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.
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
August 31, 2025
Manganese, total [as Mn]
90% over limit
Discharged 0.3632 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
June 30, 2025
Aluminum, total [as Al]
26% over limit
Discharged 0.11000001 mg/L against a permitted limit of 0.087 mg/L (MO AVG)
DMR, Limited - Numeric Violation
Manganese, total [as Mn]
164% over limit
Discharged 0.50394 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
May 31, 2025
Manganese, total [as Mn]
60% over limit
Discharged 0.30418 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
April 30, 2025
Iron, total [as Fe]
15% over limit
Discharged 1.30751999 kg/d against a permitted limit of 1.13499999 kg/d (MO AVG)
DMR, Limited - Numeric Violation
Manganese, total [as Mn]
148% over limit
Discharged 0.47216 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
October 31, 2024
Chlorine, total residual
12% over limit
Discharged 1.12 mg/L against a permitted limit of 1 mg/L (MO AVG)
DMR, Limited - Numeric Violation
Chlorine, total residual
75% over limit
Discharged 1.75 mg/L against a permitted limit of 1 mg/L (DAILY MX)
DMR, Limited - Numeric Violation
September 30, 2024
Zinc, total [as Zn]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Lead, total [as Pb]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Aluminum, total [as Al]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Copper, total [as Cu]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Nickel, total [as Ni]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Copper, total [as Cu]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Zinc, total [as Zn]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Hardness, total [as CaCO3]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Lead, total [as Pb]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Hardness, total [as CaCO3]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Carbon, tot organic [TOC]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Nitrogen, ammonia total [as N]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Aluminum, total [as Al]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Nickel, total [as Ni]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Carbon, tot organic [TOC]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Cadmium, total [as Cd]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Cadmium, total [as Cd]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
Nitrogen, ammonia total [as N]
0% over limit
Discharged 0 mg/L against a permitted limit of 0 mg/L (DAILY MX)
DMR, Monitor Only - Overdue
August 31, 2024
Manganese, total [as Mn]
102% over limit
Discharged 0.3859 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
July 31, 2024
Chlorine, total residual
202% over limit
Discharged 3.02 mg/L against a permitted limit of 1 mg/L (DAILY MX)
DMR, Limited - Numeric Violation
Manganese, total [as Mn]
295% over limit
Discharged 0.75363999 kg/d against a permitted limit of 0.19068 kg/d (MO AVG)
DMR, Limited - Numeric Violation
First flagged
April 14, 2026 (3 months ago)
Last confirmed
July 13, 2026 (24 days ago)