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k A S S O C I A T E S I N C extraction/air sparge system at the site is not warranted However, Mr Knoll also indicated that either long term monitoring or another alternative would be required prior to the site being considered for closure ATC discussed the possibility of performing a long-term groundwater extraction test at the site, to which Mr Knoll agreed The workplan for performing a groundwater extraction pump test at the site was submitted on March 1, 2001 ATC is currently trying to locate a pump capable of handling the anticipated flow rate As an alternative, a 4-inch extraction well may be required SAMPLING ACTIVITIES On June 18, 2001, ATC Associates personnel collected groundwater samples from monitoring wells MW-2, MW-3, and MW-4 The locations of the monitoring wells are shown on Figure 2 Prior to collection of groundwater samples, the depth to water, pH, electrical conductivity, and temperature were measured in the monitoring wells and recorded A minimum of three well casing volumes was purged from each well prior to sampling The wells were allowed to recover and samples were collected from each well using disposable bailers A sample was also collected from the Thornton Municipal Supply Well The groundwater samples collected from each well were submitted to State-certified Argon • Laboratories (FLAP Cert No 2359) for chemical analysis of total petroleum hydrocarbons as gasoline (TPH-g) utilizing EPA method 8015 modified, benzene, toluene, ethylbenzene, xylenes (BTEX), and methyl tert butyl ether (MTBE) utilizing EPA method 8020 Groundwater monitoring well purge and sample logs are contained in Attachment I ANALYTICAL RESULTS Laboratory analyses results detected TPHg at monitoring well MW-4 at a concentration of 7,500 pg/L At monitoring well MW-4 benzene was detected at a concentration of 12 µg/L, toluene was detected at a concentration of 9 4 pg/L, ethylbenzene was detected at a concentration of 170 pg/L, and xylenes were detected at a concentration of 52 gg/L MTBE was analyzed for at monitoring well MW-4 and was not detected above laboratory reporting limits Benzene, ethylbenzene, toluene, xylenes, MTBE, and TPHg were not detected above the laboratory- reporting limit at monitoring wells MW-2, MW-3, and the Municipal Supply Well The California Primary Maximum Contaminant Level (MCL) for benzene of I µg/L was exceeded at monitoring well MW-4 Laboratory data sheets and chain-of-custody documentation are contained in Attachment 2 GROUNDWATER FLOW DIRECTION Water level measurements were collected from monitoring wells MW-1, MW-2, MW-3, MW-4, MW-5, and MW-6 on June 18, 2001 Depth to water measurements ranged from 10 02 feet to 14 98 feet below top of casing representing a decrease in the water table elevation of approximately 1 18 feet since March 2001 The water level elevations were used to develop the groundwater contour map (Figure 2) Assuming that horizontal isotropic conditions prevail, w 1Wordpro1625821Quart1y12QR-2001 doc 4