Installation Date:
1999

Contaminants:
Tetrachloroethene, Trichloroethene, 1,1,1-Trichloroethane, 1,2-Dichloroethane, 1,1-Dichloroethene, Dichloromethane, Benzene-toluene-ethylbenzene-xylene (BTEX)

Reactive Media:
Fe⁰

Cost:
$940,000

Construction:
Funnel and Gate

Point of Contact:
Peter Kjeldsen
Technical University of Denmark
Tel: +45 45251561
Fax: +45 45932850
Email: pk@er.dtu.dk
Environmental & Resources DTU
Building 115
DTU, DK-2800
Kgs. Lyngby Denmark

A full-scale permeable reactive barrier (PRB) system was installed in 1999 to remediate ground water at Vapokon Petrochemical Works, a solvents recycling factory, in Søndersø, Denmark. The factory used distillation and other processes to purify used solvents containing chlorinated aliphatic, mainly perchloroethylene (PCE), trichloroethylene (TCE), and benzene, toluene, ethylbenzene, and xylene (BTEX). The main spill area was an open underground concrete tank, from which the used solvents were transferred from drums. The unsaturated zone and aquifer contain mainly PCE, TCE, trichloroethane (TCA), 1,2-dichloroethane (DCA), dichloroethylene (DCE), dichloromethane (DCM), and BTEX. The maximum concentration of any single chlorinated compound is 5,000 µg/L. Ground-water chemistry in the plume is anoxic, probably the result of oxygen consuming compounds, such as BTEX.

The soil at the site contains a 12-ft layer of loam and soil fillings, below which is a water-saturated sandy aquifer approximately 30 ft thick. The clay layer below the aquifer has a minimal thickness of 50 ft. The ground water flows toward a nearby rain water pond at a velocity of 3.6-4.5 ft/day and from there to a creek.

The PRB system consists of a funnel and gate and was made using sheet piling. It contains a reactive zone of 105-yd³ Fe⁰ and 45 screens. The funnel is 400 ft long. The PRB is 50 ft long, 30 ft deep, and 2 ft thick. The basic PRB design was chosen mainly due to cost and the availability of construction techniques in Denmark. Because of the site's high ground-water velocities, an upstream drainage system was incorporated into the design to reduce the natural ground-water flow velocity through the PRB to about 1,300 ft/day. Leaking of the sheet piling, which occurred while constructing the PRB, led to expensive lowering of the ground-water table and treatment of the pumped ground water in granular activated charcoal filters. The design cost was $240,000, and the installation cost was $700,000.

Several wells and piezometers are used to monitor the removal efficiency of the barrier system. For a figure showing the location of the monitoring wells at this site, see "More Information" at the end of this profile. The wells were sampled in 2000 and analyzed for chlorinated compounds, including their degradation products, and for BTEX and inorganic components as well. Slug tests were used to evaluate the permeability of the aquifer and the barrier material.

The results showed that most compounds were degrading at expected rates and that the system was achieving the goal of decreasing concentrations of chlorinated solvents below 10 µg/L. In addition, concentrations of some daughter products (DCA and DCM), which were not expected to transform in the column, were low probably, because they were degrading naturally in the anoxic plume. The reduction of BTEX concentrations may have been due to microbial reactions coupled to abiotic reactions. They were not believed to be a result of the iron particles. The inorganic analysis showed a reduction in ionic strength of the water passing through the PRB.

Concentrations at the upgradient side of the PRB for the chlorinated compounds increased over time. This change may have been due to the lower ground-water velocities introduced by the drainage system upstream of the site. Sampling will occur every six months in 2001 and probably once a year thereafter.

SITE-SPECIFIC REFERENCES

MORE INFO