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QUARTERLY MONITORING ACTIVITIES Smith Technology performed quarterly groundwater monitoring and sampling on September 18, 1997 Field work included measuring the depth-to-water in wells MW 1 through MW6 and purging and sampling the water from wells MW1 through MW6 and the nearby community well (Thornton #2) The samples were analyzed for the presence of dissolved petroleum hydrocarbons Depth to water measurements were collected on September 18, 1997 from monitoring wells MMI through MW6 The water table elevation has decreased an average of approximately 3 16 feet since the last monitoring event in June 1997 Groundwater beneath the site generally flows in a southwesterly direction with average gradient of 0 0009 ft/ft, or approximately 4 8 feet/mile Groundwater monitoring data are summarized in Table 1 A groundwater gradient map for the September 18, 1997 monitoring episode is shown on Figure 2 Groundwater samples were collected from wells MW1 through MW6 after purging and stabilization of physical parameters (pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to RESNA Industries Quality Assurance/Quality Control Plan, on file with PHS/EHD Well purge logs are included in Attachment 1 The community well was sampled through an existing sampling port Collected groundwater samples were placed on ice and transported under chain-of-custody to State-certified Argon Laboratories Samples were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) by EPA method 8020 and TPHg by EPA method modified 8015 At the request of Ms Mary Meays from PHS/EHD the groundwater samples were also analyzed for oxygenate fuel additives by EPA method 8260 Laboratory analyses detected elevated concentrations of petroleum hydrocarbons in the samples collected from wells MM3 and MW4 Groundwater samples collected from wells MW1, MW2, MWS, MW6, and the municipal well contained no detectable concentrations of BTEX or TPHg The laboratory method detection levels for BTEX and TPHg were 0 5 and 50 ppb, respectively These analytical results are generally consistent with historical levels Additionally, groundwater samples from wells MMI through MW6 and the municipal well contained no detectable concentrations of oxygenate fuel additives Analytical results are summarized in Table 1 Laboratory reports and chain-of-custody documentation are presented in Attachment 2 In accordance with PHS/EHD correspondence dated December 27, 1993, the sampling schedule of MW1 has been reduced to annual and wells MW5 and MW6 to semi-annual Wells MW2, MW3 and MW4 will continue to be sampled quarterly Additionally, the nearby community well will be sampled quarterly This schedule is based upon historical groundwater analytical data Oxygenate fuel additives were not detected in of the wells sampled and therefore ATC Associates recommends that laboratory analysis of groundwater samples for fuel oxygenates (by EPA . method 8260) be dropped from the analytical suite of future quarterly monitoring events w V43251quaa1yl3gr-1997 dm 3 • SMTH