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} }1 QUARTERLY MONITORING ACTIVITIES South Technology performed quarterly groundwater morutonng and sampling on September 18, 1997 Field work included measunng 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 MW 1 through MW6 The water table elevation has decreased an average of approximately 3 16 feet since the last monitonng 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 monitonng data are summanzed in Table 1 A groundwater gradient map for the September 18, 1997 monitonng episode is shown on Figure 2 Groundwater samples were collected from wells MW 1 through MW6 after purging and stabilization of physical parameters (pH, electncal conductivity, and temperature) The monitoring wells were purged and sampled according to RESNA Industnes 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 Laboratones 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 NIW3 and MW4 Groundwater samples collected from wells MW1, MW 2, MW5, 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 histoncal levels Additionally, groundwater samples from wells NMI through MW6 and the municipal well contained no detectable concentrations of oxygenate fuel additives Analytical results are summanzed 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 histoncal 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 monitonng events w 1943261quaA1yl3gr-1997 doc 3 • HMTH