NYC Stormwater Rule

Rain can’t soak into roofs and pavement, so it runs off. It flows into a catch basin, the street drain, and on through a sewer.

The sewer takes it to a treatment plant, or straight to a river or bay.

On the way it picks up mud and trash. The NYC Stormwater Rule sets what a construction site must do about it.

Each big job files a plan called a SWPPP (Stormwater Pollution Prevention Plan).

Two sewers

NYC has two kinds of sewer. Which one a site drains to changes where its runoff ends up.

Small, frequent storms cause much of the harm. In storm sewers their runoff carries more pollution. In combined sewers they set off most overflows.

So the rule is sized for a 1.5 in storm, bigger than 9 of 10 NYC rains.

The rule and the plan

Storm sewers (MS4) run under a State permit. That permit makes the City review SWPPPs and inspect sites.

The Unified Stormwater Rule (USWR) joined that permit program with DEP’s sewer-connection rules.

Two jobs

During construction, erosion and sediment control (ESC) keeps soil on site. After, permanent practices handle the runoff.

Who it applies to

The rule reaches only big jobs. Two size tests decide which.

The two tests

Pass either test and the project needs a DEP permit and a SWPPP, unless an exception applies. Emergency work and routine maintenance are two such exceptions; Level 2 lists the rest. Public and private projects alike.

Tally a project

Inside a SWPPP

A project that passes a size test files a SWPPP with its permit application. A qualified professional, such as an engineer or landscape architect, signs it.

Every SWPPP covers the first job, erosion control. Many add the second, permanent practices. The type of work decides; Level 2 shows how.

The rule in brief

1. Big jobs only: 20,000 sf of soil dug up, or 5,000 sf of new paving or roof. Public or private. Who it applies to
2. A qualified professional, such as an engineer or landscape architect, signs the SWPPP.
3. During construction, mud stays on site. What it requires
4. Most projects also build permanent features, such as rain gardens, sized for a 1.5 in storm. Sizing
5. DEP, the NYC Department of Environmental Protection, decides in 45 days. Getting the permit
6. Then a permit, inspections every week, and a sign-off at the end.
7. Permanent features keep a permit of their own, renewed every 5 years. During and after

Key facts

Tools

Check

Exceptions

Passing a size test is not the end. A few jobs are carved out. Many that look like exceptions are not.

Projects whose construction documents were filed with the Department of Buildings (DOB) or Small Business Services before Mar 26, 2021 or Feb 15, 2022 may fall under transition rules.

Tables 2.2 and 2.3

A project that is covered and not an exception needs a permit and a SWPPP. Two tables in the Stormwater Manual set how much that SWPPP must do.

Permanent practices have two jobs. Water quality (WQ): catch all the runoff from the 1.5 in storm. Runoff reduction (RR): make part of it soak in, evaporate or get reused.

Covered or not?

Ten projects to test the size tests, the exceptions and the tables. Pick an answer for each.

What it requires

The tables set which requirements a SWPPP carries. There are five in all; tap each one.

Five requirements

Erosion control and water quality rules are the same for both sewers. No Net Increase applies only in storm-sewer (MS4) areas.

Two chapters

Both chapters sit in Title 15 of the Rules of the City of New York (15 RCNY).

Erosion control

Erosion control is the one requirement on every covered project. Here is how it works.

Design standard: the NYS Blue Book. Drawings show standard practice, not rule text.

The measures

Also

• Concrete washout pit, so alkaline wash water stays out of the drains.
• Dewatering through a filter bag or settling tank.
• Pollution prevention for litter, chemicals and debris.

Spot the problem

A construction site with five erosion mistakes. Tap each one. How each measure works

Sizing

WQ and RR are sized as volumes of water. Each volume starts from the same math: rain depth × area × the share that runs off.

One acre, one storm

WQv

Minimum RRv

Sewer detention for new connections uses a third formula. Sewer detention

Permanent practices

Permanent practices hold the sized volume. Each works in one of two ways: retention or treatment.

Functions

The hierarchy

DEP ranks practices in tiers. Only the order of tiers differs between the two sewers.

Soil tests, setbacks and other limits decide which tier fits. Design limits

SWPPP qualifier

Everything so far, as one set of questions. The chart shows the order; the qualifier asks them for one project.

Answer the questions for one project. Who it applies to

Example projects

Four projects run through the same questions, one answer at a time.

Permit steps

Once the project and its requirements are known, the SWPPP goes to DEP.

Who signs

• Qualified professional prepares the SWPPP: a professional engineer (PE), registered landscape architect (RLA) or other NYSDEC-endorsed person. Engineering parts need a NY PE.
• Qualified inspector inspects every 7 days: a PE, RLA or CPESC (Certified Professional in Erosion and Sediment Control), or trained staff under a PE or RLA.
• Trained contractor inspects daily: the contractor’s employee.
• Developer: the owner, lessee, or whoever controls the plans.
• Applicant files in SWPTS, DEP’s online permit system.

SWPPP checklist

Both lists come from the rule’s application requirements.

Construction and closeout

With the permit in hand, work starts.

Changes

• Major SWPPP amendments: reviewed like a new SWPPP, $1,000 per disturbed acre.
• Temporary shutdown: notify 7 days ahead, inspect every 30 days.
• Over 5 acres open at once: DEP authorization, two inspections every 7 days, stabilize within 7 days.

After construction

Only projects with permanent practices.

The map

Tap a box for its explanation and source.

NYC waters at risk

DEP lists these waters as impaired: already failing their water quality standards. Sites that meet all four NNI tests can’t add more of the listed pollutant.

Look up where a site drains on DEP’s MS4 Interactive Map. Selected from Manual Table 2.4, which lists more.

Sewer detention

A new sewer connection adds a second review, by DEP’s Bureau of Water and Sewer Operations (BWSO). It asks for storage that holds back a bigger storm and lets it out slowly. The requirement

Vv and release rate

Q_dev = C_w × A ÷ 7,320 (5-yr storm, 6-min, 5.95 in/hr). Vv applies when Q_dev exceeds Q_DRR.

Design limits

Constraints

Only a documented constraint allows a lower tier. Tier 2 or 3 needs written justification.

Each practice under 1,000 sf needs at least one geotechnical boring or permeability test.

By practice

For parks

Streets

Milling and paving (Manual Chapter 7)

Street milling and paving of 20,000 sf+ needs no permit since the 2023 amendments. Manual Chapter 7 practices still apply.

Reconstruction (Chapter 6)

Street rebuilds need permanent practices only at 1 acre+ disturbed. No sewer detention (Vv) in the right-of-way.

Park paths

The example: 30,000 sf of asphalt paths through lawn, rebuilt full depth on the same alignment and width. The rule points three ways.

Three possible answers

Neither the rule nor the Manual defines “sidewalk.” Table 2.2 names “sidewalk, bike path or walking path” as separate things. That suggests a park path is not a “sidewalk” under the routine maintenance exception. Only DEP can settle it.

Covered?

Full depth exposes the soil below, so it counts as soil disturbance. Splitting contracts doesn’t avoid the threshold.

The rule doesn’t say whether a surface-only mill-and-overlay of a path counts. For streets, DEP counts milling toward 20,000 sf when it comes with a utility dig.

What changes it

ESC plan for paths

• Tight limit of disturbance. Protect lawn and trees.
• Build in segments. Seed and mulch each edge.
• Silt fence or sock on the downhill side.
• Stone entrance at the street. Stockpiles covered.
• Inlet protection on nearby catch basins.
• Daily and weekly inspections.

Keep drainage as it was. Work that alters hydrology moves to Table 2.3.

Check

Questions for DEP

Park paths

1. Is in-place park path replacement “replacement of sidewalks” (routine maintenance)?
2. Table 2.2 (ESC only) or §19.1-03.3(b)(4) (post-construction): which governs full-depth path reconstruction?
3. Table 2.2 reads “not park of residential…”. Confirm it means “part”.
4. Is a park, or a path on a school campus, “institutional development”?
5. What counts as “altering hydrology” for vegetated open space?
6. Does surface-only milling and repaving of a park path count as soil disturbance?
7. Mixed projects: does long-term management cover the whole project, or only areas draining to Table 2.3 work?
8. If Table 2.2 and the 2025 State permit’s Appendix B Table 1 differ, which controls?

City agency projects

9. Do the fees apply to Parks capital projects, and are the 2021 amounts current?
10. Maintenance easements on Parks property: standing Law Department determination, or project by project?
11. Who holds the Maintenance Permit and signs the yearly certification for Parks projects?
12. Stabilization deadline for sites under 5 acres? The City rule states one only above 5 acres.
13. Under the 2025 State permit, do RLAs need the 4-hour training themselves to inspect?

Outdated documents

14. The January 2022 FAQ predates the 2023 change to street repaving. Is there an updated FAQ?
15. When did the 2023 amendments take effect?

Quiz

Flashcards

Questions

Quick reference

Glossary

Sources

Each Source label opens a quote checked word for word against the PDF page shown.

Rule amendments effective Feb 15, 2022. Later amendments heard July 26, 2023. Manual final Feb 1, 2024. The FAQ (Jan 2022) predates the 2023 changes.

Referenced, not quoted

• 15 RCNY Chapter 31
• NYS Blue Book (2016)
• NYS Stormwater Management Design Manual
• NYC MS4 Permit NY0287890
• NYSDEC construction general permit (2025)