HomeMy WebLinkAbout1985-08-07 Septic System Design ReportSYSTEM DESIGN
FOR ROBERT RODERICK
LOT2, BLOCK 1, RINGERSWOOD
8-7-85
1. Percolation Rate, Type of System.
Percolation tests were taken previously by others and this design
is based on those results. The percolation rate for the primary
site was 9 MPI with a water table possible at 2.2 feet thus re-
quiring a mound system.
2. Proposed Flow Rate.
Size for 600 G.P.D.
3. Soil Treatment Area Needed.
600 G.P.D. x 0.83 factor is 500 Sq. Ft. of rock bed area, or a
bed 10 feet wide by 50 feet long.
4. Septic Tanks & Distribution System.
Two septic tanks of at least 1000 and 750 gallons are needed.
In addition, a third pumping tank and pump are needed for press-
ure distribution to the mound system. Distribution to the rock
bed is to be through 3 perforated laterals 40" apart. All con-
struction and materials should adhere to the provisions of the
City of Orono.
5. Mound Dimensions.
Since the ground slope is from 0-3% both the upslope and down -
slope areas can be used. With a 3 foot high mound and 4:1 side -
slopes the total dike width would be 10 feet for the bed and
I feet upslope and 13 feet downslope for a total of 34 feet.
This is greater than the minimum basal width required so the
34 feet is acceptable.
If there are any other questions, please contact me.
Sincerely,
PERCOR, INC.
Mark S. Gronberg, P.
PCA certified
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GENERAL CONSTRUCTION REQUIREMENTS
MOUND DRAINFIELD SYSTEM
TO BE USED WHERE: Seasonal perched water table is between 2 feet and 4 feet
below surface. Percolation rate in top 12" of soil is
faster than 60 MPI. Percolation rate in subsoil but above
water table is faster than 120 MPI. Where percolation rate
is 60-120 MPI, depth to groundwater shall be at least 3+
and slope must be nq more than 3%. Where percolation rate
is 30-60 MPI, depth to groundwater shall be at least 21
and slope must not exceed 6%. If percolation rate is faster
than 30 MPI, depth to ggroundwater shall be at least 31 and
slope must not exceed 6-12%.
CONNECTION TO
HOUSE House to tanks may be PVC (ASTM D-3034 or better),
cast iron or clay tile. PVC E.--ould be sand -bedded
in flat runs over long distances. No outside air test
required but joints must be tight.
TANKS Two (2) precast concrete tanks are required. Min. size
1000 gal. and 750 gal.; we recommend 2 1000's. Tanks
must have 20" manhole riser to within 12" of final
grade, and at least one 4"-6" inspection stack to
surface. Baffles must be acid resistant and may be
plastic, fiberglass, or .precast with tank.
DRAINFIELD Mound consisting of 12-21}" layer of sand on plowed, chopped,
or otherwise scarified natural surface soil. 12" rock bed
on top of sand layer, 10' maximum width X length dependent
on water use. Distribution pipe is laid in top 3" of rock.
Cover rock bed with straw or hay AND building paper. A
layer of sandy loam 6-12" thick should be placed over the
covered rock bed and a 6" layer of topsoil then placed over
the entire mound. Finished sideslopes to be 3:1 or flatter.
Grass cover should be established as soon as possible over
the mound area to reduce erosion and aid in evaporation.
THE MOST IMPORTANT STEP IN CONSTRUCTING A MOUND IS
PREPARING THE NATURAL SOIL SURFACE BY DISC -PLOWING
OR CHOPPING WITH A BACKHOE TO A DEPTH OF ABOUT 12".
When sand is pushed or dropped onto this loosened raw top-
soil (DON'T drive on it), an interface is formed which will
allow percolation to occur from the sand into the topsoil.
SEE SKETCH ON BACK OF THIS SHEET.
DISTRIBUTION The mound must use pressure distribution and requires a
pump from the se tic tanks. Distribution must be 1Y" PVC
or plastic with K" holes (turned down) every 36". Pumping
from a 2" manifold, distribution system should be 3 lengths
of pipe spaced 40" on center capped at the ends, running
the length of the rock bed (see sketch). No drop boxes or
distribution boxes are used. 4" PIPE WITH GRAVITY DISTRIB-
UTION IS NOT ACCEPTABLE IN A MOUND SYSTEM.
PUMPINtI Pump should go in a 3rd tank or in a baffled chamber of
2nd tanx. The idea is to retain the 2nd tank's capacity
for solids retention. An alarm device and reserve capacity
equal to one da,i sewage flow
are required. aa.slll� INN /S0
tK P,C>MVr_ CAekC_1T-'-( MAY INCLA.DflD - F T.@rc
LE L*SPRC Aeev+-30,4T-%-WT-
-� � Lam L .
TYPICAL -HOUND • RMOL 'I1lrJ 7mm Syrm LAYOUT
4 INCHES STRAW OR MARSH SANDY LOAM SOIL 6-17" dee;
MAY AND LAYER OF RED
ROSIN PAPER PERFORATED LATERAL
GRASS COVER 6 INCHES
12-24" SAND FILL--- TOPSOIL
MAXIMUM SLOPE —r
D TO I
OP S IL_ ---
PLOWED OR CLEAN ROCK y" BELOW PIPE, 2" OVER
DISKED SURFACE
CROSS SECTION A - A
PIPE FROM
PUMPING CHAMBER
c
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r ROCK BED -
_ 1 BR Hm. - 10'x 40,
14BRHCR. -.OIx50,
5 BR Hans - 10'x 65,
15" PVC I ( I S I LL D
PERFORATED F..-:':^ FROM
LATERALS I 1 I ROC' FD 01.
!1" Holes I Ik S F5.
every 36 F,w-rt7OT OF
�ED AREA
• TO 2'/1 4
INCHES
CLEAN ROCK d !� I o ; . t3L:
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-- SAND 10 FEET_— SAND
MAX 10'win
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PLAN VIEW
QUESTIONS ? CALL THE SEPTIC SYSTEM INSPECTOR AT 473-7357.
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0615 Ringer SubdivisionPage 4
Lot 2, Block 1 '
Peres PB21 thru PB26. Borincls RD21 thru DB23. Average perc rates
for bath primary and alternate sites are acceptable. Slopes are
nearly level at the tested sites, ranging from 0 to 3%. Mottlinq
indicated below 2', with actual water table at 3.2 to 4.21. A
standard mound system should be used due to the presence of shallow
saturation zones.
Lot 3, Block 1
Peres PB31 thru PB26. Borings B331 thru BB33. Slopes in the
primary site are approximately 6-8%, on a slight flattening
Of the 10-121 slopes surrounding it. Borings in the primary site
indicate 1 to 2 ' of loamy topsoil over a 6" layer of organic clay
topsoil over a plastic sandy clay. Actual Boater table at the
primary site was below 5'. However, the high plasticity indicates
a heavy clay that is probably saturated. The jecondary site was
mottled below 1.5 feet with an actual saturated zone at 1' depth.
Coupled with a slope of 10% the secondary site is marginal for a
mound system and would require at least 2' of sand base as part
of the design. I suggest thata standardpressure mound system
be required for both sites with addea sand depth for the secondary
system. Please note that this lot is the most tenuous in the
subdivision in terms of slope and roils consideration for using
a mound system. Should a proposed house location encroach on
either of the tested sites, careful review and possible additional
testing will be needed to ensure that a mound can still be used.
The site does not appear capable of supporting any kind of a trench
system.
Lot 4, Block 1
Peres PB41 thru PB46. Borings 3B41 thru BB43. Slopes average 50 -
71 overall. Borings indicate actual water table at 4' with mottling
at a depth of 3-4' for the primary and 2' at the secondary site.
Perc rates were fairly uniform throughout these testes. sites. A
depression/drainageway to the immediate south of the tested sites
must be avoided during construction of the systems. I would
recommend a standard pressure mound for both sites.
Lot 5, Block 1
Peres PB51 thru PB56. Borings BB51 thru BB53. Slopes are 31 to
6% overall. Mottling at the primary site started at 2.7 to 3.5'
with actual water table at 3.7 to 5.0'. This site is acceptable
for a standard mound system. The alternate site has a perc rate
considered too slow for any system by code. However, close
scrutiny shows that the peres were taken at depth in the sandy
clay subsoil, not in the topsoil. in general, throughout the entire
subdivision the testing done at a depth of 12", in the topsoil,
indicates acceptable percolation rates, with testing at 24" or more
indicating slower, marginal perc rates. In my opinion, this site
is no different than most of the others, and would have an acceptable
perc rate if tested at the 12" depth in the sandy loam topsoil.
No further'testing should be reyuirecl; a mound system is recommended.
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