Skip to main content

What is an MS4?

MS4 stands for Municipal Separate Storm Sewer Systems. MS4 permits regulate storm drains of a city or county, which are designed to collect stormwater from streets and highways. The stormwater runs through a complex system eventually finding its way to a river, bay or the Pacific Ocean–without any treatment.


To regulate and prevent harmful pollutants from washing or dumping into the stormwater system, Regional Water Quality Control Boards issue MS4 permits to operators, who much also develop a stormwater management program.

Why does an MS4 matter?

Stormwater systems directly affect our swimmable, drinkable, fishable waters. Pollution that collects or gets used on our streets, walkways, landscape, and roadways gets washed into the storm drains and released into our waters without any treatment. MS4 permits create regulations designed to ensure our waters do not become overly polluted and unsustainable.

How bad is urban runoff pollution?

Runoff pollution is a big problem for us in Orange County–it’s our number one water quality problem. Stormwater pollution contains heavy metals, trash, bacteria, and pH-affecting contaminants and accounts for more than half of the total pollution entering surface waters each year.

You witness this every time it rains and the Orange County Health Care Agency issues a public advisory to avoid entering waterways, including the ocean, for three days after a storm to avoid stormwater related illness.

What’s the process to approve an MS4 permit?

The Regional Water Quality Control Board staff and key stakeholders start the process by writing a draft MS4 permit. The Regional Board then releases the draft permit for official public comment. The Regional Board will address public comment and release a revised permit that is again open for public comment. Generally, the public has 30 days to submit official comments on draft permits before the Regional Board will take a final vote at a board meeting. Of course, public comment is usually allowed at the board meeting, and sometimes the Regional Board will request last minute revisions on the final draft, and then they vote.

What are the timelines for MS4 permits?

During the summer of 2013, Coastkeeper successfully negotiated the south Orange County MS4 permit. This spring, we expect to hear a final decision from the State Board on the Los Angeles MS4 permit that is currently on appeal because it includes a Safe Harbor Provision. This summer, Coastkeeper will be negotiating the north Orange County MS4 permit before the Santa Ana Regional Water Quality Control Board.

Which MS4 permits regulate Orange County’s waters?

Five MS4 water quality permits affect Orange County waters because, as we all know, the waterways of Southern California don’t follow our county and city lines.

  • The Orange County MS4 permit governs the storm drains that flow into north Orange County waters. We anticipate this permit to go through its draft and comment periods later in 2015.
  • Region 9’s MS4 Permit is the San Diego Region water quality permit and includes part of south Orange County.
  • Two permits in the Inland Empire influence Orange County’s water because they govern the headwaters of many of our waterways.
  • The Los Angeles MS4 permit affects water in the San Gabriel River, and it’s a high profile permit this year that may set standards for all permits in the state.

Why does the Los Angeles MS4 matter to Orange County?

The Los Angeles MS4 permit is currently on appeal with the State Board because it includes a Safe Harbor Provision, a loophole in regulation that makes it possible for pollution to our waters to increase. Additionally, it governs water quality in the San Gabriel River, which also flows into Orange County.

Simultaneously, the State Water Quality Control Board is developing guidance for MS4 permits, using the Los Angeles MS4 permit as the example. We want the state guidance to recommend strong environmental standards, and we are concerned that if the Los Angeles MS4 permit is upheld with the Safe Harbor Provision, this will set a precedent for all permits to include that loophole.

What is a Safe Harbor Provision and why does it matter?

A Safe Harbor Provision is a regulation that specifies that certain conduct will not be considered a violation of a given rule. In other words, it’s a loophole or way around a regulation, making it possible for pollution to our waters to increase. The issue is that the Safe Harbor Provision in the MS4 permits will move us backwards in environmental permit standards.

Our goal is to have the state guidance laws not include Safe Harbor Provision to ensure the the laws uphold water quality standards and set examples for other regional boards.

Currently, the Orange County MS4 draft includes a Safe Harbor Clause, and we doing all we can to get it removed.

How can I help ensure the MS4 permits protect water quality?

To make sure our waters are healthy and sustainable, we need the permits to strengthen with time. You can help by donating to our advocacy work, spreading the word about strong MS4 permits on social media and attending hearings to make your voice heard.