WORK PLANS_FILE 2 - Laserfiche WebLink

Home Browse Search

Ms. Margaret Lagorio Page 4 of 8 FEASIBILITY OF ADDITIONAL SOIL VAPOR EXTRACTION In the letter dated July 20 PHS/EHD directed that the vapor extraction system remain at the site and the feasibility of additional vapor extraction in the area of confirmation boring CB3 and old soil boring TB5 be investigated. In our May 18, 2001 Confirmation Boring and Groundwater Monitoring Well Installation Report we concluded that soil vapor extraction had succeeded in remediating vadose soil contamination to the point at which further operation of the system was not justifiable. The system has removed approximately 12,700 pounds of hydrocarbons from the subsurface. Vadose soil samples collected from within the former area of impact were all non-detect for TPHg and benzene in confirmation borings CB 1, CB2 and CB4. Only in confirmation boring CB3 was any residual vadose soil impact identified. In those samples, benzene was not detected and the chromatogram indicated that the lighter, more volatile gasoline components were absent. The samples were collected from a low-permeability silty clay. We reiterate that the hydrocarbons remaining in the vicinity of CB3 do not contain appreciable levels of toxic compounds and are not amenable to vapor extraction. The laboratory narrative and chromatograms 'for the samples in question are included in Attachment A. The locations of the confirmation borings are shown on Figure 6. Vadose soil contamination was identified in boring TB5 in 1989. However, although elevated levels of TPHg were present between the depths of 5 and 25 feet the highest benzene concentration was only 0.008 ppm and in the sample with the highest TPHg concentration benzene was not detected. The soil contamination in boring TB5 had a very low toxic component. Boring T135 was apparently located at the edge of the area of soil contamination or may have sampled a very localized impact from dispensers. Boring TB5 was offset by the following borings: TB4: Located about 10 feet southwest of TB5. Soil samples between the depths of 5 and 20 feet were non-detect for TPHg and BTEX. MWl: Located about 5 feet northwest of TB5. No odors or soil discoloration was observed when drilling. One sample was analyzed and was non-detect for TPHg and BTEX. SB22: Located about 7 feet northeast of T135. The highest concentration of TPHg was 17 ppm with 0.160 ppm benzene at 15 ft. SB21 (MW6): Located about 9 feet south of TB5. Samples from 10, 20 and 30 feet were all non-detect for TPHg. Benzene was present at 30 feet at 0.004 ppm. roek\closure\workplao4esponsa.doe