LONGMONT DESIGN-BUILD WATER TREATMENT PLANT

BOULDER COUNTY, COLORADO

Project Highlights

The project consisted of the design and construction of a new water treatment plant for the City of Longmont, Colorado on a 55-acre site in Boulder County, Colorado. The proposed facility will consist of a 30 MGD water treatment facility. The facility will include a Forebay pond for raw water storage, structures for transmitting raw water to the treatment facilities, treatment process structures, chemical storage areas, an administration building, and residuals ponds. Yard piping for conveying the raw and treated water will consist of 8-inch to 66-inch ductile iron pipe. The Forebay pond required a constructed embankment to impound the water. Because the height of the embankment exceeds 10-ft, the embankment is considered a jurisdictional dam and falls under the review of the Colorado State Engineer’s Office (SEO).

Lyman Henn provided geotechnical engineering services during design, including the design-level field investigation. Lyman Henn provided geotechnical design of the Forebay embankments and prepared construction drawings, specifications, and reports for submittal to the SEO. The Forebay embankment is a Class I Minor Dam according to the Colorado Rules and Regulations. Design of the embankments included embankment material selection, slope configuration, and seepage control elements. Lyman Henn performed seepage, settlement, and slope stability analysis, including seismic slope stability

Lyman Henn provided geotechnical services and materials testing during construction of the Longmont Water Treatment Plant including: collection of soil and aggregate samples for laboratory testing; observation and confirmation of in situ and import soil and aggregate types; in-place moisture and density testing by standard ASTM nuclear methods; observation of Forebay excavation, foundation preparation, and embankment construction; and provided ongoing geotechnical engineering support throughout construction of the water treatment plant. All field testing operations supported project specifications.