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13 November 1997 ., AGE-NC Project No 95-0128 Page 2 of 5 At the time of the original Corrective Action Plan (CAP)prepared by Upgradient Environmental, Inc , dated 16 October 1994, ground water was at approximately 50 feet below surface grade (bsg) and was impinging on soil containing approximately 20 milligrams per kilogram (mg/kg) TPH-g in the area of VW1, in which the Vertical extent of the hydrocarbon-impacted soil has been best documented Up to December 1994,when the ground water elevation started to rise above the tops of the screened intervals in monitoring wells MW1, MW2 and MW3, the highest concentration of total petroleum hydrocarbons quantified as gasoline (TPH-g) in ground water had been 540 micrograms per liter (gg/1), and often was less than the detectable concentration for the analytical method used (ND) Monitoring wells MW 1, MW2 and MW3 became drowned wells, that is, ground water rose above their screened intervals, in March 1994 Since drowning, THP-g has not been detected in the wells Figure 4 -Maximum Dissolved TPH-g Concentrations (January 1994 through March 1994) shows the estimated maximum extent and concentrations of dissolved TPH-g prior to the drowning of monitoring wells MW1, MW2 and MW3 and encounteaing the more intensely hydrocarbon- impacted soil Sampling of vapor extraction well VW1 began 7n March 1995, at which time ground water was approximately 44 feet bsg, and was impacting soil containing approximately 439 mg/kg rPH-g Ground water sampled from the well initially contained 230,000 pg/l I PH-g The high concentrations of TPH-g in samples collected from VW 1 continued until September 1996, when 0 5 feet of free product was encountered in the well At this point in time, ground water had risen to approximately 34 feet bsg, encountering sand and gravel containing as much as 65 mg/kg TPH-g A Iow concentration of hydrocarbons in coarse soil is not surprising as coarse soil has much less surface area than finer grained soil to which hydrocarbons can adhere Free product was bailed weekly from the well until Januaiy 1997, by which time approximately 15 gallons of free pioduct had been removed Since resumption of ground water sampling of VW1 in February 1997, following removal of free product, TPH-g concentrations had declined, ranging between 23,000 ALg/l and 130,000 ,ug/1, and TPH quantified as diesel (TPH-d) concentrations have generally increased Also since resumption of ground water sampling in V W 1, ground water elevation has risen to approximately 31 feet bsg and fallen back to 36 feet bsg At 31 feet bsg, ground water was encountering soil containing as much as 848 mg/kg TPI I-g Figure 5 - Curi ent Dissolved TPH-g Concentrations !October 19971 shows the current distribution of dissolved TPH-g in ground water_having come into intimate c ontact with the more intensely hydrocarbon-impacted soil Methyl tert-butyl ether(MTBE) has been detected in samples from VW 1 at concenti ations ranging from 590 ug/l to 36,000 µg/l since the analysis was initiated in March 1996 MTBE has been detected in all wells on the site with the exception of MW1 and MW3, two of the deeply drowned . wells Table 1 shows all analyses of the ground water samples collected during monitoring events conducted by AGE and the depths to ground water for each well during each monitoring event