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1 ' SRO Ms. Mary Meays r... September 29, 1995 (9347-3011) ` - - � 4�- _ The current VES (installed June 23,1993} and GWO system (installed on July 11, 1994) are composed of venting wells VEW-1 through VEW-4, and MW-3 (since July 1994) manifolded to a 5 horsepower regenerative vapor extraction blower unit and five oxygenation points (wells MW-1, MW-2, MW-3, RW-1, and RW-2)' connected to an oil-less, low-flow, air compressor, The VES and GWO system layout are shown on Figure 2. The VES unit uses granular activated carbon for emissions control (two 2000-pound carbon units in series). A conservative estimate of the radius of influence for the current VES is shown on Figure 2. The ground water recovery system (pumping 3 to 5 gallons per minute each from wells RW-1 and RW-2) commenced on March 2, 1993. Ground water recovery from RW-1 was discontinued on September 20, 1994, since no petroleum hydrocarbons were detected in the water samples collected from RW-1 during the previous,`three quarterly monitoring and sampling events (August 16, November 14, 1994 and February 22, 1995). ii F Remediation Status The initial start-up petroleum hydrocarbon extraction rate by the VES (based on air sampling conducted on April 29, 1992) was 192 pounds/day. However, based on the latest sampling event (July 3, 1995), the petroleum hydrocarbon extraction rate of the VES has dropped to 0.7 pounds per day with a corresponding decease in the efficiency of the VES. Historical (after June 23, 1993) petroleum hydrocarbon extraction rates and concentrations are graphed on Figures 3 and 4. Cumulative recovery of petroleum hydrocarbons are graphed on Figure 5. The VES operating data are summarized in Table 1. 110perating VES data have been documented in air discharge reports and other monitoring reports submitted each quarter since start up. s Laboratory analysis of the influent air sample collected on July 3, 1995, indicated a concentration of total petroleum hydrocarbons of 16 ppmv, with no benzene detected above the reported laboratory detection limits. The July 1995 extraction rate corresponding to the soil vapor hydrocarbon concentration of 16 ppmv is less than one-half of 1% of the April 29, 1992,rate of extraction. The analytical data indicates the `soil venting system has removed all of the hydrocarbons that can be practically and economically remediated by vapor extraction. The graphed concentrations shown on Figures 4 and 5-indicate that petroleum hydrocarbon extraction rates and cumulative extraction have achieved asymptotic limits. An estimated 5,772,087 gallons of ground water have been removed from the water- bearing zone beneath the site. The extracted ground water only contained an estimated 5.8 gallons of petroleum hydrocarbons. Therefore,11petroleurn hydrocarbons have only comprised 0.0001 percent of the total volume of the fluids:iremoved from the water-bearing zone beneath the site. The concentrations of dissolved petroleum hydrocarbons have decreased in the effluent water samples collected from the sewer discharge during operation of the'VES and ground water recovery system. The graphs shown on Figures 6 and 7 indicate that benzene and petroleum hydrocarbon extraction concentrations are near asymptotic limits. The historical petroleum hydrocarbon concentrations in ground water and sewer discharge samples are summarized in Table 2 and 3. 93473011.ARP 4= t: