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Ms. Katie Hower • - 3 - • 8 March 1999 <br /> 5. Although crude oil at the site has been described as being very viscous, the occasional detection of <br /> TPHd in MW-6, the detection of pyrene in MW-7, and the presence of free phase product in MW-2 <br /> show that at some point crude oil becomes soluble and impacts water quality. Therefore, the <br /> presence of crude oil in the vadose zone and particularly in the saturated zone poses a threat to <br /> water quality and should be remediated <br /> Geomatrix states that the presence of separate phase crude oil does not indicate solubility. <br /> Nonetheless, the presence of separate phase product or heavy petroleum hydrocarbons constitutes a <br /> degradation of water quality and should be addressed. Chevron should remove any separate phase <br /> product that accumulates in MW-2. <br /> Geomatrix states that detections of heavy petroleum hydrocarbons in water(such as that identified <br /> in a TPHd analysis) are likely due to either petroleum entrained on soil particles or polar non- <br /> petroleum hydrocarbons (biodegradation products or naturally occurring compounds). Geomatrix <br /> should clarify the reference to "heavy petroleum hydrocarbons" because it is confusing to call <br /> something "heavy petroleum hydrocarbons" and then say that the source is polar non-petroleum <br /> hydrocarbons. If the source of the "heavy petroleum hydrocarbons" in groundwater is petroleum <br /> hydrocarbon entrained on soil particles, then the"heavy petroleum hydrocarbons" should be <br /> remediated. If the source of"heavy petroleum hydrocarbons" is degradation of petroleum <br /> hydrocarbons, then the "heavy petroleum hydrocarbons" should be treated like any other <br /> degradation by-product, i.e., their impact to water quality should be assessed. The groundwater at <br /> the site must be remediated to background water quality and the applicable water quality objective <br /> that is technologically and economically feasible. If the source of the "heavy petroleum <br /> hydrocarbons" is biogenic, then the average background concentration should be deducted from the <br /> TPHd concentration in each well. <br /> By 1 April 1999, please address the above comments and submit a work plan to define the contaminant <br /> mass in the soil and groundwater. If you have any questions, you may call me at (916) 255-3081. <br /> -`" <br /> PHILIP ISORENA <br /> Associate Engineer <br /> PSI:psi <br /> cc: San Joaquin County Public Health Services, Stockton <br /> Mr. James Simpson, Stanislaus County Department of Environmental Resources, Modesto <br /> Ms. Dawn Zemo, Geomatrix Consultants, San Francisco <br />