The National Water Quality Inventory Report to 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 water quality impairment 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 a storm drain or sewer system, and then seeps into the environment. Again, water quality can be harmed with pesticides, fertilizers and many other man-made chemicals and pollutants that can be harmful to animals and vegetation. Industrial activity also is a source of runoff that demands stormwater sampling. Collecting a stormwater sample is called for.

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.”

In 1972, the U.S. Congress created the National Pollutant Discharge Elimination System (NPDES) as part of the Water Pollution Contract Act. The Act set a target date for the elimination of pollutant discharges, but by 1985, it became evident that the early focus on “point source” discharges (i.e., industrial activity and municipal wastewater treatment facilities) simply wasn’t comprehensive enough to fully address the problem.

Two years later, the NPDES program was expanded to include “non-point source” discharges – stormwater runoff from many varied sites (i.e., construction sites, croplands, and urban areas), as it was now understood that such runoff was a major contributor to the pollution of our surface waters. The collection of stormwater samples was an increasing need.

Today, U.S. federal and state laws covering virtually all lakes, rivers, and streams (as well as the oceans themselves), are in place to reduce pollution from stormwater 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 Run-off, Municipal Run-off, nd TMDL (Total Maximum Daily Load).

The EPA’s 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 the storm water discharge by identifying the types and amounts of pollutants present. Evaluating these data helps to determine the relative potential for the stormwater discharge to contribute to water quality impacts or water quality standard violations. And, stormwater sampling data can be used to identify potential sources of pollutants. These sources can then be either 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 permit conventions. These include sampling and data collection stipulations that must be followed. Site selection, sampler type and protocols can be determined once those rules and regulations are understood.

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 whenever 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 prior to 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 advance 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 into 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. 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 technicians in best practices of installation, operation, and maintenance helps to assure automatic systems perform as intended. Despite increased initial equipment cost, reduced labor costs throughout the project provide timely cost recovery.

  • ​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 lessen or eradicate 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, making sure there are no other pollutant sources that 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 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.

​Frequently Asked ​​Questions

If rain input is required for stormwater sampling, where should a rain gauge be lo​cated?

The rain gauge should be installed where its collector (top) has unobstructed access to rainfall. Its location should be away from trees, buildings or other objects. If vegetation serves as a windbreak, keep in min​d that unchecked growth can greatly change the conditions of the site with the passage of time.

What’s the best way to power a s​tormwater monitoring system?

Where portable equipment is used, ISCO recommends lead-acid batteries, as they hold a charge longer than other types. Automotive or deep-cycle marine batteries have a very high capacity and relat​ively low cost. Where​​ line power is available, an AC power pack can be used to convert 120 or 240 volts AC to the required 12 volts DC. For long-term applications, or where access is difficult, solar panels may be most suitable. A solar charger maintains a lead-acid battery in a fully charged condition, virtually eliminating the need to visit the site for periodic battery replacement.

What are the options for ch​ecking the status of a site without actually going there?

With a cell pho​ne modem, a site can be called to view the current parameter readings, and to check the state of the automatic sampler. A phone modem and simple computer program will give you remote access to the site information and allow changes to sampler programming.​