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0 GEDMATRIX Ms. Katie Hower Chevron Pipe Line Company 19 March 1997 Page 3 5. The potential risk to human health posed by the affected soil and groundwater will be assessed under appropriate land use scenarios. 6. After four quarterly monitoring events, site data will be compared to RWQCB draft "Low Risk Criteria" (or applicable updates) for appropriate remedial strategy or site closure. The four quarterly monitoring events may incorporate historical data, if such data represent seasonal changes and water level fluctuations. ANALYTICAL SUITE As discussed earlier,the petroleum associated with the Old Valley Pipeline is a degraded crude oil and/or Bunker C fuel oil that is composed primarily of a broad range of medium-to high-boiling petroleum hydrocarbons. In some cases, it may be necessary to fingerprint the material present to further evaluate that it is Old Valley Pipeline product. The purpose of collecting samples for chemical analysis is to evaluate the potential threat to groundwater or risks to human health posed by the residual petroleum. Accordingly, the analytical suite will be focused on providing data appropriate for that purpose. The measurement of BTEX and PNAs is important for both protection of groundwater and human health. BTEX and the low molecular weight PNAs are the most water soluble petroleum components of concern and RWQCB has WQOs for these constituents. Benzene and the carcinogenic PNAs are the most toxic constituents potentially associated with the residual petroleum. Therefore, both soil and groundwater samples will be analyzed for BTEX and PNAs. The measurement of TPH as crude oil in soil by Method 8015M (GC-FID), or equivalent, at Old Valley Pipeline sites is useful as a site investigation tool,but it is not used in health risk assessments. The RWQCB WQOs include TPH measurements for gasoline and diesel products, but not crude oil/Bunker C, in groundwater. Although gasoline and diesel products are not present at these sites,the RWQCB has made it clear that these WQOs will be applied to "gasoline-range hydrocarbons"(C4 to C12) and"diesel-range hydrocarbons" (CIO to C14) found in site groundwater samples. Accordingly,TPH measurements incorporating these ranges will be performed on site groundwater samples. Because the WQOs are for gasoline and diesel products, the groundwater samples will be quantified against gasoline and diesel standards so that the comparison to WQOs is as direct as possible. Groundwater samples will not be analyzed for fractions greater than C„ or by Method 418.1. Using TPH as WQOs at Old Valley Pipeline sites is problematic because of positive interferences to the Method 8015M measurement. Based on recent research performed by Geomatrix (Zemo and Synowiec, 1995; Zemo, 1996; Foote et al., 1996), the TPH measurement of groundwater samples has been demonstrated to be positively interfered with by both soluble non-petroleum hydrocarbons resulting from intrinsic biodegradation and non-dissolved petroleum sorbed to particulates entrained within turbid samples. This research has shown that removal of these