EHS Topic of the Month: Stormwater Sampling

The U.S. Environmental Protection Agency (EPA) has provided the following recommended procedures for collecting stormwater grab samples:
From EPA NPDES Stormwater Sampling Guidance Document (EPA 833-B-92-001, July 1992).

• Label sample containers before sampling event. (Be sure you have the appropriate container—check with the lab to be sure!) Different containers may be needed for the different tests required.
• Take a cooler with ice to the sampling site.
• Take the grab from the horizontal and vertical center of the channel.
• Avoid stirring up bottom sediments in the channel.
• Hold the container so the opening faces upstream.
• Avoid touching the inside of the container to prevent contamination.
• Keep the sample free from uncharacteristic floating debris.
• Transfer samples into proper containers (e.g., from bucket to sample container). However, fecal coliform, fecal streptococcus, phenols, and oil or grease should remain in original containers.
• If taking numerous grabs, keep samples separate and labeled clearly.

If you take the grab sample using intermediate equipment:
Use clean, decontaminated intermediate equipment and rinse equipment with site water prior to sampling. If an extension pole is used with bottles securely attached, remove the lid from the sample bottle, being careful not to contaminate the container, and follow the procedures above. If any other type of intermediate equipment is used, reach the equipment to the mid stream column of the discharge stream and collect a water sample.

Bring the sample to a clean, decontaminated area and remove the lid from each container, being careful not to contaminate the cap, neck, or the inside of the bottle with your fingers, wind-blown particles, or dripping water from your clothes, body, or overhanging structures.

Gently mix the water in the intermediate container by swirling before pouring it into the sample containers and/or field filter (if applicable). Field filter any samples prior to pouring water into sample bottles.

For low flow conditions, submerge the equipment into the entire sampling stream and fill bottles. You may have to repeat filling if the intermediate equipment is not able to contain all the volume needed to fill all the sample bottles. Repeat volume collection until bottles are filled.

Fill the sample bottles to the appropriate level depending on the analyte to be tested. Pour out a small volume if needed to create a headspace for mixing in the lab. Do not create a headspace for some analytes like volatile organics.