Consent Order Lifted Successfully: A Journey from 300+ SSOs to Near Zero

In 2001, Little Rock Water Reclamation Authority (LRWRA) entered into an agreement with Sierra Club and later Arkansas Department of Environmental Quality (ADEQ) for a Consent Order with a monumental task ahead of itself relating to removing both dry and wet-weather Sanitary Sewer Overflows (SSOs) from their 1,450 miles of gravity sewer. At this time, Little Rock was experiencing over 300 wet-weather SSO locations during larger rainfall events. Additionally, dry-weather overflows were a significant issue and addressed within the order to be remediated within five years. LRWRA first went into action addressing the dry-weather SSO problem. The agreement with the Sierra Club and then, within the CAO, was to lower dry-weather SSOs to below six (6) per 100 miles of gravity sewer. In 2001, the City was roughly experiencing twelve (12) dry-weather SSOs per 100 miles of pipe. Within two years, the City had significantly lowered the dry weather SSOs to well under the parameters set within the CAO. This was accomplished through hiring additional personnel and developing a more robust cleaning and maintenance program. Concurrently, an aggressive public outreach campaign was developed to sustain those efforts. The wet-weather SSO problem was obviously a much larger and much more expensive issue to resolve. Over 20 years, the Authority utilized a very comprehensive hydraulic model of their system blending capacity enhancement projects, which included a 61 MG equalization basin within the middle of the collection system, innovative parallel treatment schemes to maximize Wet-Weather Flows (WRF) throughput , and I/I reduction projects to reduce wet-weather overflows to near zero for the design storm event. The key to developing the needed CIP plan to reduce the wet-weather hydraulic line across the system, was to invest into having a very accurate hydraulic model. The model was calibrated with a city-wide flow monitoring program, utilizing 75 monitored basins and 12 rain gauges, that allowed a detailed understanding down to each gravity segment on how the system responded to both dry and wet-weather conditions. The calibrated model allowed LRWRA and their engineers to understand where removing I/I from the system was more cost effective than up-sizing large swaths of the interceptors and transporting through the system for treatment. However, major capacity upgrades and storage was going to be necessary to alleviate the wet-weather SSOs and the model allowed the trial and error of these combinations of projects to be completed before any design or construction commenced. Little Rock invested $500 million dollars to improve their collection system dramatically by utilizing state-of-the-art technologies and stringent construction standards to rehabilitate the aging infrastructure with a focus on removing Inflow and Infiltration (I/I). LRWRA replaced or rehabilitated192 miles of pipes and 7,000 manholes and in doing so, were able to eliminate 30% of I/I from their system, along with parallel treatment schemes with their WRFs, which enabled removing additional storage requirements to contain wet-weather flows, while at the same time, renewed aging assets in the system. At the conclusion of the deadline of the order, LRWRA had constructed a 61 MG equalization basin which included a major pump station and deep 7,000 linear foot, 48' wet-weather interceptor to feed the station. This 48' wet-weather line pulled the wet-weather flows to the pump station in a more rapid manner and dramatically pulled down the hydraulic line across half of the city. Additionally, over 30 capacity enhancement projects were completed across the sanitary system to handle those wet-weather flows. Many pump station upgrades were also undertaken and were necessary to assist with handling peak flows. In 2023, the last full year of the CAO, LRWRA encountered only four (4) wet-weather SSO locations. This was an outstanding achievement and monumental reduction of the three hundred plus SSO locations, which were occurring in the early stage of the order. LRWRA's success story culminated in their removal from the Consent Order in March 2024, marking a testament to their unwavering dedication to environmental stewardship, innovative engineering, and sustainable wastewater management practices.