head43rd and Logan Filtration and Biofiltration Project
Chollas Creek Watershed Protection

This project is currently under construction.  Construction phase photos are forthcoming.

Biofiltration Basin Design – The biofilter basin has a treatment surface area of approximately 4,800 square feet, with a maximum length of approximately 110 feet and a maximum width of approximately 65 feet.  At treatment capacity, the basin will pond approximately six inches of water.  The filtration media is approximately 18 inches thick and has a subdrain system that connects to the public storm drain system within the adjacent street.  The basin overflow feature consists of a side opening catch basin outlet structure set to capture the tributary 100-year peak runoff with a maximum water surface elevation equal to one foot below the top of the basin side slopes.  In the event that the basin outlet structure should clog or fail to function as designed, basin overflow will drain to the adjacent street over the sidewalk.  Filtration media consists of granular soils and organic materials.  The target pollutants to be removed include total and dissolved metals, bacteria, sediment, oil and grease, pesticides and trash.  The removal efficiency target is 50 to 80 percent for the 85th percentile flow based storm event, being the runoff produced from a rainfall intensity of 0.2 inches per hour.  The associated treatment flow rate from the 0.73 acre tributary watershed is approximately 0.11 cubic feet per second.  The anticipated required infiltration/filtration rate of the filter media is approximately one inch per hour, and the associated drawdown time with the basin at capacity is approximately six hours.  Due to the basin proximity to an adjacent slope, the basin will be underlain by an impermeable membrane to prohibit infiltration of filtered runoff into adjacent soils.  It is anticipated that regular maintenance will be required during the wet season to remove trash from the basin forebay.  The frequency of maintenance will depend upon the amount of rainfall and the amount of litter in the tributary watershed.  Regular maintenance will be required of the vegetation within and adjacent to the basin.  Observation of the filtration rate and treated runoff pollutant concentrations will dictate the required maintenance frequency of the filter media.

Curbside Filtration System – Each cell of the curbside filtration system is 40 inches wide by 10 feet long and contains an 18 inch thick filtration media.  This media has a subdrain system that connects to the public storm drain system within the adjacent street.  The filtration system will run parallel to the curb between the curb and sidewalk, with breaks at driveways, utility boxes, water meter clusters, and other necessary stopping points.  Flows in excess of the filtration system capacity will pass across the surface of the filtration media and exit the system back to the adjacent street gutter.  The media will consist of granular soils and organic materials.  The target pollutants to be removed include total and dissolved metals, bacteria, sediment, oil and grease, pesticides and trash.  The removal efficiency target is 50 to 80 percent for the 85th percentile flow based storm event, being the runoff produced from a rainfall intensity of 0.2 inches per hour.  The associated treatment flow rate from the 5.76 acre tributary watershed is approximately 0.92 cubic feet per second.  The anticipated required infiltration/filtration rate is approximately 5.5 inches per hour.  Within each cell, ponding above the filter media occurs within a layer of crushed volcanic rock and is not visible from the surface.  The drawdown time within the rock layer with the filter unit at capacity is less than one hour.  Runoff treated within the filtration system will be prevented from moving laterally into the street and sidewalk subgrade by a concrete liner and from infiltrating down to subsurface soils by an impermeable synthetic liner.  It is anticipated that regular maintenance will be required during the wet season to remove trash from the filtration system inlet opening.  The frequency of maintenance will depend upon the amount of rainfall and the amount of litter in the tributary watershed.  Observation of the filtration rate and treated runoff pollutant concentrations will dictate the required maintenance frequency of the filter media.

 

 

   

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