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Construction Sites and Water Runoff

Quick Tips #278

It might surprise you to hear that sediment runoff rates from construction sites are typically 10 to 20 times greater than those from agricultural lands, and 1000 to 2000 times greater than those from forested lands. To address this issue, the Environmental Protection Agency (EPA) has regulations that focus specifically on construction sites and water runoff. The Federal Water Pollution Control Act prohibits the discharge of any pollutant to a navigable water from a point source unless that discharge is authorized by a National Pollution Discharge Elimination System (NPDES) permit. Construction sites for which a NPDES permit is sought will fall into one of two categories, or phases.

Phase I

This phase addresses discharges from large construction activities disturbing five or more acres.

Phase II

Phase II affects many more entities than Phase I, because it pertains to smaller construction sites between one and five acres. Phase II can also cover construction sites under one acre if they are part of a larger common plan of development or sale with a planned disturbance of between one and five acres. To get a good sense of the requirements, a few definitions are in order.

Point source: A point source is any discernable, confined and discrete conveyance, such as a pipe, ditch, channel, tunnel, conduit, discrete fissure or container. It also includes vessels or other floating craft from which pollutants are or may be discharged. By law, the term "point source" also includes concentrated animal feeding operations, which are places where animals are confined and fed. By law, agricultural stormwater discharges and return flows from irrigated agriculture are not "point sources."

Navigable water or water of the United States: The term "water of the United States" means navigable waters, tributaries to navigable waters, interstate waters, the oceans out to 200 miles and intrastate waters which are used: by interstate travelers for recreation or other purposes, as a source of fish or shellfish sold in interstate commerce, or for industrial purposes by industries engaged in interstate commerce.

Operator: An Operator in this instance is a party or parties that have:

  • Control of construction project plans and specifications
  • Day-to-day operational control of those activities that are necessary to ensure compliance with a storm water pollution prevention place (SWPPP) for the site or other permit conditions

NPDES permit: This is a permit that translates general requirements of the Clean Water Act into specific provisions tailored to the operations of each person discharging pollutants.


Phase II construction programs require operators of Phase II small construction sites to obtain an NPDES permit if the operators are discharging pollutants from a point source to waters of the United States. The NPDES permit contains limits on what can be discharged, monitoring and reporting requirements and other provisions to ensure that the discharge does not hurt water quality or people's health. These regulated entities must implement stormwater pollution protection programs or stormwater management programs using best management practices to effectively reduce the discharge of pollutants into receiving waters. There may also be additional state, tribal or local construction site water runoff programs required in certain areas.

The EPA has recommended that the NPDES permitting authorities use their existing Phase I large construction permits as a guide in developing the Phase II permits. Although the specific NPDES permitting authority may have different requirements, the Phase II permits will typically consist of three main components:

  1. Submission of notice of intent: This notice of intent will include general information on the site and what is going to be done at the site.
  2. Stormwater pollution prevention plan (SWPPP): Almost all NPDES permitting authorities are going to require a type of SWPPP that will detail how you are going to control the runoff.
  3. Notice of termination: Once the project is completed or is taken over by another operator a notice of termination would be submitted.

Frequently Asked Questions

Q: Do I need an NPDES permit for construction site water runoff?

A: It depends on where you discharge pollutants. If you discharge from a point source into waters of the United States, you need an NPDES permit. If you discharge pollutants into a municipal sanitary sewer system, you do not need an NPDES permit, but you should ask the municipality about their permit requirements. If you discharge pollutants into a municipal storm sewer system, you may need a permit depending on what you discharge. You should ask the NPDES permitting authority.

Q: Where do I apply for a NPDES permit?

A: NPDES permits are issued by states that have obtained EPA approval to issue permits or by EPA Regions in states without such approval.


Stormwater Phase II Small Construction Program Overview

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.

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