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C A M B R I A Ms. Lori Duncan September 9, 2005 Remedial Alternatives Discussion and Approach The remediation objectives proposed in this CAP are based on a combination of the above criteria. The CAP objectives are to implement the most cost-effective remediation approach to protect human health, groundwater quality, and other sensitive receptors. Given the specific site conditions,the specific CAP objectives are to: • Remove the most heavily impacted hydrocarbons in the identified source areas; • Mitigate further hydrocarbon migration in soil and groundwater; • Continue the groundwater monitoring program to monitor water quality;and • Establish a contingency plan to expedite or enhance remediation,if necessary.. © Remediation alternatives reviewed in this CAP address these four objectives. Once hydrocarbon concentrations in soil and groundwater are reduced, natural attenuation processes may remediate any residual hydrocarbons and eventually restore the impacted area(s) to background concentrations. Cambria evaluated several remedial alternatives to achieve site remedial objectives. Remedial alternatives were selected to address the TPHg and BTEX components of fuel hydrocarbons. Past and recent subsurface investigation activities and groundwater monitoring indicate that elevated TPHg and BTEX levels are present in unsaturated and saturated soils and groundwater. DPE pilot testing confirmed the presence of these compounds in soils. The remedial technologies selected for evaluation include monitored natural attenuation (MNA), in-situ chemical oxidation, SVE with air sparging (AS), and DPE. Each of these alternatives is discussed below and evaluated on the basis of technical feasibility and cost effectiveness. Soil analytical data indicate that elevated TPHg and BTEX levels are present in vadose zone, capillary fringe, and saturated soils. TPHg and BTEX detections in saturated soils sample may be due to impacted groundwater. However, because the groundwater table depth has risen significantly in recent years, a significant portion of the source material is located in the saturated zone. MNA Natural attenuation includes allowing hydrocarbons to biodegrade naturally and implementing a long-term groundwater monitoring plan. Decreasing concentration trends are the primary indicators of natural attenuation of hydrocarbons in groundwater. Secondary indicators such as dissolved oxygen (DO) concentrations, oxidation-reduction potential, alkalinity, and nitrate, sulfate, and ferrous iron concentrations are also used to evaluate the existence of and the potential for natural attenuation. 12