ARCHIVED REPORTS XR0009987 - Laserfiche WebLink

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Interim Remedial Excavation Wright will now implement as an interim remedial action a constrained and limited excavation as shown on Figure 1 This excavation work was more fully defined as Option-1 in the CAP and is now constrained and limited to the immediate area around MW-3 and MW-9 as follows Limited Soil Excavation and Removal Soil excavation would be performed in the areas shown on Figure 1 to remove the apparent residual contaminants interpreted located in the vicinity of MW-9, MW-3 (and the former UST pit) The contaminated soil would be excavated and clean soil segregated from contaminated soil As the site is too constrained to allow soil treatment on-site, the contaminant soil will be properly disposed off-site Laboratory data from site characterization work indicates the soil will be classified as a Class 11 waste acceptable at Forward landfill, a fully permitted Class 11 facility The targeted soil of interest is that in the capillary fringe at depths of about 9 to 14 feet depending upon location (see and reference CAP Geologic Cross Sections) These areas are located near the former UST pit and MW-3 and at MW-9 The area around MW-9 is interpreted to be confined to small sandy strata that are the apparent source of the residual contaminants Excavation Approach Soil would be removed to a depth of 10- to 12-feet (into the capillary fringe and uppermost aquifer strata) or as deep as practicable, then replaced with clean fill and/or overburden soil and compacted to an engineering specification There are three constraints to this approach, the presence of the trailers, the presence of possible flowing conditions in the upper portions of the aquifer, and the presence of numerous utilities Excavation would be advanced to the nearest safest point considering to these constraints and where and when possible the utilities would be relocated and or supported with beams across the excavation area, modified in the field as necessary The presence of possible flowing conditions indicates that an engineer and or competent person with experience in shoring would need to review the site and conditions and prepare shoring plan if needed It is anticipated that the excavation and soil hauling to disposal site with backfilling and compaction immediately following the excavation work, would take up to two weeks The site would need to be fenced with 24-hour security during the period where excavations are open Open excavations would be kept to a minimum backfilling at the close of each workday as work progressed thereby minimizing displacement and discomfort to affected of tenants Groundwater is anticipated to flood the bottom few feet of the excavations The excavations will be allowed to flood and water will be pumped out to remove contaminated water and allow"back flushing" of dissolved contaminants prior to backfill The water will be stored in surface tanks (rain for rent or baker type) for characterization and disposal The tanks will be staged at the rear of the site or most likely on property to the east Verification soil and groundwater sampling will be collected and analyzed for TPHG, BTEX and MTBE and oxygenates Soil samples will be collected at least every 20-foot interval along the capillary fringe to ascertain presence or absence of Page 3