Backwash water from Colstrip’s water treatment plant was being discharged untreated to Castle Rock Lake, the city’s main source for drinking water. The City of Colstrip needed to bring the Water Treatment Plant Backwash System into compliance with Montana Department of Environmental Quality (MDEQ) standards and the current Montana Pollutant Discharge Elimination System (MPDES) permit limits. KLJ evaluated different alternatives to bring the backwash water into compliance with Total Suspended Solids and turbidity limits, finally recommending the utilization of the existing on-site clarifier and drying beds.


KLJ developed a repurpose design of an existing clarifier and sludge drying beds to treat backwash water from the City of Colstrip’s water treatment plant.



Implementing the new backwash treatment system helped bring the City’s backwash water treatment system into compliance with government regulations. Regulating the discharge to surface water is important so that America’s waters remain clean and available to all to enjoy. This ensures that lakes, rivers, and streams remain safe for drinking, fishing, and swimming.

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