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Upper Midwest Environmental Sciences Center

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 Water Quality Data
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UMESC LTRMP Water Quality Chemical QA/QC Flags

Revised 03/27/2003

The flagging system is intended to be EASY to separate the data into quality grades, e.g., Good, Questionable, or Bad.

The codes shown in the table below (0, A-P) can be assigned in any combination.  ALL of the 16 flags can be used if needed.  In the Oracle database, the numeric value of all the codes associated with a single measurement are converted to their numeric value and added together (i.e., bits 0-16 are set) to produce a single numeric flag value that ranges from 0 to 65,536 (64 K).  Note that all the nonfatal flags in combination sum to 255 and the first fatal flag has a numeric value of 256.  Thus, a flag value < 255 indicates a fatal problem with the measurement and a missing (null) value is transmitted from the lab to the Oracle database along with the flag value.

Table below lists the codes assigned in the lab.  The number in parenthesis following each code is its bit (numeric) equivalent.

Sample perfect flag = (0 Zero) Concentration below detection = (1 one) Data questionable flag = (2-255; first byte) Data useless or lost flag = (256 - 65536; 2nd byte) Sample/data quality unknown or missing flag is NULL or BLANK
Sample Perfect (0; Zero) (1) Sample conc. is below detection limit* NONFATAL SHIPMENT ERRORS FATAL SHIPMENT ERRORS
  (2) Sample delayed in shipment (256) Preservation error--sample ruined
  (4) Sample holding conditions (temperature, light) violated (512) Labeling error--sample ID uncertain or unidentifiable or sample id is inconsistent with analytical results (i.e., blank values on nonblank sample or nonblank values on blank sample
  (8) Sample condition was marginal or questionable when received--sample analyzed anyway (1024) Sample spilled, leaked, damaged, contaminated in shipment--unusable
    (2048) Sample data error--volume or weight incorrect/unusable
  (16) Deviation from standard method--result probably OK. (4096) Sample ruined/contaminated during analysis
  (32) Holding time or holding conditions violated (8192) Sample lost in lab--not analyzed
  (64) Analysis uncertain--result unreliable or suspicious. (16384) Not used
  (128) Analysis repeated (32768) Result inconsistent with other parameter measurements--if erroneous member of inconsistent set cannot be identified, all related samples are marked with this fatal flag

* Concentrations < the minimum detection limit (MDL) are also reported as negative MDL (e.g., -0.005).

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