WORK PLANS - Laserfiche WebLink

Home Browse Search

• Ms. Penny Fottrell GEOMATRU< Chevron Environmental Management Company September 12, 2002 Page 2 Soil sample analytical results are summarized in Table 1 and presented on Figure 3. Total extract- able petroleum hydrocarbons quantified as crude oil (TPHc)were detected at concentrations varying from 480 to 4,500 milligrams per kilogram(mg/kg) in samples collected from borings GP 96, GP 97,GP 117, and GP 120,where affected soil was observed. Grey green staining and a slight odor was reported between 18.5 and 20 feet bgs (bottom of boring) in boring GP 173,how- ever, TPHc was not detected in the sample analyzed from this interval. TPHc was not detected in samples from the 11 remaining borings within Site 3, confirming the observations made during drilling. Samples from the four borings where TPHc had been detected(GP 96, GP 97, GP 117, and GP 120) also were analyzed for benzene,toluene, ethylbenzene, and xylenes (BTEX)and polynuclear aromatic hydrocarbons (PAHs). BTEX were not detected in any of the samples analyzed. However, several PAHs were detected in the samples at concentrations up to 0.7 mg/kg. Groundwater was encountered at depths ranging from 5.5 to 13.5 feet bgs in borings in this area. Grab groundwater samples were collected and analyzed from borings GP 96, GP 97, GP 117 (drilled within affected soil),and GP 138 (where no affected soil was observed) with a bailer from the open borehole. Grab groundwater samples were analyzed for BTEX, TPHg, TPHd, and PAHS; results are summarized in Table 2 and presented on Figure 4. No constituents were detected above laboratory reporting limits in the sample collected from GP 138. Separate phase petroleum hydrocarbons were observed in the groundwater samples collected from borings GP 96, GP 97, and GP 117. Total extractable petroleum hydrocarbons quantified as diesel(TPHd)were detected in samples from these borings at concentrations ranging from 20,000 to 310,000 micro- grams per liter(µg/1). TPHg were also detected in the samples collected from these borings at concentrations ranging from 43,000 µg/1 and 110,000µg/1. These TPH results are due to the presence of non-dissolved petroleum in the samples (either petroleum globules or petroleum adhered to soil particles) and do not represent dissolved concentrations. Benzene and toluene were detected in the sample collected from GP 117 at 2.0 and 1.2 µg/1,respectively. PAHs were detected in all three samples at concentrations up to 110 µg/l (fluorene). DATA NEEDS Existing data were reviewed and evaluated with respect to the Consistent Technical Approach (CTA)l that is typically applied at ChevronTexaco's historic pipeline sites. Based on this review, additional information is needed to better assess site conditions and evaluate potential risks to human health from petroleum.constituents present in soil and groundwater. The major compo- nents of the CTA and the data needed to address them are summarized below. • Delineation of the Vertical Extent ofAffected Soil-The vertical extent of petroleum hydro- carbons in soil was visually delineated at boring GP96 and GP 120. GP 96 was advanced to a Geomatrix Consultants,Inc.,2001,Draft Revised Technical Approach to Site Evaluation and Decision- Making,Old Valley Pipeline Sites Central Valley Region, October;and Geomatrix Consultants,Inc., 1997, Technical Approach to Site Evaluation and Decision-Making, Old Valley Pipeline Sites—Central Valley Region,March 19.