HomeMy WebLinkAboutSCENIC VIEWS PUD - FINAL - 3-96A - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORTEarth Engineering Consultants, Inc.
EEC Project No. 1962030
May 29. 1996
Page 3
We appreciate the opportunity to be of service to you on this project. If you have any questions
concerning this report, or if we can be of further service to you in any other way, please do not
hesitate to contact us.
Very truly yours,
Earth Engineering Consultants, Inc.
Lester L. Litton, P.E.
Principal Engineer
LLL/dmf
cc: Dave Klockeman - JR Engineering
Earth Engineering Consultants, Inc.
EEC Project No. 1962030
May 29, 1996
Page 2
For construction of the wet pond, an augmentation plan to replace ground water which would
evaporate from the surface of the pond would be required. The capacity of the pond would be
controlled by the elevation of the outlet works. If water were ponded above the present ground water
elevation depth, some mounding of ground water in the vicinity of the detention pond should be
expected. Conversely, if the level of the water in the pond is below the present ground water level,
infiltration of ground water throughout the surrounding area of the pond should be expected. The
ground water flow into the pond area would be a function of the pond level in addition to the
transmissivity of the surrounding soils. We estimate the site soil would have a coefficient of
permeability on the order of 10' cm/second. The underlying bedrock would have a permeability of
10' cm/second or less. Greater quantities of water could be transmitted through more permeable
zones in the bedrock or overburden soils.
With the relatively high ground water table, a dry pond will probably require the use of a perimeter
barrier system. Although a dry pond could be developed by limiting the pond cuts to a depth of 2
feet above seasonal high ground water levels, we expect this elevation would be too shallow for
suitable functioning of the pond. Use of a barrier system would prevent an influx of ground water
into the pond and would eliminate the need for a ground water augmentation plan. The barrier
system would consist of a slurry wall or similar type structure extending from ground surface to the
top of the underlying bedrock and would extend for the circumference of the lake. The barrier wall
should be placed a sufficient distance away from the crest of the slope for development of stable side
slopes on the pond excavation. A soil/bentonite blend could be used to provide a barrier for the wall
perimeter. After the barriers are placed, the excavation for the pond could be extended to \\ hatever
depth desired with the development of a dry pond. Slight mounding of the ground water adjacent
to the structure could be expected as the ground water flo,,y is forced around the detention pond area.
From a geotechnical standpoint, construction of either a wet pond oi a dry pond is Ieasible.
Selection of the type of facility to be used may be dependent on lactors other than the technical
ability to construct the type of pond desired. We would he pleased to provide liirther
recommendations concerning construction of a wet pond or dry pond, at your request.
May 29, 1996
Rocky Mountain Research Institute
6645 East Heritage Place South
Englewood, Colorado 80111
Attn: Mr. Bill Veio
Re: Detention Pond Recommendations
Scenic Views PUD
Fort Collins. Colorado
EEC Project No. 1962030
Mr. Veio:
EARTH ENGINEERING
CONSULTANTS, INC.
We understand a detention pond will be constructed in the north -central portion of the proposed
Scenic Views PUD in Fort Collins. Subsurface explorations concerning the Scenic Views
development have been completed by Earth Engineering Consultants. Inc (EEC) over the past year.
Evaluation of the existing and anticipated high ground water levels on the sing
Ilefamily portion of
the site was also completed by Ayres Associates. A portion of our recent discussions for this project
have revolved around development of the retaining pond area and the potential for constructing a
"dry pond" versus a "wet pond." The purpose of this report is to provide general geotechnical
recommendations concerning those two alternatives.
The present ground water elevation in the proposed detention pond area ranges from approximately
5109 to 5112. Over a monitoring period of approximately one year, we have noted water level
fluctuations on the order of 1/2 foot. We understand the proposed bottom of pdiid elevation is on
the order of 5106. That pond bottom elevation would place the pond bottom below the area ground
water level and result in infiltration of ground water into the pond. The amount of water ponded
would depend somewhat on the elevation set for the outlet pipe of the structure. The maximum
depth of water in the pond area would be near the ground water level at the upslope inflow.
approximately 5,112 feet. Water levels in the pond would not be expected to rise above that
elevation based on ground water inflow (unless the `'round water table rise,) even ifthe outlet pipe
was constructed at a higher elevation.
Centre For Advanced Technology
2301 Research Boulevard, Suite 104
Fort Collins, CO 80526
(970) 224-1522 FAX 224-4564