ARCHIVED REPORTS XR0001132 - Laserfiche WebLink

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CID . San Joaquin County Public Health Services May 26, 1995 (9347-1246) �-- .��7-1 Remediation Status During the 1989 tank replacement, approximately 1,058 cubic yards of soil containing petroleum hydrocarbons were excavated from around the former steel tank locations and disposed of off site The bulk of petroleum hydrocarbons In soil and separate phase hydrocarbons encountered during subsurface investigations and well monitoring at the site were beneath, and In the vicinity of, the former steel tank basin From December 1989 to April 1990, Delta Environmental Consultants, Inc (Delta), personnel hand-bailed separate phase hydrocarbons from well MW-2 on a weekly basis According to information contained in hugro's project files, Delta used electrically powered pumps to remove separate phase hydrocarbons from wells MW-2, MW-4 and MW-7 at various Intervals from April 13, 1990 to at least August 1991 The file information indicates at least 200 gallons of separate phase hydrocarbons were removed by Delta during pumping and hand bailing At SVE startup in September 1992, the total volatile hydrocarbon concentration quantified by laboratory analysis in the Influent airstream was 9,900 parts-per-million volume (ppmv) This concentration equates to an initial recovery of approximately 407 pounds, or 68 gallons per day (gasoline by weight = b lbs/gallon) Separate-phase hydrocarbons were present in . venting/monitoring wells MW-2 and MW-4 at the time of SVE startup By September 1993 when pulsing of the vent system began, the influent hydrocarbon concentrations had dropped to about 200 ppmv Separate phase hydrocarbons have not been present in any of the wells since May 1993 The average concentrations of dissolved hydrocarbon compounds have also decreased in ground water during operation of the SVE system In September 1992, the ratio of benzene, toluene, ethylbenzene, and total xylenes (BTEX) to total hydrocarbon concentrations in the Influent airstream was approximately 27%, based on laboratory analysis By September 1993, this ratio dropped to approximately 10% Laboratory analysis of the influent air sample collected on March 27, 1995, indicates this ratio 1s currently about 7%, at a total Influent hydrocarbon mass concentration of 45 ppmv The March 1995 extraction rate corresponding to the soil vapor hydrocarbon concentration of 45 ppmv is less than one half of l% of the September 1992 rate of extraction The analytical data indicates the SVE system has effectively removed the bulk of hydrocarbons that can be remediated by vapor extraction Table I shows the hydrocarbon recovery data by the SVE system Table 2 shows historic air sampling analytical results The graphs shown on Figures 3, 4, 5, and b illustrate the trend of Influent hydrocarbon concentrations and extraction rates decreasing toward the asymptote Natural gas has been used as a supplemental fuel for operation of the oxidizer As . hydrocarbon concentrations in the influent soil vapor decrease, the consumption of natural gas by the oxidizer Increases At startup in September 1992, the soil vapor hydrocarbon concentrations were approximately 9,900 ppmv, with virtually no natural gas consumption In 9347124611 r 3 -