Lead-contaminated soil at a former skeet shooting range is stabilized and reused onsite in a solution that also solved the problem of closing a landfill.
By Alan D. Hanscom and Marc J. Richards
Excerpted from Soil and Groundwater Cleanup Online Magazine
http://www.sgcleanup.com/innovations.html
After the former Jug End Resort, Egremont, Mass., was acquired from the Resolution Trust Corp. (RTC) by the Commonwealth of Massachusetts Dept. of Environmental Management and Dept. of Fisheries, Wildlife and Environmental Law Enforcement in 1990, environmental cleanup activities were instigated to remediate lead-contaminated soil at the former Gun Club Skeet Range and to close the former Golf Course Landfill. A strategy to perform on-site stabilization of the contaminated soil and to incorporate the stabilized soil as a component of the landfill cap for closure of the landfill was developed.
Anatomy of the Site
The 470 hectare property operated as a resort from 1936 to 1985. About 40 hectares were developed for the resort and the remainder of the area consisted of undeveloped forests and meadows. When the Commonwealth acquired Jug End, the property had 40 structures, two landfills, underground storage tanks (USTs), aboveground storage tanks (ASTs), a gun club skeet shooting range, wastewater treatment lagoons, contaminated soil associated with USTs, and miscellaneous containers of oil and hazardous materials associated with the former operation of the resort, golf course and maintenance areas.
Two specific aspects of the project included the remediation of about 1500 cubic meters of lead-contaminated soil located within the former Gun Club Skeet Shooting Range and closure of an on-site landfill, known as the Golf Course Landfill.
Soils exhibiting elevated concentrations of lead were encountered in surface soils of zero to 0.3 meters within woodlands north of the skeet range. The source of the lead contamination in soil was lead shotgun pellets released during the operation of the skeet range.
Concentrations of total lead up to 1630 mg/kg were identified in soil samples collected from the surface to a depth of up to 0.3 meters below grade. Nine samples were reported to contain lead concentrations in excess of the Massachusetts Contingency Plan (MCP) risk-based target cleanup standard of 300 mg/kg for Method 1 S-1/GW-1 soil.
Levels of lead above MCP cleanup standards were identified on the northwestern side of an intermittent stream through the contaminated area. An area of about 5600 square meters was determined to be contaminated by lead shot. Based on the total lead concentrations reported in soil, toxicity characteristic leaching procedure (TCLP) lead testing was performed on soil samples exhibiting elevated total lead concentrations. TCLP lead concentrations ranged from 8.9 to 39.1 mg/L, which exceeded the RCRA hazardous waste leachable lead standard of 5.0 mg/L.
The Golf Course Landfill operated from about 1940 to 1960 during which time daily solid waste generated at the resort was disposed. The landfill was closed in 1960 by placing a layer of topsoil over the solid waste. The landfill then became a part of the existing golf course. Subsurface investigations were conducted within the landfill in 1995 to determine the lateral extent of the landfill, the existing cover thickness, and to identify if reportable releases of oil and hazardous materials had occurred. The landfill investigation did not identify contaminant concentrations in soil or groundwater which required remedial action. The existing cover thickness was determined to average about 15 cm over the total landfill area of 0.8 hectares.
Management Plan
Remedial action alternatives were evaluated for the management of the lead-contaminated soil because total lead and TCLP lead exceeded regulatory guidelines. Scenarios for RCRA-hazardous contaminated soil have typically included excavation and off-site disposal at a lined RCRA landfill for costs that can exceed $180 per metric ton.
Costs of this magnitude were unacceptable given the project remediation budget. Low cost options were identified that included on-site treatment/stabilization and subsequent reuse of the treated soil onsite. These on-site stabilization processes would remove the leachable lead characteristics of the soil and thereby deregulate the soil as RCRA-hazardous.
The simultaneous closure of the Golf Course Landfill presented an opportunity for the on-site placement of the lead-stabilized soil from the skeet range. Given the size of the on-site landfill and the expected lead-contaminated soil volume, placement of the stabilized soil within the landfill before capping was a realistic remedial option.
A Release Abatement Measure (RAM) plan was submitted to the DEP which identified response actions to manage the lead-contaminated soil. The RAM plan proposed the on-site stabilization of the soil using portland cement. Following stabilization, the soil was to be placed within the Golf Course Landfill and a minimum of a 0.6 meter cap constructed of a low permeability silt/clay soil was to be placed over the stabilized soil.
Treatability testing on the contaminated soil identified that leachable lead could be reduced to concentrations less than 0.1 mg/L. DEP approved the proposed RAM plan. During contract bid evaluation for the remediation and landfill closure, Solucorp Industries' Molecular Bonding Process was proposed. (For a description of the process, see Soil & Groundwater Cleanup, November 1997, "Metals at Midvale," pp. 6-9.)
Bench-scale Treatability Study Results
A bench-scale treatability study was performed to evaluate the stabilization process proposed by Solucorp. The study was performed to replicate field techniques to reduce the levels of leachable lead. Results of the study identified that soil could be stabilized to concentrations less than 0.1 mg/L, far below the RCRA regulatory limit of 5.0 mg/L.
Following successful stabilization of the soil during the bench-scale study, the DEP indicated that the process required the review and approval by its Innovative Technology Program before field implementation since the technology had not yet been approved for use in Massachusetts.
To evaluate the long-term stability of the stabilized soil, the Multiple Extraction Process (MEP) was performed on the soil. The MEP attempts to duplicate the leaching conditions that soil or waste may be subjected to from the effects of repeated exposure to acid rain. Multiple TCLP extractions are made from the sample to identify if contaminant concentrations increase with each extraction. The bench scale stabilized soil portion contained 2,823 mg/kg total lead and 34.3 mg/L leachable lead. Following treatment, TCLP concentrations did not increase with each MEP event and all TCLP concentrations were reported to be less than 0.1 mg/L.
To evaluate the effectiveness of the stabilized soil to be placed as a component of the landfill cap, a "Remolded Tri-Axial Variable Head Permeability Test-ASTM 5085" was performed on the stabilized soil. Results reported a permeability of 1.52 x 10-6 cm/second. These results substantially met and exceeded the DEP's Division of Solid Waste regulations for closing or capping a pre-1972 solid waste landfill
The DEP approved the use of the MBS technology to stabilize and reuse the lead-contaminated soil onsite given the positive results of the bench-scale treatability study, MEP results, permeability results and performance data related to MBS soil stabilization in other states.
Summary of RAM Plan Activities
Release Abatement Measure (RAM) Plan activities were initiated during June and July 1996. Before beginning excavation activities, the lateral extent of the lead-contaminated soil was delineated based on existing analytical results. Excavation activities were conducted within the previously defined limits. Due to woodland conditions within the excavation area, trees with trunk diameters of less than 20 cm and loose leaf litter were removed from the excavation area; large trees were left in place.
Organic surface soils up to about 0.3 meters in depth were excavated by a dozer and backhoe. Lead-contaminated soil was transported and stockpiled in the vicinity of the Golf Course Landfill, where on-site stabilization occurred. Once soil excavation began, the Commonwealth of Massachusetts as site owner became a generator of RCRA-hazardous waste. This meant the state had 90 days to manage the waste without the need to file for a RCRA permit.
Twenty-two closure soil samples were collected at the limits of the excavated area for total lead analysis to confirm that the target cleanup goal of 300 mg/kg was achieved. All closure sample results were below the established cleanup goal. Composite samples were collected from the stockpiled soil for laboratory analyses to confirm the levels of total lead before stabilization. In general, one composite sample per 150 cubic meters of soil was analyzed for total lead.
All soils excavated from the skeet shooting range were temporarily stockpiled on and covered with polyethylene sheeting within an earthen bermed area. Following pre-characterization and the mechanical soil screening of 25 mm or larger aggregate from the stockpile, the lead-contaminated soil was stabilized onsite using the MBS process.
Tailings generated from the screening process were reused onsite for soil erosion control mitigation. The screened material was loaded into the pugmill unit for treatment. Following treatment, confirmatory TCLP lead samples were collected at a frequency of one sample per 150 cubic meters of stabilized soil. All TCLP lead results were reported to be less than 0.1 mg/L.
Landfill Closure Cap Design
In accordance with DEP regulations, the closure of the landfill had to meet or exceed the DEP's Division of Solid Waste regulation for closing or capping a pre-1972 solid waste landfill. The landfill cap was designed to minimize percolation of surface water through the cap, to promote drainage of precipitation and elevated groundwater conditions, to minimize soil erosion and slopes of the cap, and to isolate the landfill wastes and lead-contaminated soil from the environment.
The final landfill cap consisted of a three layer component system. It featured an as-built thickness of about 1 meter, consisting of a 0.3 meter lead-stabilized soil layer, a 0.3 meter silt/clay layer and a 0.3 meter topsoil layer. The existing 15 cm layer of topsoil on the landfill was stripped from the landfill and stockpiled for reuse. The lead-stabilized soil was subsequently placed over the exposed solid waste and compacted.
Groundwater Monitoring
Due to the placement of lead-stabilized soil within the landfill, the DEP required two years of groundwater monitoring. During construction of the landfill cap, two existing groundwater monitoring wells were preserved and an additional well was installed outside of the landfill cap. The three groundwater monitoring wells are being sampled and analyzed for total lead on a quarterly basis for two years. All groundwater results have been below method detection limits.
Activity and Use Limitation
An Activity and Use Limitation (AUL) was implemented as required by the DEP to address closure of the landfill. These restrictions or limitations of site activities were necessary because the total lead concentrations in soil exceed applicable MCP soil standards. The AUL restricts site activities and land uses such as subsurface excavation, residential housing, gardening, public or private schools, designated playground, recreation area or daycare, for the entire area of the landfill.
Successful Site Closure
Response actions within the former Gun Club Skeet have resulted in the successful excavation, screening, stabilization and reuse of about 1500 cubic meters of lead-contaminated soil. TCLP lead concentrations were lowered to less than 0.1 mg/L for the entire volume of excavated soil. Closure of the on-site landfill allowed on-site beneficial reuse of lead-contaminated soil that would have otherwise been transported to a Subtitle D landfill following stabilization.
Advantages of the stabilization processes that lower leachable contaminant concentrations are that the soil remains in workable form and on-site reuse options can be explored. The selection of stabilization and reuse versus off-site landfill disposal enables valuable landfill space to be used for wastes better suited for disposal.
The success of cleanup activities at the former Jug End Resort, now the Jug End State Reservation and Wildlife Management Area, has enabled more than 400 hectares of valuable conservation land to be indefinitely preserved.