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rt v VTC • A S S O C I A T E S I N C wells, two monitoring wells, and one air sparge well One of these borings may be completed as a deep monitoring well to address vertical definition of the site's dissolved groundwater plume and it's potential impact to the nearby Supply Well QUARTERLY MONITORING ACTIVITIES ATC Associates Inc performed quarterly groundwater monitoring and sampling on December 16, 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 municipal supply well (Thornton #2) The samples were analyzed for the presence of dissolved petroleum hydrocarbons Additionally, at the request of PHS/EHD staff, fluid level measurements were collected from Supply Well with an electronic oil/water interface probe and an attempt was made to collect a groundwater grab sample from this well with sanitized disposable bailer Depth to water measurements were collected on December 16, 1997 from monitoring wells MW1 through MW6 The water table elevation has risen an average of 0 96 feet since the last monitoring event in September 1997 Groundwater beneath the site generally flows in a southwesterly direction with average gradient of 0 001 ft/ft, or approximately 5 4 feet/mile, with apparent mounding in vicinity of MW3 Groundwater monitoring data are summarized in Table . 1 A groundwater gradient map for the December 16, 1997 monitoring episode is shown on Figure 2 An electronic oil/water interface probe was utilized to measure depth to water within the Supply Well to determine if lubricating oil from the well's pump was present at the water table Depth to water was measured at 16 90 from to top of the sounding tube (or approximately 14 feet below ground surface) No lubricating oil was detected in the well 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 Industries Quality Assurance/Quality Control Plan, on file with PHS/EHD Well purge logs are included in Attachment 1 ATC Associates, at the request of PHS/EHD, attempted to collect a groundwater grab sample from Supply Well using a sanitized disposable bailer However, due to the angle of the well's sounding tube in relation the well casing, this methodology proved unsuccessful The Supply Well was subsequently sampled through an existing sampling port located on above ground piping leading from the well Collected groundwater samples were placed on ice and transported under chain-of custody to State-certified American Environmental Network, Inc laboratory Samples were analyzed for w 1943261quaA1y14gr-1997 dm 3