QC Procedures for Sampling

Sampling QC begins with calibration and preventative maintenance procedures for sampling equipment. The POTW’s Sampling and Quality Assurance Plan should include a calibration plan and documentation record for all field sampling and analysis equipment used. A complete document record should be kept in a QC logbook, including equipment specifications, calibration date, and calibration expiration data, and maintenance due date. The person sampling should keep in mind that field analytical equipment should be recalibrated in the field prior to taking the sample. Personnel conducting sampling should be well‐trained in the use, cleaning, calibration, and maintenance of all instruments or samplers used. Automatic sampler tubing, bottles, and the sampler itself should be cleaned prior to each sampling event. Automatic samplers should be calibrated for sample quantity, line purge, and the timing factor, if applicable. This calibration should be checked in the field to verify draw. The manufacturer’s directions should be reviewed and followed for cleaning and calibrating all equipment.

In addition to calibration procedures, the person conducting field sampling should conduct control checks during the actual sample collection to assess the performance of sample collection techniques. In general, the most common monitoring errors usually are improper sampling methodology, improper preservation, inadequate mixing during compositing and splitting, and excessive sample holding time. In addition, the inspector or sampling personnel should collect and analyze the following QC samples to check sample collection techniques.

Blanks

• Trip blank – This is a sample vial(s) filled at the laboratory with analyte‐free deionized water. The blank(s) follows the same handling and transport procedures as the samples collected during the event. The blank(s) functions as a check on sample contamination originating from sample transport, shipping, and from site conditions. Note: Expose the trip blank vial(s), to the same environmental conditions (e.g. light or temperature) as the sample vial(s) but do not open until it is time for analysis.
• Field blank/field reagent blank – These are similar to the trip blanks except they are prepared in the field with analyte‐free deionized water exactly as the sample(s) that is collected. Field blanks are used to check for analytical artifacts and/or background introduced by sampling and analytical procedures.
• Equipment/rinsate blank. Collect a blank when using an automatic sampler or other nondedicated equipment during the sampling process. The blank is a check of the equipment cleanliness. For automatic samplers, prepare blanks prior to collecting samples, by pumping deionized water that is free of organics and other analytes, through the sampler and collecting the discharge purge water in a sample container for analysis for the constituents of concern.

Field Duplicate

This is a precision check on sampling equipment and sampling technique. At selected stations on a random time frame, duplicate samples are collected from two sets of field equipment installed at the site, or duplicate grab samples are collected from a single piece of equipment at the site. Duplicate samples check analytical precision as well as evaluate the “representativeness” of the sample aliquot.

Split Samples

These are samples that have been divided into two containers for analysis by separate laboratories. These samples provide an excellent means of identifying discrepancies in the industrial users’ (or their contracted laboratory) analytical techniques and procedures. When filling split samples from a single composite jug, shake the composited sample well and half fill the sample container, then shake the composite again and fill half of the permittee’s container. Repeat the procedure for each sample collected for a specific parameter or location of interest. Sometimes a sample is split between the industrial user and the POTW, both of whom send their split of the sample to a separate laboratory for analysis. Please note that oil and grease samples cannot be split due to the nature of the pollutant.