SITE INFORMATION AND CORRESPONDENCE

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� V 204 East Lodi Page 2 The approximate rate of oxygen introduction through the air sparge wells was 12 cubic feet per minute. A decrease of petroleum hydrocarbon contamination in the monitoring wells was observed; however, it is difficult to determine whether the reduction was due to the introduction of oxygen or to an increase of the depth to groundwater. As PHSIEHD has indicated previously, depth to water measurements should be included on the same table that analytical results are summarized, so that trends in concentration changes over time may be easily observed. Also, a typical methodology used to determine the radius of influence of air sparging systems, is to monitor dissolved oxygen concentrations, since it is dissolved oxygen that enhances the biological degradation of petroleum hydrocarbons. Work Plan The work plan proposed the drilling and sampling of at least one soil boring to evaluate the progress of soil remediation. If significant soil contamination continues to be evidenced in the first proposed soil boring, an additional boring will not be attempted. PHSIEHD recommends that the possibility of converting the proposed soil boring into a vapor extraction well be evaluated, should the contamination observed through field screening suggest that an additional vapor extraction well is warranted to increase the system's effectiveness. If significant contamination is not observed in the first boring, closest to the vapor extraction system, an additional boring will be drilled and sampled to evaluate the remediation system's effectiveness farther from the vapor extraction well. PHSIEHD concurs that periodic evaluation of a remediation system's effectiveness can reduce costs associated with unnecessary remediation. As PHSIEHD has indicated previously, a limited investigation will be necessary within the building, since the former tank was located within the building. As that area of the building is used for storage and has a relatively high ceiling, it should not pose an insurmountable problem to confirm the remediation system's effectiveness in this area. PHSIEHD has provided verbal approval to implement the work plan, pending the resolution of permitting and access agreement issues. Required Remediation PHSIEHD has determined that active soil and groundwater remediation is required at this site. Significant soil contamination remains in-place continuing to degrade groundwater quality. Unique site features and the levels of groundwater contamination evidenced require that active remediation proceed, until information becomes available to demonstrate that remedial efforts have sufficiently remediated soil and groundwater contamination.