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r s • lf.c S o Concentrations of hydrocarbon compounds were detected in the ti groundwater sample collected from well MW--2 with minor concentrations detected in well MW-3. However, for minor concentrations, benzene was detected in excess othose f the DOHS action level. is o While cleanup levels are site-specific and can vary, the typical level of 1.00 mg/kg of TPH can be assumed to be the applicable soil cleanup level for the site based on informa- tion obtained from the San Joaquin Local Health District. 6.1 Soil Remediation it As hydrocarbon compounds within the soil appear to be centralized around borehole #31 it is recommended that a :,yapped excavation be conducted at the site with the vertical limit being the i.., saturated zone (approximately 301) . The initialstep of the excavation should extend radially 20, from the location of Baa borehole #3 (Figure 6) . The initial excavation quantity will equal approximately 350 cu. yards of soil which would require off-site disposal. In addition, due to the depth of this excava- tion, the excavated side walls will be laid back or shored to conform with applicable OSHA re lations. G•f excavation, the sidewalls should be sampled and analyzed nfoof the r TPH and BTX&E compounds. If the samples hydrocarbon compound concentrations exceed the required cleanup level (1,00 Jg/Kg TPH) , ;. additional excavation in the direction of the remaining "high" chemical concentrations should be conducted in 101 increments. Sidewall sampling and excavation should continue until the ! sidewall TPH concentrations are below the cleanup level. Should the stepped excavation extend to the boreholes which exhibited non-detectable hydrocarbon concentrations, the maximum quantity ` of excavation would be approximately 3,500 cubic yards (Fi ure 6) • Due to the chemical concentrations encountered, gthe protection. excavation will require proper excavation personnel The drummed borehole cuttings from boreholes #3 and currently on-site should be disposed of with the excavatednsoils. The remaining drummed cuttings o not re hazardous material. quire disposal as a .,, While other remedial alternatives such as in-situ volitalization, in-situ biodegradation and soil leaching were examined for the site, the limited extent of the chemical presesu removal and disposal is the most cost effective nce alternatives Additionally, due to the building schedule planned for the site, excavation is the most appropriate remedial measure due to the short time required for the implementation. .,.: 6.2 Groundwater Remediation Regarding the hydrocarbon presence in the groundwater, several factors such as the economic feasibility of groundwater treatment, beneficial aquifer uses, aquifer flow and compound threshold limits were assessed. """ _ 13 -