Clean Water Act discharge permit · NPDES MI0020435

MASON WWTP, Mason, MI: NPDES MI0020435 discharge permit, effluent exceedances, inspections, penalties

Administratively continuedPermit status
MajorDischarger class
35Pollutants under a numeric limit
12Pollutants with an effluent exceedance
0Inspections on file
0Formal enforcement actions

MASON WWTP, held by City of Mason, holds NPDES permit MI0020435, which discharges to Sycamore Creek. EPA’s file records it issued October 15, 2018 and expiring October 1, 2022.

MASON WWTP, Mason, Michigan: Individual permit MI0020435, held by City of Mason; Publicly owned treatment works; Administratively continued (past its expiration date and still in force until reissued); issued October 15, 2018, term to October 1, 2022, by State; discharges to Sycamore Creek; Sewage Treatment Facilities.

Nitrogen, ammonia total [as N]: 14 limits, 65 violations of any kind, 39 effluent exceedances, latest January 31, 2026, largest 780% over the limit.
BOD, carbonaceous [5 day, 20 C]: 16 limits, 66 violations of any kind, 22 effluent exceedances, latest June 30, 2025, largest 392% over the limit.
Solids, total suspended: 8 limits, 44 violations of any kind, 20 effluent exceedances, latest June 30, 2025, largest 403% over the limit.
Coliform, fecal general: 2 limits, 29 violations of any kind, 17 effluent exceedances, latest April 30, 2025, largest 200% over the limit.
Selenium, total [as Se]: 4 limits, 19 violations of any kind, 15 effluent exceedances, latest December 31, 2016, largest 245% over the limit.
Solids, suspended percent removal: 2 limits, 14 violations of any kind, 13 effluent exceedances, latest April 30, 2025, largest 187% over the limit.
Toxicity, choice of species: 2 limits, 8 violations of any kind, 8 effluent exceedances, latest June 30, 2025, largest 458% over the limit.
Oxygen, dissolved [DO]: 1 limit, 11 violations of any kind, 5 effluent exceedances, latest January 31, 2026, largest 70% over the limit.
Phosphorus, total [as P]: 4 limits, 14 violations of any kind, 2 effluent exceedances, latest May 31, 2020, largest 15% over the limit.
Copper, total [as Cu]: 4 limits, 6 violations of any kind, 2 effluent exceedances, latest July 31, 2017, largest 109% over the limit.
pH: 2 limits, 13 violations of any kind, 1 effluent exceedance, latest February 28, 2009.
Static 48 Hr Chronic Pimphales Promelas: 2 limits, 1 violation of any kind, 1 effluent exceedance, latest January 31, 2019, largest 97% over the limit.
Mercury, total [as Hg]: 6 limits, 49 violations of any kind, 0 effluent exceedances.
Silver, total [as Ag]: 4 limits, 14 violations of any kind, 0 effluent exceedances.
Flow, in conduit or thru treatment plant: 2 limits, 13 violations of any kind, 0 effluent exceedances.
Solids, total: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Arsenic, dry weight: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Selenium, dry weight: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Copper, dry weight: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Cadmium, dry weight: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Nitrogen, total Kjeldahl: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Molybdenum, sludge, total, dry weight [as Mo]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Zinc, sludge, total, dry weight [as Zn]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Lead, sludge, total, dry weight [as Pb]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Nickel, sludge, total, dry weight [as Ni]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Nitrogen, sludge, total, dry weight [as N]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Mercury, sludge, total, dry weight [as Hg]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Potassium, sludge, total, dry weight [as K]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Phosphorus, sludge, total, dry weight [as P]: 3 limits, 6 violations of any kind, 0 effluent exceedances.
Chlorine, total residual: 1 limit, 6 violations of any kind, 0 effluent exceedances.
Nickel, total [as Ni]: 4 limits, 4 violations of any kind, 0 effluent exceedances.
Cyanide [A]: 4 limits, 4 violations of any kind, 0 effluent exceedances.
BOD, carb-5 day, 20 deg C, percent removal: 2 limits, 1 violation of any kind, 0 effluent exceedances.
Toxicity [acute], Ceriodaphnia dubia: 1 limit, 0 violations of any kind, 0 effluent exceedances.
TU Static 24 Hr Acute Pimephales promelas: 1 limit, 0 violations of any kind, 0 effluent exceedances.

November 29, 2023: Reporting Violations - Late Submittal of DMRs (ST6).
April 23, 2022: Permit Violations - Discharge Without a Valid Permit (ST6).
March 1, 2022: Monitoring Violations - Improper Analysis or Lab Error (ST6).
February 17, 2022: Permit Violations - Discharge Without a Valid Permit (ST6).
May 18, 2020: Permit Violations - Discharge Without a Valid Permit (ST6).
January 11, 2020: Permit Violations - Discharge Without a Valid Permit (ST6).
June 20, 2019: Permit Violations - Discharge Without a Valid Permit (ST6).
October 31, 2018: Reporting Violations - Late Submittal of DMRs (ST6).

Michigan holds 200 Publicly owned treatment works coverages of this permit type in EPA’s file; 105 were issued before MI0020435. City of Mason holds 2 permits in Michigan.

Other permits held by City of Mason

MASON MS4-INGHAM, Mason: MI0059779, issued December 23, 2019

Coverages issued nearest MI0020435

September 27, 2018: MARTIN RTB, Saint Clair Shores, MI0025453, held by Southeast Macomb Sanitary District
September 27, 2018: CHAPATON RTB, Saint Clair Shores, MI0025585, held by 8 1/2 Mile Relief Drain Drainage District
September 28, 2018: CHELSEA WWTP, Chelsea, MI0020737, held by City of Chelsea
September 28, 2018: DEXTER WWTP, Dexter, MI0022829, held by Daniel Schlaff, City of Dexter
September 28, 2018: LOCH ALPINE SA-SCIO-WEB WWTP, Ann Arbor, MI0024066, held by Loch Alpine Sanitary Authority
October 23, 2018: DIMONDALE/WINDSOR WWTP, Dimondale, MI0053562, held by Village of Dimondale
October 23, 2018: GLADSTONE WWTP, Gladstone, MI0057676, held by City of Gladstone
November 2, 2018: LEONI TWP WWTP, Jackson, MI0045942, held by Leoni Township
November 7, 2018: SOUTH HURON VALLEY UTILITY AUTHORITY WWTP, Rockwood, MI0043800, held by South Huron Valley Utility Authority
November 27, 2018: GRANT WWTP, Grant, MI0023035, held by City of Grant

MASON WWTP among its neighbors

EPA’s permit file holds 18 discharge permits in the Headwaters Sycamore Creek subwatershed (HUC 040500040506), MI0020435 among them. Its county holds 38, 5 of them major permits; MI0020435 is a major permit.

Other permits in the Headwaters Sycamore Creek subwatershed (HUC 040500040506)

ARCOSA EPI LLC, Mason: MIS310233, minor permit, permit term to April 1, 2023
CLEANLITES RECYCLING-MASON, Mason: MIS320063, minor permit, permit term to April 1, 2023
COLUMBIA LAKE ESTATES MHC, Mason: MI0057275, minor permit, discharging to Townsend Drain, permit term to October 1, 2022
CORRCHOICE LLC, Mason: MIS310295, minor permit, permit term to April 1, 2023
GESTAMP MASON LLC, Mason: MIG250490, minor permit, discharging to SYCAMORE CREEK VIA STRM WATER RET, permit term to April 1, 2013
INGHAM CDC MS4, Mason: MI0060041, minor permit, permit term to October 1, 2027
INGHAM CDC MS4, Mason: MIG610109, minor permit, permit term to April 1, 2008
MASON MANOR MHP WWSL, Mason: MI0043036, minor permit, discharging to Sycamore Creek, permit term to October 1, 2022
MASON MS4-INGHAM, Mason: MI0059779, minor permit, permit term to October 1, 2024
ORCHID ORTHOPEDIC SOLUTIONS LLC, Mason: MIS310778, minor permit, discharging to Cook and Thorburn Drain, permit term to April 1, 2023

Identity

Facility as filed	MASON WWTP
Permittee as filed	City of Mason
NPDES ID	MI0020435
Permit status	Administratively continued (past its expiration date and still in force until reissued)
Permit type	Individual permit
Discharger class	Major discharger
Facility type	Publicly owned treatment works
Program	Publicly owned treatment works
Issued	October 15, 2018
Expiration date	October 1, 2022
Issuing agency	State
Address	Mason, MI 48854
Receiving water	Sycamore Creek
Subwatershed	Headwaters Sycamore Creek (HUC 040500040506)
Program components on file	Biosolids, POTW
NAICS	221320 – Sewage Treatment Facilities
SIC	4952 – Sewerage Systems
Other EPA IDs (FRS)	RCRA handler MIR000014118

Effluent limits and exceedances

35Pollutants on file
35Under a numeric limit
33With a violation of any kind
12With an effluent exceedance

An effluent exceedance is a discharge monitoring report value over the permit’s numeric limit (EPA’s violation code E90). A violation of any kind also counts a report not filed. Each row is EPA’s own count for that pollutant.

Pollutant or measure	Limits	Violations, any kind	Effluent exceedances	Latest exceedance	Largest exceedance, as filed
Nitrogen, ammonia total [as N]	14	65	39	January 31, 2026	780% over the limit
BOD, carbonaceous [5 day, 20 C]	16	66	22	June 30, 2025	392% over the limit
Solids, total suspended	8	44	20	June 30, 2025	403% over the limit
Coliform, fecal general	2	29	17	April 30, 2025	200% over the limit
Selenium, total [as Se]	4	19	15	December 31, 2016	245% over the limit
Solids, suspended percent removal	2	14	13	April 30, 2025	187% over the limit
Toxicity, choice of species	2	8	8	June 30, 2025	458% over the limit
Oxygen, dissolved [DO]	1	11	5	January 31, 2026	70% over the limit
Phosphorus, total [as P]	4	14	2	May 31, 2020	15% over the limit
Copper, total [as Cu]	4	6	2	July 31, 2017	109% over the limit
pH	2	13	1	February 28, 2009
Static 48 Hr Chronic Pimphales Promelas	2	1	1	January 31, 2019	97% over the limit
Mercury, total [as Hg]	6	49	0
Silver, total [as Ag]	4	14	0
Flow, in conduit or thru treatment plant	2	13	0
Solids, total	3	6	0
Arsenic, dry weight	3	6	0
Selenium, dry weight	3	6	0
Copper, dry weight	3	6	0
Cadmium, dry weight	3	6	0
Nitrogen, total Kjeldahl	3	6	0
Molybdenum, sludge, total, dry weight [as Mo]	3	6	0
Zinc, sludge, total, dry weight [as Zn]	3	6	0
Lead, sludge, total, dry weight [as Pb]	3	6	0
Nickel, sludge, total, dry weight [as Ni]	3	6	0
Nitrogen, sludge, total, dry weight [as N]	3	6	0
Mercury, sludge, total, dry weight [as Hg]	3	6	0
Potassium, sludge, total, dry weight [as K]	3	6	0
Phosphorus, sludge, total, dry weight [as P]	3	6	0
Chlorine, total residual	1	6	0
Nickel, total [as Ni]	4	4	0
Cyanide [A]	4	4	0
BOD, carb-5 day, 20 deg C, percent removal	2	1	0
Toxicity [acute], Ceriodaphnia dubia	1	0	0
TU Static 24 Hr Acute Pimephales promelas	1	0	0

Inspections, violations and enforcement

8Single-event violations

Date	What EPA recorded	Agency
November 29, 2023	Reporting Violations - Late Submittal of DMRs	ST6
April 23, 2022	Permit Violations - Discharge Without a Valid Permit	ST6
March 1, 2022	Monitoring Violations - Improper Analysis or Lab Error	ST6
February 17, 2022	Permit Violations - Discharge Without a Valid Permit	ST6
May 18, 2020	Permit Violations - Discharge Without a Valid Permit	ST6
January 11, 2020	Permit Violations - Discharge Without a Valid Permit	ST6
June 20, 2019	Permit Violations - Discharge Without a Valid Permit	ST6
October 31, 2018	Reporting Violations - Late Submittal of DMRs	ST6

Inspections

EPA’s inspection file holds no inspection for NPDES MI0020435.

Formal enforcement and penalties

0 formal actions, 0 of them with a penalty assessed. Federal and state penalties are separate figures from separate authorities and are shown as each was filed, never added together.

Informal enforcement

EPA’s informal enforcement file holds no action for NPDES MI0020435.

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Figures from EPA’s ICIS-NPDES download, loaded October 14, 2026.

This public-records page covers Clean Water Act discharge permit NPDES MI0020435 for the MASON WWTP in Mason, MI, held by City of Mason and discharging to Sycamore Creek, with the permit listed as administratively continued. The page lists 35 for the Major Discharger class, 12 pollutants under a numeric limit, and 12 pollutants with an effluent exceedance.