Patapsco Wastewater Plant

The Patapsco Wastewater Treatment Plant is the second largest sewage treatment plant in Maryland. It sits at Wagner's Point on the Patapsco River in South Baltimore and cleans the used water that leaves homes, businesses, and industries before returning it to the river, which flows into Baltimore Harbor and on to the Chesapeake Bay.

The plant is owned and operated by Baltimore City, through its Department of Public Works. The state does not operate the facility but sets the plant's pollution limits, inspects the facility, and enforces the law when requirements are not met.

The plant treats approximately 63 million gallons of wastewater each day, serving about 450,000 residents across a 184-square-mile area that includes Baltimore City and portions of Baltimore, Anne Arundel, and Howard counties. The facility uses advanced secondary treatment with Enhanced Nutrient Removal (ENR), followed by disinfection, to protect public health and improve water quality before the treated water is returned to the environment.

Regulatory history and the consent decree

In 2021 and 2022, the plant experienced serious equipment and staffing problems and released far more nitrogen and phosphorus than its permit allowed. In January 2022, the state sued Baltimore City over permit violations at the Patapsco and Back River plants. The environmental group Blue Water Baltimore joined the case.

The case was settled in November 2023 with a consent decree — a legally binding, court-enforced agreement. It set an enforceable schedule of repairs and required the City to properly staff the plants, post quarterly progress updates, hold public meetings, hire an independent engineer, and pay a $4.75 million penalty, with nearly $2 million set aside for local water-quality and habitat grants.

Performance has improved significantly. The state continues to inspect the plant, track its performance, require corrective action, and assess penalties when violations occur, all under the consent decree and the plant's discharge permit.

Investing in repairs and clean water

Under the Moore-Miller Administration, Maryland has committed more than $87 million in grants and loans to the Patapsco plant. In January 2026, the Board of Public Works approved more than $18 million for additional equipment repairs and rehabilitation.

These investments have led to significant improvements in performance. Since 2019, nitrogen pollution at the Patapsco plant has dropped by more than 78 percent, and phosphorus pollution is down about 80 percent. The charts below track nutrient discharges by calendar year.