On October 9, 2014, the EPA was notified by the Assiniboine and Sioux Tribes (Tribes) of a sanitary sewer overflow (SSO) from the Poplar waste water treatment plant?s (WWTP) collection system that discharged from a manhole into a storm drain leading to the Poplar River. On November 17, 2014, the EPA was notified by the Tribes of a second SSO from the WWTP?s collection system that discharged into the Poplar River. The City of Poplar (City) failed to provide the EPA with a written submission within 5 days of becoming aware of the October 9 and November 17, 2014 SSOs. In addition, the City had effluent limit exceedances in their outfall discharges to the Missouri River, failed to submit monthly Discharge Monitoring Reports (DMR), and failed to conduct proper operation and maintenance of the WWTP and collection system. The Order requires that the City identify cause(s) of the SSOs and repair the system, submit an operation and maintenance plan, and immediately come into compliance with the requirements in their permit.