Wastewater treatment facilities (WWTFs) in the basin provide Total Phosphorus (TP) removal through advanced wastewater treatment processes, followed by direct discharge or further treatment through land application. Some WWTFs are also required to remove total inorganic nitrogen (TIN) to meet permit limits. There are currently five permitted WWTPs in the basin that discharge to Cherry Creek waters. Another, Plum Creek Water Reclamation Authority, is located outside the watershed but applies some of its treated effluent as irrigation water within the watershed. All six of these facilities have TP effluent limits; three have TIN limits as well.
Wastewater and industrial process wastewater sources, as well as reclaimed water treaters, are limited in the amounts of phosphorus they are allowed to discharge to the Cherry Creek Reservoir watershed. Limits contained in the point source discharge permits in the basin effectively reduce nutrient concentrations in the receiving streams. For example, TP discharge limits for WWTPs, which for most dischargers are less than 0.05 mg/L TP as a 30-day average, are significantly less than the flow-weighted TP concentrations currently entering the reservoir from aggregated sources (surface and groundwater inflows, precipitation). Drinking water treatment plant discharges have to meet a phosphorus effluent limit of 0.2 mg/L.
All WWTFs in the basin met their phosphorus discharge limits in 2018. Actual concentrations discharged by wastewater treatment plants continue to be consistently below their permit limits and well below the 0.200 mg/L flow-weighted phosphorus concentration goal established for flows into the reservoir. Wastewater treatment facilities also met their TIN limits in 2018.
Control requirements for point source dischargers were effective in reducing phosphorus concentrations to the watershed and reservoir.
* The flow weight avergage concentration must be ≤ 0.005 mg/L TP, divided by the land application return flow factor.
** TP Limit is a 30-day average unless a 90-day average is approved by the Division at the request of the discharger.
*** No TIN permit limit.