This document is the TN 1.03 Storm Water Quality Units. It describes the storm water treatment, sizing and conclusion.

The ADS Storm Water Quality Unit (SWQU) is designed to remove pollutants from storm water during a storm event. ADS has modified its standard N-12 ® pipe to include weir plates at certain locations and heights to help facilitate sediment and oil removal from storm water. A bypass pipe is included in the storm water quality unit, so the system can focus on treating the “first flush”. After the “first flush” has entered the system, the bypass pipe directs high volumes of storm water around the system.

Relatively high concentrations of pollutants may be flushed into storm drains during a first flush. First flush pollutant concentrations are relatively high at the beginning of storms and drop off over time. Although it may vary based on site conditions, the first flush can contain over 80% of the pollutants that will be transported off a site.

It is a widely accepted practice to provide treatment for the first flush as opposed to treating the entire design storm event. Treating the first flush provides a high level of storm water quality at a much lower cost to the developer. The storm water runoff, which follows the first flush, is generally assumed to be relatively clean in comparison. Providing treatment for this “clean water” can often double, if not triple, the cost of treatment at a minimum.

The treatment of the contaminated storm water is achieved through the use of weir plates installed at various locations within the unit. The storm water will enter the Sediment Chamber, which consists of an upright weir for trapping sediment. A second chamber, or Oil Chamber, uses an inverted weir to trap oils, grease, and debris.

Field and lab testing of the unit results are listed.

Sizing a Storm Water Quality Unit formulas are provided.

In conclusion, the ADS SWQU provides a cost efficient treatment option for a variety of applications while achieving removal efficiencies that meet or exceed most local minimum requirements for storm water treatment. The treatment of both settling and floating pollutants provides a good first level management technique that offers the user the opportunity to use the device in either a stand- alone configuration or as a step in a treatment train.