U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Fractured Bedrock Project Profiles

Last Updated: December 31, 2010

Point of Contact:
Byron Mah
USEPA 5 Post Office Square, Suite 100
Mail Code OSRR07-1
Boston MA 02109-3912 
Tel: 617-918-1249 
Email: mah.byron@
epa.gov

Auburn Road Landfill
Londonberry, NH


Hydrogeology:

The Site is underlain by glacial overburden which overlies the bedrock. The glacial deposits are predominantly thick outwash deposits which overlie a discontinuous basal till unit. The outwash deposits are predominantly well-graded sand and gravel which range in thickness from 0 feet (ft) in the southern portion of the Site (i.e., south of the landfills); and generally thicken northward where they are approximately 75 ft thick north of the Site in the vicinity of Whispering Pines
Pond. Where present, the discontinuous till is up to 20 ft thick and consists of sand, gravel, silt, and clay mixtures.

Locally, bedrock underlying the Site consists of an un-named member of the Berwick Formation which is similar in composition but contains more calc-silicate (up to 15%) than the remainder of the Formation. A thin band of the late Devonian two-mica granite (part of the New Hampshire Plutonic Suite) trending northeast-southwest is encountered in the southern portion of the Site and is similar to the Concord Granite. Bedrock classifications from four bedrock core logs (B 301A, B 302A, B 303A, B 304A) retrieved in 1992, indicate that the site is underlain by gneiss, pegmatite, quartzite, schist, breccia, and mylonite.

Groundwater at the Site occurs in two hydrogeologic units: the overburden and the bedrock aquifers. The overburden aquifer consists of the saturated portions of the outwash and discontinuous till units. Groundwater flow within the overburden aquifer is consistently towards the north and northwest. Hydraulic conductivities within wells in both the outwash deposits and the till vary from approximately 0.1 to 140 ft per day. Groundwater flow within the bedrock aquifer is consistently towards the north and northwest.

Targeted Environmental Media:
  • - Fractured Bedrock

Contaminants:

The main plume is approximately 720 feet at its widest and 2,400 feet long.

Major Contaminants and Maximum Concentrations:
  • - Arsenic (494 µg/L)
  • - Vinyl chloride (82 µg/L)
  • - 1,2-Dichloroethene (330,000 µg/L)
  • - 2-Butanone (MEK) (12,000 µg/L)
  • - Trichloroethene (1,600 µg/L)
  • - Tetrachloroethene (8,500 µg/L)
  • - Benzene (12 µg/L)
  • - Toluene (6,500 µg/L)

Site Characterization Technologies:

  • - Coring

Remedial Technologies:

  • - Other (Monitored Natural Attenuation)
Comments:
The original 1989 ROD called for pump and treat. However, this was amended in 1996 to MNA when it was found that all of the organic contaminant concentrations had dramatically fallen and the arsenic plume was stable.
Remediation Goals:

The cleanup goals were MCLs.


Status:

The 1996 Amended ROD incorporated the interim groundwater cleanup levels established in the 1989 ROD. However, all of the contaminants of concern except one (arsenic) were either no
longer found or were confined to a single well, MW-102A, which directly abuts the Old Town Landfill. Trans 1,2 dichloroethylene, 2-butanone, toluene and lead were all an order-of magnitude
or greater below their cleanup levels.

Long term monitoring for arsenic continues. The concentrations are trending downward albeit slowly.

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