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Former Lyoth Loading Station - 3 - 8 October 1998 Chevron Pipe Line, San Joaquin Co. Comparison of Site Data with Appendix B of Tri-Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites (Criteria for Low Risk Vadose Zone/Low Risk Groundwater Designation) 1. Criteria for Low Risk Vadose Zone Designation a. Demonstrate that only the vadose zone has been affected. The site does not meet this criterion because the soil contamination goes below the water table and the contamination in the vadose zone has not been remediated. b. The release or leak has been stopped and sources of hydrocarbons in the vadose zone have been removed or permanently contained. The release has been stopped but the sources of contamination in the vadose zone have not been removed or permanently contained. c. Petroleum hydrocarbons remaining in the vadose zone do not impact or threaten waters of the State. The presence of separate phase product (which is being removed quarterly) in MW-2, occasional detection of TPHd, and the one-time detection of pyrene in MW-7 show that the waters of the State are being impacted. TPHd was detected in MW-6 in April 1997, October 1997, and January 1998 at 140 ppb, 85 ppb, and 60 ppb, respectively. Only 140 ppb exceeds the Board's water quality objective of 100 ppb for TPHd. However, Chevron uses silica gel cleanup in the analysis. TPHd testing should follow the same procedure required for PAHs. The decision as to whether the site meets this Criterion C should be made after confirmation of the TPHd levels at the site. d. No significant risk to human health and safety exists or is anticipated following remediation. This criterion does not apply because no remediation is being proposed. 2. Criteria for Low Risk Groundwater Designation a. Contaminants remaining in the vadose zone must not reverse or threaten to reverse the mass reduction rate of groundwater pollutants. See comments in Lc above. b. Separate phase product has been removed to the extent possible. As stated in Lc above, separate phase product is being removed every quarter, but more should be done to facilitate separate phase product removal, such as removing contaminated soils. Contaminated soil removal to levels which do not pose a water quality threat also should eliminate occasional detections of TPHd in groundwater. c. No existing water supply wells, deeper aquifers, surface waters or other receptors are threatened by pollutants remaining in the aquifer. The vertical extent of groundwater contamination has not been defined. Consequently,the threat to the next groundwater body has not been determined.