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SIX YEARS OF INTENSIVE MONITORING OF THE 1ST PRB TO TREAT A MIXED WASTE PLUME: USCG SITE IN ELIZABETH CITY, NC
Citation:
Puls*, R W., R T. Wilkin*, C J. Paul*, F P. Beck*, P J. Clark*, AND M S. McNeil*. SIX YEARS OF INTENSIVE MONITORING OF THE 1ST PRB TO TREAT A MIXED WASTE PLUME: USCG SITE IN ELIZABETH CITY, NC. Presented at RTDF Meeting, Washington, DC, 11/6-7/2002.
Description:
Permeable reactive barriers (PRBs) for the restoration of contaminated ground water are no longer innovative. PRBs have evolved from innovative to accepted, standard practice, for the containment and treatment of a variety of contaminants in ground water. Like any remedial technology, the decision to use PRBs will be conditioned by the nature of the natural system, the target contaminants, and treatment objectives. In the past 6 years, more than 60 sites have implemented this technology to treat chlorinated solvent compounds, fuel hydrocarbons, and various inorganic contaminants in ground water. The USCG site near Elizabeth City, North Carolina, used PRB technology to address a mixed waste plume (chromate and chlorinated solvent compounds) emanating from a chrome plating shop located within hangar 79 on the base. A continuous wall composed of 100% Peerlessa iron was installed using a deep trenching machine in June,1996. The wall is about 150 feet long, extends to about 24 feet below ground surface and is about 2 feet thick.
After six years of intensive monitoring at the site (>150 discrete sampling points), the wall has contained the chrome plating shop plume and has successfully removed chromate to much less than target levels (<0.10 mg/L). There has been consistent degradation of all contaminants over 6+ years. Geochemical parameters, which are monitored in addition to contaminant concentrations, have changed little over this time period. There has been some change in plume dynamics and configuration over time and this will be discussed. In addition to the chrome plating shop plume there is evidence of another plume, largely composed of chlorinated solvent compounds. This plume is distinct and appears to have a different source. There may be more than one. Nonetheless, these compounds are removed to less than target levels (maximum contaminant levels or MCLs set for ground water quality) where they enter the wall in the vast majority of in-wall and down gradient sampling locations, and no changes in removal behavior have been observed over 6+ years. Research has also been conducted on long-term performance of the wall in terms of inorganic precipitate accumulation within the wall and microbial activity changes since wall installation. This work will be presented in a separate presentation