The dry season is upon us in the Puget Sound region. If you are a stormwater permittee, you may be tempted to relax your implementation of stormwater best management practices (BMPs). However, it is just as important to keep up with your BMPs during the summer as you would in any other season.
Dry conditions generate and build up sediment. This can lead to elevated turbidity levels in stormwater, as well as other pollutants, such as copper and zinc that often adhere to sediment. These elevated parameter levels tend not to be observed during the summer due to the lack of stormwater discharge, but do show up in laboratory test results when the rains resume in the fall.
Keep in mind that under the Industrial Stormwater General Permit (ISGP), permittees are required to sample stormwater discharge during the first storm event after October 1st. It is not uncommon to observe “first flush” effects in stormwater samples taken early in the fall. This means that unusually high levels of parameters, such as turbidity, are found in stormwater. These levels, which built up over weeks or months, are washed out all at once, instead of being carried off repeatedly at lower levels during the rainy season. This can trigger a corrective action unless permittees collect multiple samples and average the results to bring their parameter levels below the ISGP benchmark values.
You can reduce the likelihood of corrective action, or the need to collect multiple samples to avoid a corrective action, by continuing to implement your BMPs during the dry season. Key BMPs include:
- Keeping your site clean, including regular sweeping where necessary.
- Regular inspections to identify potential problems, such as sediment buildup.
- Making sure that any treatment structures or devices are maintained properly.
- Increasing the frequency of BMP implementation when necessary.
Freer Consulting is available to assist you with designing and implementing effective best management practices. Contact us at 206-285-9044 or firstname.lastname@example.org.