Many older cities in the United States are served by combined sewers - PDF document

1 Many older cities in the United States a
Many older cities in the United States are served by combined sewers. A combined sewer carries both sewagerunoff, and one for wastewater from homes and businesses. No new combined sewers have been built in theDistrict since the early 1900s. Combined sewers are located mostly in the older developed areas of the District.hat Is a Combined Sewer Overflow?During dry weather, sewage from homes and businesses is conveyed (step 1, shown at right) to the DistrictÕs Wastewater Treatment Plant at Blueto the Potomac River. During certain rainfall conditions, the capacity of a combined sewer maybe exceeded. When this occurs, the excess flow,runoff, is discharged to the Anacostia River, PotomacRiver, Rock Creek and tributary waters. If thesewould be widespread street flooding and basementbackups. There are a total of 53 CSO outfalls in Starts Anacostia As part of its plan for reducing combined sewer overflow (CSO)discharges, WASA has begun the process of separating part of the CSO area east of the Anacostia River. The process will involve allow the complete elimination of one CSO outfall.his will reduceCSO discharges and will improve water quality.to minimize disruption and provide the best benefit. After that isdone, engineers will design the separation program, and thenwww.dcwasa.com and in local newspapers. We will use the meetings Background on Your Combined Sewer System More Background on Your Combined Sewer System How Can CSOs Affect the Environment CSOs can adversely affect the quality of our receiving waters by contributing to lowpublic due to the high flow of water that may exit these sewers (outfalls) and thepotentially harmful substances that may also be present. The public is advised to stayaway from any sewer pipe discharge. For small rainfalls, the effects of CSOs on thereceiving waters typically last less than 24 hours. For larger rainfalls, greater than one inch of rain, the effects of CSO on water quality can last up to three days.here Are the CSO Locations? here are 10 CSO locations on the Potomac River, 15 CSO locations on the AnacostiaRiver, and 28 CSO locations along Rock Creek and its tributaries. The location of each outfall is shown on the mapbelow. WASA has also posted a sign at each CSO outfall, similar to what is shown above. These overflows

2 are permittedby WASAÕs discharge permit
are permittedby WASAÕs discharge permit from EPA. hen Do CSOs Occur? CSOs should only occur during wet weather. Whether anoverflow occurs, and its magnitude, depend on many factors,including rainfall volume, intensity, and if it has rained inprevious days. CSOs typically overflow more in wet yearsthan dry years. In a year with average rainfall, WASA estimatesthat CSOs in the Anacostia and Potomac Rivers overflow aboutto 80 times per year with associated overflow volumes ofabout 2,142 and 1,063 million gallons respectively. In RockCreek, CSOs are predicted to overflow about 30 times peraverage year with an overflow volume of about 40 milliongallons per average year.hat Is a Dry Weather Overflow? he sanitary flow collected in the combined sewer during dryweather is routed to the Blue Plains Wastewater TreatmentPlant through facilities called regulators. During wet weather,the regulators are designed to let the excess flow (or CSO)discharge directly to a river or creek. During dry weather should not be discharged to receiving waters. However, regulators can become blocked by debris, trash, orother materials. When this occurs, the regulatorÕs functionscan be impaired and can result in overflows. These arecalled Dry Weather Overflows (DWOs). WASA has an intensive maintenance and inspection program to prevent DWOs fromoccurring. When a DWO does occur, WASA corrects it andyou see a CSO outfall discharging during dry weather, callDCWASA at 202-612-3400.ou can learn more about CSOs by visiting ASAÕs web site, www.dcwasa.com, or by at 202-727-2634. DonÕt litter or use catch basins as trash receptacles or hazardous substances such as gasoline, oil, and antifreeze.hese simple measures can reduce the impact of CSOsand make our rivers cleaner.hat is WASA Doing about CSOs?ASA has proposed an aggressive plan for reducing CSOs andimproving water quality called a Long Term Control Plan (LTCP).he plan calls for constructing storage tunnels to capture CSOsduring rain events, providing a 98% reduction in CSO to theAnacostia River, and a 96% reduction in CSO overall. The planis currently being reviewed by EPA. Details on the plan can befound on WASA's web site. Serving the Public ¥ Protecting the EnvironmentLocation ofSewer Systemor general WASA information, call 202-787-2000