HomeMy WebLinkAbout1980-10-22 Site Evaluation Report‘
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SITS EVALUATION RSPORT
FOR HARRISON R. JOHNSTON,JR,
ORONO, MINNESOTA
10-22-80
During October 17-22, 1980 all five proposed lots in the sub
division of Harrison Johnston, Jr. were tested for the suitability
of supporting on-site drainfleld systems. Six percolation holes
were tested on each lot and three soil borings taken on each lot
to determine both^ primary and alternate drainfleld sites. The
percolation holes were dug 6 inches in diameter to the 4 foot depth
except the alternate site on lot 1, block 2 where holes 5-6 were
dug 2 feet deeo to test for a shallow trench system. The holes were
dug with both power and hand augers.
The soil borings were dug with hand augers and were 6 inches
in diameter to the 4 foot depth and 3 inches in diameter to the re
maining depth. Some very pemeable soils were found on most lots
and all lots bad sufficient percolation rates to qualify for stan
dard drainfleld systems. Ihe alternate site on lot 1, block 1 will
require shallower trenches to avoid the water table. ‘The trenches
on the primary site of lot 1, block 3 will also need to bo const
ructed fairly shallow and an interceptor drain should be used to
divert runoff water from this site since the lot is bowl shaped
and collects runoff water.
Better soil was encountered shallower on the alternate site
of lot 1, block 2 so shallow trenches should be used here. In lot
3 of block 1 a pump will probably be needed since the best soils
exist on top of the hill. It also might be necessary to use pumps
on other lots depending on tht placement of the houses. Additional
design information for the individual houses will be needed prior
to construction. It is imperative that these tested area not be
disturbed since there are some steep sidehill slopes on some lots
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and some prohibitive soils and water tab* near th^ marshes which
may oreclude any other areas being used for drainfields.
If any additional information is needed, please contact me.
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JOHNSTON PROP:5RTy
LOT 2, BLOCK 1
Percolation Results
Hole 11 o,
P-1
P-2
P-3
P-4
P-,S'
P-6
Material
Coarse Sand
Coarse Sand
lit* Bm« i^'lne Sand
Lt« Brn. Fine Sand
Coarse Sand
Lt» Bm. Ned. Sand
Tile avg, percolation rate for holes l-4(priinary site) = 1.6 MPI,
The avg. percolation rate for holes 5-6(alt. site) * 2.1 I.PI.
Percolation Rate
1.1 Min./inch
1.0
1.7
2.$
1.3
2.9
Soil Borings
S.B, J 1
DeDth(ft.)
O.O-l.O
1.0-2.0
2.0-3.!?
3.5-6.0
6.0-8.0
Katerial
Black Loan
Gray Brown Loam
Brown Medium Sand
It. Bm. Medium Sand
Lt. Gray Bm. Fine Sand
No mottled soil or water table after 24. hours.I
S.B. / 2
0eoth(ft.)
0.0-1.2
1.2-1.5
1.5-1.7
1.7-3.0
3.0-3.6
3.0-5.0
5.0-6.5
Material
Black Loam
Hard Brown Clay
Brown Clay Loam
Brown Loam
Brown Medium Sand
Lt. Brown Pine Sand
Coarse Sand(Rock encountered)
No mottled soil or water table after 2k hours.
6.B. 3
Dapth(ft.)
0.0-1.3
1.3-2.6
2.6-3.7
Material
Black Loam
Brown Clay Loam
Brown Loam
brovm Medium Sand
5.5-8.0 Gray Bm. Coarse Sand
No mottled soil or water table
after 24 hours.
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TO:Jeanne Mabusth, Zoning Administrator
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FROM:Michael Gaffron, On-Site Systems Manager
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DATE:
SUBJECT:
October 30, 1980
#582 H. R. Johnston, 925 Willow Drive South - SUBDIVISION
On-Site Systems Review
On October 28, 1980, I reviewed the five proposed new building sites
for the above referenced subdivision as per the attached survey.
Each lot (save Lot 4, Block 1 with existing house) appears to have
2.0 acres of dry buildable land. However, due to proximity to adjacent
wetlands and the accompanying water table a portion of each lot is
unsuitable for use as drainfield. All lots had areas tested which meet
the requirements for standard tren h drainfield systems. These designated
tested drainfield areas on certain lots are the only available acceptable
sites for drainfield. In every case, assuming a long term water table
exists at approximately the 930* elevation, no drainfield trenches
(2* depth standard) should be allowed below elevation 935* in order to
ensure a 3* separation between trench bottoms and water table. In
addition, where individual lot testing indicates a water table depth,
the above 3* separation must be adhered to. Following is a detailed
review of each lot.
Lot 1, Block 1
Testing indicates soil and water table conditions are suitable for a
standard trench drainfield system. This lot has some alternate house
location possibilities. However, the tested site and in fact the entire
lot should be left undisturbed until a final house location is determined.
Lot 2, Block 1
As in Lot 1, testing found sandy soils suitable for a standard drainfield
system. Various house locations may be possible. An excavation crossing
the lot has not severely dcunaged drainfield areas, but no further excavation^
or disturbance should be allowed until final house location is determined.
3, Block 1Lot
This is probably the most critical lot of the subdivision in that a limited
area is available for use as drainfield. The tested area is at the highest
point of the lot due to extreme slopes. An excavation near the northwest
corner of the lot may have affected the extent of the area available for
drainfield. By creating an outlet for sidehill seepage from trenches above
the excavation. However, due to the extremely fast percolation rates and
sandy soils and the existence of untested but probably suitable area for
drainfield to the east on the lot, the effect of this excavation is only
slight.
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#582
October 30, 1980
#582 H.R. Johnston
925 Willow Drive South
Page 2 i
Lot 3, Elockl (Cont.)
When this lot is developed, care must be taken to make sure the house
location does not encroach on the area to be preserved for drainfield.
I suggest that for this lot (and for all subdivisions in the City) that
the tested drainfield sites be somehow entered on the title or deed for
the property so that prospective buyers are made aware of the restrictions
on the lot.
Lot 4, Block 1
This lot contains the existing H.R. Johnston home. Although the lot
as proposed contains only 1.64 acres, adequate area has been previously
tested and exists for use as future drainfield. A relocation of the lot
line between Lots 3 and 4 to give each property approximately 1.8 acres
would serve no purpose as far as drainfield sites are concerned.
Lot 1* Block 2
The soils on this lot are considerably different than those of the
westerly lots. Loam and clay lo2un soils are indicated, and the percolation
rates were understandably slower. This lot contains 2.4 acres and has a
somewhat limited number of possible house locations which would allow a
gravity-flow drainfield system. The lot is acceptable for a standard
trench drainfield. Care must be taken during developinant of the lot
that drainfield trenches are kept away from the pothole in the center
of the lot.
Lot 1, Block 3
This lot has loamy soils with a fairly good percolation rate. The tested
drainfield sites are to the immediate southwest of the existing paved
driveway and due to slope conditions appear to be the only likely sites
for use as drainfield. Again, care must be taken to preclude disruption
of these sites prior to development. It appears that the suggested location
of the house would be on the north end of the lot approximately on the
existing driveway.
Summary
Each of the five proposed new lots should be acceptable for standard trench
drainfield systems. Fortunately, this is one of the few areas of Orono
having sandier soils. Certain lots as indicated may have limiting sites
due to water table and slope constraints. As the engineer’s report states,
it is imperative that the tested sites not be disturbed by further
excavation, grading or filling until permits are issued for specific
house locations. I recommend approval of the subdivision as per preliminary
plan with the above recommendations.
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