MS4 Stormwater Management

Ordinance #384 – Stormwater Management

Act 167 Stormwater Management Plan Update

When it Rains: Understanding Stormwater Management

Homeowners Stormwater Guide

What is the MS4 Program?

Certain stormwater regulations associated with the Federal Clean Water Act are administered under the Municipal Separate Storm Sewer System (MS4) Program. In Pennsylvania, the MS4 program is managed by the Pennsylvania Department of Protection.

What is Required under the MS4 Program?

Operators of a small MS4 must obtain a NPDES permit and develop and implement a Stormwater Management Plan (SWMP) according to the details of their specific permit. Mandatory elements of the SWMP include six (6) Minimum Control Measures (MCMs). Each MCM has a number of associated Best Management Practices (BMPs) that explain in more detail how the MCM can be carried out. The MCMs are:

  1. Public Education and Outreach on Stormwater Impacts
  2. Public Involvement / Participation
  3. Illicit Discharge Detection and Elimination
  4. Construction Site Stormwater Runoff Control
  5. Post-Construction Stormwater Management in New and Re-Development Activities
  6. Pollution Prevention / Good Housekeeping for Municipal Operations

What is Stormwater Runoff?

Stormwater runoff is precipitation (rain or snowmelt) that flows across the land. Stormwater may infiltrate into soil, discharge directly into streams, water bodies, or stormdrains, or evaporate back into the atmosphere. In the natural environment, most precipitation is absorbed by trees and plants or permeates into the ground, which results in stable stream flows and good water quality. Things are different in the built environment. Rain that falls on a roof, driveway, patio, or lawn runs off the surface more rapidly, picking up pollutants as it goes. This stormwater runoff flows into streams or storm drains that empty into waterways like the Allegheny, Monongahela and Ohio rivers.

Why Can Stormwater Runoff be a Problem?

Poorly managed stormwater runoff can cause many problems. These include:

Flooding. As stormwater runs off roofs, driveways, and lawns, large volumes quickly reach streams, causing them to rise and flood. When more impervious surfaces exist, flooding occurs rapidly and can be severe, resulting in damage to property and harm to people.

Pollution. Stormwater running over roofs, driveways, roads, and lawns will pick up pollutants such as oil, fertilizers, pesticides, dirt/sediment, trash, and animal waste. These pollutants “hitch a ride” with the stormwater and flow untreated into local streams, polluting our waters.

Stream Bank Erosion. When stormwater flows into streams at unnaturally high volumes and speeds, the power of these flows can cause severe stream bank erosion. Eroding banks can eat away at streamside property, create dangerous situations, and damage natural habitat for fish and other aquatic life. This erosion is another source of sediment pollution in streams.

Threats to Human Health. Stormwater runoff can carry many pollutants, such as toxic metals, organic compounds, bacteria, and viruses. Polluted stormwater, especially coming from combined sewer overflows, can contaminate drinking water supplies and hamper recreational opportunities as well as threaten fish and other aquatic life.

What Can You Do to Help?

As a homeowner, you can help avoid the problems associated with stormwater runoff by:

  • reducing impervious areas (hard surfaces like roofs, paved areas) so that rain soaks into the ground
  • planting native trees and plants which help infiltrate stormwater and increase evaporation and transpiration
  • managing stormwater on-site with rain gardens, rain barrels, and similar practices
  • following the lawn care practices described in this guide

By doing many small things on your property, you can have a big impact on improving stormwater management and water quality in our region.