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: January 7, 2011

Point of Contact:
Sairam Appaji
USEPA 1445 Ross Avenue Suite 1200
Mail Code: 6SF
Dallas TX 75202-2733 
Tel: 214-665-3126 
Email: appaji.sairam@
epa.gov

Prewitt Abandoned Refinery
Prewit, NM


Hydrogeology:

The Site is located near the southwest edge of the Rio San Jose Basin. The topography of the area at the Site is typified by a linear valley floor to the north and rocky uplands to the
south. There are three major stratigraphic units at the site. These are in ascending order, the San Andres/Glorieta Formations, the Lower Chinle member, and the Sonsela Sandstone Bed. The Sonsela Sandstone Bed includes seven sandstone beds and eight partings. Two of the upper
sandstone beds have splits that have been identified. A thick continuous parting labeled the upper confining bed separates the two upper sandstones from the lower five. Claystone, shale,
and siltstone partings also occur between sandstone beds and vary in thickness and lithology across the site. Two prominent north-trending faults are identified in the western half of the site. The fault offsets are less than 40 feet, with offset decreasing higher in the stratigraphic section. Small- to medium-scale fractures are common in all stratigraphic units.

The Site is situated above two significant aquifers. The Sonsela Sandstone Bed comprises seven sandstone beds, designated A through G, each separated by claystone/mudstone partings. The uppermost sandstones are the F and G, which are separated from the E through A sandstones by the upper confining bed. Groundwater in the F sandstone is perched upon the upper confining bed and flows north according to the dip of the upper confining bed top structure, although fractures in the upper confining bed may allow fluid migration between the F and E sandstones. The A through E sandstones are separated by partings consisting of claystone, mudstone, shale and siltstone. Where present, these partings are aquitards, as they restrict but do not prevent the flow of groundwater. The preferential flow path for ground water is horizontal through the sandstone beds. A lesser amount of water flows vertically through low permeability parting.

Targeted Environmental Media:
  • - Fractured Bedrock
  • - Light Non-aqueous Phase Liquids (LNAPLs)

Contaminants:

As of 2010, the vertical and lateral extent of the plume has not been defined.

Major Contaminants and Maximum Concentrations:
  • - Benzene-toluene-ethylbenzene-xylene (BTEX) (27,000 µg/L)
  • - Benzene (3,900 µg/L)
  • - Lead (167 µg/L)
  • - Naphthalene (920 µg/L)
  • - Tetrachloroethene (100 µg/L)
  • - Trichloroethene (30 µg/L)
  • - Toluene (6,200 µg/L)
  • - Xylenes (9,600 µg/L)

Site Characterization Technologies:

No technologies selected.


Remedial Technologies:

  • - Soil Vapor Extraction
    • In Fractured Bedrock Vadose Zone
  • - Multi Phase Extraction
  • - Other (air injection in vadose zone bedrock)
Comments:
The initial system consisted of 53 dual phase (SVE/GW) pumping wells placed in source areas that started in 1996. It was designed to treat up to 5,000 gallons per day. A phase II system was initiated with batch injection of nutrients, initially at six wells, to enhance in-situ biodegradation of BTEX constituents in groundwater using a nutrient injection system. As of 1999 the system had recovered about 55,000 gallons of product.
Virtually all of the Site is owned by the Navajo Nation.

The NAPL recovery system was suspended in the early 2000s. The multiphase extraction system was suspended in 2002 because it was not functioning as expected and has not been restarted.
Remediation Goals:

Cleanup goals were set at MCLs.


Status:

During active NAPL recovery NAPL thicknesses were reduced to trace levels. The 2010 five year review found that NAPL had returned to several wells with thicknesses reach three feet.

The 2010 five year review also found Since the suspension of the active remediation system, BTEX concentrations in monitoring wells have rebounded in some wells and concentrations are significantly above remediation goals. Benzene concentrations in MW-10S, a leading edge plume well, have ranged in concentrations from 840g/L to 1,400 g/L from April 2005 to June of 2009. Since suspension of active remediation, analysis of samples collected from MW-21S, also completed in the E Sandstone Unit, report concentrations of benzene from 2,100 g/L to 3,100 g/L. It is not known how far contaminants have migrated beyond MW-10S or MW-21S.

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For more information on Fractured Bedrock, please contact:

Ed Gilbert
Technology Assessment Branch

PH: (703) 603-8883 | Email: gilbert.edward@epa.gov