Geosynthetics April/May 2022 - 25

Case study
Lining the 70 Ranch
Raw Water Reservoir
A geosynthetic liner system is custom made for a difficult
site on the eastern Colorado plains.
By Ronald K. Frobel and Ray Peebles
I
rrigation water in the western United States has always been a major concern for
farming and ranching, especially in drought years. Water can be both scarce and
expensive, and planning for future water storage and accessibility based on projected
use is of paramount importance for irrigation districts. These considerations were
of particular interest to the United Water Conservation District (UWCD) (today
called the United Water and Sanitation District), Greenwood Village, Colo., when
planning for storage and future use of water in Weld County, just to the northeast
of Denver. To this end and as part of the overall water use plan, the UWCD initiated
investigation and selection of a site for a storage reservoir in 2012. Based on feasibility
studies and access to off-season stream water from the South Platte River, the
UWCD selected a 250-acre (101-ha) site east of Kersey, Colo., at a location known
as 70 Ranch. Engineers began site investigations and the preliminary design for the
reservoir in 2013. They completed site geology and geotechnical investigations in
2014, and the design engineer provided design alternatives for the reservoir around
the same time (Civil Resources LLC 2014).
Geotechnical considerations and alternatives
Many pond and reservoir sites can be excavated into native soils that are sufficient
to retain water or are in an area where clay deposits allow for a compacted clay liner
(CCL) with acceptable and economical water loss. Seepage rates can also determine
whether the cost of water collected versus lost is economical. However, the 70 Ranch
Raw Water Reservoir site was a challenge due to the geotechnical investigation
that revealed limited available cohesive site soils and strata that could hold water.
Additionally, the quality and porosity of bedrock was considered highly variable.
The extensive site investigation included numerous borings and test pits
throughout the proposed reservoir site, as well as a proposed embankment dam
centerline alignment and slurry wall alignment. The investigation encountered
native soils consisting of sand, silty sand, clay and gravel at depths ranging from
ground surface to 100 feet (30.5 m) below ground surface. Bedrock was encountered
at depths ranging from 40 to 100 feet (12.2 to 30.5 m). Site investigators found small
clay lenses, and the bedrock varied from relatively porous sandstone to siltstone but
with no significant clay strata.
PROJECT HIGHLIGHTS
70 RANCH RAW WATER RESERVOIR LINER
OWNER
United Water Conservation District
LOCATION
Weld County, Colo.
GENERAL CONTRACTOR
Fiori & Sons Inc.
DESIGN ENGINEERS
Civil Resources LLC Consulting Civil Engineers
R. K. Frobel & Associates Consulting
Geosynthetics Engineers
GEOMEMBRANE/MANUFACTURER
Scrim reinforced polypropylene (fPP-R)
geomembranes, Cooley Group Inc.
GEOMEMBRANE PANEL FACTORY FABRICATION
Environmental Protection Inc.
GEOTEXTILE PRODUCT/MANUFACTURER
10 ounces per square yard (339 gsm)
nonwoven geotextile, SKAPS Industries
GEONET COMPOSITE PRODUCT/MANUFACTURER
8-200-8 geonet composite, SKAPS Industries
GEOCELL/MANUFACTURER
6-inch (152-mm) geocell, Presto GeoSystems
GEOSYNTHETICS SUPPLY AND INSTALLATION
Consolidated Divisions Inc.
ELECTRICAL LEAK LOCATION SURVEY
Leak Location Services Inc.
Ronald K. Frobel, P.E., is owner/principal of R. K. Frobel
& Associates Consulting Geosynthetics Engineers in
Evergreen, Colo.
Ray Peebles is global product and market manager for
Cooley Group Containment Solutions in Pawtucket, R.I.
All figures courtesy of the authors.
www.GeosyntheticsMagazine.com
25

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Geosynthetics April/May 2022

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