CSO
Priorities for Remediation
•
Sensible Solutions Timeline
•
How CSO Priorities are Decided
•
CSO Task Force
Six CSOs
were selected as priorities for remediation, based on environmental and health
concerns. See How Priorities are Decided.
CSO
4a & 4b Dry Weather Overflows Prevented
(Note: CSOs 4a & 4b have been remediated.)
Flows from the backwashing of filters at the Porter potable water filter plant were entering the Prices Run Collection System and causing dry weather overflows at CSO 4b. To prevent these overflows, a diversion dam was constructed from 26th and Pine and connected to the Prices Run relief sewer. This provided a straight unobstructed path for the backwash flows. Only excess wet weather flows will be able to pass over the side dam and enter the Prices Run relief sewer. The dam at the diversion chamber at 13th and Locust was also raised to contain the flow in the Prices Run interceptor and prevent dry weather overflows at CSO 4a. These solutions have had the added effect of increasing the amount of wet weather flow captured and passed to the treatment plant.
CSO
28 and 29
(Note: CSOs 28 & 29 have been remediated.)
CSO 28 and 29 formerly discharged into small streams with limited capacity to assimilate them. Thus, these CSO were identified by DNREC and the City of Wilmington, prior to creation of the CSO Task Force, as ranking highest in priority. When combined with CSO 30, they account for 30% of annual City of Wilmington CSO volume. CSO 30 was not included in this group, since the City made $750,000 in improvements to CSO 30 in 1996. Since the existing dam was raised and screens were installed to store excess sewage flow and divert it to the treatment plant, CSO 30 is listed in the second priority group.
In July 2005, as part of the CSO control program undertaken by the City of Wilmington, DNREC and the EPA, underground storage tanks were buried in Canby Park to capture a large portion of runoff. The tanks are designed to hold up to 2.7 million gallons of combined stormwater and sewage so it can be treated at Wilmington's Wastewater Treatment Plant after the rain has ended. During the construction, CSOs 28 & 29 were diverted to these underground storage tanks.
Above: CSOs 28 and 29
respectively.
CSO 27 Progress
Following the recommendations of the CSO Task Force, a solution for CSO 27 has been developed, designed and is ready for construction. A 30-inch diversion sewer will be installed along the banks of Silverbrook Run, through a small section of the Town of Elsmere, connecting CSO 27 to an underground sewage retention tank located in Canby Park. This will help reduce the frequency of overflows into Silverbrook Run since the pipe will carry combined sewage that once discharged into the creek and store it in the large tank buried in Canby Park for later treatment.
During construction of the Canby Park Storage tank and modifications to the existing sewer system, a future connection pipe to CSO 27 was installed in anticipation of this project. This will greatly reduce the construction activity in public space.