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City of Sheridan HDS Replacement

Sheridan, Wyoming

Stormwater Treatment


City of Sheridan


MC2 Engineering


SSR Construction/Wilson Brothers


Winter 2014-2015

Technical Description:

  • (4) CDS® hydrodynamic separators

The city of Sheridan Wyoming’s maintenance department was having problems maintaining their existing stormwater infrastructure. While hydrodynamic separators (HDS) were being used, they had limited maintenance access. The existing units had openings of only 8”-12”, which does not allow for access or movement by a vactor hose in the sump, resulting in frequent maintenance events. The problem became so bad the city decided to look for new stormwater treatment devices that could replace the existing HDS systems.

Contech partnered with the city to install a CDS hydrodynamic separator to test the system’s ability to screen, separate and trap trash, debris, sediment, and hydrocarbons from stormwater runoff without clogging. The indirect screening capability of the CDS allows for 100% removal of floatables and neutrally buoyant material debris 2.4mm or larger. Water velocities in the swirl chamber continually shear debris off the treatment screen, making it the only non-blocking screening technology available in a hydrodynamic separation system.

The ability to retrofit existing structures was also an important factor in choosing the CDS. The ability of the CDS to accept multiple inlets and utilize a surface curb inlet proved beneficial. The internal bypass of the CDS allowed for the conversion of some of the systems that were previously offline to be placed inline. This eliminated a number of diversion manholes/boxes, minimized excavation, and provided cost savings to the project.

The trial was a success, and the city installed additional CDS units. “By using the CDS units within the project limits, they reduced the overall cost of the project due to the smaller excavations and reduction in manholes of comparable storm treatment systems.  Performing maintenance on these treatment systems is also easier on our street crew considering how much sediment can be removed with each cleaning,” said Joe Schoen, City of Sheridan Engineer.

Technical Description:

  • (4) CDS® hydrodynamic separators

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