7.0 RECOMMENDATIONS

Since concentrations of soil and groundwater contaminants were identified that exceed CDPHE regulatory action levels; it appears that remedial activities should he performed to prevent further contaminant migration. The horizontal extent of contamination appears to be restricted to a relatively small area; therefore, removal of contaminated soils at the apparent source area adjacent to borings B-I/B-7 would likely provide mitigation measures that would inhibit further contaminate migration. Wells MW-l/MW-2 could serve as points of compliance for future groundwater monitoring to determine if remedial activities were successful.

Groundwater is approximately 3 feet bgs, so excavation adjacent to the maintenance building could easily result in sloughing that would result in instability of the building pad. Removal of the contaminated soil by excavation makes this alternative difficult, if not impossible, without damaging the building. Redevelopment plans for the airport likely include demolition of the maintenance building. However, no definite time frame was provided for implementing the redevelopment plans.

If CDPHE approves, we recommend waiting to perform soil remediation until the building is removed. in the interim, semi-annual groundwater monitoring could be performed at monitoring wells MW-l, MW-3, and MW-5 to provide information regarding migration of VOCs. Monitoring well MW-i would serve as the point of compliance. Since the groundwater gradient at the site is extremely flat, groundwater levels would also be measured to monitor groundwater flow direction for potential changes.

When the building is removed, contaminated soils could he excavated and removed from the site. Applicable groundwater remediation systems could then be evaluated as additional subsurface information is obtained during soil excavation. Potential groundwater remediation may include air sparging, ozone sparging, introduction of oxygenated compounds, and pump and treat technology.