The Auburn Road Landfill site comprises 200 acres of land located next to the northeast corner of the intersection of Auburn Road and Old Derry Road in the town of Londonderry. Waste disposal historically took place at the site in four areas referred to as the town dump, tire dump, septage lagoon and solid waste areas. Landfilling operations on the property were terminated in January 1980. The four disposal areas were found to be the source of volatile organic compounds (VOCs) in surface waters and groundwater at the site. Due to the presence of this contamination, the site was added to the National Priorities List by the United States Environmental Protection Agency (EPA) in 1983.
Between 1986 and 1988, EPA excavated and removed a total of 2,314 drums from the town dump and tire locations. During the follow up Remedial Investigation/Feasibility Study, it was determined that contaminated groundwater was flowing off-site toward some nearby drinking water supply wells. Since the majority of residents in the vicinity of the site depended on bedrock wells for their water supply, EPA expedited the protection of public health by constructing a water line in 1987 to provide a new water supply to residents affected or potentially affected by site contaminants.
In 1989, EPA selected a source control action remedy to prevent contact with on-site waste materials and to minimize the additional release of contaminants into the environment by constructing multi-layered caps over each disposal area. The source control action remedy was completed in the fall of 1994.
The 1989 remedy selection also called for a management of migration action to bring groundwater quality within the State's drinking water standards utilizing groundwater extraction and treatment. Subsequent environmental monitoring data indicated that concentrations of VOCs had decreased to acceptable levels and the groundwater pump and treat action was no longer deemed necessary. EPA therefore amended the 1989 cleanup remedy to provide for institutional controls and monitored natural attenuation at the site in place of a groundwater pump and treat remedy.
Site conditions continue to be monitored and the use of groundwater for drinking purposes is prohibited until the groundwater quality has reached acceptable levels. In 2000, EPA, DES and the potentially responsible parties signed a negotiated consent decree (CD) that included a scope of work for the long-term site management plan. The CD was entered on March 10, 2000 in the US District Court for the District of New Hampshire. The CD was approved by the District Court on March 15, 2000.
The potentially responsible parties conducting the management of migration action continue to monitor groundwater, surface water and sediment at the site. Samples are collected in the spring and fall and analyzed for arsenic and VOCs.
Well installation, sampling, and data analysis activities were conducted as part of a supplemental hydrogeological investigation in the fall of 2006 at the site. The work was documented in the 2007 Annual Report for the site. In addition to the 2007 Annual Report, EPA and DES conducted a Five-Year Review of the remedial actions implemented at the site. This was the fourth Five-Year Review Report and was completed in September 2007.
DES issued a Groundwater Management Permit in the fall of 2007. The GMP establishes an area known as a Groundwater Management Zone within which it is acknowledged that groundwater is contaminated above drinking water standards and includes actions required to eventually return groundwater to drinking water standards.
In the spring of 2008, an evaluation of the site arsenic data using the Monitoring and Remediation Optimization System (MAROS) was performed to assist EPA and DES with groundwater data trend analysis and long-term monitoring optimization at the site. Evaluation of historical groundwater arsenic data for the site supports the statistical analysis of trends presented in the fourth Five-Year Review Report. These trends indicate a decrease in dissolved mass of arsenic in the overburden aquifer since landfill capping in 1994.
ata identified in the fourth Five-Year Review Report was used in the development of an updated solute transport model for the site. The upgraded model provided a better understanding of arsenic concentrations in groundwater. The model was constructed to simulate arsenic concentrations representative of both pre- and post-capping conditions and also attempted to update and establish more accurate timeframes for groundwater arsenic concentrations to reach cleanup goals for the site.
As a result of recommendations and follow-up actions noted in the fourth Five-Year Review Report, EPA issued an ESD in August 2009 to document change in the arsenic cleanup standard from 50 ppb to 10 ppb to ensure the protectiveness of the MNA remedy at the site. In February 2010 the Source Control Operations and Maintenance Report was issued to EPA and NHDES for the 2009 landfill inspections and soil gas monitoring. The report represents the completion of 15 years of O&M post-closure activities at the site.
EPA completed the fifth Five-Year Review for the site in September, 2012. Within this Five-Year Review, the EPA found that the remedy associated with the water supply line was protective of human health. The EPA found that capping of the three disposal areas to prevent direct contact with wastes and reduce flushing of contaminants through the landfill wastes is also protective of human health and the environment. Therefore, EPA determined that the current groundwater remedy, natural attenuation, was protective of human health and the environment in the short-term because no current risks are present at the Site in groundwater, surface water and/or sediments.
However, during the eighteen years since capping of the landfills was completed, there has been limited progress towards attaining cleanup levels for arsenic in groundwater. The 2009 ESD which lowered the cleanup level for arsenic to coincide with the updated MCL has also significantly lengthened the projected time to achieve site closure. Overall, the extent of arsenic contamination in groundwater at the Site has decreased, but elevated concentrations continue to persist within the overburden aquifer.
The long-term monitoring program needs to be modified to better assess water levels and geochemical conditions in the aquifer, previous modeling efforts need to be updated to determine a more accurate estimate of cleanup times, alternatives to natural attenuation need to be evaluated, and the potential vapor intrusion pathway must be evaluated. A USGS study is currently underway to characterize the hydrogeologic framework, and identify potential preferential groundwater flow paths for landfill leachate; and assess arsenic transport processes and potential geochemical reactions controlling arsenic concentrations at the site. Following completion and publication of the USGS study results, EPA and DES will meet with the Responsible Parties in 2013 to discuss the path forward for the site.