Mobile Soil Washing
This site consisted of a former service station truck stop with hydrocarbon contamination resulting from leaking underground storage tanks (USTs). After the USTs were removed, a site investigation was performed that indicated the need for substantial soil remediation to mitigate the residual contamination. It was also assumed that an active groundwater treatment system would be required. Through the process of preparing the Remedial Action Plan (RAP),it was determined that a mobile on-site soil washing technique operated by an experienced soil washing firm would best address the site’s remediation criteria related to cost, technical feasibility, and timeliness.
Subsequently, the soil washing firm negotiated a fixed price process fee basedon 5,500 cubic yard (cy) requiring soil washing to remediate the soils. Given that the unit rate did not allow for excessive reprocessing of soils that failed to test below the state established cleanup criteria, the soil washing firm decided to utilize an on-site laboratory to provide real-time quality control (QC) analytical data for the processed materials. Soil contamination levels at the site significantly exceeded state enforcement standards in soil media. In addition, laboratory data obtained by previous consultants indicated benzene contamination in excess of 6,000 parts per million (ppm).
The system processed soils at a rate of thirty-nine cubic yards per hour with QC samples being collected every hour for analyses in the mobile laboratory. The samples were analyzed for BTEX, 1,2-dichloroethane, gas range organic (GRO) and diesel range organics (DRO). The results were reviewed by the soil washing firm’s site manager for compliance with the cleanup criteria. If the results for any given lot exceeded the criteria, that particular lot was flagged for rewashing. If consecutive QC samples failed to meet the criteria, operations were halted and a system diagnoses performed. By project end, 6,000 cubic yards of soil were processed over a forty-five day period, and the mobile laboratory analyzed 232 sample by SW-846 method 8021 and Wisconsin’s
modified methods for GRO and DRO.
In evaluating the cost effectiveness of utilizing a mobile laboratory for this project, we cannot only examine the relative fixed laboratory fees. Te remain on budget and assure profitability for the soil washing firm, the project
required real-time data with a turnaround time measured in minutes rather than days. This project experienced two major and several small periods of unscheduled down time due to system malfunctions. Which were detected by the on-site laboratory. This early detection capability saved the soil washing firm more than $100,000 in costs associated with rewashing potentially
contaminated soil.
• Mobile laboratory costs for the project totaled $27,000.
• At the process rate of 39 cubic yards per hour, a 24-hour expedited analyses from a fixed lab could have resulted in 300-600 cubic yards (5-10 percent to the total project’s volume) being improperly processed before the site manager would be aware that the problem existed. This represented a potential loss of $17,000-$35,000 per incidence for the soil washing firm
• If that risk had been acceptable, the fixed lab fees for this project, assuming 232 samples analyzed for SW-846 Method 8021 and Wis. Modified GRO/DRO with a 24-hour turnaround, would have cost $74,240 (232 samples x$160.00/sample x 200% for rush delivery).