2004-03-02_REVISION - M1978056 - Laserfiche WebLink

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Soil Remediation Report and Treatment plan February l2, 2004 Varra Companies, Inc. Page 2 of 8 Durham Pit 1 I7 Greeley, Colorado CGRS was retained by Varra to provide consulting and oversight of the remediation project. Field screening techniques such as monitoring volatile organic hydrocazbon concentrations with a photoionization detector (PID) and visual observations were employed by CGRS to determine the extent of excavation. When field- screening observations indicated that the hydrocazbon impacted soil had been removed, representative soil samples were obtained from the limits of the excavation, including the excavation sidewalk and bottom to document that adequate cleanup levels were achieved. The extent of excavation encompassed an azea of approximately 990 squaze feet and extended to a depth of approximately 9-feet below ground surface (bgs}. The deepest post excavation sampling point extended to a depth of approximately 12-feet bgs and no groundwater was encountered. The estimated in-place volume of soil removed from the excavation is approximately 330 cubic yards, which equates to approximately 4301oose yards when considering a bulking factor of 30 percent. The excavated soil was stockpiled on a concrete pad to prevent cross-contamination with the underlying soil. The stockpile is located south of the truck scales building in the central azea of the site pending treatment. A site map depicting the excavation azea is included as Figure 2. Photographs of the excavation are included in Attachment A. Soil Lithology Soil lithology in the excavation area consists of sand and gravel fill from the surface to approximately 2-feet below ground surface (bgs). Interbedded layers of clay and clayey-silt with some discontinuous sand lenses extend from approximately 2 to 9-feet bgs. Below 9-feet is coarse sand and gravel. Field screening observations indicate that the vertical migration of diesel was impeded by the fine clay and silt soils underlying the area of the release. Characteristics observed such as black organic discoloration corresponding with PID readings in excess of 100 parts per million (ppm) indicate petroleum hydrocarbons were retained in the clay and silt. Field screening of the underlying sand indicated the absence of organic vapors and no appazent discoloration below 9-feet bgs was observed. As excavation proceeded, the apparent discoloration of the soil provided a visual marker for determining the vertical and horizontal extent of contamination, -which was confirmed with the PID. The fuel depot excavation is located approximately 25-feet above the Tract A excavation dewatering trench. Based on the elevation to water in the trench, it is estimated that depth to groundwater is in excess of 15-feet below the base of the excavation. Sampling CGRS obtained sixteen confirmation soil samples from the outer limits of the excavation, including thirteen from the sidewalk at depths ranging from 4 to 8-feet bgs and three from the bottom at approximate depths of 10 to 12-feet. Soil sample locations aze depicted on Figure 3. Sidewall samples (Sample ID prefixes WW, EW, 1VW and SW) were spaced at distances ranging from approximately 12 to 20-feet along the perimeter of the excavation- The camnrle the and lg~tinne were_shneen to~e,[pond wi h coil hori one hat 3ppea*ed _ most impacted during excavation, exhibited evidence of possible residual contamination based on appearance, as well as random locations. The bottom sampling points (Sample IDs B-1, B-2 & B-3) generally correspond with the azea below the release location and below the zone where the most elevated PID concentrations were detected in the overlying soil. Five soil samples were also obtained from the soil stockpile (Sample IDs SP-1 through SP-5) to document hydrocazbon concentrations in the excavated soil. Soil samples were obtained using a hand auger as well as the excavator bucket. Soil samples were placed in laboratory supplied glass sampling jars with Teflon lined lids, were placed on ice in a sample cooler and were delivered to the testing laboratory with chain-of-custody documentation.