7301 EVERGREEN WAY EVERETT CHEVROLET 2017-03-01

Groundwater is present beneath the Site at depths ranging from less than 2 ft bgs to 18 ft bgs; therefore, dewatering may be necessary to facilitate excavation and backfilling. 4.3.5 Test Pit S-1: Based on the soil analytical data, EEC anticipates the approximate depth of the test pit will be 9 ft bgs. As soil is removed, subsurface conditions will be inspected for soil lithology and visual and/or olfactory evidence of impact (e.g. staining, odors, etc.). Grab soil samples will be collected every approximate 2 ft bgs and screened using a PID to the maximum depth of the test pit. If no evidence of impact is observed, one soil sample will be selected for laboratory analysis from terminus depth of the test pit (approximately 9 ft bgs). The purpose of the test pit is to confirm soil at this location is below MTCA Method A screening levels. If evidence of impact is observed during the completion of the test pit, impacted soils will be excavated. Confirmatory soil samples will be collected once the anticipated excavation vertical and lateral extents are achieved. A minimum of five confirmatory soil samples will be collected from the excavation. One confirmatory soil sample will be collected from the base of the excavation at approximately 9 ft bgs. One confirmatory soil sample will be collected from each sidewall of the excavation. Soil samples will be selected for laboratory analysis based on the highest PID reading or area exhibiting visual or olfactory evidence of impact. The purpose of this area excavation is to remove soil exceeding the MTCA Method A Cleanup Levels. Soil samples will be analyzed for TPHo using Method NWTPH-Dx in conjunction with the silica gel method. Soil samples will be submitted to an accredited laboratory with an expedited, three-day TAT. Upon completion of the sampling activities, the test pit and/or excavation will be backfilled with "clean" soil as detailed in Section 4.3.4. 4.4 Groundwater Monitoring Long-term compliance groundwater monitoring will be conducted on monitoring wells MW-1, MW-7, and MW-8 at a quarterly frequency for one year, analyzing for TPHo only. Based on the monitoring results, additional groundwater monitoring or well decommissioning activities may be recommended. Groundwater sampling will be conducted via the low flow sampling technique. Groundwater samples will be analyzed for TPHo using Method NWTPH-Dx in conjunction with the silica gel cleanup. The groundwater samples will be submitted to an accredited laboratory on a standard (two-week) TAT. 4.5 Remediation Waste Disposal Excavated materials will be staged either in on-Site roll-off bins pending waste characterization and subsequent off-Site disposal at a properly permitted facility or placed onto plastic sheeting for subsequent use as backfill material as described in Section 4.3. Materials placed into the on-Site roll-off bins should be free of moisture to the extent practical. Water generated during excavation activities (dewatering) will be placed in 55-gallon drums staged on Site pending waste characterization and subsequent off-Site disposal at a properly permitted facility. Depending on the volume of water encountered during excavation activities, a vacuum truck (vac truck) may be required. Decontamination and development water generated during groundwater sampling activities will be 017386-174(123) 9 THIS DOCUMENT IS PRINTED ON RECYCLED PAPER Encore Environmental Consortium,LLC