- Pump and treat using a permeable reactive treatment cell
- Three extraction wells are being used to remove groundwater at the site. The system extracts an average of 3 gallons per minute
- The Tacony Treatment Cell or TTC is located near the monitoring well with the highest VOC concentrations (MW-9). The TTC is four feet in diameter and is filled with 22 tons of zero-valent iron filings around a four-inch diameter extraction well. The thickness of the iron filings layer was calculated to provide a 10 hour detention time
- Zero-valent iron reacts with the chlorinated hydrocarbons to form less-chlorinated and non-chlorinated hydrocarbons
- EW-1 and EW-2 are six-inch extraction wells with no reactive media. They were located to influence the hydraulic capture zone
- Extracted groundwater is discharged to the City of Philadelphia sanitary sewer system
CERCLA and State
Record of Decision (ROD) signed on July 21, 1995
USACE, Baltimore District
10 S. Howard Street
Baltimore, MD 21201
|Points of Contact:|
US EPA, Region 3
1650 Arch Street
Philadelphia, PA 19103-2029
Lee Park Suite 6010
555 North Lane
Conshohocken, PA 19428
- 4,214 µg/L PCE
- 579 µg/L TCE
- 2,800 µg/L cis -1,2-DCE
- 64.6 µg/L trans-1,2-DCE
- 2,000 µg/L vinyl chloride
The source of chlorinated solvents in the groundwater is not known.
Type/Quantity of Media Treated:
Before treatment began, an area in the vicinity of MW-9 was contaminated in addition to an area approximately 300 feet downgradient of MW-19
During the first year of operation, approximately 1.8 million gallons were extracted from the aquifer beneath the site, of which 393,165 gallons were treated by the TTC
The contaminated aquifer is between 8 and 35 feet below ground surface (bgs). The aquifer can be described as heterogeneous and anisotropic, with hydraulic conductivities ranging from 2.3 to 29.4 gal/day/ft2
Purpose/Significance of Application:
This project demonstrates that an extraction well that is surrounded by permeable reactive media (iron filings) is a viable treatment alternative at sites contaminated with chlorinated solvents.
Regulatory Requirements/Cleanup Goals:
- PADEP established the groundwater remediation goal of achieving background levels, which are based on the analytical quantitation limits of EPA SW-846 Test Method 8240. The remediation targets are 5 µg/L for PCE, TCE, and DCE and 10 µg/L for vinyl chloride
- The City of Philadelphia does not allow water to be discharged to the sewer system at concentrations exceeding 2.13 mg/L of total toxic organics
- The TTC is demonstrating conversion of PCE and TCE to less-chlorinated hydrocarbons when compared to untreated groundwater at MW-9, which is located approximately 15 feet away. PCE and TCE were not detected at the TTC, however, intermediate reaction products (cis-1,2-DCE and vinyl chloride) were observed
- Three of the six target monitoring wells are meeting the remedial standards and a fourth well met the standards in April 1999 but exceeded these levels in June 1999
- The sewer discharge meets the City of Philadelphia limit on total toxic organics
The total project cost was $607,336, which includes the capital costs ($416,777), one year of operation and maintenance ($16,880), and other related costs ($132,417).
The TW site is located on 14.2 acres of land adjacent to the Delaware River in northeast Philadelphia. The site was constructed and established as an armor plate assembly facility in 1943. The site was used for warehousing operations from the 1950s through 1992, when the site was vacated. During this time, there were several periods of inactivity and numerous changes in accountability for the site.
Site investigations at the TW site indicate that the groundwater in several areas is contaminated with chlorinated solvents and that soil contamination around MW-9 may be a potential ongoing source of contamination. Use of barriers constructed from zero-valent iron has been demonstrated to be an effective treatment method at other sites contaminated with chlorinates solvents. At TW, groundwater in the vicinity of MW-9 is drawn through a bed of iron filings surrounding an extraction well. As the groundwater passes through the bed, it is treated through reductive dehalogenation reactions. The treated water is combined with untreated groundwater from two other on-site extraction wells and is discharged to the city sanitary sewer.
Results from the first year of operation indicate that reductive dehalogenation reactions are occurring, but not to completion. Permeable reactive extraction wells are applicable for many sites, especially where contamination is migrating off-site. In these cases, the hydraulic control provided by pumping may be necessary or the installation of an interceptor wall may not be feasible. Permeable reactive extraction wells have advantages over traditional pump-and-treat systems in that treatment occurs in situ, so above-grade structures are not required. This may be desirable for sites subject to vandalism or sites that are highly visible.