Proper Storm Water Sampling Techniques
Is your sample collection a function of going out on a rainy day and just collecting a sample from any storm water you find? If it is, you are unnecessarily exposing yourself and your company to liability – exposed to citizen suits, civil enforcement and criminal prosecution.
Sampling is one of the most important functions in a facility’s compliance with the storm water discharge permit. In this case, the sampling discussed is the sampling conducted in compliance with a Clean Water Act storm water discharge permit under the National Pollutant Discharge Elimination System (“NPDES”) program (which, in most cases, is delegated to the state). Improper sampling methods could cause the storm water samples to exceed NPDES permit levels. The exceedences are required to be reported and, ultimately, could be the basis for a citizen suit, agency civil enforcement and/or even a criminal prosecution.
Despite the importance of properly conducting the sampling and getting representative samples of the discharge, environmental managers are typically unaware that there are proper sample collection techniques (and improper sampling techniques).
Here are some of the basic elements of proper sampling techniques:
- The persons assigned to collect the sample collected should be qualified; that is trained appropriately for the sampling process and aware of the permit requirements.
- Read the NPDES permit and be familiar with the permit sampling requirements and discharge limitations.
- This includes training on exact locations of sample points (place markers or signs at sample locations) so that there is no confusion and samples are always taken at the same point.
- Before going out to sample make sure the sample kit is complete: chain-of-custody forms, calibrated pH meter or litmus paper, and lab bottles.
- Because the NPDES permit is a “discharge” permit, make sure only water that is being discharging from the facility is sampled (puddles or standing water are not appropriate for discharge sampling).
- Always wear gloves when sampling and change gloves in between sample locations so you do not cross-contaminate samples.
- Collect samples directly into the lab bottles in the sample kit.
- Collect flowing storm water (do not scrap the bottom of the channel or storm drain and do not collect standing water). When collecting sheet flow it is proper to use sandbags to force the storm water to flow over the bag into the lab bottle so that dirt and debris are not included in the sample (dirt and debris may shoot the TSS through the roof).
- Fill the lab bottles to the bottom of the neck (do not overfill). There will need to be some room in the lab bottle for an acidic preservative.
- Take pH reading of sample within fifteen (15) minutes of collection and write the value on the chain-of-custody form.
- Make sure the lids on the lab bottles are tight so that the sample does not leak.
- Place the lab bottle samples in a cooler with ice to keep them cold until they arrive at the lab. Arrange with your lab for courier service to pick up the samples or have someone drop the samples off at the lab as soon as possible.
Finally, conduct annual refresher training so that everyone with responsibility for taking samples is on the same page and knows what the specific rolls are when it comes time to sample.
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