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REMEDIATION TESTING AND DESIGN March 29 , 1993 To determine the general vapor flaw chai.acteri,tics in various wells and at a number of vacuum levels . step testarig was performed in all vacuum e_.traction wells and in rionit_r well 9W-3 Step test vacuums ranged from 5 to 22 inches of mercury ( "Hg i with flow rates rai.gin- from 10 to 55 scfm ' At the request of Ultramar, the vapor probes were left in the ground and will be sealed at the surface and plumbed into the treatment system manifold This modification in the scope of work required a formal workplan modification/proposal submittal to PHS/EHD for approval A copy of this submission is contained in Appendix A RESULTS Soil Gas Screening ` Results of the LSCS are presented in Table 1 FID yield screening at all probe locations , with the exception of P-7 and P-9 , showed no 1 detectable hydrocarbons The TVH concentration measured in P-7 was the highest of the probes at 1 , 200 ppmv, and the TVH at P-9 was 140 ppmv Both of these probes are located in the former UST area. P-7 ' within the backfilled tangy: pit and, P-9 located below the former pit Generally, the probes exhibited very poor vapor flow characteristics , requiring a vacuum of 9 to 10 inches of mercury for a flow rate of 10 cubic feet per hour ( cfh) Probes P-7 and P-6 (both completed within the backfilled UST pit) exhibited favorable vapor flow of 20 cfh at a vacuum of less than 1 inch of mercury Soil gas screening of the vacuum extraction and monitor wells generally showed high TVH concentrationLz ( see Table 1 ) The highest TVH readings were recorded in the "b" zone vacuum extraction wells . Laboratory analyses of the soil gas samples collected in airbags showed significant levels of TPHg and BTEX from the wells tasted. Table 2 is a summary of the laboratory analyses performed for soil gasses from selected wells The complete laboratory report ( including chromatograms ) is included in Appendix B The results of the air bag analyses generally correspond well with the TVH readings except for monitor well MW-3 . , The "a" zone wells contained elevated levels of BTEX and TPHg Figure 3 shows the distribution of TPHg in soil gas from the "a" zone . The highest levels of BTEX and TPHg, were noted in the "b" zone wells Figure 4 shows the distribution of TPHg in soil gas from the "b" zone Soil gas samples from VW-2a and VW-2b were collected for laboratory analysis following the 1-hour flow tests r conducted in each of those two wells This analysis ( see Table 2) showed a slight decrease from BTEX and TPHg levels recorded prior to flow testing t - Vacuum Extraction Testing Table 3 contains VEFT field data for extraction from well VW-2a. The results of this test show that vacuum ,e:traction works well in the "a" zone and that extraction from the "a" zone also produce's vapor flow in the "b" zone , in the zone near the water table and within the 3