TerraFirma Earth Technologies, Ltd.

Owner:

100 St Paul LLC

Architect:

HKS Architects Inc.

General Contractor:

GE Johnson Construction Company

Client:

Matt Glenn - Project Manager

(720) 420-9712

GE Johnson Construction Company

Scope Of Work

Project Specifications:

The project required the use deepwell dewatering wells as the primary means of dewatering, and the supplemental use of vacuum wellpoints for the multiple, smaller but deeper  foundation features. In addition to the groundwater control, extensive groundwater treatment and filtration was utilized in order to comply with the States stringent discharge permit requirements.

Site Conditions

The geology generally consisted  of fill extending up to 11 ft. below ground surface (bgs), underlain by natural alluvium soils consisting predominantly of clean to clayey sand with sandy clay and gravel lenses. These natural sands extended to depths between 50 and 72 ft. bgs (elevation 5249 to 5274 ft. msl). The alluvium was underlain by bedrock consisting of claystone and sandstone of the Denver Formation.

System Design

The original design included widely spaced deepwell dewatering wells meant to maximize drawdown, while minimizing the rate of groundwater flow, in an effort to prevent migration of potentially contaminated groundwater from adjacent properties. There was concern that the ground water was contaminated from three sources: chemicals from a dry cleaning business, hydrocarbons from a previously demolished fuel station, and dissolved metals, which occur naturally in the earth.

The modified system meant adding mini-vacuum wells directly adjacent to the building’s elevator pits and a permanent dewatering sump pit that TerraFirma was able to custom design on the job, making for a unique hybrid of dewatering methods to better suit the actual soil and jobsite conditions.

By isolating the supplemental dewatering to just those few areas needing it, TerraFirma saved precious time and reduced costs. Also, by limiting supplemental dewatering efforts to just those few areas, we reduced the required amount of groundwater to be pumped, thereby reducing the risk of pulling in contaminants identified on adjacent properties during the investigative phase of the project.