pH is near neutral ranging from approximately 6 to 8.

A large impacted area contains three distinct groundwater plumes. The largest plume is dominated by selenium. The second plume is primarily arsenic, with lesser selenium. The smallest plume contains both selenium and arsenic. Primary Selenium Plume pH is near neutral, typically ranging from approximately 6 to 8. Oxidation-reduction conditions are generally oxic near the surface throughout most of the plume, except in wetland areas. At depth, redox conditions are generally suboxic to sulfidic. The maximum dissolved selenium concentration in groundwater at the source has fluctuated between approximately 5,000 and 24,000 µg/L. At the source, dissolved arsenic is generally immobile. It is present in groundwater at depth, but current transport is limited, likely due to oxidizing conditions. Historically, transport of arsenic to depth was likely driven by dense, acidic solutions. Dissolved arsenic concentrations at the source typically range from 600 to 1,000 µg/L. Downward hydraulic gradients and pumping from deep wells have driven both lateral and vertical migration of the selenium plume. Recent measurements show dissolved selenium concentrations above action levels at elevations as low as approximately 3,600 ft amsl, with concentrations of about 150 to 400 µg/L. At elevations between 3,750 and 3,800 ft amsl, concentrations range from approximately 900 to 1,200 µg/L. At elevations between 3,900 and 4,000 ft amsl, concentrations range from about 400 to 3,000 µg/L. Dissolved arsenic concentrations exceeding action levels have also been detected at depths corresponding to approximately 3,600 ft amsl beneath the source area. Ground surface elevation in the source area is approximately 4,350 ft amsl, decreasing to approximately 4,200 ft amsl toward the downgradient extent of the plume. Primary Arsenic Plume Current groundwater pH is near neutral, generally between 6 and 7. Historically, the central portion of the plume may have had pH values below 6. Since the early 1990s, pH has increased in select monitoring wells. Redox conditions are not well characterized. Dissolved arsenic concentrations in groundwater have steadily declined since the early 1990s. Peak concentrations were as high as approximately 20,000 µg/L. Active groundwater extraction began around 2000. Current maximum arsenic concentrations are typically between 1,000 and 2,000 µg/L. This plume is generally shallow. Source material is likely present as solid-phase contamination, and transport to groundwater appears to occur primarily through leaching rather than migration of aqueous solutions. Groundwater extraction has likely induced deeper migration than would have occurred under natural conditions. The extraction well is screened to approximately 130 ft below ground surface (bgs). In most areas, elevated arsenic concentrations are observed between about 40 and 60 ft bgs. At one location, elevated arsenic has been detected at approximately 160 ft bgs. Within this plume, dissolved selenium concentrations are generally much lower, typically ranging from 50 to 100 µg/L. However, near the extraction well, selenium concentrations have increased in recent years to between approximately 1,000 and 2,000 µg/L. Mixed Selenium and Arsenic Plume Releases of acidic solutions have resulted in transport of both selenium and arsenic to groundwater. Current pH conditions are near neutral (approximately 6 to 7). Historically, localized zones of acidic groundwater have occurred, particularly following release events. pH values below 1 were measured in multiple wells in the past. In one area following a release, pH was measured at approximately 3.5. In both cases, pH returned to near-neutral conditions over a period of roughly 10 years. Redox conditions are not well defined. Groundwater with elevated dissolved selenium is typically found within approximately 50 ft bgs, while groundwater with elevated dissolved arsenic is generally present within about 80 ft bgs. Recent dissolved selenium concentrations range from approximately 50 to 300 µg/L, while dissolved arsenic concentrations range from approximately 10 to 30 µg/L.

Regarding molecular modeling of selenium-selective sorbents, this is conceptually interesting given the co-occurrence of selenium and arsenic. However, from our perspective, interest would depend on how directly the work translates into field-deployable and demonstrably effective treatment media under site-relevant conditions (e.g., near-neutral pH, variable redox, and elevated concentrations). At present, our focus is on technologies with established performance in similar settings. We would be open to learning more if you have examples of applied or field-demonstrated outcomes.

Potentially of interest as a supplemental monitoring tool, particularly for high-frequency or real-time data collection in dynamic areas (e.g., wetlands). However, regulatory compliance monitoring would still rely on established analytical methods.

Yes, we would be interested in supporting a targeted, small-scale study to assess and validate a selenium transformation/immobilization approach. That aligns well with the intent of this Partnering Request. At this stage, we are looking for proposals that: Clearly articulate the technical concept and underlying mechanism, and Outline a focused study scope that demonstrates the feasibility and potential for scale-up and field application We view the initial effort as a way to evaluate whether the approach shows enough promise to warrant further development and potential larger-scale implementation.

A large impacted area contains three distinct groundwater plumes. The largest plume is dominated by selenium. The second plume is primarily arsenic, with lesser selenium. The smallest plume contains both selenium and arsenic. Primary Selenium Plume pH is near neutral, typically ranging from approximately 6 to 8. Oxidation-reduction conditions are generally oxic near the surface throughout most of the plume, except in wetland areas. At depth, redox conditions are generally suboxic to sulfidic. The maximum dissolved selenium concentration in groundwater at the source has fluctuated between approximately 5,000 and 24,000 µg/L. At the source, dissolved arsenic is generally immobile. It is present in groundwater at depth, but current transport is limited, likely due to oxidizing conditions. Historically, transport of arsenic to depth was likely driven by dense, acidic solutions. Dissolved arsenic concentrations at the source typically range from 600 to 1,000 µg/L. Downward hydraulic gradients and pumping from deep wells have driven both lateral and vertical migration of the selenium plume. Recent measurements show dissolved selenium concentrations above action levels at elevations as low as approximately 3,600 ft amsl, with concentrations of about 150 to 400 µg/L. At elevations between 3,750 and 3,800 ft amsl, concentrations range from approximately 900 to 1,200 µg/L. At elevations between 3,900 and 4,000 ft amsl, concentrations range from about 400 to 3,000 µg/L. Dissolved arsenic concentrations exceeding action levels have also been detected at depths corresponding to approximately 3,600 ft amsl beneath the source area. Ground surface elevation in the source area is approximately 4,350 ft amsl, decreasing to approximately 4,200 ft amsl toward the downgradient extent of the plume. Primary Arsenic Plume Current groundwater pH is near neutral, generally between 6 and 7. Historically, the central portion of the plume may have had pH values below 6. Since the early 1990s, pH has increased in select monitoring wells. Redox conditions are not well characterized. Dissolved arsenic concentrations in groundwater have steadily declined since the early 1990s. Peak concentrations were as high as approximately 20,000 µg/L. Active groundwater extraction began around 2000. Current maximum arsenic concentrations are typically between 1,000 and 2,000 µg/L. This plume is generally shallow. Source material is likely present as solid-phase contamination, and transport to groundwater appears to occur primarily through leaching rather than migration of aqueous solutions. Groundwater extraction has likely induced deeper migration than would have occurred under natural conditions. The extraction well is screened to approximately 130 ft below ground surface (bgs). In most areas, elevated arsenic concentrations are observed between about 40 and 60 ft bgs. At one location, elevated arsenic has been detected at approximately 160 ft bgs. Within this plume, dissolved selenium concentrations are generally much lower, typically ranging from 50 to 100 µg/L. However, near the extraction well, selenium concentrations have increased in recent years to between approximately 1,000 and 2,000 µg/L. Mixed Selenium and Arsenic Plume Releases of acidic solutions have resulted in transport of both selenium and arsenic to groundwater. Current pH conditions are near neutral (approximately 6 to 7). Historically, localized zones of acidic groundwater have occurred, particularly following release events. pH values below 1 were measured in multiple wells in the past. In one area following a release, pH was measured at approximately 3.5. In both cases, pH returned to near-neutral conditions over a period of roughly 10 years. Redox conditions are not well defined. Groundwater with elevated dissolved selenium is typically found within approximately 50 ft bgs, while groundwater with elevated dissolved arsenic is generally present within about 80 ft bgs. Recent dissolved selenium concentrations range from approximately 50 to 300 µg/L, while dissolved arsenic concentrations range from approximately 10 to 30 µg/L.