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EVALUATION OF LAB DATA

SW1091TC SEDIMENT DATA-COLLECTION TECHNIQUES Castle Rock and Vancouver Washington. EVALUATION OF LAB DATA. Larry Freeman lfreeman@usgs.gov. WERE THERE LARGE PARTICLES IN THE SAMPLE?. INDICATED BY POOR COMPARISON BETWEEN SETS, OR UNUSUALLY LOW SAND BREAK VALUES.

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EVALUATION OF LAB DATA

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  1. SW1091TC SEDIMENT DATA-COLLECTION TECHNIQUES Castle Rock and Vancouver Washington EVALUATION OF LAB DATA Larry Freeman lfreeman@usgs.gov

  2. WERE THERE LARGE PARTICLES IN THE SAMPLE? • INDICATED BY POOR COMPARISON BETWEEN SETS, OR UNUSUALLY LOW SAND BREAK VALUES.

  3. LOOK TO SEE IF SAMPLE CONTAINER WAS OVERFILLED? INDICATED BY TOO HIGH OF WEIGHT FOR WATER/SEDIMENT MIXTURE. Scrutiny should be given to sample results: If PINT BOTTLE SAMPLE NET WEIGHT IS > ~470 GRAMS. If LITER BOTTLE SAMPLE NET WEIGHT IS > ~ 800 GRAMS.

  4. CHECK FOR EXCESSIVE TIME BETWEEN SAMPLE TIME AND LAB ANALYSIS? COULD RESULT IN ARTIFICIALLY INCREASED CONCENTRATION DUE TO: -EVAPORATION -CHEMICAL REACTIONS CAUSING PRECIPITATES. -BIOLOGICAL GROWTH

  5. WATCH FOR INCORRECT COMPOSITING OR ANALYSIS • COMPARE LAB REPORTS WITH YOUR FIELD NOTES AND SAMPLE LOG SHEETS. • CHECK DATES AND TIMES THAT DON’T MATCH FIELD NOTES OR RECORDED DATA. • POOR DATA MATCHES CAN INDICATE POSSIBLE SAMPLE SWITCHING. CHECK AGAINST POOR MATCHES FROM ANOTHER DATE OR ANOTHER STATION. • BOTTLE SWITCHES CAN HAPPEN IN THE FIELD, IN THE OFFICE AND IN THE LAB (although rare).

  6. LOOK FOR COMPUTATION ERRORS • SHOULD BE RARE WITH COMPUTER GENERATED DATA. • MORE COMMON WITH HAND CALCULATIONS ON BEDLOAD AND BED MATERIAL LAB REPORTS. • CHECK HAND CALCULATIONS DONE BY LAB TECHNICIAN.

  7. LOOK FOR DIFFERENCES IN PAIRED SAMPLE SETS TRY TO EXPLAIN BEFORE INVALIDATING A SAMPLE. -LOOK FOR DATE/TIME ERRORS -FIELD NOTE ERRORS -LAB COMPUTATION ERRORS. -IF ALL ABOVE ARE CORRECT, THEN SEEK A HYDROLOGIC EXPLANATION. OMITTING A SAMPLE IS ALWAYS THE LAST RESORT AND MUST BE JUSTIFIED!

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