ARCHIVED REPORTS_XR0009227 - Laserfiche WebLink

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�' 7I Working To Restore Nature Excavated soils are currently being aerated on site Final disposition of remediated sods will be determined upon successful aeration In subsequent investigations, RESNA personnel advanced six soil borings (MWi-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 August 2, 1993, by RESNA personnel Water level measurements were collected from each site monitoring well (Table 1) prior to purging and sampling activities In accordance with San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) correspondence dated May 5, 1993, monitoring wells MW 1, MW2, MW3, MW4, MW5, and MW6 were sampled. J Groundwater elevations across the site have dropped an average of 1.96 feet since the last monitoring event in May 1993 A groundwater gradient map was calculated using the August 2, 1993 groundwater elevation data The groundwater gradient depicts an anomalous,/ groundwater plateau for the eastern portion of the site, which may be due to soil heterogeneity. The gradient magnitude Is between 0 008 to 0 028 feet per foot or 42 to 148 feet per mile in a south-easterly direction j 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 Purge water determined through laboratory analysis to be free of petroleum hydrocarbons will be disposed of through surface discharge. Groundwater samples were collected from each well after stabilization of groundwater parameters (pH, electrical conductivity, temperature) Water samples were collected using dedicated disposable balers. 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 ('IPHg) using modified EPA method 8015 Prof Diak1QUARTLYI3QR-1993 FNL 2