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1 <br /> RM Associates 701-0102 <br /> 2 4 4 Pre-remediation Mass Calculations of TPHg and Benzene Dissolved in <br /> Groundwater <br /> Two spreadsheets presenting the mass calculations for pre-remediation TPHg and benzene <br /> ' respectively are presented as Item V in Appendix C Based on measured and estimated parameters <br /> the total amount of TPHg is calculated at 52 4 pounds and the amount of benzene is calculated at 2 6 <br /> pounds Again an error margin of at least 50 percent should be assumed for these estimates <br /> 3.0 REMEDIATION SYSTEM AND EFFECTIVENESS <br /> 3.1 Co-extraction of Soil Vapor and Groundwater <br /> Soil vapor extraction (SVE) and groundwater extraction' at ite began on February 1 , 1998 and continued until the system was shut down on February 21( , when the treated water'disc` arge <br /> line was removed to accommodate further development of the site It was assumed at that time that <br /> further groundwater extraction at the site would either no longer be necessary or if further pumping <br /> were necessary, wastewater would have to be discharged into a storm drain under NPDES <br /> ' permitting <br /> Soil vapor and groundwater were co-extracted from four co-extraction wells illustrated on Figure <br /> 2 as EW-I through EW-4 Soil vapor was extracted at a rate of approximately 100 cubic feet per <br /> minute, and groundwater at a rate of 6-10 gallons per minute Both extracted soil vapor and <br /> groundwater were treated by filtration though granular activated carbon The discharge of treated <br /> groundwater was permitted by the City of Manteca Department of Public Works and the discharge <br /> of treated soil vapor was permitted by the San Joaquin Valley Unified Air Pollution Control District <br /> (Permit Unit N-3920-1-0) <br /> During the two-year duration of the remediation project, nearly 6 3 million gallons of groundwater <br /> and 84 million cubic feet of soil vapor have been extracted from four soil vapor and groundwater co- <br /> extraction wells at the site <br /> A diagram of the groundwater and soil vapor extraction and treatment system is presented in <br /> ' Appendix D as Item I A log of groundwater production and recovery of dissolved product (TPHg <br /> and Benzene) is presented in Table 4, and the groundwater treatment system influent and effluent <br /> analyses are presented in Table 5 Table 6 is a log of the production and analysis of extracted soil <br /> ' vapor and an estimate of recovered TPHg <br /> 3.1 Groundwater Cleanup <br /> ' that are most significant cant for assessing the achievement of the remediation program are the <br /> The data g g p �' <br /> groundwater monitoring results presented in Table 2, but particularly Figures 5 through 8 Figures <br /> 5 through 8 illustrate the decline in TPHg and benzene concentrations over the remediation period <br /> and following, for monitoring wells BEI-MW3 and BEI-MWI, respectively TPHg and Benzene <br /> ' Page 5 of I I <br />