US20020057944A1

US20020057944A1 - Storm water inlet pollution trap

Info

Publication number: US20020057944A1
Application number: US09/844,487
Authority: US
Inventors: Jeff Adams; Jay Jantzen; Diana Loudenslager
Original assignee: Oklahoma State University
Current assignee: Oklahoma State University
Priority date: 2000-04-29
Filing date: 2001-04-27
Publication date: 2002-05-16
Also published as: WO2001083900A1; AU2001259247A1

Abstract

Pollutants are captured at a particular point of entrance into a storm water runoff system, such as at curb inlets. An inventive device takes advantage of existing storage volume within storm water inlets and is installed therein with little or no retrofitting necessary to secure the device. Storm water enters the apparatus where water energy is reduced and flow length is increased, increasing water detention time and allowing for the removal of soil sediment, floating debris, hydrocarbons and other pollutants utilizing settling tendencies and trapping areas. A damping system reduces pollutant resuspension and redirects high flows away from deposited sediment.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of prior filed, copending U.S. provisional patent application Ser. No. 60/200,694, filed 29 Apr. 2000.[0001]

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a pollution control apparatus, and, more specifically, to an apparatus for attachment to a storm water inlet, such as a curbside inlet, for collecting storm water pollution, such as sediment, floating debris and floating residues, from storm water runoff.

2. Background

It has been reported that forty percent of our nation's rivers, lakes and streams are considered unfit for fishing, swimming, drinking or aquatic life. Urban streams have substantially more problems because high sediment loads affect many aspects of water quality, including water temperature, pH, total suspended solids, total dissolved solids, nutrients, metals, pesticides, and bacteria. Sediment loads from lands undergoing urbanization are up to 50 times more than those in rural areas. It is excessive sediment, generated as anthropogenic waste, that often overwhelms the “assimilative capacity” of a stream and damages its biological components.

A primary cause of diminished water quality is urban storm water runoff. Urban runoff is a pollutant that consists of soil sediment, floating organic matter, floating man-made debris, chemicals, and other residues. The quality of urban runoff is thus an important issue due to the negative effects it can have on ecological systems and water body volume. Urban runoff carries large amounts of soil sediment which increases the turbidity of water, causes siltation of reservoirs, lakes and ponds, and ultimately adversely impacts aquatic plants, invertebrates and fish.

One of the greatest contributors to sediment entering storm water systems comes from construction sites, where soil is exposed and can easily erode and be transported into the drainage system. The major problem at construction sites is the period of time that disturbed surfaces lay exposed, more than a year at 25% of the sites. Most cities have the authority to regulate construction sites to make sure they are complying with regulations to reduce the amount of sediment coming from the sites. Covering exposed soil, setting up filter fences and straw bales, reseeding exposed soil and using gravel at exits and entrances are all practices used to reduce soil erosion from construction sites.

Soil can also be distributed throughout a city on rooftops and on streets by wind. Having a combination of high winds and large amounts of agricultural land in more rural areas sets up the conditions for large amounts of soil to be deposited on streets throughout a city. The soil is then washed into the storm water system in a rain event.

Soil can also come from the thousands of vehicles that travel the streets. Vehicles collect soil from back roads and alleys, then transport it to the city streets, where the soil can easily be washed into the storm water systems. Soil contributors come from many different places, and the same is true with contributors of municipal trash and debris that enters the storm water systems.

Municipal trash is especially difficult to eliminate because of the wide variety of contributing sources. Municipal trash has several opportunities to slip through the sanitation removal system. For example, animals, weather, and people all add to the enormous amount of trash that is available to be carried into a storm water system. In addition to sediment and municipal trash, natural debris like tree limbs, grass clippings, and leaves, contribute to the problems in storm water systems.

There are many other sources and types of pollutants that enter urban runoff. Petroleum products, fertilizers, chemicals, pesticides, and fecal bacteria are all pollutants found in urban runoff. The key contributor to all of these pollutants is man and his mishandling and misuse of products.

Many cities are actively seeking procedures and devices that can improve the quality of storm water runoff. The problem is currently being addressed in two principal ways. First, most cities regulate construction sites. Regulation ensures that construction sites have the proper erosion control devices installed to limit the amount of soil coming from a construction site, both from water flow and from traffic flow. Second, significant funds are expended on cleaning city streets with sweepers and manually cleaning out storm water inlets. Due, however, to budget and manpower constraints only a minimal level of maintenance is generally performed, enough only to keep storm water systems functioning.

The current control methods fall drastically short of meeting pollution control goals. Present methods do not stop any sediment or debris present in runoff streams from entering and passing through the storm water system nor do they serve to remove or filter any floatable contaminants. In addition, current systems do not allow for an easy and efficient clean out method.

The optimum improvement to the quality of storm water runoff would consist of eliminating the aforementioned pollutants while maintaining high flow rates to eliminate flooding potential, recognizing that there will be an expected variation in the degree to which any or all of the pollutants can be removed and to what degree the flowability in the system can be maintained.

It is thus an object of the present invention to provide a device that will effectively remove a large portion of the pollutants entering a storm water runoff system while maintaining a high level of flowability in the system.

It is a further object of the invention that the device be simple to construct, install and maintain as well as effective in trapping pollutants entering storm water sewer systems.

SUMMARY OF THE INVENTION

These and other objects are achieved by capturing pollutants at a particular point of entrance into a storm water runoff system, such as, for example, at curb inlets. The inventive device takes advantage of existing storage volume within storm water inlets and is installed therein with little or no retrofitting necessary to secure the device. Storm water enters the apparatus where water energy is reduced and flow length is increased, increasing water detention time and allowing for the removal of soil sediment, floating debris, hydrocarbons and other pollutants utilizing settling tendencies and trapping areas. A damping system reduces pollutant resuspension and redirects high flows away from deposited sediment.

Thus, in accordance with the objects of the invention there is provided a method for water detention within a storm water sewer system to allow for the trapping and collection of soil sediment, floating debris, hydrocarbons and other pollutants wherein a waste water stream is routed to a housing suspended below a storm water inlet wherein, depending upon the amount of flow, the stream follows one of two possible flow paths. In low flow conditions the stream is directed such that its flow length and retention time within the housing is increased, thus allowing for the settling out of sediment and for the capture of floating debris and residues. In high flow conditions the stream is diverted to an alternate shorter flow path out of the housing so as not to cause a resuspension of collected sediment.

A preferred trapping device for use in accomplishing the aforedescribed method includes a two piece housing consisting of front and back portions slidably received together to form a generally rectangular structure to accommodate a common configuration of a storm drain. The device may be shaped so as to conform to other common storm drain configurations or may be specially adapted to fit particular applications. Accordingly, the particular shape of the housing can be varied as needed to complement, for example, round or square drains. For illustrative purposes, the following description will refer as an example to a device for use under a generally rectangular curb inlet.

A top, hopper-type portion of the device is provided with a lip, being appropriately sized and adapted to be engaged between the lip of the curb inlet grate and the ledge upon which the grate typically rests. The length of the device is such that it is suspended beneath the grate within the curb inlet so as not to impede water flow beneath the structure.

Water flowing through the grate is directed by an upper surface of the housing into a first detention area within the housing whereupon, under low flow conditions, the water proceeds through a damper into a second larger detention area defined by the walls of the housing. The sediment laden water has a relatively long residency time in the second detention area, thus allowing sediments to settle out from the water. The damper serves to increase the flow length of the sediment laden water stream and minimizes resuspension of sediments contained in the second detention area. Flow between the first and second detention areas is controlled through the adjustment of the damper. In the preferred embodiment, the damper comprises overlapping plates and the degree of separation between the plates controls the flow rate between the first and second detention areas. As the water level rises in the second detention area it climbs upward along the walls of the housing where it eventually advances through a fluid passageway located between the first detention area and the walls of the housing. The water exits the housing through apertures located in the housing walls. The exit points are vertically spaced at a point below the water head in the first detention area so that floating debris and residues are trapped in the first detention area above the exit points.

During high flow conditions, when the rate of water flow into the first detention area surpasses the maximum rate of flow through the damper, water overflows the first detention area to be released through the exit points in the walls of the housing. In this manner, resuspension of the sediments captured in the second detention area is avoided.

The inventive device is maintained by periodic removal of the trapped pollutants. Access is afforded to the interior of the device through the removal of the curb inlet grate, whereupon the pollutants are removed by vacuum suction or other means.

The inventive device is simple and has no moving parts that will wear out, break or reduce efficiency over time. It can easily be adapted into any existing curb inlet or other storm water inlet and optimizes storage volume while maintaining a flow path long enough for adequate efficiency. Pollutant removal is easily accomplished, and the device is very cost effective and manageable.

A better understanding of the present invention, its several aspects, and its objects and advantages will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the attached drawings, wherein there is shown and described the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a general embodiment of the present invention. [0026]
FIG. 2 is an exploded view of the components of the device of FIG. 1. [0027]
FIGS. [0028] 3A-G are partial cross sectional views of an upper portion of a general embodiment of the present invention.
FIG. 4 is a perspective view of the inventive device shown installed in its typical environment. [0029]
FIG. 5 is a perspective view of the preferred embodiment of the inventive device. [0030]
FIG. 6 is a perspective view of the front piece of the device of FIG. 5. [0031]
FIG. 7 is a perspective view of the back piece of the device of FIG. 5.[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The main objective of the preferred embodiment of the invention is to remove soil sediment, floating debris, and a limited amount of floating residues from storm water runoff. The floating residues that the device addresses are primarily floating hydrocarbons deposited on streets and parking lots from vehicular oil leaks. The floating debris is generally a combination of man-made trash and organic material such as leaves, grass clippings, and tree limbs. The trapping of soil sediment focuses on the larger sizes of silt and sand. Before explaining the preferred embodiment in detail, however, it is important to understand that the invention is not limited in its application to the details of the construction illustrated and the steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. [0033]
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and particularly referring to FIGS. [0034] 1-3, the inventive device 10, shown generally in a fully assembled condition, has a front 12 and a back 14. The device 10 comprises a housing 16 consisting of two side panels 18, 20, a back panel 22, and a front panel 24 to form a generally rectangular structure. The device 10 may be of a unitary structure or comprise a multi-piece design, such as the particularly preferred two-piece embodiment described in detail below. The purpose of FIGS. 1-3 is to provide a general description of the salient features of the invention.
One or more of the panels are provided with [0035] apertures 25 which serve as water exit points. The size of the apertures 25 are calculated to release the maximum flow rate known for the inlet to which it is attached. At the top portion of the device 10 there is an upper surface comprising a hopper 26 formed of a plurality of angled surfaces 28. The hopper 26 is provided with a lip 46, being appropriately sized and adapted to be engaged between the lip of a curb inlet grate and the ledge upon which the grate typically rests. The length of the device 10 is such that it is suspended beneath the grate within the storm water drain so as not to impede water flow from the bottom of the drain into the storm water system piping.
In addition to supporting the [0036] device 10 in a suspended position under the inlet grate, the hopper 26 and angled surfaces 28 function to lengthen the flow path of the device 10 and to direct water flowing through the grate into a first detention area 34. A set of vertical fins 30 affixed at the terminus of the angled surfaces 28 extends the flow path vertically to within the first detention area 34 while maintaining adequate dimensions between the side panels 18, 20 and front panel 24, the purpose of which will become evident from the ensuing description. The vertical fins 30 extend downward in the device 10 to a point below the apertures 25 in the side and front panels 18, 20, 24.
The [0037] first detention area 34 is created within the bounds of diverter 32, a pair of blockers 36 and damper 38. The diverter 32, shown formed from three segments, separates the first detention area 34 from the side and front panels of the housing. The diverter 32 extends above the level of apertures 25 in order than the water head in the first detention area 34 be maintained above the level of the apertures 25. This allows floating debris and residues to remain above the exit point of the device and within the first detention area 34 under low flow conditions. The blockers 36 are fixed between the vertical fins 30 and the side panels 18, 20 to prevent the flow of water around the diverter 32 and through the apertures 25 and to provide added structural integrity. The diverter 32 may be tacked to side panels 18, 20 and front panel 24 for support. The damper 38, shown as overlapping plates 40, 42 serves to separate the first detention area 34 from a larger second detention area 44. The height of the diverter 32 may be varied relative to the aperatures 25 to alter flow characteristics.
Water flowing through the inlet is directed by [0038] angled surfaces 28 at the top of the housing 16 into the first detention area 34 whereupon, under low flow conditions, the water proceeds through the damper 38 into the second larger detention area 44. The sediment laden water has a relatively long residency time in the second detention area 44. The allowable flow through the damper 38 may be adjusted, but in the preferred embodiment the distance between the plates 40, 42 comprising the damper is about 2.5 to 3 inches which, considering the other dimensions of the structure, allows for a flow rate of approximately one cubic foot per second (cfs). As the water level rises in the second detention area 44 it climbs upward through a fluid passageway 45 provided between the diverter 32 and side and front panels 18,20,24. The outflow pattern from the second detention area 44 is shown with a dotted arrow in FIG. 3F. The rising water from the second detention area 44 leaves the device through apertures 25.
During high flow conditions, when the rate of water flow into the [0039] first detention area 34 surpasses the maximum rate of flow through the damper 38, water overflows the first detention area 34 over diverter 32 to be released through the apertures 25 in the side and front panels of the housing 16. The outflow path under high flow conditions is illustrated in FIG. 3F with a solid arrow. Having this alternate flow path for high flow conditions reduces resuspension of the sediment that has settled out of the water within second detention area 44 by limiting the amount of flow that passes through the second detention area during periods of high volume runoff.
The inventive device is maintained by periodic removal of trapped pollutants. Access is afforded to the interior of the [0040] device 10 through the removal of the inlet grate, whereupon the pollutants may be removed by vacuum suction, scooping or other means. It is contemplated that a trap door may be designed into the damper 38, such as a door having a handle and a magnetic latching system, to provide easier access into the second detention area 44. The bottom of the housing 16 might also be rounded for ease of maintenance. It is further contemplated that weep holes might be located along the side of the device 10 (covered by a shield) allowing for standing water to escape the device without releasing sediment.
FIGS. [0041] 5-7 illustrate a particularly preferred two piece device. The two piece device consists of a front piece 100 and a back piece 102. The back piece is provided with a tube 104 along each of its vertical mating edges into which the rod 106 of the front piece 100 may be slidably received. FIG. 6 best illustrates the structure of the front piece 100 wherein, as it has been previously described, there is provided hopper 126, vertical fins 130, lip 146, apertures 125, diverter 132, blockers 136 and damper 138.
As shown best in FIG. 7, [0042] back piece 102 possesses two plates 140, 142 which, along with plate 141 in the front piece 100, comprise the damper 138. It will be noted that plate 140 in the back piece 102 mates with plate 141 in the front piece 100. The degree of separation between plate 140 and plate 142 controls the flow rate from the first detention area 134 to the second detention area 144.
Typical installation of the device will be described in relation to FIG. 4. The device is dimensioned so that its lip may be engaged between the storm [0043] water inlet grate 48 and the ledge 50 upon which the grate 48 rests. The length of the device is such that it is suspended beneath the grate 48 within the storm water drain 52 so as not to impede water flow from the bottom of the drain 52 into the storm water piping system 54. With reference to the preferred embodiment described above, it would be typical to remove the grate 48 in order to first insert the back piece 102 of the device through the opening into the drain 52, whereupon the lip of the back piece is positioned upon a ledge on the curb side of the drain 52. It is common that the curb side of the drain is inset somewhat so that what will be seen from above after insertion of the back piece are basically the mounting tubes 104. The front piece 100 is then similar inserted through the opening so that its mounting rods 106 are slidably received in tubes 104 and the lip of the front piece is positioned upon a ledge on the street side of the drain 52. The grate 48 is then replaced, and the device is thus suspended for operation. Other suspension means such as hooks, hangers and other fasteners also may be utilized if so desired.
It should be further recognized that the aforedescribed description and drawings refer to a device for installation on the left side of a curb inlet. Center and right side devices are, of course, within the scope of the invention. [0044]
The type of material used in the construction of the device may be varied according to strength, durability and thickness requirements and the overall acceptable cost of manufacture. A prototype device was constructed of plexiglass but it is anticipated that a low cost nylon molded product could be used for commercialization, with other suitable materials including fiberglass, metals or heavy duty plastics such as polyethlene. [0045]
The details of the construction illustrated and described above in connection with the preferred embodiment of the invention may be modified by one skilled in the art to achieve particular desired operating parameters and pollutant removal efficiencies. The pollutants that are being addressed can only be effectively captured within a given range of parameters. The design parameters include: concentration of pollutant, flow rate of runoff, and limited flow restrictions. Pollutants have different environmental impacts depending on their concentration and potency. For example, 100 grams of soil sediment will not have the same environmental impact as 100 grams of motor oil. Because of the different environmental impacts, water quality standards are set in place by organizations such as the Environmental Protection Agency (EPA) to monitor storm water runoff quality. The storm water is monitored for pollutants that exceed set concentrations. One quart of motor oil has the potential to contaminate 250,000 gallons of water based on the water quality set by the EPA (City of Laguna, 2000). Accordingly, small amounts of motor oil or other hydrocarbons have the potential to cause large environmental problems. [0046]
For example, the components of the device may be arranged and dimensioned to vary the efficiency of removing soil sediment from storm water. Removing soil sediment is a process that is governed by Stoke's law. Stoke's law is an equation used to determine the settling velocity of particles based off of the particle size: [0047]
Vs={fraction (1/18)}[(d ² /v)*(SG−1)],
wherein [0048]
Vs=settling velocity; [0049]
d=particle diameter; [0050]
g=gravitational constant; [0051]
v=kinematic viscosity; and [0052]
SG=specific gravity of the particles. [0053]

Using a SG of 2.65 and assuming quiescent water at 68° F., the Stoke's law equation reduces to: Vs=2.81d ². Using the following USDA table for particle sizes <2 mm in diameter, the resulting settling velocity for various classes of sediment can be calculated.



	CLASS	SIZE (diameter)

	Very coarse sand	2.0-1.0 mm
	Coarse sand	1.0-0.5 mm
	Medium sand	0.5-0.25 mm
	Fine sand	0.25-0.10 mm
	Very fine sand	0.10-0.05 mm
	Silt	0.05-0.002 mm
	Clay	<0.002 mm

Knowing the calculated settling velocities enables further calculations to be made to determine what theoretical particle size can be removed for a given flow length and flow rate. The maximum flow rates for typical curb inlets are given below. [0055]

max flow flow rate flow rate

# of curb inlets rate(cfs) curb(cfs) grate(cfs)

1 4.1 2.5 1.6

2 8.2 5 3.2
The max flow rate for a single inlet is equal to 4.1 cubic feet per second (cfs). Using the maximum flow rate in units of cubit feet per second and dividing the flow rate by the flow area, given in feet squared, the flow velocity can be calculated having units of feet per second. After obtaining the flow velocity, a flow length can be established that will allow the time needed, based off the settling velocity, for a certain particle size to settle out of the flow path. [0056]
To determine the actual particle size that will settle out of the flow, one skilled in the art will know to determine how far from the main flow path the particle will have to be before it will settle out of the flow stream. The size of the device, constrained by the curb inlet opening, also must be taken into account which limits the use of optimal longer flow lengths. A flow capacity that will allow efficient sediment removal without adversely affecting resuspension must also be determined. [0057]
Calculations can be made to size various parts to achieve the required flow rates. The required flow rates are based on the amount of maximum flow the device must pass and the amount of flow the device will direct through a longer flow path. The flow calculations may be made, for example, using the following weir and orifice flow equations: [0058]
Weir Flow [0059]
Q=CLH ^{({fraction (3/2)})},
wherein [0060]
Q=flow rate in cubic feet per second; [0061]
L=weir length in feet; and [0062]
H=head in feet. [0063]
The weir flow calculations are used to determine the length and height that is needed to pass the max flow and the redirected flow. [0064]
Orifice Flow [0065]
Q=C′A(2gH)^(½),
wherein [0066]
Q=flow rate in cubic feet per second; [0067]
A=cross-sectional area of the orifice in square feet; [0068]
g=gravitational constant; [0069]
H=the head on the orifice; and [0070]
C′=the orifices coefficient. [0071]
The orifice equation is used to calculate the height, given a length, which will pass the redirected lower flow. [0072]
With reference to the trapping of floating pollutants and floating debris, the construction of the components of the device may be arranged and dimensioned to vary the size and placement of storage areas to allow for the inflow of floating pollutants and debris but to otherwise separate the storage areas from the direct flow path of the water to avoid the submergence of the pollutants into the water stream. [0073]
The present invention will be further understood with reference to the following non-limiting experimental example. [0074]

EXAMPLE

A full-scale prototype was designed to simulate hydraulic characteristics, pollutant removal efficiency, and maximum flow capacity. The prototype testing was divided into two specific setups. First, a setup was used that allowed soil to be introduced into the device at a known concentration at relatively low flows ranging from 0.2 to 0.6 cubic feet per second. A second setup was used to introduce high flow rates ranging from 3 to 4.1 cubic feet per second. The second setup did not introduce additional soil; it was used primarily to insure that the maximum design capacity would pass through the device. [0075]
Before the prototype testing proceeded, many testing considerations were addressed. The considerations included the concentration of the soil and water mix, the flow rates, the duration of a testing event, the water entrance conditions, and the types of soil that would be introduced to the mix. A concentration of 3000 mg/l was determined for the soil and water mixture. The concentration of 3000 mg/l was determined based earlier studies in which samples of sediment-laden water were collected and 3000 mg/l was the maximum concentration encountered. [0076]
To address flow rates, an assumption of a critical flow rate was made. The critical flow rate is the flow that allows adequate sediment removal without resuspending the settled particles. A critical flow rate of 1 cfs was used. This flow rate governed the equations used to calculate the dimensions of the prototype. The dimensions, calculated using 1 cfs as the critical flow, are the dimensions of orifices and weir heights that restrict the flow through the sediment detention area to under 1 cfs. Test flows of 0.2, 0.4, and 0.6 cfs were used in the sediment laden water test. These flows were used because they represent the target range for most efficient sediment capturing, and the sediment laden water test was restricted by a maximum of 0.7 cfs. The flow of the maximum capacity test was simply placed at the maximum design flow of 4.1 cfs to insure the device could pass the maximum flow. [0077]
The duration of a testing event was calculated based upon of three pieces of data. First, the maximum flow encountered by a single curb inlet is 4.1 cubic feet per second (cfs). Second, the assumption was made that the maximum flow was encountered during a one hour, one hundred-year flood event. Third, the amount of runoff needed for wash-off is 0.2 inches. The one hour, one hundred-year flood event produces an intensity of 4.1 inches per hour (Haan, Barfield, Hayes, 1994). To produce a flow of 4.1 cfs, an intensity of 4.1 inches per hour must be distributed over 0.99 acres. Using the calculated area, the 0.2 inch wash-off amount, and a predetermined test flow rate, the duration of a test event can be calculated. The duration calculated is the duration needed to produce the volume of water that would be produced from 0.2 inches of rainfall over the calculated area with the given concentration of 3000 mg/l. [0078]
The sediment-laden water was introduced to the device using a mockup of a curb inlet. The mockup was used to insure that entrance conditions were similar to real world conditions. The water was introduced into a cavity that would distribute a gradient of sheet flow with the deepest area being next to the curb and the shallow area extending away from the curb. [0079]
There were two types of soil tested, with one of the soils being introduced with two different characteristics. The first soil type tested was a red clay soil. The soil was prepared from a stockpile of soil. It was sieved using a # 8 sieve. The process of sieving eliminated large aggregate, which aided distributing the proper rate of soil into the water flow. The red clay soil was introduced at a moisture content of 1% and at a moisture content of 10.7%. The difference in moisture content introduced a variance in the amount of aggregate the soils possessed. The amount of aggregate effected the dispersion of the soil in the water. An increase in dispersion reduces the capturing efficiency of the device because the effective particle size is reduced. The second soil tested was a sandy soil. The sandy soil was introduced to compare two very contrasting soil types. [0080]
The testing procedure for the sediment-laden water was a 6-step process. The first step was to determine the soil moisture content (MC) of the soil sample. The soil moisture data is important in determining the mass of soil that needs to be introduced into the water. In order to an equivalent weight of dry soil, it takes more soil at a higher moisture content than soil at a lower moisture content. The concentration of 3000 mg/l is equivalent to 3000 mg of dry soil (0% MC) in one liter of water. Knowing the soil moisture content allows the mass of soil to be adjusted to allow for the proper concentration. The second step was to calculate the flow time and amount of soil to introduce for each flow rate. For each flow rate (0.2, 0.4, and 0.6 cfs), the total volume of water used and the total mass of soil used remains constant. The variables in the test were the duration and rate of soil introduction. The third step was to place the device onto the scales that measure the change in weight of the device. The scales and device were then placed in position under the curb mockup and the device was filled with water and weighed. The fourth step was to calibrate the flow of water using a combination of a known size orifice plate and its corresponding manometer differential. For a given size orifice plate, a valve can be adjusted that changes the manometer differential. Once a target differential was reached that corresponds to the test flow rate, the test was ready to begin. The fifth step was to introduce soil at the given rate for the calculated duration. The soil was introduced into the [0081] water flow 30 ft. before the device. The 30-foot distance allowed the soil to become adequately mixed before it entered the device. The soil was metered into the device by introducing a known mass of soil into the stream every minute for the duration of the test. The final step was to stop the flow and let the water drain to the same level as measured previously. When the water was at the previously measured level, the weight of the device was measured.
Using the sediment-laden setup, other properties of the device were examined. The removal of floating pollutants was another performance characteristic the device was designed to address. To simulate motor oil as an environmental pollutant, mineral oil was placed into the water flow. The device is designed to keep the floating residue out of the direct flow path. The mineral oil was placed into the flow stream then the flow rate was increased from 0 cfs until the turbulence became to high to capture the oil. When the turbulence became too high the oil was submerged into the flow path and exited the device. The threshold for capturing oil was found to be 0.5 cfs. [0082]
Floating debris (domestic trash and grass clippings) was also introduced into the device to allow visual inspection of the flow characteristics of the floating debris. Much of the floating debris was successfully captured in the device. The flow path allows for larger debris (3″), to pass into the storage area, but the outlet from the storage area is reduced to 1 inch. [0083]
The testing procedure for the maximum flow capacity was set up to test two characteristics. The first, and primary, goal was to insure the device could pass the maximum design flow of 4.1 cfs. The second goal was to see how maximum flow conditions affect previously settled particles. The testing was set up in a channel that allowed the introduction of high flows. Once the device was lowered into the channel, sand particles were placed in the bottom of the device to see whether the sand particles would become resuspended. After the device was filled with sand, a flow of 4.1 cfs was introduced to the device. The flow was maintained for 10 minutes. The final procedure was to drain the device and visually insure that no sediment was lost during high flows. [0084]

Experimental Results

Five (5) different sediment-laden test were run under various conditions. The following table is a summary of the data collected from the sediment-laden tests. After each test, a change in weight was found by subtracting the final weight from the initial weight. The change in weight is proportionally related to the mass of soil collected. There is a difference because the soil particles that displace the water and water have different densities. The conversion from the change in weight to the actual mass of soil collected can be calculated from the following equation: [0085]
Weight of soil trapped=ΔW * (SGsoil/(SGsoil−SGwater)),
wherein [0086]
SG=specific gravity; [0087]
SGoil=2.65; and [0088]
SGwater=1. [0089]

Particle densities for most mineral soils vary between the narrow limits of 2.60 to 2.75 g/cm ³. A particle density of 2.65 may be assumed if the actual particle density is not known (Brady & Weil, 1999). Clay and sand samples were measured by mass and placed in a known volume of water to calculate the particle density. Particle density was calculated on the sand and clay soil samples, and the densities ranged from 2.54 to 2.66 g/cm³. Since there was such a narrow range in densities, the assumption of 2.65 g/cm³was used as the particle density for both soil types.



	SOIL	FLOW	DURATION	MASS OF SOIL
TEST #	TYPE	RATE (cfs)	(min)	INTRODUCED	MC soil

1	WET CLAY	0.6	15.40	107.5	10.73%
2	WET CLAY	0.4	33.25	149.0	10.73%
3	WET CLAY	0.2	50.00	111.5	10.73%
4	DRY CLAY	0.4	15.00	68.4	1.00%
5	SAND	0.4	16.60	62.7	2.32%

		CONCENTRA-
	MASS OF	TION	DELTA WEIGHT	MASS OF SOIL
TEST #	DRY SOIL	(mg/l)	OF DEVICE	TRAPPED	% EFFICIENCY

1	95.97	2772.9	50	80.30	83.00%
2	133.01	2669.9	66	106.30	79.00%
3	99.5	2656.4	45	72.50	73.00%
4	67.72	3013.3	9	14.50	21.00%
5	61.25	2462.7	32	51.52	84.00%

The particle size distribution of the soil entering the device compared to the particle size distribution that remains in the device can be a very instrumental comparison. Knowing the capability of the device on a particle size basis enables the efficiency of the device to be projected to a multitude of soil types. [0091]
One procedure for conducting such a particle size analysis involves passing a measured amount of a soil sample (such as 65 grams of silt or clay soil or 115 grams of sandy soil) through a #4 and #10 sieve, whereupon the mass of the soil retained is measured and recorded. The soil that passes through the #10 sieve is soaked in a solution of sodium hexametaphosphate solution for 16 hours to aid in the dispersion of soil aggregate. The solution is then added to a glass sedimentation cylinder and demineralized water is added until the total volume is equal to 1000 ml. The 1000-ml solution is stirred to ensure the particles are adequately dispersed and the hydrometer is immediately placed into the solution. Hydrometer readings are taken at 15, 30, 60, and 120 seconds and at 5, 15, 30, 60, 240, and 1440 minutes. The hydrometer and sieving procedures produce values that are usable to calculate particle sizes in mm and the percentage of finer particle sizes contained in the sample. [0092]

Device Maintenance

The maintenance on any single device can vary greatly depending on a number of variables, including sediment concentration and rain events and intensities. For example, Oklahoma City encompasses an area of 650 square miles. Within this area, there are approximately 200,000 curb inlets. Over this large area, a rain event may only affect certain portions of the area. Of the area effected by a rain event, there could be a variety of activities that could alter the concentration of soil particles flowing in the water. Construction sites, gardening, muddy roads, and the amount of impervious versus pervious ground can drastically change flow conditions and concentrations. The maintenance schedule will simply be an approximation using the following parameters: weather data collected from the Oklahoma City area, an average concentration of 3000 mg/l of soil particles in the run off water, and the requirement of 0.2 inches of runoff to wash off a developed area (thus runoff exceeding the 0.2 inches of rainfall is considered relatively free of sediment). The final parameters are the drainage area and the storage volume of the device. Using these parameters an expected filling time of the device can be calculated. The filling time also takes into consideration that organic matter will consume a portion of the volume. [0093]
To illustrate, soil samples were collected from existing curb inlets. These soil samples were analyzed for both particle size analysis and percent organic matter. Four samples were collected from the Oklahoma City area. The four samples were placed in an oven for 4 hours at 105° F. to remove moisture from the samples. After the soil was dry, it was weighed. The dry soil sample was placed in the muffle furnace at 550° C. for 24 hours. The muffle furnace was used to burn off the organic matter. The soil sample was weighed again, and the differential in weight corresponded to the loss of organic matter. The four samples had an average of 11.75% organic matter. Soil particles have a particle density of 2.65 g/cm[0094] ³and organic matter has a particle density of 1.1 g/cm³(Brady & Weil, 1999). Using these two densities, a weighted average of particle densities was calculated:
[(88.25*2.65g/cm ³)+(11.75*1.1g/cm ³)]/100=2.47 g/cm ³
The soil and organic matter that will fill the device will accordingly possess an average particle density of 2.47 g/cm[0095] ³. The 3000 mg/l is the concentration of suspended particles in solution, so the average density of the suspended particles is estimated at 2.47 g/cm³.
The preferred inventive device has a volume of 8 cubic feet. The amount of time needed fill the 8 cubic feet storage volume is dependent on the number of rain events that exceed 0.2 inches of runoff per year, as well as the area that each inlet services, the concentration of the suspended particles in the run-off, and the trapping efficiency of the device. The number of rain events that exceed 0.2 inches of runoff is dependent on the curve number that best represents an urban area. Using a conservative curve number of 95 allows for the amount of rain needed to produce 0.2 inches of run-off (the wash off amount). Turn now to the formula: [0096]
Q=(P−0.2S)²/(P+0.8S),
wherein [0097]
S=(1000/CN)−10; [0098]
P=accumulated precipitation (inches); [0099]
S=parameter; [0100]
Q=runoff (inches); and [0101]
CN=curve number (95 for a conservative # for urban areas). [0102]
Runoff begins after 0.2S of rainfall has fallen. Using the equation, it takes 0.52 inches of rainfall to initiate runoff. Using the value of 0.52 inches, we examine previous weather data to see how many 0.52 inch rainfall events occur each year. Every 0.52 inch rainfall event will not produce the concentration of 3000 mg/l because it takes a significant amount of time between events to accumulate the particles to produce that concentration. [0103]
As further example, the Oklahoma City area incurred approximately 40 rain events over 0.5 inches between 1997 and 1999. Although many of the events were not spaced far enough apart to allow adequate time for a build up of sediment, all 40 events were used in the approximation to ensure a conservative estimate on device fill up time. [0104]
The service area of a single curb inlet was previously calculated from the maximum of 4.1 cfs delivered during a 100 year flood event. The service area is thus calculated to be 43200 feet squared. Refer now to the following data and formulae: [0105]
SERVICE AREA=43200 ft[0106] ²
SOIL DENSITY=2.47 g/cm[0107] ³
STORAGE VOLUME=8 ft[0108] ³
RAIN EVENTS/YEAR=13.3 events/year [0109]
CONCENTRATION=3000 mg/l [0110]
WASH OFF AMOUNT=0.2 inches [0111]
EFFICIENCY=65% [0112]
cm ³/year=[(0.2in)(1ft/12in)(43200 ft ²)(1 liter/0.0353 ft ³)(3 g/liter)(13.3 events/year)]/[(2.47g/cm ³)]
SEDIMENT ENTERING THE DEVICE(cm³/year)=3.29 E ⁵=11.64ft ³/year
SEDIMENT RETAINED IN DEVICE=(11.64 ft ³/year)(0.65 efficiency)=7.6 ft ³/year
Using conservative values for both the curve number and the number of wash off events produces a volume of sediment per year that is more than what should be expected. The volume of sediment trapped per year was approximately 7.6 ft[0113] ³/year, and the device has a holding capacity of 8 ft³. Dividing the holding capacity by the expected sediment volume per year produces a fill up time of approximately one year.
While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of the process of assembly without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the experimental methods set forth herein for purposes of exemplification. [0114]

Claims

What is claimed is:

1. A storm water inlet pollutant trap for managing a water flow through a storm drain and extracting pollutants therefrom, comprising:

a housing adapted to be suspended below a storm water inlet, said housing including therein:

an upper surface to direct the water flow;

a first detention area at an upper portion thereof into which the water flow is directed;

a second detention area below said first detention area;

a damper separating said first detention area from said second detention area;

at least one aperture positioned at least partly below the level of said first detention area; and

a passageway leading from said second detention area to said aperture;

wherein under low flow conditions the water flow proceeds from said first detention area through said damper into said second detention area and ultimately through said passageway to exit via said aperture; and

wherein under high flow conditions the water flow bypasses said second detention area by overflowing said first detention area to exit via said aperture.

2. The storm water inlet pollutant trap according to claim 1, wherein said housing comprises a two piece structure.

3. The storm water inlet pollutant trap according to claim 1, wherein said damper comprises overlapping plates.

4. The storm water inlet pollutant trap according to claim 1, wherein said housing is generally rectangular in shape.

5. The storm water inlet pollutant trap according to claim 1, wherein said upper surface empties into said first detention area at a point below the level of said aperture.

6. A method for managing a water flow through a storm drain and extracting pollutants therefrom, comprising:

routing the water flow to a housing suspended below a storm water inlet;

under low flow conditions, routing the water flow along a first flow path into a first detention area in said housing and then through a damper into a second detention area and ultimately through a passageway to exit via an aperture in said housing; and

under high flow conditions, routing the water flow along a second flow path bypassing said second detention area by overflowing said first detention area to exit via said aperture.