Patent Abstract:
A treatment system for collecting storm water from an industrial area and removing suspended and dissolved pollutant materials from the storm water. Storm water is accumulated and delivered to a filtration apparatus in which suspended pollutants are removed by filtration, while dissolved materials, particularly heavy metals including zinc and copper, are removed by chemical chelation in a bed of compost filter media having a high humic acid content and which is kept consistently moist. A sparger provides for wide and generally uniform distribution of the storm water over the bed of filter media and provides for slow passage of the storm water through the filter bed, thus giving a long contact time of the storm water with the filter media in order to promote and enhance chemical chelation progress to chemical equilibrium and removal of a high percentage of dissolved metals, and particularly dissolved copper and zinc.

Full Description:
The present application is directed to treatment of water, especially storm water runoff, to reduce levels of contaminants such as heavy metals, and in particular is directed to a storm water filter treatment apparatus that includes a bed of filter media in a conveniently constructed water treatment container. 
     BACKGROUND OF THE INVENTION 
     Heavy metals such as copper, zinc, and lead are common pollutants in solution and in suspension in industrial storm water runoff in the U.S. The U.S. Environmental Protection Agency regulates the quantity, quality, and ongoing monitoring of storm water runoff from industrial facility sites pursuant to Multi-Sector General Storm Water regulations contained in the Clean Water Act. 
     Heavy metals exist in industrial runoff primarily from rainfall contact with automobiles, tire wear, brake pad wear, hydraulic oil, engine oil, building structures, specifically metal roofs, gutters, and metal siding, as well as construction residue, asphalt treatments, machining and manufacturing waste, metal primers and paint, and any exposed materials that may be stored externally at a facility. Particularly when rain falls at a high rate, as during a storm, and after a period of little precipitation, storm water runoff from an industrial area may carry significant amounts of contaminants. 
     There is little to no published literature or research on the control and mitigation of storm water runoff from industrial sites. There is however substantial state and federal regulation of storm water runoff from industrial sites. The result is that industrial sites often find themselves with permits for storm water discharge that limit constituents such as chemical oxygen demand, total suspended solids, oil and grease, turbidity or color, and limit metals such as copper, zinc, and lead, all of which may be construed to be deleterious to downstream receiving water bodies. 
     Various structures and methods for removing various suspended and dissolved impurities from storm water are disclosed in, for example, Stewart et al., U.S. Pat. No. 5,322,622; Herman et al., U.S. Pat. No. 7,037,423; Knutson et al., U.S. Pat. No. 5,707,527; Lenhart, Jr. et al., U.S. Pat. No. 6,027,639; Allen II et al., U.S. Pat. No. 8,110,105; Aberle et al., U.S. Pat. No. 7,214,311; Aberle et al., U.S. Pat. No. 7,419,591; Hersey et al., U.S. Pat. No. 7,517,450; Hersey et al., U.S. Pat. No. 8,110,099; Buelna, U.S. Pat. No. 6,100,081; Lambert, V et al., U.S. Pat. No. 8,216,479; Adams et al., U.S. Pat. No. 8,147,688; and Schluter et al., U.S. Pat. No. 7,186,058. 
     Various shortcomings in treatment of storm water runoff remain despite the prior art mentioned above, in that the storm water treatment apparatus disclosed is undesirably expensive to manufacture and maintain, that large areas of land may be required to contain various components of such systems, and that the effectiveness of the storm water treatment systems previously available is less than desired. 
     What is desired, then, is a storm water treatment system that can be constructed at a moderate cost, that is not particularly complex, and that is more effective than previously known storm water treatment systems. 
     SUMMARY OF THE INVENTION 
     In response to the above-mentioned shortcomings of the prior art, the present invention provides an answer to at least some of the shortcomings of the prior art, as defined in the claims that are part of the present disclosure. 
     As one aspect of the present invention, a storm water catchment and treatment apparatus is disclosed that is designed to reduce significantly the total copper and total zinc contained in industrial site storm water runoff. 
     In one embodiment, the storm water treatment system disclosed includes the use of high quality compost which is high in humic acid and which may be manure-based, leaf-based, or woody biomass-based, as a filtering and capture media, and which capitalizes specifically on the fact that humic acid is a chemical chelating and sequestering agent effective for the capture of copper, zinc and other storm water contamination likely to be found in industrial site runoff, including some organic compounds of interest. 
     One embodiment of the system disclosed herein includes a distribution system intended to ensure complete and intimate contact of the storm water over a large surface area of the filter media, and the embodiment disclosed provides for continuous wetting of the compost media that ensures fresh and active compost rich in humic acid at all times. 
     In a treatment container embodying an aspect of the invention, length, width, and height dimensions maximize the distribution of storm water through the amount of filter media available for treatment of storm water in order to result in very low flow velocity through the filter media, to maximize contact time between the storm water and compost filter media so that the chelating reaction between the heavy metals of the storm water and the humic acid in the compost can reach equilibrium and be complete. 
     The foregoing and other objectives and features of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially diagrammatic perspective view of a storm water drainage and treatment system which is an embodiment of the present invention. 
         FIG. 2  is a partially cutaway isometric view of a storm water treatment container according to the present disclosure. 
         FIG. 3  shows a structural formula of a humic acid molecule. 
         FIG. 4  shows a structural formula of a phenolate radical. 
         FIG. 5  shows a structural formula of an amine radical. 
         FIG. 6  shows a structural formula of a carboxylate radical. 
         FIG. 7  is a sectional view of the storm water treatment container shown in  FIG. 2 , taken along line  7 - 7 . 
         FIG. 8  is a top plan view of the storm water treatment container shown in  FIG. 2 . 
         FIG. 9  is a sectional view of the storm water treatment container shown in  FIGS. 2, 7 and 8 , taken along line  9 - 9  in  FIG. 8 . 
         FIG. 10  is an isometric view, at an enlarged scale, showing construction of a storm water infeed tank that is associated with the storm water treatment container as shown in  FIGS. 2 and 8 . 
         FIG. 11  is a side elevational view of the sparger included in the treatment container. 
         FIG. 12  is a sectional view taken along line  12 - 12  in  FIG. 11 , at an enlarged scale, showing a detail of the construction of a sparger pipe. 
         FIG. 13  is a schematic diagram of a storm water treatment system similar to that shown in  FIG. 1 . 
         FIG. 14  a partially cutaway, partially schematic, perspective view of an overflow buffer container for filtrate that may be included in the storm water treatment system disclosed herein. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings that form a part of the disclosure herein, and referring first to  FIGS. 1 and 2 , a storm water collection and treatment system  20  shown in  FIG. 1  may be used to collect runoff from an area  22  in which storm drains  24  collect runoff into underground collection pipes  26 . Catch basins in storm drains  24  may include fabric filter inserts to retain larger granular and suspended solids to prevent clogging of the collection pipes  26  and downstream conduits and protect system pumps. The underground collection pipes  26  may lead to one or more intermediate collection containers  28 , such as a drainage consolidation trench that may have been available before installation of the storm water collection and treatment system disclosed herein, or that may be constructed specifically to receive and accumulate quantities of runoff collected from the drainage area  22 , as a buffer to deal with surges in runoff quantity. 
     In the exemplary storm water collection and treatment system  20  shown in  FIG. 1 , a utility trench may be used as the intermediate collection container  28  to accumulate a sizeable quantity of runoff water. Discharge pipes  30 ,  32 ,  34 , and  36  may be associated with the intermediate collection container  28  and may be used eventually to discharge treated water to a sewer system or other final discharge receptacle after treatment in the collection and treatment system  20 , as will be explained more fully presently. The discharge pipes  30 ,  32 ,  34 , and  36  may serve as emergency overflow discharge conduits in an extremely exceptional situation. 
     A storm water delivery pipe  38  drains the intermediate collection container  28 , or if there is no intermediate collection container  28  it accumulates the runoff carried through the several underground drain pipes  26  and delivers the consolidated amounts of storm water to a collection container  40 . At least one pump  42  is arranged to pump accumulated storm water from the collection container  40  through a feed pipe  44  to a feed tank  46  associated with the treatment container  48 . A secondary water supply pipe  50 , such as a pipe connected to a source such as a municipal water supply is also connected with the feed tank  46 . 
     A conduit  52  leads from an outlet end  54  of the treatment container  48 , to carry treated storm water to the discharge pipe  30 . An emergency overflow discharge pipe  56  may lead from the treatment container  48  to the intermediate collection container  28 , or to another emergency path for discharge of untreated water in extremely unusual situations as will be explained in greater detail presently. 
     Referring next to  FIG. 2 , the treatment container  48  has a length  58 , a width  60 , and a height  62 . The feed tank  46  is mounted atop the treatment container  48  and may be supported by it, at the inlet end  64  of the treatment container  48 . The length  58 , width  60 , and height  62  of the treatment container  48  may be comparable to those of a highway semi-trailer or intermodal cargo container, in order that the treatment container  48  may be convenient to transport over a highway between its point of manufacture and a location where it is to be installed. In one embodiment, as depicted here, the treatment container  48  may be made by suitably strengthening and modifying a 45-foot cargo container. 
     A manhole  66  may be provided in the top of the feed tank  46 . Water introduced into the feed tank  46  through the feed pipe  44  is allowed to rise within the feed tank  46  to the level of the upwardly open mouth  68  of a sparger  70  that extends upward within the feed tank  46 . The sparger  70  is supported within the treatment container  48  and extends horizontally along its length near the top of the treatment container  48 . 
     As will be explained more fully below, a filter bed  72  is contained within the treatment container  48  beneath the sparger  70 . The filter bed contains media which may be principally a compost of high-quality manure or yard debris, rich in humic acid. 
     Composts based on cattle manure or yard debris, particularly leaves are particularly rich in humic acid. This is particularly important with respect to storm water treatment, in that humic acid, whose structure is illustrated in  FIG. 3 , is a very strong metal chelator, meaning that the chemical structure of humic acid has a distinct affinity to attract cationic metals such as copper, zinc, lead, manganese and others. The “O” or phenolate radical  80 , “N” or primary amine radical  82 , and “COOH” or carboxylate radical  84 , because of their relationship to the benzene ring structures  86  to which they are attached in the humic acid monomer, contribute to the ability of humic acid to strongly attract metal ions. The phenolate radical  80 , primary amine radical  82 , and the carboxylate radical  84  are shown, respectively, in  FIGS. 4, 5, and 6 . 
     The three radicals  80 ,  82 , and  84 , shown in  FIGS. 4, 5, and 6 , exist as integral parts of the humic acid structure and are termed “ligands.” Humic acid is a polymeric compound, often with at least 1,000 of the monomeric structures such as those shown in  FIG. 3 . The radicals  80 ,  82 , and  84  are “electron-rich” anions and therefore have a need to bond with +2 or +3 valence cations such as Cu++, Zn++, Fe++, or Al+++. When a metallic cation such as one of these bonds to a ligand structure such as a phenolate, amine, or carboxylate radical, the resulting bond is called a chelate. Chelates form very strong bonds and are highly stable, particularly within the pH range of 5.5 to 7.5, which is consistent with the pH of stormwater. 
     Therefore, while the prior art has described the use of compost in connection with treating storm water, there has not been an explanation of how and why compost works as an effective “cleanser” of heavy metals from storm water. It is in part through this chelating ability that the storm water treatment system described herein has achieved 83% to 96% removal rate for copper and 91% to 97% removal rates of zinc from industrial site storm water runoff. These removal rates have been achieved even at relatively low inlet concentrations and can provide final outlet concentrations well below 0.020 mg/L for total copper and 0.12 mg/L for total zinc. The treatment system disclosed herein routinely achieves similar results for effluent with a large percentage of the loading coming from dissolved zinc and dissolved copper, which are particularly problematic pollutants. 
     Referring next to  FIG. 7 , which is a sectional view of the treatment container  48  and the feed tank  46  from one side, it can be seen that the overall exterior length dimension  58  of the treatment container  48  is approximately 45 feet, and its height  62  is about 9 feet. The width  60 , shown in  FIGS. 8 and 9 , is about 8 feet. 
     The compost filter media bed  72  is supported within the treatment container  48 , and may have a depth  88  in a range of 1.5 feet to 6 feet, and in one embodiment a depth  88  of about three feet. A depth as shallow as one foot of compost may risk having the compost media fail to remain suitably even in depth. The treatment container  48  may, for example, be a converted 45-foot long intermodal cargo container, strengthened as necessary to contain the weight of the filter bed  72  and any load of water, which in an extremely exceptional case might fill the entire container, for a total of around 15,000 gallons. As may be seen in  FIG. 7 , the filter bed extends from the inlet end  64  toward the outlet end  54 , but does not extend over the entire length  58 . Instead, the filter bed  72  may extend for a lesser distance  90  of about forty-two feet, leaving a space of about three feet at the outlet end  54  in which one or more pumps  92  may be located. A pump  92  is shown connected to the filtrate discharge pipe  52 . As may be seen also in  FIG. 9 , the treatment container  48  has an underframe  94  extending horizontally at its bottom. A solid plate floor  96  is supported atop the underframe  94  and extends over the full length  58  and width  60  of the treatment container  48 . 
     Spaced upwardly apart from the plate floor  96  and supported on suitable framework (not shown) is a water-permeable support platform  98  that may be of a material such as expanded metal, extending over the full length  90  of the bed  72  and the full width  60  of the treatment container  48 . Supported by the permeable expanded metal or similar support  98  is a layer  100  of a strong water-pervious architectural fabric such as a non-woven fiber blanket durable enough and with a great enough permeability to allow water to drain freely from the filter media bed  72  into a space  102  which may have a height  104  of, for example, about 11 inches. For example, a geo-textile fabric such as a non-woven material available from Propex, Inc. of Chattanooga, Tenn. under the name Geotex 801, which is equivalent to a woven mesh size of about 80, has been found to be satisfactory. 
     Supported on the fabric layer  100  is the bed  72  of filter media, for which there is room for a depth  88  of six feet, although a lesser depth may be chosen. Preferably, the compost used as the filter media may be a mixture of relatively coarse granular compost and relatively fine compost. About eighty percent (80%) of the compost used in the bed may be placed into the bed first and may be relatively coarse particles, with particle size ranging up to two inches. The remaining twenty percent (20%) may be of relatively fine particle size, such as less than 0.1 inch, and down to dust. It may be placed atop the coarser compost and allowed to work its way down and be washed into the spaces between the larger particles beneath. The fabric layer  100  is capable of retaining even the fine particles of compost. For example, Geotex 801 is a non-woven geo-textile of polypropylene fibers, needle-punched to form a stable fabric network resistant to ultraviolet degradation and to biological and chemical environments normally found in soils. It has an apparent sieve-opening size of 80 (U.S.) and initially provides for a water flow of 110 gallons per minute per square foot, or 4,482 liters per minute per square meter. Thus, with the forty-two feet by eight feet size of the filter bed  72 , equal to 336 square feet, 36, 960 gallons per minute can flow through the bottom containment fabric layer  100 , which therefore will not impede the flow of filtrate from the filter bed  72 . 
     Atop the bed  72  of compost material is a top cover layer  106  of water-pervious fabric, which may be the same as or similar to the fabric layer  100  and which may rest atop the compost material of the filter media bed  72 . Supported closely above or in contact with the fabric layer  106  is an upper retaining member  108  of rigid yet storm water-permeable material such as expanded metal. The upper retaining member  108  may be supported in one of several sets of supports spaced apart at various heights along the sides of the treatment container  48  and is preferably supported at a selected height close to the upper layer  106  of water-permeable fabric, in order to keep the fabric layer  106  in its desired location covering the top of the filter media. Geo-textile fabric filter material may essentially wrap the entire volume of compost filter media to ensure that the compost does not become plugged or otherwise compromised by sand, grit, or mud. 
     The treatment container  48  may have a sheet metal cover or, alternatively, may be covered by a watertight fabric, but in any case the top of the treatment container should be easy to uncover. Once the effectiveness of the compost filter media in the bed  72  begins to decrease as a result of loading of the media with matter removed from suspension in storm water, or when the humic acid content is consumed by chelation of dissolved metal ions, the compost filter bed media can be removed easily by raising and removing the expanded metal retainer member  108 , which may be made up of several smaller pieces easily assembled and attached to each other, to allow removal of the permeable top layer cover  106  and then removal of the particulate compost filter media. 
     The sparger  70  extends along the filter bed, where it may be centrally located between the opposite sides  110  and  112  and suspended from transversely extending spreader bars  114 , maintaining a spacing between the sides  110  and  112 , and from other transversely extending sparger support members  116 , which may, for example, be pipes or angle irons. 
     As may be seen best in  FIGS. 10, 11 and 12 , the sparger  70  includes a standpipe portion  118  that extends upward within the feed tank  46  by a distance  119  of, for example, two feet, so that storm water pumped into the feed tank  46  through the feed pipe  44  from the collection container  40  can rise within the feed tank  46  to the height of the mouth  68  of the sparger  70 , allowing the water to calm somewhat and flow into the mouth  68  of the sparger  70  with some regularity. The sparger  70  is provided with holes spaced apart along its length and about the lower half of its circumference, in order to distribute storm water introduced into the mouth of the sparger pipe evenly onto the top of the filter bed  72 . As may be seen in  FIG. 12 , there are holes  120  on each side and extending horizontally through the wall of the sparger pipe  70  to direct a spray of water laterally away from the sparger pipe toward a respective one of the sides  110  and  112 . There are also holes  122  which may be oriented at forty-five degrees below horizontal in order to emit streams of storm water downwardly and laterally to a smaller distance away from the center line of the treatment tank  48  on each side of the sparger pipe  70 . The holes  120  and  122  are spaced apart from one another along the length of the sparger pipe  70 , with a spacing such as, for example, 10.6 inches between consecutive ones of the holes  120 , which may be, for example, seven-sixteenths inch in diameter. The lower holes  122  may be spaced apart from one another by 15.75 inches and each hole  122  may have a diameter of five-sixteenths inch, for example, to achieve distribution of storm water over the entire filter bed as a result of flow into the intake  68  of the sparger  70 . In order to allow the sparger  70  to drain when there is no inflow of storm water, a weeper hole  124  may be provided in the bottom of the sparger pipe  70  near each end. The sparger  70  thus ensures the entire width and length of the compost filter media is wetted during a storm water event to ensure maximum surface area contact. 
     The supply feed pipe  50  to the feed tank  46  can supply water, as from an outside or municipal water supply, to the sparger  70  when needed to ensure the compost filter media is continuously wetted. It is this feature in particular that keeps the compost active and rich in humic acid necessary for the capture of heavy metals from storm water. 
     The water supply provided via the feed pipe  50  can be programmed or operated under manual control as required to keep the filter bed material moist, either by regular observation of the filter bed  72 , or by routinely delivering water to the feed tank  46  after a predetermined number of days without rainfall in a significant amount. It is important, however, that the filter media be maintained in a moist condition in order to continue to support biological activity within the compost material in order to continue to develop and maintain humic acid within the compost material. 
     When a significant rainfall occurs and runoff travels to the storm drain inlets  24  shown in  FIG. 1  in sufficient quantity to accumulate in the collection tank  28  and eventually enter into the collection container  48 , it is pumped into the feed tank  46  by the pump  42  and then runs through the sparger  70  to be distributed atop the filter bed  72 . After passing through the filter bed into the filtrate collection space  102  beneath the expanded metal bottom layer  98 , the filtrate, or treated storm water, is drawn from the space  102  by the filtrate pump  92  and discharged through the discharge pipe  52  at the outlet end of the treatment container  48 . 
     This configuration ensures that storm water is conveyed through a collection system and over 99% of the storm water is carried into contact with the compost filter media in the bed  72 . 
     Because of the unique physical construction of the compost filter, the manner in which the storm water is evenly distributed to the entire length and width of the compost media, and the sheer volume of the compost media in the bed  72 , water flow velocity through the system is very low, which results in extended contact time between the humic acid rich compost and the metal laden storm water. This is critical in that it allows complete chemical reaction equilibrium to be reached between dissolved metals in the storm water and the humic acid in the compost. The design velocity of water through the filter media in the bed  72  is a mere 0.42 inches or less per minute. Therefore, if the compost media bed is 6 feet (72 inches) in depth, at the design down flow velocity of 0.42 inches per minute, it takes storm water 2.86 hours to travel from the top of the compost bed to the bottom of the compost bed. 2.86 hours is a very significant amount of contact time between the dissolved metals and humic acid. Additionally, because of the chemical reaction occurring with the humic acid present in the compost as well as the natural aerobic biology present in the compost, the compost generates heat. Heat is in turn a catalyst which speeds the chelating chemical reaction between the metals in the storm water and the humic acid in the compost. The rate of reaction in this system follows the Arrhenius Rate Law of Chemical Kinetics. The Arrhenius equation is complex and is known as:
 
 k=Ae   (−E     a     /RT)   [Equation 1],
 
wherein
         K=reaction rate;   A=reaction frequency factor;   e=mathematical exponent function (natural logarithmic base) approximately equivalent to 2.71828;   E a =activation energy;   R=universal gas law constant; and   T=absolute temperature.
 
Referring to this equation in simpler terms, we can say the following:
 
Reaction Rate= k[A]   a   [B]   b   [Equation 2],
 
wherein
   K=rate constant;   A=concentration of substance A (the metals in storm water in this case); and   B=concentration of humic acid present in the compost.       

     In chemistry, one reactant is often present in excess as compared to the other reactant. For these purposes, the humic acid concentration will always exceed the concentration of heavy metals in storm water. In chemical kinetics, we would therefore write that equation as:
 
Rate= k[A]   1   ×[B]   2  
 
     This essentially means that the rate of this reaction will proceed as a function of the square of the humic acid concentration. Further, if we look back to the Equation 1 above, we can see a temperature factor, T. Mathematically, it can be determined that for each 10° C. rise in temperature of the bed  72  of compost filter media, the rate of reaction will double. 
     The equilibrium concentration between the metals in the storm water and the humic acid in the compost is therefore reached at a continually increasing rate of speed as the reaction raises the temperature—a speed which ensures that the equilibrium reaction occurs in considerably less time than 2.86 hours (i.e., the time storm water takes to permeate from the top of the compost bed  72  to the bottom of the compost bed, with a depth  88  of six feet). 
     For example, the intermediate collection container  28  may have a capacity of 8,850 gallons, and the storm water collection container  40  may have a capacity of 7,750 gallons, in addition to the capacities of the various pipes interconnecting the storm drains  24  with the intermediate collection container  28  and the collection container  40 . With this capacity, the storm water treatment system  20  described can easily deal with collecting the volume of rainfall on an area  22  of, for example, 3.5 acres served by the storm water collection and treatment system  20 , resulting from a relatively rare rainfall event delivering 1.8 inches of rain in a period of six hours (27,154 gallons per acre-inch multiplied by 3.5 acres equals 171,071 gallons), or an average of 0.417 cubic feet or about 3.12 gallons per second. 
     In  FIG. 13 , a schematic diagram of a storm water collection and treatment system similar to that shown pictorially in  FIG. 1  and described hereinabove, with respect particularly to the treatment container  48  and feed tank  46 , shows that there may be, for example, a pair of pumps  42  in the collection container  40 , with a water level sensor  130  arranged to operate a first pump  42   a  of a lower capacity, such as forty gallons per minute (40 gpm) when water in the collection container  40  is detected by a sensor  132 , and to start a second, larger-capacity (e.g., 125 gpm) pump  42   b  when the water level has reached a predetermined level as determined by the sensor  130 , and to send an alarm when the water level has reached an even higher point and appears to overwhelm the capacity of both pumps  42   a  and  42   b  together. An overflow drain  134  may be provided to protect the collection container  40 . 
     Similarly, with respect to the treatment container  48 , a first pump  92   a  may be energized by a control panel  140  when water is detected in the space  102  by a sensor  138 , which may also be arranged to control a valve in the secondary water supply pipe  50 . When the water level has risen to a higher level, a control panel  142  energizes a second, larger-capacity pump  92   b  in parallel with the smaller-capacity pump  92   a , and at a chosen higher level can provide an alarm signal. The discharges from the pumps  92  proceed as previously explained through the discharge pipe  52  and into the discharge pipe  30  and, depending on the volume of discharge through the pipe  52 , may also be directed into the discharge pipe  32 , as well. Scuppers  150  may also be provided in the treatment container  48 , as shown in  FIG. 9 , to provide a discharge route for overflow. 
     Should the flow of water into the feed tank  46  and into the treatment container  48  become so great that the pumps  92  are overwhelmed, or should electrical power to the pumps  92  be interrupted and water level overflow the space  102  and rise high enough, the overflow pipe  56  can carry a portion of the excess water to the intermediate collection container  28 , which can act as a buffer at least temporarily. If the quantity of water in the intermediate collection container  28  becomes excessive, water may overflow, as shown in  FIG. 14 , into an overflow inlet  148 , which may be in the form of a semi-cylindrical standpipe rising along a wall of a utility trench, allowing excess water to flow down into the inlet of the discharge pipe  30 . 
     As examples, several measurements were made of the performance of the system after rainfall events. Sampling for tests was accomplished after a large enough rain event so that there would have been enough flow from rain runoff to go entirely through the treatment container  48 . Storm water runoff from the area  22  should be great enough in volume to go completely through the treatment container after a rain event of roughly 0.25 inch rainfall in a period of 24 hours or less. A sampling valve  152  may be provided in the feed pipe  44  to the feed tank  46 , and a “before treatment” sample is taken from that point in the system, before the water is deposited into the feed tank  46  leading to the mouth  68  of the sparger  70 . 
     Samples of treated water may be taken through a sampling valve  154  provided for that purpose in the outlet conduit  52 , at the outlet end  54  of the treatment container  48 . 
     The performance of the system, as measured in each of six separate tests, is shown in Table 1 below, entitled Removal Efficiency Information for Certain Materials. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Removal Efficiency Information for Certain Materials 
               
             
          
           
               
                   
                 Cu Total 
                   
                 Cu Dissolved 
                   
                 Zn Total 
                   
                 Zn Disolved 
                   
               
               
                 Test 
                 (mg/L) 
                 Removal 
                 (mg/L) 
                 Removal 
                 (mg/L) 
                 Removal 
                 (mg/L) 
                 Removal 
               
             
          
           
               
                 Number 
                 Inlet 
                 Outlet 
                 Efficiency 
                 Inlet 
                 Outlet 
                 Efficiency 
                 Inlet 
                 Outlet 
                 Efficiency 
                 Inlet 
                 Outlet 
                 Efficiency 
               
               
                   
               
             
          
           
               
                 1 
                 0.047 
                 ND (0.0100) 
                     89% 1   
                   
                   
                   
                 0.368 
                 0.0276 
                 93% 
                 0.405 
                 0.0166 
                 96% 
               
               
                 2 
                 0.036 
                 0.0060 
                 83% 
                   
                   
                   
                 0.414 
                 0.0216 
                 95% 
                 0.780 
                 0.0219 
                 97% 
               
               
                 3 
                   
                   
                   
                 0.0497 
                 0.0054 
                 89% 
                   
                   
                   
                 0.398 
                 0.0347 
                 91% 
               
               
                 4 
                   
                   
                   
                 0.048 
                 0.0064 
                 87% 
                   
                   
                   
                 0.320 
                 0.0115 
                 96% 
               
               
                 5 
                 0.165 
                 0.0198 
                 88% 
                   
                   
                   
                   
                   
                   
                 0.858 
                 0.0792 
                 91% 
               
               
                 6 
                 0.070 
                 0.0111 
                 84% 
                   
                   
                   
                 0.614 
                 0.0396 
                 94% 
               
               
                   
               
               
                 Note 
               
               
                   1 The indicated removal efficiency is an estimate because the outlet concentration was below the method detection limit of 0.0100 mg/L for this analysis, so the concentration was taken at ½ of the detection limit or 0.0050 mg/L. 
               
             
          
         
       
     
     As shown in Table 1, the average removal efficiency for total copper content was determined to be 84%, with a range of 83% to 89%. 
     The average removal efficiency for dissolved copper was 88%, with a range of 87% to 89%, as shown in tests three and four. 
     The average removal efficiency for total zinc was 94%, with a range of 93% to 95%. 
     The average removal efficiency for dissolved zinc was 94%, with a range of 91% to 97%. 
     The removal efficiencies determined and shown in Table 1 are particularly impressive with respect to removal of dissolved copper and dissolved zinc, which are the most difficult pollutants to remove, among those normally subject to regulation in industrial storm water runoff permits. The results obtained were consistently below the very low regulatory thresholds permitted by states such as Oregon (0.020 mg/L for copper and 0.12 mg/L for zinc) and Washington (0.0144 total copper and 0.117 mg/L for total zinc). 
     The filter system operates with a water velocity through the filter media that is dependent on the flow rate of the pumps operating in the system. The storm water treatment system  20 , as shown in  FIGS. 1 and 13 , flows at 45 gallons per minute under quote normal unquote conditions and at 165 gallons per minute when the rain intensity increases to the high flow rate set point. The 45 gallon per minute and 165 gallons per minute rates correspond to vertical mean space velocity through the media bed at 0.11 in./m or 0.42 in./m, respectively. The treatment system  20  has been tested a number of times, and there seems to be little variation in efficiency of removing pollutants during rain events of different magnitudes. 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Technology Classification (CPC): 8