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i Date August 9,2004 Quarter 2nd Quarter, 2004 •1 Based on the review of the analytical and hardcopy data(chain-of-custody records, blanks, dilutions, holding tunes, LCS/LCSD results,MS/MSD results, and surrogate recoveries),the data are acceptable as reported by the laboratory with the following limitations • The reported results for gasoline range organics (GRO) in sample MS-1B may be biased low as demonstrated by a low surrogate recovery due to matrix interference • The elevated reporting limits reported in the methanol analysis of sample MW-5 was due to matrix interference • The elevated reporting lints were the result of dilutions performed by the laboratory in order to quantitate a target analyte DISCUSSION. Depth to water at the site was approximately 44 feet below ground surface (bgs) during this quarterly event Generally, the groundwater surface intercepts the vapor extraction wells (VW) screened interval Monitoring wells (MW) are generally screened 10 to 15 feet below the groundwater surface The deep nucrosparge (MS) wells are generally screened 20 feet below the groundwater surface and the air sparge(AS) wells, which are the deepest wells on the site, are generally screened 30 feet below the groundwater surface The air sparge wells are currently not sampled as part of our quarterly sampling program. GRO,benzene, toluene, ethylbenzene, total xylenes(BTEX),methyl tert-butyl ether(MtBE),and 1,2-dichloroethane (1,2-DCA)were reported above the method detection limits in groundwater samples collected from the site wells this quarter Generally, GRO,benzene and MtBE reported lower concentrations this quarter This is very apparent in the shallow vapor wells VW-4,VW-10 and VW-I 1 located in the source area In these vapor wells, GRO dropped from a high of 1,500 imcrograms per liter (j.g/L) to 150 ug/L,benzene dropped from 120 yg/L to 2 6 p.g/L and MtBE dropped from 4 6 ug/L to 2 8 ug/L Benzene and MtBE are laterally defined to the north by VW-2 and VW-5,to the south by VW-1,to the east by VW- 7 and VW-12, and to the west by VW-10 Although several of these wells reported concentrations of MtBE, the concentrations are below the secondary maximum contaminant level (MCL) of 5 Ag/L Although our shallow screened well network does not laterally define GRO,the concentrations in the source area are low(<150 Ag/L) Vertical definition of the groundwater is monitored by wells MS-1B, MS-2B, and MS-3B GRO and benzene were reported in these wells at a concentration of 120 ug/L and 2 6 ug/L, respectively MtBE was not reported in these wells Proposed Future Activities: Short Range (<2 years) — continue to conduct quarterly groundwater momtormg and monitoring the natural attenuation of the contammants Air bubbling will continue to aid in natural attenuation Long Range(>2 years)—When natural attenuation has reduced the size of the impacted area such that the lateral and vertical extent is defined by the current monitoring well network, and a downward trend can be shown, site closure will be requested Groundwater elevations generally decreased relative to the previous sampling event The mferred direction of groundwater flow across the site was toward the northwest to northeast with an average hydraulic gradient of 0 001 ft/ft fig K 5WPr0cessU5 BP ARC0102130\Quarurlyl2 QTR 0412130 GWMR 2Q04 doe Page 2