RESOLUTION OF 

              SEDIMENT CHEMISTRY QUALITY ASSURANCE CODES


       If results for these QC samples did not fall within 
       certain pre-established control limits, the analysis of 
       a batch of samples was not considered acceptable.  These 
       and other quality control issues are coded in four data 
       qualifier codes (QA_CODE) or "flags" used in the Louisianian 
       Province sediment chemistry data file: 

          CH-A CODE

          The "CH-A" code indicates that an analyte was not detected. 
          When the "CH-A" code is used, the concentration field is left
          blank and the method detection limit for the analyte in that
          particular sample is reported under DETLIMIT.  

          CH-B CODE

          It is sometimes possible for a laboratory to detect an analyte
          and report its concentration at a level which is below the
          calculated method detection limit for the sample.  In these
          situations, the analyst is confident that the analyte was present
          in the sample, but there is a high degree of uncertainty in the
          reported concentration.  The "CH-B" code is used to flag
          reported values which are below the calculated method
          detection limit for the sample.  Such values are considered
          estimates only and should be used with discretion.

          CH-C          

          The CH-C code indicates that the laboratory experienced
          minor deficiencies meeting the QC requirements, but the
          overall data quality is judged to be reliable for EMAP
          assessments.

          CH-I CODE

          Some analytes are difficult to quantify because they co-elute
          with other closely related analytes.  This phenomenon is called
          "matrix interference".  When this occurs, the suspect
          analyte(s) are given a "CH-I" code and concentration is left
          blank.

          CH-M CODE

          Samples werer lost or destroyed. 

          CH-X CODE

          In favor of expediency, a laboratory may elect to cease
          reporting some of the analytes.  EMAP protocol only requires
          that the laboratory analyze a given list of chemicals;  when
          they go beyond this list and report additional chemicals, we
          include them in our data.  The "CH-X" code indicates that an
          analyte has been excluded from a given set of data. 

          Only "unflagged" or CH-E coded values are considered valid
          and useful for most assessment purposes.

          CH-Z CODE

          Some of the analytes listed represent the sum of concentrations of
          similar analytes (e.g., PCB_TOT is the sum of the concentrations
          of all PCB congeners).  In the event that the concentrations for
          all of the individual analytes included in the sum are non-detects
          (have CH-A code) the sum is missing.  This is not technically a
          non-detect, but a sum of non-detects, hence the CH-Z code.