Technology:
Based on site assessment results, electrical resistance heating (ERH), an in situ thermal remediation technology, was selected to treat the source area and dissolved plume at the site. The design of the system included the following: - The ERH remediation treatment area consisted of 13,040 square feet (sq ft) at the dry cleaning facility and an adjacent parking lot, located near the southern end of the shopping center.
- Electrical energy was applied over total depth intervals of approximately 4 to 31 feet below ground surface (bgs) beneath the building and 10 to 31 feet bgs beneath the parking lot.
- The ERH system included 62 electrode/vapor recovery wells, of which 19 were installed inside the building and 43 were installed outside the building. The vapor recovery wells were co-located with the electrodes.
- The electrodes consisted of 50% steel shot and 50% graphite.
- The total air extraction rate was estimated at approximately 440 standard cubic feet per minute (scfm).
- The daily energy application rate was 398 kilowatt (kW).
- Seven temperature monitoring points (TMP) were placed in the electrode field area to measure and track the subsurface temperature at multiple depths during ERH system operation.
- Vapor recovery was performed using a 40-horsepower (hp) positive displacement blower.
- Above ground treatment equipment included a condenser/heat exchanger, fan/cooling tower, condensate storage tanks, and vapor-phase granular activated carbon vessels.
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Cleanup Authority:
Virginia Department of Environmental Quality (VDEQ) Voluntary Remediation Program (VRP)
Contacts:
VDEQ Contacts
Jerry Grimes
Virginia Department of Environmental Quality
Office of Remediation Programs
629 E Main St
Richmond, VA 23219
Phone: 804-698-4207
Email: gjgrimes@deq.virginia.gov
Meade Anderson
Voluntary Remediation Project Officer
Virginia Dept. of Environmental Quality
629 E Main St
Richmond, VA 23219
Phone: 804-698-4179
Fax: 804-698-4383
E-mail: jmanderson@deq.virginia.gov
Consultants
David Fleming
Thermal Remediation Services, Inc. (TRS)
7421-A Warren SE
Snoqualmie, WA 98065
Phone: 425-396-4266
Fax: 425-396-5266
Art Taddeo
Senior Project Manager
AECOM
Technology Park Drive
Westford, Massachusetts 01886 |
Contaminants:
tetrachlorethene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), vinyl chloride, benzene |
Waste Source:
Historical operations and practices associated with the Former Woodbriar and Westwood Dry Cleaning Facility. The 2005 site investigation identified a presumed source area beneath the former dry cleaning facility; the source area was adjacent to a floor drain in the facility. |
Type/Quantity of Media Treated:
Groundwater (quantity not documented); soil (quantity not documented); and soil gas. |
Purpose/Significance of Application:
The goal of the remediation was to heat the subsurface long enough to reduce baseline concentrations of PCE and other chlorinated volatile organic compounds (CVOC) by 99.92%. The ERH system was selected based on its ability to rapidly remove the contamination mass that was leaching into the groundwater and also remove contaminants already dissolved in the groundwater. In addition, the residual heat from the process increases biological activity and natural attenuation processes that degrade CVOCs in the groundwater after the ERH system is discontinued. |
Regulatory Requirements/Cleanup Goals:
The goal of the remedial action plan was to achieve the VDEQ VRP Tier II screening levels for both soil and groundwater; these levels are consistent with unrestricted site use.
Table 1: VRP Tier II Screening Levels (AECOM 2006)
|
Compound
|
Groundwater standard (µg/L)
|
Soil standard (ug/Kg)
|
PCE |
5 |
378 |
TCE |
5 |
43.7 |
Cis 1,2-DCE |
70 |
483 |
Trans 1,2-DCE |
100 |
995 |
Vinyl chloride |
2 |
15.8 |
|
Results:
After shut-down of the ERH system on December 12, 2007, groundwater, subsurface soil, and subsurface soil gas were monitored from December 28, 2007 through June 2008. Analytical results from a pre-heating baseline sampling event in 2004 and a post-heating sampling event in June 2008 show the following:
Groundwater: - PCE, TCE, cis-DCE, and VC concentrations still exceeded the VDEQ VRP Tier II groundwater screening values for unrestricted use at several locations at the site.
- The average reduction of PCE concentration in groundwater wells located within the ERH system area was 98.8%.
- The largest decreases in PCE concentrations were observed in wells near the source area within the building.
- PCE concentrations from samples collected outside of the building ranged from 3.0 µg/L to 2,600 µg/L.
- The highest TCE concentration (98 µg/L) after treatment was detected at monitoring well located outside of the treatment zone.
- TCE concentrations within the building ranged from below detection limits (bdl) to 32 µg/L.
- Cis- 1,2 DCE concentrations ranged from 2.1 µg/L within the building to 300 µg/L outside of the building.
- There were increases in chlorides and ethenes indicating the degradation of CVOCs.
Soil- After treatment, no soils exceeded the VDEQ VRP Tier III levels and no impacted vadose soils were detected off-site.
- Residual CVOC concentrations that exceed particular VDEP VRP Tier II levels remain in some parts of the site.
Soil Gas
After treatment, the following were noted:- PCE concentrations across the total treatment area ranged from 1.9 µg/L to 32,000 µg/L.
- TCE concentrations ranged from 510 µg/L near the source area to undetected outside of the building.
- A human health risk assessment of remaining vapor concentrations indicated that the cumulative cancer risks and hazard indices at the several sub-slab gas points were above risk targets for potential on-site future residents and commercial/industrial workers via an inhalation exposure pathway.
- Indoor air concentrations indicated that the site building slab is effective in mitigating vapor intrusion from subsurface CVOCs remaining after the ERH treatment.
- Cumulative cancer risks and hazard indices indicated by soil gas samples collected off-site were below acceptable risk targets for potential on-site residents or commercial/industrial workers.
These results indicate that CVOC concentrations in several soil and groundwater samples remained above the VRP Tier II goals after ERH cleanup activities were complete. As a result, the goal of unrestricted site use had not been obtained as of the June 2008 post-treatment sampling result. |
Cost Factors:
Cost information is not available. |
Description:
The Former Woodbriar and Westwood Dry Cleaning Facility was a dry cleaning facility located on the southern portion of the Brookhill Azalea Shopping Center at 114 Azalea Avenue in Richmond, Virginia. Small spills and releases of chlorinated volatile organic compounds (CVOC) occurred during the general operation of the dry cleaning facility from about 1965 through 1995. Analytical results from the initial Phase II site investigation conducted in October 2003 indicated the presence of CVOCs in groundwater samples. As a result, the site was recommended for, and accepted into, the VDEQ VRP in June 2004. Additional sites assessments in 2005 and 2006 indicated the presence of PCE, TCE and cis 1,2-dichloroethene (cis DCE) in the soil and groundwater that exceeded Federal Maximum Contaminant Levels (MCLs). The site investigation identified a presumed source area adjacent to a floor drain located beneath the former dry cleaning facility. The dissolved CVOC plume began beneath the building footprint and moved in the direction of the groundwater flow (south and southwest of the site).
Based on site assessment results, ERH, an in situ thermal remediation technology, was selected to treat the source area and dissolved plume at the site. The ERH system would volatize CVOCs in the subsurface which would then be collected and passed through a vapor treatment system at the site. The ERH system began operation on September 22, 2006, and was shut-off on December 12, 2007. After the ERH system was turned off, the vapor treatment system continued to operate for an additional two weeks to further collect and treat any residual contaminant stream.
Post-remediation groundwater and soil monitoring were conducted from December 28, 2007 through June 2008. Results indicated that the remedial actions performed at the site achieved significant mass removal of the contaminants of concern in a time frame of approximately 1 year. Dissolved phase PCE concentrations detected in the source area were reduced by approximately 99% and the VDEQ VRP Tier II screening levels for selected compounds were attained in groundwater samples from several on-site monitoring wells. However, CVOC concentrations in several soil and groundwater samples remained above the VDEQ VRP Tier II goals after ERH cleanup activities were complete based on sampling and analysis performed in June 2008. As a result, the goal of unrestricted site use had not yet been obtained. The potential risks posed by these residual contaminants will be mitigated through institutional controls (ICs) placed at the site, including a deed restriction that limits the use of groundwater and a soil management plan. |
