Assessing your Site and Proposed Project will help to provide a good foundation for your SWPPP

Following are the important steps in Assessing your Site and Proposed Project:

Visit the Site

The people responsible for site design and drafting the SWPPP should conduct a thorough walk-through of the entire construction site to assess site-specific conditions such as soil types, drainage patterns, existing vegetation, and topography.

Avoid copying SWPPPs from other projects to save time or money. Each construction project and SWPPP is unique, and visiting the site is the only way to create a SWPPP that addresses the unique conditions at that site.

Assess Existing Construction Site Conditions

Assess the existing conditions at the construction site, including topography, drainage, and soil type. This assessment, sometimes called fingerprinting is the foundation for building your SWPPP and for developing your final site plan. In this assessment, use or create a topographic drawing that:

• Indicates how storm water currently drains from the site, and identify the location of discharge points or areas

• Identifies slopes and slope lengths. The topographic features of the site are a major factor affecting erosion from the site

• Identifies soil type(s) and any highly erodible soils and the soil’s infiltration capacity

• Identifies any past soil contamination at the site

• Identifies natural features, including trees, streams, wetlands, slopes and other features to be protected

In most cases, the site designer can compile all this information on a digitized drawing  that can then be adapted to show the planned construction activity, the phases of construction, and the final site plan.

Identify Receiving Waters, Storm Drains, and Other Storm water Conveyance Systems

Your Storm water pollution prevention plan (SWPPP) should clearly identify the receiving waters and storm water systems through which storm water from your site could flow. Many states require planning for a specific storm event or storm events.

These storm events are referred to by their recurrence interval and duration such as 1-year, 6-hour storm or a 100-year, 24-hour storm. These events then translate into a specific rainfall amount depending on  average conditions in your area.

Describe Your Construction Project

Your Storm water pollution prevention plan should contain a brief description of the construction activity, including:

• Project type or function (for example, low-density residential, shopping mall, highway)

• Project location, including latitude and longitude

• Estimated project start and end dates

• Sequence and timing of activities that will disturb soils at the site

• Size of the project

• Estimated total area expected to be disturbed by excavation, grading, or other construction activities, including dedicated off-site borrow and fill areas

• Percentage of impervious area before and after construction

• Runoff coefficient1 before and after construction

• Soil types

• Construction site location and any nearby waters or wetlands

• Describe and identify the location of other potential sources of storm water contamination, such as asphalt and concrete plants, stucco operations, paint and concrete washout, and such

Identify Pollutants and Pollution Sources

 Identify the pollutants and sources that are likely to be found on the site. The principle pollutant of concern, of course, is sediment.

There are, however, other pollutants that may be found, usually in substantially smaller amounts, in storm water runoff from construction sites. These can include nutrients, heavy metals, organic compounds, pesticides, oil and grease, bacteria and viruses, trash and debris, and other chemicals. After identifying the pollutants and sources, be as specific as possible in your SWPPP about the BMPs you will use to address them.

Non-Storm water Discharges

Most permits will require you to identify any non-storm water discharges in your SWPPP. Certain non-storm water discharges may be allowed under the terms and conditions of your permit, however, you should make every effort to eliminate these discharges where possible. You should identify these sources in your SWPPP and identify pollution prevention measures to ensure that pollutants are not introduced to these discharges and carried to nearby waterbodies.

Permanent Storm water Controls (Post‑Construction)

A Storm water pollution prevention plan compiled in support of coverage under EPA’s Construction General Permit, however, needs to include a description of all permanent storm water controls that will be constructed along with the buildings, roads, parking lots, and other structures. You should incorporate sediment and erosion controls into your SWPPP for areas where permanent storm water controls, such as wet ponds, swales, and bioretention cells are to be constructed.

Author – Bio

Understanding the hydrologic and other natural features of your site will help you develop a better SWPPP and, ultimately, to more effectively prevent storm water pollution. Quest Consultants provides Storm water pollution prevention plan (SWPPP) services and also has experts who help their clients in developing effective SWPPP plan. For more information visit www.questepa.com.