Long-term contaminant migration control by sensitive water body
ECT installed a synthetic media system at an industrial site in Massachusetts in 2011 to treat 15 gpm of contaminated groundwater. The contamination averaged 20 µg/l of 1,4-dioxane and 3,000 µg/l of chlorinated volatile organic carbon (cVOC) compounds. Though part of a larger, 100-gpm hydraulic control remedy, this treatment system has a modular design that allowed two years of operation as an interim treatment process prior to incorporation into an underground parking garage in a new apartment complex. The objectives of the treatment system are to: (1) provide long-term contaminant migration control toward a sensitive water body; and (2) learn from this smaller system in anticipation of replacing an existing 100-gpm air stripper treatment system operating closer to the source area.
Since air stripping does not remove 1,4-dioxane, a new technology had to be selected to address the suite of site contaminants and comply with treatment requirements. Synthetic media, specifically AMBERSORB™ 560, was identified as the technology more capable than other 1,4-dioxane treatment technologies to achieve operational reliability and compliance objectives. This new technology also complied with tight permit limits (1,4-dioxane less than 3.0 µg/l, that dropped to 0.3 µg/l in 2014), while simplifying the process design and reducing long-term operating costs.
The full-scale system design was based on the results of extensive bench and pilot testing. Water is pumped in an up-flow mode through media vessels operated in series, i.e. lead-lag- operation. The 1,4-dioxane and other contaminants preferentially adsorb to the media. When media capacity is reached, steam regeneration is performed in the vessel in a down-flow mode. Vessels are regenerated one at a time, leaving the remaining vessel in service to maintain continuous groundwater extraction and consistent treatment efficiency.
Contaminants consistently removed to non-detect levels
Influent 1,4-dioxane concentrations have ranged from 8 to 60 µg/l. The ECT team optimized process operations to reliably comply with the original 1.6 ug/l compliance target, and consistently achieves EPA Method 522 detection limits of 0.2 ug/l. The other contaminants, total cVOCs, have also been consistently removed to non-detect levels for the entire operating period.
The results of this first full-scale application demonstrate that synthetic media systems present a simple and more reliable alternative to advanced oxidation for 1,4-dioxane treatment, producing consistent, reliable results. The system has proven to be straightforward and easy to operate, providing predictable results over a range of treatment conditions.