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W Remedial Action Plan Addendum January 14, 1993 Southland Store No. 20304, 455 Grant Line Rd., Tracy, CA 7 and 470 parts per billion (ppb), respectively. These concentrations are an order of magnitude below the average concentrations reported for MWA and MW-8 during the March to September 1992 sampling period. Assuming an average pumping TPH-G concentration of 500 ppb, that carbon has a 5 percent adsorption (by weight) capacity for petroleum hydrocarbons, and a Horn► rate of 40 gpm, the saturation time of one 1,0004b GAC unit is calculated to be approximately 200 days. A �- conservative estimate of potentially extractable TPH-G mass from the dissolved-phase is 50 lbs, because the two proposed GAC units have a combined TPH-G adsorption capacity of approximately 100 lbs. Assuming source removal is achieved in conjunction with groundwater extraction, the original carbon in the two GAC units has sufficlent capacity to treat the extracted groundwater to permissible limits for the duration of the project. V The effluent wastewater from the GAC units will discharge under the force of gravity to a downgradient storm main tie-in located approximately 150 feet north of the site on Buthmann Avenue. The extraction/treatment system module will be constructed off site, then delivered and +� installed adjacent to the west end of the existing site structure. The system will be designed to shut down in the event of a high-pressure condition within the treatment unit or a low water level in the groundwater extraction well. The treatment system's conditional status will be continuously Nwe monitored by a remote telemonitoring system linked to the Groundwater Technology Concord office. Figure 6 illustrates the proposed extraction/treatment system layout relative to existing site landmarks. 3.2 System Permits +.• Before the construction/installation phase can proceed, permits must be obtained from the appropriate local and regional authorities. A description of the permit requirements is presented i below: Discharge Permits. Permits to discharge treated groundwater to both surface waters and to land will be obtained from the RWQCB-CV under the authority of the General Order program. Because the Phase I technical approach does not involve generation of off-gas, permits from the San Joaquin Valley Air Pollution Control District (SJVAPCD) will not be required at this time. The SJVAPCD issued an Authority-to-Construct (ATC) to Southland for +- this site that does not expire until August 4, 1994. If the Phase II remedial strategy requires A3263AI-SLL GROUNDWATER EILD TECHNOLOGY,INC. 4