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County officials say interim pump-and-treat was suspended after October data showed chromium plume moved deeper; working group to reevaluate next steps
Summary
Los Alamos County staff told the Board of Public Utilities on Nov. 19 that New Mexico Environment Department and partners suspended a limited pump-and-treat interim measure after October samples showed chromium concentrations increasing at depth and the interim action appeared to push the plume downward; the county has been invited into the working group and expects multiple meetings to consider adaptive site management.
County utility staff reported new October sampling data and a change in the interim remedy for a chromium groundwater plume during the Board of Public Utilities meeting on Nov. 19.
Philo Beckett told the board the county received a letter saying the limited pump-and-treat interim measure had been suspended after SIMR Well 3 test results indicated the interim action was driving the plume downward. "It's brand new data," he said, and explained that recent sampling showed chromium concentrations increased at deeper intervals as samples were taken every 20 feet.
Beckett said the technical working group — which includes Environmental Management (EM), the State Engineer's Office, the New Mexico Environment Department (NMED), the Pueblo de San Ildefonso, and Los Alamos County — will reconvene. He said the county was asked to participate and that group members plan two to four meetings before the end of the year to consider adaptive site management and the next technical steps.
Board members pressed staff on several points, including whether the samples exceeded regulatory limits and whether the interim measure had been intended to push the plume away rather than down. Beckett said the interim action was intended to contain movement, but the recent data indicate the plume shifted downward and that the team needs to regroup to determine whether the interim response caused unintentional effects.
Beckett told the board he had only recently reviewed the new data and expected more detailed information from the third-party review team and regulators in subsequent meetings. The board asked staff to report back with further findings and analysis when available.
What’s next: County staff will participate in the working-group meetings, monitor findings from SIMR Well 3 and related sampling, and provide updates to the board as the technical team develops adaptive site-management options.
