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Ms. Connie Davis/Aggregate Industries - F Street July 2002 QMR/Closure Request Project Number 1001018 Pl1Rl1GON September 20, 2002 Page 5 with results from April 2002 with the exception of slight decreases of the toluene, ethlybenzene and xylenes concentrations observed in the groundwater sample collected from MW-3 and slight decreases of the BTEX concentrations observed in the groundwater sample collected from MW-4. The Maximum Contaminant Levels (MCLs) for BTEX are also summarized in Table 2. As seen from Table 2, the MCLs for BTEX are 5.0; 1,000; 700 and 10,000 µg/L, respectively. Those standards are the statewide interim organic pollutant standards published in "The Basic Standards for Ground Water" Regulation 41, (5 CCR 1002-41). It should be noted that TEPH is not regulated by a numeric standard in Colorado at this time. As seen from Table 2, BTEX concentrations observed in the groundwater samples collected from the site during July 2002 did not exceed the CGS. The July 2002 sampling episode was the fifth event in which BTEX concentrations observed in groundwater samples collected from the site did not exceed the MCLs. 4. CONCLUSIONS AND RECOMMENDATIONS The following conclusions are made based on information obtained during the quarterly groundwater sampling activities. 1. Groundwater was observed at depths ranging from approximately 6.2 to 24.5 feet below grade during the July 2002 sampling event. Free-phase product was not observed during the July 2002 sampling episode. 2. The regional groundwater flow generally appeared to be in a northeasterly direction with a northerly component on the east side of the site on July 29, 2002 and the hydraulic gradient was estimated to range from approximately 0.005 to 0.02 for the overall site. The regional groundwater flow direction and hydraulic gradients estimated for the September 2001, October 2001, January 2002, April 2002 and July 2002 events are generally consistent with each other. 3. The local groundwater flow direction appeared to be to the northeast in the vicinity of the spill azea with a northerly component east of the spill area on July 29, 2002 and the hydraulic gradient was estimated to range from approximately 0.002 to 0.005 for the spill area based on the July 2002 groundwater elevation data. The local groundwater flow direction and hydraulic gradients estimated for the September 2001, October 2001, January 2002, April 2002 and July 2002 events are generally consistent with each other with the exception of the January 2002 flow-direction and gradient estimates.