PROJC00141

• Contract/PO #: C150135
• Contractor Name: Silt Water Conservancy District
• Contract Type: Loan
• Water District: 0
• County: Garfield
• Bill Number: MC3
• Loan Projects - Doc Type: Feasibility Study

b. Install collection measures for each seep area. If the seepage exit conditions
can adequately be defined, this might be done after the reservoir is drawn down so
that the work could be performed without interference from seepage spray. The
collection features might include such items as chipping collection channels in the
exposed tunnel rock, installation of pipes, plates, etc. bolted to the tunnel rock and
epoxy gfout to seal opening around collection features.

Following is our estimate of the costs associated with this option:

Collection Features
Sample Tests
25% Contingency
Design
Inspection/Completion

$20,000
2,000
5,500
4,500
5,000

T ota! Estimated Cost

$37,000

Note that the above costs assume that Silt WCD personnel will obtain samples and
transport them to the testing laboratory. Sample testing costs are only for the first year. It
would be expected that some periodic sampling and testing would be required on a long-
term basis. It must also be noted that, if the monitoring indicates the possibility of void
development, other methods would 00 required to prevent further void enlargement.

2. It would 00 expected that creation or enlargement of subsurface voids would be
accompanied by a reduction in seepage pressures along the seepage paths. Although not as
reliable as the collection, measurement and sampling of seepage discharge water discussed
above these pressures could be monitored by piezometers. If the seepage path is known
with some confidence, so that the piezometers could be installed along that path, the cost
for piezometer insta1lation is estimated as follows:

Piezometer Installation
25% Contingency
Design
Inspection/Completion

$15,000
3,750
3,500
6,000

T ota! Estimated Cost

$28,250

3. The seepage entty area could be sealed. Unless the entJy area is successfully
identified this method would require an informed assumption regarding the location of
entty areas. Assuming the previously noted possible seepage entry areas, it is estimated
that about 17,000 sq ft of area would need to be sealed. This would cover the area shown
as disturbed by spillway excavation on the 1909 enlargement plans extending down to
about gage elevation 40 (five feet below the presumed seepage initiation level of 45) as well
as extending about 50 feet onto the embankment. This could be accomplished either with
placement of a synthetic liner or a compacted clay blanket. The work would consist of the
following: