Little Blue Valley Sewer District Excess Flow Holding Basin


The project site is located on the southeast quadrant of I-470 and Raytown Road in Kansas City, Missouri. The Little Blue Valley Sewer District has a 72-inch interceptor sewer that runs through this site. Storm water infiltration and inflow from upstream sources have caused peak flows to exceed the capacity of the District’s interceptor sewer at times of significant wet weather. During these significant wet weather events, the Atherton Wastewater Treatment Plant (WWTP) has had to divert flows around the biological treatment and disinfection process. The excess flow holding basin will temporarily store excess wet weather flows, thereby decreasing the burden on the interceptor and reducing peak flows at the WWTP. A diversion structure will restrict flow in the 72-inch Little Blue Interceptor during significant wet weather events. The interceptor will surcharge to a point where flow is diverted by gravity into the holding basin. The holding basin has a storage capacity of approximately 83-million gallons at a 15-foot operating depth, and a footprint of roughly 23 acres. The primary cell will be concrete lined with steep interior side slopes to facilitate wash down operations to remove solids, thereby reducing potential odors. When the primary cell reaches capacity, which is approximately 14-million gallons, the flows will spill into the secondary cell through a baffle and weir control structure. This structure will contain the majority of solids and floatables to the primary cell, which will assist in reducing potential odors. The secondary cell will be clay lined with a turf surface and moderate side slopes for ease of maintenance. When the WWTP has recovered from the wet weather event, the holding basin will drain by gravity back into the 72-inch Little Blue Interceptor sewer. The addition of bioxide to the influent flow will further reduce the potential for odors.

The new cast-in-place diversion structure includes a new sluice gate installed on the existing 72-inch interceptor sewer.

The structure is designed to be cast around the existing pipe and the pipe is to be removed within the structure.

The sluice gate is designed to operate at approximately 35 feet of head. The basin discharge system includes two new sluice gates installed on a 48-inch gravity sewer which discharges back to the diversion structure. The two sluice gates control discharge from each of the two holding cells, and are designed to operate at approximately 29 feet of head for the primary cell and 22 feet of head for the secondary cell. The District also operates a gate structure on the interceptor sewer immediately downstream of the Longview Lake dam. Twin 54” sewers run under Longview Lake to this gate structure where the interceptor becomes a 72-inch sewer. During the course of the project, it was determined that this structure required structural modification and the sluice gates required replacement. The existing sluice gates and ancillary equipment will be removed, the structure will be rehabilitated and structurally modified, and two new sluice gates will be installed. The sluice gates are designed with approximately 90 feet of head.