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2007 CA-NV-AWWA ANNUAL FALL CONFERENCE Tracer Studies Modified Step-Dose Method

2007 CA-NV-AWWA ANNUAL FALL CONFERENCE Tracer Studies Modified Step-Dose Method. October 25, 2007 Presented by: Guy Schott, P.E. Associate Sanitary Engineer CA Department of Public Health Drinking Water Field Operations Branch 707-576-2732 guy.schott@cdph.ca.gov.

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2007 CA-NV-AWWA ANNUAL FALL CONFERENCE Tracer Studies Modified Step-Dose Method

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  1. 2007 CA-NV-AWWA ANNUAL FALL CONFERENCETracer Studies Modified Step-Dose Method October 25, 2007 Presented by: Guy Schott, P.E. Associate Sanitary Engineer CA Department of Public Health Drinking Water Field Operations Branch 707-576-2732 guy.schott@cdph.ca.gov

  2. What to Expect from This Presentation • Information on how to shorten a long tracer test and still receive valid results. • End of Presentation Contest: Guest t10/T for a circular contact tank.

  3. Definitions • t10 – is defined as the amount of time it takes for 10% of a non-reactive material to pass through a basin. • T: Theoretical Detention • t10/T: Short-Circuiting Factor

  4. Step-Dose Method – a continuous tracer feed added throughout test (3 to 4 * T).

  5. Slug-Dose Method – The entire amount tracer is added at the beginning of test (3 to 4 * T).

  6. Why is Tracer Test Carried Out to 3 to 4 * Theoretical? • To validate mass added to mass recovered. • Step-Dose: If dose at 2.0 mg/L, should see around 2.0 mg/L leaving tank. • Sludge-Dose: If 10 lbs of tracer is added, should recovery close to 10 lbs leaving tank.

  7. Reasons Why Mass Recovery Different from Mass Dosage • Flow meter(s) not accurate. • Mass added is not what you think it is. • Chemical feed pump • Solution strength • Math error • Error in lab analysis • Unknown by-pass flow around clearwell If we can minimize the errors above, then a different test method may be applied.

  8. Modified Step-Dose Method • Similar to Step-Dose Test • Differences: • Shorter test duration: tracer is discontinued when 10% of mass has exit reactor (< Theoretical Detention Time) (big advantage) • Allows for higher dosage (5 to 10 mg/L of F) • Increased analytical sensitivity at the 10% dose rate measurement • Test Application – suitable for long test duration under the Step-Dose test.

  9. Modified Step-Dose Test To minimize errors: • Must conduct physical measurement of applied chemical (mL/min) to verify dosage in mg/L • Must verified fluoride solution strength • Should be confident in the accuracy of flow meter • Must be confident in your analytical equipment & procedures

  10. Application of Modified Step-Dose Test Out T = 4.2 Hr 3T = 12.6 Hr In t10/T = 0.1 Actual Test Completed in 30 Minutes (save 12 hours of work)

  11. Application of Modified Step-Dose Test Out T = 1.7 Hr 3T = 5.2 Hr t10/T = 0.5 In Actual Test Completed within 1 hour (save 4.2 hours of work)

  12. Modified Step-Dose Test A tracer test was conducted on each clearwell on same day • Saved 15 hours in sample collecting and testing • Saved 3 hours in travel time for second test • Total Saved: 18 hours

  13. Out In Application of Step-Dose vs. Modified Step-Dose Test t10/T = 0.69 (Modified Step-Dose Method) t10/T = 0.70 (Step-Dose Method, no correction for flow meter) t10/T = 0.67 (Step-Dose Method, corrected for 5% error in flow meter)

  14. How Much Tracer to Add in a Modified Step-Dose Test 1. Theoretical based on CSTR Modeling 2. Based on shutting off feed pump when effluent concentration is at 25% of influent dosage.

  15. Modified Step-Dose Test • Approximate equation for determining dosage for desired peak concentration. Where DPEC is desired peak effluence concentration based on shutting off tracer feed pump when effluent concentration is at 25% of influent dosage concentration.

  16. Special Tank Design t10/T = ?

  17. Tracer Study Data Base To receive copy of California’s tracer data base, send email to: Guy Schott guy.schott@cdph.ca.gov Summarizes results of tracer tests and respective tank configurations.

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