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Second Quarter 1993 Monitoring Report Laidlaw Corp , 1444 Tillie Lewis Dr,Stockton,CA Project No 150002 00 Page 2 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 5, 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 PHSIEHD correspondence dated May 5, 1993, monitoring wells MW2, MW3, and MW6 were sampled Groundwater elevations across the site have risen an average of 5 45 feet since November 1992 A groundwater gradient map was calculated using the May 5, 1993 groundwater elevation data A variant groundwater gradient exists beneath the site with an average magnitude of approximately 0 015 ft/ft or 79 ft/mile in a southeasterly direction (Figure 2) C/ Prior to groundwater`sample collection, a minimum of 3 casing volumes of water was purged from wells MW2, MW3, and MW6 All purged water was contained onsite in DOT approved 55-gallon drums pending analytical results Groundwater samples were collected from each of the three wells 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 Petroleum hydrocarbon constituents were detected at various levels in wells MW2 and MW3 BTEX levels in wells MW2 and MW3 were below the respective Maximum Contaminant Levels (MCLS) established by the Department of Health Services Contaminant concentrations in well MW3 were greatly reduced this quarter compared to previous levels Laboratory results are summarized in Table 2 Laboratory reports and chain-of-custody documentation are presented in Attachment 2 STOCKPILED SOIL Excavated stockpiled soils previously documented to be impacted by petroleum hydrocarbon constituents have remained on site since March 1991 excavation The stockpiled soil has been aerating in accordance with the exemptions specified in San Joaquin Valley Unified Air Pollution QUARTLYI2QR 1993 FNL