| TECH-TIP - Plan for Optimized Water Quality Sampling
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TECH-TIP - Plan for Optimized Water Quality Sampling

In addition to the sampling and analysis required for regulatory purposes, process control sampling is a critical part of understanding water treatment plant and distribution system operations and performance.  The results of water quality sampling may be used to help utilities make operational adjustments that enable them to work towards, and eventually achieve, optimization.  Optimizing water quality sampling and analysis starts with the sample itself.  Quite simply, “the analysis is only as good as the sample” - meaning that samples collected must be representative of the process in order to produce accurate and meaningful results.  If a sample is not collected, preserved, stored, or transported correctly, this may result in inaccurate results and, potentially, inaccurate process decisions being made.  This quarter’s Partnership for Safe Water Tech-Tip focuses on sampling and steps utilities can take to help ensure accurate and optimized sample collection procedures.


Develop a Plan

Self-Assessment for Water Treatment Plant Optimization, the Partnership for Safe Water’s new treatment plant self-assessment guidance, discusses water quality sampling as part of its chapter on Application of Operational Concepts.  The guidance discusses the importance of creating a sampling plan that identifies, at minimum, specific sampling locations, parameters to be tested, target values, sampling frequency, and the party performing the sampling (whether it is a staff member or online analyzer).  This may be summarized in a formal sampling plan or schedule, as displayed in the figure below.  It is important to identify the critical process control points where water quality data is required to quickly make treatment decisions that may impact the plant’s optimization status. 



A similar plan may be developed for distribution system sampling.  One example of this is a sampling plan for disinfectant residual monitoring locations.  The Partnership’s Self-Assessment Guide for Distribution System Optimization describes optimized sampling sites for disinfectant residual monitoring.  These sites include distribution system locations that may be at the highest risk for residual loss, such as low flow areas of the system, areas with high water age, and areas of the system containing unlined cast iron mains.  An optimized distribution system sampling plan for disinfectant residual monitoring will include as many types of the Partnership’s optimized sampling locations as possible.  The sampling plan should be shared with utility staff, so that all parties involved in the process are aware of utility sampling parameters, frequencies, and responsibilities.  A sampling plan is a living document that may be modified and updated over time to best fit the utility’s optimization goals.  For example, if areas of the distribution system are identified that consistently exhibit low disinfectant residual concentrations, these sites may be added to the sampling plan to be more closely monitored during future sampling events.


It’s all in the Details

Once the sampling plan is established, all staff members involved with water quality sampling should have an understanding of the specific sample collection, preservation, and storage requirements for the type of sample collected and the parameter(s) being analyzed.  Staff should also be aware of and trained in the use of any specific techniques required to ensure accurate sampling, such as sterile sampling techniques for the collection of bacteriological samples.  Knowledge of the sample volume required to perform the necessary analyses is also an important part of sampling. 


Different types of parameters have different requirements in terms of the acceptable containers used for sample collection.  For example, metals may be collected in plastic bottles, while samples for organic parameters, such as total organic carbon, total trihalomethanes, and haloacetic acids must be collected in glass bottles.  Some outside laboratories will provide sampling containers that are pre-filled with a preservative compound, such as sodium thiosulfate as a dechlorinating agent for coliform testing.  If this is the case, all individuals performing water quality sampling should be aware of the presence of the preservative, with instructions not to rinse the bottles prior to sample collection, so as not to inadvertently dispose of the preservative compound.  Additionally, sample storage times can vary based on parameter.  Some parameters, such as disinfectant residual, must be analyzed immediately (on site is optimal) for accurate results, while others, such as most metals, may be stored for a longer period of time prior to analysis, provided that they are preserved correctly.  If samples are transported to an outside lab for analysis, samplers should ensure that the samples are shipped under the proper temperature conditions and that sample holding times are adhered to.  Be sure to follow up with the outside lab to ensure that the samples were received and that results were reported to any outside agencies in a timely manner, if applicable.


A full discussion of sampling procedures for every water quality parameter is outside the scope of this article.  However, additional information regarding sampling techniques, containers, preservation, and holding times may be accessed in Standard Methods for the Examination of Water and Wastewater or in the USEPA’s Quick Guide to Drinking Water Sample Collection.   


Train and Confirm

With a variety of staff members potentially involved in water quality sampling procedures, it is important to ensure that staff are trained in water quality sampling techniques and consistently performing sampling correctly.  The use of standard operating procedures (SOPs) for sampling can help to ensure that consistent sampling practices are followed across the utility.  SOPs should be reviewed and updated periodically, as appropriate.  It may also be beneficial for staff involved in sampling to attend periodic training to introduce and review sampling techniques.  Partnering a new employee with an experienced staff member is just one way that this training may be achieved.  Many utilities have implemented additional measures, such as training videos, mentoring, and competency testing to improve sampling accuracy, helping to ensure consistently accurate and meaningful water quality analysis results.