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Efficient Suction Dredging Techniques for Placer Examination

Learn about the general principles of suction dredging for placer examination, including dredge size, personnel requirements, equipment selection, and safety measures. Get insights on developing a working face, air supply options, tools needed, and certification requirements.

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Efficient Suction Dredging Techniques for Placer Examination

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  1. SUCTIONDREDGINGTECHNIQUES Placer Examination Techniques

  2. GENERALPRINCIPLES The size of the dredge is directly proportional to the dynamics of the stream • Width • Depth • Thickness of the overburden • Logistics • Size of dredge used by the operator

  3. NUMBER OF PEOPLE • 1 to 3 people • Small dredge (4-inch or less), 1-2 people • Medium dredge (4 to 6-inch), 2-3 people • Large dredge (6-inch plus), 3+ people • Although some prefer to dredge alone, efficiency drops and danger increases.

  4. NUMBER OF PEOPLE • One person operates the nozzle • Second person moves boulders and tends the dredge. • If water is deep, a third person is included as the dredge tender on the surface while 2 are always under water.

  5. NUMBER OF PEOPLE • 1 person is 60% as efficient as 2 people • Move boulders • Tend dredge • Alternate with nozzle operator • Tender provides sample security on exams • Safer than working alone

  6. DREDGESELECTION • Large enough for the material being dredged • Enough suction to pull the material to the sluice • Deep enough water to float the dredge • Drafting • Deep enough to keep the intake submerged • Size is consistent with State regulations

  7. PERSONALEQUIPMENT • Each examiner maintains his/her own equipment • Wetsuits • Face mask and snorkel • Gloves • Footwear • Knee pads • Weight belts NEVER, EVER WEAR SUN SCREEN!

  8. TOOLS • Hand tools – pry bars • Long breaker bars • Come-alongs • Shovels and rakes • Rubber mallet • Rope • Crevice tools

  9. DEVELOPING A WORKING FACE • If a hole is not ready a working face is needed. • Move boulders and get them out of the way • Make a hole you can work in • Work upstream • Get it all and break up bedrock • Keep a controlled and consistent feed • Observe what you are dredging – check for Au

  10. AIR SUPPLY Two types of air supply • Snorkel • Shallow water with thin gravel layer • Easy maneuverability • Hookah • Deep water – over 3 feet deep • Compressor, air lines, harness, regulator, reserve tank, filters, maintenance

  11. SAFETY • Working under water, often swift water • Under large boulders, stumps, embankments • Limited visibility • Moving heavy objects, carrying equipment • Depending on supplied air • Extended periods in cold water • Possible contaminated water • Using hand tools in conditions with limited visibility

  12. CERTIFICATION • Forest Service in California (Region 5) requires open diver certification

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