Abstract:
A separator tank for separating and trapping contaminants in rainwater and runoff is disclosed. According to one embodiment of the present invention, the separator tank comprises a container having a bottom wall, side wall, and top wall defining an internal chamber; an insert located inside of the internal chamber, the insert comprising a weir defining an intake area between the weir and the side wall; and a round-edged orifice positioned within the intake area; an inlet conduit for introducing an influent liquid into the intake area; wherein the weir is positioned such that the weir induces the influent liquid to flow in a swirling motion within the intake area. According to another embodiment of the present invention an insert for a separator tank is disclosed. The insert includes a weir defining an intake area for receiving an influent liquid; and a round-edged orifice positioned within the intake area.

Description:
This application claims priority to provisional application Ser. No. 60/950,996, filed Jul. 20, 2007, entitled, “Separator Tank,” the disclosure of which is incorporated herein by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention generally relates to separator tanks adapted to receive rainwater from a storm sewer or drain, and, more particularly, to separator tanks having a high flow rate through their lower chambers, while achieving high levels of separation and removal efficiency. 
   2. Description of Related Art 
   In general, separator tanks are structures adapted to receive rainwater and runoff from a storm sewer or drain. The tanks separate and entrap free and floating oils, grease, hydrocarbon, petroleum products, and total suspended solids (TSS), as well as sorbed contaminants like nutrients, heavy metals, and hydrocarbon and petroleum products, that are transported as suspended solids. Once the various contaminants have been separated or entrapped, the semi-clarified water may be discharged into municipal receiving sewers or water courses. Examples of separator tanks are disclosed in U.S. Pat. Nos. 4,987,148; 5,498,331; 5,725,760; 5,753,115; and 6,068,765, the disclosures of which are incorporated by reference in their entireties. 
   SUMMARY OF THE INVENTION 
   A separator tank for separating and trapping contaminants in rainwater and runoff is disclosed. According to one embodiment of the present invention, the separator tank comprises a container having a bottom wall, side wall, and top wall defining an internal chamber; an insert located inside of the internal chamber, the insert comprising a weir defining an intake area between the weir and the side wall; and a round-edged orifice positioned within the intake area; an inlet conduit for introducing an influent liquid into the intake area; wherein the weir is positioned such that the weir induces the influent liquid to flow in a swirling motion within the intake area. 
   According to another embodiment of the present invention an insert for a separator tank is disclosed. The insert includes a weir defining an intake area for receiving an influent liquid; and a round-edged orifice positioned within the intake area. 
   According to another embodiment of the present invention, the insert includes a weir defining an intake area for receiving an influent liquid; an orifice positioned within the intake area; and a drop tube in fluid communication with the orifice, the drop tube comprising a base formed by two wings. 
   According to another embodiment of the present invention, the insert includes a weir defining an intake area for receiving an influent liquid; an orifice positioned within the intake area; and a drop tube in fluid communication with the orifice, the drop tube comprising at least one vertical vane. 
   According to another embodiment of the present invention, the insert includes a weir defining an intake area for receiving an influent liquid; an orifice positioned within the intake area; and a drop tube in fluid communication with the orifice, the drop tube comprising a base formed by two wings; a back wall; and a front wall. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, the objects and advantages thereof, reference is now made to the following descriptions taken in connection with the accompanying drawings: 
       FIG. 1  is a perspective view of a prior art separator tank. 
       FIG. 2  is a perspective view of the upper chamber of a prior art separator tank. 
       FIG. 3  is a perspective view of an insert for a prior art separator tank. 
       FIG. 4  is a cross-sectional view of a separator tank according to one embodiment of the present invention. 
       FIG. 5  is a perspective view of the insert for a separator tank according to one embodiment of the present invention. 
       FIG. 6  is a plan view of the insert for a separator tank according to one embodiment of the present invention. 
       FIG. 7A-7B  is a plan and section view of an orifice plate located in the insert according to one embodiment of the present invention. 
       FIG. 8  is a perspective view of the drop tube according to one embodiment of the present invention. 
       FIG. 9  is a plan view of the drop tube according to one embodiment of the present invention. 
       FIG. 10  is a longitudinal cross-section view of the drop tube according to one embodiment of the present invention. 
       FIG. 11  is a front view of the drop tube according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Disclosed embodiments of the present invention and their advantages may be understood by referring to  FIGS. 1-11 , wherein like reference numerals refer to like elements. 
   Referring to  FIG. 1 , a known separator tank, disclosed in U.S. Pat. No. 5,498,331, is illustrated. Separator tank  100  may generally be in the shape of container  102  having bottom wall  104 , side wall  106 , and top wall  108 . Bottom wall  104  and top wall  108  may generally be circular and flat. Side wall  106  may be substantially cylindrical. Bottom wall  104 , side wall  106 , and top wall  108  may define internal chamber  110 . In one embodiment, insert  112  may divide chamber  110  into upper chamber  114  above insert  112 , and lower chamber  116  below insert  112 . 
   Referring to  FIG. 2 , insert  112  has top surface  208 . Top surface  208  may generally be said to lie in a single horizontal plane, except for weir  210 , which extends above top surface  208 . In one embodiment, side wall  106  has inlet opening  200  located adjacently above top surface  208 . Side wall  106  may also have outlet opening  206  located adjacently above top surface  208  and spaced peripherally away from inlet opening  200 . Conduit  118  may be connected to inlet opening  200  through which liquid may be introduced into the separator tank. Further, conduit  120  may be connected to outlet opening  206 . Conduit  120  permits liquid to flow out of the separator tank. 
   Insert  112  may include a first opening  202 . Opening  202  may be disposed between inlet opening  200  and weir  210 . A second opening  204  may be on the outlet side of weir  210 . Openings  202  and  204  are such that liquid, without having to overflow weir  210 , may flow through inlet opening  202  to outlet opening  204 . To do so, liquid first flows through inlet opening  202  into the lower chamber  116 , through lower chamber  116 , and then up through second opening  204  into upper chamber  114 . 
   Referring to  FIG. 3 , insert  112  may include a drop pipe  300  and a riser pipe  304 . Drop pipe  300  may be connected to and extend downwardly from first opening  202 . Drop pipe  300  may have T-connection  302 . T-connection  302  may allow for distributing the entering liquid in opposite directions within lower chamber  116 . Riser pipe  304  may be connected to and extend downwardly from second opening  204 . Riser pipe  304  permits water from lower chamber  116  to flow upwardly into upper chamber  114 . 
   Referring now to  FIGS. 4 and 5 , separator tank  400  is shown according to one embodiment of the present invention. In addition to the features described above, in one embodiment, separator tank  400  includes various modifications and enhancements. These modifications and enhancements may include, for example, offsetting the position of insert  112  relative to inlet  118 , increasing the height of weir  412 , modifying first opening  202  to drop tube  402 , providing at least one vertical vane  410  in drop tube  402 , modifying the base of drop tube  402 , and modifying the back wall of drop tube  402 . Each of these modifications may contribute to increasing the treatment flow rate through separator tank  400 , while still maintaining high levels of separation and/or removal efficiency. Each modification will be described below. 
   Referring to  FIG. 5 , insert  112  is shown according to one embodiment of the present invention. In this embodiment, insert  112  may have a substantially circular outer perimeter, sized to fit within the cylindrical side wall of separator tank  400 . Insert  112  may include weir  412 , first opening  202 , orifice  502 , drop pipe  402 , riser pipe  404 , second opening  408 , and vent  406 . In another embodiment, one or more of these elements may be provided separately. 
   Referring to  FIG. 6 , insert  112  may be positioned such that weir  412  may be located between inlet  118  on one side of separator tank  400  and outlet  120  on the other side. In one embodiment, weir  412  may define a substantially circular intake area for receiving influent liquid. In another embodiment, weir  412  may define a partially circular or semi-circular intake area. In still another embodiment, weir  412  may define a rectangular intake area. In still another embodiment, weir  412  may define a polygonal intake area. In one embodiment, insert  112  or weir  412  may be positioned such that weir  412  induces the influent liquid to flow in a swirling motion within the intake area. For example, weir  412  may be offset from the center line of inlet  118  to induce swirling. In one embodiment, weir  412  may be offset from the center line of inlet  118  by about 5°, as best shown in  FIG. 6 . In this embodiment, as influent liquid enters the intake area, the influent liquid may have an angular momentum about orifice  502  causing the influent to swirl and form a controlled vortex. Further, in this embodiment, the influent liquid may form a controlled vortex consistently in the same direction during each flow event, which in turn may allow separator tank  400  to handle increased flow rates. Moreover, the controlled vortex may ensure that all floatables, such as oil, are forced down drop pipe  402 . Other degrees of offset or positions for weir  412  may be used as necessary and/or desired. 
   In another embodiment, inlet  118  may be tangential to separator tank  400 , thereby obviating the need to offset insert  112 . In this embodiment, the shape of weir  412  may be changed as necessary and/or desired to accommodate a tangential inlet. 
   In one embodiment, the height of weir  412  may be increased relative to prior art separator weirs. Increasing the height of weir  412  allows for the intake area to handle a greater flow rate. This embodiment leads to an increased pressure gradient, especially during high flow rates, that drives the liquid through separator tank  400 . Further, the increased height of weir  412  may allow for greater flow, which in turn may allow for the formation of a stronger and more controlled vortex. 
   Referring to  FIGS. 7A and 7B , orifice  502  is shown according to one embodiment of the present invention. Orifice  502  may be located in the intake area between inlet  118  and weir  412 . Orifice  502  may be positioned anywhere within the intake area. In one embodiment, orifice  502  creates first opening  202  through which influent liquid may enter drop pipe  402 . In one embodiment, orifice  502  may be modified to have a rounded entrance, as shown in  FIG. 7B . Orifice  502  may generally be said to have two diameters: an outside diameter  704  and an inside diameter  702 . Outside diameter  704  and inside diameter  702  may be sized appropriately for the environment in which separator tank  400  may be used. Outside diameter  704  may be equivalent to where the rounded edge of orifice  502  aligns with top surface  208  of insert  112 . The inside diameter  702  may be equivalent to where the rounded edge of orifice  502  aligns with the inside diameter of drop tube  402 . In another embodiment, the diameter of drop tube  402  may be larger than inside diameter  702 . The diameters of orifice  502  may be changed as necessary and/or desired. 
   Rounding the entrance of orifice  502  may increase the treatment flow rate to lower chamber  116 . This increase in flow rate may be achieved because rounding the entrance of orifice  502  reduces the pressure drop of the liquid as it flows from above insert  112  into drop pipe  402 . Further, rounding the edge of orifice  502  may prevent flow separation and resistance to flow. The radius of the rounded edge may be changed as necessary and/or desired. 
   Referring to  FIGS. 8-11 , drop tube  402  is shown according to one embodiment. In this embodiment, drop tube  402  may have a modified base and include at least one vertical vane  410 . Drop tube  402  may be integrally formed with insert  112  and extend into the lower chamber  116  of separator tank  400 . 
   As shown in  FIG. 9 , drop tube  402  may have a plurality of vertical vanes  410  protruding from the inside wall of drop tube  402 . Vertical vanes  410  serve to dissipate the vortex that is created in the intake area. As the influent liquid flows downward through drop tube  402 , vertical vanes  410  create mini-vortices off the end of each vane  410  that swirl in the opposite direction of the vortex. Thus, vertical vanes  410  dissipate the vortex and may create an equal distribution of flow within drop tube  402 . Vertical vanes  410  may also reduce the formation of eddies, which may lead to a more uniform velocity profile through drop tube  402 . Reducing the high velocity jets may thereby reduce the chance of re-entraining any contaminates that have already accumulated in lower chamber  116 . The shape, size, number, and/or location of vertical vanes  410  may be changed as necessary and/or desired. 
   Referring to  FIG. 10 , drop tube  402  may be modified to terminate at a base that may be comprised of two wings  806 . Wings  806  extend outwardly from drop tube  402  and comprise the base for drop tube  402 . In one embodiment, wings  806  may extend in opposite directions. Drop tube  402  may have two openings  804  through which liquid exits drop tube  402  and enters lower chamber  116 . In one embodiment, wings  806  may be angled slightly downward to prevent solids from accumulated on the base. Wings  806  may also prevent resuspension of contaminants already inside lower chamber  116 . In one embodiment, wings  806  direct the flow of the influent liquid into lower chamber  116  in a perpendicular direction to that of the normal direction of flow in lower chamber  116 . By introducing the influent liquid into lower chamber  116  in this manner, the residence time of the liquid in lower chamber  116  may be increased, and therefore the liquid may have an increased settling and separation time. 
   Referring to  FIGS. 10 and 11 , drop tube  402  may have back wall  810  and front wall  808 . In one embodiment, the arc length of back wall  810  may be greater than the arc length of front wall  808 . Modifying back wall  810  may prevent the influent liquid, as it exits drop tube  402 , from impinging the nearest separator tank wall, which may be directly behind drop tube  402 . In this embodiment, back wall  810  may reduce re-entrainment and excessive turbulence. 
   The following examples are included to demonstrate preferred embodiments of the claimed subject matter. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the claimed subject matter, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the scope of the claimed subject matter 
   EXAMPLE 
   A separator tank with the modifications and enhancements described above was tested to illustrate the capture efficiency of sediment, for five (5) flows, at 100, 200 and 300 mg/L concentration per flow. The tested separator tank consisted of a 6-foot diameter by approximately 6-foot high upper receiving chamber and 8-foot diameter by approximately 6-foot high lower settling chamber. An insert was mounted within the separator tank. The insert incorporated a semi-circular weir, 11-inch orifice plate, 18-inch inlet drop tee, 24-inch vertical outlet riser-pipe and 6-inch oil port. The unit had a 24-inch diameter inlet and outlet pipes, with the inlet invert tangent to the insert floor and inlet to outlet differential of 1-inch. The inlet pipe was oriented with a 1% slope and both pipes are centered within the unit. The modifications and enhancements included offsetting the inlet by 5°, increasing the height of the weir, providing four vertical vanes in the drop tube, providing two wings at the base of the drop tube, and increasing the arc length of the back wall of the drop tube. The hydraulic capacity and sediment removal efficiency was evaluated for the separator tank. 
   To determine the hydraulic capacity, preliminary flow (gpm) and water level (inches) within the unit were measured for 3 flows ranging from 0 to 1347 gpm (3.0 cfs). The maximum flow attained prior to breaching the bypass weir was 1122 gpm (2.5 cfs). Sediment removal efficiency tests were conducted at five (5) flows ranging from 281 to 1,403 gpm (0.63 to 3.13 cfs) with influent sediment concentrations of 100, 200 and 300 mg/L. The results are detailed below. 
   During the testing, the sediment concentration in the influent was measured in two ways. First, the sediment concentration was measured directly by placing iso-kinetic samplers in the water stream and a sample was collected. Second, the sediment concentration was measured indirectly by weighing the mass of the sediment metered into the measured flow and a concentration was calculated. Effluent sediment concentration was measure using iso-kinetic samplers in the flow. Removal efficiency was calculated using the direct measurements for influent and effluent. Adjusted removal efficiency was calculated using the indirectly measure influent concentration and the directly measured effluent concentration. 
   Sediment Removal Efficiencies at 125% Design Flow (1,403 gpm, 3.13 cfs) 
   1. 300 mg/L 
   The average flow recorded for the entire test was 1400.7 gpm (3.12 cfs), with a standard deviation (SD) of 2.91. The recorded temperature for the test was 75.4 degrees F. The measured influent sample concentrations ranged from 253.8 mg/L to 349.1 mg/L, with a mean concentration of 284.9 mg/L and SD of 39.8. The effluent concentrations ranged from 162.9 mg/L to 182.6 mg/L, with a mean concentration of 174.1 mg/L and SD of 8.4. The average background concentration was 0.8 mg/L. The resulting sediment removal efficiency for the indirect method was 38.9%. The adjusted influent concentrations ranged from 300.1 mg/L to 311.5 mg/L, with a mean concentration of 304.2 mg/L and SD of 4.5. The corresponding adjusted removal efficiency was 42.8%. 
   2. 200 mg/L 
   The average flow recorded for the entire test was 1401.4 gpm (3.12 cfs), with a standard deviation (SD) of 6.4. The recorded temperature for the test was 75.4 degrees F. The measured influent sample concentrations ranged from 177.8 mg/L to 220.0 mg/L, with a mean concentration of 196.3 mg/L and SD of 18.6. The effluent concentrations ranged from 122.1 mg/L to 139.2 mg/L, with a mean concentration of 132.3 mg/L and SD of 7.1. The average background concentration was 5.54 mg/L. The resulting sediment removal efficiency for the indirect method was 32.6%. The adjusted influent concentrations ranged from 199.1 mg/L to 204.0 mg/L, with a mean concentration of 201.8 mg/L and SD of 2.2. The corresponding adjusted removal efficiency was 34.4%. 
   3. 100 mg/L 
   The average flow recorded for the entire test was 1401.1 gpm (3.12 cfs), with a standard deviation (SD) of 3.3. The recorded temperature for the test was 75.2 degrees F. The measured influent sample concentrations ranged from 78.3 mg/L to 115.1 mg/L, with a mean concentration of 97.1 mg/L and SD of 16.5. The effluent concentrations ranged from 79.8 mg/L to 88.9 mg/L, with a mean concentration of 84.0 mg/L and SD of 3.3. The average background concentration was 1.96 mg/L. The resulting sediment removal efficiency for the indirect method was 13.5%. The adjusted influent concentrations ranged from 98.1 mg/L to 98.7 mg/L, with a mean concentration of 98.4 mg/L and SD of 0.3. The corresponding adjusted removal efficiency was 14.6%. 
   Sediment Removal Efficiencies at 100% Design Flow (1,122 gpm, 2.50 cfs) 
   1. 300 mg/L 
   The average flow recorded for the entire test was 1122.0 gpm (2.50 cfs), with a standard deviation (SD) of 2.39. The recorded temperature for the test was 76.9 degrees F. The measured influent sample concentrations ranged from 241.5 mg/L to 368.0 mg/L, with a mean concentration of 297.5 mg/L and SD of 51.9. The effluent concentrations ranged from 105.5 mg/L to 132.6 mg/L, with a mean concentration of 120.4 mg/L and SD of 11.3. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 59.5%. The adjusted influent concentrations ranged from 98.5 mg/L to 306.8 mg/L, with a mean concentration of 304.2 mg/L and SD of 3.7. The corresponding adjusted removal efficiency was 60.4%. 
   2. 200 mg/L 
   The average flow recorded for the entire test was 1121.6 gpm (2.50 cfs), with a standard deviation (SD) of 3.51. The recorded temperature for the test was 76.7 degrees F. The measured influent sample concentrations ranged from 157.9 mg/L to 253.2 mg/L, with a mean concentration of 190.1 mg/L and SD of 38.2. The effluent concentrations ranged from 72.3 mg/L to 86.9 mg/L, with a mean concentration of 80.4 mg/L and SD of 6.1. The average background concentration was 3.5 mg/L. The resulting sediment removal efficiency for the indirect method was 57.7%. The adjusted influent concentrations ranged from 197.4 mg/L to 203.1 mg/L, with a mean concentration of 201.1 mg/L and SD of 2.3. The corresponding adjusted removal efficiency was 60.0%. 
   3. 100 mg/L 
   The average flow recorded for the entire test was 1118.3 gpm (2.49 cfs), with a standard deviation (SD) of 2.6. The recorded temperature for the test was 75.7 degrees F. The measured influent sample concentrations ranged from 100.8 mg/L to 121.8 mg/L, with a mean concentration of 110.3 mg/L and SD of 8.0. The effluent concentrations ranged from 46.8 mg/L to 62.0 mg/L, with a mean concentration of 55.9 mg/L and SD of 7.8. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 49.3%. The adjusted influent concentrations ranged from 98.5 mg/L to 99.4 mg/L, with a mean concentration of 99.0 mg/L and SD of 0.3. The corresponding adjusted removal efficiency was 43.5%. 
   Sediment Removal Efficiencies at 75% Design Flow (842 gpm, 1.88 cfs) 
   1. 300 mg/L 
   The average flow recorded for the entire test was 840.7 gpm (1.87 cfs), with a standard deviation (SD) of 2.2. The recorded temperature for the test was 77.9 degrees F. The measured influent sample concentrations ranged from 406.4 mg/L to 452.3 mg/L, with a mean concentration of 436.8 mg/L and SD of 18.9. The effluent concentrations ranged from 86.5 mg/L to 95.7 mg/L, with a mean concentration of 92.0 mg/L and SD of 3.4. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 78.9%. The adjusted influent concentrations ranged from 305.7 mg/L to 319.2 mg/L, with a mean concentration of 314.9 mg/L and SD of 4.9. The corresponding adjusted removal efficiency was 70.8%. 
   2. 200 mg/L 
   The average flow recorded for the entire test was 842.4 gpm (1.88 cfs), with a standard deviation (SD) of 2.2. The recorded temperature for the test was 78.7 degrees F. The measured influent sample concentrations ranged from 256.2 mg/L to 290.4 mg/L, with a mean concentration of 276.4 mg/L and SD of 13.4. The effluent concentrations ranged from 56.7 mg/L to 79.9 mg/L, with a mean concentration of 73.4 mg/L and SD of 9.5. The average background concentration was 1.5 mg/L. The resulting sediment removal efficiency for the indirect method was 73.4%. The adjusted influent concentrations ranged from 198.7 mg/L to 205.5 mg/L, with a mean concentration of 202.8 mg/L and SD of 2.6. The corresponding adjusted removal efficiency was 63.8%. 
   3. 100 mg/L 
   The average flow recorded for the entire test was 841.6 gpm (1.88 cfs), with a standard deviation (SD) of 2.03. The recorded temperature for the test was 76.5 degrees F. The measured influent sample concentrations ranged from 85.4 mg/L to 130.2 mg/L, with a mean concentration of 104.4 mg/L and SD of 18.7. The effluent concentrations ranged from 31.5 mg/L to 46.6 mg/L, with a mean concentration of 37.9 mg/L and SD of 6.4. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 63.7%. The adjusted influent concentrations ranged from 98.6 mg/L to 102.6 mg/L, with a mean concentration of 101.6 mg/L and SD of 1.5. The corresponding adjusted removal efficiency was 62.7%. 
   Sediment Removal Efficiencies at 50% Design Flow (561 gpm, 1.25 cfs) 
   1. 300 mg/L 
   The average flow recorded for the entire test was 560.2 gpm (1.25 cfs), with a standard deviation (SD) of 1.0. The recorded temperature for the test was 76.3 degrees F. The measured influent sample concentrations ranged from 287.1 mg/L to 375.5 mg/L, with a mean concentration of 339.6 mg/L and SD of 34.6. The effluent concentrations ranged from 82.8 mg/L to 97.9 mg/L, with a mean concentration of 91.5 mg/L and SD of 6.0. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 73.0%. The adjusted influent concentrations ranged from 298.7 mg/L to 317.0 mg/L, with a mean concentration of 311.7 mg/L and SD of 7.0. The corresponding adjusted removal efficiency was 70.6%. 
   2. 200 mg/L 
   The average flow recorded for the entire test was 560.4 gpm (1.25 cfs), with a standard deviation (SD) of 1.2. The recorded temperature for the test was 76.6 degrees F. The measured influent sample concentrations ranged from 200.7 mg/L to 246.2 mg/L, with a mean concentration of 224.7 mg/L and SD of 16.8. The effluent concentrations ranged from 48.6 mg/L to 64.3 mg/L, with a mean concentration of 55.6 mg/L and SD of 7.0. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 75.2%. The adjusted influent concentrations ranged from 196.9 mg/L to 205.3 mg/L, with a mean concentration of 202.7 mg/L and SD of 3.1. The corresponding adjusted removal efficiency was 72.6%. 
   3. 100 mg/L 
   The average flow recorded for the entire test was 558.3 gpm (1.24 cfs), with a standard deviation (SD) of 9.0. The recorded temperature for the test was 77.2 degrees F. The measured influent sample concentrations ranged from 100.8 mg/L to 122.4 mg/L, with a mean concentration of 114.8 mg/L and SD of 8.5. The effluent concentrations ranged from 25.9 mg/L to 29.4 mg/L, with a mean concentration of 28.1 mg/L and SD of 1.4. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 75.6%. The adjusted influent concentrations ranged from 100.8 mg/L to 102.5 mg/L, with a mean concentration of 101.5 mg/L and SD of 0.7. The corresponding adjusted removal efficiency was 72.4%. 
   Sediment Removal Efficiencies at 25% Design Flow (281 gpm, 0.63 cfs) 
   1. 300 mg/L 
   The average flow recorded for the entire test was 280.7 gpm (0.63 cfs), with a standard deviation (SD) of 0.4. The recorded temperature for the test was 75.6 degrees F. The measured influent sample concentrations ranged from 318.8 mg/L to 363.0 mg/L, with a mean concentration of 331.2 mg/L and SD of 18.3. The effluent concentrations ranged from 25.6 mg/L to 41.7 mg/L, with a mean concentration of 31.8 mg/L and SD of 7.4. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 90.4%. The adjusted influent concentrations ranged from 286.5 mg/L to 307.3 mg/L, with a mean concentration of 293.3 mg/L and SD of 9.2. The corresponding adjusted removal efficiency was 89.2%. 
   2. 200 mg/L 
   The average flow recorded for the entire test was 280.9 gpm (0.63 cfs), with a standard deviation (SD) of 0.4. The recorded temperature for the test was 75.5 degrees F. The measured influent sample concentrations ranged from 200.9 mg/L to 234.4 mg/L, with a mean concentration of 216.8 mg/L and SD of 15.5. The effluent concentrations ranged from 13.2 mg/L to 21.8 mg/L, with a mean concentration of 16.0 mg/L and SD of 3.4. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 92.6%. The adjusted influent concentrations ranged from 189.1 mg/L to 193.7 mg/L, with a mean concentration of 193.3 mg/L and SD of 1.9. The corresponding adjusted removal efficiency was 91.7%. 
   3. 100 mg/L 
   The average flow recorded for the entire test was 281.1 gpm (0.63 cfs), with a standard deviation (SD) of 0.4. The recorded temperature for the test was 75.4 degrees F. The measured influent sample concentrations ranged from 77.5 mg/L to 140.5 mg/L, with a mean concentration of 101.6 mg/L and SD of 24.4. The effluent concentrations ranged from 4.7 mg/L to 9.6 mg/L, with a mean concentration of 6.8 mg/L and SD of 2.2. The average background concentration was negligible. The resulting sediment removal efficiency for the indirect method was 93.3%. The adjusted influent concentrations ranged from 95.9 mg/L to 102.8 mg/L, with a mean concentration of 99.4 mg/L and SD of 3.2. The corresponding adjusted removal efficiency was 93.1%.