HomeMy WebLinkAbout1980-10-30 Site Evaluation Reportr
TO:
FROM:
DATE:
Jeanne Mabusth, Zoning Administrator
Michael Gaffron, On-Site Systems Manager
October 30, 1980
Jj.
SUBJECT: #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 trench 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 damaged drainfield areas, but no further excavation
or disturbance should be allowed until final house location is determined.
Lot 3, Block 1
S
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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[;
October 30» 1980
#582 H.R. Johnston
925 Willow Drive South
Page 2
Lot 3, Block 1 (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.
I Th(
Lot 1, Block 2
The soils on this lot are considerably different than those of the
westerly lots. Loam and clay loam 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 development 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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SITS EVALUATION REPORT
i-'Oa 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-slte drainfield systems. Six percolation holes
were tested on each lot and three soil borings taken on eacln on nn^h 1 stfc
to determine both ^ orimarY - -fn fjfainfield sltes^^^e
olatlon holes were dug 6 inches in diameter to the 4 foot depth 1
olos ^-6 were ^
, vhehoTe^Sere
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A except \
Vdug2f,
the alternate cite on lot 1, block 2 where holo^
feet deeo to teat for a shallow trench system
dug^fith 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 pexvieable soils were found on most lots
and all lots liad sufficient percolation rates to qualify for stan
dard drainfield systems, Tho 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 be const
ructed fairly shallow and an interceptor drain should bo used to
divert runoff water from this site since the lot la bowl shaped
\ of lo
Better soil was encountered shallower on the alternate site
®^loJ^L^block 2 80 8halloi^trenohe^8hot^^beusedhor^TSTot
3 or Diock 1 a pump will probably be needed since T;ne oest 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
and some prohibitive soils and water tabi i. near tl)> marshes which
may nreclude any other areas being used for drainfields.
If any additional information is needed, please contact me.
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JOHNSTON PROPISRTr
LOT 1, BLOCK 2
Peroolation RasuIbs
Matorial
Yellow B3?n. Clay Loam
Yellovj Brn. Clay Loam
Brown Loam
Brown Clay Loam
Brown Loam
Brown Loam
Ihe av;:. percolation rata for holes l-4(orinary cito) = 39,5 KPI,
'fhe av^. percolation rate for holes 5-6(alt. site) =24.3 MPI,
Hole Lo,
P-1
P-2
P-3
P-U
P-5
P-6
Percolation Rate
43.6 Hln./lnoh
U8.0
22.9
43.6
21.6
26.7
3oll Borings
S.B. 1
DeothCft.)
0.0-1.0
1.0-3.0
3.0-6.0
6.0-7.0
7.0-8.0
No mottled
S.B. f 2
l)eoth(ft.)
Katerial
Gray Brown Loam
Brown Clay Loam
Yellow Brown Clay Loam
Bm. Sandy Olay Loam
Light Gray Brown Clay
soil present water table after 2l|. l^oura.
1
0. )-O.0
o.a.2.0
2.0-4.2
4.2-6.5
.0
No mottled
Katerlal
Gray Black Loam
Brown Clay Loitim
Yellow Brown Clay Loam
Lt. Bm. Silty Clay Loam
Lt. 3m, Clj^y Loam
soli and no water table after 24 houra.
1
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DenthLft.)
0. >-'\7
0.7-1.7
1.7-3.3
3.3-6.0
Material
Black Loam
Brown. Loam
Brown Clay Loam
Yellow Bm. Cl. Loam
6.0-7.0 Lt. Bm. Med« Sand
7.0-0.0 Coarse Sand» OraTel
No mottled soil or water table
after 24 hoiirs.
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