HomeMy WebLinkAbout20053530.tiff STATE OF COLORADO
Weld County Planning Department
COLORADO GEOLOGICAL SURVEY GREELEY OFFICE
pen
Department of Natural Resources JAN 2 9 2004 E-MAILED
1313 Sherman Street, Room 715
Den RECEIVED
Denver,Colorado 80203 1 2G OA-
Phone 303.866.2611
Fax 303.866.2461 DEPARTMENT OF
NATURAL
RESOURCES
January 23, 2004 Bill Owens
Governor
Russell George
Jaqueline Hatch Executive Director
Weld County Department of Planning Services Legal Description: Ron cottony
NW'/4 of Cl,T2N,12.67W Division Director
1555 N. 17"'Avenue of the 6th P.M. Ron Cattany
Greeley, CO 80631 Acting State Geologis
and Director
Subject: Review of Moorea Manor North P.U.D. Sketch Plan
Case No.PK-1048,Weld County,CO; CGS Unique No. WE-04-0016
Dear Ms. Hatch:
Colorado Geological Survey has completed its review of the above-referenced project. We reviewed the
parcel immediately south of this site, Moorea Manor, on October 9, 2001 (WE-02-0021)and on March 5,
2003 (WE-03-0029). I understand the applicant proposes to subdivide this 45.2-acre parcel into eight
residential lots of approximately 4.4 to 7.7 acres each. Individual sewage disposal systems (ISDS)are planned
for each of the eight new lots, and the applicant states that domestic water service will be provided by Central
Weld Water County District. I have several comments regarding the proposed development.
1. Soils and bedrock. With this referral, I received an Engineering Geology Report prepared by Church and
Associates, Inc., dated November 26,2002. This report describes the results of a geotechnical
investigation consisting of three soil test borings and limited laboratory testing. Church's test results
indicate that the subsurface soils consist of silty, clayey eolian(wind-deposited) sands and sandy clays
exhibiting moderate strength characteristics. The underlying bedrock consists of Laramie Formation
claystone and sandy shale, and exhibited low to moderate swell potential and high bearing capacity. A
sample of eolian sand from one of the test borings exhibited minor collapse under pressure when wetted.
Considering the potentially hydrocompactive soils and expansive bedrock present at this site, it is very
important that site-specific maximum bearing and minimum dead-load pressures are determined and
incorporated into individual foundation and footing designs. Church's report contains appropriate
recommendations for additional, site-specific geotechnical investigations to determine soil strengths,
swell potential and groundwater levels, and to provide specific recommendations for structural design.
This will help minimize the risk of foundation damage due to differential settlement and heave.
Additional foundation damage due to compaction and differential settlement can occur if water infiltrates
the soils adjacent to and beneath the foundation as a result of, for example, residential irrigation. Proper
grading, compaction and drainage must be incorporated into the development plans.
I agree with Church(page 4)that, based on limitations discussed in the Soil Conservation Service Soil
Survey, excavations into some of the onsite sands, especially those on the northern portions of lots 1
through 4, may create unstable slopes which could cave. Care will need to be taken during construction to
minimize the heights of cuts and the duration that cuts are left open and unsupported. Shoring may be
required.
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2005-3530
Jaqueline Hatch
January 23, 2004
Page 2 of 2
2. Groundwater. According to the Soil Survey, the surficial soils underlying most of proposed lots 5 and 8
present severe limitations for construction of dwellings due to wetness and possible flooding.
Groundwater was encountered in a test boring on proposed lot 4 at a depth of only 7.3 feet below the
ground surface. Full-depth basements may not be feasible on all lots, and should not be considered for
lots 3, 4, 5 and 8 unless more detailed, site-specific information is obtained about local and seasonal
depths to groundwater. Groundwater levels may rise seasonally, and perched water is likely to form
above clayey, less permeable soil layers and on top of the bedrock surface as a result of irrigation and
infiltration from ISDS. We recommend that individual perimeter foundation drain systems be constructed
to help prevent infiltration of perched water(if basements are planned), and to help control wetting of
potentially collapsible or expansive soils in the immediate vicinity of the substructure. It is critical that
the perimeter drains, if constructed, are sloped to discharge to an interior pumped sump or a gravity outlet
that discharges water as far as possible away from all structures.
3. Drainage. With this referral,we received a Drainage Report(TEAM Engineering,March 2003). According
to the drainage rerport, two detention ponds will be needed,one for lots 6 and 7, and one for lots 1-5 and lot
8. The dimensions,volumes, locations, intake channels and outfalls of these detention ponds are not shown
on the Sketch Plan drawings or in the Drainage Report.
4. Oil/gas wells. Three oil/gas wells are present on the property,and several tanks and separators exist both on
and adjacent to this property. Building envelopes on lots 1,2,3,4, 5 and 7 should be delineated to
specifically exclude all property within the required setback radius from oil and gas wells and related
facilities. Prospective residents should be advised and a plat note should be included informing buyers that
the oil/gas wells and related equipment may be loud,may pose a visual nuisance, and will require ongoing
servicing,maintenance and access via local roads. All wells,pumps,processing facilities and tank batteries
within the residential development should be fenced and locked, with warning signs posted to protect
residents from hazards associated with the machinery and possibly tainted soils.
5. ISDS. The Weld County Soil Survey describes the soil units present over most of the new planned lots as
having slight limitations for septic systems, except in the area surrounding the Lupton Bottom Ditch. The
soils within this area have severe limitations for septic systems due to saturated soils. Church describes
the results of four preliminary percolation tests in their Preliminary Percolation Test Report, dated
November 27, 2002. Tests were performed only on proposed lots 1 and 6, and results ranged from 27 to
80 minutes per inch. For all lots, individual percolation tests will be needed to design ISDSs, and the area
surrounding the ditch should be avoided.
We would like to review this project again at preliminary or final plat to verify that building envelopes comply
with oil&gas facility setback requirements,and to verify that detention ponds and drainage channels have been
correctly sized and located.
Thank you for the opportunity to review and comment on this project. If you have questions or need
clarification of issues identified during this review,please call me at (303) 866-2001, or e-mail
jill.carlson@state.co.us.
Sincerely,A-10)-%__,
J 1 Carlson, C.E.G.
Engineering Geologist
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