The flexible approach
- By Randall Erickson
- Jun 01, 1999
The Lord-Shope Landfill National Priorities List (NPL) Superfund site is the 400th "construction complete" NPL site. Its completion was marked by a ceremony attended by Carol Browner, administrator of the U.S. Environmental Protection Agency (EPA). The site's remedial action is comprised of a combination of technologies to both close the landfill and address the contaminants of concern both within the landfill and the downgradient plume.
The closure of the landfill consisted of an upgradient compacted clay cut-off wall and a composite cap. The remediation also included soil vapor extraction (SVE) to address volatile organic compounds (VOCs) within the landfill and surrounding soils and a groundwater extraction and treatment system. Monitored natural attenuation was applied within the plume downgradient of the landfill to supplement the groundwater extraction and treatment system.
Due to heterogeneous subsurface conditions, the design and construction had to accommodate significant uncertainties. The remediation has been successful in addressing the uncertainties due to a flexible observational approach to design and construction and a cooperative effort among Lord Corporation, EPA, the Pennsylvania Department of Environmental Protection (PADEP) and the local community. EPA demonstrated its confidence in this project by including this site, with a limited number of others, to have reduced oversight.
The Lord-Shope site is located in Girard Township, near Erie in northwestern Pennsylvania. The site, owned by Lord Corp., includes a 4-acre inactive industrial waste landfill and adjacent areas of affected groundwater. The site was active from the mid-1950s until 1979, and rises approximately 20 feet at its highest point. Industrial waste, including spent adhesives, solvents, cutting oils, acids and caustics, along with miscellaneous paper, wood and rubber wastes, was disposed of at the site.
In 1982, Lord implemented a landfill closure, based on a consent order and agreement with PADEP. The closure consisted of removal of 81 exposed drums of waste, construction of a composite cap over the landfill, construction of an upgradient cutoff wall, and continued site monitoring. The cap included a compacted clay layer, a 30-mil PVC geomembrane and a vegetative soil layer. The cutoff wall was constructed by excavating a trench upgradient of the landfill, and filling the trench with compacted clay placed in lifts to the ground surface. The objective of the closure activities was to reduce the impact of the landfill on groundwater by reducing leachate generation. The cap reduced infiltration of precipitation, and the cutoff wall lowered the groundwater table to reduce groundwater flow through the landfill.
Remedial design and action
Under the provisions of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), also known as Superfund, the site was placed on the NPL in 1983. In 1987, Lord entered into a consent order with PADEP to conduct a remedial investigation and feasibility study (RI/FS). EPA signed a record of decision (ROD) in 1990 based upon the RI/FS. In 1991, Lord entered into a consent decree to conduct a remedial design and remedial action (RD and RA). The RD was completed in 1994 and included groundwater treatment and soil vapor extraction pilot studies. Based upon the results of the RD, the RA included the construction of three remedial systems, including the landfill and soil vapor extraction system (LSVES), the groundwater recovery system (GWRS) and the groundwater treatment system (GWTS). Work on the RA began in the fall of 1994, and the systems became operational in June 1996.
An observational approach
Aquifer response at this site had been shown to be inherently difficult to predict, due to the significant heterogeneity of the water-bearing zones. Therefore, an observational approach was used to develop an optimized system for groundwater extraction. The observational approach included characterization of stratigraphic conditions involving closely-spaced test borings, the installation of wells at favorable locations determined on the basis of the test borings, performance of pumping tests and evaluation of data from the testing to determine the zone of capture. The process would have been repeated in subsequent phases if required to control migration.
However, a significant response to pumping was observed in many of the observation wells during testing of the initial installation. This observed drawdown was sufficient to overcome the natural hydraulic gradient in the area located immediately north of the landfill. The resultant zone of capture corresponds to the portion of the plume with the highest VOC, alcohol and ketone concentrations, and therefore, subsequent phases of the observational approach were not implemented.
The installed GWRS is currently controlling the migration of groundwater immediately downgradient of the source area. In addition, the applicability of monitored natural attenuation was evaluated. This evaluation was based on the historical water quality data, hydraulic properties of water-bearing zones, the evaluation of the pump test data, published information regarding transport properties and biodegradability of the organic constituents that have been observed in the groundwater, and comparison to published case histories involving the primary organic constituents. Improved groundwater quality downgradient of the landfill was documented following the installation of the landfill cap and upgradient cutoff wall. This improved groundwater quality was the result of the landfill cap, the cutoff wall and the apparent natural attenuation of the chemicals emanating from the landfill. Groundwater quality has continued to improve through the operation of the GWRS.
An optimated GWRS
Monitored natural attenuation within and beyond the zone of capture, in combination with operation of the currently installed GWRS and GWTS and associated remedial components - e.g., landfill cap and upgradient cutoff wall - addresses the groundwater component of the remedial action. The combination of the observational approach and implementation of monitored natural attenuation has resulted in an optimized GWRS. The two wells included in the GWRS pump at a combined flow rate of approximately 14 gpm.
Groundwater from the recovery wells is pumped to an equalization tank located in the treatment building. Oxidation of dissolved iron is accomplished by the addition of potassium permanganate solution to the equalization tank. Groundwater is then conveyed through granular media pressure filters to remove suspended solids and to the air stripper for removal of target VOCs. Treated effluent, not stored for backwash purposes, is pumped to the effluent discharge point, a tributary of Elk Creek located in the southwestern portion of the site. The system also includes a sludge holding tank and a plate and frame filter press to dewater sludge prior to off-site disposal.
Lord implemented an LSVES in the landfill area and two adjacent areas known as the "toe" and the "crest" areas. The LSVES consists of a vapor extraction system, vapor collection header system, vapor treatment system (thermal oxidizer), monitoring components and controls. The LSVES treatment equipment is located outside and adjacent to the groundwater treatment building. The vapor extraction/treatment portion of the LSVES includes a thermal oxidizer, blower(s), demister, condensate removal tank (secondary), condensate water pump, controls and instrumentation.
The design and implementation of vapor extraction within a landfill environment required consideration of factors not typically associated with soil vapor extraction. The initial methane concentrations in the vapor from the landfill were as high as 70 percent. This required consideration of explosion hazards. Also, the presence of biodegradable materials, as evidenced by methane concentrations at elevated levels, results in the potential for a landfill fire when vapor extraction is implemented.
Oxygen is introduced into the subsurface as a result of vapor extraction. Vapor extraction typically utilizes a higher applied vacuum and increased rate of vapor movement as compared to landfill gas recovery systems. The vapor extraction was therefore carefully monitored and controlled to avoid introducing excess oxygen, which might result in aerobic conditions conducive to a landfill fire. Temperatures within the landfill and extracted vapor were measured; oxygen levels and opacity were also monitored initially and methane levels are monitored. Although no problems have been encountered, contingency measures were developed. These include system shutdown, pulsed operation and injection of a fire suppressant.
LSVES extraction system
The LSVES extraction system includes three vapor extraction wells located in the landfill, six vapor extraction wells located in the crest area and a buried horizontal extraction pipe located in the toe area. Each extraction well and horizontal extraction pipe has a vacuum gauge and valve for monitoring and balancing the system.
Temperature probes have been installed at each extraction well in the landfill and in the header pipe to monitor extracted vapor temperature.
Temperature probes and vacuum gauges have also been installed in 12 wells constructed in the landfill to monitor the temperature and vacuum within the landfill. A thermal oxidizer treats the VOCs through combustion. The LSVES has removed a significant mass of VOCs and continues to reduce the VOC source remaining in the landfill and surrounding soils.
The LSVES, GWRS and GWTS operate automatically with only occasional on-site inspections and operations. The systems are monitored and controlled using a personal computer. Remote monitoring, control and recovery of data are performed. An alarm system has also been provided to alert the operator of unfavorable operating conditions via an automatic dialing system, and will shut down the systems in the case of a malfunction.
The GWRS, GWTS and LSVES have been operating as designed and are being maintained in accordance with the approved operation and maintenance manual. The LSVES will be operated until VOC recovery reaches a point of diminishing returns. It is anticipated that operation of this system will continue for a year or more. The GWRS, GWTS and monitored natural attenuation are expected to operate for a more extended duration, dependent upon the results of continued monitoring.
This article originally appeared in the 06/01/1999 issue of Environmental Protection.