Options for Solids and Floatables Control
Authors:
- Curt Courter, P.E. - Hazen and Sawyer
At Issue
Over 700 U.S. cities in more than 30 states have combined sewer systems, which, by design, discharge diluted raw sewage into many of the nation’s waterways. Now three decades have passed since the Clean Water Act was enacted and federal and state regulatory agencies have refocused their efforts to address the water quality issues of our nation’s lakes, streams and rivers. In part because of the United States Environmental Protection Agency’s (USEPA) landmark 1994 Combined Sewer Overflow (CSO) Control Policy and their Guidance for Nine Minimum Controls (NMCs), and in part because they are the most visible, the communities and authorities responsible for operation and maintenance of wastewater collection systems continue to be the primary target for enforcement. In recent years there has been a flurry of Consent Orders and other similar legal agreements (Orders) requiring wastewater collection system operators to eliminate sanitary sewer overflows (SSOs) and bring CSOs into compliance with the CSO Control Policy. Of the Orders that address CSOs, many include provisions to re-evaluate the authority’s NMC compliance and more particularly, control of solids and floatables.
Case Studies
The Consent Decree recently entered into by the city of Jeffersonville Indiana, requires that “alternatives evaluated as part of the LTCP shall include, at a minimum… (x) construction of facilities for removing floatables from CSO Discharges.” In another example, EPA Region IV and the State of Kentucky have recently finalized Orders with all 17 of the CSO communities in Kentucky. These orders all require the submission of Reports detailing the communities’ NMC compliance and what is to be done if not in compliance. Louisville Metropolitan Sewer District (MSD), the first Kentucky sewer district required to submit their NMC compliance documentation under these orders, submitted compliance documentation detailing their numerous early action solids and floatables control projects including street sweeping, catch basin inserts, proprietary manufactured screening controls and engineered controls such as a baffle chamber. Louisville’s original program was similar to what many others around the country have traditionally included; solids and floatables controls constituting installation and operation of controls at only a small percentage of high priority outfalls.
In other areas such as New York City, Washington D.C., and Detroit, capture by skimmer boat or by boom in the water course continue to be viable options. In both cases it is argued that numerous constructed controls at every outfall are considered too costly to be a minimum control. These communities have left the remaining outfalls to be addressed during future long term control planning. However, Louisville’s program was not accepted as submitted, because it left many overflow points without control. In response, Louisville MSD moved quickly and installed some type of simple solids and floatable control, originally consisting mainly of wooden baffles and coarse bar racks, at every outfall or diversion where feasible. As a result, Sanitation District No. 1 of Northern Kentucky (SD1), the next Kentucky sewer authority to submit on compliance and the second largest CSO authority in USEPA Region IV, developed a pilot program to look at the effectiveness and O&M requirements of these simple solids and floatables controls.
What Will Be Presented
Owing to the need to address this issue, this presentation will focus on the source control, in-system control, and end-of-pipe control technologies available to address solids and floatables from CSOs and stormwater outfalls, including traditional technologies such as street sweeping, baffles, bar racks, screens, nets, and booms, as well as emerging technologies. Many new source control products have become available in the last few years particularly from the pre-cast concrete industry, including examples of “Green” controls. The information presented will be based on literature reviews, case studies, and the authors’ CSO control experience with existing installations. Information on design requirements, effectiveness, cost, and O&M requirements for the various types of controls will be identified.
Read a relevant WE&T article from the same author.
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