ARCHIVED REPORTS XR0010492 - Laserfiche WebLink

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I ' DISCUSSION PHS/EHD stated that if soil samples from the two requested additional soil borings demonstrated significant reduction in gasoline concentrations since 1990, and if the mass/volume of gasoline remaining in the soil could be calculated, then PHS/EHD would reconsider the site for closure ' The gasoline concentrations in soil have been greatly reduced since 1990 In the vicinity of SW- 2W (tank pull sidewall sample collected at a depth of 13 feet on January 23, 1990), soil boring Location B was drilled on July 20, 1994 and SB1/MWI was drilled on October 25, 1995 (Attachment A) In this area, the TPHg concentration in soil in 1990 was 1600 ppm at 13 feet, in 1994, it was 19 ppm at 26 feet, and 2 5 to 3 6 ppm from 26 to 31 feet, and nondetectable from 32 to 41 feet, and in 1995, TPHg was nondetectable from 25'/2 to 701/2 feet In the vicinity of boring B-5 drilled on October 5, 1990, boring Location A was drilled on July 20, 1994 (Attachment A) In this area, the TPHg concentration in soil has been nondetectable I However, the benzene concentration in 1990 was 0 068 ppm at 25 feet, and in 1994 it was 0 008 ppm at 251/2 and 31 feet The analytical results indicate that gasoline constituents in the soil have been reduced over tune through natural biodegradation to levels below current laboratory detection limits This progression of natural biodegradation was supported by the biophysical laboratory results of soil samples collected at the site I The mass/volume of gasoline remaining in the soil cannot be calculated since the gasoline concentrations in soil from SBI through SB3 were nondetectable However, approximate extent of soil impaction and the mass of benzene were calculated for two separate dates Through August 1992, an estimated 2200 cubic yards of soil was impacted by approximately 0 36 pounds (0 05 gallons) of benzene By August 1994, an estimated 370 cubic yards of soil was impacted by approximately 0 013 pounds (0 0018 gallons) of benzene, a decrease of approximately 96 % _ from August 1992 The estimated extent of soil impaction and mass calculations for August 1992 and August 1994 are included in Attachment E i Analytical results of groundwater samples collected from wells MW1 through MW3 on November 10, 1995 and December 12, 1995 confirmed that groundwater beneath the site has Inot been impacted by petroleum hydrocarbons SUMMARY AND CONCLUSIONS IGroundwater I o No impact to groundwater was identified during the hydropunch sampling investigation conducted in 1994 I o No impact to groundwater was indentified in monitoring wells MW1 through MW3 installed during the current phase of investigation groundzelnorm 6sumrepor 95 6