As part of the regulatory requirements for wastewater treatment plant operation, the Village received its final National Pollutant Discharge Elimination System (NPDES) permit from the Illinois Environmental Protection Agency (IEPA) on October 31, 2014. Part of the NPDES permit for all dischargers to the Fox River, including the Village of Cary, are new limits on phosphorous.​  ​In accordance with the Village's NPDES permit conditions, a Feasibility Study and final engineering design for the improvements were completed.  Construction began in late 2017 and were completed in 2018 according to the village's permit condition schedule.

The Village implemented a biological phosphorus removal (BPR) process that enables the Village to meet the requirements in a cost effective and scalable manner. The improvement reduces the overall use of chemicals in the wastewater treatment and phosphorus removal process, while also improving water quality in the Fox River.

In addition, improvements to the primary digester mixing system and a new ultraviolet (UV) disinfection system were also completed as part of this project.

Construction of the BPR process, digester mixing system, and UV disinfection system improvements to the Village of Cary Wastewater Treatment Plant were financed by the Clean Water State Revolving Fund (SRF).  The SRF program is administered by the Illinois Environmental Protection Agency and receives a portion of its money to fund these types of projects from the U.S. Environmental Protection Agency.  SRF programs operate in each state to provide communities the resources necessary to build, maintain, and improve the infrastructure that protects one of our most valuable resources: water.