- 4200 S. Gun Club Road, Arapahoe County.
- Immediately northeast of the intersection of Quincy Avenue and Gun Club Road in Aurora, approximately 15 miles southeast of downtown Denver.
- Consists of approximately 480 acres, where an estimated 138 million gallons of liquid industrial waste were disposed.
- Township Section 31.f, the Denver Arapahoe Disposal Site (DADS), an operating municipal solid waste landfill northeast of the intersection of Gun Club Road and East Hampden Avenue, forms the northern boundary of the site.
- Lowry Landfill is owned by the city and county of Denver, and operated by Waste Management of Colorado.
- From 1965 to 1980 liquid industrial wastes were co-disposed of with solid industrial and municipal wastes in approximately 78 unlined pits over approximately 200 acres of the 480-acre site.
- From 1980 through 1990 Waste Management of Colorado Inc. continued municipal solid waste disposal for Denver.
- By the late 1980s 10 million tires had accumulated on-site.
History of containment activities
- The site was placed on the National Priorities List in September 1984.
- The U.S. Environmental Protection Agency (EPA) conducted the Phase I Remedial Investigation from late 1984 to mid-1986.
- The investigation found contamination in groundwater, surface water, soils and sediments.
- The primary contaminants of concern are volatile organic compounds.
- To address contamination in each of the areas of concern, EPA divided the site into six operable units (OUs):
- OU 1: Shallow groundwater and subsurface liquids.
- OU 2: Landfill solids.
- OU 3: Landfill gas.
- OU 4: Soils.
- OU 5: Surface water and sediments.
- OU 6: Deep groundwater.
- In 1984, Denver constructed an underground barrier wall (North Boundary Barrier Wall) and water treatment system (Old Water Treatment Plant) at the landfill to collect the shallow groundwater and remove volatile organic chemicals.
- From 1985 through 2000, shallow groundwater collected from the North Boundary Barrier Wall was treated with a combination of air stripping and carbon adsorption.
- The treated water was returned to the groundwater system in an injection trench located north of the North Boundary Barrier Wall.
- From 1989 to 1991, 120 million pounds of tires (10 million tires) at the site were shredded and placed in an on-site monofill for later reuse. These tire chips were shipped off-site to a cement kiln for energy recovery purposes.
Record of Decision
In March 1994 EPA and the state of Colorado signed the Record of Decision identifying the remedial objectives and remedial actions for the site.
The containment remedy involved:
- Installing underground barrier walls (slurry walls) and groundwater collection systems on the site.
- Constructing of a new water treatment plant to treat the highly contaminated groundwater.
- Dogging three accessible waste pits which were under the old tire piles.
- Collecting and flare-burning landfill gas.
Over the years, the remedy has been modified to take into account new technologies and new information.
- The North Boundary Barrier Wall Injection Trench is no longer a remedy component.
- The ground water monitoring network is not shown.
The liquid industrial wastes at the site include:
- Sewage sludge.
- Metal plating wastes.
- Petroleum-derived products.
- Pesticides and industrial solvents.
Small amounts of radioactive materials have also been detected in the waste pits, sediments, groundwater and soils.
This is likely due to a combination of naturally occurring radionuclides, along with hospital wastes and other household or commercially related low-level radioactive materials historically disposed in the landfill (e.g., lantern mantles and smoke detectors).
More than 50 chemicals of concern have been identified through the risk assessment process. These include but aren't limited to:
- Volatile organic compounds (e.g., vinyl chloride, 1,2-dichloroethane, 1,1- dichloroethylene).
- Semi-volatile organic compounds (e.g., 1,4-dioxane).
- Polynuclear aromatic hydrocarbons (e.g., benzo(a)anthracene).
- Metals (e.g., arsenic and lead).
- There is and has been a surface water standard for 1,4 - dioxane since 2005.
- The facility is currently working to delineate the ground water plume extent.
Groundwater, surface water, soils and sediments on-site are contaminated.
The heavily contaminated on-site shallow groundwater is not used as a drinking water source.
Because of the large volume of liquid waste destined to remain on-site as part of the containment remedy, it will be necessary to maintain ongoing diligent operation of the containment systems.
Groundwater and landfill gas monitoring will be necessary to ensure the remedy remains effective.
- A landfill gas extraction and treatment (enclosed flare) system was constructed in summer 1996 and has been operating since January 1997.
- Landfill gases from the Denver Arapahoe Disposal Site Section 31 were combined with Lowry Landfill gases to allow for more efficient continuous operation of the flare treatment system.
- The combined landfill gas from the Denver Arapahoe Disposal Site and Lowry Landfill is now used as fuel for internal combustion engines to generate electricity.
- A replacement wetlands was constructed in April 1997.
- Floods damaged the constructed wetlands during the summers of 1997 and 1998.
- Repairs to the constructed wetlands were completed in April 1999.
Underground barrier walls
In May 1998, the underground barrier walls (slurry walls), located on the south side of the site, the southern half of the east side of the site and the southern half of the west side of the site, were completed.
- The first generation of performance and compliance monitoring wells were installed in April 1998.
- The groundwater extraction trench at the toe of the landfill (North Toe Extraction System) was constructed in December 1997, but was not operational until 2005.
In 1998, a pipeline was constructed to take treated effluent to the Metro Wastewater Reclamation District's Publicly Owned Treatment Works, initially via Aurora Wastewater pipeline.
- The new water treatment plant was completed in March 2000 and started receiving groundwater from the North Boundary Barrier Wall and other smaller groundwater extraction operations at the site at that time.
- The new water treatment plant started accepting groundwater from the North Toe Extraction System in 2005.
Groundwater from the site are routinely treated, tested and discharged to the Publicly Owned Treatment Works.
- Since extracted groundwater is effectively removed from the site, a potable water line was installed in 1998 to provide water necessary to augment the aquifer water removed through groundwater extraction.
- This potable water is polished with granular activated carbon to remove residual chloride ions which can create trihalomethanes in the aquifer, and this water is recharged to the shallow groundwater aquifer through the trench and/or wells located immediately north of the North Boundary Barrier
- Wall. While potable water injection is used for ground water augmentation/water rights purposes, this potable water injection process is not a component of the ground water containment remedy.
Former tire piles
In September 1998, excavation started on waste pits in the Former Tire Pile Area and construction was started on a treatment cell for contaminated material removed from the waste pits. Excavation of the middle waste pit was completed in April 1999.
- The remainder of the former tire pile area waste pit remedy (north and south waste pits) was re-evaluated due to difficult excavating conditions and fugitive air emissions control issues.
- A relatively innovative in-place heating and contaminant extraction process was tested on the South pit, which resulted in removal of approximately one- half of the contamination.
- The North and South Former Tire Pile Area Waste Pit remedy is now focused on more conventional methods involving pumping of floating and sinking free product.
- Floating free product, composed primarily of organic compounds (e.g., gasoline) tends to be less dense than water and accumulates and floats on the water table as Light Non-Aqueous Phase Liquid (LNAPL).
- In contrast, Dense Non-Aqueous Phase Liquid (DNAPL) tends to be denser than water. DNAPL tends to accumulate and sink.
- Unless an appreciable proportion of LNAPL and DNAPL are removed from contact with groundwater, these liquids will likely result in ongoing contamination of groundwater.
The North Face Landfill cover was completed in September 1999.
- During the first Five-Year Review, in 2001, surface depressions due to settling on top of the landfill mass were found. These were filled with clean fill and the cover was regraded in 2002.
- In March 2004, the Potentially Responsible Parties (PRPs) developed an Engineering Design and Operations Plan proposing a relatively proactive approach that, if and when implemented, should effectively compensate for
- ongoing settling and minimize the need for future backfilling and regrading operations.
The oldest inactive asbestos monofill is located on the east side of the main landfill mass.
The second inactive asbestos monofill is located in the northwest corner of the site, and as of February 2008 the active asbestos monofill is located in the west central portion of the site.
The active asbestos monofill is nearing capacity. Approval has been given for the development of a fourth asbestos disposal area in the northeast portion of the site.
Former Tire Pile Area Waste Pit Remedy
Due to unanticipated conditions experienced during initial excavation of the north Former Tire Pile Area waste pit, Denver and Waste Management developed a feasibility study to re-evaluate the Former Tire Pile Area Waste Pit Remedy for the North and South Former Tire Pile Area waste pits.
- The Former Tire Pile Area Feasibility Study was approved by EPA on Dec. 30, 2004.
- EPA prepared a Proposed Plan for the Former Tire Pile Area waste pits and EPA's preferred remedial alternative is currently being implemented.
- This remedy involves the direct extraction of floating and sinking free product (LNAPL and DNAPL) through vertical extraction wells in and immediately adjacent to the North and South Former Tire Pile Area waste pits.
- Extraction of product will continue at each extraction well until the floating product is less than 6 inches thick and the sinking product is less than 6 inches thick for a period of at least 30 days.
- Once this performance standard is met, the respective extraction wells will be abandoned.
- Several extraction wells have already met the performance metric and been abandoned.
Groundwater Monitoring Plan
In February 2005, the Groundwater Monitoring Plan was approved by EPA and initiated by the Potentially Responsible Parties. EPA approved a revised ground water monitoring plan in July 2015.
- The Groundwater Monitoring Plan is designed to provide a single integrated groundwater compliance and effectiveness (performance) monitoring program that supersedes the multitude of pre-existing compliance and effectiveness monitoring plans for the site.
- The overall objective of the compliance component of the groundwater monitoring program is to demonstrate that the remedy components collectively result in attainment of the performance standards for groundwater along the point of compliance.
- The focus of the Groundwater Monitoring Plan is on intra-well statistical analysis of water quality data collected from the groundwater compliance and performance network wells.
- An intra-well analysis typically evaluates water quality trends at multiple individual sampling points (or wells) through time.
- The Record of Decision for the site establishes performance standards for a number of chemicals that must be achieved in groundwater.
- Attainment of the performance standards at the point of compliance helps ensure the protection of human health.
- The Groundwater Monitoring Plan also establishes decision rules, based on the trends determined from statistical analysis, to determine when and where additional actions may be necessary.
Regarding the effectiveness monitoring program, the overarching objective of the containment features constructed and operated at the site is to prevent groundwater from being transported from source areas beyond the point of compliance at levels above performance standards.
Three remedy components have been implemented to achieve containment of contaminated groundwater at the site:
- The perimeter slurry wall, located at the south end of the site.
- The North Toe Extraction System, located at the north toe of the main landfill mass.
- The North Boundary Barrier Wall, located north of the Superfund site.
The specific design objectives vary among the different containment features at the site, but each feature ultimately provides a mechanism for hydraulic control with the overarching objective of preventing contaminants transported by groundwater from crossing the regulatory boundary, also called the Point of Compliance.
- For example, the slurry wall's purpose is to both inhibit clean groundwater inflow and contaminated groundwater outflow, whereas the North Boundary Barrier Wall collects groundwater to limit down gradient flow to the north beyond the area of groundwater containment created by groundwater extraction at the North Boundary Barrier Wall.
- As all of these systems are intended to provide hydraulic control, they have similar purposes and objectives; however, given the differences in hydraulic controls provided by each containment feature, the criteria applied to evaluate effectiveness are distinct and detailed in the 2015 Groundwater Monitoring Plan.
In an ongoing effort to lower concentrations of 1,4-dioxane in off-site groundwater to or below the performance standard, EPA approved a North End (i.e., off-site) Work Plan for an initial response action in 2006. The focus of the off-site efforts are in Section 31 (Denver Arapahoe Disposal Site), located immediately north of the Superfund site.
Currently, groundwater extraction is occurring in three offsite areas:
- The MW113 Area, located immediately north of the North Boundary Barrier Wall.
- The MW77 Area, located northeast of the site.
- The MW156 Area, located almost 1 mile north of the site.
An off-site pipeline was constructed in December 2007 to facilitate transport of extracted groundwater from these and possibly other off-site areas to the water treatment plant.
In July 2007, EPA also approved a North End Groundwater Monitoring Plan. This plan is focused on intra-well statistical analysis of 1,4-dioxane groundwater quality data in selected off-site monitoring wells, where the off-site 1,4-dioxane plume is located. The North End Groundwater Monitoring Plan is similar to the 2015 plan except that it involves only performance monitoring wells (i.e., there are no off-site compliance wells). Data analysis, contemplated in the North End Groundwater Monitoring Plan, is identical to the 2015 on-site Groundwater Monitoring Plan.