ARCHIVED REPORTS_REMEDIAL INVESTIGATION REPORT 2000

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07 February 2000 AGE-NC Project No. 95-0143 k. Page 3 of 5 surveyed casing elevation (Table 1). Between August and November 1999, ground water elevations decreased an average 1.03 feet. During the November 1999 monitoring event, ground water was within the screened interval of MW-16, MW-17. Ground water was from 0.2 feet to 6.6 feet above the screened interval in the remaining 7 monitoring wells. Ground water was within the screened intervals of each vapor well for free product determination. Measurable free product was not encountered at the site. The approximate hydraulic gradient was calculated to be 0.0008 ft/ft with a northeasterly flow direction on the subject property. Ground water elevation was higher in wells VW1 through VW4, indicating ground water mounding. Ground water elevation contours for the November 1999 monitoring event are illustrated in Figure 4. 3.2. ANALYTICAL RESULTS OF WATER SAMPLES During the November 1999 monitoring event,TPH-g was detected in samples collected from MW3, MW-6, MW-7 and MW-9 at concentrations of 210,000 parts per billion (ppb, reported as micrograms per liter), 1,400 ppb, 1,100 ppb and 14,000 ppb, respectively. BTEX compounds were detected in these wells at concentrations as high as 58,000 ppb (toluene in the sample from MW-3). Petroleum hydrocarbons were not detected in the samples collected from MW-10,MW-14,MW-15, MW-16 or MW-17. TBA was detected in the sample from MW-7 at a concentration of 6.4 ppb. Other oxygenates were not detected at the site during the November 1999 sampling event. Measurable free product was not encountered in any of the wells on the site. Analytical results of ground water samples collected during the November 1999 monitoring event are summarized on Table 2. Analytical results of historical ground water samples are summarized on Tables 3 and 4. The laboratory report (MAI Laboratory I. D. Nos. 25492-25500) and chain-of-custody forms are included in Appendix B. The concentration of dissolved oxygen in ground water remained generally stable at the site relative to previous monitoring events. Dissolved oxygen data are summarized on Table 5. 3.3. OPERATION OF SVE/IAS UNITS The SVE system operated at a capacity of approximately 278 cubic feet per minute (cfm) with a burner temperature maintained near 1450°F. The lower explosive limit (LEL) of the intake gas stream was approximately 5 to 6 percent. Field measurements of flow, vacuum and organic vapor concentration in the air stream from each extraction well were measured on a periodic basis. Due to the tight soil formation and limited screen interval, a vacuum of near 50 inches of water was maintained on wells VW 1,VW2,VW3 and VW5 Advanced GeoEnvironmental,Inc.