Company reports progress on selenium plume capture and treatment; EPA Superfund process active

Company representatives and local officials provided a technical update on groundwater contamination, selenium plume capture and treatment, and the site’s status in the federal Superfund (CERCLA) process.

The presenter said selenium moves farther and faster than other constituents at the site and described a plume map showing contours for 50, 100 and 500 parts per billion (ppb). To intercept migrating groundwater, the company said it installed three plume capture wells and began operating them in February 2017; those wells were routed to the plant and, beginning in 2021, to a dedicated selenium treatment facility.

The presenter said the treatment facility became operational in 2021 and that the company designed the system for 400 gallons per minute (gpm) and has operated it up to roughly 500 gpm. The company described the reactor media as granulated activated carbon (GAC) supporting bacteria that reduce dissolved selenate to elemental selenium, which is then filtered and removed. The company said its design target was approximately 95% selenium removal and a surface‑water objective of less than 5 ppb; the presenter reported treated effluent concentrations “closer to 2 ppb” and the system consistently achieving removal in the high‑90s percentage range during operations described at the meeting.

The presenter said two additional capture wells on the west side are in place and should be operational in June or July 2025; those wells are expected to provide an additional ~200 gpm into the treatment plant and to increase overall capture. The company said reactor backwash and solids are dewatered and managed to the plant’s lined S02 landfill and that treated water is routed to the plant’s non‑contact cooling pond before discharge.

On the regulatory track, the presenter explained the difference between the Record of Decision tied to the 1997 remedy (which relied on monitored natural attenuation) and the CERCLA supplemental remedial investigation (SRI) and focused feasibility study (FFS) process now underway after EPA’s five‑year review determined the remedy needed reassessment. The presenter said the company signed a consent order with EPA in 2021 to reinitiate the CERCLA process for a supplemental remedial investigation and that the company has submitted technical reports and anticipates delivering the SRI report in 2025 subject to EPA review and comment.

The presenter discussed potential source‑area actions that could accompany water‑treatment remedies during the FFS, saying both water treatment and source removal (excavation/capping) are likely candidates for EPA’s consideration. He asked for continued cooperation with local officials and said the company plans regular community updates as the SRI and FFS progress.