Subsurface Treatment for Arsenic Removal

Subsurface treatment for arsenic removal (STAR) is an innovative technology for treatment of arsenic in groundwater at the wellhead. The STAR technology can result in large cost savings when compared with conventional above-ground treatment methods. The goal is to create a subsurface biogeochemical barrier composed of reactive iron hydroxide minerals and iron bacteria within the aquifer surrounding a water-supply well. Following emplacement of the geochemical barrier, the well will yield water that will meet or exceed the arsenic drinking standard of 10 ppb. The primary objectives of the Phase I research project are to: (1) demonstrate practical methods to achieve arsenic sequestration by increasing dissolved oxygen concentrations in the aquifer; and (2) develop diagnostic tools for assessing the performance and design of systems in varied hydrogeologic settings. The STAR technology stems from a baseline re-engineering of the proven and commercially available technology developed by Subsurface Technologies, Inc., for the in situ treatment of dissolved iron and manganese. This research project builds on what has been learned about subsurface iron and manganese removal and will adapt these principles to removal of dissolved arsenic. The two primary approaches for modification of geochemical conditions within an aquifer surrounding a water-supply well are: (1) creation of an oxidizing zone around the well through installation of a ring of air diffuser wells; and (2) alternating injection and withdrawal of oxygenated water at the production well itself (push-pull). During Phase I, Daniel B. Stephens & Associates, Inc., proposes to test the STAR technology at an existing water-supply well that currently exceeds the U.S. Environmental Protection Agency drinking water standard for arsenic. The proposed research plan addresses all relevant parameters, including geochemical reaction rates, aquifer heterogeneity, and groundwater residence time within the treatment zone. Subsurface arsenic treatment offers significant advantages over conventional above-ground treatment technologies. Unlike conventional treatment plants, the capital costs associated with construction of above-ground facilities are not incurred. Furthermore, the proposed technology generates little or no waste. In contrast, conventional above-ground arsenic treatment plants continuously generate large volumes of waste sludge, brine, or spent treatment media requiring disposal. With the STAR technology, naturally occurring arsenic is left below ground in the aquifer, and no arsenic-bearing wastes are generated. Finally, unlike conventional treatment plants, the STAR technology does not require a skilled operator to maintain the system. The researchers believe these advantages will be particularly important for small community water systems providers.