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1 9110 Thomton road, Stockton, California April 27, 1994 The Southland Corporation Page 5 Mto a time constraint Concentration of total petroleum hydrocarbons in extracted air from these wells ' measured in the field ranged from zero to two percent LEL Data collected during the tests are summarized in Tables 3 and 4 ' Laboratory analysis of air samples collected during the tests indicated that the only BTEX component detected was xylenes and it was detected only In extracted air from wells MW-4, VP-2 and MW-12 at concentrations of 2, 0 5, and 0 6 micrograms per liter (Ng/L), respectively TPH-G ' was detected in samples collected from wells MW-1, MW-4, VP-3, VP-1, VP-2, MW-2, MW-8, MW-10, MW-12 and MW-5 at concentrations ranging from 18 to 74 Ng/L (fable 5) The laboratory analytical report is presented in Attachment 4 Radius of Capture ' The radius of capture defines the region within which vapor in the vadose zone can be induced to flow toward and into a vapor extraction well by the applied vacuum Radius of capture is typically ' estimated by obtaining vacuum measurements at the extraction well and at wells located at varying distances from the extraction well (MW-1), during the test Measured vacuum readings obtained from the test are then plotted against distance of the observation points from the test well An approximation of the radius of capture may be obtained by determining the distance at which an induced vacuum of 0 1 IW is observed due to the applied vacuum It is assumed that beyond this distance, the pressure gradient (driving force) is negligible and will not effectively transport vaporized ' hydrocarbons to the extraction well Vacuum at the extraction well (MW-1) and induced vacuum readings at observation wells MW-4, PW-3, MW-3, VP-4, 17A, VP-3, VP-2, MW-2, VP-1 and MW-5 were plotted against distance of the observation wells from the extraction well (Figure 10) Based on the assumption discussed above, the radius of capture of MW-1 at an applied vacuum of 20 5 IW is determined to be approximately 100 feet Hydrocarbon mass extraction rate ' Results of the test were used to estimate potential hydrocarbon mass extraction rate should the vapor extraction system be reactivated Flow rate obtained during the test using a 1 5-hp blower was approximately 83 cubic feet per minute (ft3/min) Based on this flow rate and the highest ' TPN-G concentration detected in the sample collected from VP-3, potential hydrocarbon mass extraction rate is estimated as follows ' 83 fe air x 74 gg TPH-G x 28 32 L x 1 lb x 1440 min = 0 5516s TPH-G min L air fe 454x 106 Pg day day GROUNDWATER TFCHNOLOCY