Stormwater runoff from critical source areas, such as parking lots, vehicle fueling and maintenance stations, and public works storage areas, may contain pollutant loadings of hydrocarbons, toxic trace metals, nutrients, pathogens, and/or other toxicants and pollutants that are greater than the loadings of “normal” stormwater runoff (Bannerman, et al. 1993;
Pitt, et al. 1995; Claytor and Schueler 1996). One alternative to end-of- pipe treatment for stormwater runoff is to treat the more contaminated runoff from problem sources before this runoff mixes with the runoff from other areas (Bannerman, et al. 1993; Pitt, et al. 1995; Claytor and Schueler 1996). Critical source area treatment devices need to incorporate a variety of treatment processes that can be targeted for different classes of pollutants of concern and to respond to the variability of stormwater quality conditions that can originate from different types of critical source areas (Pitt, et al. 1999). This paper will describe one such device, the UpFloTM Filter that has undergone development and testing under the EPA’s SBIR and ETV programs.
There are many stormwater control practices, but all are not suitable in every situation. It is important to understand which controls are suitable for the site conditions and can also achieve the required goals. This will assist in the realistic evaluation for each practice of: technical feasibility, implementation costs, and long-term maintenance requirements and
costs. It is also important to appreciate that the reliability and performance of many of these controls have not been well established, with most still in the development stage. This is not to say that emerging controls cannot be effective, however, they do not have a large amount of historical data on which to base designs or to be confident that performance criteria will be met under the local conditions. The most promising and best understood stormwater control practices are wet detention ponds. Less reliable in terms of predicting performance but showing promise, are stormwater filters, wetlands and percolation basins. Grass swales also have shown great promise during the EPA’s Nationalwide Urban Runoff Program (NURP) and during more recent research (EPA 1983; Nara 2005).
Most stormwater needs to be treated to prevent harm either to the surface waters or the groundwaters. One approach is to treat the runoff from critical source areas before it mixes with the runoff from less contaminated areas. Some features of critical source areas include large paved areas, heavy vehicular traffic, and outdoor use or storage of problem contaminants or heavy equipment. The control of runoff from relatively small critical source areas may be the most cost effective approach for treatment/reduction of stormwater toxicants. However, in order for a treatment device to be usable, it must be inexpensive, both to purchase and to maintain, and effective. Outfall stormwater controls, being located at the outfalls of storm drainage systems, treat all the flows that originate from the watershed. The level of treatment provided, of course, is greatly dependent on many decisions concerning the design of the treatment devices. Source area controls are, of course, physically smaller than outfall controls, and are therefore generally easier to use on a crowded site, but there could be a large number of them located in a watershed. In all cases, questions must be answered about the appropriate level of control that should be provided, and what stormwater control devices should be used.
The first concern when investigating alternative treatment methods is determining the needed level of stormwater control. This determination has a great affect on the cost of the stormwater management program and needs to be carefully made. Problems that need to be reduced range from sewerage maintenance issues to protecting many receiving water uses. Many treatment objectives may need to be examined for a number of source area or ourfall treatment practices. Large levels of stormwater control are likely needed to prevent excessive receiving water degradation through hydromodifications and pollutant discharges. Numeric treatment goals usually specify about 80% reductions in suspended solids concentrations (Hans de Bruijn, et al. 2003). In most stormwaters, this would require the removal of most particulates greater than about 10 μm in diameter, about 1% of the 1mm size needed for removal to prevent sewerage deposition problems (Pitt, et al. 2005). Obviously, the selection of treatment goals must be done with great care, as large differences in costs can occur.
Upflow filtration, which is the chosen treatment technology for this research, has shown promising results. (See the “Future Research” section of Clark 2000). Extensive research on flow type and potential suitable media for downflow filtration has been carried out by Clark and Pitt (1999) and Clark (2000). But such information is not available for upflow filtration. Pratap (2003) and Gill (2004), further studied and analyzed upflow filtration at a lab scale and evaluated several media for potential treatment effectiveness. The primary objective of this research, funded by SBIRI and SBIR2 research by the US EPA, was to develop and test a full scale upflow filter.