ARCHIVED REPORTS_2003 FEASABILITY STUDY REPORT AND SITE ASSESSMENT WORK PLAN

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S E C O R • 2003 Feasibility Study Report and Site Assessment Work Plan July 18, 2003 Page 18 biodegradation of off-site hydrocarbons. The groundwater oxygenation points would be installed along the northwest property line (near well MW-47A), continue around the northern-most property corner (near well MW-50B) and end along the northeast property line (near well MW-51A). Groundwater oxygenation points would also be installed along a section of the access road that separates the retention ponds from tanks #134 and#135. Groundwater oxygenation points would be approximately 25 feet deep and spaced every 15 on center along the access road, 20 feet on-center from well MW-47A to MW-19A, and 30 feet on center from MW-19A to MW-51 A. The remedial system will include approximately 67 groundwater oxygenation points. Each groundwater oxygenation point would be equipped with a flow gauge, butterfly valve and pressure gauge to control airflow and pressure. In-line auto-drains would also be installed at each groundwater oxygenation point to ensure condensate removal in the transfer pipe. The groundwater oxygenation points would be connected via above grade pipe to an on-site air compressor with a series of in-line filters to remove particulates. Airflow to each groundwater oxygenation point would range from 0.5 standard cubic feet per minute (SCFM) [minimum] to 2.0 SCFM (maximum). A process flow diagram of the groundwater oxygenation system is presented as Figure 10. Semi-annual off-site groundwater sampling would be conducted to evaluate the bio-degradation potential in the saturated zone and compliance with the WQOs. 7.0 EVALUATION OF REMEDIAL ALTERNATIVES • Each remedial alternative identified to meet the objectives of this feasibility study, is evaluated below. 7.1 Groundwater Barrier The proposed groundwater barrier should deter or prevent further off-site migration of hydrocarbons in the saturated zone. Therefore, the proposed groundwater barrier should act as a containment system around the terminal and protect off-site property and sensitive receptors (streams, creeks, rivers, production wells and private wells). This remedial alternative should also enhance the off-site degradation of hydrocarbons in the saturated zone and allow current hydrocarbon concentrations to degrade to levels near or consistent with the Basin Plan's WQOs. This outcome would be possible as the groundwater barrier prevents or deters the continued migration (or mass flux) of hydrocarbons from the terminal to off-site properties. Thus, existing off-site hydrocarbons could continue to degrade in either an anaerobic and/or aerobic environment without the continued mass flux of hydrocarbons originating from the terminal. This remedial alternative is considered to have long-term effects on the reduction of off-site hydrocarbon impacts. As long as the barrier remains in place, off-site properties and sensitive receptors should remain protected. A possible condition such as a dramatic drop in regional groundwater levels could prevent the groundwater barrier from protecting off-site properties and receptors. Groundwater levels would have to drop approximately 20 feet to prevent the groundwater barrier from functioning properly. In this situation, hydrocarbons could potentially migrate offsite. This remedial alternative is not considered to have short-term effects on the reduction of hydrocarbons in the subsurface. This remedial alternative is designed to reduce the mass flux of hydrocarbons from the terminal. Therefore, this is a long-term approach, which should contain on- I:\Chevron\1001621\REPORTS\2003\2003FS\FS 2003 revD.doc