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1992 3rd QTR Monitonng Report . Laidlaw corp , 1444 Tllhe Lewis Dr , Stockton,CA October 05, 1992 Page 2 In a two phased approach beginning on March 27, 1991, RESNA personnel advanced six soil borings (MWl-MW6) in the vicinity of the former underground storage tank and subsequently converted them to groundwater monitoring wells at depths of approximately 30 feet below grade The purpose of these borings was to investigate and define hydrocarbon impaction in soil and groundwater The boring/well locations are plotted on Figure 2 Phase I and II field activities, in addition to the associated analytical results, are discussed in detail in RESNA's "Problem Assessment Report" dated May 20, 1992 QUARTERLY MONITORING AND SAMPLING Groundwater monitoring and sampling was conducted on August 18, 1992, by RESNA personnel Water level measurements were collected from each site monitoring well prior to purging and sampling Groundwater monitoring of wells MW 1 through MW6 indicate an average decrease of 3 6 feet in the groundwater table elevation since March 1992 A groundwater gradient map was calculated using the August 18, 1992 groundwater elevation data A variant groundwater gradient exists beneath the site with a magnitude of approximately 0 01 - 0 028 ft/ft or 52 8 - 148 ft/mile in a southeastern direction (Figure 2) Prior to groundwater sample collection, a minimum of 3 casing volumes of water was purged from each well All purged water was contained onsite in DOT approved 55-gallon drums pending analytical results Groundwater samples were collected from each of the six wells after stabilization of groundwater parameters (pH, electrical conductivity, temperature) The water samples were collected using a disposable bailer Field purge logs are contained in Attachment 1 Groundwater samples were placed on ice and transported under chain-of-custody protocol to state-certified RESNA Environmental Laboratories in Fremont, 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 wells MW1, MW5 and MW6 Aromatics were detected at various levels in wells MW2, MW3, and MW4 Only ethylbenzene in well MW3 (2200 ppb) was present at levels above the State Primary Maximum Contaminant Levels Laboratory results are summarized on Table 2 Laboratory reports and chain-of-custody documentation are presented in Attachment 2 Laidlaw Corporation will continue with groundwater monitoring and sampling The next round of sampling will be performed in November 1992 • QUARTLYIQR090992 DRF