HomeMy WebLinkAbout1981-05-04 Septic System Design ReportTO: Jeanne A. Mubusth, Zoning Administrator
FROH: Michael P. Gaffron, Septic System Inspector
DATE: May 4, 1981
SUBJECT: Septic Testing, McCleary Property, 3445 Bayside Road
#589
I have reviewed the site evaluation report submitted by
Carl Borg on behalf of Mr. McCleary, and wish to make
the following comments:
1. Testing was done the beginning of April. In nearly
all. holes the water table vas round to be at a depth
of 1.0-1.8 feet below the surface. This coupled with
my bori:.•js in December 1979 indicate that the water -
table fluctuates, but is probablv at least 1 foot
below the surface dur_ng most of the year in the areas
tested. (which are the highest portions of the property)
2. Percolation tests were taken at a depth of 15", and
where water table was below the hole an average percolation
rate of 17 minutes per inch was found. The black silty
organic clays of the site are underlain by seams of
sand and gray silty clay.
3. Cased on the above findings, it seems that the major
limiting site factor is the water table, which nor -ally
for a mound system would have to be at least 2 to 3
feet below the surface as a minimum. The design
proposed by the applicants site evaluator includes
adding a layer of fill from the site over the natural
surface to increase the depth to water table to 2 feet
or more. This appears to be the best method as long
as A) the material used for fill is essentially the
same organic silty clay as that on the drainfield
site; and B) the fill material and existing soil are
Plowed or scarified to minimize any layering effect
that could occur, which might create a permeability
boundary and cause lateral seepage.
4. The proposal incorporates . separate rockbed for each
house within a single sand mound/berm. This method
will allow for separation of each residence's effluent
and will help to determine liability should system
failure ever occur.
S. The existing well/hand pump system should be properly
filled and sealed prior to any construction on the
site.
Septic Testin„ McCleary Property
May 5, 1981
page 2
6. Inherent in the design proposed are individual separate
septic tanks and holding tanks for each residence.
These should be located on the individual lots so that
the only pipe(s) crossing lot lines are the three
pressure distribution manifolds from the residences.
7. The propov- design meets criteria for a mound system
within the sheet flow flcodplain area.
8. Further items needing to be addressed include:
a) Can the proposed layout be constricted within the
applicant's proposed lot line arrangement an,1 still
allow for a driveway_ on the common to ? A staled
site plsn should be submitted to review, showing
all proposed improvements.
b) What are the provisions for an alternate drainfield
site? If none exists, I would recommend that if
failure occurs, the holding tank system for all
waste wculd he required.
c) Subheading (3.) of rry memo of 1-21-81, still needs
to be addressed. (ownership and responsibility
for maintenance and repair)
For _'e record, the technical justification for allowing
a graywater mound/holding tank system on this site is
a) adequate area exists for a mound system; b) adequate
percolation rates were demonstrated where the water table
F :rrc,itted; c) the proposed system is d-signed to com;,ersate
fcr the high water table. (Note that, normally, no system
would have been allowed in this area, and holding tanks
as well as the mound system ate a variance to the on -site
ordinance) d, the holcin3 tank/graywater combination will
reduce the on -site trpgtment required for:
BOD - by approximately 50%
N - by approximately 80%
P - by approximately 50%
Total water use by approximately 40%
(Based on Manual of Cray Water Treatment Practice
Table 8 p. 77)
Hence the system will not have as great an imp:;ct on the
soil/water system of the area as a total mound system
would, and should net create any undue pollution or health
problems for the area.
703
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