FLOOD01124

• County: Boulder
• Stream Name: South Boulder Creek
• Title: South Boulder Creek/ Flatirons
• Date: 12/5/1997
• Prepared For: Boulder
• Prepared By: Consultants
• Floodplain - Doc Type: Community File

. MAY 27 '97

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RECEIVED.
MAY 2 7 1997

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Colorado Water
Conservation Board

April 1 , 1997

Post.lt. Fax Note
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Co.

Mr. Ed McDowell
Flatiron Companies
P. O. Box 229
Boulder, Colorado 8030S

Fax,

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Pl1one'N
~ax'

Subject:

Levee at Deepe Farm Pit
Boulder, Colorado
Job No. 25,385

Mr. McDowell:

Enclosed are the results of our field and laboratory investigation we have
completed to date for the levee. Figure 7 shows the maximum section of the levee
of Station 122+00. We have summarized our completed analyses on the enclosed
drafts of the partially completed forms that will eventually be a part of the submittal
to FeMA. In summary, our preliminary opinions that the embankment meets the
FEMA certification criteria is continuing to be confirmed as our analyses are being
finished.

Figure I shows the locations of our test holes and test pits. Figures 2 through
6 are the summary logs of our test holes and test pits and the results of our field
permeability tests. Figure 8 shows the typical gradation of the levee fill and Table II
shows the summary of the percents compaction we calculated at the density test
locations. Table I shows the results of our laboratory tests.

The test pits TP.1 through Tp-3 were drilled (excavated) with a large pier hole
drilling rig using a 42.inch diameter auger. The levee fill was very rocky and the
rocks were numerous and close together. Our inspection ofthe test pits revealed
the rocks were 'embedded in a densely compacted, clayey, sand matrix and it was
impossible to pry the rocks loose without loosening the matrix when we dug the
holes for the sand cone density tests. The "pilot hole" for the nuclear gauge probe
had to be advanced by driving a pointed steel rod into the ground with a sledge
hammer. .

, .~.

Review of the gradation test.results (Figure 8) of two typical samples of the
levee fill shows that the levee fill is quite rocky and the samples had 40% to 45%
larger than the 114 inch size. Review of the percents compaction in Table II show a
range for the 15 tests (two of which were in the foundation ground at the bottom of
the fill) 75 percent to 103 percent. In our judgment these test. results are not
reflective of the effort it took to excavate the test pits or the density of the fill as
evidenced by the difficulties in excavating for the sane:! cone tests or advancing the
"pilot hole" for the nuclear gauge. In our opinion, the levee fill is well compacted but

CTL/THOMPSON, INC.
CONSUL. TING ENGINeeRS
197, WEST 12TH "'VENUE . OENVE'l. CO~O'lADO 80204 . (303) 825.077'