Pump and Treat of Contaminated Groundwater at the Mid-South Wood Products Superfund Site, Mena, Arkansas

Site Name:

Mid-South Wood Products Superfund Site


Mena, Arkansas

Period of

Status: Ongoing
Report covers: 9/89 - 12/97


Full-scale cleanup
(interim results)


Bill Fletcher
B&F Engineering, Inc.
928 Airport Road
Hot Springs National Park, AR 71913
(501) 767-2366

Pump and Treat

- Groundwater is extracted using 15 wells, at an average total pumping rate of 24 gpm
- Extracted groundwater is treated with oil/water separation, filtration, and carbon adsorption, and discharged to a surface water under a NPDES permit

Cleanup Authority:
CERCLA Remedial
- ROD Date: 11/14/86

EPA Point of Contact:
Shawn Ghose, RPM
U.S. EPA Region 6 (6SF-AP)
1445 Ross Avenue
Dallas, TX 75202-2733
(214) 665-6782
State Point of Contact:
Mike Arjmandi
Arkansas Department of Pollution
Control & Ecology
P.O. Box 8913
8001 National Drive
Little Rock, AR 72219-8913
(501) 682-0852

Semivolatiles - halogenated: pentachlorophenol (PCP); PAHs; heavy metals (chromium); and nonmetallic elements (arsenic)

- Maximum concentrations detected during RI include PCP (10,230 mcg/L), fluoranthene (263 mcg/L), chrysene (37 mcg/L), benzo(a)anthracene (35 mcg/L), Cr (183 mcg/L), and As (18 mcg/L)

Waste Source:
Improper disposal, on-site spills

Type/Quantity of Media Treated:
- 100.6 million gallons treated as of December 1997
- DNAPL and LNAPL observed in groundwater at the site
- Extraction wells are located in 2 aquifers
- Hydraulic conductivities were not provided for this site

Purpose/Significance of Application:
Groundwater contaminated with wood treating chemicals; system optimization performed after eight years of operation; groundwater contamination had been reduced to one localized area of concern.

Regulatory Requirements/Cleanup Goals:
- The cleanup goal stated in the ROD was to treat the groundwater contamination to levels that posed no health or environmental risk. Remedial goals were specified for PCP (0.20 mg/L), benzo(a)anthracene (0.01 mg/L), benzo(a)pyrene (0.01 mg/L), benzo(b+k)fluoranthene (0.01 mg/L), chrysene (0.01 mg/L), arsenic (0.05 mg/L), and chromium (0.05 mg/L).
- The performance goal for the recovery system was to provide containment of the plume on site.

- Groundwater contamination has been reduced to one localized area of concern. Between April 1989 and May 1996, average concentrations of total contaminants in the groundwater were reduced 32%, from 0.14 to 0.09 mg/L, with concentrations of contaminants reduced to below cleanup goals in 29 of 35 wells monitored in May 1996. It is estimated that the pump and treat system will operate for a minimum of five more years to reach the specified goals.
- Monitoring data indicate that the plume has been contained. Because contamination was found along rock fractures and not in a continuous plume, plume size reduction could not be measured. During the first seven years of operation, 363 kg of PCP were removed by the system; data were not provided to estimate mass removal for other contaminants.

Cost Factors:
Estimated costs for pump and treat were $1,212,600 ($465,300 in capital and $747,300 in O&M), which correspond to $13 per 1,000 gallons of groundwater extracted and $4,510 per pound of PCP contaminant removed.

The Mid-South Wood Products site was originally developed in the late 1930s to produce untreated wood posts. In 1955, the facility added pressure treating to its process, and from 1967 to 1977, the site was operated as a PCP and creosote wood treatment facility. In 1977, the PCP plant was abandoned and a new plant was built to treat the lumber with a chromated copper arsenate (CCA) wood treating process. From 1978 to 1981, the Arkansas Department of Pollution Control & Environment sampled drinking wells near the site, investigating the source of a fish kill that occurred in November 1976. The source was ultimately determined to be an unauthorized release of wastewater from a waste pond at the site. Further contamination of the site resulted when liquids and sludge from the pond were sprayed on and around land farm areas at the site. The site was placed on the NPL in 1983 and a ROD was signed in November 1986.

An interim extraction system was built in late 1984 and operated from early 1985 until 1989. The system consisted of three pairs of extraction wells and French drains, and was designed to collect contaminated groundwater from shallow depths where flow and contamination were expected to be the greatest. An expanded extraction system, which began operating in the summer of 1989, consisted of nine shallow extraction wells and six deep extraction wells (drilled into bedrock formations at depths up to 170 ft bgs). In February 1997, three major changes were made to optimize system operations. Five recovery wells were removed from operation, five other wells began a period of on-off operation (three months on, three months off), and the sampling frequency for 12 monitoring wells was decreased. Groundwater contamination at the site has been reduced but has not yet met all remedial goals. It is estimated that the pump and treat system will operate for a minimum of five more years to reach the specified goals.