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• 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 SAMPLING ACTIVITIES On March 29, 2001, ATC Associates personnel collected groundwater samples from monitoring wells MW-2, MW-3, MW-4, MW-5, and MW-6 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 1 ANALYTICAL RESULTS Laboratory analyses results detected TPHg at monitoring well MW-4 at a concentration of 3,400 pg/L At monitoring well MW-4 benzene was detected at a concentration of 10 µg/L, toluene was detected at a concentration of 8 4 pg/L, ethylbenzene was detected at a concentration of 65 pg/L, xylenes were detected at a concentration of 23 pg/L, and MTBE was detected at a concentration of 21 gg/L However, MTBE was analyzed for at monitoring well MW-4 by EPA Method 8260 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, MW-5, MW-6, and the Municipal Supply Well The California Primary Maximum Contaminant Levels (MCLs) for Benzene and MTBE of 1 pg/L and 13 pg/L respectively, were exceeded at monitoring well MW-4 GROUNDWATER FLOW DIRECTION Water level measurements were collected from monitoring wells MWA, MW-2, MW-3, MW-4, MW-5, and MW-6 on March 29, 2001 Water level elevations ranged from 0 23 feet above mean sea level to 0 10 feet above mean sea level, representing an increase in the water table elevation of approximately 0 99 feet since December 2000 The water level elevations were used to develop the groundwater contour map (Figure 2) Assuming that horizontal isotropic • conditions prevail, groundwater in the uppermost aquifer beneath the site generally flows in a westerly direction There is some mounding present in the vicinity of monitoring well MW-3 w 1Wordpro1625821Quardy\1QR-2001 doc 4