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T 1 Working To Restore Nature In subsequent investigations, RESNA personnel advanced six soil bonngs (MW1-MW6) in the vicinity of the former underground storage tank and converted them to groundwater monitoring wells at depths of approximately 30 feet below grade The purpose of these borings was to investigate and define the extent of hydrocarbon impaction in soil and groundwater The boring/well locations are plotted on Figure 2 Field activities performed at the site are summarized in separate Problem Assessment Reports submitted by RESNA on May 30, 1991 and May 20, 1992 QUARTERLY MONITORING AND SAMPLING Groundwater monitoring and sampling of site wells was conducted on May 2, 1994 by RESNA personnel Water level measurements were collected from each site monitoring well (Table 1) prior to purging and sampling Groundwater elevations across the site have risen an average of 0 63 feet since the last monitoring event in February 1994 The groundwater gradient was calculated using the May 2, 1994 groundwater elevation data and is illustrated on Figure 2 The figure depicts a variant gradient between 0 024 to 0 015 ft/ft, or 127 to 79 feet per mile in a southeasterly direction In accordance with San Joaquin County Public Health Services, Environmental Health Division i (PHS/EHD) correspondence dated May 5, 1993, wells MW2, MW3, and MW6 were sampled this quarter Prior to groundwater sample collection, a minimum of 3 casing volumes of water was purged from each monitoring well All purged water was contained on-site in DOT approved 55-gallon drums pending analytical results Groundwater samples were collected from each well after stabilization of groundwater parameters (pH, electrical conductivity, temperature) Water samples were collected using dedicated disposable bailers Field purge logs are contained in Attachment 1 Groundwater samples were placed on ice and transported under chain-of-custody protocol to state-certified Sequoia Analytical in Redwood City, California All samples were analyzed for benzene, toluene, ethylbenzene, xylenes (BTEX) using EPA method 8020, and total petroleum hydrocarbons as gasoline (TPHg) using modified EPA method 8015 Dissolved petroleum hydrocarbons and BTEX constituents were not detected in monitoring well MW6 The samples collected from MW2 and MW3 contained low levels of dissolved constituents The sample collected from MW2 contained benzene, ethylbenzene, toluene and TPHg at 0 57, 4 5, 0 80 and 82 parts per billion (ppb), respectively The sample collected from MW3 contained ethylbenzene, toluene and TPHg at 1 6, 1 7 and 110 ppb, respectively The benzene, ethylbenzene and toluene Ievels in wells MW2 and MW3 were below the Primary and Secondary Maximum Contaminant Levels (MCLs) for ethylbenzene and toluene established by �l 15000212QR-1994 FNL 2