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1 Gea[ogiraI Terluita Inc Page 13 Dual Phase Extraction Pilot Test Report Project No 723 2 November 12, 2004 preferential pathways This situation needs to be confirmed before committing to a full scale injection treatment technology ' S Applied Process Technologies Inc (APT) concluded that a pilot test needs to be performed to confirm injection radius of influences from short screened points rather than the 20 foot screen in MW-9 GTI concurs with this conclusion for the reasons outlined in ' Section 6 0 6 The high organic content of the soils means that much more oxidant will be necessary to treat the gasoline plume to overcome the scavenging effect of the soil matrix ' GTI makes the following recommendations ' 1 Perform a limited cone penetrometer testing (CPT) survey in the vicinity of the 41 contaminant plume, centered on MW-9, to confirm the site lithology between the five- f foot soil sampling intervals used in the past ' 2 Investigate the applicability of using fracture technology to enhance the low permeability conditions of the clay soils and if favorable, perform a pilot test to determine its ' effectiveness for holding the enhanced permeability over time 3 Perform a limited air sparging pressure test by attaching an air compressor to wells GP-1 through GP-3 and measuring resulting influences (if any) in the adjacent wells. This can effectively determine whether or not conductive sand/silt layers are present in the screened intervals of these wells (20 - 30 feet bgs) 4 Once the above information is obtained, perform a cost analysis of possible corrective ' actions including the following alternatives a Monitored natural attenuation b Excavation only c Combined ISCO technology with enhanced permeability formation fracturing d Limited excavation with in situ chemical oxidation This would involve using large diameter augers (up to 3 foot radius) to remove soil and then backfill the boreholes with a more conductive material (sand/gravel) This would physically remove a significant portion of the soil contamination and allow greater dispersion/contact area for oxidant injection ' e Conventional methods such as air sparging with soil vapor extraction or dual phase extraction, which would need a pilot test as well S Develop a corrective action plan (CAP) based on the above cost analysis and submit it to ' San Joaquin County for approval 6 The Regional Water Quality Control Board-Central Valley Region (RWQCB-CVR) has expressed concerns over oxidant injections into groundwater They have required laboratory analyses to determine if certain metals and other groundwater parameters are affected by the oxidant injection Well MW-9 should be sampled for RWQCB-CVR ' chemicals of concern and/or Table 1 parameters to determine if the pilot test has resulted in adverse impacts to groundwater quality 1