Technical Description:
(4) CDS® Hydrodynamic Separators
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The cost of land development within metro Phoenix, Arizona, continues to rise as the cost of construction increases. Challenges for developers in Arizona include more stringent regulations as the state battles to preserve its most valuable resource, water. In addition, many local agencies are considering additional development standards to improve groundwater recharge and the quality of existing waterbodies while reducing flooding.
For example, the City of Scottsdale aims to preserve regional ecology and the natural environment by conserving the area's stormwater. The city provides strict stormwater requirements to achieve this goal. The city requires most sites to provide onsite retention of a 100-year, 2-hour storm event. When this is not feasible or practical, at a minimum, Scottsdale will require retention or treatment of the first 0.5 inches of stormwater runoff onsite.
In 2020, Mark-Taylor Companies constructed a new apartment complex called San Artes in Scottsdale. The multifamily community includes 25 three-story buildings with 552 units and a single-story amenity building on approximately 30 acres. Engineers in the area would typically meet stormwater requirements by retaining the required 100-year, 2-hour volume of stormwater runoff in retention basins onsite. However, this could not be done as the project location had a significant offsite flow that had to be diverted around the property. Also, the site was a tributary to an offsite regional basin, which met the required retention storage volume but still had to meet the first flush policy for water leaving the site.
Kimley-Horn was the civil consultant designing the project and the master development. They resolved both challenges by diverting the offsite flows to the regional retention basin with channels around the site. The remaining stormwater requirement for San Artes was to provide retention or treatment of the first flush or the first 0.5 inches of direct runoff onsite. First-flush basins are a standard solution to meet this requirement. Unfortunately, first-flush basins would not be ideal because the high-end apartments did not want trash and other pollutants visible to their tenants. Additionally, first-flush basins would reduce the available land space. Underground detention of the first flush was not selected due to the high cost and significant space required.
Treatment of the first flush was achieved using CDS hydrodynamic separators. The construction team selected the Contech CDS because it significantly reduced the project cost from original estimates and was available to meet the project schedule. The CDS is a reliable, locally approved first flush treatment system.
The CDS hydrodynamic separator uses swirl concentration and continuous deflective separation to screen, separate and trap trash, debris, sediment, and hydrocarbons from stormwater runoff. Using CDS hydrodynamic separators is becoming a popular method of meeting the first flush policy in the City of Scottsdale and surrounding areas because it provides significant savings compared to retention systems while providing more space for leasable square footage, parking, and amenities.
Contech supported the engineer with optimized designs using the CDS and aided the contractors throughout the installation of the (4) 10-foot internal diameter CDS systems to ensure smooth integration with the site. Today, the 4 CDS units provide a total treatment of 76 cubic feet per second to meet the owner and City of Scottsdale stormwater regulations.
"The CDS met the project requirements, provided cost savings, and shorter lead time for the construction team," said Traver Jones of Kimley-Hall. "Contech was good to work with through the design of the structures. The installation went well."
Technical Description:
(4) CDS® Hydrodynamic Separators
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