An analysis is no better than the sample.
Without reliable data, operational changes can lead to discharge permit violations. Regulatory requirements must be considered in the development of any sampling program. National Pollutant Discharge Elimination System (NPDES) permits issued by the EPA or the state usually specify sample type and location, sampling parameters, frequency, and analytic methods. While NPDES permits typically are concerned with establishing effluent limits, of the quality of the discharge, they also often require sampling and analysis of influent and unit treatment processes.
Sampling logs are part of the records needed to ensure a program's integrity. Therefore, accurate descriptions of the sampling procedures used should always be recorded. Several preliminary steps are necessary after parameters for analysis have been established but before sampling begins. The first step is to check each facility's NPDES permit requirements and determine the type of sample needed. For example, grab samples are required for microbial testing, pH, total residual chlorine (TRC), dissolved oxygen (DO), oil and grease, settleable solids, and temperature. The other type of sampling procedure, compositing, is undertaken by BOD, total suspended solids (TSS), or nonfilterable residue, ammonia-nitrogen, and phosphorus. Grab samples are analyzed immediately.
Composite samples are collected manually and flow-proportioned or collected using an automatic sampler. The next step is obtaining a sufficient number of plastic or glass sample containers and determining the appropriate preservation method and holding times. Several considerations are important when choosing a sampling location: 1) the water should be well mixed; 2) the location should be accessible; 3) the location should yield a representative sample; 4) surface scum should be avoided; 5) the location should allow collection without the influence of side walls; and 6) the sample should not be collected from the bottom.
After collection, preserving the samples should be considered. Refrigeration, incubation, and chemical addition are among the choices. Much depends on the nature of the water that is being sampled. That is, whether it is subject to alteration with time or might react with a chemical method. Common sense determines the method to be used. The same is true of handling the sample containers. For example, the containers should be rinsed two or three times with the liquid or water to be sampled, immediately before the sample is to be taken, unless the container has been sterilized or prepared with a chemical preservative. There are specific procedures, however, for taking the sample and the type of container used. The important point is to get a sample that is representative of the water being analyzed, and seeing that it arrives at the laboratory in the same condition as it was in the stream.
Flow-proportional samples can be collected manually and combined before analysis. If samples are to be combined manually to form composites, the flow at the time each sample was collected should be recorded on the sample log sheet. Because there are no holding times for DO, TRC, pH and temperature, these parameters must be observed in the field, when possible.
"Proper Sampling Techniques." By Charlene Givens, president, Givens and Associates Wastewater Co., Cumberland, Indiana. Operations Forum, April 1997.
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|Title Annotation:||analysis of effluent discharges|
|Author:||Billings, Clayton H.|
|Date:||Jun 1, 1997|
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