Presentation on theme: "Dewatering & Coastal Issues H 2 0 & Erosion Control Workshop UCF Stormwater Management Academy March 15-16, 2007 Jim Smoot, PhD, PE Molly Wood, PE U.S."— Presentation transcript:
Dewatering & Coastal Issues H 2 0 & Erosion Control Workshop UCF Stormwater Management Academy March 15-16, 2007 Jim Smoot, PhD, PE Molly Wood, PE U.S. Department of Interior U.S. Geological Survey
Dewatering Operations INTRODUCTION Overview of Dewatering Technologies Overview of Dewatering Technologies Selection, Design, and Operational Considerations Selection, Design, and Operational Considerations CONTROL TECHNOLOGIES Sediment Traps Sediment Traps Sediment Basins Sediment Basins Weir Tanks Weir Tanks Dewatering Tanks Dewatering Tanks Gravity Bag Filters Gravity Bag Filters Sand Media Filters Sand Media Filters Pressurized Bag and Cartridge Filters Pressurized Bag and Cartridge Filters Chemical Treatment - Continuous Chemical Treatment - Continuous Chemical Treatment - Batch Chemical Treatment - Batch
Control Technology Selection Does water have quality problems other than sediment (e.g. odor, sheen, foam, discoloration)? Is it feasible to manage water without discharge to stormwater system or receiving waters? Additional approaches and technologies beyond the scope of this manual may be needed – consider consulting a water quality treatment expert Retain water on-site (infiltrate) Discharge by agreement to sanitary sewer Transport for off-site disposal Star t Will sediment settle in a reasonable time and produce low enough turbidity? Design Weir Tank or Dewatering Tank System Design Sediment Trap or Sediment Basin Design Gravity- Bag, Pressurized- Bag, Cartridge, or Media Filter- System Consider chemical treatment alternatives Select and test chemicals and dosages Design Chemical Treatment System No Yes No Select Appropriate BMP Yes
Comparison of Dewatering Technologies Treatment Technology Group Treatment Technology Pollutant TreatedDesign Flow (gpm) Footprint (sq. ft.) Sediment Traps & Sediment Basins Sediment TrapsSediment25 to 500Varies Sediment BasinsSediment25 to 500Varies Weir Tanks & Dewatering Tanks Weir TanksSediment, Metals, Oil & Grease 60 to 1001,800 Dewatering TanksSediment, Metals, Oil & Grease Varies1,200 to 1,500 FiltersGravity Bag FilterSediment and Metals300 to 800100 to 400 Sand Media FilterSediment, Metals, BOD80 to 1,00017 to 450 Pressurized Bag and Cartridge Filter Sediment, Metals, BOD, and Hydrocarbons 50 to 1,000200 to 320 Chemical Treatment Continuous Chemical Treatment SedimentVaries Batch Chemical Treatment SedimentVaries
SEDIMENT TRAPS A sediment trap is a temporary basin formed by excavation and/or construction of an earthen embankment or low drainage area to detain sediment-laden runoff and allow sediment to settle out before discharging. Sediment traps are generally smaller than sediment basins.
SEDIMENT BASINS A sediment basin is a temporary basin with a controlled release structure that is formed by excavation or construction of an embankment to detain sediment-laden runoff and allow sediment to settle out before discharging. Sediment basins are generally larger than sediment traps.
WEIR TANKS AND DEWATERING TANKS A weir tank separates water and waste by using weirs. The configuration of the weirs (over and under weirs) maximizes the residence time in the tank and determines the waste to be removed from the water, such as oil, grease, and sediments. A dewatering tank removes debris and sediment. Flow enters the tank through the top, passes through a fabric filter, and is discharged through the bottom of the tank. The filter separates the solids from the liquids. Weir Tank Dewatering Tank
FILTERS A gravity bag filter is a square or rectangular bag made of non-woven geotextile fabric that collects sand, silt, and fines. Generally, sand filters provide a final level of treatment. Water is treated by passing it through canisters filled with sand media. They are often used as a secondary or higher level of treatment after a significant amount of sediment and other pollutants have been removed using other methods. A pressurized bag filter is a unit composed of single filter bags made from polyester felt material. The water filters through the unit and is discharged through a header. Vendors provide bag filters in a variety of configurations. Some units include a combination of bag filters and cartridge filters for enhanced contaminant removal. Cartridge filters provide a high degree of pollutant removal by utilizing a number of individual cartridges as part of a larger filtering unit. They are often used as a secondary or higher (polishing) level of treatment after a significant amount of sediment and other pollutants are removed. Units come with various cartridge configurations (for use in series with bag filters) or with a larger single cartridge filtration unit (with multiple filters within).
CHEMICAL TREATMENT Chemical treatment includes the application of carefully selected chemicals such as polymers (e.g. PAM), alum, and other flocculants to waters to aid in the reduction of turbidity by more efficient removal of fine suspended sediment. Batch Continuous