Platte 15: Denver’s First CLT Mid-rise Sits on Dry, Uncontaminated Soil

By Sue Rose

DENVER — The highly anticipated Platte 15 multi-use mid-rise structure, located at 15th and Platte streets in Denver, has reached its final depth of 28 ft. below ground surface. The installation of the temporary dewatering system by TerraFirma Earth Technologies is complete, and is in the maintenance phase. The General Contractor Adolfson & Peterson Construction has completed the excavation and is currently pouring the rat slab and installing the waterproofing for the foundation.

Two Firsts for Platte 15

Besides being Denver’s first mid-rise building made from cross-laminated timber (CLT) and offering a reduced carbon footprint, Platte 15 is the site of a rarely utilized means of groundwater control, known as ejector well dewatering.

“Though more costly up front, in the long run, this unusual use of ejector dewatering wells in controlling the ground water within soils typical to downtown Denver, has proven more reliable, and more cost efficient,” said David Giles, president of TerraFirma Earth Technologies.

There are generally three means employed by the dewatering contractor in controlling groundwater: vacuum wellpoints, deepwells, and ejector wells. The most commonly known in the Denver area are deep wells (sometimes referred to as sump wells).

Mr. Giles explained their differences: “Most contractors shy away from the ejector wells due to up-front costs; however, they are more often the best solution for Denver soil conditions (water-bearing alluvial soils over shallow bedrock). We are glad to see that the General Contractor, Adolfson & Peterson Construction (AP), made the best decision for dewatering this project. Though ejector wells are typically utilized in much deeper excavations, they are well suited here because of the necessity to lower the groundwater to the very top of the confining bedrock. TerraFirma installed 64 ejector wells along the perimeter of the site.

According to AP’s Project Manager Shawn Brannon, Platte 15 is using the CM/GC delivery method, which gave AP the opportunity to employ the “choosing by advantage” process when hiring contractors. “This ensures a collaborative project team offering the best solutions for the particular project’s requirements, rather than choosing contractors simply by cost,” said Mr. Brannon.

“TerraFirma was consulted well in advance of groundbreaking. Getting the project on firm ground is critical to the success of a project. We needed TerraFirma’s expertise early in the preconstruction phase. They were able to give us a detailed solution to the site conditions that we could detail out before we broke ground,” said Mr. Brannon. He added that the owner, Crescent Real
Estate, applauded the “choosing by advantage” process and that it made the entire team engage wholeheartedly in the preconstruction problem-solving effort, which was a year in the making.

As is true of many construction sites in the downtown Denver area, the preliminary geotechnical and environmental sampling reports revealed groundwater that was contaminated. “To deal with the contaminated groundwater, TerraFirma teamed up with BakerCorp,” explained Mr. Giles. “Their extensive experience in the downtown area and knowledge of its groundwater chemistry, as well as their working relationship with the various regulatory agencies involved, has proven invaluable. In the end, we returned purified, drinkable water to the Platte.”

Photo courtesy of Josh Peltier, TerraFirma Technologies.

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