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RELATED APPLICATION  
     I claim the benefit of my prior now abandoned Provisional Application Ser. No. 60/337,545 filed Dec. 1, 2001, entitled Stormwater Runoff Treatment Train. This application is a continuation in part of my prior application Ser. No. 10/040,611 filed Jan. 9, 2002, now U.S. Pat. No. 6,869,528, which in turn claims the benefit of Provisional Application Ser. No. 60/271,065 filed Feb. 26, 2001. 
    
    
     BACKGROUND OF THE INVENTION  
     This invention is intended to improve the quality of stormwater runoff from developed impervious surfaces. Stormwater runoff from impervious surfaces like parking lots contains many different contaminants, such as sediments, nutrients, heavy metals, and organic chemicals. In most developed areas of the United States, this runoff is collected in pipes and discharged directly into a stream or other water body. The present invention provides a means by which some of the environmentally detrimental constituents may be removed from the water. 
     During the last ten years, a new industry has developed to treat stormwater runoff. To date, the main focus of this industry has been removing suspended solids from the water. Solids can be removed by physical separation, which is most easily achieved by reducing water velocities and allowing the solids to settle out of the water. This is the theory behind the ponds, sediment basins, and hydrodynamic separators that comprise the majority of commercially available stormwater treatment devices. Much of the pollution in stormwater runoff, however, is not suspended, but instead dissolved in the water. These dissolved contaminants require more effective treatment, hence a filter is often used. However, all of the devices now in use become quite inefficient when there is a high rate of flow through them. 
     Assume that the runoff water from a filling station has both suspended contaminants and dissolved contaminants. This runoff water will be cleaned by my invention as follows: Such runoff water first enters a gravity particle separator such as is taught in my U.S. Pat. Nos. 5,746,911 and 6,264,835. The disclosures of these patents are incorporated herein by reference. This particle separator removes suspended contaminants from the runoff water. The output of the particle separator is fed to a reservoir which is so big that it will hold all of the water from a prolonged hard rain lasting several hours. The output of the reservoir is fed through a limiter to a filter which removes dissolved contaminants from the water. The filter conforms to my copending patent application Ser. No. 10/040,611, filed Jan. 9, 2002, now U.S. Pat. No. 6,869,528 of Mar. 22, 2005 (the disclosure of this patent is incorporated herein by reference), see also patent application publication US/2002/0117435 A1. Such a filter is inefficient if the flow therethrough exceeds a given rate. The aforesaid limiter prevents the flow to the filter from exceeding said given rate. 
     SUMMARY OF THE INVENTION  
     The present invention avoids the inefficiency of the prior art by storing the incoming water in a reservoir and limiting the flow rate from the reservoir to the device or devices that clean the water. For example, during a prolonged rainstorm the water collects in a reservoir which has a flow limiting device at its output that limits the flow rate to a rate at which the flow cleaning device (gravity separator, filter, etc.) can efficiently clean the water. 
     The invention contemplates that any suitable flow limiting device may be used to limit the rate of flow of water from the reservoir to the fluid cleaning device (gravity separator, filter, etc.) to a rate that the cleaning device can handle efficiently. The prior art teaches many such flow limiting devices, per se. They range from a float (on the surface of the water in the reservoir) controlling a valve in the outlet of the reservoir to a small induction motor driving a pump, which motor during high rates of flow acts as a generator and thereby controls the rate of flow of water. To summarize, the output of the reservoir is preferably held to a relatively constant rate of flow that renders the filter or other cleaning device efficient. 
     The present invention involves a single process for the treatment of stormwater runoff. The invention relies on extended detention to remove sediments and associated pollutants (many detrimental pollutants adsorb, or attach themselves, to the surface of suspended sediment particles). Following extended detention, the water is transferred to a filter, which removes dissolved pollutants, as well as any very small suspended particles that escape from the extended detention phase. The present invention includes a pump that regulates flow through the filter unit, as well as mechanisms to clean the filters with excessive maintenance requirements. 
     The present invention improves upon the prior art in several significant ways. The prior art relies solely on gravity flow to drive stormwater runoff through the treatment process. The present invention, however, uses a pump or other energy source to drive the water in cases where the elevation differences on the site are not sufficient to impart this energy. This energy sources makes the present invention far more flexible than the prior art in terms of range of applications. 
     The prior art also overwhelmingly relies on a single technology to treat stormwater runoff. The present invention, though, incorporates different technologies, each aimed at a different constituent of stormwater runoff. While the application of any one of these technologies is a commonly used treatment method that is generally effective for a single contaminant species, the combination of the several methods allows the stormwater treatment device to remove a broad range of potential pollutants. 
     A filter is hereby defined as a porous device for removing impurities from a liquid passed through it. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a block diagram of the Preferred Form of the Invention. 
         FIG. 2  is a block diagram of a First Modified Form of the Invention. 
         FIG. 3  is a block diagram of a Second Modified Form of the Invention. 
         FIG. 4  is a sectional view of the discharge end of a third modified form of the invention. 
         FIG. 5  is a schematic drawing of one form that the particle  201  may take. 
         FIG. 6  is a sectional view of the filter used with this invention. 
         FIG. 7  is a plan view of the filter  305  for the preferred form of the invention. 
         FIG. 8  is a cross-sectional view of each of the layers  310   310 A and  310 B. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     The present invention combines several different technologies for the treatment of Stormwater runoff into a single train. The invention includes (a) a physical separator to remove suspended particles, with specific gravities greater or less than one, from water, (b) a filter that removes dissolved contaminants, as well as small particulate contaminants that escape from the separator, from water, and (c) the associated means and conveyances required to deliver the water to each phase of the treatment device. 
     Preferred Form of the Invention 
     The preferred form of the invention is shown in  FIG. 1 . An inlet means  101  delivers the influent runoff rainwater to the system. The inlet means discharges the contaminated water into a physical separator  201 . This physical separator is a device such as is disclosed in my U.S. Pat. No. 5,746,911 and 6,264,835. The disclosures of these two patents are incorporated herein by reference. The separator  201  relies on gravity to separate suspended particles with a density greater than the density of water from the influent water, and the water exiting the separator  201  has a significantly lower concentration of suspended pollutants than the influent water. A conduit  102  accepts the water exiting the separator, and delivers the water to a large reservoir  202 . This reservoir contains a regulated discharge means  103  that controls the flow rate of the water leaving the reservoir. This discharge means conveyance that has the capacity to regulate the flow rate. A pump, for example, may have a control or other means to limit end control the rate of flow through the pump. The regulated discharge delivers the water to a second conduit  104 , which delivers the water to the filter  203 . The filter  203  is a device such as that described in my prior copending patent application Ser. No. 10/040,611, filed Jan. 9, 2002 and entitled Filtering System for Runoff Water. This application has matured into U.S. Pat. No. 6,869,528, the disclosure of which is incorporated by reference. Intended to remove both dissolved and particulate pollutants from water by use of a filter media, the filter  203  may use any of various types of media to accomplish this removal, end the media may be tailored for the specific contaminants expected in the stormwater runoff. The water passes through the filter  203  and then enters a conduit  105  which delivers the treated water to an outfall such as a river. 
     Rainwater that runs off of a parking lot, or off the pavement of a filling station, passes via inlet  11  into inlet tank  12  (see  FIG. 5 ). When the water is entering tank  12  at a very low rate, the surface water and/or oil, in the inlet tank drains via weir  13  and pipe  122  to a main separation tank  21  where the oil floats on clean water. That clean water is fed via pipe  20  to an outlet conduit  18 . When the inlet flow increases to an intermediate rate, a pipe  14  of inverted L-shape feeds clean water from the inlet tank  12  to the outlet conduit  18 . When the inlet fluid has a very large flow rate, as might occur during a heavy downpour of rain, the fluid level in the inlet tank  12  rises to a level at which there is a direct flow from inlet  11  into the outlet conduit  18 . 
     The conventional prior art relies on gravity separation to remove oils from stormwater runoff. Free oils can be removed by this method, but emulsified and dissolved oils cannot. The present invention makes use of a fine filter media to trap those oils that cannot be removed in a conventional gravity separator. Used in conjunction with the gravity separator of  FIG. 5 , the filter shown in  FIGS. 6 to 8  comprises apparatus for the removal of oils from runoff water. 
     The filter comprises a number of cylindrical cells, such as  310 A,  310 D,  310 C, etc. Each cell is a complete filter and comprises several layers or laps such as a lap composed of coarse filtering material  326 , a lap such as the first porous barrier, a lap such as a second or fine filtering material, a lap such as a second porous barrier and a lap such as a drain. 
     The filter has two opposing sides, one of which sides comprises the upper ends of the cells  310 ,  310 A and  310 B of  FIGS. 6 and 8  and the other of which sides comprises the lower end of said cells  310 ,  310 A and  310 B. 
     In  FIGS. 6 and 7 , there is a tank  300  that has an inlet conduit such as pipe  301 , a clean water outlet conduit such as pipe  302 , and an overflow outlet conduit such as pipe  303 . The clean water outlet pipe  302  is at a substantially lower elevation than the inlet pipe  301 , and the overflow outlet pipe  303  is at the same elevation as the inlet pipe  301 . There is a spillway  301 A at the end of inlet pipe  301  that extends to the edge of the filter mechanism  305 . The clean water outlet conduit  302  and overflow outlet conduit  303  may be kept separate to maintain segregated waste streams, or may be combined into a single outlet conduit. 
     The filter mechanism  305  is shown in  FIGS. 7 and 8 . The filter mechanism is divided into concentric filter cells  310  and  310 A by inner walls  311 , and surrounded by outer wall  312 . Outer wall  312  is taller than inner walls  311 .. A reservoir  313 , with one side, in this case the bottom side, perforated. The reservoir is formed by outer wall  312  and the tops of the filter cells  310  and  310 A,  310 B, etc. 
     Each interior filter cell  310 ,  310 A and  310 B is constructed as shown in  FIG. 8 . The inner walls  31  constitute the vertical boundaries of the cell, and perforated plate  325  constitutes the floor. The entire filter mechanism  305  is held above the floor of tank  300  in any suitable way. A drain  324  is fastened along the inside of the inner walls  311 . The drain is bounded by barrier  323 , which separates the drain  324  from a fine filter media  322 . Barrier  323  is a geotextile or similar device that is fine enough to retain fine filter media  322 , but porous enough to allow water to pass through it. A second barrier  321  separates the fine filter media  322  from a coarse material  320 . Barrier  321  is a geotextile or similar device that is fine enough to retain fine filter media  322 , but porous enough to allow water to pass through it. Barrier  321  extends along the top of the fine filter media  322  to the inner wall  311 . 
     The tank  300  is a large chamber. Inside of the large chamber is a smaller chamber  312  containing the filter cells  310  and  310 A. Each filter cell, such as those shown in  FIGS. 7 and 8 , has a first passageway along the vertical center line of the cell and containing the first filter media  320 . A second passageway, is in the form of drain  324 . The fine (second) filtering media comprises the second filtration media. 
     The filter cell  310 A is shown in  FIGS. 5 and 6 . An inner wall  311  forms one vertical boundary, while the outer wall  312  forms the other vertical boundary. Perforated plate  325 , drain  324 , barrier  323 , fine filter media  322 , barrier  321 , and coarse material  320  are arranged as they are in the aforementioned interior filter cell  310 . 
     When the runoff entering inlet pipe  301  has a low rate of flow, the water is passed from spillway  301 A into reservoir  313  above filter mechanism  305 . Because the oil entering the system is emulsified or dissolved, the oil does not remain on top of the water in reservoir  313 , but is instead mixed throughout the water. From reservoir  313 , the water flows into each lap of coarse material  320 . Coarse material  320  has a large volume of voids and provides little resistance to the flow of water, that the water is distributed evenly throughout coarse material  320 . 
     The water fed to a layer or lap of coarse material  320  may flow from the coarse material  320  in three directions. First it may flow in a direction away from the center of the filter to the first drain, secondly it may flow toward the center of the filter to the first drain, and thirdly the water may flow from the coarse material  320  vertically downward to the fine filtering material. 
     As coarse material  320  becomes saturated, the runoff water will penetrate barrier  321  and enter fine filter media  322 . Fine filter media  322  provides significantly more resistance to flow than does coarse material  320 . Furthermore, the finer particles create a more tortuous flow path, allowing for longer contact time between the runoff water and the fine filter media  322 , and therefore more efficient pollutant removal. As the fine filter media  322  slowly becomes saturated, the filtered runoff water will then penetrate barrier  323  and enter drain  324 . 
     Drain  324  is simply an open space that allows the water to flow down along interior wall  311  or outer wall  312  to perforated plate  325 . The water flows through the perforations in plate  325  and back into tank  300 . From tank  300 , the water flows to outlet outlet pipe  302  which delivers the filtered runoff water to a sewer or stream. 
     When runoff water enters the inlet pipe  301  at a high rate of flow, the fine filter media  323  restricts the flow through filter cells  310  and  310 A, and therefore restricts the flow through filter mechanism  305 . In this case, the overflow outlet pipe  303  accepts the excess water from the surface of the reservoir  313  through overflow inlet  303 A. Overflow pipe  303  delivers the unfiltered water to a sewer or stream. This can be the same sewer or stream that clean water outlet pipe  302  discharges to, or it can be a different discharge point. 
     The runoff water may vary from a very low rate to a very high rate. At high rates the filter  203  is inefficient. 
     The reservoir  202  is preferably so big that it will hold all the water from a prolonged hard rain, lasting several hours, but the outlet pipe of the reservoir is so small (or has a restriction) limiting the flow, or has other suitable means for controlling the flow, so that the flow rate therethrough is not only within the capacity of the filter but takes at least one hour to drain the reservoir. 
     First Modified Form of the Invention 
     The function of the reservoir  202  and the pump  103  (or other flow limiting device) is to take the widely varying incoming flow and convert it to a relatively steady, more constant, flow rate and thereby improve the efficiency of the filter  203 . 
     A second form of the invention is shown in  FIG. 2 , in which the physical separator and reservoir are combined into a single unit  204 . In this case, the inlet conduit  101 , regulated discharge means  103 , conduit  104 , filter  203 , and discharge conduit  105  are as described in the preferred form of the invention, and serve the same purposes. 
     In this form of the invention, a single large container  204  acts as both physical separator and reservoir. The container is capable of holding all the water from a prolonged hard rain, and the conduit  104  is sized or designed such that it takes at least one hour to fully drain the tank. 
     Second Modified Form of the Invention 
       FIG. 3  illustrates another form of the invention, in which the filter  203  can be backwashed without additional equipment. In  FIG. 3 , the inlet conduit  101 , physical separator  201 , reservoir  202 , regulated discharge  103 , conduit  104 , filter  203 , and outlet conduit  105  are as described in the preferred form of the invention, and serve the same purposes. However, an additional backwash water source  205  and backwash water collector  206  are also included. This source  205  may be a container that is part of the system, or it may simply be a connection to which a separate container can be joined. In addition to the backwash water source  205 , four valves are also included in this form of the invention. During normal operation, valves  106  are open, and valves  107  are closed. In this case, the second modified form of the invention functions in the same manner as the preferred form. 
     With normal use, filters become clogged, and require maintenance. This form of the invention allows the filter  203  to be backwashed without additional equipment. To do this, valves  106  are closed, and valves  107  are opened. The backwash water source  205  discharges water through the filter  203 . This reverse flow cleans the filter, and the wash water is collected in backwash water collector  206 . The backwash water is removed from the backwash water collector and disposed of. 
     Third Modified Form of the Invention 
       FIG. 4  shows apparatus that may be added to the outlet conduit  105  of the invention. In this case, fluid in outlet conduit  105  does not flow by gravity. Instead, pump  207  imparts the necessary energy to the water to provide effluent flow from the invention. Conduit  105  leads to recharge trench  208 , which allows the treated water to percolate into the surrounding soils, recharging the groundwater. Alternatively, conduit  105  could flow to high-elevation outfall  209 , which is above conduit  105  in elevation. This form of the invention can be used on sites in which elevation constraints limit the choice of treatment methods for stormwater runoff. 
     “Runoff water”, as used in this specification and claims, is defined as stormwater from impervious surfaces like parking lots, and filling stations, and contains contaminants. 
     Fourth Modified Form of the Invention 
     The filter of  FIGS. 6 to 9  may be inverted so that water enters the lower end of the filter and is discharged from its upper end. Such a filter is shown in  FIGS. 9 and 11  of my parent U.S. Pat. No. 6,869,525. The reservoir feeding the inverted filter may have a by-pass outlet which allows water in the reservoir above a given level to by-pass the filter. Such a by-pass is well known and is shown in said U.S. Pat. No. 6,869,528. Such a by-pass is a form of limiter since it limits the pressure of the water entering the filter.

Summary:
A system is provided for treating runoff water in which there is a separator and a filter for cleaning the water. A reservoir is provided to hold large quantities of water during prolonged rainstorms. The output of the reservoir is fed to the filter. The rate of flow from the reservoir to the filter is controlled and limited to flow rates at which the filter can efficiently clean the water.