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