ARCHIVED REPORTS XR0010941 - Laserfiche WebLink

Home Browse Search

t rainfall, depth to groundwater and presence of conduits in the subsurface) and the chemistry of these fuels to estimate the concentrations of hydrocarbons which can be left in place without threatening groundwater. This site was determined to have a medium leaching potential (Table 4). In such a case, the recommended maximum allowable TPH (diesel) concentration is 1000 ppm with B/X/T/E concentrations of .31.31111 . The TPH(diesel) concentrations detected in several of the samples from Derickson Trucking did exceed this limit. Risks to the surface environment due to vapors emanating from the impacted soil mass is considered to be very minimal due to the low volatility of diesel fuel and the distance of the site from potential receptors. 7.0 Recommendations Based on the findings discussed above, AGI recommends excavation of the affected soil mass with convention excavating equipment to depth of approximately 25 feet. An excavator can reach a depth of approximately 20 feet, however, sloping and benching. of the sides of the excavation will be required to allow the machinery and personnel to safely operate below this depth. In the opinion of AGI , if impacted soils are removed to this depth, the bulk of the affected material will be eliminated. If a 300 to 550 square foot surface area is excavated to 25 feet, 275 to500 cubic yards of soil will be .removed, s however these are estimates of the maximum quantities which may be involved. During excavation operations a geologist will monitor soil removal to ensure that only significantly impacted soils are removed and that unnecessary excavation is avoided. Further protection for the site can be provided by placing an impermeable clay or concrete seal over the excavated area as a final step to prevent seepage of surface op waters through any remaining contaminated soils. Bloremediation on the property offers the best approach to treat the excavated material. Diesel fuel does not volatilize, however, it is readily degraded into harmless substances through the action of bacteria which are generally present in the soil or E can be added through the addition of commercially available cultures. The bioremediation site is usually prepared by spreading the affected soil in a layer one to two feet in thickness on plastic sheeting within a bermed enclosure. A layer of clean soil can be placed below the contaminated to protect the plastic liner during tilling or disking operations. Alternatively, if space is limited, thicker piles can be constructed and oxygen introduced through a series of perforated pipes placed near the base of the pile manifolded to a blower. Optimal bacterial growth is maintained by periodically tilling (aerating) the pile, maintaining soil moisture and adding fertilizer. Plastic sheeting covering the pile prevents drying out, prevents blowing dust and helps maintain elevated temperatures. Reduction of hydrocarbon concentrations to the level of 100 ppm may take three to six months. Another, albeit more costly alternative, is disposal of the soil at a proper landfill. This has an advantage in that the entire project may be completed in several days. `� 11