PROJ00318

• Contract/PO #: C153618
• Contractor Name: Greeley, City of
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: SB 87-15
• Loan Projects - Doc Type: Feasibility Study

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at the crest as revealed by the boreholes. The embankment material In the old
dam was wet, gray, silty sand and gralle1, poorly compacted down to the contact
wi th sl i ght1y weathered foundati on bedrock. The wall s of the test pi t were
unstable because of the high phreatic surface within the embankment. Test pit
PP-13, along with the bore holes, indicate the 1972 crest and downstream slope
modifications were accomplished by excavating the entire dam crest down to the
service spillway conduit elevation and backfill ing the crest and downstream
slope wi th materi a1 s from the reservoi r area. It appears the vegetati on may
not have been removed prior to flattening the downstream slope. An
interpretive section through the dam is shown on Figure V.2.

Test pit PP-12 penetrated the upstream face of the dam, perpendicular to the
centerl ine, beginning from the berm at approximately elevation 9490: The
surface of the slope was covered with a single layer, up to four feet thick,
of hard angular riprap. The riprap is underlain by less than a foot of dark
gray to brown, clayey sand with ol'ganics, presumed to be the impervious
blanket placed during the 1972 repairs. Below the blanket layer, the pit
exposed a grayish-green sequence of alternating lenses of coarse to fine sand
with gravel, and sandy clay with organic material as was encountered in the
bore holes. The walls of the pit Were unstable due to the infiltration of
ground water through the pervious sand layers. A third test pit, PP-4, was
excavated through b1 ack organi c reservoi r sediments immedi ate1y upstream of
the out1 et works i n1 et to a depth of 8.0 feet, at whi ch ei ther bedrock or
large boulders were encountered.

2.1.3.2 Auxiliary Spillway

Three test pits, PP-7, PP-9, and PP-10, were excavated upstream of the
auxiliary spillway. All three pits revealed basically the same condition;
three to ni ne feet of sandy gravel 91 aci a1 till over1yi ng sl i ght1y weathered
bedrock. Test pit PP-B was excavated downstream of the auxiliary spillway
overflow section in the grassy area where seepage occurs when the reservoir is
filled. The test pit encountered sandy gravel to a depth of 15 feet at which
point bedrock was revealed.

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