Onondaga County's Resilient Combined Sewer System: The Implementation of Green and Gray Infrastructure to Reduce CSOs and Increase System Resiliency and Capacity

Since January 1999, Onondaga County, New York has been complying with an Amended Consent Judgment (ACJ) which includes control of combined sewer overflows (CSOs) to the tributaries of Onondaga Lake. In November 2009, the ACJ was again amended to incorporate green infrastructure (GI) strategies to further reduce wet weather from entering the combined sewer system (CSS) along with requiring other upgrades at the Metropolitan Wastewater Treatment Plant (Metro). This was the first court order in the country to require the use of GI, and the new program was named Save the Rain. Since 2009, Save the Rain has resulted in the construction of over 230 GI projects and more than 10 large-scale gray infrastructure projects and four small-scale, yet significant system optimization projects. Overall, the County has achieved the remarkable milestone of 98.1% CSO capture and elimination to date while also significantly improving water quality in Onondaga Lake and it's CSO-receiving tributaries and increasing resiliency in the combined sewer system. This presentation will highlight how utilizing both GI and gray infrastructure has provided the County with the opportunity to not only abate CSOs, but also increase conveyance capacity and resiliency in a combined sewer system that dates to as early as the 1850s. Discussion topics will include: - The County's standards for enhanced CSO abatement design including over-designing systems to ensure that they are designed for managing the storms of today and the future. In an ever-changing world due to the effects of climate change, the County's efforts to plan ahead to design for the storms of the future are an excellent example of building resilience into conveyance systems. - Stormwater quantity monitoring results of completed GI projects indicating greater than expected performance. Volumes into and out of several GI projects were metered to demonstrate GI's performance to the regulators. Findings from the metering period versus the original design intent will be provided along with a summary of the important conclusions that were made regarding the effectiveness of GI. - How the inclusion of GI allowed the County to decrease their total financial commitment without sacrificing CSO abatement goals. GI has been found to be more cost-effective than traditional gray infrastructure in the County's CSO abatement program. By constructing more GI, the overall program expenditures have been less than originally budgeted allowing the County to do more and go further with the program. The specific cost savings of GI vs. gray infrastructure will be provided allowing the attendees to takeaway information that will be extremely valuable for their own stormwater and CSO programs. - Oversized design of the Clinton and Lower Harbor Brook CSO Storage Facilities providing a total 11.4 MG of CSO storage. By oversizing these two facilities the County has planned for the future with larger facilities capable of managing larger storms. Examples will be provided for larger storms that have occurred since the facilities were operational showing the benefits of oversizing the facilities. - The financial impacts of oversized GI and gray infrastructure designs and how the County creatively managed available funding to the greatest extent possible. - Other methods developed by the County for resourcefully increasing capacity within the combined sewer system including required stormwater offsets for private development. Within the combined sewer system, the County requires a 2:1 offset. That is, for every 1 gallon of sanitary flow added to the system, 2 gallons of flow must be removed. Developers have been creative in meeting this requirement by installing GI, lining sewers, lining manholes, gray water usage. - Projections of system performance during extreme events and future climate change utilizing the County's combined sewer system SWMM model. The SWMM model has been an incredibly useful tool for planning projects and assessing system performance. The methods in which the model has been utilized along with results will be provided.