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GEOMgTgIX Ms. Katie Hower Chevron Pipe Line Company 19 March 1997 Page 4 interferences by a silica gel cleanup and/or lab filtering with a glass fiber(0.7µm) filter is required to assess dissolved petroleum in groundwater. Although both sources of interference are potentially present in both the purgeable and extractable TPH measurements, the conventional sample preparation for purgeable TPH analysis has not yet been modified to accommodate cleanup because of the potential for loss of volatiles. As discussed earlier, due to the age of Old Valley Pipeline releases, sites affected by residual crude oil/Bunker C have likely reached chemical equilibrium. The lack of BTEX and PNAs in groundwater samples tends to indicate that intrinsic biodegradation has been and continues to be active at these sites. Based on data from several Old Valley Pipeline sites, detections of TPH are expected to be relatively stable over the quarterly monitoring period. Calculations of biodegradation rates may not be applicable at these sites; the combination of the age of the - petroleum, limited plume migration, and low concentrations will be used to demonstrate that mass is decreasing and potential beneficial use of groundwater will be restored. In summary, the following analytical suite is recommended for Old Valley Pipeline sites: Reporting Measurements Methods Purpose Limits' • Soil Samples BTEX 8020 SURA 0.005 mg/kg PNAs 8310/8270 _ SURA various TEPH(Cg-C36) 8015M w/crude std SI 10 mg/kg Fingerprint GC-FID As necessary N/A • Groundwater Samples BTEX 8020 WQOs/RA 0.5 µg/l PNAs 8310/8270 WQOs/RA various TPPH (C4-Ct2) 8015 w/gasoline std WQOs 50 µg/1 TEPH (C1a-C24) 8015M w/diesel std WQOs 50 µg/l SI= site investigation RA=risk assessment WQO = water quality objective (Region 5) ' For undiluted samples with no matrix interferences. COMPARISON OF SITE DATA TO RWQCB "LOW RISK CRITERIA" Site data will be compared to the draft RWQCB "Low Risk Criteria" (RWQCB, 1996), or applicable updates, to determine an appropriate remedial strategy or request closure. Based on