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: June 23, 2005

Point of Contact:
Karen Brody
ERM
399 Boylston St. 6th. Fl.
Boston MA 02116 
Tel: 617-646-7874 
Fax: 617-267-6447
Email: Karen.Brody@
erm.com

DNAPL Site
Boston, MA


Hydrogeology:

The surficial geology comprises fill over glacial till. The sandy fill has an estimated thickness of 0 to 15 ft. Inspection of split-spoon samples from the till indicated a series of high angle fractures throughout the deposit. The fractures act as planes of weakness upon which the till is easily broken apart.

Bedrock include diorite, gabbro, basalt and schist.

Targeted Environmental Media:
  • - Dense Non-aqueous Phase Liquids (DNAPLs)
  • - Fractured Bedrock

Contaminants:

The original release migrated through the till along fracture planes to the bedrock surface, where its lateral migration appears to have been largely restricted to a bowl-shaped bedrock depression. Residual TCE DNAPL then migrated into bedrock fractures and appears to have been largely restricted to shallow bedrock, due to the high competency and low yield of the bedrock.

The primary pathway for the dissolved phase TCA migration is generally downward via advective flow through bedrock fractures into deeper bedrock. The primary porosity of the rock is estimated at 0.5 percent. Thus, the bedrock aquifer consists of the interconnected secondary porosity.

Major Contaminants and Maximum Concentrations:
  • - 1,1,1-Trichloroethane (250,000 µg/L)

Site Characterization Technologies:

  • - Borehole Geophysics
    • Other (Unknown geophysical imaging)
  • - Other (FLUTe liners)

Comments:
The results from the FLUTe liners showed that DNAPLs were located at fracture zones that were indicated in geophysical imaging.


Remedial Technologies:

  • - Thermal Treatment (In Situ)
    • Radio Frequency Heating
  • - Soil Vapor Extraction
    • In Fractured Bedrock Vadose Zone
Comments:
The treatment system includes a network of nine, 100-foot deep, eight-inch diameter boreholes, an RF generator, a four-probe transmitter array, and an SVE system for control and treatment of vapors. The target ground-water treatment temperature is 50 to 60 degrees Celcius. Start-up took place in December 2003 and the power output reached a maximum of 18.9 kilowatts.

Monitoring data collected after the first six months indicated that elevated ground-water temperatures were measured over an area of approximately 2,000 square ft. The maximum ground water temperature measured has been 45 degreesC. Based on the ground-water temperature monitoring, each RF antenna has a radial heating influence of approximately 15 ft. Measurements of downhole electric field intensity show that the effective vertical radiation interval is approximately 15 ft. Therefore, the total treatment volume using four antennae is estimated at 30,000 cubic ft.

The average TCA concentration in and adjacent to the treatment area has decreased from 115,000 micrograms per liter to 24,000 ug/l following six months of treatment , an estimated decrease of 79%. Both abiotic and biotic degradation are occuring.

In June 2005, average TCA conc. decreased 92% in the treatment zone, and DCE decreased 61%. Two hundred and fifty feet downgradient of the source TCA conc. decreased 69% and DCE decreased 43%. This was reported in the Eighth International In-Situ and On-Site Bioremediation Symposium, June 5-9 in Baltimore.
Remediation Goals:

This was source zone treatment and adjacent ground-water treatment levels have not been established yet.


Status:

The RF heating system has been operational for 17 months. The maximum ground water temperature achieved was 52 degrees - 2,000 sq. ft. at a depth of 50 ft.

Top of Page