In order to ensure the quality of POTW sampling, the POTW should develop a general plan that lays out all of its procedures for conducting sampling to meet the requirements under its pretreatment program. Here, this plan is referred to as the Sampling and Quality Assurance Plan, or simply the plan. Many POTWs have a plan(s) that encompasses the information suggested here, but they are called something different, such as SOPs. It does not matter what it is named; however, it is important for POTWs to have documented procedures for QA/QC, sample equipment maintenance, sample collection, sample documentation, sample shipping, chain‐of‐custody (COC) procedure, and safety. This plan should be used by all inspectors and/or sampling personnel so that samples are collected consistently and the data are of high quality and will be admissible in court, if necessary. The plan should ensure that representative samples are collected; 40 CFR part 136 sample collection and preservation procedures are followed; sample integrity is maintained; safe practices are followed during sampling events; and QA/QC procedures are followed. The inspector should contact the laboratory in advance of any sampling to discuss the sampling plan and QA/QC procedures, to allocate laboratory time, and obtain sample identification numbers and field and trip blanks.
The Sampling and Quality Assurance Plan should be a guide, or reference, for inspectors and sampling personnel. Based on review of the Sampling and Quality Assurance Plan, the inspector or sampling personnel should customize a sampling action plan specific for each industrial user. The Sampling and Quality Assurance Plan, in general, should lay out all preparation and sampling actions for the sampling team. Not all items in the POTW’s plan will apply to all industrial user sampling events. In certain situations, the inspector and sampling personnel may need to deviate from procedures outlined in the plan due to uncontrollable circumstances at the industrial user facility. The inspector has discretion to deviate from the plan if, in the opinion of the inspector, circumstances at the facility warrant such a change. Whenever possible; however, the elements in the plan should be followed for consistency. If circumstances arise in the field that make it unrealistic or physically impossible for the procedures to be followed, the inspector should document any deviation from the plan and the reason for the deviation.
QA/QC Procedures
QA/QC procedures are tools that are necessary to maintain a specified level of quality in the measurement, documentation, and interpretation of sampling data. The QA/QC procedures the POTW will use to assure data of good quality for both industrial users and POTW sampling and for industrial user self‐monitoring should be specified in the Sampling and Quality Assurance Plan (Keith 1991). QA is the program function used to prevent mistakes and assure the quality of measurement data, while QC is the process of carrying out those procedures stated in the QA Plan. The QA activities of the plan should be general while QC activities are specific. A QA program should control the quality of the data through use of set procedures to meet the program requirements. A QC program is designed to ensure the routine application of procedures necessary for the measurement process to meet prescribed standards of performance (e.g. through instrument calibration and analysis of reference unknowns). A program describing the schedule for calibration is QA, while the actual calibration procedures are QC.
All data generated or used by the POTW must be of known, defensible, and verifiable quality. This includes data that are generated through self‐monitoring at the industrial facility. Therefore, the industrial user should also have QA/QC procedures in place to ensure the adequacy of the data submitted as part of its periodic compliance report. All inspections, and the data obtained as a result of the inspection, have the potential to be used in an enforcement proceeding and should be treated as potential evidence to be admitted in court.
To produce evidence that is admissible in an enforcement action, QA and QC procedures are necessary both in the field (during sampling) and in the laboratory (Keith 1991). The QA/QC procedures used in the field are separate from those used in the laboratory, but both are crucial for obtaining reliable data. Both laboratory and field QA/QC are discussed in this section. QA/QC procedures are used to obtain data that are both precise (degree of closeness between two or more samples) and accurate (degree of closeness between the results obtained from the sample analysis and the true value that should have been obtained). By following QA/QC procedures, the POTW’s confidence in the validity of the reported analytical data is increased.
QA Procedures for Sampling
A QA program for sampling equipment and for field measurement procedures is necessary to ensure data of the highest quality. The inspector should recognize the importance of implementing QA in sample collection to minimize such common errors as improper sampling methodology, poor sample preservation, and lack of adequate mixing during compositing and testing. Again, each of these activities should be a part of the POTWs Sampling and Quality Assurance Plan, so that all POTW sampling personnel are familiar with the proper sampling procedures. QA checks will help the inspector determine when sample collection techniques are inadequate for the intended use of the data. In addition to the general plan components discussed in Section 4.5.1, the POTW’s Sampling and Quality Assurance Plan should also contain these field QA elements which sampling technicians should understand and apply:
- The required analytical methodology for each regulated pollutant; special sample handling procedures; and the precision, accuracy, and detection limits of all required analytical methods.
- The basis for selecting the sampling and analytical methods. For example, each analytical method should consist of approved procedures. Where the method does not exist, the Sampling and Quality Assurance Plan should state how the new method will be documented, justified, and approved for use.
- The number of analyses for QC (e.g. the percentage of spikes, blanks, or duplicates), expressed as a percentage of the overall analyses [e.g. 10% (one duplicate sample per 10 samples)] to assess data validity. Generally, the QA program should be approximately 15% of the overall program, with 10% and 5% assigned to laboratory QC and field QC respectively. The Sampling and Quality Assurance Plan should include shifting these allocations or decreasing these allocations depending on the degree of confidence established for collected data.
- Frequency and procedures to calibrate and maintain field instruments and automatic samplers.
- A performance evaluation system that addresses the following areas:
- Qualifications of personnel for a particular sampling situation
- Determining the best representative sampling site
- Sampling techniques (including the location of sampling points within the wastestream, the choice of grab or composite samples, the type of automatic sampler, special handling procedures, sample preservation procedures, and sample identification)
- Flow measurement, where applicable
- Completeness of data, data records, processing, and reporting
- Calibration and maintenance of field instruments and equipment
- Use of QC samples, such as field duplicates, or splits to assess the validity of the data
- Training of all personnel involved in any function affecting data quality
By following these QA procedures, the inspector or sampling personnel can ensure that proper quality data is obtained during compliance sampling.
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