| Site Type: Long Term/National Priorities List (NPL) |
Map this site in Cleanups in My Community
| Nashua,  New Hampshire|
| Hillsborough County
| Street Address: ||GILSON RD |
| Zip Code: || 03062 |
| Congressional |
| EPA ID #: ||NHD099363541 |
| Site ID #: ||0101115 |
| Site Aliases: ||Gilson Road Site|
| Site Responsibility: ||Federal, State |
| NPL LISTING HISTORY |
| Proposed Date ||10/23/1981|
| Final Date ||09/08/1983 |
The 28-acre Sylvester hazardous waste dump site is located in a rural, residential area of Nashua, New Hampshire. The site was operated as a sand borrow pit for an undetermined number of years. During the late 1960s, after much of the sand had been removed from the property, the owner began an illegal waste disposal operation within a six-acre portion of the site apparently intending to fill the excavation. Household refuse, demolition materials, chemical sludges, and hazardous liquid chemicals were dumped at the site. The household refuse and demolition materials usually were buried, while the hazardous liquids were allowed to percolate into the ground adjacent to the old sand pit or were stored in steel drums that were placed on the ground. Approximately 1,000 people live in an adjoining mobile home park. The site is adjacent to Lyle Reed Brook, which flows through the trailer park and enters the Nashua River, a source of drinking water. The Merrimack River is 11 miles downstream and is also a source of drinking water.
Threats and Contaminants
The illegal waste disposal activity at the site was first discovered in late 1970. The first indication that liquid hazardous wastes were being dumped occurred in 1978, when State personnel observed drums being stored at the site. Prior to 1979, the site operator discarded refuse and demolition debris in the mined portion of the site. In 1979, available information shows that approximately 1,300 55-gallon drums containing hazardous waste material were disposed at the site. Records discovered during investigation at the site also indicate that over 800,000 gallons of liquid hazardous wastes were discharged into a leach field at the site between January and October 1979. A court order was issued in late 1979 prohibiting all future disposal of hazardous wastes on the site.
EPA and the State have performed cleanup actions to contain and treat contaminated soils and ground water at the site. Barriers to prevent access to the site and to abate the migration of contaminated ground water have also been installed.
Response Action Status
|Immediate Actions ||In 1979, the State removed 1,000 drums from the site. In early 1980, the EPA built a fence around the disposal area and removed 1,314 accessible drums found at the surface. The movement of the ground water contaminant plume was monitored and an access road was built. Between 1981 and 1982, the EPA installed a ground water interception and recirculation system to temporarily pump and recirculate the contaminated ground water to prevent it from reaching Lyle Brook and from further contaminating the aquifer. The City of Nashua extended municipal water to the area surrounding the site in 1983. |
|Slurry Wall/Cap ||The State built a slurry wall surrounding a 20+ acre area and an impervious membrane cap to prevent any further migration of the contamination to on-site ground water. In May 2014, EPA's Ada, Oklahoma lab released a report evaluating the effectiveness of the wall after 30 years of use. That report found the cap and slurry wall were still functioning as designed. |
|Ground water Treatment ||In 1986 the State built a treatment facility to remove toxic substances in the ground water within the slurry wall. The 300-gallon-per-minute treatment process consisted of a combination of physical, chemical, and biological treatments. The process involved pumping the ground water from within the slurry wall containment area and treating it via filtration and air-stripping to remove contaminants. The contaminants were then destroyed by incineration. The treated water was injected into the aquifer to control ground water migration. |
In addition, a vacuum extraction system was installed to clean up the large amounts of toluene in the ground water and soils in the southern portion of the site.
Active ground water treatment was completed in early 1996 after the EPA and State determined that the concentration of contaminants in ground water were below the cleanup levels established in the selected cleanup remedy. During the ten year period of operation, the treatment plant handled nearly 1 billion gallons of water and removed and destroyed over 216 tons contaminants from the ground water. The State is continuing to perform periodic monitoring at the site.
|Sediment Assessment ||In 2005, a limited area was found to contain arsenic-contaminated sediments in a stream/wetlands area adjacent to the capped area of the site. Subsequent sampling has found that the concentrations in the sediments warrant continued monitoring but that no immediate action is required. The State has posted the area to inform the public of the potential exposure to this limited sediment area. |
|Institutional Controls ||In October 2013 the City of Nashua changed the area of groundwater use restrictions at and near the site by increasing the northern extent of the restrictions based on the occurrence of arsenic in groundwater. This change was done in conjunction with the neighboring Four Hills Landfill. |
|Enforcement Highlights||Several Consent Decrees were entered into by the EPA, the State, and numerous potentially responsible parties requiring the reimbursement of past costs and the implementation of the cleanup actions at the site. |
Construction of all cleanup remedies at the site have been completed. Removing the drums, installing a fence, supplying public drinking water, capping the 20+ acre disposal area and enclosing it with a 100-foot deep slurry wall and pumping-and-treating ground water for 10-years have reduced the risk of exposure to hazardous materials at the site. In September 2014, the fifth Five Year Review for the site was performed, and it was determined to be protective of human health and the environment. Groundwater monitoring will continue to ensure the continued effectiveness of the cleanup.
Current Site Status
In early 2000, the New Hampshire Department of Environmental Service (NHDES) implemented institutional controls on the property to ensure that the ground water would not be used. During 2009, monitoring of the groundwater continued at and surrounding the site. Sporadic exceedences of the cleanup levels have still been observed; however, the ground water at or near the site is not being used for drinking water purposes and municipal water is provided to the surrounding area. Ground water monitoring will continue by the State on a periodic basis (expected to be annual monitoring). An Explanation of Significant Differences (ESD) was signed by EPA in September 2002 which documents an adjustment to the alternative cleanup limits (ACLs) for two groundwater contaminants at the site.
EPA issued a fifth Five-Year Review on September 4, 2014. That Five-Year Review found the Site to be protective of human health and the environment in the short-term, and made the following findings:
1. The State of New Hampshire Department of Environmental Services (NHDES) has conducted remedy implementation, and operation and maintenance activities in accordance with all applicable decision documents.
2. Extending the water supply line to the nearby residents in 1983 continues to be protective of human health.
3. The Alternative Cleanup Levels (ACLs) for the Contaminants of Concern (COCs) have been met except for chlorobenzene. Chlorobenzene slightly exceeds the ACL in 2 wells within the slurry wall and 3 wells immediately adjacent to, but outside of, the slurry wall.
4. Other Contaminants of Concern (OCOCs) have emerged since the ACLs were established. These OCOCs are arsenic and 1,4-dioxane. The concentrations of these OCOCs in groundwater, both inside and outside the slurry wall, exceed criteria set for drinking water (i.e., AGQS’s and MCL’s) that may pose a human health risk, but the waterline and recent groundwater use restrictions by the City of Nashua for this area have addressed this potential current risk.
5. Low concentrations of volatile organic compounds in groundwater immediately outside the slurry wall do not pose a potential exposure to indoor air in homes surrounding the Site using the EPA and NHDES protocols.
6. Arsenic occurs in sediments in Lyle Reed Brook. An assessment of aquatic life in Lyle Reed Brook indicates that although arsenic in sediments are elevated, there is no demonstrated effect to biota.
7. During the Site inspection for this Five-Year Review, EPA and NHDES found additional areas of stained sediment where groundwater breaks out, indicating the potential for additional arsenic-contaminated sediments. Further sediment sampling is required to determine if arsenic is present.
8. The Institutional Controls in the form of a municipal ordinance, approved in October 2013 by the City of Nashua, for groundwater, and warning signs for Lyle Reed Brook are in place and in compliance. At this time, no one is currently using groundwater.
9. A study by EPA’s Ada, Oklahoma lab has found that the 30-year old cap and slurry wall are still functioning as designed for the hydraulic containment of contaminants.
10. The containment and groundwater remedies are protective of human health and the environment in the short-term but not in the long-term.
The former Treatment Plant building from the North (on top of the capped area).
Looking north towards the trailer park and Nashua River from on top of the capped area.
Links to Other Site Information
Newsletters & Press Releases:
Federal Register Notices:
Reports and Studies:
|Five Year Review Report, September 22, 1994 (251 KB)   |
|Second Five Year Review Report, September 30, 1999 (923 KB)   |
|Third FiveYear Review Report, September 17, 2004 (506 KB)   |
|Fourth Five Year Review Report, September 14, 2009 (Initial file is 23.7 MB with link to additional PDF)   |
|Final Report: Technical Assistance for the Gilson Road Superfund Site, Nashua, New Hampshire - MAROS Evaluation, September 2009 (2.55 MB)   |
|Fifth Five Year Review Report, September 4, 2014 (2.41 MB)   |
New Hampshire Department of Environmental Services, 29 Hazen Drive, Concord, NH 03302
OSRR Records and Information Center, 1st Floor, 5 Post Office Square, Suite 100 (HSC), Boston, MA 02109-3912 (617) 918-1440
|EPA Remedial Project Manager: ||Darryl Luce |
|Address: ||US Environmental Protection Agency|
5 Post Office Square, Suite 100
Mail Code OSRR07-1
Boston, MA 02109-1367
|Phone #: ||617-918-1336 |
|E-Mail Address: ||firstname.lastname@example.org |
|EPA Community Involvement Coordinator: ||Rodney Elliott |
|Address: ||US Environmental Protection Agency|
New England Regional Laboratory
11 Technology Drive
Chelmsford, MA 01863-2431
|Phone #: ||617-918-8372 |
|E-Mail Address: ||email@example.com |
|State Agency Contact: ||Michael Summerlin |
|Address: ||NHDES 29 Hazen Drive, PO Box 95|
Concord, NH 03302-0095
|Phone #: ||603-271-6778 |
|E-Mail Address: ||firstname.lastname@example.org |