Note: Descriptions are shown in the official language in which they were submitted.
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STORMWATER TREATMENT APPARATUS AND ORIFICE
Background of the Invention
Field of the Invention
Apparatus for treatment of stormwater runoff through volume-control-based
detention
and minimization of pollutant remobilization.
Description of the Related Art
This invention relates generally to liquid purification and separation and,
more
specifically, to an apparatus for separation of pollutants in urban stormwater
runoff from the
runoff water. This apparatus utilizes gravitational separation and tortuosity,
resulting from a
plurality of baffles both perpendicular to and oblique to the primary water
flow direction, to trap
substances less-dense and more-dense than water. This invention is
differentiated from prior art
by improved resistance to pollutant remobilization, resulting from an
iterative experimental
hydraulic design process. In addition, this invention provides a degree of
retention through
volume-control that exceeds that provided by existing gravitational, sub-
surface, stormwater
treatment systems.
Impacts of stormwater runoff on receiving environments have been documented
extensively in engineering and scientific literature. Section 402 of the
Federal Clean Water Act
(CWA) regulates stormwater discharges through the National Pollutant Discharge
Elimination
System (NPDES). Treatment of stormwater runoff using best tnanagement
practices (BMPs) is a
typical requirement of state and local regulations, as well. In the 1990s,
there has been growing
interest in 'ultra-urban / space limited' BMP's, such as sand filters, water
quality inlets, and,
reservoir/vault type of structures. Space constraints, high property values,
soil conditions, and
the proximity of other building foundations often preclude the use of
conventional, space-
intensive stormwater BMP's such as detention ponds. For in- :fill construction
or redevelopment
in built-up urban areas, where pollutant loads from urban runoff are usually
the greatest,
unconventional stormwater treatment technologies may be necessary.
Vault-type treatment technologies have been widely used for stormwater
treatment in urban
areas; however, the effectiveness of these devices for removal of suspended
solids and oil and
grease has been only marginal. A great weakness of these types of devices has
been that large
CA 02420148 2003-02-26
storm events tend to flush out the system, thereby releasing pollutants that
were previously
removed.
Prior art in the field of this invention of which the applicant is aware
includes the
following:
= U.S. Pat. No. 4,127,488, Bell, J.A. et al., Nov. 1978, Method and apparatus
for separating
solids from liquids.
= U.S. Pat. No. 4,136,010, Pilie, R.J. et al., Jan. 1979, Catch basin
interceptor.
= U.S. Pat. No. 4,328,101, Broden, C.V., May 1982, Device for separating
particulate matter
from a fluid.
= U.S. Pat. No. 4,363,731, Filippi, R., Dec. 1982, Device for regulating the
flow of waste
waters.
= U.S. Pat. No. 4,383,922, Beard, H.J., May 1983, Waste water clarifier.
= U.S. Pat. No. 4,983,295, Lamb, T.J. et al., Jan. 1991, Separator.
= U.S. Pat. No. 4,985,148, Monteith, J.G., Jan. 1991, Improved separator tank
construction.
= U.S. Pat. No. 5,004,534, Buzzelli, V., Apr. 1991, Catch basin.
= U.S. Pat. No. 5,186,821, Murphy, D.T., Feb. 1993, Wastewater treatment
process with
cooperating velocity equalization, aeration, and decanting means.
= U.S. Pat. No. 5,342,144, McCarthy, E.J., Aug. 1994, Stormwater control
system.
= U.S. Pat. No. 5,520,825, Rice, W.M., May 1996, Oil-water separator.
= U.S. Pat. No. 5,536,409, Dunkers, K.R., July 1996, Water treatment system.
= U.S. Pat. No. 5,637,233, Earrusso, P.J., June 1997, Method and apparatus for
separating
grease from water.
= U.S. Pat. No. 5,679,258, Petersen, R.N., Oct. 1997, Mixed immiscible liquids
collection,
separation, and disposal method and system.
= U.S. Pat. No. 5,759,415, Adams, T., June 1998, Method and apparatus for
separating
floating and non-floating particulate from rainwater drainage.
= U.S. Pat. No. 5,788,848, Blanche, P. et al., Aug. 1998, Apparatus and
methods for separating
solids from flowing liquids or gases.
= U.S. Pat. No. RE30,793, Dunkers, K.R., Nov. 1981, Apparatus for water
treatment.
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In addition to the patents listed above, a number of inventions in the general
field of
stormwater treatment methods and devices were discovered during the patent
search. The
inventions listed below have an element or elements similar to the invention
disclosed herein;
however, additional elements, details of elements, and/or applications of the
inventions differ
significantly from the forms and functions of the present invention. While the
inventions listed
below are intended to provide stormwater treatment, the principle of operation
for many of these
devices is filtration rather than sedimentation.
= U.S. Pat. No. 4,298,471, Dunkers, K.R., Nov. 1981, Apparatus for
equalization of overflow
water and urban runoff in receiving bodies of water.
= U.S. Pat. No. 4,377,477, Dunkers, K.R., Mar. 1983, Apparatus for
equalization of overflow
water and urban runoff in receiving bodies of water.
= U.S. Pat. No. 4,664,795, Stegall, W.A. et al., May 1987, Two-stage waste
water treatment
system for single family residences and the like.
= U.S. Pat. No. 4,747,962, Smissom, B., May 1988, Separation of components of
a fluid
mixture.
= U.S. Pat. No. 4,865,751, Smissom, B., Sept. 1989, Separation of components
of a fluid
mixture.
= U.S. Pat. No. 5,080,137, Adams, T.R., Jan. 1992, Vortex flow regulators for
storm sewer
catch basins.
= U.S. Pat. No. 5,232,587, Hegemier, T.E. et al., Aug. 1993, Stormwater inlet
filters.
= U.S. Pat. No. 5,322,629, Stewart, W.C., June 1994, Method and apparatus for
treating
stormwater.
= U.S. Pat. No. 5,403,474, Emery, G.R., Apr. 1995, Curb inlet gravel sediment
filter.
= U.S. Pat. No. 5,437,786, Horsley, S.W. et al., Aug. 1995, Stormwater
treatment
system/apparatus.
= U.S. Pat. No. 5,480,254, Autry, J.L. et al., Jan. 1996, Storm drain box
filter and method of
use.
= U.S. Pat. No. 5,549,817, Horsley, S.W. et al., Aug. 1996, Stormwater
treatment
system/apparatus.
= U.S. Pat. No. 5,702,593, Horsley, S.W. et al., Dec. 1997, Stormwater
treatment
system/apparatus.
3
CA 02420148 2003-02-26
= U.S. Pat. No. 5,707,527, Knutson, J.H. et al., Jan. 1998, Apparatus and
method for treating
stormwater runoff.
= U.S. Pat. No. 5,730,878, Rice, T., Mar. 1998, Contaminated waste water
treatment method
and device.
= U.S. Pat. No. 5,744,048, Stetler, C.C., Apr. 1998, Clog resistant storm
drain filter.
= U.S. Pat. No. 5,770,057, Filion, G., June 1998, Overflow water screening
apparatus.
= U.S. Pat. No. 5,779,888, Bennett, P.J., July 1998, Filtering apparatus.
= U.S. Pat. No. 5,810,510, Urriola, H., Sept. 1998, Underground drainage
system.
= U.S. Pat. No. 5,840,180, Filion, G., Nov. 1998, Water flow segregating unit
with endless
screw.
= U.S. Pat. No. 5,890,838, Moore, Jr. Et al., Apr. 1999, Stormwater dispensing
system having
multiple arches.
= U.S. Pat. No. 5,972,216, Acemese, P.L. et al., Oct. 1999, Portable multi-
functional modular
water filtration unit.
= U.S. Pat. No. 5,985,157, Leckner, J.P. et al., Nov. 1999, Filter device.
Previous vault or box type treatment devices used in wastewater or stormwater
treatment
applications acted as "flow-through" systems. In these previous devices,
incoming flows enter
the device, take a given period of time based on baffles and size to flow
through the device, and
then exit the device. If flows were coming in continuously, they would enter
and exit the device
at the same flow rate. Previous devices have different systems within the
vault to channel,
divert, or reduce flow rates inside the vault in order to facilitate gravity
separation. All of these
devices are somewhat effective at settling out particles down to a certain
size or specific gravity,
but none of these devices are effective at removing the very small size range
of particles that
make up the majority of toxic pollutants in storm water runoff. These
particles are typically in
the 100-micron and smaller size range, and simply will not settle out of the
water if there are
horizontal flow velocities present.
Most currently available stormwater treatment devices are designed to reduce
the
concentrations of pollutants in stormwater by screen, filter or enhanced
gravitational separation
(i.e. swirl concentrators). However, such systems provide little or no
detention capture volume to
mitigate the runoff peaks for small or large runoff events. In other words,
these systems function
as flow-through devices, resulting in the lack of capture volume and overall
poor treatment
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performance. Specifically, much of the settleable materials trapped or
deposited during more
numerous smaller runoff events are agitated and remobilized, and wash out of
these devices
when larger and more intense runoff events occur.
Properly sized and maintained wet detention ponds (retention ponds) provide
some of the
most effective stormwater treatment available. Because of site-specific
limitations, however
many desirable features of wet detention ponds are not utilized in real world
conditions.
Available surface area, possible thermal pollution, attractive nuisance
liabilities, mosquitoes and
long-term maintenance access and disposal are some of the difficulties that
must be addressed
with a surface pond.
Summary of the Invention
This stormwater mitigation system solves these problems and more, and includes
the
benefits of a properly designed retention pond.
The apparatus advantageously settles particles down to a size of 100 microns
and smaller
out of suspension in the stormwater by utilizing a unique volume control
design. The vault of
the present invention is designed to treat a given volume of stormwater
runoff, as opposed to a
given runoff flow rate as treated in other devices. In so doing, the
horizontal flows for the entire
volume of water to be treated can be nearly eliminated, such that with a
reduced flow rate very
small particles may drop out of suspension and collect on the bottom of the
vault. This is
accomplished through a combination of physical space to capture and hold water
to be treated,
restriction of flow out of the apparatus at a slower flow rate than flow into
the apparatus, and
vertically stacked pools of water with reduced or eliminated relative flow
velocity.
Features that are thought to provide such consistently high quality treatment
advantageously include; a permanent pooi (i.e., a pool essentially
continuously present after it is
first filled) to eliminate the resuspension of pollutants, extended quiescent
settling conditions to
promote retention of the Total Suspended Solids ("TSS") and floatable
materials, subsurface
conditions that curtail the resuspension of deposited sediment, sufficient
volume to retain runoff
from the majority of runoff events and capture and treat the "first flush" of
the larger events,
flow control system to attenuate the runoff flow rates from the majority of
storm events and
prevent flushing of the captured pollutants, and large surface area that
promotes oxygen transfer
to reduce pollutant remobilization.
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An aspect of this invention is to provide an apparatus for removal of
pollutants with
densities greater than and less than water from stormwater runoff.
Another aspect of this invention is to provide an apparatus that retains and
immobilizes
trapped pollutants, even during periods when flows are high.
Another aspect of this invention is to accumulate pollutants that are less and
more dense
than water until a time when the apparatus is cleaned out.
Another aspect of this invention is to minimize velocity in the vicinity of
the bottom of
the apparatus to minimize resuspension of deposited sediments and associated
pollutants. The
slower the velocity of water in at least part of the device, the more
effective will be the removal
of particles.
Another aspect of this invention is to provide an apparatus that can provide
treatment of
stormwater for larger tributary drainage areas by addition of modular
sections.
Another aspect of this invention is to collect stormwater runoff and release
it at a
controlled rate over a specified period of time via an outflow opening.
Other aspects and advantages will become apparent hereinafter.
In one embodiment, the apparatus includes a by-pass manhole, apparatus
chambers
including a plurality of interior baffles, and a junction box. This apparatus,
along with properly
sized and installed ancillary appurtenances, will advantageously collect and
hold floatable debris,
runoff bed load particulate material, free oil and grease, settleable
sediments and those dissolved
pollutants including metals, nitrogen and phosphorus nutrients, and soluble
organic compounds
the may adsorb or adhere to the surface of sediments and organic debris in
stormwater. This
apparatus, properly installed and utilizing a properly sized outflow opening
aperture installed
within an outlet opening, can capture and control the release of site runoff,
significantly reducing
erosion and stream degradation due to urbanization of the riparian habitat,
and helps restore pre-
development runoff rates to urbanized areas.
In one embodiment, the apparatus is a below grade modular concrete stormwater
control
device that is designed to manage and treat stormwater runoff by diverting a
predetermined
capture volume (or water quality capture volume) into the apparatus. As would
be understood by
one of ordinary skill in the art, the capture volume is typically sized, for
example, between the
mean and the maximized runoff event as defined in "Urban Runoff Quality
Management," Water
Environment Federation (WEF) Manual of Practice No. 23 and American Society of
Civil
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Engineers" (ASCE) Manual and Report on Engineering Practice No. 87. The
capture volume is
surcharged into detention storage (the active pool).
This capture is brought about by a volume control diversion weir that directs
the design
capture volume runoff into the apparatus with a minimum hydraulic loss into
the apparatus.
Any subsequent flow beyond that of the design capture volume is allowed to
bypass the
apparatus via a volume control diversion weir returning to the stormwater or
runoff collection
system and/or receiving waters.
During wet weather and periods of site runoff, the detention time of the
capture volume
may be optimized to promote quiescent sedimentation within the active pool
whereby settable
solid particles less than 100 microns in size with a specific gravity greater
than water will
descend and insoluble oil droplets and marginally buoyant debris will float to
the surface.
One aspect of the invention is a rectangular chamber of variable length, width
and height
assembled in a modular fashion. The rectangular chamber contains a system of
overflow and
underflow baffles, both perpendicular to and oblique to the primary direction
of flow from the
inlet to the chamber to the outlet from the chamber, which are located at
opposite ends of the
rectangular chamber. The baffles in the chamber serve several purposes
including: flow
momentum and energy dissipation, creation of a tortuous flow path, retention
and immobilization
of pollutants less and more dense than water, minimization of resuspension of
sediments, and
minimization of remobilization of floatable pollutants into the water column.
The primary
process for pollutant removal is gravitational separation, which occurs while
water is detained in
the chamber.
A baffle configuration for minimization of resuspension of trapped sediments
and
associated pollutants was first conceptualized by the inventors and then
optimized by iterative
experimentation involving three dimensional velocity measurements and dye
visualization for a
plurality of baffle configurations using a geometrically and hydraulically
scaled physical model.
Baffle configurations were evaluated for both dynamic (chamber filling and
draining) and
steady-state (chamber full with inflow rate equal to outflow rate) conditions.
This exhaustive
experimentation indicates that the baffle configuration of the invention
disclosed minimizes
resuspension of fine and coarse sediments and associated pollutants to a
degree that exceeds the
capabilities of prior art. In addition, a trapezoidal underflovv baffle, the
shape of which was
optimized during hydraulic experimentation, impedes material less dense than
water from
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entering the outflow section and exiting the vault. The trapezoidal
configuration has the
advantage of decreasing the downward velocity of water approaching and then
moving under the
baffle and into the outlet section and, thereby, decreases the risk of
entraining floatable pollutants
trapped behind the trapezoidal baffle into the flow passing into the outlet
section. As a result, the
plurality of interior baffles and the weir configuration advantageously are
designed to provide
minimum re-suspension of settable solids from within the permanent pool.
In one aspect, the apparatus has an inlet that delivers water to the chamber
from a
tributary surface land area, either directly or via storm sewer system piping.
Water entering the
cphamber passes through a system of underflow and overflow baffles both
perpendicular to and
oblique to the primary direction of flow from the inlet to the outlet, which
is located at the end of
the rectangular chamber opposite the inflow. As water enters the chamber, the
water level in the
chamber rises above the permanent pool water surface elevation, which normally
is less than or
equal to the elevation of the invert of the outflow opening. Outflow from the
chamber is
controlled by an opening that is sized to provide a specified time for the
water in the chamber to
drain from the elevation at which the chamber is fiill to the elevation of the
permanent pool.
When the rate of inflow is greater than the rate of outflow, the water level
in the chamber will
rise to the elevation at which the chamber is full. Once the chamber is full,
any flow in excess of
the outflow rate under full conditions will bypass the chamber via an overflow
structure 294.
When the rate of outflow is greater than the rate of inflow, the water surface
elevation in the
chamber will decrease at a rate controlled by the size of the outflow opening,
and the water
surface elevation will decrease to the elevation of the outflow opening
invert, at which time
outflow will cease. For convenience and brevity, this chamber inflow volume,
as described in
previous applications, is herein called a capture volume.
By slowly metering out storm runoff back to the external environment, the
apparatus is of
great benefit as it not only removes pollutants but also duplicates runoff
conditions that exist
prior to urban development. This prevents erosion of stream channels, and also
prevents a
discharge of rapidly flowing runoff that would simply pick up more sediment
after treatment.
Another aspect of the invention is a stormwater treatment apparatus, including
a
receptacle adapted to receive water flowing from a surface drainage area, the
receptacle having a
bottom and a top, the receptacle having an inlet and an outlet, the inlet and
the outlet being in
fluid communication with one another; and at least one baffle positioned
within the receptacle
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between the- inlet and the outlet, the baffle extending from the bottom of the
receptacle, a first
portion of the baffle and the bottom of the receptacle forming an angle
therebetween.
A stormwater treatrnent apparatus varies from other types of treatment
apparatus, such as
septic tanks, in that stormwater treatment apparatus must capture a wide
variety of particles of
different sizes and compositions in a pulsed hydraulics environment, as
opposed to the more
constant flow environment of a septic tank. A stormwater treatment apparatus
also differs from
septic tanks in that the goal is to permanently trap sediments and other
pollutants less or more
dense than water, rather than to degrade organic matter and other
biodegradable substances and
in that a stormwater treatment apparatus is much larger than septic tanks,
desirably having a
volume of at least 500 cubic feet, more desirably at least 600 cubic feet and,
preferably, at least
750 cubic feet. Generally, this apparatus size advantageously is sized to
include an active pool
volume sufficient to treat the capture volume of the area being treated.
Additionally, one vault or
more than one vault maybe used, depending on the topography of the area being
treated, and size
of the vault(s) being used. Factors effecting the size and number of vaults
used in the apparatus,
besides capture volume, include manufacturing capability, transportability to
site, modularity of
apparatus, cost of construction and installation, site topography, ease of
installation, and
apparatus footprint.
The apparatus advantageously substantially reduces bottom velocities, thereby
greatly
reducing resuspension of sediments. In particular, the angle formed between
the first portion of
the baffle and the bottom of the receptacle is desirably between 30 and 60
degrees, at is desirably
inclined in a downstream direction. Further, the height of the baffle is
desirably at least two feet
to limit the washing out of sediment. To facilitate manufacture and cleaning
the baffle desirably
includes a second portion, the second portion of the baffle extending from the
bottom of the
receptacle and forming an angle with the bottom of the receptacle, the angle
being roughly 90
degrees.
The apparatus desirably includes an inlet baffle positioned between the inlet
and the
outlet, the inlet baffle spaced from said bottom and extending between
generally opposing walls
and an outlet baffle positioned between the inlet and the outlet, the outlet
baffle spaced from said
bottom and extending between generally opposing walls of the receptacle. The
lower end of the
outlet baffle is desirably positioned below said outlet. The outlet baffle
advantageously may
define a horizontal cross-section between a first baffle extending from said
bottom and said
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outlet baffle larger than the horizontal cross-section between said first
baffle and a vertical plane
tangent to an upstream side of said outlet baffle. This has the effect of
reducing the velocity of
fluid. In this regard, it is desirable that outlet baffle defines a center
section and at least one
outer section which extends toward said outlet from said center section.
Advantageously,
however, the spaces between the outlet baffle and the opposing walls are
sufficiently large to
permit cleaning and to facilitate manufacture.
Yet another aspect of the invention is an apparatus for cleaning stormwater
run-off, the
apparatus including a vault having a top, a bottom, two sides, a front and a
back, the vault
comprising a first baffle extending from the bottom of the vault; a second
baffle extending from
the bottom of the vault, an inlet section having an opening and an outlet
section having an outlet
opening.
The apparatus also advantageously includes vertically stacked columns of
water, defined
by, in one embodiment, varying horizontal flow rates and bounded by baffles
creating regions of
lower horizontal flow rate. When the vault is filling or full, there is a
column of water, called for
convenience an "active pool," that is filling via the inlet, draining via the
outlet, or both. This
pool is the water being held, treated, and released by the invention. As the
active pool is treated,
sediments settle to the floor of the vault. As a result, when there is water
in the active pool, it has
a significantly higher velocity than the water in the permanent pool. A
typical flow velocity for
the active pool is two to three feet per second.
In order to retain sediments and to prevent them from running out of the vault
as it
empties, and in order to prevent resuspension of the sediments as the vault
refills at a later time,
the apparatus advantageously includes a permanent pool. The permanent pool
sits immediately
below the active pool and receives most or all sediments as they drop out of
the active pool. Due
to the shape, design and spacing of the baffles surrounding and within the
permanent pool and
active pool, the permanent pool is an inactive pool (a permanent pool that has
minimal to no flow
velocity.) Based on tests, the inactive permanent pool of the preferred
embodiment of this
invention maintains flow velocities typically below 0.15 feet per second.
One of the failings of prior "flow-through" systems was their inability to
settle small
particles from smaller storm flows without resuspending those particles in
later large storm flows
due to turbulence and currents that reach all areas of the prior vaults. The
present apparatus, by
creating an active pool that fills, holds and drains immediately above an
inactive permanent pool,
CA 02420148 2007-09-21
eliminates small particle re-suspension. Even in prior systems, simply
applying baffles to create
a physical barrier to sediments moving horizontally through the system,
without creating a
permanent pool, is only effective for larger, heavier particles: in prior flow-
through systems,
smaller and finer particles, which form the majority of toxic pollutants, are
left without an
inactive permanent pool area to reside in and are simply suspended (or re-
suspended) in the flow
as it moves from compartment to compartment and exits.
A further advantage of vertically stacked pools including a permanent pool is
that of
maintaining a compact footprint or plan area. By both treating the incoming
volume of water
and storing sediments in the same plan area more water volume can be treated
on a given site.
Finally, the present invention advantageously includes an overflow structure,
in one
embodiment integral to the outlet section of the vault. When inflow of
stormwater exceeds the
volume capacity of the treatment system, the overflow structure diverts excess
stormwater flow
without substantially effecting the ability of the system to effectively treat
the full volume of
stormwater already in the vault.
In accordance with an aspect of the present invention, there is provided a
method for
purification and separation of a liquid, the method comprising inputting the
liquid into a
receptacle through an inlet opening; communicating the liquid through an
active pool to an outlet
opening, the outlet opening defining a permanent pool level; interrupting the
flow of the liquid
around at least one inlet baffle after the inlet opening; interrupting the
flow of the liquid around
at least one outlet baffle before the outlet opening; and settling sediments
from the flow in the
active pool into at least one inactive pool formed by at least a first pair of
inactive pool baffles,
each of said pair of inactive pool baffles extending upward from a bottom of
said receptacle, but
not above said permanent pool level, said inactive pool gravitationally below
the active pool.
According to another aspect of the present invention, there is provided a
method for
purification and separation of a liquid, the method comprising inputting the
liquid into a
receptacle through an inlet opening; interrupting the flow of the liquid
around at least one inlet
baffle after the inlet opening; communicating the liquid through an active
pool to an outlet
opening, the outlet opening smaller than the inlet opening; interrupting the
flow of the liquid
around at least one outlet baffle before the outlet opening; settling
sediments from the flow in the
active pool into at least one permanent pool, said permanent pool
gravitationally below the active
pool; and trapping materials heavier than water using at least one modular mid
section of the
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receptacle, wherein the at least one mid section is in fluid communication
with the inlet opening
and the outlet opening and includes at least one baffle, the trapping of
materials heavier than
water being accomplished via the reduction of the rate of flow with the at
least one baffle.
According to another aspect of the present invention, there is provided a
method for
purification and separation of a liquid, the method comprising inputting the
liquid into a
receptacle through an inlet opening; communicating the liquid through an
active pool to an outlet
opening, the outlet opening defining a permanent pool level; reducing the flow
rate of the liquid
by directing said liquid around at least one inlet baffle after the inlet
opening; reducing the flow
of the liquid by directing said liquid around at least one outlet baffle
before the outlet opening;
and, settling sediments from the flow in the active pool into at least one
inactive pool formed by
at least a first pair of inactive pool baffles, each of said pair of inactive
pool baffles extending
upward from a bottom of said receptacle, but not above said permanent pool
level, said inactive
pool gravitationally below the active pool.
Brief Description of the Drawings
One embodiment of this invention, the best mode, is illustrated in the
attached drawings,
in which like numerals indicate like components throughout the several views.
Views include:
FIG. 1-- a plan (from a perspective above the apparatus) view of the apparatus
that is the
subject of this invention;
FIG. 2-- a profile (side elevation) view of the apparatus;
FIG. 3-- a cross-sectional view of the inlet section of the apparatus (cross-
section 1-1
shown on FIG. 1 and FIG. 2);
FIG. 4 -- a cross-sectional view of the outlet section of the apparatus (cross-
section 2-2
shown on FIG. 1 and FIG. 2);
FIG. 5-- a detailed (enlarged) profile view of the inlet section baffle
configuration;
FIG. 6-- a detailed plan view of the outlet section;
FIG. 7-- a detailed view of the outflow opening configuration;
FIG. 8-- an illustration of baffle spacing for this invention for even and odd
numbers of
chambers for a multi-chambered apparatus (the number of midsections depicted
in this view,
four for the even illustration and five for the odd illustration, are specific
examples of the
generalized odd and even baffle spacing rules and are not intended to be
restrictive);
Ila
CA 02420148 2003-02-26
FIG. 9-- an illustration of a modified embodiment of the present invention,
including an
external bypass structure;
FIG. 10 -- an illustration of the apparatus, in one embodiment, incorporating
a gravity
dynamic flow control orifice; and,
FIG 11 -- a detail plan view of the apparatus, in one embodiment,
incorporating an
integral overflow bypass structure.
Detailed Description of the Preferred Embodiment
The drawings illustrate one embodiment of an apparatus 100 for separation of
pollutants
that are less and more dense than water from stormwater runoff. Referring to
FIG.. 1 and FIG.
2, the apparatus 100 consists of a top 140, a bottom 160, an inlet end 170, an
outlet end 150, a
left side 300, and a right side 310 (left and right are relative to the view
from the inlet end 170 to
the outlet end 150). These sides define a rectangular chamber with an inlet
section 110, an outlet
section 120, and one or more midsections 130.
The length of the most basic configuration of the apparatus 100 is desirably
at most 20 ft,
more desirably at most 18 ft 6 in, and, most preferably, 17 ft 6 in (inside
dimension); and the
width of the apparatus id desirably at most 10 ft, more desirably at most 8 ft
6 in, and, most
preferably, 7 ft 6 in (inside dimension); the height of the apparatus is 6 ft
or 8 ft (inside
dimensions). Outside dimensions and inside dimensions may vary due to
structural strength
requirements of the apparatus 100. Desirably, the length of the apparatus 100
increases in 4-ft.,
8-fft, or 16-ft increments as additional midsections 130 are ernployed. The
top 140 and bottom
160 are desirably parallel to each other and are separated by a distance of 6-
ft or 8-ft (inside
dimensions). The left side 300 and right side 310 are desirably parallel to
each other and are
separated by a distance of at most 10-ft, more desirably 8-ft 6-in and,
preferably, 7-ft 6-in (inside
dimensions). The inlet end 170 and the outlet end 150 are desirably parallel
to each other and,
for the most basic configuration, are desirably separated by a distance of at
most 20-ft and, more
desirably, 17-ft 6-in (inner dimension). The distance between the inlet end
170 and the outlet
end 150 desirably increases by 4-ft, 8-ft, or 16-fft increments as additional
midsections 130 are
employed. The thickness of the inlet end wall 170, the outlet end wall 150,
the left side 300, the
right side 310, and the bottom 160 is desirably at least 3-in and, preferably,
6-in or more. The
thickness of these walls may increase or decrease as structural needs of an
installation dictate.
12
CA 02420148 2003-02-26
The thickness of the top 140 of the apparatus 100 is at least 3-in and,
desirably, 6-in or more but
may increase or decrease as structural needs of an installation dictate.
Based on experience gained after the filing of the original application, it is
currently
believed that the preferred dimensions for the apparatus are a length of about
eighteen feet (along
the longest dimension of the apparatus), a width of about eight feet, and a
depth of about eight
feet. As the apparatus is made larger, though, it advantageously can treat a
larger capture
volume of stormwater. The preferred method of increasing the size of the
apparatus is to add
modular midsections to increase the length and treatment capacity of the
apparatus. Desirably,
the apparatus can thus range from a basic configuration of about eighteen feet
in length to
compound, large configurations of approximately one hundreci feet in length
including a plurality
of midsections. As topographical, footprint, transportation, manufacturing and
capture volume
requirements change, these structural dimensions may similarly change.
The ability to increase the size and treatment capacity of the apparatus 100
by addition of
modular midsections 130 is advantageous for manufacturing since the apparatus
100 can be
manufactured in a wide range of incremental sizes using the same set of forms
for precasting. In
addition, the modular construction is favorable for applications requiring a
large apparatus 100 as
the modular sections 110, 120, and 130 can be transported on one or more
trucks and then
assembled on-site. The incremental sizing may be advantageous for performance
at improving
water quality as well when the apparatus 100 is sized according to
manufacturer's
recommendation. For example, if a user, based on sizing calculations,
determines that the
required capacity of the apparatus 100 necessary to achieve a desired
performance is equivalent
to the capacity of a midsection with a length of 11-ft, then the user would
specify that 2
midsections 130 are needed, one 8-ft long and the other 4-ft long (or two 8-ft
long sections),
since midsections 130 are discrete components and 1 mid-section 130 would not
provide the
required capacity. As a result of this modular, incremental sizing, the
apparatus 100 specified by
the user would always have a capacity equal to or in excess of that required
and would, therefore,
provide a minimum degree of desired treatment.
A plurality of baffles 220 and 250 are positioned between the inlet end 170
and the outlet
end 150. The primary direction of flow is defined as the direction from the
inlet end 170 toward
the outlet end 150 in the horizontal plane. In the disclosed embodiment, the
primary direction of
flow is perpendicular to the inlet end 170 and the outlet end 150 and parallel
to the top 140,
13
CA 02420148 2003-02-26
bottom 160, left 300, and right 310 sides. There are two types of overflow
baffles employed in
this invention. These baffles are referenced as components 220 and 250.
Component 220 is a
hybrid baffle, and component 250 is an angled baffle. The results of extensive
hydraulic testing
indicate that the baffle configuration illustrated, as well as the claimed
baffle configurations
using various combinations of hybrid 220, vertical, and angled 250 baffles, is
highly effective at
minimizing resuspension of trapped sediments and associated pollutants.
Velocity
measurements and dye visualization experiments indicate that the apparatus 100
disclosed herein
provides a degree of reduction of resuspension that significantly surpasses
that of existing art.
Referring to FIG. l; FIG. 2, and FIG. 5, the hybrid baffle 220 consists of a
vertical
section 240 that is perpendicular to the primary flow direction and an angled
section 230 that is
oblique to the primary direction of flow, forming an angle, a, with the
horizontal plane (angle a
is depicted in FIG. 5). Preferably, the vertical baffle section 240 has a
length of 1-ft and the
angled section of the baffle 230 rises from the top of the vertical section
240 at a 45 angle for a
distance of 1-$ in the horizontal plane and a distance of 1-ft in the vertical
plane. Preferably, the
total vertical rise for a hybrid baffle 220 is 2-ft from the chamber bottom
160, and the horizontal
projection is 1-ft 3-in. in the downstream direction (including thickness of
the vertical section
240). An angle other than 45 may be used for the hybrid baffle 220 as long
as the lengths of
components 230 and 240 are adjusted to provide a total rise of 2-ft and the
downstream end of
component 230 does not extend beyond the dimensions of the top 140, bottom
160, and walls
300, 310, and 170 of the precast unit containing the baffle. Desirably, the
angle a is between 00
and 90 , and, more desirably, between 30 and 60 degrees
The angled baffle 250 rises 2-ft from the bottom of the chamber 160. An angled
baffle
250 is illustrated in FIG. 1 and FIG. 2 in plan and profile views,
respectively. For the best mode,
the baffle 250 forms an angle, a, of 45 with the chamber bottom 160. An angle
other than 45
may be used, provided that a vertical rise of 2-ft is maintained and that the
downstream end of
the angled baffle 250 does not project beyond the end of the associated 8-ft
midsection 130.
Hybrid baffles 220 and angled baffles 250 may be interchanged to create
numerous
embodiments; however, the best mode utilizes a single hybrid baffle 220 in the
inlet section 110
and angled baffles 250 in midsections 130, the spacing of vvhich is described
below. Other
shapes and heights of baffles, up to the full depth of the permanent pool have
been tested and are
14
CA 02420148 2003-02-26
viable alternates to the "best design" shown herein and are part of the design
claims of this
apparatus 100.
Extensive hydraulic experimentation and testing of baffle configurations and
types was
conducted to determine baffle geometry that effectively reduced velocities in
the lower section of
the apparatus 100 where sediments accumulate after settling out of the water.
As will be
appreciated by one of skill in the art, the creation of this reduced velocity
region results in a
region of little or no velocity near the gravitational bottom of the vault.
That is, this region
comprises an inactive permanent pool. Initial testing indicated that angled
baffles 250 were
more effective than vertical baffles at decreasing bottom velocities in the
apparatus' midsections
130. The inventors initially tested angled baffles 250 for the purpose of
examining the effect of
the angled baffles 250 on flow passing over the crest of the arigled baffles
250. In the process of
this experimentation, the inventors discovered that the angled baffles 250 had
a favorable effect
on bottom velocities between two angled baffles 250 separated by a distance of
16-ft or less. A
hybrid baffle 220 was developed and tested for the purpose of achieving a
reduction in bottom
velocities in the midsections 130 comparable to that found using an angled
baffle 250, while at
the same time decreasing the length in the horizontal plane consumed by the
angled baffle 250
by a distance equivalent to the product of the height of the vertical portion
of the baffle 240 and
the tangent of the angle 90 - a. This reduction in the horizontal distance
required to
accommodate the hybrid baffle 220 allows the inlet section 110 to be
shortened, resulting in a
reduction in the amount of material necessary to fabricate the inlet section
110. In addition, the
vertical portion 240 of the hybrid baffle 220 has the advantage of improved
access for a hose or
vacuum to clean out the area beneath the baffle 220. An angled baffle 250
permits access
beneath the baffle 250 for cleaning only where the distance between the under-
surface of the
baffle 250 and the bottom of the chamber 160 (inside dimension) is greater
than the diameter or
height of the intake component of the vacuum or pumping cleaning system. For
both angled 250
and hybrid 220 baffles, the experimentation conducted indicated that both
types of baffles 250
and 220, performed very well at evenly distributing flow across the width of
the apparatus 100.
Water is supplied to the apparatus inlet section 110 via an inlet pipe or
other conveyance
180 carrying water from the tributary drainage area to the inlet of the
apparatus 190. The invert
of the inlet aperture 190 is desirably at least 3-ft above the chamber bottom
160 (inside
dimension). The apparatus 100 may also receive water from the tributary
drainage area directly
CA 02420148 2003-02-26
rather than via an up-gradient, piped storm sewer system. An example of this
configuration
would be an apparatus 100 installed to receive water from a manhole chamber
below a curb-side
drop inlet.
The inlet section 110 consists of several distinct components that are shown
in FIG. 1,
FIG. 2 in plan and profile views, respectively. FIG. 3 shows a cross-section
(1-1) of the inlet
section 110, and FIG. 5 shows details of the baffle configuration for the
inlet section 110. The
dimensions of the inlet section 110 are defined by the inlet end wall 170; the
top 140, bottom
160, left 300, and right 310 sides; and a plane perpendicular to the primary
direction of flow
located a prescribed distance from the inside dimension of the inlet end wall
170 in the
downstream direction. This prescribed distance is defined by the length
dimension of the precast
segment containing the energy dissipation baffle 200 and the most upstream
hybrid 220 or
angled 250 baffle and, most preferably is 4-ft 9-in. The dimensions of the
inlet section 110,
exclusive of baffles, desirably are equivalent to the dimensions of the outlet
section 120,
providing the advantage of having the capability to cast inlet 110 and outlet
120 sections using
the same form. The inlet section 110 desirably includes a manhole 135 for
access to the inlet
section 110 for maintenance. The cover of the manhole 135 is desirably vented
to allow
exchange of air between the inside of the apparatus 100 and the surface
atmosphere to prevent
anoxic conditions from developing in the permanent pool. The permanent pool is
defined as the
volume of water and trapped pollutants in the apparatus 100 above the bottom
of the chamber
160 and below the invert of the outflow opening 280.
A component of the inlet section 110 is a flow energy dissipation baffle 200
that is
perpendicular to the primary direction of flow. The energy dissipation baffle
200 is parallel to
the inlet end wall 170 and is positioned so that the side of the energy
dissipation baffle 200
facing the inlet wall 170 is desirably at most 1-ft 6-in and preferably 1-ft
from the inner side of
the inlet end wall 170 in the primary direction of flow. The energy
dissipation baffle 200
desirably is connected to the left side 300 and right side 310 from a distance
of desirably at most
2-ft and preferably 1-ft 6-in above the chamber bottom 160 (inside dimension)
to a distance of
desirably at most 1-ft, and preferably 6-in from the chamber top 140 (inside
dimension). The
energy dissipation baffle 200 desirably has a thickness of 3-in., The purpose
of the flow energy
dissipation baffle 200 is to decrease the energy of the incoming flow. For the
apparatus 100
described herein, the decrease in flow energy translates to a decrease in the
velocity of the
16
CA 02420148 2003-02-26
incoming water. The space 210 is provided between the top of the energy
dissipation baffle 200
and the top 140 of the apparatus 100 for the purpose of allowing overflow for
high flows and for
the purpose of providing access for maintenance. Hydraulic testing indicates
that the energy
dissipation baffle 200 is effective at decreasing flow energy. The inventors
examined several
options for spacing between the inlet end wall 170 and the flow energy
dissipation baffle 200 and
found that the above-described spacing provided a good balance between the
effectiveness of
energy dissipation and the space necessary to access the area between the
inlet end wall 170 and
the baffle 200 for maintenance.
Another element of the inlet section is the inlet overflow baffle 220. The
inlet overflow
baffle 220 is a hybrid baffle (described above). The inlet overflow baffle 220
desirably is
connected to the chamber bottom 160 and the left 300 and right 310 sides of
the chamber so that
water can only pass over the top of the baffle, defined by component 230. The
vertical portion
240 of the inlet overflow baffle 220 desirably is located a distance of at
least 2-ft 6-in, more
desirably at least 3-ft, and preferably 3-ft 6-in from the inlet end wall 170
(inside dimensions).
The thickness of the inlet overflow baffle 220 is desirably 3-in. The vertical
rise for the inlet
overflow baffle 220 is desirably at most 3-fft, more desirably at most 2-ft 6-
in, and, preferably, 2-
ft, and the horizontal distance in the direction of flow is desirably at most
2-ft, more desirably at
most 1-ft 6-in, and, preferably, 1-ft 3-in (including the baffle thickness of
3-in) for the best mode.
A midsection 130 of the apparatus 100 is defined by a top 140, a bottom 160, a
left 300,
and a right 310 side that desirably are connected at 90 angles to form an
open-ended rectangular
section. FIG. 1 and FIG. 2 depict an apparatus 100 with two, 8-ft midsections
130. The
apparatus 100 desirably has at least one midsection 130 but may have
additional midsections
130. Desirably, the midsections 130 have a length of 16-fft, more desirably 4-
ft, and, preferably,
8 ft. Angled baffles 250 desirably are spaced at 4-ft increments, more
desirably at 8-ft
increments, and, preferably, at 16-ft increments in midsections 130. For
midsections 130
requiring angled baffles 250 to achieve this spacing, an angled baffle 250
(described above) is
attached to the bottom of the midsection 130 so that the downstream tip of the
angled baffle 250
coincides with the end of the midsection 130. Such an angled baffle 250 in a
midsection 130 is
shown in FIG. 1 and FIG. 2 in plan and profile views, respectively. While an
angled baffle 250
desirably is used in the midsections 130, vertical, hybrid, or other baffle
shapes 220 may be used.
Since baffle 220 and 250 spacing is preferably 16-ft and midsections 130 are
added in 4-ft, 16-$,
17
CA 02420148 2003-02-26
or 8-ft increments, not all midsection segments 130 will need baffles 220 and
250. FIG. 8
illustrates baffle 220 and 250 spacing. As FIG. 8 indicates, baffles 220 and
250 preferably are
spaced every 16-feet, and a baffle 220 and 250 is desirable at the end of the
most downstream
midsection 130. Therefore, for an even number of midsections 130, desirably
with a length of 8-
ft (four as an example in FIG. 8), all overflow baffles 220 and 250 are
preferably spaced 16-feet
apart. For an odd number of midsections 130, desirably with a length of 8-ft,
(five as an example
in FIG. 8), however, spacing is preferably 16-feet between all overflow
baffles 220 and 250 with
the exception of the spacing between the penultimate and ultimate downstream
baffles 220 and
250 at the end of the most downstream midsection 130. The number of
midsections 130
depicted in FIG. 8 are shown as exainples of even and odd numbers of
midsections 130 and
should not be interpreted as restrictive specifications. Each midsection 130
desirably will have a
manhole 135, allowing access through the top of the chamber 140 for
maintenance. Desirably,
all manholes 135 will be vented to prevent development of anoxic conditions in
the permanent
pool and will be of sufficient size to allow the contents of the apparatus 100
to be pumped out as
a part of regular maintenance. Manholes 135 positioned above midsections of
the apparatus 100
desirably will have a collar 145 with approximately the same inner diameter as
the manhole that
extends into the chamber 3-in below the top 140. The purpose of the collar 145
is to limit the
surface area of the water and associated floatable pollutants in the chamber
that could potentially
be forced out of the apparatus 100 via vents in manhole access areas 135 when
the apparatus 100
fills completely.
The midsection 130 components of the apparatus 100 are the primary treatment
and
pollutant collection chambers. During the time that water is detained in the
apparatus 100,
sedimentation occurs, resulting in deposition of sediments and associated
pollutants with
densities greater than water on the bottom 160 of the midsections 130. The
configuration of
baffling 220 and 250 is such that sediments deposited on the bottom 160 of the
midsections 130
resist resuspension during subsequent runoff events. Once the thickness of the
sediment layer on
the bottom 160 of the midsections 130 increases to a prescribed depth, the
apparatus 100 is
cleaned via a pump-out or other method to remove the permanent pool and
trapped pollutants
from the apparatus 100 for disposal.
In addition to sediment removal, the midsections 130 of the apparatus 100
collect and
retain materials less dense than water. During the time that water is detained
in the apparatus
18
CA 02420148 2003-02-26
100, materials that are less dense than water rise toward the water surface.
Since flow from the
midsections 130 passes to the outlet section 120 by flowing beneath the
trapezoidal baffle 260,
pollutants on the water surface in the midsections 130 are retained on the
upstream side of the
trapezoidal baffle 260. Due to the elevation of the invert of the outlet
opening 280, the surface of
the permanent pool in the apparatus 100 desirably remains at least 1-ft above,
and, preferably, 1-
ft 5-in above the highest elevation at which water can pass below the
trapezoidal underflow
baffle 260. As described below, the trapezoidal geometry of the underflow
baffle 260 is
advantageous for prevention of entrainment of pollutants collected on the
surface of the mid-
sections 130 into the flow beneath the trapezoidal baffle 260 entering the
outlet section 120.
Desirably, a mat or mats composed of material capable of absorbing petroleum-
based
hydrocarbons with densities less than that of water will be placed in the
midsections 130 of the
apparatus 100 for the purpose of immobilizing these pollutants. Manholes 135
will be large
enough to permit removal of the absorbent mats.
A detailed plan view of the outlet section 120 is shown in FIG. 6, and a
detail of the
outflow opening configuration 280 is shown in FIG. 7. The dimensions of the
outlet section 120
are defined by the outlet end wall 150; the top 140, bottom 160, left 300, and
right 310 sides; and
a plane perpendicular to the primary direction of flow located 4 ft 9in from
the inside dimension
of the outlet end wall 150 in the upstream direction. The dimensions of the
outlet section 120,
exclusive of baffles, are equivalent to the dimensions of the inlet section
110, providing the
advantage of having the capability to cast inlet 110 and outlet 120 sections
using the same form.
One component of the outlet section 120, is a trapezoidal underflow baffle
260. In the
plan view (FIG. 1 and FIG. 6), the trapezoidal underflow baffle 260 desirably
consists of a center
segment parallel to the outlet end wall 150 and a pair of outer segments. The
center segment is
located desirably at least 2-ft, more desirably 3-ft, and, preferably 4-ft
from the outlet end wall
150 (inside dimension of end wall to upstream side of trapezoidal baffle 260).
The center
segment of the baffle 260 is centered with respect to the left 300 and right
310 sides of the
chamber. Preferably, the length of the center segment 260 is 1-ft and, as a
result, the distance
between the ends of the center segment of the baffle 260 and each wal1300 and
310 is 3-ft 3-in.
In the plan view, the trapezoidal baffle extends from the ends of the center
segment to the
corners defined by the intersection of the left side wall 300 and the outlet
end wall 150 and the
right side wall 310 and the outlet end wall 150. In the profile view (FIG. 2),
the trapezoidal
19
CA 02420148 2003-02-26
baffle 260 is located so that the bottom of the baffle 260 desirably is at
most 1-ft 11-in and,
preferably, 1-ft 6-in above the bottom of the chamber 160 (inside dimension).
The baffle 260
extends to the top of the chamber 140 and is joined to the top of the chamber
140 along the
trapezoidal-shaped top edge of the baffle 260 displayed in the plan view (FIG.
1 and FIG. 6).
The trapezoidal underflow baffle 260 desirably is also attached to the sides
of the apparatus 100
where the left and right sides 300 and 310, respectively, form corners with
the outlet end 150
from a distance, preferably, 1-ft 6-in above the bottom of the chamber 160
(inside dimension) to
the top of the chamber 140.
Initially, the inventors tested a simple, vertical underflow baffle with a
thickness of 3-in
that was positioned in a plane entirely perpendicular to the outlet end wall
150. This incarnation
of the underflow baffle was located a distance of 4-ft from the outlet end
wall 150 (inside
dimension of end wall to upstream side of underflow baffle) and resulted in an
area of 5.625 ft2
between the downstream end of the angled baffle 250 and the upstream side of
the underflow
baffle in the plan view (see FIG. 1). The inventors investigated the
trapezoidal underflow baffle
260 of the present invention for the purpose of decreasing the velocity of the
flow passing
through the plane between the downstream end of the angled baffle 250 and the
upstream side of
the underflow baffle 260 in the plan view. The area in the plan view between
the downstream
end of the angled baffle 250 and the upstream side of the underflow baffle 260
is preferably
18.625 ft2. Comparison of the areas between the underflow baffle and the
upstream angled
baffle 250 for the vertical underflow baffle configuration and the trapezoidal
underflow baffle
260 configuration indicates that for equivalent rates of flow passing between
the upstream angled
baffle 250 and the underflow baffle, the velocity for the vertical baffle
configuration preferably
would be 3.3 times greater than the velocity for the trapezoidal baffle 260
configuration. The
lower velocity attained using the trapezoidal baffle 260 configuration of the
present invention is
advantageous for protection from entrainment of pollutants residing on the
surface layer of the
midsections 130 into the flow from the midsection 130 to the outlet section
120. Desirably, the
angle between the center segment of the baffle and the outer segments of the
baffle is between
90 and 180, more desirably between 120 and 160 , and, preferably 130 .
Another component of the outlet section 120 is outlet screening 270 which is
designed to
keep trash and/or debris from clogging the outlet opening 280. The outlet
screening 270 consists
of fine screening or a fine mesh configured as a semi-circle, arch, rectangle,
or straight screen in
CA 02420148 2003-02-26
front of the outflow opening 280. The screening is attached to the outlet end
wall 150 a
horizontal distance in front of the outlet opening that is proportionate to
the outlet opening size,
but no less than 2 times the diameter of the outlet opening and to the bottom
160 and top 140 of
the chamber so that all water passing through the outflow opening 280 will
have first passed
through the screening 270. The screening 270 will be attached in a manner that
will permit
removal and cleaning of the screening via an access manhole 135 located in the
top of the outlet
section 120. The cover for the manhole 135 will be vented to allow exchange of
air between the
inside of the apparatus 100 and the surface atmosphere to abate development of
anoxic
conditions in the permanent pool and to relieve air pressure as the apparatus
fills and drains with
water.
The outflow opening 280, shown in FIG. 1, FIG. 2, and FIG. 4 is the device
controlling
the release of water from the apparatus 100. A detail of the outflow opening
280 components is
shown in FIG. 7. The outlet desirably consists of an 8-in diameter pipe 290,
desirably extending
from 3-in upstream of the outlet end wall 150 (inside dimension), through the
outlet end wall
150. The end of the pipe 290 that is inside the apparatus 100 desirably is
covered with an 8-in
cap 282. An opening 280 that is sized to provide a predetermined time for the
water in the
chamber to drain from the elevation at which the apparatus 100 is full to the
elevation of the
permanent pool is machined into the 8-in cap 282. The opening 280 is
manufactured so that the
lowest point of the opening is preferably at least V2-in above the lowest
point of the 8-in pipe 290
at the end where the cap 282 is attached.
An advantage of creating the outflow opening aperture 280 in a cap 282 that is
placed
over the end of the outflow pipe 290 that is inside the outlet chamber is that
the opening size can
be changed as desired during maintenance by replacing the cap 282 with another
cap 282 with a
different sized opening 280. This flexibility in opening 280 sizing is
advantageous for providing
an apparatus 100 that can provide an array of treatment levels. The opening
aperture size 284
dictates the time that water is detained in the apparatus 100. A smaller
opening aperture size 284
would result in detention of water for a longer period of time than that
afforded by a larger
opening size. The treatment efficiency of an apparatus 100 will increase as
the time that water is
detained increases. Therefore, the level of treatment can be adjusted by
increasing the opening
size (decreasing the level of treatment) or decreasing the opening size
(increasing the level of
treatment). Another advantage of the outflow opening configuration 280, is
that the positioning
21
CA 02420148 2003-02-26
of the opening invert, preferably, a distance of 2-ft 11-in above the bottom
160 and downstream
of all baffling 200, 220, 250, and 260 results in release of water with the
lowest sediment
concentrations through the opening 280. An outflow opening 280 positioned
lower than that in
the illustrated embodiment would draw more water from the lower part of the
outlet section 120,
which would contain more suspended sediments. An outflow opening 280
positioned higher
than that in the illustrated embodiment would result in a greater permanent
pool volume that
would need to be pumped out during maintenance.
The apparatus, being an off line type below grade structural stormwater
control device, in
one embodiment manages the recommended capture volume - sized for a mean
runoff event
following the sizing criteria as outlined in, for example, the "Urban Runoff
Quality
Management", WEF Manual of Practice No. 23, and ASCE Manual and Report on
Engineering
Practice No. 87 or other source known to one of ordinary skill in the art.
Storm events are, in one embodiment, handled by diverting that percentage of
stormwater
events from the site storm drainage collection system. The apparatus
advantageously provides
adequate time for the capture volume within the active pool for pollutants
with specific gravities
of lesser or greater than water to be captured within the hydraulically
designed plurality of
baffling within the permanent pool (i.e., permanent pool), reducing sediment
resuspension,
retaining floating debris and hydrocarbons, and trapping neutrally buoyant
trash.
As known to one of ordinary skill in the art, a mean runoff event is typically
defined, for
example, as the event resulting from the "mean storm precipitation depth,
which is the depth of
all runoff-producing storms (total precipitation of 2.5 mm or 0.10" or more)
from a long-term
precipitation record for a given location, using a six-hour separation to
define each storm event.
This "mean storm event capture volume" will typically result in the capture of
roughly 70% of
all runoff-producing events in their entirety or approximately a "two-year
storm," defined as a
stormwater event that occurs on average once every two years, or statistically
has a 50% chance
on average of occurring in a given year. Other methods for determining the
capture volume can
similarly be employed, depending on site requirements.
FIG. 9 illustrates one embodiment of the present invention, including an
external bypass
structure. In this embodiment, the apparatus 100 inflow rate is controlled by
a site-specific
designed control weir 410 housed within a bypass manhole 400 of the type well-
known to those
of ordinary skill in the art. Influent enters the system from a drainage
system, as well known to
22
CA 02420148 2003-02-26
one of skill in the art, from a sewer system main or, for example, an inflow
pipe 184. The
properly sized weir 410 diverts the site runoff into the apparatus 100 through
the apparatus
influent pipe 180. Bypass pipes 430 divert excess water volume beyond the
maximum capture
volume by diverting excess water volume over the control weir 410 and through
the bypass pipes
430. The bypass manhole 400 is typically accessed by an access manhole 135.
The energy dissipation baffle 200 is so located to diffixse and create a
laminar flow of the
turbulent high velocity stormwater runoff on entry into the apparatus 100. The
baffle is angled
to extend toward the front of the vault as it extends downward. The reduced
energy stormwater
is diverted in less turbulent lower velocity downward against the bottom of
the apparatus 100,
and under the energy dissipation baffle 200 to be directed upward by the
hybrid baffles 220. The
capture area between the energy dissipation baffle 200 and the: inlet end wall
provides an area for
the capture and retention of the larger and more buoyant trash. and debris, as
known in the art, in
a forebay trash compartment 440. This trash area is accessed via a manhole 135
for subsequent
collection and removal of sequestered debris via vacuum suction lift or other
mechanical means.
Advantageously, the forward angled energy dissipation baffle 200 permits easy
access via the
manhole 135 while providing additional energy dissipation.
The hybrid-baffles 220 (including, for example, 230, 240 and 250) are so
located with
respect to the energy dissipation baffle 200 to direct the initial and
subsequent stormwater inflow
in an upward direction thereby providing a laminar flow pattern in the active
pool 450 reducing
the turbulence in the inactive permanent pool 460 to near zero, thus
preventing resuspension of
previously settable materials. The available active pool 450 above the
permanent pool 460
provides a vertically stacked water column desirably sized to accommodate the
design capture
volume.
This ability to exploit the vertically stacked water column configuration
provided by the
preferably rectangular design of the apparatus 100 enhances the ability to
capture stormwater
runoff from a site. By simply selecting the appropriate water volume, the
apparatus 100 can
significantly reduce erosion and stream degradation from increased flows due
to urbanization
and help restore pre-development runoff rates. Due to an effective stacked
water column volume
control, the apparatus has superior pollution removal and retention
capabilities the apparatus
advantageously mitigates downstream erosion and riparian habitat degradation
through retaining
and slowly metering out the capture volume, through the properly sized outflow
opening aperture
23
CA 02420148 2003-02-26
284 installed within outlet opening 280, flow from each event.
Intermediate angled baffle(s) 220 are so arranged to provide optimum volume
and
sediment control spacing by maintaining the upward directional stability of
the stormwater
inflow. These sediment control baffles 220 advantageously provide an
uninterrupted quiescent
area of capture volume to sequester settable solids and pollutants, reducing
the probability of
resuspension during the introduction of stormwater into the apparatus. The
longitudinal spacing
of the angled baffle(s) 220 is preferably optimized to providle a minimum of
one manhole 135
access for every approximately 64 square feet of pollutant capture area for
subsequent collection
and removal of sequestered sediment and hydrocarbon material via vacuum
suction lift or
mechanical means. In one embodiment, the minimum size for the bypass manhole
400 is
typically around 36" by 36" square or, alternatively, 48" inside diameter.
There typically is a
30" minimum spacing between the bypass manhole 400, outlet box 470 and the
main tank 480 of
the apparatus 100 to allow sufficient space for the installation and sealing
of influent connection
pipes 180 and effluent connection pipes.
As known to one of ordinary skill in the art, the influent connection pipes
180, effluent
connection pipes 290, and bypass pipes 430 are typically supplied and cut to
proper length
depending on the topography, flow, and specific requirements of a particular
site. Similarly, the
dimensions of the apparatus will vary based on site requirements.
The decant period or drain down time is optimized to allow for the gravity
separation of
pollutants with either a specific gravity less than or greater than water. The
retention time of the
capture volume in the stacked water column provides a quiescent period for
enhanced settling,
and is consistent with recommendations shown in "Removal Rate vs. Detention
Time for
Stormwater Pollutants as defined in "Effectiveness of Extended Detention
Ponds" authored by
Grizzard et al., 1986 or other similar period recommendations as commonly
known to those of
skill in the art.
In one embodiment, the process capture volume stormwater flow rate is metered
by a
fixed aperture orifice 280 to insure proper retention of the capture volume
and regulate
maximum discharge flow rate. In one embodiment, a flow control orifice may be,
for example,
mounted in a sealed outlet tee fitting with a standpipe 490 top rim at such
elevation to prevent
flow "short circuiting" at maximum water levels.
The orifice 280 is desirably protected from neutrally buoyant material by a
removal
24
CA 02420148 2003-02-26
screen 270, which desirably typically includes a minimum net opening area of
about 25 to 50
times the opening of the orifice, and preferably about 35 times the opening of
the orifice. The
orifice 280, standpipe 490, and screen 270 are preferably constructed of non-
metallic non-
corrosive materials.
FIG. 10 provides an illustration of the apparatus, in one embodiment,
incorporating a
dynamic flow control orifice.
Unlike previous devices, the dynamic flow control orifice system 500 is a
moveable
orifice that differs from all other previous devices, as its primary purpose
is to control the time
for outflow of stormwater from said stormwater mitigation system, by
maintaining a constant
discharge rate throughout a majority of the discharge volLUne without
utilizing any outside
mechanical or electrical force or power. The dynamic flow control orifice
system 500 does so by
utilizing a properly sized and located orifice 510 within a buoyant floatation
collar 520 protected
from surface contamination via a solid shield 530 and from neutrally buoyant
materials by a
screen 540. A combination of gravity and buoyancy thus keeps the dynamic flow
control orifice
system at an advantageous position in the apparatus without outside influence,
while the height
of the orifice 510 is adjustable relative to the water surface by adjusting
the vertical distance
between the orifice 510 and the flotation collar 520. The vertical adjustment
of the orifice 510
advantageously maintains the predetermined discharge flow rate through the
great majority of
retained capture volume. The action arm 550 is typically pivoted on a non-
mechanical swing
joint 560 to arc through the entire vertical range of the retained capture
volume, and permits the
orifice to move with the water level. By comparison, a fixed outlet orifice
280 as shown in FIG.
9, for example, typically does not move with the vault water level.
The preferred construction material for this component is synthetic
hydrophobic material
with non-corrosive fasteners, however, any suitable material such as plastic,
fiberglass, and the
like are to be considered included within the description and application of
this apparatus. The
simplified gravity dynamic flow control orifice described presently herein can
advantageously be
applied to any water treatment system, including the embodiments described
herein and other
systems known to artisans of ordinary skill in the art.
FIG. 11 provides a detailed plan view of the apparatus, in one embodiment,
incorporating
an integral overflow bypass structure. In one embodiment, this stormwater
treatment apparatus
is an integrated system whereby the above mentioned bypass manhole 400, volume
control weir
CA 02420148 2003-02-26
410 and junction box 470 are combined and advantageously made integral within
the confines of
the stormwater treatment apparatus itself, as a typically unitary below grade
modular precast
concrete stormwater control and treatment device that is designed to manage
and treat
stormwater runoff by diverting the design water quality capture volume into
the apparatus as a
surcharged detention storage volume defined as the active pool and controlled
release of said
capture volume, with sediments stored in the permanent pool. The preferred
construction
material for all structural components is precast concrete however, any
suitable material such as
plastic, fiberglass, steel, cast in place concrete, and the like are
applicable to this apparatus.
The integral bypass structure apparatus utilizes a novel, properly sized
integral weir
appurtenance 410 to divert the predetermined design capture volume water
volume into the
modular apparatus 100 from a stormwater collection system connected by, for
example, a
collection system inflow pipe 184. This capture of the capture volume is
brought about by a
integral volume control diversion weir 410 that directs the design runoff into
the apparatus
through the apparatus inflow pipe 180, with a minimum hydraulic loss into the
apparatus 100.
Any subsequent flow beyond that of the design capture volume is allowed to
bypass the
apparatus 100 via the integral volume control diversion weir 410 returning to
the stormwater or
runoff collection system or receiving waters through a collection system
outflow pipe 292.
Stormwater treated by the apparatus is returned via a discharge pipe 280 to
the combination
junction box 470 / bypass manhole 400 for return to the stortnwater or runoff
collection system
or receiving waters through the collection system outflow pipe 292.
In one embodiment the integral bypass system is preferably configured with the
apparatus
100 aligned perpendicular to the collection stormdrain that is to be
intercepted. The bypass
headworks is advantageously configured to provide a minimum footprint, through
integration of
the bypass manhole 400 and junction box 470 with the entire apparatus, while
allowing for a
trash and debris collection assembly to be incorporated into the integrated
apparatus treatment
train. The size of the bypass headworks 400, junction 470 and integral weir
410 elevation
relative to the apparatus is typically established by the maximum design flow
rate in the
collection stormdrain that is to be intercepted. The headworks size typically
corresponds to the
minimum required for the integral weir 410 size, location and materials of the
stormdrain main
and inflow pipes 184. Depending on the topography of the stormwater collection
system for
which the apparatus 100.is going to be connected, the position of the
stormwater collection
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CA 02420148 2003-02-26
system inflow pipe 184 and stormwater collection system outflow pipe 292 may
be
advantageously altered and placed in different positions on the junction box
470 / bypass
manhole 400, as apparent to one of ordinary skill in the art, in order to
minimize the footprint of
the apparatus 100.
As would be apparent to one of ordinary skill in the art, the apparatus should
typically be
designed to withstand an AASHTO ("American Association of State Highway and
Transportation Officials") or ASTM ("American Society for Testing and
Materials") C 890 H-20
traffic loading with 1.0' - 6.0' of earth cover. The apparatus is flexible and
can be designed to
withstand other anticipated loads as designated by the site engineer and
specific site
requirements.
To ensure acceptable hydraulic loading rates, promotion of settling and
retention of
pollutants, and enable proper maintenance, the minimum permanent pool liquid
depth is typically
between 1' to 3', or larger for large embodiments of the apparatus. To provide
a minimum
hydraulic loading ratio in order to promote the settling of particles from the
stormwater flow,
there is typically a minimum of approximately one square foot of surface area
for about each
about 60 gallons of total liquid capacity.
The apparatus typically has a minimum of three access openings for
maintenance,
preferably at the inlet section, center section, and outlet section, but the
number of openings is
foreseen to vary based on site requirements. Openings typically have a minimum
clear opening
of about 30" in diameter, and are typically located over each compartment of
the apparatus.
There typically is an additional access opening for every about 8' of
interception length in the
center section of the apparatus. In one embodiment, there typically is an
additional access
opening on the bypass manhole and outlet box.
The disclosed apparatus offers the designer and the developer a new degree of
freedom in
solving a large number of stormwater quality problem situations. Most existing
structural
stormwater treatment systems rely on a flow through rate calculation to size
their technologies,
thereby not fully considering the hydraulic or water quality impacts on the
receiving waters. The
method, as defined in "Urban Runoff Quality Management," WEF Manual of
Practice No. 23,
and ASCE Manual and Report on Engineering Practice No. 87, addresses these
concerns. Those
concerns have previously defied reasonable economical solutions using
previously available
27
CA 02420148 2003-02-26
structura.l stormwater mitigation systems, but are advantageously resolved by
the present
apparatus.
This method may also be modified, as known to artisans of ordinary skill, for
example, to
allow sizing of the capture volume using the mean runoff volume as defined,
for instance, by
Discroll, et al. 1989 and to accommodate an approximate recommended six hour
drain down
time.
The capture volume stacked water column provides the most efficient use of
available
system footprint. Owing to this feature, the apparatus typically requires a
minimum of about
three feet, and preferably about five feet, of vertical temporary water
storage capacity, as
apparent to artisans of ordinary skill. This temporary stacked water column is
accomplished in
the standard apparatus arrangements by use of a bypass weir sized to provide a
minimum of
backwater while insuring the full capture volume potential of the selected
vault. Alternate
system configurations accomplish the stacked water column configuration by
providing the
necessary vertical separation within the stormdrain piping system itself or by
using a pumped
system. These systems can use, for example, an external bypass, an internal
bypass, a surface
bypass, pumped discharge, and/or a bypass with a fall system.
As is typically known to those of skill in the art, the external apparatus
"bypass with
weir" configuration is advantageously with the vault aligned parallel to and
offset approximately
three feet clear from the collection stormdrain that is to be intercepted. The
bypass manhole is,
in one embodiment, located approximately eight feet up gradient from the
apparatus influent.
The size of the bypass manhole and weir elevation relative to the apparatus is
typically
established by the maximum design flow rate in the collection stormdrain that
is to be
intercepted.
For example, in one embodiment, as familiar to one of skill in the art, the
influent pipe
typically has a minimum of about 1% slope to the apparatus, and is preferably
constructed of
SDR-35 PVC. The influent pipe typically exits the bypass manhole at about 45
degrees to the
stormdrain flowline with, in one embodiment, a 1/8-turn elbow located near the
apparatus. The
effluent pipe is typically about 8" SDR 35 PVC and has a slope at about 1%
from the apparatus
to the junction box, sized equivalent to the bypass manhole. The orifice
operating head is
typically calculated from the vault soffit to the springline of the effluent
pipe. Due to the fact
that the apparatus operates with a surcharge water column, all pipe sizes and
angles are based on
28
CA 02420148 2003-02-26
smooth wall SDR 35 PVC pipe in order to advantageously provide a flexible
watertight
connections a all penetrations. However, other constructions are also useable
based on specific
site conditions and requirements, as known to artisans of ordinary skill in
the art.
A junction box is, in one embodiment and as familiar to one of skill in the
art,
approximately parallel, approximately 3 feet clear from the collection
stormdrain, and
approximately 8 feet down gradient from the apparatus effluent. The size of
the junction box is
established by the design flow rate in the collection stormdrain, maximum pipe
size penetrations
and relative piping angles, and is similar to those typically used for the
"bypass manhole."
The "bypass with fall" arrangement is similar to the standard configuration
with regard to
the bypass manhole, junction box and influent / effluent pipe sizes. However,
the bypass
manhole does not require a weir in this arrangement. The orifice operating
head is calculated
from the vault soffit to the springline of the effluent pipe.
The "pumped discharge" arrangement is also similar to the standard
configuration with
the bypass manhole, by-pass pipe elevation and junction box, except that the
effluent is
discharged through a duplex pump system uniquely designed to be contained
within the
apparatus or junction box.
The pump positive operating head is calculated from the vault soffit. The pump
discharge rate is calculated based on the outflow rate form the apparatus.
The "surface by-pass" is unique in that because by definition the flowline of
the storm
drainage is on surface above the apparatus. The orifice operating head is
calculated from the
surface hydraulic grade line to the springline of the effluent pipe. While
this arrangement does
not require a dedicated bypass manhole or junction box it does require a drop
inlet or catch basin
at similar locations to the turning manholes as shown on the "overflow with
weir" arrangement.
The preferred "standard internal bypass" configuration, as shown in FIG 10, is
with the
vault aligned perpendicular to the collection stormdrain that is to be
intercepted. The bypass
headworks is so configured to provide a minimum footprint while allowing for a
trash and debris
collection assembly to be incorporated into the apparatus treatinent train.
The size of the bypass
headworks and weir elevation relative to the apparatus shall be established by
the maximum
design flow rate in the collection stormdrain that is to be intercepted. The
headworks size
corresponds to the minimum required for the size, location and materials of
the stormdrain main
and influent pipes. The orifice operating head is calculated from the vault
soffit to the springline
29
CA 02420148 2003-02-26
of the effluent pipe.
The description given herein describes particular embodiments of the present
apparatus,
and other embodiments are foreseen and included herein and can be adapted by
artisans of
ordinary skill in the art, such that the present invention should be defined
only by the following
claims and equivalents thereof.
