Forest Lawn Creek is being separated from a combined sewer system to reduce the combined sewer overflows that occur in the area. Burns & McDonnell was hired to evaluate routing options for the Forest Lawn Combined Sewer Overflow (CSO) project and to design the sewer separation. Project elements include: creek separation, sewer separation, green infrastructure evaluation and extensive public engagement.
Forest Lawn Creek discharges to an existing combined sewer, and the flow is conveyed by large diameter pipe to CSO-105. The creek is in an established neighborhood, so a major challenge was to consider how to separate the creek with minimal disruption to the neighborhood and utilities in the neighborhood. The team studied several options to separate the creek flow from the combined flow and to transfer the clean creek flow to the Minne Lusa channel and eventually into the Missouri River. Critical elements of the project included neighborhood sewer separation, sanitary sewer design, tunneling large diameter pipe, and outfall evaluation and design. Our engineering design team applied hydraulic modeling on this project, using HEC-RAS, XPSWMM and InfoWorks.
Our conceptual evaluation included two sanitary sewer routing options, three storm sewer options, three outfall options and one neighborhood sewer separation option. We evaluated the costs of constructability and conducted broad public outreach to determine how to minimize neighborhood disruption and to work with utilities in the construction zone.
The green infrastructure evaluation reviewed watershed studies, storage options, costing, constructability and maintenance. We used the results from this evaluation to study how to detain upstream flows to reduce pipe size downstream. By managing peak flow upstream, the design decreased the diameter of tunneled storm sewer downstream, resulting in lower construction costs. Multiple trenchless technologies are used in the design, benefiting the client through cost savings and minimized neighborhood disruption.
During the preliminary design stage, our team contacted the utility companies to address concerns related to the location of their facilities. Our team will coordinate with area utilities through the final design. Extensive public outreach continues as a critical part of this project as it moves into the construction phase, keeping utility companies, residents and business owners informed about alignments, schedules and plans. The design team gathered valuable information about the area, including historical flooding and business traffic patterns.
- Sewer separation
- Storm sewer design
- Watershed studies and hydrology
- Green infrastructure design
- Field investigation
- Smoke testing and CCTV inspection