HomeMy WebLinkAbout1983 soils and site investigation reviewTO: Jeanne A. Mabusth, Zoning Administrator
FROM: Michael P. Gaffron, On Site Manager
DATE: June 15, 1983
SUBJECT: Proposed Subdivision for Willow Properties,
Gary Peterson - Soils and Site Investigation
Review
I have reviewed the ten proposed lots and wish to make the
following comments:
Based on the Hennepin County Soil Survey, soils on
this property include Lester loams and clay loams,
Hayden loams, Hamel loams and LeSeur loams, as
well as a good deal of marsh. Tested sites are
located on the higher, better-drained soils. Some
areas of sandy soil were reported on the most
easterly lots. Based on the soils and water table
data submitted, shallow trench or standard trench
systems appear suitable for all lots. Following is
a summary of the soils data for each site:
Lot 1 Block 1 - Percolation Rate Average 22 MPI both
sites
- Primary site - slope 5% - mottling at 3.5’ - water
table at 3.5' - modified shallow trench system*
Maximum Trench Depth 6" into original soil
- Alternate site - slope 8% - mottling at 4.0'
Water table at 4.9' - shallow trench system - maximum
trench depth 12" into original soil
Lot 2 Block 1 - Percolation Rate Average 18 MPI both sites
- Primary site - slope 7% - mottling at 4.2', 5.0' - water
table at 4.5' , 5.5' - shallow trenches - Maximum Trench
Depth 14" into original soil.
- Alternate site - slope 8% - mottling at 3.3' - water
table at 3.3' - modified shallow trenches* - maximum
trench depth 4" into original soil
Lot 3 Block 1 - Percolation Rate Average 23 MPI both
sites
- Primary site - slope 10% - mottling at 4.0', 4.5' -
water table at 4.0', 5.5' - shallow trenches -
maximum trench depth 12" into original soil
- Alternate site - slope 8% - mottling at 3.5' - water
table at 3.6' - modified shallow trenches*- Maximum
Jeanne A. Mabusth
June 15, 1983
page 2
Trench Depth 6" into natural soil
Lot 4 Block 1 - Percolation Rate Average 19 MPI both
sites
- Primary site - slope 12% - mottling at 5.0', 5.8' -
water table at 7.7', 7.2' - standard trenches - maximum
trench depth 24" into original soil
- Alternate site - slope 14% - mottling at 5.0' - water
table not encountered - standard trenches - maximum trench
depth 24" into original soil
Lot 5 Block 1 - Percolation Rate Average 8 MPI (primary
site) 28 MPI (alternate site)
- Primary site - slope 7% - sandy soils, mottling not en
countered, water table at 5.3', 6.0'- standard trenches
- maximum trench depth 28" into original soil
- Alternate site - slope 7% - mottling at 5.0' - water
table at 5.2' - standard trenches - maximum trench depth
24" into original soil
Lot 6 Block 1 - Percolation rate average 13 MPI (primary
site) 19 MPI (alternate site)
- Primary site - slope 9% - mottling not encountered - water
table at 7.5', 7.8' - standard trenches
- Alternate site - slope 10-12% - mottling at 4.3', water
table at 6.8' - shallow trenches - maximum trench depth 16"
into original soil
Lot 1 Block 2 - Percolation Rate Average 26.3 MPI both sites
- Primary site - slope 8% - mottling at 5.5', 5.9', water
table at 5.6', 5.9' - standard trenches - maximum trench
depth 30" into original soil
- Alternate site - slope 7% - mottling at 3.5', water table
at 4.3' - modified shallow trenches* - maximum trench
depth 6" into original soil
Lot 2 Block 2 - Percolation rate Average 31 MPI both sites
— Primary site — slope 5% — mottling at 3.5' — water table
at 3.6', 3.7' - modified shallow trenches*
- Alternate site — slope 5% - mottling at 3.0' - water table
at 3.2' - modified shallow trenches* or Mound - maximum
trench depth - at soil surface (see note below re modified
trenches)
Lot 3 Block 2 - Percolation Rate Average 10 MPI both sites
- Primary site — slope 8% - mottled at 4.5', 5.0' - water
Jeanne A. Mabusth
June 15, 1983
page 3
table at 4.5', 5.3' - shallow trenches - maximum trench
depth 18" into original soil
- Alternate site - slope 6% - mottled at 3.8', water
table at 3.8' - modified shallow trenches* - maximum
trench depth 10" into original soil
Lot 4 Block 2 Percolation Rate Average 14 MPI both sites
- Primary site - slope 7% - mottling at 4.4', 5.5’ -
water table at 4.4', 5.6' - shallow trenches - maximum
trench depth 17" into original soil
- Alternate site - slope 5% - mottling at 4.0' - water
table at 6.4' - shallow trenches - maximum trench depth 12"
into original soil.
*Modified Shallow Trenches - where water table or mottling
is between 3.0' and 4.0' below the surface, a standard
12" rock depth (6" under pipe, 2" over) must be used in
conjunction with an appropriate depth of fill material
to retain a 3.0' separation between the bottom of trenches
and the water table or mottling. Fill should consist of
material classified as loamy sand (USDA classification).
The original soil must be dryer than the plastic limit
before placing fill. The original surface must be scarified
or disced to break up the surface vegetation mat. The
loamy sand fill must be placed over the entire area so that
no trench will be located less than 10' from the edge of
the fill. The depth of fill required will depend on the
allowable depth of excavation into original soil based on
the water table or mottling.
I recommend that the subdivision be approved as proposed. The
developer should be warned to keep all traffic, fill excavation,
etc. away from the tested drainfield sites. In some cases
where road construction will be near the tested sites, extra
caution must be taken.
MPG;jl