Reactive Barriers are in-ground or insitu treatment systems that use specialty engineered media or bio-organisms to clean contaminated soil and groundwater. Reactive barriers can be permeable or impermeable and may use media such as iron filings, carbon, peat moss, and bacteria. Reactive barriers can be used to treat a variety of organic compounds and heavy metal contamination. The significant advantage of reactive barriers is that they can be effective without pumping, mass excavation of contaminated soil, above-ground treatment facilities or off site disposal. The installation of reactive materials can be subdivided into two categories: 1) one-time (buried) installations, and 2) replaceable (cassette) installations. The one-time installation is the case where the reactive media is simply buried in a trench. The primary design variable is the width of the reactive media and the volume required for the lifetime of the installation. Cassette installations require a permanent underground structure such as a slotted tank, large diameter manhole, or similar receiving structure. The cassette system anticipates changing the reactive media or using a sequential treatment system. Piping valves, and connections can be necessary with cassette systems so the installations are usually more complicated and costly.
The efficiency of reactive barrier installations can be significantly improved by forcing the flow of groundwater through the reactive barrier. The funnel and gate installations often use slurry cutoff walls as wingwalls to funnel groundwater into a permeable reactive barrier or gate. Slurry cutoff walls can also be used to encircle contamination and permit a single vessel of permeable reactive media inside the containment to economically treat a controlled volume of groundwater. Special bacteria or high carbon fly ash can be added to the soil-bentonite slurry cutoff wall to create an impermeable reactive barrier.
The construction of reactive barriers for buried installations can be made more economical using proven slurry trench and soil mixing methods. For permeable reactive barriers, the Bio-polymer drain method can be used to install the media without the need for dewatering, sheeting or shoring. Injecting reactive media via soil mixing can treat soil contamination in one application without excavation or other invasive methods.
INQUIP installed the first commercial permeable reactive barrier in 1994. This funnel and gate used cement bentonite and soil cement bentonite slurry walls to funnel ground water through an iron filings gate on a congested industrial site in California. INQUIP also installed the first commercial impermeable reactive barrier in 1996. A soil- bentonite slurry wall was installed containing a high carbon fly ash additive in the backfill around a sludge landfill in Michigan.