PROJ01754

• Contract/PO #: FS0043X
• Contractor Name: Colorado Department of Corrections
• Contract Type: Miscellaneous
• Water District: 0
• Loan Projects - Doc Type: Application

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Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists

Attachment E, 7 pages

2390 South Lipan Street
Denver, CO 80223
phone: [phone]
fax: [phone]
email: [e-mail]
www.kumarusa.com

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Office Localions: Colorado Springs, Fort Collins, Colorado
Branch Office: Pueblo, Colorado

April 10, 2003

Mr. John Gillogley
Office of Facility Management Services
Colorado Department of Corrections
2862 South Circle Drive
Colorado SpTings, Colorado 80906

Subject:

Geotechnical Engineering Evaluation, ReseTvoir Lining System, Rifle
COTrectional Center Reservoir No.1, Rifle, Colorado

Project No. 03-1-210

Dear Mr. Gillogley:

This letter presents the results of a geotechnical engineering evaluation of the
perfoTmance of the reservoir lining system for the Rifle Correction Center (RCC)
Reservoir No.1, located near Rifle Colorado. The project site is shown on Fig. 1.
Seepage analyses were performed to estimate the average permeability of the
reseTvoir liner under existing conditions, and the estimated seepage rate if the
design permeability had been achieved for the initial and bentonite-amended
reseTvoir liner. The estimated, maximum allowable permeability that will allow
minimum water release requirements to be met was also evaluated. The possible
causes of excessive seepage in the TeservoiT, and Tecommendations for reducing
seepage Tates so that water release requiTements can be satisfied are also presented
in this letter. The evaluation was performed in accordance with the scope of work
pTesented in OUT Proposal No. P-03-200 dated March 3, 2003.

BACKGROUND AND PROJECT DESCRIPTION
The existing TeservoiT was constructed in 1998, and has a storage capacity of
about 34 acre-feet of water under nOTmal operating conditions. The reservoir was
generally formed by excavating up to about 20 feet into a natural hillside, and
constructing a homogenous earthfill embankment dam on the downhill side of the
reservoir. Based on design drawings for the oTiginal dam prepared by GMS, Inc.
(March 1998), the dam generally consists of a homogenous earthfill dam with a
14-foot wide seepage cutoff trench extending from 5 to 7 feet below the pre-
existing sUTface grade. Clayey soils obtained from the reservoir excavation were
used to construct the embankment. The design drawings also show a 12-inch thick
sand dTain and collection toe drain beneath the downstream side of the dam.

Based on information provided to us regarding the construction of the dam and
reseTvoir IineT, we undeTstand that the oTiginal reseTvoir liner consisted of 12-inch
clay Ii neT that was formed by scarifying, moisture conditioning and compacting the
upper 12 inches of natural clayey soil exposed at the surface of the excavated
Teservoir. Based on the original geotechnical engineering study for the project