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MA • Working To Restore Nature GROUNDWATER MONITORING AND SAMPLING RESNA personnel performed quarterly groundwater monitoring and sampling on June 24, 1994. Field work consisted of measuring the depth-to-water 1n wells MW 1 through MW6, purging and sampling the water from wells MW2, MW3, and MW4, and analyzing the samples for the presence of dissolved petroleum hydrocarbons The water table elevation has dropped an average of approximately 124 feet since the last monitoring event 1n March 1994 Groundwater monitoring data are summarized 1n Table 1 Groundwater beneath the site flows southwest with an overall gradient of 0 001 ft/ft, or approximately 5 3 feet/mile A groundwater gradient map for the June 24, 1994 monitoring episode 1s shown on Figure 2 Groundwater samples were collected from wells MW2, MW3, and MW4 after purging and stabilization of physical parameters(pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to RESNA's Quality Assurance/Quality Control Pian, on file with PHS/EHD Well purge logs are included 1n Attachment 1 LABORATORY ANALYSIS Collected groundwater samples were placed on ice and transported under chain-of-custody protocol • to state certified Sequoia Analytical Laboratory Samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) and TPHg by EPA methods 8020 and modified 8015, respectively. Laboratory analyses detected elevated concentrations of petroleum hydrocarbons in the samples collected from wells MW2, MW3, and MW4. Results are generally consistent with historical levels Analytical results are summarized in Table 2. Laboratory reports and chain-of- custody documentation are presented in Attachment 2 OTHER SITE ACTIVITIES On June 24, 1994, monitoring well purge water, accumulated from on-site groundwater sampling events, was transported and treated off site by Petroleum Recycling Corp (U S EPA ID # CAD083166728) under State Manifest Number 93194083 A copy of the manifest 1s included as Attachment 3. A review of the site's historical groundwater data was conducted at the request of PHS/EHD Depth to water measurements indicate groundwater beneath the site has consistently flowed west____erly, with slight variations to the north and south directions since ground water monitoring was initiated 1n November 1990 The lateral extent of the dissolved contaminant plume associated with the former underground fuel storage tank has been essentially defined, except 1n the vicinity of well MW4, north of the former tank. It is unclear whether contamination at MW4 can be attributed to the former tank or from a potential off-site contributing source The next sampling round is scheduled for the third quarter of 1994 and the subsequent monitoring report submitted by October 31, 1994 150081/QUARTLY/2QR 1994 FNL