HomeMy WebLinkAbout1980-10-30 Memo, Review of Soil CharacteristicsTO: Jeanne Mabusth, Zoning Administrator
FROM: Michael Gaffron, On -Site Systems Manager
DATE: October 30, 1980
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 debAgnated
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
This is probably the most critical lot of the s%itjivision 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.
October 30, 1980
i582 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.
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. /
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 recom-iend approval of the subdivision as per preliminary
plan with the above recommendations.
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