ARCHIVED REPORTS XR0000029 - Laserfiche WebLink

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KLEiNFELDER depth-to-groundwater and total-depth measurements be performed in all wells They ' also requested that the following quarterly report include contaminant-mass-estimates and fate and transport models for dissolved gasoline and benzene ' The October 2004 quarterly groundwater-monitoring event indicated that the groundwater elevation decreased approximately 2 76 feet from the previous event ' performed in June 2004 During this event, the average depth to groundwater was 48 fib feet bgs (-32 01 feet msl) The elevations ranged from -31 50 to -32 43 feet msl ' The groundwater flow was easterly to southeasterly at a gradient approximately 0 003 feet per linear foot Benzene concentrations increased in wells MW-1, MW-7, MW-11, ' MW-12, SP-1, and PZ-2 TPH-G concentrations increased in wells MW-11 , MW-12, SP-1, SP-4, and PZ-1 DIPE was the only oxygenate detected The plume of t petroleum-impacted groundwater covers a portion of the southern side of the subject site The TPH-G and benzene plume extends just beyond the property boundaries Historic measurements indicate that the plume is stable and decreasing in most wells, ' while increasing in some down-gradient wells In addition, the October 2004 report included the current calculations for the mass contaminant values in groundwater of benzene and TPH-G The calculated total mass in groundwater for benzene was 1 8 Kilograms (Kg) and the calculated total mass in groundwater for TPH-G was 70 7 Kg ' Fate and transport models for benzene and TPH-G were presented, as well The model for benzene predicts that the concentrations decrease rapidly at a conservative distance of 30 feet from the source to be within the associated MCL The model indicates that the concentration of benzene may exceed its associated MCL beyond the southern property boundary based on the current concentration results for well MW-11 However, it does not appear to pose a risk to potential receptors through the groundwater ingestion exposure route The model for TPH-G predicts that the ' concentrations decrease rapidly at a conservative distance of 24 feet from the source to be within the goal of 50 mg/L The model indicates that the concentration of TPH-G I may exceed its associated goal beyond the southern property boundary based on the current concentration results for well MW-11 However, it does not appear to pose a ' risk to potential receptors through the groundwater ingestion exposure route The January 2005 quarterly groundwater-monitoring event indicated that the groundwater elevation increased approximately 3 21 feet from the previous event performed in October 2004 During this event, the average depth to groundwater was 45 48 feet bgs (-28 80 feet msl) The elevations ranged from -28 22 to -29 38 feet msl C23-484517-BOOISAC5R610 Page 5 of 12 September 14, 2005 ' Copynght 2005 Kleinfelder Inc