I recently participated in the NC Stormwater BMP Inspection and Maintenance Certification Update with Dr. Bill Hunt and Bill Lord, and I have to say that I was impressed. It had been 3 years since I had last taken the course, and although I am engaged in stormwater issues on a daily basis, it was great to get a fresh new perspective from the two people whom I consider as the premier resource in the advancement of stormwater awareness. I wanted to share a few topics that were addressed during the class that I thought were important to remember as we continue to fight the battle that is stormwater:
When cutting vegetation in the bottom of a dry detention basin, it is best to mow perpendicular to the flow of water. In case the low areas of the basin are soggy and wet, tire tracks will create small "level spreaders" and not skinny channels.
On slopes where it is difficult to get any vegetation to grow, using a 10-10-10 fertilizer and lime when aerating and over-seeding works really well. It is very important, however, to make sure that we try and keep the fertilizer and lime out of the bottom of the basin and out of contact with as much stormwater as possible. The idea is to improve the health of the soils, not increase nutrient levels in our stormwater.
Dr. Bill Hunt completed a study where he took the sediment from multiple forebays from different locations and found that NONE of the samples exceeded the thresholds, or even came near, for being considered as a hazardous material. That being said, where possible, it is best to use the sediment removed from trickle channels, inlets, flumes, etc. on site. Putting this material on the slopes of the basin or any area where vegetation is having difficulty growing is very beneficial. This material is high in nutrient content, and as long as we stabilize sufficiently enough that we are not reintroducing it to the stormwater, it is okay to reuse.
In sand filters, the top layer of sediment and "gunk" can just be raked INTO the sand filter. A metal rake used to break this material up and mix it with the top layer of sand is perfect. This material has all of the bacteria and microbes that consume oils and other pollutants. In the past, it was thought best to completely remove and dispose of. This can save time and money while improving the function of the system.
Be mindful of using equipment in Biofiltration, or infiltration, basins since the weight could cause over-compaction in the sub-soils. Over-compaction can decrease infiltration rates causing the whole system to underperform. If this occurs, costly replacement of the media is the only solution.
Regenerative Stormwater Conveyance is an effective method in repairing damaged channels.
I recommend that whoever reads this check on the expiration date of their certification. If you are not currently certified, then it is a must for anyone interested in the stormwater industry. Click this link for more information: http://www.bae.ncsu.edu/topic/bmp-im/
Michael Brewer, Director
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