EVAPOTRANSPIRATION, MIST EVAPORATORS AND BASE INJECTION; INNOVATIVE ALTERNATIVES TO PUMP AND TREAT

During the early to mid 1990s the Department of Energy (DOE) constructed and planned implementation of several pump and treat systems at the Savannah River Site (SRS). The pump and treat systems involving VOCs are the simplest and most successful, systems involving radionuclides and metals are the most complex and least successful. Generally the DOE has learned that pump and treat systems are more expensive to operate that originally planned and must operate for longer periods of time than expected. Because of these issues the DOE complex as a whole has been looking for other alternatives to pump and treat.

Evapotranspiration is being used at the Savannah River Site to manage the release of tritiated and VOC contaminated groundwater to a tributary of the Savannah River. Specifically, contaminated groundwater that discharges to seeplines along Fourmile Branch is collected behind a sheetpile dam, and is dispositioned using land application techniques. The sheetpile collection system has proven to be successful in reducing tritium flux to the branch by 75%. Irrigation of a 22 acre mixed pine and hardwood forest has effectively transferred approximately 80% of the contaminated water to the atmosphere.

Low energy misting evaporators are being considered to further disposition tritiated water and VOCs at the SRS. Misting evaporators that employ high efficiency blowers and misting nozzles are planned for use during the winter months when transpiration is low. These evaporators will maximize the evaporative losses by using the sensible heat in the atmosphere. Misting evaporators are also being considered as a low cost highly effective alternative to VOC air strippers.

Base injection techniques are being tested as a method of controlling metals contamination in acidic plumes. Acid plumes are present in several areas of the site where nitric acid was discharged to seepage basins and pits. The acid conditions mobilize naturally occurring metals and radionuclides, as well as metals and radionuclides that were present in the acidic releases. A large-scale test involving the injection of 4 million gallons of liquid base is being performed as an alternative to pump and treat systems.

Innovative technologies are an important component of the SRS environmental restoration program. Innovation is critical to cost effective remediation.