CITY OF HELENA — NPDES permit MT0028720: limits, due date and EPA's record

NPDES permit MT0028720 · Minor POTW · effective, expires 2027-06-30 · EPA's file as of 2026-09-19

EPA's record, 2025-09-01 to 2026-08-31

Reporting

Reports are due about 28 days after each monitoring period ends (read off this permit's own late-day counts in EPA's filings).

Limits in force (25)

Outfall	Parameter	Statistic	Limit	Months
002	Flow rate	MO AVG	report only	all year
002	Flow rate	MO AVG	report only	all year
002	pH	DAILY MN	>= 6 SU	all year
002	pH	DAILY MX	<= 9 SU	all year
002	Solids, total suspended	MO AVG	<= 30 mg/L	all year
002	Solids, total suspended	DAILY MX	<= 45 mg/L	all year
002	Solids, total suspended	MO AVG	<= 80 lb/d	all year
002	Hardness, total [as CaCO3]	SINGGRAB	report only	all year
002	Arsenic, total recoverable	MO AVG	<= 10 ug/L	all year
002	Arsenic, total recoverable	DAILY MX	<= 10 ug/L	all year
002	Arsenic, total recoverable	MO AVG	report only	all year
002	Zinc, total recoverable	MO AVG	<= 40 ug/L	all year
002	Zinc, total recoverable	DAILY MX	<= 80 ug/L	all year
002	Zinc, total recoverable	MO AVG	report only	all year
002	Aluminum, dissolved [as Al]	MO AVG	<= 64 ug/L	all year
002	Aluminum, dissolved [as Al]	DAILY MX	<= 158 ug/L	all year
002	Cadmium, total recoverable	MO AVG	<= .14 ug/L	all year
002	Cadmium, total recoverable	DAILY MX	<= .35 ug/L	all year
002	Cadmium, total recoverable	MO AVG	report only	all year
002	Copper, total recoverable	MO AVG	<= 3.1 ug/L	all year
002	Copper, total recoverable	DAILY MX	<= 8.9 ug/L	all year
002	Copper, total recoverable	MO AVG	report only	all year
002	Duration	TOTAL	report only	all year
002	Chlorine, total residual	MO AVG	report only	all year
002	Chlorine, total residual	DAILY MX	<= .09999 mg/L	all year