MANCHESTER WATER WORKS - MERRIMACK RIVER TREATMENT PLANT
NPDES ID: NH0001621
E — SNC: Effluent violation (monthly average limit)
The facility discharged more of a pollutant than its permit allows, based on a monthly average.
This quarter: 3 effluent violations, 1 single-event violation.
Violations
May 31, 2026
Manganese, total [as Mn]
67% over limit
Discharged 0.3178 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
April 30, 2026
Manganese, total [as Mn]
781% over limit
Discharged 1.67979999 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
Iron, total [as Fe]
120% over limit
Discharged 2.49699998 kg/d against a permitted limit of 1.13499999 kg/d (MO AVG)
DMR, Limited - Numeric Violation
November 30, 2025
Manganese, total [as Mn]
1043% over limit
Discharged 2.17919998 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
Iron, total [as Fe]
136% over limit
Discharged 2.67859998 kg/d against a permitted limit of 1.13499999 kg/d (MO AVG)
DMR, Limited - Numeric Violation
September 30, 2025
Manganese, total [as Mn]
143% over limit
Discharged 0.46308 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
First flagged
April 14, 2026 (5 months ago)
Last confirmed
September 15, 2026 (5 days ago)