The city of Española has not yet fixed a problem with the plant’s ultraviolet disinfection system.
The malfunction led the sewer plant to discharge sewage-tainted water into the Rio Grande in December and January, at levels that exceeded its environmental permit.
In the meantime, the plant has been using chlorine tablets to disinfect the water.
Chief Plant Operator Carlos Rodriguez said a subcontractor for engineering firm Molzen-Corbin is waiting on test results needed to finish diagnosing the problem.
Rodriguez said the discharge violations will likely earn the plant a warning from the federal Environmental Protection Agency.
Agency spokesman David Bary said the Agency is still reviewing the case.
The new $14 million sewer plant opened last year.