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1.0 Summary of Site Investigation, Cleanup and Monitoring One (1) underground double wall fiberglass 8,000 gallon, storage tank (UST) containing diesel fuel for a backup generator at the Wastewater Treatment Plant (WWTP) was removed from the site in January 1998 under San .loaquin County Environmental Health Department (EHD) permits. One (1) above ground diesel storage tank is currently located adjacent to the former tank pit. Soil. samples collected as a part, of the underground tank removal revealed Total Petroleum Hydrocarbons as Diesel (TPHD) in soil atl,I milligram,,.; per kilogn,m (mg/kg) and in groundwater at 580 milligrams per liter (m,gil). On the basis of this data, the EHD requested additional, site investigation. The former tank pit is located within the WWTP property between several large treatment ponds. Between 2003 and 2008, the site area underwent extensive construction and development for WWTP use. Four (4) exploratory borings: (B-1, B-2, B-3 and B-4) were drilled and sampled around the WWTP former UST in February 2003. No petroleum hydrocarbon constituents or fuel oxygenates were reported in soil sample's collected during the 2003 assessment. Groundwater samples from three of borings, were reported to contain low levels of dissolved TPHD [810 micrograms per liter(ug/1) or less]. A fourthgroundwater sample, collected from boring B-2, was reported to contain 33,000 ug/l TPHD. BTEX. MTBE and related oxygenates were not revealed in any groundwater sample collected. Wright drilled and sampled five (5) additional borings (13-5, B-6, B-7, B-8 and B-9) in October 2008. Soil and, groundwater samples were collected and analyzed for TPRD only since previous analysis had indicated that gasoline and related fuel compounds were not present below this site. Up to 490 ug/1 TPHD dissolved concentrations were detected in groundwater samples collected during the 2008 assessment. The highest concentration was reported in boring B-5, located 60 feet north of the f6riner tank location, Groundwater collected ftorn boring B-6, drilled adjacent the 2003 B-2, was reported to contain only 170 ug/l. The laboratory report indicated that the TPED detected was higher boiling than typical diesel fuel. EHD required installation of one groundwater monitoring well following a review of Wright's 2003 and 2008 studies near Wright Boring B-5. The well (designated WESMW-I) was placed in the vicinity of boring B-5 and used in conjunction with nearby existing WWTP groundwater monitoring wells MW.HP-5, MWHP-6, MWHP-7 and MWHP-8. The latter Nvells were installed by CH2M Hill to monitor water quality and water levels below the WWTP. Wright uses the CH2M wells for water level data only for groundwater direction plots (see Figure 2). It is our understanding from a limited review of the existing CIUM I-lilt wells that they are screened in the same aquifer strata as that screened by well WFSMW-1. The new well was designated "N[W)VES-l" to avoid confusion with the CI-12M Hill monitoring wells, In their letter dated September 23, 2010, the EHD requested that a Closure Summary Report (CSR) be prepared in order to comprehensively review site data and to determine 4W)/CSR/Rcpt Page 3 of 17