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Merrimack W W T F

Sewage treatment plant, major discharger, Merrimack, New Hampshire. NPDES permit NH0100161 expired May 31, 2019; its limits still apply. Last 12 months: over a limit 3 times (last August 2026). Source: EPA ECHO, Oct 22, 2026.

Reports due
About 15 days after each period: form A monthly (29 values), form B quarterly (10 values)
Last report on file
September 2026
Oct 2024 – Sep 2025
4 values over a limit, 0 required values missing, 0 of 13 reports late

Last 12 months (Oct 1, 2025 – Sep 30, 2026)

Period endingParameterReportedLimit
May 2026pH, minimum6.15 SU≥ 6.5 SU
July 2026pH, minimum6.42 SU≥ 6.5 SU
August 2026pH, minimum5.73 SU≥ 6.5 SU

Limits in force (39)

ParameterStatisticLimitMonths
BOD, 5-day, 20 deg. Cmonthly averagereport only (mg/L)all year
BOD, 5-day, 20 deg. Cweekly averagereport only (mg/L)all year
BOD, 5-day, 20 deg. Cdaily maximumreport only (mg/L)all year
BOD, 5-day, 20 deg. Cmonthly average≤ 1199 lb/dall year
BOD, 5-day, 20 deg. Cdaily maximum≤ 2581 lb/dall year
BOD, 5-day, 20 deg. Cmonthly averagereport only (mg/L)all year
BOD, 5-day, 20 deg. Cweekly averagereport only (lb/d)all year
pHminimum≥ 6.5 SUall year
pHmaximum≤ 9 SUall year
Solids, total suspendedmonthly averagereport only (mg/L)all year
Solids, total suspendedweekly averagereport only (mg/L)all year
Solids, total suspendeddaily maximumreport only (mg/L)all year
Solids, total suspendedmonthly average≤ 1473 lb/dall year
Solids, total suspendeddaily maximum≤ 3255 lb/dall year
Solids, total suspendedmonthly averagereport only (mg/L)all year
Solids, total suspendedweekly averagereport only (lb/d)all year
Nitrogen, ammonia total [as N]daily maximumreport only (mg/L)Jul–Sep
Phosphorus, total [as P]monthly average≤ 164.8 lb/dApr–Oct
Hardness, total [as CaCO3]daily maximumreport only (mg/L)Jul–Sep
Nickel, total recoverabledaily maximumreport only (mg/L)Jul–Sep
Zinc, total recoverabledaily maximumreport only (mg/L)Jul–Sep
Aluminum, total recoverabledaily maximumreport only (mg/L)Jul–Sep
Cadmium, total recoverabledaily maximumreport only (mg/L)Jul–Sep
Lead, total recoverabledaily maximumreport only (mg/L)Jul–Sep
Copper, total recoverabledaily maximumreport only (mg/L)Jul–Sep
Flow, in conduit or thru treatment plantmonthly average≤ 5 MGDall year
Flow, in conduit or thru treatment plantdaily maximumreport only (MGD)all year
Flow, in conduit or thru treatment plantweekly averagereport only (MGD)all year
Chlorine, total residualmonthly average≤ .85 mg/Lall year
Chlorine, total residualdaily maximum≤ 1 mg/Lall year
E. coli, colony forming units [CFU]monthly geometric mean≤ 126 CFU/100mLall year
E. coli, colony forming units [CFU]daily maximum≤ 406 CFU/100mLall year
Flow, process wastewatermonthly averagereport only (MGD)all year
Flow, process wastewaterdaily maximumreport only (MGD)all year
Flow, process wastewaterweekly averagereport only (MGD)all year
BOD, 5-day, percent removalmonthly average minimum≥ 85 %all year
Solids, suspended percent removalmonthly average minimum≥ 85 %all year
LC50 Static 48Hr Acute Ceriodaphnia dubiadaily minimum≥ 100 %Jul–Sep
LC50 Static 48Hr Acute Pimephales promelasdaily minimum≥ 100 %Jul–Sep

How strict are these limits?

Cited limits by parameter: New Hampshire's rules and the federal ones.

Check this month's numbers Email me before each report is due

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On EPA ECHO: Facility report · DMR history

Your permit document is the final word. As JSON: /api/v1/permits/NH0100161 · MCP: https://passage-data.com/mcp