Harrisburg Westside Sanitary Sewer Improvements

The City of Harrisburg has experienced rapid growth due to its presence in the Sioux Falls metropolitan area. This has required its infrastructure to grow at the same pace, and has created challenges with multiple lift stations throughout town. These challenges demanded extensive maintenance, and with expansion anticipated to continue, the City hired Banner to prepare a master plan for extending sewer to 7,100 acres west of the City.

The area extended from the main lift station at the south end of the city, west towards I-29, and north to Sioux Falls city limits along three branches. While the City knew it would take years for the area to fully develop, they wanted to consider if it was more cost-effective to oversize downstream sewer interceptors for full basin build-out, or install smaller interceptors with future parallel interceptors to support flows, or use cross-connections to meet future demands. The City also requested information on when sewer flows will exceed the capacity of existing lift stations and interceptors within the project area and the timing of the recommended improvements to address these issues.

The study included detailed condition and capacity assessments for the Coyote, Honeysuckle, Tiger, and South Cliff Avenue lift stations within the study area that were aging and required extensive maintenance for city staff. The remaining life of the lift station components were determined. The capacity of the lift station components was also evaluated, using ANSI/Hydraulic Institute Standards 9.8 requirements to guide the evaluation of wetwell capacity.

The Facility Plan used LIDAR data to define the service area and develop the sewer basins and sub-basin boundaries. Lift station calibrations and pump run time data provided information on existing sewer flows, while future land use plans guided projections of future sewer flows. A sanitary sewer model was developed using SewerGEMS and was essential in evaluating sewer interceptor sizing and alignments, as well as cross-connections between the three branches for the 15.3 square mile area with elevations ranging from 1376 to 1550.

Opinions of probable costs were prepared for the alternatives, and O&M cost impacts were also considered. Banner determined that two trunk sewer mains with a cross connection provided the most cost-effective solution to support future growth. The Phase I improvements were needed immediately due to capacity shortfalls in the existing system. The Phase I improvements included a 36"/30” Parallel Interceptor in Subbasin 1A from the Main Lift Station to Cliff Avenue, a 24" Interceptor in Subbasins 1A, 3A, and 3B from the 30" Interceptor to Creekside Avenue and Willow Street, and a 24” Interceptor from the southeast corner of Basin 3D to north of Tom Sawyer Trail. The Phase I improvements allowed for decommissioning three of the City’s lift stations with, potentially saving the City up to $263,500 over 10 years. The Phase II improvements in Subbasins 2C and 2D would be needed in 5-10 years to support the cross connection, depending on the rate of development. They included extending the 36"/30” Interceptor in Subbasins 1A and 1D from Cliff Avenue to Minnesota Avenue and a 21” Cross Connection from Subbasins 2C to 1D. To facilitate having developers share in the overall cost of the sewer interceptors, as allowed by codified law, per-acre cost recovery fees were developed.

This study was completed as a Facility Plan, including environmental review, allowing the City to submit for State loan and grant funding to aid in financing the recommended improvements. After the study findings were presented to the City Council, Banner worked with the Southeastern Council of Governments (SECOG) to facilitate the public hearing and funding application documents.