10.08.2014  |  News

Stormwater Sampling Tips


Fall has officially begun, and in the Pacific Northwest, the rains have come right along with the change in seasons. We hope to see the storms make it down into California as well. Many industrial stormwater permit holders will be out sampling soon to catch the first storm event of the fall. And with that in mind, we have prepared a few sampling DOs and DO NOTs.

Remember that the results of your stormwater sampling ultimately become a driver for your stormwater management program and the decisions that come along with it. The analytical results of your sampling compared to your permit benchmarks (and soon to be called Numeric Action Levels in California) drive your response, not just in actions but also in investment in stormwater best management practices (BMPs) and even the design and implementation of treatment. In short, good sampling techniques and proper sampling locations are critical to getting representative data.

Safety First!

  • DO understand the stormwater conveyance system and come prepared for challenges like confined spaces, powerful fast-moving water, poorly illuminated areas, and low oxygen environments.
  • DO come with the right tools for the job. Manhole/catch basin cover lifters can save fingers. Long sampling poles fitted with dippers can help collect water from hard to reach outfalls and pipes.

Location, Location, Location!

  • DO collect samples downstream of all stormwater BMPs. We have seen many clients sampling upstream of installed BMPs (e.g. catch basin inserts, settlement ponds, etc) and may potentially getting sample results that exceed benchmarks unnecessarily. Make sure your sampling takes advantage of all of the good things you are doing.
  • DO collect samples of flowing or cascading water. If water is moving fast or pipes are full of flowing water, target the mid-line of the discharge stream.
  • DO NOT sample from still, stagnant, or non-flowing water (e.g. collection sumps). This also means that you should not sample from submerged outfalls.
  • DO NOT drag sample collection containers along the bottom of ditches or catch basins and stir up sediment during sampling. Use extreme care when sampling from shallow flowing water, especially in unlined ditches.
  • Remember, most agencies require sampling from all facility discharge locations as near as possible to where they mingle with downstream waters or have other specifications for selecting sampling locations.

Cleanliness is next to…

  • DO use accredited laboratory sample containers that have been pre-cleaned, with preservative added (if needed), and sealed.
  • DO thoroughly clean and rinse your stormwater collection apparatus prior to sampling as well as in between sampling locations. With total metal benchmarks in the low parts per billion, even a container that looks clean may have dust, dirt, and traces of metals that will impact your sampling results. Rinse the outside of the sample containers with DI water to help prevent against cross contamination.
  • DO wear appropriate personal protective equipment (PPE) for sample collection. This is not just for personal protection, but also prevention of cross-contamination of collected samples from dirty hands. Remember to change your gloves before handling bottles and sampling at each location.

Safe Transport

  • DO fully understand the sampling techniques and requirements of your governing jurisdiction. They are often complicated and specific.
  • DO label each sample container with sample location, date, and time.
  • DO carefully pack sample containers to prevent shifting during transport.
  • DO immediately place samples on ice in a cooler after collection and transport to the accredited laboratory.


The US EPA has developed a water sampling procedure for sampling ambient water for trace metals.

Your state agency will likely also have sampling guidance that you should consider. A few helpful links include:

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