“We support your state” is one of the easiest claims for a stormwater software vendor to make, and one of the hardest for a buyer to check. MS4 permits differ by state, by type of permittee and by permit version, and a configuration that was right two years ago can be wrong today.
This post explains what actually varies, using the federal rules and two real permits as examples, and ends with questions to ask any vendor. It is not legal advice; your permit and your permitting authority are the final word on what applies to you.
General permits and individual permits
A regulated small MS4 is covered in one of a few ways (40 CFR 122.33):
- A general permit. The permitting authority issues one permit that covers many permittees, and each one joins by filing a notice of intent. EPA’s municipal sources page notes that most Phase II MS4s are covered by statewide general permits, while some states use individual permits.
- An individual permit. The permittee applies for, and receives, a permit written for it.
- A co-permittee arrangement. A small MS4 in the same urban area as a larger permitted system can, if that system agrees, join the larger system’s permit as a limited co-permittee.
Why it matters: a general permit’s text applies to many cities at once, but your obligations still depend on your notice of intent, your stormwater management program and any conditions specific to you. An individual permit is written for one permittee, so a vendor cannot configure it from a statewide template.
Phase I and Phase II
The federal program has two generations, defined in 40 CFR 122.26:
- Phase I covers medium and large systems: incorporated places with 100,000 or more people at the 1990 Census, certain counties, and systems the permitting authority designates. The places and counties are listed in Appendices F through I of 40 CFR Part 122. EPA describes Phase I systems as covered by individual permits.
- Phase II covers small MS4s located in an urban area with a population of 50,000 or more, as determined by the latest decennial Census, and small MS4s the permitting authority designates (40 CFR 122.32). Small MS4s are not only cities and counties: the rule names state departments of transportation, and EPA’s page mentions non-traditional MS4s such as public universities, hospitals and prisons.
A vendor should be able to tell you which of these it is configuring for you. NPDESTracker is built for Phase II programs and is not marketed as a complete Phase I program system. A larger agency can ask about scoped work on specific workflows, such as inspections and follow-up.
Permit versions
NPDES permits are effective for a fixed term of no more than five years (40 CFR 122.46). Then they are reissued, and the new version can change requirements, deadlines and the questions in the annual report. Between reissuances, a permit can also be modified.
A real example: Washington’s Western Washington Phase II Municipal Stormwater Permit has been in effect since August 1, 2024, and expires July 31, 2029. Ecology’s permit page says annual reports for a calendar year are due by March 31 of the following year, and that Ecology has already started the reissuance process for the 2029 permits. A configuration built today should say which version it follows, and it should be ready to change when the next version is issued.
Administrative continuation
Permits are not always reissued on time. When an EPA-issued permit expires and the permittee has applied for a new one on time, the conditions of the expired permit continue in force until the new permit takes effect, and a continued permit remains “fully effective and enforceable” (40 CFR 122.6). States that run their own NPDES programs can continue permits in a similar way where state law allows.
Another real example: EPA’s page for the Massachusetts small MS4 general permit says “The 2016 MA MS4 General Permit has been administratively continued.” That permit was signed in 2016, became effective July 1, 2018, was modified with changes effective January 6, 2021, and has a draft replacement. A vendor that shows only “expired” or only “current” is throwing away information you need: which version is in force, which modifications apply, and what is coming next.
Reporting cycles come from the permit
Do not let anyone guess your reporting schedule. The federal rule sets a floor: annual reports during the first permit term, then reports in years two and four of later terms unless the permitting authority requires more frequent reports (40 CFR 122.34). Many permits require more than that. The schedule that applies to you is the one in your permit.
The same rule also says what a report must contain at a minimum: the status of compliance with the permit, the results of information collected, the activities planned for the next cycle, and any changes to the program. A vendor’s report template should be traceable to your permit’s own version of those requirements.
Why sources and dates matter
Every fact in a permit setup should be traceable: where it came from, when it was read, and what the source actually says. Without that, you cannot tell a verified requirement from a vendor’s assumption, and you cannot tell when something needs updating.
Hold every vendor to that standard, including us. On this site, the permits page separates the one permit with an implemented annual report template, Western Washington Phase II, from the state pages that are preliminary planning references and not verified production coverage, and the Washington Phase II page links to Ecology’s own permit pages. For any other permit, ask us which permit and version we would configure, what we have checked, and when we checked it.
Questions to ask any vendor
- Which permit, by number and version, are you configuring for us?
- Is it a general permit or an individual permit, and how do you reflect our notice of intent or our individual conditions?
- For each requirement, can you show me the page of the permit it came from?
- When did you last check the permitting authority’s page, and what did it say about the permit’s status?
- If our permit is administratively continued, how does your software show that?
- What happens to our workspace when the permit is reissued or modified?
- Where did our reporting schedule come from?
- What is verified, what is assumed, and what still needs verification?
A vendor that answers with sources and dates is giving you something you can check. A vendor that answers with a map of the country colored in is giving you a slogan.
Where to go next
The permits page explains what is implemented for Washington and what the other state pages are, and the Washington Phase II page shows the implemented annual report template and Ecology’s sources. The Phase II MS4 software page covers the product side. If you want to walk through your own permit, request a private demonstration.
Sources
- 40 CFR 122.26: definitions of large, medium and small MS4s
- 40 CFR 122.32: which small MS4s are regulated
- 40 CFR 122.33: general permits, individual permits and co-permittees
- 40 CFR 122.34: small MS4 permit requirements, records and reports
- 40 CFR 122.6: continuation of expiring permits
- 40 CFR 122.46: duration of permits
- U.S. EPA, Stormwater Discharges from Municipal Sources
- U.S. EPA, Massachusetts Small MS4 General Permit
- Washington State Department of Ecology, Western Washington Phase II Municipal Stormwater Permit
Sources checked October 17, 2026.