On January 17th, 2020, the City of Rifle was issued a Notice of Violation/Cease and Desist Order (NOV/CDO) from the Colorado Department of Public Health and Environment (CDPHE). The NOV/CDO was served in response to discharge permit violations for dissolved copper by the City’s wastewater treatment facility. Domestic wastewater treatment works are not designed to remove metals. Even though the main constituents of sewage were effectively treated and removed, copper that was present in the water was not removed. The facility experienced intermittent non-compliance in 2015 – 2017, which became more continuous in 2018. In 2018, the City contracted with SGM Engineering for compliance assistance. The source of copper coming into the treatment plant was determined to most likely be from the normal corrosion of copper pipes and fixtures in the water distribution system.
The discharge permit limits for dissolved copper at the facility are 28 ug/L (.000028 gram/liter) for the daily maximum and 17 ug/L for the monthly average. The limits are designed to be protective of aquatic life, specifically the Colorado pike minnow and razorback sucker. Both fish are considered threatened/endangered by the US Fish & Wildlife Service (USFWS). The segment of the Colorado River in which the treatment facility’s discharge is located is considered critical habitat for the threatened/endangered fish. Setting such conservative discharge limits for constituents like metals is standard practice for CDPHE when dealing with critical habitat.
In comparison, the human health standard for copper is much higher; the action level for copper in the Colorado Primary Drinking Water Regulations is 1,300 ug/L. This level is fifty times higher than the standard for the threatened/endangered fish. The highest dissolved copper concentration in the facility’s discharge was 121 ug/L. At no time did the copper violations jeopardize public health or the agricultural water supply.
III. Permit Violations and Solution
During the period of 2015 to 2020, the wastewater treatment facility experienced thirteen daily maximum copper violations and ten monthly average copper violations. The daily maximum violations ranged from 29.7 ug/L to 121 ug/L. The monthly average violations ranged from 18.8 ug/L to 46.2 ug/L.
To return to compliance, a chemical dosing system was designed by SGM Engineering and installed. The system does a polysulfide coagulant to the facility’s treated water, which causes the copper to precipitate. Once the copper is in a solid phase, it is no longer as bio-available to the aquatic life in the Colorado River. Since it is no longer considered dissolved, any copper being discharged does not violate the facility’s permit limits. The facility has not had any further copper violations since the polysulfide dosing system came online.
IV. Supplemental Environmental Project (SEP)
In lieu of fines, the City of Rifle has opted to complete a supplemental environmental project (SEP). The SEP will be undertaken as a settlement to the CDPHE enforcement action for the wastewater treatment facility’s violation of the Colorado Water Quality Control Act. The SEP will consist of a study conducted on the City’s stormwater system that discharges to Rifle Creek. The study will seek to quantify water quality impacts caused by the stormwater system and the results will be used to design a construction project to help mitigate the impacts. Re-sampling and analysis of the stormwater outfalls and Rifle Creek itself will determine the success of the project.