Env 247 Overview of Stormwater

ManagementMarch 1, 2011

Sources of Stormwater Runoff

1. Sheet flow over impervious surfaces or other structures

2. Runoff including agriculture, urban areas, construction, and forestry

3. Municipal Stormwater Management Systems Large, small, and urban municipal separate storm sewer

systems (MS4s)

4. Industrial Facilities/Activities5. Construction Activities

Managing Stormwater Discharges through the National Pollutant Discharge

Elimination System (NPDES) Permit

1. Point Sources that discharge into waterways are subject to permitting requirements –• Municipal Stormwater Collections Systems including MS4s • Certain industrial discharges• Other outfalls that directly discharges into waterways

2. Non-point Sources are subject to “general permits” • Stormwater runoff due to construction activites

Typical Stormwater Outfall –Point Source

A Case Study – Managing Stormwater Runoff from a

Constructon Site

Pollutants Commonly Discharged from Construction Sites

1. Sediment2. Solid and sanitary wastes3. Phosphorous (fertilizer)4. Nitrogen (fertilizer)5. Pesticides6. Oil & grease7. Concrete truck washout8. Construction chemicals9. Construction debris

A Case Study – Managing Stormwater Runoff from a Constructon Site –

Permitting System

US EPA has issued a “general permit” that authorizes the discharge of pollutants in stormwater discharges associated with construction activity that disturbs one acre or more of land.

Site owners must submit a Notice of Intent (NOI) to operate under the “general permit”

In NC, site owners can submit a “land disturbance permit” application in lieu of an NOI that contains methods to comply with the general permit requirements.

Content of Land Disturbance Permits

Land disturbance permits contain administrative requirements consistent with the requirements outlined in the General Permit, including:

1. Equipment operation & maintenance practices to avoid the release of fuels, lubricants, etc. onto the ground;

2. Material handling practices regarding the use of pesticides, herbicides and fertilizers;

3. Building material waste handling;

4. Litter & sanitary waste handling;

5. Monitoring & reporting requirements; and,

6. Site inspection requirements.

Best Management Practices (BMPs) to Prevent Erosion and Sediment Runoff

Erosion controls designed to either: (1)prevent erosion through protection and preservation of soil or (2)prevent sediment runoff before the runoff is discharged from the site include:

Stabilization PracticesStructural Practices

Example of sedimentation entering a storm drain

Best Management Practices -Stabilization

Stabilization reduces erosion potential by (1) intercepting water so that it infiltrates into the ground instead of running off the surface and (2) slowing the velocity of runoff, thereby promoting deposition of sediment and includes such practices as:

1. Temporary seeding2. Permanent seeding3. Mulching4. Sod stabilization5. Vegetative buffer strips6. Contouring and protection sensitive

areas

Best Management Practices -Structural Practices

Structural Practices involve the installation of devices to divert, store, or limit runoff to prevent water from flowing on disturbed areas where erosion may occur, and include:

1. Earth dikes2. Silt fences3. Drainage swales4. Check dams5. Pipe slope drains,6. Temporary stormwater diversions

Stormwater Management

Stormwater management measures are measures applied to reduce pollutants in stormwaster discharged from the site after completing construction activities, and include:1. Onsite infiltration of runoff2. Flow attenuation by vegetation or natural

depressions3. Outfall velocity dissipation devices4. Stormwater retention basins5. Artificial wetlands6. Stromwater detention structures.