The site is located in the Valley and Ridge Physiographic province, which is underlain by folded and faulted sedimentary rocks. The Liberty Hall formation underlies the site, and consists of interbedded dark gray to black, calcareous, slatey mudstone and dark gray, medium to coarse-grained bioclastic limestone. The bedrock in this area is covered by a yellowish to reddish clay and silt that varies in on-site thickness from 6 to 15 ft.

In this area, both the bedrock and overlying clay and silt serve as water-bearing zones. In the clay and silt zones, ground water occurrence and movement are primarily through pore spaces, along relict geologic structures (saprolitic features), and in areas where deep soils have formed, along ped faces. In the bedrock, ground water flow is through secondary pore space in the form of fractures. The shallow bedrock can be deeply weathered around those fractured zones creating clay and silt zones within the bedrock. Since the overburden clay and silt zone has a relatively thin (<5 ft) saturated zone, the bioremediation efforts are primarily focused on the bedrock zone. Soil vapor extraction is being used to supplement the biremediation efforts in the clay and silt overburden.

• Fractured Bedrock

The treatment zone is a source area.

• Trichloroethene (var)
• cis-1,2-Dichloroethene (var)
• 1,1-Dichloroethene (var)
• Vinyl chloride (var)
• 1,1,1-Trichloroethane (var)
• Acetone (var)
• Isooctane (0 µg/L)

• Borehole Geophysics
  • Single Point Resistance
  • Natural Gamma
  • Caliper
• Pumping Tests
• Coring

• Soil Vapor Extraction
  • In Unconsolidated Overburden
  • In Fractured Bedrock Vadose Zone
• Bioremediation (In Situ)
  • Aerobic Oxidation

The results from the pilot testing and full scale operation of cometabolic bioremediation in a fractured bedrock setting indicate that this technology may be capable of approaching drinking water standards from initially very high VOC concentrations.

During the pilot test and subsequent full scale operation, significan reductions in the target VOCs have been observed in all monitoring wells located within the treatment area and two wells located downgradient. One well located at the former source (an underground waste solvent tank) contained the highest VOC concentrations on-site (initial average isopropanol concentrations of 5,500,00 ug/l). Recent results reported at 350,000 ug/l which is a 94% reduction.
Reductions of TCE, cis-DCE and VC were on the order of 99.9% to 99.99%.

As of February, 2004 ground water from a number of the monitoring wells contains VOCs above drinking water standards after approximately four years of system operation. This is attributed to the extremely elevated initial VOC concentrations and persistent residual source in discrete subsurface locations within this source area. Soil vacuum extraction is being used to further remove the persistent residual material. In September 2004, the VOC concentrations have reached drinking water standards in some of the monitoring wells in the source area. At other monitoring wells, the VOC concentrations are at levels consistent with off-site VOC concentrations in ground water where monitoring natural attenuation is the selected remedy.

The results have been sufficiently favorable to support application of this technology to other site source areas, given its proven ability to reduce the parent chlorinated solvents, their daughter products, acetone, and isopropanol concentrations.

In addition to the primary targeted contaminants, the average concentration of isopropyl ether prior to bioremediation amendment injection was 91 ppb. Following one year of operation the isopropyl ether concentration was reduced to 21 ppb. At the end of two years of bioremediation system operation, the isopropyl ether concentration had reduced to 10 ppb.