||The NBC's two largest Wastewater Treatment Facilities (WWTFs) receive a mixture of residential, commercial, and industrial wastewater; and during rain events, stormwaters flow from ten Rhode Island cities and towns.
At the turn of the century, many urban areas across the nation built their sewer systems to carry both sewage and stormwater run-off in the same pipe. This is called a combined sewer. Both of NBC's WWTFs have been designed in this manner, and during a rain event enormous amounts of stormwater runoff enter the NBC sewer system. During dry weather, NBC's Field's Point WWTF receives on average, 45 million gallons/day (mgd) of wastewater, and its Bucklin Point WWTF receives about 24 mgd. During a rain event, however, wastewater flow can swell to as much as 200 mgd and 100 mgd, respectively. The additional hydraulic loading caused by the influx of stormwater into the combined sewers and the various contaminants found in stormwater increase treatment costs and decrease the effectiveness of the WWTFs to fully treat conventional pollutants found in municipal wastewater. Also, and most importantly, during heavy rain storms, combined flows can exceed the capacity of the sewer system resulting in the discharge of raw untreated sewage into local rivers and the Narragansett Bay. This is a combined sewer overflow.
To help minimize untreated wastewater from overflowing into water bodies during periods of heavy rain, the NBC has constructed an underground tunnel that will capture a major portion of stormwater flow from most rain events for eventual treatment. The underground combined sewer overflow tunnel is about three miles long and is expected to be completed in 2008. Because of the cost associated with treating stormwater and problems associated with treating pollutants often found in the stormwater flow, NBC has great interest in both reducing the amount of stormwater received at its facilities and minimizing the types and amount of contaminants in the stormwater.
With these concerns in mind, in 2004, the NBC applied for and received a $35,000 EPA Grant to develop a Stormwater Pollution Prevention Project. The Project consists of non-regulatory, free, in-depth site assessments of stormwater activity at local industries, and the promotion of applicable Best Management Practices (BMPs) to reduce the amount of stormwater leaving these facilities, and to minimize contamination of stormwater that does find its way into the sewer and/or the surrounding environment. To date, seven comprehensive site visits have been completed with facility owners. Checklists being used on the site visits were originally "field tested" on several auto salvage yards within the state last summer, during a separate EPA Grant-funded project (see description of RI DEM's salvage yard project).
Stormwater BMPs currently being encouraged include simple procedures, such as covering all outdoor chemical storage areas when not in use, covering fuel delivery/storage areas, and promoting the use of Low Impact Development (LID). LID focuses on using such technologies as green roofs, rain barrels and cisterns, and area gardens to retain and reduce stormwater runoff. All of these actions help local businesses comply with RI stormwater regulations, as well as with the NBC's Stormwater Discharge Permit Requirements.
A free, half-day workshop to address local stormwater requirements and concerns is being planned for the end of May, and will be co-sponsored by the RI DEM and the University of Rhode Island.