This site is one of several Superfund hazardous waste sites in Colorado. A site qualifies for the National Priorities List (NPL or Superfund list) when the U.S. Environmental Protection Agency (EPA) determines there is a release or threatened release of hazardous substances that may endanger public health, welfare or the environment. In Colorado, the lead agency for Superfund remediation may be either the EPA or the Colorado Department of Public Health and Environment. The EPA has the lead on the Lowry Landfill Superfund Site (the Site).
The Lowry Landfill is located immediately northeast of the intersection of Quincy Avenue and Gun Club Road in Aurora, Colorado, in Arapahoe County, approximately 15 miles southeast of downtown Denver. The Site consists of approximately 480 acres, where an estimated 138 million gallons of liquid industrial waste were disposed. 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 and operated by the City and County of Denver. 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, ten million tires had accumulated on site.
History of Containment Activities
The site was placed on the National Priorities List in September 1984. The US Environmental Protection Agency 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
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 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 infiltration 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 onsite monofill, for later reuse. Subsequently, these tire chips were shipped offsite to a cement kiln for energy recovery purposes.
Record of Decision (ROD)
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 are not 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), and metals (e.g., arsenic and lead).
Groundwater, surface water, soils and sediments onsite are contaminated. Current health risks from the site are limited because access to the Site is restricted and offsite groundwater used as drinking water is not contaminated by wastes from the Site. The heavily contaminated onsite shallow groundwater is not used as a drinking water source. Because of the large volume of liquid waste destined to remain onsite as part of the containment remedy, it will be necessary to maintain on-going diligent operation of the containment systems. Groundwater and landfill gas monitoring will be necessary to ensure the remedy remains effective.
Underground Barrier Walls
In 1998, a pipeline was constructed to take treated effluent to the Metro Wastewater Reclamation District's Publicly Owned Treatment Works. 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 November 2002.
Groundwater and landfill gas from the site are routinely treated, tested and discharged to the Publicly Owned Treatment Works. Since 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 trihalomethanes, and this water is recharged to the shallow groundwater aquifer through the trench located immediately north of the North Boundary Barrier Wall.
Former Tire Piles
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 the EPA on December 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 six (6) inches thick and the sinking product is less than six (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.
The Groundwater Monitoring Plan
In February 2005, the Groundwater Monitoring Plan was approved by EPA and initiated by the Potentially Responsible Parties. The Groundwater Monitoring Plan is designed to provide a single integrated groundwater compliance and effectiveness (performance) monitoring program that supercedes 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 intrawell statistical analysis of water quality data collected from the groundwater compliance and performance network wells. An intrawell 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. 3 remedy components have been implemented to achieve containment of contaminated groundwater at the 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 limits both 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 February 2005 Groundwater Monitoring Plan.
In an ongoing effort to lower concentrations of 1,4-dioxane in offsite groundwater to or below the performance standard, EPA approved a North end (i.e., offsite) Work Plan for an initial response action in 2006. The focus of the offsite efforts are in Section 31 (Denver Arapahoe Disposal Site ), located immediately north of the Superfund site. Currently, groundwater extraction is occurring in 3 offsite areas:
An offsite pipeline was constructed in December 2007 to facilitate transport of extracted groundwater from these and possibly other offsite areas to the water treatment plant. EPA and the Colorado Department of Public Health and Environment are currently considering a proposal to amend the North End Work Plan for the initial response action to facilitate a more flexible approach targeted at accelerating removal of 1,4-dioxane mass from the offsite plume.
In July 2007, EPA also approved a North End Groundwater Monitoring Plan. This plan is focused on intrawell statistical analysis of 1,4-dioxane groundwater quality data in selected offsite monitoring wells, where the offsite 1,4-dioxane plume is located. The North End Groundwater Monitoring Plan is similar to the 2005 plan, except that it only involves performance monitoring wells (i.e., there are no offsite compliance wells). Data analysis, contemplated in the North End Groundwater Monitoring Plan, is identical to the 2005 onsite Groundwater Monitoring Plan.
Bonnie Lavelle, EPA Remedial Project Manager
John Dalton, EPA Community Involvement Coordinator
Lee Pivonka, State Project Manager
State Public Involvement Coordinator
888-569-1831 Ext. 3373 (Toll-free)