Presented by: Guy Schott, P.E. Associate Sanitary Engineer CA DHS-Drinking Water Program

1. 2002 CA-NV-AWWA ANNUAL FALL CONFERENCEOCTOBER 17, 2002Tracer Studies Common Problems & Mistakes Presented by: Guy Schott, P.E. Associate Sanitary Engineer CA DHS-Drinking Water Program 707-576-2732 gschott@dhs.ca.gov

2. Information to get out of Presentation • Assist utilities in determining if a tracer study was conducted properly. • Present information that can help utilities and consultants to avoid conducting a poor tracer test.

3. Issues • Tracer Selection • Sample Frequency • Run Length • Tracer Mass Recovery • t10 Calculations for Reactors in Series • Chemical Feed Pump (Step-Dose)

4. Tracer Selection Most common tracers: • Fluoride (low analytical cost) • Lithium (high analytical cost), requires very little tracer mass in tracer test. Others • NaCl • Rhodamine WT • Calcium • Zinc Tracer should be non-reactive

5. Appropriate Tracer Selection Consider tracer reaction, quantity & analytical cost Example: 10 lbs of Lithium Chloride vs. 2,000 lbs of NaCl Density current may result with NaCl & not practical to dose large quantity; use Lithium Mistakes Seen: • Fluoride tracer used in sedimentation Problem: fluoride reacts with alum. • Consider lithium

6. Sample Frequency Must have adequate number of samples to define mass recovery curve. Mistakes Seen: Save money on sample analysis, thus take less samples – Results In: Inadequate samples and poor results – test run invalidated.

7. Example – Lack of Samples Deficient samples, Unaccounted tracer mass lost

8. Example – Lack of Samples Deficient samples, Unaccounted tracer mass gain

9. Test Run Length • Ideally, 3 to 4 theoretical detention times (T) • Less may be adequate if situation calls for it. Mistakes Seen: Inadequate test runs (.4T to 1.5 T) Results In: inadequate tracer mass recovery - test run invalided.

10. Goal: high mass recovery (90 – 100 %) 80% - 90% (fair to good recovery) Verify mass recovery: Mistakes Seen: Incorrectly calculated mass dosed. Use wrong molecular weight. Results In: Improved or poor mass recovery. Tracer Mass Recovery & Calculated Error

11. Two tanks in series: Check Results (does it make sense): real example of short test run and mass recovery Tracer Tank 1 Tank 2 Sample pt. 1 Sample pt. 2 96% recovery 0.8T run time (Tanks 1 & 2) Does this make sense? Check run time and mass recovery calculations

12. Two tanks in series: Check Results (does it make sense): example of short test run and mass recovery Tracer Tank 1 Tank 2 Sample pt. 1 168% recovery, 1.5T run Time (Tank 1) Sample pt. 2 96% recovery, 0.8T run Time (Tanks 1 & 2)

13. Two tanks in series: T10 Calculations for Reactors in Series Tracer Tank 1 Tank 2 Sample pt. 1 t10 = 10 minutes Sample pt. 2 t10 = 53 minutes (overall) Wrong: 53 min. – 10 min = 43 min (t10 for Tank 2 alone) This method cannot be used to determine t10 for Tank 2 alone.

14. Chemical Feed Pump (Step-Dose) • Select reliable chemical feed pump for tracer test. (Problem Seen: Erratic feed pump – results in poor tracer test) • Throughout test, analyze samples down stream of feed pump before reactor to verify tracer dosage. • High tracer dosages will overcome any minor variations in chemical feed pump.

15. Develop Tracer Protocol • A well developed test protocol can result in a successful test. • Submit to DHS for review and comments.

16. Reference • Tracer Studies in Water Treatment Facilities: A Protocol and Case Studies American Water Works Association Research Foundation ISBN 0-89867-857-9

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