HomeMy WebLinkAbout1979-05-08 Septic System Design ReportLy 8, 1979
545 Indian Mound
Wayzata, Minnesota 55391
David Nitz Company (612) 473-4224
1989 Fogerness Point Road
Wayzata, Minnesota 55391
Re: Lot 2, Block 3 of 'avid Nitz subdivision, Orono, MN
Dear -Mr. Nitz:
The drainfield information was based on percolation tests
and soil borings performed in April 1979.
The soils on the site include Lester silty cam. The
average percolation rate for the primary f.L_ld is 22.1
minutes per inch and 14.3 minutes per inch for the secon-
dary field. The locations of the percolation test holes,
soil borings, and the proposed drainfield areas are indi-
oated in Figure 1. The individual percolation raters are
,,
given in Table 1 and the soil boring logs are given in
Table 2.
Because of the high water table a shallow trench system
•
with pressure and gravity distribution is recmmended for
the site. I have enclosed plans and specifications for
such a system (Figures 2-4).
Stated percolation rates are averaged for the locations
shown and no guarantee is implied or expressed that these
conditons exist for the entire area.
If you have any questions, please feel free to call.
Sincerely,
E. A. HICKOK AND ASSOCIATES
Larry L. Johnson
Geologist
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SPECIFICATIONS FOR PROPOSED ON -SITE SEWAGE DISPOSAL SYSTEM •
SHALLOW TRENCH: DISTRIBUTION THROUGH GRAVITY FLOW
C
LOCATION: Lot 2, Block 3 of David Nitz subdivision
Orono, Minnesota
DATE: May 6, 1979
I. SEWAGE TANK - TWO 1000-gallon LIQUID CAPACITY tanks, IN SERIES,
manufactured and installed in compliance with the
following specifications. See Figure 1 for location.
1. MATERIALS
A. General
All tanks, regardless of material or method of construction shall
be:
(1) Water tight
(2) So designed and constructed as to withstand all lateral earth
pressures under saturated soil conditions with the tank empty.
(3) So designed and constructed as to withstand a minimum of seven
feet of saturated earth cover above the tank top.
In addition, the following specif: ions apply to specific mater-
ials as indicated.
S. Precast Concrete Tanks
(1) Precast concrete tanks shall be constructed of at least a
40000 psi (pounds per square inch) core test, air entrained
concrete mix.
(2) Precast concrete tanks shall be cured to at least a seven-day
strength before installation.
C. Fiberglass and plastic Tanks
Fiberglass and plastic tanks shall be designed and constructed to
meet the requirements in Section I - a. above.
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(a) 'rhe jui;if or joints shill ►x- ►wrmant•ntly sealed so as to
be watertic►ht..
• (4) Bottoms
(a) Any tank not having an integrally cast bottom shall not be
installed when the water table is closer than three inches
to the bottom of the excavation.
(b) If the bottom is poured -in -place concrete, it shall be
at least four inches thick and extend to at least four
inches outside the tank wall. A concrete mix of at
least one part cement, two parts washed sand and three
parts washed rock shall be mixed before placement in
the excavation.
(c)
If a starter ring is used, it shall be constructed of a
4,000 psi core test concrete mix, cured to a seven-day
strength before installation. It shall extend at least
one inch beyond the tank wall, inside and out. A bottom
shall be poured of concrete mix defined in Section (b)
above. It shall extend at least two inches above the
starter ring and shall be at least four inches thick.
(d)
If a precast bottom is used, it shall be made of a 4,000
psi core test concrete mix, cured to a seven-day strength
before installation. It shall xtend at least one inch
beyond the tank wall, or be ca integrally with the
bottom section.
(e)
A sectional tank not having an integrally precast bottom
shall have a four -inch thick bottom poured within the
tank walls.
(5)
Covers
•
(a) Any tank cover not integrally cast with the tank shall be
so installed that the joint with the tank sidewall is
permanently sealed so as to be watertight.
(b) All covers shall be so designed and constructed as to
withstand a minimum of seven feet of saturated earth cover
above the tank top.
•
F. Inlet and Outlet Device Materials
(1) Inlet and outlet devices shall be sanitary tees, or baffles
constructed of acid resistant concrete, acid resistant
fiberglass or plastic.
-3-
(2) Sanitary tees shall be ylucd to the inlet or outlet. pipes.
Baffles shall be integrally cast with the tank, affixed with
• a permanent waterproof adhesive or affixed with stanless
steel connectors, top and bottom.
2. DESIGN
All tanks, regardless of material or method of construction, shall
conform to the follov-ng design criteria:
A. The LIQUID DEPTH of any septic tank of compartment thereof
shall be not less than 30 inches. A liquid depth greater
than six and one-half feet shall not be considered in de-
terinining tank capacity.
B. No tank or compartment thereof shall have an inside horizontal
dimension less than 24 inches.
C. Inlet and outlet connections of the tank thereof shall be sub-
merged by means of vented, sanitary tees or baffled.
D. The space in the tank between the liquid surface and the top
of the inlet and outlet baffles or sanitary tees shall be not
less than 20 percent of the total required liquid capacity,
except that in horizontal cylindrical tanks this space shall
be not less than 15 percent of the total required liquid
capacity.
• E. The inlet baffle or sanitary tee shall extend at least six
inches but not more than 20 percent of the total liquid depth
below the liquid surface and at least one inch above the crown
of the inlet sewer.
:7
F. The outlet baffle or sanitary tee and the baffles or sanitary
tees between compartments shall extend below the liquid surface
a distance equal to 40 percent of the liquid depth except that
the penetration of the indicated baffles or,sanitary tees for
horizontal cylindrical tanks shall be 35 percent of the total
liquid depth. They also shall extend above the liquid surface
as required in D. above. In no case shall they extend less
than six inches above the liquid surface.
G. There shall be at least one inch between the underside of the
top of the tank and the highest point of the inlet and outlet
devices. •
H. The inlet invert shall be not less than three inches above the
outlet invert.
-4-
• D. Metal Tom. ,ks
Metal tanks shall have a wall thickness of at least eight gauge
corrosion resistant alloys and shall be coated inside and out
with at least one coat of bitumastic seal, Koppers 300-M, or by
other equivalent means. Tanks shall be carefully installed so as
not to puncture or damage the seal coating.
E. Block or Sectional Tanks
(1) Rectangular Blocks
V
(a) Rectangu-ar blocks shall be laid on an approved bottom.
Block shall be at least eight inches thick, constructed
of a 4,000 psi core test concrete mix, and cured to a
28-day strength before installation.
(b) Rectangular blocks shall be laid either with mortar
join:z or filled cores.
' (c) There ahall be at least two coats of 1/4 inch thick
concrete plaster placed on the inside of the block tank.
There shall be at least two hours elapsed time between
coats. The plaster coat shall start at the bottom course
and work up.
(2) Circular Block Tanks
(a) Circular blocks shall be carefully placed on an approved
bottom. Circular blocks shall be at least two inches
thick and constructed of a 4,000 psi core test concrete
mix, cured to a 28-day strength before installation.
(b) There shall be at least two coats of 1/4 inch thick
concrete plaster placed on the Inside of the block tank.
There shall be at IL-ast two hours elapsed time between
coats. The plaster coat shall start at the bottom course
and work up.
(3) Sectional Tanks
(a) A sectional tank shall have an entire section cast as an
integral unit.
(b) A sectional tank shall have two or more sections and shall
have at least one joint below the level of the outlet in-
vert of the tank.
(c) Sectional tanks shall have an integLally cast bottom, or
shall be laid on an approved bottom.
:7
-2-
I. The inlet and outlet shall be located opposite each other along
• the axis of maximum dimension. The horizontal distance between
the nearest points of the inlet and outlet devices shall be at
least four feet.
•
J. Sanitary tees shall be at least four inches in diameter. Inlet
baffles shall be no less than six inches or no more than 12
inches measured from the end of the inlet pipe to the nearest
point on the baffle. Outlet baffles shall be six inches meas-
ured from beginning of the outlet pipe to the nearest point on
the baffle.
K. Aceess to the septic tank shall be as follows:
(1) There shall be one or more manholes, at least 20 inches least
dimension, and located within six feet of all walls of the
tank. The manhole shall extend through the cover to a point
within 12 inches but no closer than six inches below finished
grade. The manhole cover shall be covered with at least six
inches of earth.
(2) There shall be an inspection pipe of at least four inches
diameter or a manhole over both the inlet and outlet devices.
The inspection pipe shall extend through the cover and be
capped flush or above finished grade. A downward projection
of the center line of the inspection pipe shall be directly
in line with the center line of the inlet or outlet device.
L. Multiple tanks
(1) Where more than one tank is used to obtain the required liquid
volume, the tanks shall be connected in series.
(2) Each tank shall comply with all other provisions of Section J.A.
(3) No more than four tanks in series can be used to obtain the
required liquid volume.
MAINTENANCE SUGGESTIONS
Inspect the tank annually and have the tank cleaned when the scum is
3 inches or less above tie outlet baffle and/or when the sludge level
is 8 inches or less below the outlet baffle.
3 LOCATION
A. The sewage tank shall be placed so that access is convenient
for the removal of liquids and accumulated solids.
B. The sewage tank shall be placed on firm and settled soil
capable of bearing the weight of the tank and its contents.
-5-
C. Sewage tanks shall be set
back the following distances from
•
the features given below:
Feature
Minimum Setback Distances (feet)
Water Supply Well and Buried
50
Water Suction Pipe
'
Buried Pipe Distributing
10
Water Under Pressure
.Feature
Minimum Setback Distances (feet
Buildings
10
Property Lines
10
The ordinary High Water Mark of:
Natural Environment Lakes
150*
and Rivers
Recreational Development
75*
Lakes and Rivers
General Development
50*
•
Lakes and Streams
Wild River
150*
Scenic River
100*
Designated Tributaries
75*
Wild, Scenic, and Recreational
75*
Rivers
•
*Required for new developments and where practicable, for existing
developments.
4. SURFACE FLOODING
Sewage tanks shall not be placed in flood plains delineated by local
ordinances adopted in compliance with the Statewide Standards for
Mana ement of Flood Plain Areas of Minnesota Minn. Reg. NR85-93 ,
or in areas for which regional flood information is available from
the Department of Natural Resources, except that in areas where ten
year flood information is available from and/or approved by the
Department of Natural Resources.
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• II. PUMPING
•
A 600-gallon capacity tank, placed in series with the sewage tank,
shall be manufactured and installed in compliance with the
following specifications. See Figure 1 for location.
1. PUMPING CHAMBER
A. The pumping chamber shall be watertight and constructed of
sound and durable materials not subject to excessive corro-
sion or decay.
w
B. There shall be one or more manholes, at least 20 inches
least dimension and preferably located directly above the
dosing device. The manhole shall extend through the dosing
chamber cover to final grade and shall be so constructed
as to prevent unauthorized entry.
2. PUMPS FOR PRESSURE DISTRIBUTION
A. A pump shall deliver the dose to the soil treatment area.
B. The prmp discharge capacity shall be at least 450 gallons
per hour for each 100 square feet of rock bed area but no
more than 2700 GPH.
C. The pump shall be cast iron or bronze fitted and with stain-
less steel screws or constructed of other sound, durable and
corrosion -resistant materials.
D. The quantity of effluent delivered for each pump axle shall
be no more than 25 percent of one day's sewage flow. Use
150 gallons/bed?•oom to estimate daily flow.
E. The pump discharge head shall be able to overcome the pipe
friction los3 and the elevation difference between the pump
and the distribution system.
F. An alarm device shall be installed to warn of pump failure.
For dwellings, there should be reserve storage volume equal
to one day's sewage flow based on 150 gallons per bedroom.
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III. DISTRIBUTION OF EFFLUENT
• 1. BY GRAVITY FLOW OVER THE SOIL TREATMENT AREA
A. Level Ground
Where the elevation difference of the ground surface does not
exceed 28 inches in any direction within the soil treatment area,
the sewage tank effluent may be directed to the soil treatment
area through a distribution box. (See Figure 2).
(1) The box shall be watertight with a removable cover and
shall be constructed of durable materials not subject to
excessive corrosion or decay. The minimum inside dimen-
sion shall be at least ten inches.
(2) The inverts of all outlets shall be at the same elevation
as measured from a liquid surface in the bottom of the box.
(3) The inlet invert shall be at least one inch above the outlet
inverts.
(4) The outlet inverts shall be at least four inches above the
distribution box floor.
(5) Each drainfield trench line shall be connected separately
to the distribution box and shall not be subdivided.
. When sewage tank effluent is delivered to the distribution
box by pump, either a baffle wall shall be installed in the
distribution box or the pump discharge shall be directed
against a wall or side of the box on which there is no
outlet. The baffle shall be secured to the box and shall
extend at least one inch above the crown of the inlet
flow line.
E
B. Sloping Ground
Where the elevation difference of the ground surface exceeds
28 inches in any direction within soil treatment area a drop box
shall be installed at the head end of each lateral line.
Connections between drop boxes shall be by watertight p�.pes.
(See Figure 3).
(1) The drop box shall be watertight and constructed of durable
materials not subject to excessive corrosion or decay. The
minimum inside dimension shall be at least ten inches,
unless the box is to be used as a valve box. Then each
outlet shall have at least eight inches of sidewall space
and the side of any outlet shall be at least six inches
from any corner.
_R_
• (.1 'I'hkI ii►v.'I I „1 tlie i1►let 1)il}u shc,I I he! Lit Iu,i:.1 4J110 IIlk-I►
hiyh..1 t 11,11i t hey invert. of t.he: out.10t I,il,t, to I lit' nt'xt
I. rCnch.
(;) The i►►vcrt of the out.I.et pipe to the next trench shall
be at lust two inches higher than, the invert of the
outlet pipe of the trench in which the box is located.
(4) When sewage tank effluent is delivered to the drop box by
a pump, the pump discharge shall be directed against a
„wall or side of the box on which there is no outlet.
(5) The drop box shall have a removable cover either flush
or above finished grade or covered by no more than six
inches of soil.
IV. DRAINFIELD - Final treatment and disposal of all sewage tank
effluent shall be by means of soil treatment.
1. SIZING
Indicated average percolation rate is 22.1 minutes per inch for
the primary site and 14.3 minutes per inch for the alternate
site.
• A. Total drainfield area is = 1050 ft2 (Required soil treatment
area based on a 4-bedroom house)
B. Drainfield trench bottom width is 3'.
C. TOTAL lineal feet of drain the is 350.,,
D. This requires 5 laterals of 70 feet in length.
See Figure 1 for typical placement.
E. Minimum spacing of laterals is 7.5
0
feet from center to center.
Lot 2, Mock 3
. TABLE 1
PERCOLATION RATES AND DEPTH TO THE WATER TABLE
KI
10
Depth to
Seasonal High
Water Table
Hole (Minutes/inch) (feet)
P1 35.5 --
P2. 13.1 --
P3 21.3 --
P4 18.4 --
P5 13.7 --
P6 14.9 --
SB1 -- 4.o
SB2 -- 5.0
SB3 -- 78.0
Average percolation rate of Primary Site (Holes 1,2,3,4) = 22.1 min./in.
Average percolation rate of Secondary Site (Holes 4 & 5) = 14.3 min.in.
Percolation Rate
TABLE 2
SOIL LOGS
Soil Boring #1
Depth Material Depth
0-1.0' Topsoil dZrk brown 0-2.0'
1.0-2.0' Brown sandy clay loam 2.0-4.0'
2.0-6.0' Tan sandy clay loam; 4.0-6.0'
mottling at 4.0'
6.0-8.0' Brown silty sand; 6.0-8.o,
saturated
Material
Topsoil brown
Tan silty clay loam
with same sand
Brown silty clay
loam; mottling at 5.0'
Brown silty sand
L__
TABLE 2 (continued)
• SOIL LOGS
Soil Boring #3
Depth Material
0-1.0' Topsoil dark brown
1.0-2.0' Brown sandy clay
2.0-3.0' Tan sandy clay, loose
3.0-6.5' Brown silty clay, with
• some sand, loose
6.5-8.0' Brown silty sand, loose;
no mottling
•
•
•
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