of groundwater withdraw and recharge such that the proper groundwater supply is available to all rights holders. Therefore, the reuse of Well No. 5 would not significantly deplete groundwater supply. In addition to directly withdrawing from the groundwater basin, the proposed project would add impermeable surfaces to the project site, which could affect percolation of storm water into the groundwater basin from the project site. However, the project site is not within a groundwater recharge area and the site currently contains impermeable surfaces. As such, the project s affect on groundwater recharge would be negligible and not a significant impact. Impact HYD-3: As a result of the Cypress Street Reservoir Project, the City of Lomita plans to reactivate its Well No. 5, which was inactivated due to high concentrations of iron, manganese, and color. The proposed project includes a water treatment facility to ensure the water withdrawn from Well No. 5 achieves drinking water standards. With the implementation of the proposed water treatment facility, the reuse of Well No. 5 would not be a significant impact. As a result of the Cypress Street Reservoir Project, the City of Lomita plans to reactivate its Well No. 5 to supplement the City s water supply. Reactivation of this well will require treatment of the well water to remove the contaminants that have rendered the water unacceptable. In order to select a treatment system which produces water that meets or exceeds all applicable drinking water quality standards, the City sampled the well water, analyzed the contaminants requiring elimination, and undertook a pilot water treatment program to ascertain its efficacy in eliminating those contaminants and its cost-effectiveness. A complete recitation of the City s experience is presented in a report prepared on March 11, 2003 by Tetra Tech, Inc., which is available for review at the City of Lomita as part of the project file. A summary of that activity follows. Between November 2000 and February 2003, the City sampled the well on numerous occasions (see the Water Sampling Reports contained in the Well No. 5 Treatment Facilities Preliminary Design Report, which is contained in Appendix D of this document). Each sample was analyzed by Los Angeles County s Environmental Technology Laboratory. The concentrations of contaminants exceeding the maximum contaminant levels (MCL) of the State Drinking Water Standards are presented in Table In 2006, the Layne GeoSciences/COLOG Group collected an analyzed additional water samples from Well No. 5. The findings of this water quality analysis, which are included in Appendix D of this EA/EIR, are consistent with Lomita s previous findings. Table Well Water Sampling Data Sampling Manganese, Iron, mg/l Date mg/l Apparent Color, units 11/27/ /6/ /16/ <5 4/30/ /20/2002 No data a 0 6/4/ /13/ City of Lomita Cypress Street Reservoir Project

8 Table Well Water Sampling Data Sampling Manganese, Iron, mg/l Date mg/l Apparent Color, units 10/1/ /9/2003 Not detected /30/2003 No data b /6/2003 No data b Maximum Minimum Average MCL a The 5/20/2002 sample was analyzed for color only. b The 1/30/2003 and 2/6/2003 samples were not analyzed for iron. As shown in Table 3.4.1, with the exception of one sample, the iron contents of the well water were either below or slightly above the MCL. Manganese concentrations, however, were consistently above the MCL, but only by a small margin. With regard to color, out of the 11 samples analyzed, only 2 exceeded the MCL. The one sample that showed the maximum color level also showed the maximum concentration of iron. Since both color and iron contents of this sample are considerably higher than the ranges indicated by the other samples, these values can reasonably be discarded. It should be noted that taste and odor problems noted in the 1993 report, were not detected in any of the samples. The coliform bacteria MNP s for all the samples analyzed were shown to be less than 2 per 100 ml which, for all practical purposes, is an indication of the absence of bacterial contamination. The data presented in Table indicates that treatment of the well water required to comply with the State Drinking Water Standards could be accomplished by a system that is designed primarily for iron and manganese removal. With the absence of bacterial contamination, a full scale disinfection system that includes chlorination equipment and a chlorine contact tank is also unnecessary, particularly when the State has no such requirements at this time. However, the treated water should be provided with a chloramine residual before discharge to the new reservoir as commonly practiced for the handling of ground water. The water quality data presented in Table was further examined to establish the design bases for the well water treatment system. As discussed above, the maximum iron concentration and color level were discarded and the next highest values were selected as the design concentrations for these parameters. With regard to manganese concentrations, as all of the values presented in Table appear to fall within a close range, the maximum concentration as shown in Table was selected as the design concentration. Table presents a summary of the selected design values. Table Design Concentrations Parameter Design Values Iron, mg/l 0.62 Manganese, mg/l 0.09 Color, Units 20 City of Lomita Cypress Street Reservoir Project

9 For iron and manganese removal, a commonly employed process is chemical oxidation of the dissolved iron and manganese into insoluble precipitates to be followed by removal of these precipitates by means of a manganese greensand filter. While a variety of oxidizing chemicals, such as potassium permanganate, chlorine gas and sodium hypochlorite solution have been used successfully, a preliminary evaluation of these chemicals indicated that the mixed oxidant produced by an on-site generation system manufactured by Miox Corporation would offer this project a number of advantages, including minimal hazardous materials handling and storage and costeffectiveness. Using an electrolysis process, the Miox system produces from common salt and water a solution that contains sodium hypochlorite at a concentration of 0.4 percent. The solution also contains trace amounts of hydrogen peroxide and other oxidants. Miox has not disclosed precisely the nature of the trace oxidants, but their testing and experience with actual installations show that these trace oxidants enhance the effectiveness of sodium hypochlorite and lower dosages of mixed oxidant (compared to conventional sodium hypochlorite) would be required to oxidize iron and manganese. The mixed oxidant is also expected to be effective in reducing the color in the water. Since the mixed oxidant solution produced by the Miox system contains a low concentration of sodium hypochlorite, storage of the mixed oxidant is not subject to the Uniform Fire Code regulations for storage and handling of hazardous materials like chlorine gas or commercially available sodium hypochlorite solution. The raw materials required for production of the mixed oxidants are only common salt and water. Hence, the Miox system requires no delivery or storage of any hazardous material. In September 2002, a pilot plant, consisting of a mixed oxidant generation system furnished by Miox and a manganese greensand filter furnished by the Loprest Water Treatment Company, was procured by the City for onsite testing. The testing was performed over the period from September 25 through October 10, For the purpose of comparison, tests for treatment of the well water with both conventional sodium hypochlorite solution and Miox s mixed oxidant were performed. For the test runs with each type of oxidant, the filter was tested at the two filtration rates of 8 and 10 gpm per square foot of media surface. Samples of the raw and treated water were collected during the various test runs and analyzed by the City for iron, manganese and chlorine residual. The test results are summarized in a report prepared by the Loprest Water Treatment Company, which is available for review at the City of Lomita as part of the project file. The data show that both types of oxidant could reduce iron from concentrations of 0.49 mg/l and 0.37 mg/l manganese from concentrations of around mg/l to levels well below the MCL s of the State Drinking Water Standards with a filtration rate of either 8 or 10 gpm per square foot of media surface. The data also showed the mixed oxidant dosage required to be considerably lower than that required of the conventional sodium hypochlorite solution. To examine the capability of the pilot plant in color removal, the City analyzed two samples of water that had been injected with the mixed oxidant but not filtered and one sample of water that had been oxidized and filtered. The analysis results showed that while some color was present in the unfiltered samples, no color was detected in the in filtered sample. In addition to this analysis, a sample of the raw well water was delivered to the laboratory of Miox for further evaluation of the mixed oxidant s capability for color removal. (Miox s report is available for review at the City of City of Lomita Cypress Street Reservoir Project

10 Lomita as part of the project file.) As indicated by these reports, treatment with the mixed oxidant followed by greensand filtration is capable of removing the color of Well No. 5 groundwater. These pilot plant testing data confirm the capability of the mixed oxidant to remove iron, manganese and color. The data also indicate that the use of Miox s mixed oxidant would be more cost effective than conventional sodium hypochlorite solution due to the considerably lower chemical dosages required. In light of these considerations, the Miox system coupled with a manganese greensand filter were selected as the major components of the water treatment system for Well No. 5. The pilot plant testing data were also used as the bases for sizing of the Miox system and the manganese greensand filter. With this proposed treatment system in place, as proposed, the proposed project would not result in providing water that does not meet drinking water standards to the constituents of the City of Lomita Water Department. Impact HYD-4: The proposed project would alter the drainage pattern of the project site. However, the proposed alternation of onsite drainage would not result in substantial erosion or siltation on- or off-site. This impact is less than significant. The proposed project would marginally increase the amount of impervious surfaces at the project site and could marginally increase the site s runoff. However, the proposed project would not alter any watershed boundaries and would not alter the course of, diminish the water supply of, or otherwise alter, any stream or river. Therefore, the proposed project would not substantially alter the existing drainage pattern of the site or area, and would not cause any related significant erosion or siltation impacts. Impact HYD-5: The proposed project would alter the drainage pattern of the project site. However, the proposed alteration of onsite drainage would not result in flooding. This impact is less than significant. The proposed project would not alter any watershed boundaries and would not alter the course of, diminish the water supply of, or otherwise alter, any stream or river. However, as discussed above, the proposed project would marginally increase the amount of impervious surfaces at the project site and could increase the site s runoff. To handle the increase in runoff, the proposed project includes drainage improvements. These improvements include onsite catch basins and an 18-inch reinforced concrete pipe (RCP) storm drain, which will carry site runoff, reservoir overflow, and drain water from the reservoir away from residences to an existing LACFCD 60-inch storm drain approximately 400 feet north of the reservoir site. Runoff from the proposed facility would be largely equal to the site s existing runoff and the proposed drainage improvements are designed to prevent on- and off-site flooding. As such, the proposed project would not alter drainage patterns in a manner that would cause flooding, and the project would cause no related significant impacts. Impact HYD-6: The proposed project would alter the site s drainage and, as a result, could affect runoff flowing into the storm drain system. However, the project would not create or contribute runoff water that exceeds the capacity of City of Lomita Cypress Street Reservoir Project

11 existing or planned storm water drainage systems or provides substantial additional sources of polluted runoff. This is a less-than-significant impact. As discussed above in impact HYD-5, the proposed project includes storm drain improvements consisting of onsite catch basins and an 18-inch reinforced concrete pipe (RCP) storm drain. The storm drain would deliver runoff, reservoir overflow, and drain water to an existing 60 storm drain parallel to, and south of, Pacific Coast Highway. This 60 drain and the City s existing storm water system are adequate to handle the proposed project. Local runoff will be essentially the same after construction as before construction. Historically, the local runoff has flowed northerly down the hill in Cypress Street to the catch basins in the gutter and into the 60-inch storm drain. After construction, runoff from the reservoir site will be collected in the new 18-inch storm drain pipe which will connect to the 60-inch storm drain, essentially the same quantity of flow as before. The only difference is that the storm drain will also carry any overflow or drainage from the reservoir. Overflow would only occur if the control system did not stop flow to the reservoir when it is full. If there is overflow detected, the control system will send an alarm to the City s control center, from which the overflow can be terminated. Drainage from the reservoir will occur when it is removed from service for internal cleaning or inspection. As part of the drainage, the water in the reservoir would be drawn down by normal outflow until there would be only a foot or two of water remaining. That remaining water would be discharged to the drain line and to the storm drain. This maintenance work would not be scheduled during a storm event or during the rainy season when the storm drain might have heavy flow. The project s only runoff pollution source is exposed sediment during construction and typical urban pollutants (i.e. trash, remnant vehicle/equipment fluids, sediment, etc.). As discussed, these pollutants would be reduced to the maximum extent practicable in accordance with NPDES requirements. Therefore, the proposed project would not significantly impact the storm water drainage system. Impact HYD-7: The proposed project would place a 5-million gallon reservoir upslope from people and structures. As such, rupture of the reservoir and release of water could cause loss, injury, or death as a result of flooding. However, as designed, the probability of failure of the proposed Cypress Street Reservoir has been calculated to be less than 0.2 percent, which is considered very low. Therefore, the project s potential to expose people or structures to substantial adverse flooding effects is considered a less-than-significant impact. The proposed project site is not located within a designated 100-year or 500-year flood zone, and the project site is not within the vicinity of a levee or a dam. However, the project could increase flood hazard. The proposed reservoir would store up to 5 million gallons of water, and in the event the reservoir tank is damaged, water releases are possible. Given the topography of the surrounding area, flows would likely travel northward, down Cypress Street, or southward into the adjacent quarry. A Structural/Seismic Risk Assessment for the Proposed Cypress Street Reservoir (URS, 2005, as City of Lomita Cypress Street Reservoir Project

12 contained in Appendix C of this EA/EIR) was prepared to determine the structural adequacy of the proposed reservoir. Impact GEO-6 in Section 3.3 of this EA/EIR details the analysis and results of this risk assessment. In summary, the probability of failure of the proposed Cypress Street Reservoir has been calculated to be less than 0.2 percent, which URS considers very low. For comparison, URS concludes, [the] calculated probability of an uncontrolled release of water from the new Cypress Street Reservoir is much smaller than the probability of failure of buildings in the City of Lomita in the event of very large earthquakes. 3 URS further recommends that a probability this low should be taken as assurance that the proposed design of the reservoir will provide reasonable assurance that the life-safety of the inhabitants on Cypress Street is adequately protected. 4 Therefore, the project s potential to expose people or structures to a significant risk of loss, injury, or death involving flooding, including flooding as a result of failure of proposed reservoir is considered a less-than-significant impact CUMULATIVE IMPACTS The proposed project would generate water pollutants during construction and operation, which would contribute to cumulative water quality impacts. However, the project would be required to comply with the SQMP, which is a regional plan designed to reduce the pollutant levels of receiving waters. Thus, the plan is intended to achieve a cumulative reduction in water pollutants. Compliance with this SQMP ensures the project s contribution to cumulative water quality impacts is not considerable. The proposed project would not contribute to any other cumulative hydrology or water quality impacts MITIGATION MEASURES None required LEVEL OF SIGNIFICANCE AFTER MITIGATION The proposed project would not significantly impact hydrology or water quality. The following table is a summary of the thresholds of significance, potential impacts, and associated mitigation measures. 3 URS. May 31, Letter to Mr. Tom Odom, City Administrator, City of Lomita, Subject: Structural/Seismic Risk Assessment for the Proposed Cypress Street Reservoir Phase II. (Contained in Appendix C of this EA/EIR.) 4 URS. November 21, Structural/Seismic Risk Assessment for the Proposed Cypress Street Resroivr Phase II. (Contained in Appendix C of this EA/EIR.) City of Lomita Cypress Street Reservoir Project

13 Table Summary of Thresholds of Significance, Impacts, and Mitigation Measures for Hydrology/Water Quality Threshold of Significance Applicable Mitigation Measures Level of Significance Violate any water quality standards or None required waste discharge requirements. Substantially deplete groundwater supplies None required 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. Result in providing water that does not meet drinking water standards to the constituents of the City of Lomita Water Department. None required Substantially alter the existing drainage None required pattern of the site or area, including through the alteration of the course of a stream or river, in a manner which would result in substantial erosion or siltation on- or off-site. Substantially alter the drainage pattern of None required the site or area, including through the alteration of the course of a stream or river, or substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or offsite. Create or contribute runoff water which None required would exceed the capacity of existing or planned storm water drainage systems or provides substantial additional sources of polluted runoff. Otherwise substantially degrade water quality. None required Place housing within a 100-year flood None required No impact 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. None required No impact Expose people or structures to a None required 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 None required No impact mudflow. City of Lomita Cypress Street Reservoir Project

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