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The National Water Quality Inventory Report to the U.S. Congress provides a general assessment of water quality based on biennial reports submitted under the Clean Water Act. The report states that approximately 30 percent of identified cases of impaired water quality reported in the United States are attributable to stormwater discharges.

When there is a storm event or snowmelt, stormwater runoff can flow directly into lakes, streams, rivers, and oceans, affecting water quality. In developed areas, runoff enters storm drains or sewer systems and then seeps into the environment. Runoff can be contaminated with pesticides, fertilizers, and many other man-made chemicals and pollutants that can be harmful to animals and vegetation. Industrial activity can also be a source of runoff requiring sampling.

Regarding stormwater samples, per the State of Washington Department of Ecology, “Stormwater management activities include keeping rainwater clean and using best management practices at sites or regional facilities to treat or infiltrate water before it's discharged. Stormwater monitoring and tracking stormwater quality helps us understand how well these activities by permittees and/or best management practices are working.”

Today, U.S. federal and state laws covering virtually all lakes, rivers, and streams (as well as oceans) are in place to reduce stormwater pollution from runoff. To operate, those industries and municipalities affected by such regulations must comply with ever-increasing demands for stormwater runoff control and stormwater sample reporting.

Complete details of federal stormwater monitoring rules, regulations, and practices can be found on the U.S. Environmental Protection Agency website. The stormwater program includes industrial run-off, construction site runoff, municipal runoff, and TMDL (Total Maximum Daily Load).

The EPA’s National Pollutant Discharge Elimination System (NPDES) Storm Water Sampling Guidance document explains that, “Data that characterize storm water discharges are valuable to permitting authorities and permittees for several reasons. First, stormwater sampling provides a means for evaluating the environmental risk of stormwater discharge by identifying the types and amounts of pollutants present. Evaluating these data helps determine the relative potential for the stormwater discharge to contribute to water quality impacts or standards violations. Sampling data can also be used to identify potential sources of pollutants. These sources can then be eliminated or controlled more specifically by the permit.”

The first step in taking a stormwater sample is to become fully aware of and comply with all local, state, and federal rules, regulations, and stormwater permit conventions. These include sampling and data collection stipulations. Once those rules and regulations are understood, site selection, sampler type, and protocols can be determined.

There are several stormwater sampling techniques, from manual sampling to automated devices for water, wastewater and stormwater sampling, like the stormwater monitoring and measurement instruments and equipment designed, built and offered by Teledyne ISCO. This includes rain gauges, samplers, flowmeters, telemetry, and data management tools that can be used when a storm event occurs.​

When filling a sample container by hand, the container type and volume collected are dependent on the constituents to be tested. Refer to 40 CFR 126 (Code of Federal Regulations) for guidance on container types, minimum volumes, and preservatives for various pollutants. Typically, when filling a bottle from a stream, you should:

• Sample at the vertical and horizontal centers of the channel.
• Face the mouth of the bottle upstream.
• Avoid floating debris.
• Avoid stirring bottom sediment. If bottom sediment is disturbed, move upstream.
• Label containers before collection to reduce the risk of sample mix-ups. Manual sampling can be used for any sampling event. However, it is best suited for base flow sampling during dry weather or as a backup for automatic sampling.
  

Automatic sampling uses instrumentation to monitor site conditions and perform sample collection without the constant presence of a technician. With automatic equipment, a technician can set up the system days or weeks before a sample event occurs and work elsewhere until it’s time to collect samples. When that happens, the equipment activates and collects the sample per advanced programming.

Built-in systems store sample collection data, which may then be used for compliance records or detailed analysis. The information can be quickly forwarded for analysis via one of numerous telemetry options, or a technician can return to the site and retrieve the samples and data.

It is important to select a sampler and accessories that will meet your program requirements now and in the future. Seek out a manufacturer with experienced sales representatives and sound technical support to assist you with these considerations and assure long-term success.

Advantages of automatic sampling are reduced labor cost and convenience. Despite increased initial equipment cost, reduced labor costs throughout the project provide timely cost recovery. With automatic instruments, technicians will make fewer trips and often spend considerably less time on site. This increases the number of sites that can be serviced in a given time period, thereby increasing productivity and reducing costs.

Safer working conditions are also likely with automatic equipment. Technicians can wait to retrieve samples until storms have passed. Training your technicians in best practices of installation, operation, and maintenance helps to assure automatic systems perform as intended.​

Stormwater Sampling Acc​​uracy: Solutions to Widespread Problems

While crucial for environmental monitoring and regulatory compliance, sampling presents unique challenges that can compromise data accuracy and reliability. This section explores common issues that environmental professionals encounter during sampling and provides practical solutions to overcome these obstacles.

• ​Risk of device failure is always possible (e.g., power failure, programming error, flood damage).
• There can be physical hazards to manual sampling. An automatic sampler can mitigate this problem.
• Accessibility can be an issue. Again, an automatic sampler may be called for.
• Improper site selection. It is important to consider the intended use of the sample data. If the sample collection stations are not defensible, neither is the sampling data. 
• Take samples downstream of the discharge point, ensuring no other pollutant sources could contaminate the samples. 
• If conducting a water quality assessment, target specific geographic areas or land use categories. After selecting a location, consider the stream channel. 
• There are three types of channels: storm runoff pipe, drainage ditch, and natural streams.
• Water levels may not cover the collection tube intake. Check the flow rate and rainfall/influent sampling parameters before deployment.
• User error. Proper training, experience and care can alleviate this.
• Obstructions in the tube intake. Whenever samples are collected, all equipment should be checked for proper function.

With ever-evolving regulations and increasing environmental concerns, the importance of accurate, reliable sampling cannot be overstated. Remember that successful stormwater sampling is about more than just collecting water – it's about gathering actionable data to inform decisions that protect our environment.

Teledyne ISCO, with its decades of experience and cutting-edge technology, continues to be at the forefront of this critical field. Our range of automatic samplers, flow meters, and data management tools are designed to meet the complex demands of modern stormwater monitoring programs.

​Frequently Asked ​​Questions