St. Louis Gateway Arch Park – Luther Ely Smith Square

St. Louis, MO



St. Louis Gateway Arch Park Rainwater & Condensate for Irrigation, Toilets & Cooling Towers

In the early 1930s, civic leader Luther Ely Smith presented the idea of building a memorial to help revive the St. Louis riverfront and to memorialize the nation’s westward expansion. After a nationwide design competition, construction of the St. Louis Gateway Arch began in 1959 with the final section of the Arch was secured in 1965. In 2009, the CityArchRiver project envisioned a major upgrade to the St. Louis Gateway Arch park’s grounds to celebrate the upcoming 50th anniversary of the Arch and connect the Gateway Arch grounds with the East and West riverfronts and with the region. One of the 10 design goals was to incorporate sustainability, which is where Wahaso came in.


More challenging than designing a rainwater harvesting system that simply harvests rainwater from a clean roof surface, harvesting and treating stormwater for reuse requires special considerations along the entire treatment process. Contaminants in stormwater run-off can include hydrocarbons, nitrates, organic matter, and animal waste. To be used for irrigation, treated water would need to be clean, clear, and free from these harmful pathogens. The Park Service was also insistent that the harvesting equipment not interfere with the sightlines of the park.


Water Supply Sustainability Index (2050)

Project Details


St. Louis, MO


Michael Van Valkenburgh Associates and the National Park Service


Plumbing Engineer, Civil Engineer, Commercial Contractors, Commercial Architect




Rainwater and Condensate for Irrigation, Toilets and Cooling Towers


September 2015

Project Gallery


It was critical that most of the suspended solids in the stormwater runoff would be removed before they entered the storage system, so to deliver a complete solution, Wahaso brought in two other partners: SunTree Technologies and Oldcastle Precast. SunTree Technologies recommended their Nutrient Separating Baffle Box system to remove sediment, organic material, and hydrocarbons from large storm flows entering the cistern. The system holds trash above the standing water line and uses a series of baffles to remove suspended solids to less than 350 microns.

Oldcastle Precast supported the design and engineering of the Storm Capture system for this project and was designed to hold 37,000 gallons of pre-treated stormwater below-grade in nine pre-cast modules. Oldcastle also helped to resolve the sightlines requirement by providing an additional module to contain all the harvesting equipment below-grade. An 8’ X 10’ pre-cast equipment room was delivered with ventilation, sump pump, ladder, and large access doors to avoid confined space restrictions. Once suspended solids are removed, Wahaso’s filtration and sanitation skid was designed to further sanitize the water as well as to minimize maintenance of the system. Special high-intensity UV units are utilized in the system to eliminate any potentially harmful pathogens, even if the water is cloudy. To minimize maintenance requirements, a special 50-micron filter was installed that is capable of self-cleaning while it is operating, eliminating the need to replace bag filters.


Wahaso’s stormwater harvesting system was installed and started up in time to join in the opening celebration of the Luther Ely Smith Square in the Fall of 2015. In the following Spring of 2016, harvested water was available and provided for irrigation of the lawns and landscaping.

The use of a below-grade water storage system and equipment room provides that the park will remain clear of obstructions so that attendees can focus on the beautiful Gateway Arch and surrounding park.