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'00 Pine Street ^Cth Floor San Franc-.sco. CA •=-111 1 ,1151434-9400 • Fax r415� 434-1365 GEOMATRIX 8 March 1995 Project C2677E Mr. Don O. Culbertson Chevron Pipe Line Company P.O. Box 5059 RE:CEIV San Ramon, California 94583 APR 10 1995 Subject: TPH Detections in Groundwater Samples: ENVIRONMOTAL HEALTH What Do They Mean? PERMIT/SERVICES Dividend Property Tracy, California Dear Mr. Culbertson: Pursuant to our discussion during the meeting among representatives of RWQCB, Chevron Pipe Line Company, and Geomatrix Consultants, Inc. (Geomatrix), on 23 September 1994, we have developed this technical memorandum on the topic of Total Petroleum Hydrocarbon (TPH) detections in groundwater samples. A few groundwater samples recently collected at the Dividend property had detections of TPH as crude oil when analyzed by EPA Method 8015. Our review of the EPA Method 8015 chromatograms suggested that the samples contained non-soluble petroleum fractions and therefore the quantitation did not accurately represent concentrations of dissolved petroleum constituents. Published research indicates that non-dissolved constituents are not generally mobile in groundwater at natural hydraulic gradients. The mobility of non-dissolved constituents at the Dividend property would be further restricted by the low hydraulic conductivity of the fine-grained sediments at the site. During the meeting, RWQCB staff were unclear about the mechanism(s) by which non- soluble petroleum hydrocarbons could end up in a water sample and, as a result, how the reported TPH concentration would not be representative of dissolved (therefore mobile) constituents. This is an important technical question, and the answer requires an understanding of the chemical nature of petroleum hydrocarbon compounds and the analytical methods used for measurement of petroleum constituents. This letter provides a summary of pertinent information about the chemical structure of petroleum hydrocarbon compounds (PHCs), an evaluation of the water-soluble fraction (WSF) of fresh PHCs, keys to determination of the presence of non-WSF in water samples, a discussion of how non-WSF can be included in a water sample, and recommendations for groundwater sampling and analysis at the Dividend property. The material presented herein is based on published work and in-house unpublished work. We have cited references where appropriate and included copies of chromatograms for your review and use. Geornatrix Consultants, Inc. Enmineers.heolnm-:!s .vin t nvirnnmentai Scientist,