Do I need a stormwater permit for a warehouse or dock?

The Arizona Department of Environmental Quality (ADEQ) issues the industrial stormwater Multi-Sector General Permit, or MSGP. ADEQ's page says the MSGP identifies 29 sectors of industrial activity that are subject to permitting for industrial stormwater discharges. The current version is the 2024 MSGP, effective January 16, 2025.

Two conditions have to be true before a site needs coverage:

1. 1The site's industrial activity falls within one of the listed sectors.
2. 2Its stormwater will discharge to protected surface waters.

ADEQ says a facility must have permit coverage when both apply. It also says that if industrial stormwater will not discharge to protected surface waters, either directly or by way of a conveyance such as a street or ditch, stormwater permit coverage is not required. In that case ADEQ offers an optional No Discharge Certificate. Whether a Valley site's runoff reaches a protected surface water through the storm system is a technical question. Ask ADEQ or a qualified consultant instead of guessing.

Phoenix's code describes a SWPPP as a site-specific written document that identifies potential sources of stormwater pollution and describes the practices the operator will use to reduce them. It is a working plan for the site, not a form to file and forget. The permit relies on best management practices, since, as ADEQ notes, stormwater is not treated the way wastewater is before it is discharged. Sites that need coverage file a Notice of Intent through myDEQ, and must complete a Stormwater Pollution Prevention Plan (SWPPP) before they submit it. Application fees depend on site size in acres, with annual fees each year the permit is active. This page does not state amounts, and you can see them on ADEQ's fee page.

A loading dock by itself is not a sector. Coverage attaches to the kind of business the site runs, not to the presence of a dock. EPA's Sector P fact sheet covers land transportation and warehousing activities, and it lists motor freight transportation facilities (SIC codes 4212 through 4231) among the categories that require coverage under an industrial stormwater permit. The fact sheet describes the activities of concern as vehicle and equipment maintenance, such as fluid changes, mechanical repairs, parts cleaning, painting and fueling, and equipment cleaning, such as tank washouts.

That tells you where to look. A distribution site with a fleet shop, a fueling island or a truck wash is closer to the activities EPA describes than a building that only receives pallets and ships them. Other sectors may apply to a manufacturer or a recycler, whatever their dock looks like. ADEQ publishes a list of sectors, and the safest step is to confirm your SIC code with ADEQ directly instead of assuming.

Questions to ask:

• What is the site's SIC or industrial activity code?
• Does the site do vehicle maintenance, parts cleaning, fueling or equipment washing outdoors?
• Are materials, waste, fluids or equipment stored outside, where rain can reach them?
• Where does the lot's storm drainage go? Follow the pipe to see whether it reaches a street, a ditch or a retention basin.

If a site would otherwise be regulated but keeps its industrial materials and activities covered, ADEQ offers a No Exposure Certificate (NEC). ADEQ's FAQ says:

• The site's industrial materials and activities must be covered by a storm-resistant shelter and not exposed to rain, snowmelt or runoff.
• A storm-resistant shelter includes completely roofed and walled buildings, and structures with only a top cover, as long as material under them is not subject to run-on and runoff of stormwater.
• You get the certificate through myDEQ, where the system asks 11 yes-or-no questions from EPA's exposure checklist. A "yes" to any question means you are not eligible and must get an NOI.
• The NEC lasts five years and is nontransferable. If you sell the property, cancel it and the new owner applies if eligible.
• You do not need a SWPPP with an NEC, though ADEQ recommends a plan to inspect the site so it keeps qualifying.
• ADEQ does not approve your claim in advance. You certify that the information is true, and ADEQ or the city that receives the discharge can inspect to verify it.
• Exclusion applies to the whole site, not to single areas. If any activity or material is exposed, the site should apply for an NOI instead.

An indoor dock with doors, where trucks back in and materials stay under cover, is easier to defend as "no exposure" than an open yard with stacked pallets and leaking equipment. But a dock apron that trucks cross with fluids dripping is a different case. The final call is yours to certify, so be careful.

A state permit is not the only stormwater rule. Cities have their own. Phoenix City Code 32C-104, for example, requires a person who conducts an activity on nonresidential property with the reasonable potential to affect the quality or volume of stormwater to prepare a written stormwater management plan. The code presumes a plan is not required for activities inside completely enclosed structures or other areas permanently inaccessible to contact with stormwater. And the city's code says an authorization under a state permit does not excuse a person from preparing that plan when the city requires it.

Other Valley cities have their own versions, so check yours. Also keep in mind the basic rule that only stormwater goes into a storm drain. See can you hose a parking lot into the storm drain and where does a loading dock drain go. And for the sewer side, see does a loading dock drain need an oil separator.

### What to do

1. 1Find your site's SIC code. Your business license, insurance paperwork or a tenant's registration may list it.
2. 2List outdoor activities and materials, and note which are under cover.
3. 3Trace where your storm drains lead.
4. 4Ask ADEQ, or a stormwater consultant, whether the MSGP applies. Ask your city separately about any stormwater management plan.
5. 5If an NEC or NOI is in place, put the renewal date on the calendar and keep the inspection records.
6. 6In a lease, decide who holds the certificate and who inspects. The NEC cannot be transferred with the building.

A warehouse is not automatically covered, and a dock does not create the duty on its own. The permit depends on the sector, the activity and whether rain reaches your materials. Do a short walk-through, ask ADEQ and the city in writing, and keep a copy of what they say. If you are unsure, asking first is easier than answering a violation notice later.