University tracer study finds no dye at Red Hill Shaft; carbon‑pack hits under review for cross‑contamination

Researchers running a dye‑tracer test to ground‑truth groundwater flow near Red Hill reported early results that contradicted some expectations: direct sampling and downhole fluorometers have not recorded rhodamine WT at Red Hill Shaft, while several activated‑carbon packs have produced low, extracted dye signals that investigators now suspect could be from field cross‑contamination.

"So far to the present date, we have not seen any evidence of dye influx," Don Thomas, the project lead, told the committee. The team injected 50 pounds of rhodamine WT in multiple pulses at monitoring well RHMW‑08 and is monitoring a network of surrounding wells using direct laboratory fluorometry, semi‑continuous downhole fluorometer transducers and periodic carbon‑pack deployments.

Thomas said the carbon‑pack extractions had yielded several low‑level detections at wells including NMW‑27, RHP‑03, NMW‑30, RHMW‑02 and RHP‑01, but the pattern does not show the sustained rising concentrations expected from an advancing dye plume. "We have begun to suspect that we're having cross‑contamination issues," he said, and noted evidence of dye at a wellhead that suggests handling contamination.

Investigators said the absence of dye at Red Hill Shaft so far implies either slower transport times, flow along different (deeper or lateral) layers than expected, or that some monitoring methods are sampling different hydraulic zones. The team will continue monitoring through October (field work end date) and will do a forensic review of field protocols and carbon‑pack handling before drawing final conclusions.

Researchers said the study provides new constraints for groundwater models in a geologically complex, multilayered volcanic aquifer and that continued sampling and method verification are needed before the results can be interpreted for public‑health or remediation planning.