Lexington water staff outlines MS4 monitoring changes, new maintenance manual and countywide sampling plan

Lexington water-quality staff on Sept. 18 gave planning commissioners an overview of updates to the city’s MS4 (municipal separate storm sewer system) program, including new criteria to prioritize illicit-discharge screening, a maintenance manual for stormwater control facilities and a countywide water-quality monitoring program the division plans to implement after state approval.

Bailey Young, a Water Quality staff member, told commissioners MS4 is the state permit that authorizes Lexington to discharge stormwater runoff into waters of the Commonwealth and that Lexington is one of two Phase 1 communities in Kentucky with a permit tailored to the city. "MS4 stands for municipal separate storm sewer system," Young said, emphasizing the permit’s role because runoff from urban activities can carry oil, pet waste, fertilizer and other pollutants directly to creeks and rivers.

Young said the division continues to perform the permit-required dry-weather screening of larger outfalls and is working with consultant Tetra Tech to adopt a new, risk-based approach for illicit-discharge detection and elimination. Under the current program, Young said, any outfall 36 inches or larger is sampled after a 72-hour dry period if it is flowing; if benchmarks are exceeded, staff attempt to locate and eliminate the non-stormwater source. The proposed change would let staff prioritize subwatersheds and inspect smaller pipes in higher-risk areas — potentially inspecting down to 18 inches in diameter in high-priority neighborhoods, 24 inches in medium-priority areas and 36 inches in low-priority areas — and would be submitted to the state before year-end for possible rollout in 2026.

Young described other program work: Lexington and Fayette County maintain "just under 2,800 stormwater control facilities" and perform roughly 5,200 inspections each year. "We have just under 2,800 stormwater control facilities in Lexington and Fayette County. We inspect those based on varying frequency ... and we do just under 5,200 inspections annually," Young said. The division is finishing a maintenance manual with Tetra Tech that Young said will clarify responsibilities for property owners and include inspection checklists; staff aim to publish the manual in January 2026.

On monitoring, Young said staff moved from a single-watershed approach in 2023 to a countywide monitoring program for 2024–2025, with 64 sampling sites chosen to improve trend detection. The countywide program will include quarterly grab samples, wet-weather sampling and biological work such as fish and macroinvertebrate assessments; Young said the program will include volunteer participation and a quality-assurance plan to be submitted to the state before implementation, likely in early 2026.

During the discussion commissioners raised questions about homeowner use of lawn chemicals and fertilizers. "We do see a ton of nutrients. So fertilizer is a major issue, and we're seeing, like, really high levels of nitrogen and phosphorus," Greg Lubeck, deputy director of Water Quality, said in response to a commissioner question about whether fertilizer and yard chemicals show up in monitoring. Young and Lubeck also described field observations staff report to engineering when constructed facilities do not match designs — examples included improperly planted green infrastructure, lack of vegetation in stabilized soil, detention-basin grading that prevents proper drainage and invert elevation differences between design and field conditions.

Young said the division has convened well-attended stakeholder groups to discuss manufactured treatment device protocol, constructed-wetland design, green infrastructure, plan certification and sureties, and temporary stormwater controls. She said the division will continue work groups to refine manuals and procedures and to respond to questions about stormwater in expansion areas.

Commissioners did not take formal action; staff said they will submit the updated screening approach and the monitoring quality-assurance plan to the state and return with materials as approvals are received.