The basis for landfill closure, remediation, and redevelopment

Reuse and recycle

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Introduction

The Lexington County Highway 321 landfill site was recently awarded the U.S. Environmental Protection Agency’s (EPA) Region 4 Excellence in Site Reuse: Superfund Redevelopment Award.

This site, located in West Columbia, S.C., contains several waste disposal areas that were active from the 1950s through 1988. The waste areas varied from uncontrolled dump sites used by citizens to a former sand pit that was later permitted for municipal and industrial solid waste in Lexington County.

In 1990, the landfill was officially closed and capped for the first time. This cap consisted of a kaolin clay cover system, which ultimately failed when the cap eroded. The cap system was reconstructed and it quickly failed again.

In 1993, after several studies of groundwater and landfill gas migration by the EPA and the South Carolina Department of Health and Environmental Control (SCDHEC), the site was placed on the EPA’s Superfund National Priority List (NPL) and the process to successfully close the landfill began.

Understanding the need to use recycled materials in the cap system and to minimize costs, the landfill closure was designed to utilize recycled tire chips in the drainage layer of the cap. Groundwater remediation was required at the site to prevent off-site migration of impacted groundwater. To assure stability of the landfill cover system, the treated groundwater was used for irrigation water at the site to sustain a healthy stand of grass. Further, landfill gas collection was required to remediate off-site gas migration.

Finally, understanding that sites that are reused generally have higher success rates for landfill closure, Lexington County worked with a small golf driving range operator to promote site redevelopment, including constructing a tee box into the final cover system on the landfill. Since this final closure of the landfill in 2000, reuse of the property has expanded to include a citizen’s convenience center, a miniature golf course, and the University of South Carolina (USC) golf practice facility.

This article will outline the steps taken to prevent the failures of past closures as well as the inherent planning for reuse of materials and future redevelopment during all phases of closure. In each instance, Lexington County worked with the SCDHEC and the EPA to ensure that the proposed redevelopment of the property would not negatively impact the landfill closure features.

The site’s closure has remained successful for the past 11 years, groundwater remediation is nearing conclusion, landfill gas recovery from off-site properties has been successful, and each year thousands of people enjoy this property as a golf driving range, a miniature golf course, a convenience center, and as the USC golf practice facility currently referred to as “The Coop.”

Site history

The Highway 321 Landfill Superfund site originally consisted of several properties with several different owners. The largest tract of land was operated as a sand mine. The sandpit operation was active until sometime in the 1960s.

Adjacent to the sand mine was Stanley Pond. Reportedly, this pond was used as an uncontrolled dump by citizens in the area. The remaining properties were undeveloped prior to the closure of the sand mine. Although Stanley Pond was used as an uncontrolled dump, it is presumed that the remainder of the site remained free of waste until landfill operations were started adjacent to and in the old sand mine area in the 1960s.

The Superfund area contains three waste areas: the Highway 321 Landfill, the Bray Park Dump, and the Old Cayce Dump (see site map). There were a few areas of limited waste outside these three units. Of these, the Highway 321 Landfill is the largest. This landfill unit filled the former sand mine on the property. The Highway 321 Landfill began operation as an unlined facility in 1972 under ownership and operation of Lexington County. In 1988, the landfill ceased waste disposal operations when facility capacity was reached.

The Bray Park Dump was used by the cities of Cayce and West Columbia from the mid-1960s to 1970. These landfills were also unlined. The Old Cayce Dump was used as an uncontrolled waste area from the 1940s through the 1960s in and around the former Stanley Pond.

This waste unit was closed in 1969 and covered in 1972. During the time of waste disposal in these areas, there was minimal to no regulation of what types of wastes were placed in the these areas.

Historical landfill gas collection

In 1986, a landfill gas collection system was installed by Cargan, a private developer, at the site and the gas was piped to Foster Dixiana and Gaston Copper for industrial uses. Active landfill gas collection by this system ceased in the early 1990s.

Initial landfill closure, designation as a Superfund site

In 1990, the first closure attempt was started at the Highway 321 Landfill. This closure was completed with the installation of a low permeability kaolin clay cover.

Between 1990 and 1993, the landfill cover system at this site failed twice primarily due to poor vegetative cover and stormwater management. Both failures resulted in waste migration outside the landfill footprint due to significant erosion of the landfill cover.

Between 1992 and 1994, a remedial investigation was performed for submittal to the U.S. EPA. On Sept. 29, 1994, a Record of Decision (ROD) for the site was signed by the EPA. A Remediation Feasibility Study (RFS) was completed in March 1994 and a Unilateral Administrative Order was executed by the EPA on June 13, 1995. These documents required the final closure of both the Highway 321 Landfill and Bray Park Dump, plus excavation of the Old Cayce Dump for consolidation into the Bray Park Dump. (This last item was later modified in a 1998 ROD amendment, discussed below.)

A Remedial Design Work Plan was prepared and accepted by the EPA and SCDHEC in October 1996. In November 1996, construction of the final cover system began.

Waste consolidation

Throughout the remedial work plan process, the possibility of returning the site to the tax base of Lexington County was a priority. Therefore, prior to landfill cover construction, waste consolidation took place to remove waste from extraneous areas and to allow for more potentially reusable acreage.

Waste was removed from the area immediately adjacent to Highway 321 and other areas and consolidated with the Bray Park Dump. Overall, approximately 100,000 cubic yards of waste was removed and reinterred in the Bray Park Dump.

Landfill cover design and construction

The third (final) cover system at this site was designed to consist of—from bottom to top—a 12-in. intermediate cover and base, geosynthetic clay liner (GCL), a 6in.-thick tire chip layer, a geotextile filter fabric, and 12in. to 18in. of soil for vegetative support.

Additionally, the design included stormwater management features, including a landfill cap perimeter berm and downchutes to carry stormwater down the sideslopes and away from the landfill.

To reduce the cost of landfill cover construction, Lexington County opted to install the landfill cover with its own public works personnel, an unusual approach for many potentially responsible parties (PRPs) at that time. Although this added some time to the construction schedule, it saved the county a significant amount of money.

Use of sand processing waste fill

Prior to installation of the GCL, the landfill was regraded to fill the many eroded areas of the existing cover and to remove areas that were considered to be too sandy for a firm subgrade.

Sand processing waste fill material from a mine located across the street was brought to the site for use in regrading. This sand process included the addition of polymers to settle out fine materials from the sand, making a clayey silty material for the cover. This alleviated the burden of removing waste material on local businesses and assisted the county with reduced fill hauling costs due to the close location of the source material.

Once the area was regraded, GCL panels were placed with a minimum 6-in. overlap. Bentonite powder was placed at each seam to ensure cover integrity. In areas where existing gas vents were encountered, the vents were cut off near the ground and the GCL was placed over the vent. A hole was cut in the GCL to accommodate the vent and then the vent pipe was replaced.

The GCL layer was tied to the downchutes located around the perimeter of the flat top portion of the cap. The downchutes were also lined with GCL and the GCL from the cap had a minimum 2-ft overlap with the downchute GCL and was seamed with bentonite powder.

To assist in site drainage, a drainage media consisting of a 6-in. layer of tire chips was utilized. This layer carries water that infiltrates the vegetative support layer across the landfill and down a specially designed stormwater chute, as described above. More specifically, this layer relieves pressure on the GCL to greatly diminish the potential of further infiltration into the waste mass. This project utilized all the waste tires in the state of South Carolina at the time, plus some in Georgia. For this use, nominal 1in. tire chips with minimal steel thread showing were used.

In general, the tire chips had hydraulic properties that were between a 78-stone and sand, depending on compressive loading. The transmissivity of the 1in. nominal tire chip was 0.30cm3/sec, while the weight of the tire chips (33lbs/ft3) was significantly less than that of either sand or 78-stone. This made the tire chips ideal, especially due to their significantly reduced cost compared to stone or sand.

Golf driving range included in cover design

The Par Tee Driving Range has been operating on the Highway 321 Landfill site since the early 1990s. As part of the cover construction, a tee box was designed and constructed at the site to assist this local business in maintaining a presence on the landfill. This assisted the county in creating further redevelopment. The construction of the tee box also used waste fill material from the local sand quarry.

Old Cayce Dump record of decision (ROD) amendment

The Old Cayce Dump was originally planned to be excavated due to shallow waste and thin waste thicknesses as summarized in the Remedial Investigation and ROD.

However, during site construction, the waste in this area was found to be beneath groundwater and thicker than originally measured. This made dewatering necessary for waste removal and significantly increased the estimated costs of this portion of the remedial action. Due to the location of nearby houses and a ballpark, as well as these cost factors, a ROD Amendment was executed to allow this waste area to be closed in place with the same cover system design as the Highway 321 Landfill unit cover system.

Site hydrogeology

The site is located in the Coastal Plain Physiographic Province of South Carolina in West Columbia. The higher elevations of the site are underlain by the Pinehurst Formation which consists of loose windblown sands up to 50ft thick. These are underlain by the Lower Tertiary Unit which consists of a sequence of three fine to coarse clayey and silty arkosic and quartz sands separated by kaolinitic clays of tertiary age.

This formation has been alternately referred to as the Black Mingo and Huber formations. The uppermost sands of this sequence form the uppermost aquifer at the site. The Middendorf Formation underlies the Lower Tertiary Unit at depths ranging from 75–150ft deep at the site.

At the downgradient edge of the site, the uppermost aquifer extends to a depth of approximately 35ft below grade. At that depth the top of the uppermost kaolinitic aquitard in the Lower Tertiary Unit sequence is encountered.

During the many investigations performed at the site between the 1970s and the 1990s, groundwater impact was detected in the uppermost aquifer. Remediation of the uppermost aquifer was required in the ROD.

Groundwater recovery, treatment, and reuse

As stated above, groundwater in the uppermost aquifer was found to be impacted by the unlined landfill.

Detected contaminants included inorganic metals such as manganese, lead, and iron and organic constituents such as benzene, chlorobenzene, trichloroethene, methylene chloride, and 1,4-dichlorobenzene. Semivolatile constituents detected included naphthalene and bis(2ethylhexyl)phthalate. Due to the low concentrations of contaminants found in the groundwater, it was determined that aeration through spray heads would be sufficient to treat the groundwater.

Although contaminant concentrations were low, approximately 1,000ft of downgradient property line was affected and required collection of groundwater to prevent off-site migration.

To evaluate groundwater flow rates and capture zones, a step-drawdown aquifer test was performed, followed by a 24-hour aquifer pump test. The data gathered during these tests were analyzed and used in the EPA’s Well Head Protection Area (WHPA) model to evaluate zones of capture.

It was determined that each well would have a radius of influence of approximately 50ft. Therefore, 18 groundwater recovery wells were installed in areas requiring prevention of off-site migration. Each well was installed to the full depth of the uppermost aquifer and was constructed with 6-in. diameter PVC screen and riser pipe. Groundwater was recovered through electric pumps set in each well with controllers that actuate the pump based on water level.

From each well, water is pumped to a central sump/pump station. This station is also controlled by level controllers that will shut down the wells if the pumps in the central sump area cease to function properly.

From the central sump the water is pumped to the spray head system located at the edge of a 1.1million-gallon pond. The water is sprayed over the pond to remove the low concentrations of contaminants. In general, the organic constituents are released through the spray aeration, as are the inorganic constituents that precipitate out at the edge of the pond.

A secondary pumping system from the pond is then utilized to spray the water from the pond through the irrigation system that was installed in the vegetative layer of the cap. The recovered groundwater is used to water grass on the cover of the landfill to maintain healthy vegetation at the site which is vital for the long-term stabilization of the cover system.

Landfill gas collection

Although the Cargan Landfill Gas System had been in use while the landfill was in operation, landfill gas collection ceased sometime prior to 1994. Diminishing landfill gas extraction had been noted prior to the end of operations.

During installation of the final cover system, landfill gas was noted on two adjacent properties. Based on data collected, a landfill gas collection system was designed to recover gas from off-site properties and prevent further landfill gas migration.

This system consists of eight active landfill gas collection wells and 37 passive vent wells located in the Highway 321 Landfill, Bray Park Road Landfill, and Old Cayce Dump.

The eight active landfill gas collection wells were installed to a depths ranging between 17 and 29 feet deep due to the thin layer of waste in this area. These wells were installed in 36in.-diameter boreholes.

The wells are connected to a blower/flare system that collects and destroys the landfill gas. Four piezometers were installed between the active recovery wells to determine that the radius of influence of each recovery well was sufficient to produce intersecting radii of influence. In general this has been the case and the system has been very effective in landfill gas remediation from off-site properties. The figure below depicts the remediation of the landfill gas plume on one off-site property between 1999 and 2006.

Site redevelopment

Site redevelopment has been the goal of this remedial strategy since 1994. Thus far, the site has been redeveloped in the following ways:

Par Tee golf driving range Although the Par Tee Driving Range existed on the landfill prior to final closure activities, the vision of enhancing this facility to ensure that this business would be an anchor for future landfill development was a key part of the remedial objective. The construction of the tee box during final cap construction as well as the incorporation of irrigation water in this portion of the landfill helped ensure the future viability of this business and of redevelopment of the property in general.

Mini-golf course

After completion of the final landfill closure, a mini-golf course was developed at the site. U.S. EPA and SCDHEC personnel assisted in the review/approval of this site design and reuse.

USC golf team practice facility Since 2010, the University of South Carolina has worked with Lexington County, U.S. EPA, and SCDHEC to redevelop portions of the Highway 321 Landfill into a golf practice facility for its golf team. Phase 2 of golf facility construction took place in 2011 and currently nine acres are used for this purpose.

Bray Park Road ballpark Although this ballpark was in existence prior to remedial efforts at the site, remedial strategies have taken the continued use of this site during and after construction into account.

Lexington County Convenience Center A portion of the site along Highway 321 has been reused to develop a convenience center for citizens in this portion of Lexington County.

Conclusion

The long-term stability of the landfill capping system and ultimate redevelopment at this site remained the key focus of the vision for this site throughout the remedial process. Using “waste” materials (fill soil and tire chips) assisted the county in providing a remedial solution that was economical and repurposed materials that others considered waste.

This same strategy was utilized with groundwater. Reuse of the treated groundwater ensured long-term stability of the cap. Furthermore, assisting local businesses in developing this property ensures that the cap is not neglected and that any erosion is noted and corrected quickly.

Overall, maintaining this vision of reuse and redevelopment has provided the citizens of Lexington County with a properly closed landfill property that they will enjoy using long into the future. This transformation and the process by which the remedial strategy was implemented prompted the U.S. EPA to award this site with the Region 4 Excellence in Site Reuse: Superfund Redevelopment Award for 2012.

Joan Smyth, P.G., is a principal and senior hydrogeologist with SmithGardner Inc. in Raleigh, N.C.
Stacey Smith, P.E., is president and senior engineer at SmithGardner.

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