U.S. patent number 3,919,848 [Application Number 05/471,325] was granted by the patent office on 1975-11-18 for full flow leaching pit.
Invention is credited to A. Eugene Sullivan.
United States Patent |
3,919,848 |
Sullivan |
November 18, 1975 |
Full flow leaching pit
Abstract
The infiltrative capacity and fluid storage capacity of leaching
trenches, beds, and pits (collectively called leaching "fields"
herein) are increased by means of fluid accumulators placed within
the field and spaced from the side and bottom walls thereof by
infill (crushed stone, gravel stone, etc.). Effluent discharged to
the field accumulates in the infill until it exceeds a
predetermined level with respect to the accumulators and then
proceeds to fill the accumulators. When the effluent level in the
infill later subsides, effluent is discharged from the accumulators
into the infill for drainage into the soil.
Inventors: |
Sullivan; A. Eugene (Medford,
MA) |
Family
ID: |
23871181 |
Appl.
No.: |
05/471,325 |
Filed: |
May 20, 1974 |
Current U.S.
Class: |
405/43;
210/170.08 |
Current CPC
Class: |
E03F
1/002 (20130101); Y02A 20/40 (20180101); Y02A
10/30 (20180101) |
Current International
Class: |
E03F
1/00 (20060101); E02B 011/00 () |
Field of
Search: |
;61/10,11,12,13
;210/17,117,118,148,263,170,153,143 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Taylor; Dennis L.
Attorney, Agent or Firm: Cesari and McKenna
Claims
Having illustrated and described the preferred embodiments of my
invention, I claim:
1. A structure for placement in a leaching field to which effluent
is applied for disposal, said structure comprising an effluent
accumulator in the form of a cistern for temporarily storing excess
effluent therein and having means forming a fluid transfer channel
therein communicating directly with the field surrounding said
accumulator and positioned to admit effluent to said accumulator
from said field when the level of effluent in said field is above a
given level and to discharge effluent therefrom when the level of
effluent in said field is below a given level.
2. A structure according to claim 1 in which said means
comprises
A. at least one generally unrestricted fluid inlet channel
communicating between the exterior and interior of said
accumulators at an upper portion thereof, and
B. at least one fluid outlet channel communicating between the
interior and exterior of said accumulator at a lower end thereof
and restricting the inflow of effluent therethrough.
3. A structure according to claim 2 in which said fluid outlet
channel includes a valve operable to facilitate effluent outflow
but restrict effluent inflow.
4. A structure according to claim 3 in which said valve comprises a
flapper valve responsive to the difference in effective hydrostatic
head between the interior and exterior of said accumulator to
regulate the flow of effluent through the outlet channel.
5. A structure according to claim 1 in which said means
comprises
A. at least one generally unrestricted fluid inlet channel
communicating between the interior and exterior of said accumulator
at an upper portion thereof, and
B. at least one fluid outlet channel communicating between the
interior and exterior of said accumulator at a lower portion
thereof and substantially restricted in cross section with respect
to the cross section of the fluid inlet channel to thereby restrict
the effluent flow rate therethrough
6. A structure according to claim 1 in which said means comprises a
fluid channel forming a siphon communicating between the interior
and exterior of said accumulator.
7. A structure according to claim 6 in which said siphon is formed
from first and second vertically extending fluid channels connected
to each other at upper portions thereof and terminating on the
interior and exterior, respectively, of said accumulator at lower
portions thereof.
8. A structure according to claim 1 in which said accumulator
comprises a cistern of generally rectangular cross-section and
extended length.
9. A structure according to claim 1 in which said accumulator
includes fluid distribution channels formed in an upper portion
thereof and extending along the length of said accumulator for
carrying effluent from an effluent source and distributing it about
the exterior of said accumulator.
10. A structure according to claim 9 in which said channels each
include
A. a protuberance on one end thereof, and
B. means forming a corresponding recess on the other end thereof
for receiving the protuberance of an adjacent accumulator therein,
whereby generally continuous distribution channels are formed in
accumulators aligned end to end.
11. A structure according to claim 1 in which said accumulator has
an inwardly tapering cross-section from the top to the bottom
thereof to thereby elevate the center of gravity of effluent
therein.
12. A structure according to claim 1 in which said accumulator is
constructed to provide greater effluent storage capacity at an
upper portion thereof than at a lower portion to thereby elevate
the center of gravity of effluent within said accumulator.
13. A structure according to claim 1 comprising upper and lower
accumulator sections, and in which said means comprises
A. means in said upper section for restricting effluent inflow
thereto when the effluent exterior thereof is below a given level,
freely admitting effluent to the interior thereof when the effluent
is above said level, and discharging effluent therefrom when the
exterior effluent level is below the interior effluent level,
B. means in said lower section for discharging effluent therefrom
when the exterior effluent level is below the interior effluent
level, and
C. fluid-transfer means interconnecting the upper and lower
sections for supplying effluent to the lower section from the upper
section when the effluent in the upper section exceeds a
predetermined level.
14. A structure according to claim 13 in which
A. the means in said upper section comprises
1. a relatively unrestricted fluid channel in an upper portion of
said section for admitting effluent to the interior of said
section, and
2. a fluid outlet channel communicating between the interior and
exterior of said section at a lower portion thereof and restricting
the inflow of effluent therethrough, and
B. the means in said lower section comprises a fluid outlet channel
communicating between the interior and exterior of said section at
a lower portion thereof and restricting the inflow of effluent
therethrough.
15. A structure according to claim 14 in which said both fluid
outlet channels include valves operable to restrict effluent inflow
and provide generally unobstructed effluent outflow.
16. An effluent accumulator temporarily storing therein effluent
supplied thereto from a leaching field in which said accumulator is
placed and into which said effluent is discharged for disposal, and
thereafter releasing it for discharge to said field, said
accumulator comprising a generally fluid-impermeable cistern for
placement within said field and having
A. means defining a relatively unobstructed fluid inlet channel
extending between an upper portion of the exterior of said
accumulator and the interior thereof for admitting effluent to said
accumulator from said field when the fluid level in said field is
above that within said accumulator, and
B. means defining a fluid outlet channel extending between a lower
portion of the interior of said accumulator and the exterior
thereof and constructed to restrict effluent inflow therethrough
while providing relatively unobstructed effluent outflow
therethrough when the fluid level in said field is below that
within said accumulator.
17. An accumulator according to claim 16 which
A. has bottom and side walls and a roof defining an enclosed volume
for storage of effluent therein,
B. is of generally rectangular cross section and extended length
for placement in a leaching trench.
18. An accumulator according to claim 17 including means defining a
covered manhole extending through said roof and providing access to
the interior of said accumulator.
19. An accumulator according to claim 16 which includes means in
said roof defining effluent distribution channels for receiving
effluent from a source and distributing it exterior of said
accumulator.
20. An accumulator according to claim 16 which is generally
cylindrical in shape for placement in a leaching pit.
21. An accumulator according to claim 16 which is of generally
rectangular cross section and extended length for placement with a
number of similar accumulators side by side and end to end in a
leaching bed.
22. An accumulator according to claim 16 which has at least side
walls and a roof, said side walls tapering inwardly from said
roof.
23. An accumulator according to claim 16 in which said fluid outlet
channel includes a valve responsive to the difference in
hydrostatic head between the effluent level exterior to said
accumulator and that interior thereto to discharge effluent from,
and restrict its admission to, said accumulator.
24. A leaching field for the disposal of effluent, comprising
A. at least one effluent accumulator for subsurface placement in an
excavated void forming said field for periodically storing effluent
therein and subsequently discharging it to the void exterior
thereof, said accumulator comprising a fluid-confining cistern
having flow-regulating means
1. providing a fluid channel communicating between the interior of
said accumulator and the field exterior thereto,
2. admitting effluent inflow thereto when the effluent exterior
thereof is above a given level,
3. discharging effluent therefrom when the exterior effluent level
drops below the interior effluent level, and
B. means for carrying effluent to the void exterior to said
accumulator for disposal therein.
25. A leaching field according to claim 24 in which said flow
regulating means includes
A. means defining an inlet channel extending between the exterior
of the accumulator at an upper portion thereof and the interior of
the accumulator and supplying effluent to the interior thereof when
the exterior effluent level is at or above the level of said
channel at the exterior of said accumulator,
B. means defining an outlet channel extending between the interior
of said accumulator at a lower portion thereof and the exterior of
said accumulator and operable to discharge effluent from the
accumulator when the exterior effluent level drops below the
interior effluent level.
26. A leaching field according to claim 25 which includes a valve
responsive to the difference in hydrostatic head between the
interior and exterior of said accumulator and positioned within
said outlet channel to control effluent flow therethrough.
27. A leaching field according to claim 26 in which said
accumulator has a generally rectangular cross section for placement
in a leaching trench or bed.
28. A leaching field according to claim 26 in which said
accumulator has a generally cylindrical cross-section for forming a
leaching pit.
29. A leaching field according to claim 26 in which said
accumulator has side walls tapering inwardly from an upper portion
thereof to therby store effluent at a higher gravitational
potential than in a non-tapered accumulator.
30. A leaching field according to claim 24 in which the means for
carrying effluent to said void comprises at least one distributor
channel
1. formed integral with said accumulator and extending along the
length thereof,
2. adapted to transport effluent therein,
3. in communication with said void over at least one segment
intermediate said ends for supplying effluent to said void.
31. A leaching field according to claim 24 in which said
accumulator has
A. upper and lower fluid-storage sections,
B. an overflow conduit connecting the upper and lower sections and
having an upper end thereof terminating in an upper portion of said
upper section for passing effluent to said lower section when the
effluent in said upper section exceeds a given level.
32. A leaching field according to claim 31 in which said flow
regulating means comprises
1. a first fluid channel in said upper section communicating
between an exterior upper portion of said accumulator and the
interior thereof for admitting effluent to said upper section when
the effluent level exterior to said accumulator is above said given
level, and
2. second and third fluid channels, in said upper and lower
sections, respectively, communicating between an interior lower
portion of the corresponding section and the exterior thereof and
each having a valve therein responsive to differences in
hydrostatic "head" between the interior and exterior of the
corresponding section for discharging effluent from the
corresponding section when the effluent level exterior to said
section drops below the effluent level interior thereto.
Description
BACKGROUND OF THE INVENTION
A. Field of the Invention
The invention relates to leaching fields and, more particularly,
comprises an improved form of leaching field, as well as structures
for use therein.
B. Prior Art
Leaching fields in the form of trenches, pits or beds are in common
use to discharge the effluent from a septic tank or waste water
treatment facility into the soil for filtration and subsequent
run-off into undergound fluid channels. typically, these fields are
formed from an appropriately shaped void which is subsequently
filled in with various layers of crushed stone, gravel stone or
rock (hereinafter callectively called "stone"). The stone provides
a porous infill and separates the soil surfaces of the void from
direct contact with an effluent discharge element such as a porous
pipe which receives effluent from a septic tank, dosing tank, or
other source and discharges it into the infill for subsequent
infiltration into the earth.
In the case of leaching pits, the discharge element is a porous
tank; in the case of leaching trenches, or beds the discharge
elements are one or more porous pipes placed within the infill and
running along the length of the trenches or beds. A typical trench
is 30 inches wide, 36 inches deep and 75 feet long and filled with
stone; a wider trech, commonly called a "gallery", is of the order
of 6 feet wide and 6 feet deep and is also filled with stone. A
typical pit may be up to 10 feet in diameter and 6 feet deep and
uses "construction" block to form a porous, generally cylindrical
wall through which effluent flows into the soil.
The leaching or infiltrative capacity of pits and trenches depends
on the infiltrative capacity of both the side and bottom walls of
the pit or trench. As the pits and trenches age, however, the
bottom wall or face becomes less and less porous and the side walls
or faces assume increasing importance. This is especially the case
in a leaching pit. However, in present pits and trenches, this side
wall capacity is greatly under-utilized, since the effluent
infiltrates these sidewalls only when enough of it has been
discharged into the void ("loading") to raise the effluent level
within the void to a height sufficient to cover the sidewalls. In
contrast, the bottom face of the pit or trench, as well as the
lower side wall surfaces, are wetted during each loading and
therefore perform a major share of the leaching or filtering during
the early stages of their existance. This hastens the failure of
these surfaces, since they thereby accumulate an excessive amount
of particulate material from the effluent. The deterioration
process is regenerative, that is, as the infiltrative capacity of
the bottom and lower portion of the side wall surfaces
deteriorates, effluent discharged into the void covers these
surfaces for increasingly longer periods of time before adsorption.
The flooded surfaces are thus maintained under anaerobic conditions
which greatly retard the decomposition of the organic constituants
of the effluent and facilitate the growth of slimes which
accumulate on these surfaces and ultimately block them.
This problem may be alleviated to a certain extent by making the
trenches and pits narrower and deeper to thereby obtain a
substantially larger ratio of side wall surface to bottom wall
surface for a given volume. However, in order to accomodate the
same loading as the wider trenches or pits, it is necessary to
construct a larger number of them and this increases the cost of
the disposal system. Also, this requires additional pipelines and
somewhat more complicated fittings such as distribution boxes, and
this further adds to the cost. Further, there are practical lower
limits to the trench or pit widths which can be dug with equipment
current in use, as well as limits on the number of trenches or pits
which can be dug in the generally limited disposal area.
Leaching beds, in contrast, are characteristically shallow voids of
broad lateral and longitudinal extent. Typically, such a bed is of
the order of 18 inches in depth and may be 50 feet or more in width
and length. Formerly the voids were filled in with stone, but this
has been superseded by the use of precast chambers having generally
open side and end walls butted together side by side and end to end
to cover the bottom (infiltrative) surface of the bed. This exposes
the entire infiltrative surface to the effluent within the
chambers. However, unless the bed is loaded with a very high
loading, infiltration of the effluent frequently tends to occur
predominantly in the vicinity of the effluent discharge source and
thus the field is not loaded uniformly.
SUMMARY OF THE INVENTION
A. objects of the Invention
Accordingly, it is an object of the invention to provide an
improved leaching system.
Further, it is an object of the invention to provide an improved
leaching trench, bed or pit.
Yet a further object of the invention is to provide an effluent
accumulator for leaching trenches, beds, and pits.
Still a further object of the invention is to provide an effluent
accumulator for a leaching field to temporarily store effluent
during periods of high loading and release it during periods of
decreased loading.
Another object of the invention is to provide an effluent
accumulator whose operation is self-adjusted to the infiltrative
capacity of the leaching void in which it is placed.
Still another object of the invention is to provide a leaching
field system which more effectively distributes effluent over
vertical soil interfaces.
B. brief Description of the Invention
In accordance with the present invention, I more effectively
utilize the side wall infiltrative capacity of leaching trenches
and pits, and provide a more uniform loading of leaching beds, by
constructing the trenches, beds or pits (hereinafter simply called
"fields") with the aid of a number of hollow "accumulators" placed
within the fields to store effluent during periods of high
loadings, and subsequently release it during periods of lesser
loadings. These accumulators are in the form of covered cisterns
preferably having bottom, side and top walls. They are placed
directly in the leaching voids and are spaced apart from the side
walls of the void, and typically from the bottom walls also, by
means of a narrow layer of infill having a correspondingly small
fluid holding capacity.
The accumulators occupy a substantial portion of the excavated
volume of the field, so that the available free volume of the
excavated void exterior to the accumulator is quickly filled by a
much smaller effluent loading than is the case without them. When
so filled, the side walls are completely "wetted" and the effluent
infiltrates, or permeates, through them and through the bottom
faces of the excavated void at loadings that previously would have
been adequate for wetting the bottom face alone. Further, each
accumulator, being hollow, has an effluent storage capacity
substantially greater than that of the infill it displaces. When a
loading in excess of the storage volume of the exterior void is
applied to the field, the excess is temporarily stored in the
accumulators and then released to the void as the effluent level
diminishes. Thus, not only is the excess loading accomodated, but
the effluent within the exterior void is replenished from the
accumulators as it recedes; this tends to maintain the wetting of
the side walls for a longer time.
In a preferred embodiment of the invention, each accumulator has at
least one fluid inlet channel extending through an upper side wall
or top wall, together with at least one fluid outlet channel at a
lower level in a side or bottom wall of the accumulator. The fluid
outflow channel is constructed to either partially or fully
restrict fluid in flow to the accumulator when the effluent level
in the void exterior to the accumulator is rising and to allow free
outflow when this level again recedes. Full restriction is
accomplished by means of a one-way valve positioned to open
outwardly of the accumulator and responsive to a difference in
hydrostatic "head" between the effluent exterior and interior to
the accumulators to close and prevent fluid inflow when the
exterior effluent level is higher than the effective interior level
and to open and allow fluid outflow when the reverse condition
prevails. The valve is effectively a static type of restriction.
Partial restriction is accomplished by restricting the cross
section of the outlet channel to thereby restrict the flow rate
through it; its effectiveness depends on filling the void exterior
to the accumulator at a rate much faster than the rate at which any
significant amount of effluent can flow into the accumulator
through the orifice. This is essentially a dynamic type of
restriction.
In accumulators using valves, as long as the fluid level in the
void exterior to the accumulator is below that of the accumulator
fluid inlet channel, no effluent passes into the accumulator.
However, when the outside effluent level reaches the level of the
fluid inlet channel, it begins to spill into the accumulator where
it is temporarily stored. The outlet channel valve is held closed
during this time, preferably by means of the difference in
hydrostatic "head" between the exterior and interior of the
accumulator. When the outside effluent level again recedes and
drops to a level below that of the stored effluent in the
accumulator, the valve in the outlet channel opens and effluent
flows out from the accumulator through this channel and into the
infill within the void. The outflow continues until the accumulator
is emptied or until the next loading of sufficient volume to bring
the outside level above the accumulator level. Thus, with each
loading, the sidewalls of the field are wetted to a substantially
greater height than is the case in present systems. Further, this
is accompanied by a substantial increase in the storage capacity of
the field.
In accumulators using an outlet channel of restricted size, during
dynamic conditions in which the effluent level exterior to the
accumulator is rapidly changing, little effluent flows into the
accumulator until the exterior level rises to the level of the
inlet channel. The accumulator then fills with the excess effluent.
When the loading ceases, quasi-static conditions are approached
during which the effluent exterior to the accumulator begins
leaching into the earthen surface, typically at a much slower rate
than that at which it was applied to the exterior void.
Concurrently, a slow equalizing fluid flow occurs through the
outlet orifice, this flow being into the accumulator as long as the
exterior fluid level is above the interior fluid level ("positive
head") and out of the accumulator as long as the exterior level is
below the interior level ("negative head").
In another form of accumulator, a siphon takes the place of the
inlet and outlet channels. This siphon is preferably formed within
the walls of the accumulator, and has a first vertically extending
leg terminating within the accumulator at its bottom end and
horizontally bridged at its upper end to a second vertically
extending leg terminating exterior to the accumulator at its lower
end. A trap (which may be formed by a U-shaped bend in the lower
end of the exterior leg of the siphon) prevents blockage by air
bubbles forming in the bridge. As the effluent in the void exterior
to the accumulator rises, the effluent level within the exterior
(second) siphon leg raises correspondingly until it reaches the
level of the horizontal bridge and then starts to flow downwardly
into the accumulator through the interior (first) leg. Thereafter,
the accumulator receives and stores the remainder of the effluent
loading. When the exterior level recedes to a level below that
within the accumulator, reverse flow takes place and the
accumulator discharges its contents into the exterior void, the
interior level following the exterior level downwardly as it does
so. The operation is thus similar, though not identical, to that of
the valved or restricted orifice accumulators, and, again, the side
wall surfaces of the void are wetted over a substantially longer
period than would normally be the case.
The accumulators may be supplied in any desired size or shape.
Advantageously, however, they comprise shallow, elongated, cisterns
of generally rectangular or even somewhat V-shaped cross section in
the case of leaching trenches and beds, and somewhat deep cisterns
of cylindrical rectangular or even V-shaped cross sections in the
case of leaching pits. Preferably, they are of precast concrete or
other durable material, and may be formed in two or more sections
(i.e., roof and side and bottom surfaces) to facilitate
manufacture; a covered manhole extending through the roof
facilitates inspection and maintenance. However, many variations
are possible; for example it is possible to omit the bottom wall
and rest the side walls directly on or in the soil, relying on the
limited bottom soil porosity to contain the excess effluent for a
time period.
Two or more accumulators may be vertically stacked to further
increase the wetting of the upper side wall areas. In this
configuration, the accumulators are each of much less vertical
extent then the excavated void in which they are placed and are
interconnected so that effluent is supplied to a lower accumulator
only after the preceding upper accumulator is filled. For this
purpose, each is supplied with an outlet channel, but only the
uppermost accumulator has an inlet channel. Thus excess effluent is
stored at the highest level first, as opposed to filling the
accumulator from the bottom up as in the case of a single, deeper
accumulator. As the effluent recedes, the accumulators empty in
sequence, the uppermost first. The stacked accumulators have the
effect of reducing the effective exterior hydrostatic "head" which
the upper accumulators see, and these thus discharge their contents
at a higher level on the side wall, thus further facilitating upper
side wall wetting.
Fields using the accumulators are most advantageously loaded with
the aid of dosing tanks. These provide a measured loading which can
be adjusted to load the exterior voids to a predetermined height,
e.g. to the level of the fluid inlet channels of the accumulators
within the field. Under "normal" loading conditions, the field is
preferably designed and proportioned so that the loading in a given
part of the field substantially completely permeates into the field
surfaces prior to a further loading. During periods of higher than
normal use, the accumulators then perform their temporary storage
function.
DETAILED DESCRIPTION OF THE INVENTION
The foregoing and other and further objects and features of the
invention will be more readily understood on reference to the
following detailed description of the invention when taken in
conjunction with the accompanying drawings in which:
FIG. 1 is a pictorial illustration of a trench-type leaching field
constructed in accordance with the present invention;
FIG. 2 is a cross sectional view taken along the lines 2--2 of FIG.
1;
FIG. 3 is a view in perspective of the accumulator of FIGS. 1 and
2, with portions broken away for clarity;
FIG. 4 is a side sectional view of a simple form of valve that may
be used in the present invention;
FIG. 5 is an enlarged, fragmented vertical sectional view along the
lines 5--5 of FIG. 2 and illustrating a preferred form of valve
construction in accordance with the present invention;
FIG. 6 is a view in perspective of the valve of FIG. 5;
FIG. 7 is a view in perspective of an accumulator for use in wide,
deep trenches known as "galleries;"
FIG. 8 is a pictorial view of a pit type of leaching field
constructed in accordance with the present invention, with portions
of one of the accumulators used therein broken away for
clarity;
FIG. 9 is a vertical sectional view along the lines 9--9 of FIG.
8;
FIG. 10 is a view in perspective of a leaching bed constructed in
accordance with the present invention;
FIG. 11 is a vertical sectional view along the lines 11--11 of FIG.
10;
FIG. 12 is a vertical sectional view of an accumulator having a
restricted orifice instead of a valved outlet channel;
FIG. 13 is a vertical sectional view of an accumulator having a
siphon instead of inlet and outlet channels;
FIGS. 14 - 16 are vertical sectional views of still other forms of
accumulator in accordance with the present invention.
In FIG. 1, a septic tank or waste water treatment facility receives
effluent from a house or other facility (not shown) and applies it
to a dosing tank 10 for carriage to a distribution box 12 and
thence through pipes 14, 16, 18 and 20 to a series of trenches 22,
24, 26 and 28 for disposal there by infiltration into the earth. A
typical trench is shown in cross section in FIG. 2. The trench 22
comprises an excavated void having one or more generally
rectangular cisterns or accumulators 30 centrally disposed therein
and surrounded by crushed rock or gravel 32. A layer of filter sand
34 may be positioned at the bottom of the trench. Pipe 14 carries
the effluent from the distribution box 12 into the trench 22 and
distributes it along the length thereof through openings such as
aperture 14a and 14b in that portion of the pipe within the
trenches. Pipe of this nature is commonly used in subsurface sewage
disposal systems and is frequently of a type known as "Orangeburg"
pipe or is of vitrified clay having perforations along its extent.
This pipe is positioned within the in-fill of crushed rock exterior
to the accumulator, and the trench is then covered to grade with a
layer of selected backfill 36.
Alternatively, the effluent may be carried along the trench by
means of built in fluid channels 38 forming troughs which carry the
effluent and having projections 38a and indentations 38b which mate
with each other when aligned to carry effluent down a row of
accumulators. When these channels are provided the effluent is
applied directly to them from the distribution box 12.
The accumulator 30, which is shown more clearly in FIG. 3, has a
bottom wall 42, side walls 44, and the top wall of roof 46. Fluid
inlet channels 48 are formed in the side walls of the accumulator
adjacent the top thereof; corrspondingly, fluid outlet channels 50
are formed in the side walls of the accumulator at the bottom
thereof. These channels comprise apertures extending through the
walls of the accumulator to allow liquid flow therethrough. The
fluid inlet channels are open, that is, unobstructed to fluid flow;
however, as shown more clearly in FIG. 4 through 6, the fluid
outlet channels include valves in them which prevent the inflow of
liquid but which, when opened, allow the outflow of liquid. A
manhole 51 having a cover 53 provides access to the interior of the
accumulator.
A simple form of such a valve is shown in FIG. 4 and comprises a
thin cylindrical flapper plate 52 having a projecting tab 54 on a
portion of its periphery which snugly fits into a slot 56 (shown
exaggerated in size for clarity) in the wall of the fluid outlet
channel 50. The tab and flapper plate are advantageously formed
integral with each other and from a tough, flexible, resilient
material such as a polypropylene. The channel 50 is in the form of
a stepped outwardly-flaring cone having an intermediate lip 58
against the face of which the outer periphery of the back face of
the flapper 52 abuts. When the force exerted by the fluid on the
exterior of the accumulator (the exterior being on the right in
FIG. 4) is greater than that exerted by the fluid within the
accumulator (the interior of the accumulator being on the left in
FIG. 4), the rear peripheral face of the flap 52 abuts tightly
against the face of lip 58 to thereby form a fluid-tight seal which
prevents fluid from escaping from the interior of the accumulator.
When the force exerted by the fluid on the exterior is less than
that exerted by the fluid on the interior due to the different
"heads" or effluent levels, the flapper plate 52 pivots about the
tab 56 to thereby open and discharge stored effluent from the
accumulator. A screen 60 closes off the outer section of channel 50
from the infiltration of stone and other large materials which
would prevent opening of the valve but otherwise allows relatively
unimpeded fluid flow through it.
As effluent is discharged into the trench 22 through pipe 14, it
fills the bottom of the trench and then starts rising so as to
"wet" the side walls. When the effluent level of the trench reaches
the level of the fluid inlet channel 48, it ceases rising in the
trench and instead begins to fill the accumulator 30. This prevents
surface "breakthrough" caused by excessive loading. For this
purpose, the fluid-storage capacity of accumulator 30, together
with that of the trench 22 up to the level of the inlet channels
48, should be sufficient to accomodate the normal loading applied
to the stone 32. This will insure that effluent "breakthrough" at
the surface does not occur. Indeed, because the infiltrative
capacity of all leaching surfaces decreases with time, it may be
desirable to have the accumulative capacity of the accumulator 30
somewhat larger than the design value calculated from the initial
maximum anticipated loading, so as to allow for the retention of
effluent from one loading to another within the void exterior to
the accumulator which occurs as the infiltration surfaces age.
As long as the effluent level exterior to the accumulator is
greater than the effluent level within the accumulator, the outlet
valve in the fluid outlet channel 50 remains closed and effluent
does not flow out from the accumulators. When, however, the
exterior effluent level drops below that within the accumulator,
effluent flows outwardly from the accumulator and discharges into
the crushed stone surrounding the accumulator. Thus, the valve
responds to the difference in height between the levels within and
outside the accumulator and the accumulator acts as a controlled
effluent-dosing device, storing effluent when the level in the
trench exceeds a certain height and discharging it when the
effluent level again drops below the interior level. In this
respect, the accumulators are condition-responsive to their
environment. The infiltration capacity of various trenches will
change as a function of time, and this change may be a somewhat
different function for each of the trenches. Regardless of this
change, however, the accumulators always sense the effluent level
within the trenches in which they are placed and respond by first
storing and subsequently releasing effluent to maintain a
substantial side wall setting over a longer interval than would be
the case without them.
A preferred from of valve is shown in FIGS. 5 and 6 and comprises a
generally cylindrical glange 60 having a flapper plate 62 attached
thereto by means of a pivot 64. A generally circular groove 66 in
the face of the plate 62 seats an O-ring 68 which butts against a
flat face 70 of the flange 60. The plate 62, when seated against
face 70 of flange 60, closes off a generally cylindrical fluid
channel 72 extending through the flange and prevents fluid flow
therethrough. A finger 74 from the rear face of the flapper plate
62 and limits movement of the flapper plate when it pivots (in a
clockwise direction) about pivot 64.
The valve 60 is attached to the channel 50 on the interior side
thereof by means of threaded bolts 76 extending through apertures
77. The remote ends of the bolts are seated in the wall of the
accumulator by means of a hardenable sealing compound 78 or are set
in during molding. A collar 80 butts against the interior wall of
the accumulator and may be embedded therein; it provides a
generally flat surface against which a washer 82 rests. One face of
the flange 62a is pressed tightly against the washer 82 by means of
the bolts 76 and nuts 84 threaded on these bolts.
As presently contemplated, the accumulator of the type shown in
FIG. 3 is advantageously formed of concrete and has exterior
dimensions of 8 feet long, 24 inches wide, and 30 inches high
interior dimensions of approximately 18 inches by 18 inches
(thereby providing side and bottom walls 3 inches thick and a top
face 9 inches thick), and fluid outlet channels located
approximately 15 inches above the interior bottom face. The
accumulator is located in a leaching trench approximately 36 inches
wide and 45 inches high. It is laterally centered in the trench so
that its outside walls are approximately 6 inches from the adjacent
side walls of the trench. It is vertically spaced approximately 6
inches above the bottom space of the trench. The void within the
trench exterior to the accumulator is filled with crushed stone to
the level of the top of the accumulator or or even somewhat above
this level, and the trench is back-filled with selected backfill to
grade. A manhole approximately 12 inches in inside diameter extends
between the interior of the accumulator and grade. Because the
stone in the void is somewhat porous (typically having a porocity
of 0.40) effluent discharged into the trench on either side of the
accumulator in sufficient volume is able to fill the trench on both
sides of the accumulator because of the porous connecting
underpassage through the stone beneath the accumulators.
With the dimensions above stated, the leaching trench of the
present invention has a total leaching area per linear foot along
the trench of 7 square feet, namely, a bottom leaching area of 3
square feet and a side wall leaching area (measured up to the
invert of the inlet channel) of an additional 4 square feet for a
total of 7 square feet. A conventional trench of the same
dimensions requires approximately 21 gallons per linear foot to wet
the bottom and side wall faces in contrast to approximately 12
gallons in the present invention. Further, the conventional
leaching trench has a total effluent storage volume per linear foot
of approximately 21 gallons, while the trench of the present
invention has a storage capacity in excess of 26 gallons. Thus, the
trench of the present invention requires smaller loadings to wet
the side wall areas for leaching but has a much greater effluent
storage capacity so that it is capable of taking loadings
substantially greater than those which can be taken by the
conventional trench.
Turning now to FIG. 7, an accumulator that is expressly adapted for
use in wider trenches or "galleries" is shown. The accumulator 100
has a bottom wal 102, side walls 104 and a top wall 106. A manhole
108 extends through the top wall in the vicinity of an outlet
channel 110; an inlet channel 112 is provided at the upper wall of
the accumulator. Effluent transfer channels 114, 116 are formed
integrally with two of the side walls at the upper ends thereof.
Channel 114 has a tapered end section 118 for receiving the end of
a preceding accumulator which carries effluent to the channel 114
and a tubular extension 120 which nests with a subsequent
accumulator to pass effluent to the channel of that accumulator. As
was previously the case, the outlet channel 110 has a one-way valve
in it to restrict fluid flow. The fluid channel 116 is constructed
in a similar manner and will not be described further. The
accumulators 100 are placed end to end, and they are spaced from
the bottom and side walls thereof by crushed stone, as was the case
with the accumulators of FIGS. 1 through 3.
Typical dimensions presently contemplated for the accumulator 100
are a width of 5 feet, a height of 41/2 feet, and a length of 5
feet. The bottom and side walls are 4 inches thick and the top roof
is 8 inches thick. The manhole 108 has an inside diameter of 2 feet
and provides access to the interior of the accumulator for
inspection and maintenance of the accumulator and outlet channel
valve.
FIGS. 8 and 9 show an alternate form of the present invention as
embodied in a leaching pit. As there shown, a distribution box 150
receives effluent via a pipe 152 from a dosing tank (not shown) and
discharges it to a number of leaching pits (illustratively shown as
three in number) 154, 156, 158 via pipes 155, 157, 159. A cross
section of the pit 156 is shown in detail in FIG. 9. The pit 156
has an accumulator in the form of a hollow cistern 160 having a
bottom wall 162, a side wall 164, and a top wall or roof 166. A
fluid transfer channel 168 in the form of a trough is formed
integral with the side wall at the upper portion thereof and has
open channels 170 through which effluent is carried to the pit 156.
Effluent is carried to the channel 168 by pipe 157. (The channel
168 may, of course, be omitted and effluent deposited in the pit
directly by pipe 157). Fluid inlet channels 172 are formed at the
upper portions of the side walls, while fluid outlet channels 174
are formed at the lower portions of the side walls; the outlet
channels have valves 175, for example, of the type shown in FIGS. 4
and 5, incorporated therein. The accumulator is spaced laterally
from the side walls 180 of the pit, as well as vertically from the
bottom face 182 of the pit, by a layer 184 of crushed rock.
As was previously the case with the leaching trenches, the effluent
rises in the gravel layer 184 until its level reaches that of the
fluid inlet channel 172, at which time it begins to spill into the
accumulator 160 for storage. When the outside effluent level (the
level in the stone 184) recedes, the valves 175 open to discharge
fluid into the stone for infiltration into the side and bottom
faces of the pit. The operation of this form of the invention is
substantially identical to that of the leaching trench described
earlier, and thus need not be described in further detail.
As a specific example of this embodiment of the invention, the
accumulator 160 may take the form of a cylindrical tank 61/2 feet
high and 8 feet in diameter. The side and bottom walls are 5 to 6
inches thick and the top wall nine inches thick, and the tank is
advantageously formed of concrete. The bottom of the fluid inlet
port is located 5 feet above the inside bottom face of this
accumulator. The accumulator is spaced from side and bottom walls
of the pit by 6 inches of stone. A conventional leaching pit 61/2
feet deep and 8 feet in diameter has the same available bottom and
side wall leaching area (approximately 230 square feet) and the
same storage capacity (approximately 1,900 gallons); however, the
conventional leaching pits requires a substantially greater loading
(1,900 gallons) to wet the side wall faces as well as the bottom
face than the leaching pit of the present invention which requires
only approximately 445 gallons to accomplish this, Thus,
substantially smaller loadings are required to wet the side wall
faces with the present invention, as contrasted to conventional
leaching pits.
The accumulators of the present invention may also be used in
leaching beds. In this application, the accumulators are placed
side by side and end to end and are spaced by layers of stone from
the side and bottom faces of the bed. An example of this is shown
in FIGS. 10 and 11 in which a number of accumulators 200a-i are
placed side by side and end to end on a stone layer within a
leaching bed. The units are similar to those shown in FIGS. 1
through 3. They may have jutting lips 202 around the upper
periphery thereof to thereby laterally space each chamber slightly
from the other chambers to thereby prevent blockage of the inlet
and outlet channels of each chamber by the adjacent chamber. The
accumulators are supplied with effluent in the usual manner from
pipes 210, 212, 214 from a distribution box or dosing tank 216
which in turn is fed from a septic tank (not shown) or other
effluent source.
The accumulators 200 function in the manner previously described,
that is, effluent is applied to the distribution channels within
the accumulators and these channels distribute the effluent to the
stone-filled void exterior to the accumulators. When the level of
effluent in this stone layer rises to the level of the inlet
channel, the accumulators begin to fill and retain the effluent
until the outside level again drops, at which time the accumulators
discharge their contents to the stone-filled void.
FIGS. 12 through 16 show still further variations of the
accumulators of the present invention. In FIG. 12, an accumulator
220, such as of the type shown in FIGS. 1 through 3, is in the form
of an elongated cistern of generally rectangular cross section
having the usual distribution channels 222, 224 at the upper
portion thereof, and fluid inlet channels 226, 228 extending
through the side walls. In place of the expected outlet channel of
FIGS. 1 through 3, however, the accumulator 220 has one or more
restricted orifices 230 adjacent to the bottom thereof and
extending through the sidewalls. The orifices 230 may
advantageously by cylindrical or even somewhat tapered in shape,
with an effective cross section of quite limited size, such as
fractions of an inch.
It will be understood that the size of the orifice depends on the
rate at which effluent is to fill the void in which the accumulator
is placed, and the rate at which the effluent level thereafter
recedes on permeating into the surrounding soil. It is dimensioned
such that only a small fraction of the effluent loading applied to
the trench can flow from the trench into the accumulator through
the orifice while the level in the exterior void is rising to the
level of the inlet channel 226, but must be large enough to allow a
reasonable outflow rate from the accumulator through this orifice
when the effluent level again drops. Thus, the precise orifice size
will be a compromise between these two variables. The accumulators
otherwise function in the manner described in connection with the
accumulators in the preceding figures, and will not be described in
further detail.
FIG. 13 is a cross section of a further embodiment of the
invention, having the shape of an elongated cistern of generally
rectangular cross section in which the inlet and outlet channels
are replaced by a siphon. The accumulator 250 has fluid
distribution channels 252, 254 in the upper portion thereof and a
siphon 256 in one of the sidewalls thereof. The siphon has a
U-shaped 256 trap 258 in a lower portion thereof to prevent
possible blockage of the siphon by trapped air bubbles.
The operation of the siphon is such that effluent rises in the
stone-filled void exterior to the accumulator 250 when it is placed
in a trench until the exterior effluent level reaches the height of
the "invert" 260 of the siphon 256. When this occurs, effluent
starts flowing into the accumulator 250. The flow thereupon
continues once initiated, so as to tend to equalize the respective
"hydrostatic" heads exterior to, and interior of, the accumulator.
As the exterior level recedes, the accumulator replenishes it until
its contents are fully discharged.
It should be noted that for loadings which are not substantially
greater than normal, this form of accumulator may actually lower
the fluid level exterior to the accumulator during loading when the
siphon action starts.
In FIG. 14, which is a vertical cross sectional view of a further
form of accumulator in accordance with the present invention, an
accumulator 300 has a bottom wall 302, side walls 304, a roof 306,
and a covered manhole 308 extending through the roof. Distribution
channels 310 are formed in the roof 306. The side walls 304 slant
inwardly toward the bottom of the accumulator so that the
horizontal cross section of the accumulator progressively decreases
going from the top to the bottom. Inlet channels 312 and an outlet
channel 314 are formed in the side walls. A one-way valve, 316 is
formed in the outlet channel 314. The accumulator is preferably
placed in a correspondingly tapered trench or pit.
As noted previously, the outlet channel valve operates on the
difference in effective hydrostatic head between the exterior of
the accumulator and the interior of the accumulator. Regardless of
the cross section of the accumulator, the interior head seen by the
valve 316 depends only on the level of the effluent within the
accumulator above this valve. However, the height of the center of
gravity of the effluent within the accumulator depends directly on
the cross-sectional shape of the accumulator. By tapering the
accumulator inwardly at the bottom portion thereof, as shown in
FIG. 14, the effective center of mass is raised to a greater height
than it is in an accumulator with a rectangular cross section such
as is shown in FIGS. 1 through 3. Thus, for a given fluid storage
capacity, the effective center of gravity is at a higher potential
energy in the accumulator of FIG. 14. This means that effluent
begins to flow outwardly from the accumulator 300 at a
correspondingly greater effluent level than is the case with an
accumulator of non-tapered cross section. The taper of the
accumulator of FIG. 14 is approximately 30 degrees. This represents
a reasonable compromise between the incremental increase in
effluent center of gravity obtained by tapering the accumulator and
the increased difficulty of forming a tapered trench or pit.
Another way in which the effective center of gravity of effluent
within an accumulator can be elevated is shown in FIG. 15 in which
first and second accumulators 350, 352 of generally rectangular
cross section are vertically stacked on one another, e.g. in an
elongated trench as 354 as shown in FIG. 15. Accumulator 350 has a
bottom wall 356, side walls 358, and a top wall 360. Inlet and
outlet channels 362, 364, respectively, are formed in the side
walls 358, and a one-way valve 366 is positioned in the outlet
channel 364. Fluid distribution channels 368 are formed in the
upper wall 360. These channels receive effluent from a source such
as a distribution box or from preceding accumulators, and
distribute it to the exterior void 354. The lower accumulator 352
has an outlet channel 370 only; a one-way valve 372 is placed in
this outlet channel. An overflow pipe 374 interconnects the
accumulators 350 and 352. The pipe 374 is so positioned that
effluent must fill the accumulator 350 to the level of the top 374a
of this pipe before it begins to spill into the lower
accumulator.
The operation of the accumulators 350, 352, is as follows: Assume
that both of these accumulators are initially empty and that a
loading has just been applied to the void 354. The effluent level
in this void rises to wet the side walls until it reaches the level
of the inlet channel 362. At this point, it begins spilling into
the accumulator 350. The level within this accumulator continues to
rise toward the top 374a of the overflow pipe 374. If the loading
ceases before the effluent level within the accumulator 350 reaches
the top of this pipe, none of the effluent in the accumulator 350
is passed to the accumulator 352. If, however, the loading
continues so that the effluent levels within the accumulator 350
reaches the top 374a of the overflow pipe, effluent begins to spill
into the lower accumulator as long as the loading is applied. When
the loading ceases, accumulation of effluent within the
accumulators 350, 352 also ceases.
When the exterior effluent level drops to a point such that its
effective "head" is less than the effective "head" of the effluent
within the accumulator 350, the valve 366 has unbalanced forces
acting on it and therefore opens outwardly to discharge the
contents of the accumulator 350. During this time, the valve 372 of
the accumulator 352 is held in the closed position and remains in
this position until the accumulator 350 has completely emptied and
the effective exterior head has dropped below the effective
interior head of the accumulator 352. At this point, valve 372
opens and accumulator 352 begins to discharge its contents into the
void 354. Thus, the initial excess effluent is accumulated at a
higher gravitational potential than would be the case with a
single-section accumulator, and the level at which the side walls
are wetted is thus maintained at a higher level for a greater
length of time than would normally be the case.
So far the accumulators of the present invention have been
illustrated and described as having completely enclosed bottom
walls so as to retain the effluent within the accumulator until it
is released at the appropriate time. It will be understood,
however, that even this bottom wall may be eliminated where the
bottom face of the soil in which it is placed is of limited
permeability either because of the nature of the soil itself or
because it is treated to reduce its permeability in connection with
the installation of accumulators. In such cases, the limited
permeability of the bottom face of the soil serves to retain the
effluent in the accumulators during the necessary storage interval,
until the effluent level in the exterior void has receded
sufficiently to allow discharge of the accumulated contents to the
void.
An accumulator of this type is shown in vertical cross section in
FIG. 16, in which an accumulator 350 has side walls 352, a roof 354
with a manhole 356 extending through it, effluent inlet channels
358, and an effluent outlet channel 360. A one-way valve 362 is
placed in the outlet channel. Effluent distribution channels 364
are formed on the roof of the accumulator for distributing effluent
to the void exterior to the accumulator. The operation of this
accumulator is essentially the same as was described in connection
with FIGS. 1 through 11, that is, effluent is accumulated within
the accumulator 350 when the exterior effluent level reaches that
of the inlet channel 358 and is discharged therefrom when the
exterior effluent level recedes below the level of the effluent
within the accumulator.
Numerous other changes in the various details of the invention set
forth above to accomodate the chambers to their environment and to
the functions they are to perform will suggest themselves to those
skilled in the art, and it is intended that the foregoing be taken
as illustrative only, and not in a limiting sense, the scope of the
invention being defined with particularity in the claims appended
hereto.
CONCLUSION
From the foregoing it will be seen that I have provided an improved
leaching field in the form of a trench, pit, or bed. The leaching
fields of the present invention have substantially the same
available infiltrative surface as conventional fields, but require
substantially less loading to wet the side wall faces in the case
of trenches and pits, and maintain this wetting for a longer
period. Further, in the case of leaching trenches, the storage
capacity of the trench is substantially increased as compared to
that of conventional trenches.
The leaching fields of the present invention are formed with
accumulators in the form of hollow casings having one or more fluid
inlet channels at the upper portion thereof and one or more fluid
outlet channels at the lower portion thereof. The fluid outlet
channels restrict fluid inflow by means of valves, restricted
orifices, siphons, or the like and operate so as to maintain the
effluent exterior to the accumulator at a higher level than it
would have in the absence of the accumulator. This insures greater
wetting of the side walls than is otherwise obtainable and greater
storage capacity for a given wetting level.
The increased wetting of the sidewalls provided in the case of
trenches and pits leads to numerous advantages. To begin with, the
increased infiltrative capacity encountered in soils having
multiple vertically-separated layers or strata is utilized to the
fullest. Further, elevating the effective level in the field
increases the hydrostatic head or hydraulic gradient and thereby
increases the effluent infiltration rate. Further, each time the
field is dosed with effluent, a substantial volume of air in the
field is displaced; as the effluent permeates into the soil, and
its level thereby recedes, fresh air is drawn into the field and
this contributes to restoring aeorbic conditions. Additionally, the
cyclic raising and lowering of the effluent level in the field
assists in sloughing off the biomass which forms on the vertically
inclined surfaces, thereby extending the effective filtration life
of the sidewall surfaces.
* * * * *