This report evaluates the potential to use stormwater runoff in lieu of withdrawals from a freshwater body to meet water needs of different power plant processes. The report will be of value to environment, generation, and planning managers within power companies.
Stormwater originates as a result of precipitation events and can flow on the surface as runoff into surface water bodies or enter groundwater. In urban areas, stormwater is channeled into storm sewers, which discharge into surface waters. The principal goal of stormwater infrastructure design is to move water away from structures and roadways following precipitation events and minimize accumulation. In the past, stormwater has rarely been thought of as a resource. Much of the older stormwater management literature deals with design of physical infrastructure to handle large peak flows during major storms or practices to minimize contaminant loading from urban or suburban stormwater to natural water bodies. This report is a broad-scale examination of issues related to use of stormwater by power plants and sets the stage for more site-specific analyses in the future.
To evaluate the potential to use stormwater runoff in lieu of withdrawals from a freshwater body to meet water needs of different power plant processes.
There are several constraints associated with use of stormwater or, indeed, any alternate water source:
- volume and timing of available resource compared to demand;
- water quality needed for use and eventual discharge; and
- location of source relative to point of use.
This report examines the first two constraints in some detail by considering conditions in different geographic regions of the United States. Locations examined are generally urban areas with major existing electric generation and spanning a wide range of precipitation conditions. The first metric evaluated is volume of stormwater generated (chapter 2). Following this is a discussion of typical contaminants observed in stormwater (chapter 3). Given median stormwater chemistry, the use of these waters for different purposes within power plants is explored in chapter 4. An important aspect of this analysis is that not all water uses within power plants require the same quality of water, and some needs can be met with much poorer quality water than others. A number of treatment technologies are discussed in chapter 5 along with associated/estimated costs. Chapter 6 provides the main conclusions of this study and identifies future directions for this work, including the need for developing more detailed case-study analyses at selected locations.
Stormwater can be a meaningful resource for power plant use; however, several engineering-type analyses need to be performed on a site-specific basis to better understand the feasibility of its use. Once an estimate of stormwater volume is obtained, and it is determined that this volume can substantially contribute to the water needs of a power plant, the next consideration is transport distance to the point of use and costs of developing the conveyance system. Rainfall hydrographs can be used to estimate timing of flows and costs of storage to provide for water when there is no stormwater. Finally, costs associated with the system to treat stormwater to different degrees (for different uses within power plants) need to be estimated.
Two sources of stormwater were discussed and evaluated–onsite and offsite. The relatively small volume, compared to process demand, of onsite stormwater generated during rainfall events can be used without treatment in flue gas desulfurization (FGD) systems, ash systems and cooling towers in coal-fired plants, and in cooling towers in combined–cycle, oil/gas and nuclear plants. Offsite stormwater, on the other hand, can provide a significant volume of water; therefore, chemical constituents must be characterized and evaluated more carefully since they may make it unsuitable without some form of treatment. Plant location with respect to large urban areas and regional climate are critical components when evaluating stormwater since offsite stormwater could potentially supply over half of the water requirements for some plants.
Growing societal demands on U.S. water resources will result in pressure on the electric power industry to increase its water use efficiency and reduce its total freshwater use. The power industry is already engaged in conserving water on many fronts–developing dry cooling, dry scrubbing, and dry ash handling technologies; creating new and innovative recycling systems for treating and reusing water for various plant functions; and pioneering ways to make use of abundant and untapped supplies of municipal waste water and other non-traditional sources. Scientific and technical research will create even more new opportunities for the power industry to develop improved and less costly technologies and procedures for conserving freshwater.