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06 December 1995 <br /> AGE-NC Project No. 95-0100 <br /> Page 5 of 13 <br /> 4.3. COLLECTION AND ANALYSIS OF SOIL VAPOR SAMPLES <br /> A total of 4 vapor samples were collected at two-hour intervals from the inlet of the extraction well <br /> for measurement of hydrocarbon concentrations in the extracted vapor. The samples were collected <br /> _ in Tedlar bags using an air pump connected to the vapor inlet. The samples were transported under <br /> chain-of-custody to McCampbell Analytical Inc. (MAI) in Pacheco, California. Each sample was <br /> analyzed within 72 hours for TPH-g and BTE&X in accordance with EPA methods 8015m and 8020, <br /> respectively. <br /> 4.4. RESULTS OF VAPOR EXTRACTION TEST <br /> The in-.situ soil vapor extraction (SVE) pilot test was performed at the site to determine the suitability <br /> of the site for the SVE method of remediation. The in-situ SVE test performed at the site indicted <br /> that the site would be amenable to SVE. <br /> During most of the test, vacuum readings at the extraction well (VE I) ranged between 1.4 and 2.35 <br /> inches of water. Vacuum readings at VE2, located 15 feet southeast from VE 1, were 0.07 inches of <br /> water initially, as measured from the lower screen interval. After four hours the vacuum in VE2 <br /> increased to 0.085 inches. After 5.5 hours, vacuum readings in the upper and lower intervals were <br /> 0.05 and 0.07 inches of water, respectively. At the end of the test (8.0 hours), the influence measured <br /> in the upper and lower screened intervals was 0.065 and 0.08 inches of water, respectively. <br /> The measured vacuum at VE2 was plotted versus distance from the extraction point (VE 1) on a semi- <br /> logarithmic scale (Figure 4). The theoretical radius of influence of the extraction well at a specific <br /> vapor pressure can be read from the graph. Typically, the value of 0.1-inch of vacuum represents the <br /> minimum pressure to mobilize hydrocarbons. A theoretical radius of influence of approximately 15 <br /> feet could be derived from the graphed data. In application, an effective radius of influence of <br /> approximately 10 feet is more likely to occur. <br /> — A relatively low flow rate was achieved during the pilot test, due to the poor performance of the IC <br /> engine. The engine was limited due to low levels of free oxygen in the soil and the relatively high <br /> concentrations of extracted carbon dioxide. Therefore, a great volume of supplemental fuel (propane) <br /> was required to operate the unit at an optimum rate. <br /> 4.5. ANALYTICAL RESULTS OF SOIL VAPOR SAMPLES <br /> Four soil vapor samples were submitted for analysis. TPH-g was detected at concentrations ranging <br /> from 19,000 ppb to 24,000 ppb. BTE&X were detected in the vapor samples at concentrations <br /> ranging from 220 ppb (ethylbenzene, VS 1) to 2,600 ppb (toluene, VS3). Analytical results of the <br />