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Posted on September 10, 2018 at 5:40 PM by Ryan Hiniker
Drainage update 9/10/2018
Upcoming Drainage Hearings or Meetings:
Filtering for the Future:
We are always looking for ways to improve water quality all across our county. We have a unique opportunity to work with our local SWCD, Crystal Waters Project, and private landowners to install a couple areas with iron sand filters. We are hoping to install two smaller tank style filters and one larger sand filter saturation area, possibly along the City of Lake Crystal storm retention ponds. These two different styles of filtration both try to achieve the same end result, which is reduce phosphorus and phosphates in our water.
The University of Minnesota, Twin Cities, has actually been studying these iron sand filters for a number of years. They are testing primarily in metro areas to clean up storm water runoff. There are a few different styles of filters that have been tested and all have their own merits. The Minnesota Pollution Control Agency is even backing this research and has added a couple of the filter designs to their stormwater manual. The two major designs that are tested and talked about most are iron sand basin design and the iron sand bench or buffer for wet basins or ponds.
So, you’re wondering just what is the difference between these two styles? The iron sand basin is designed to be a dry basin area most of the time, and only filters when there is a rain event. The second design is the bench or buffer along a wet basin, and it is designed to filter the water only in peak flows or flood stages in heavy rain events. Both of these designs are not meant to be constantly wet, as this would affect the ability for the filter to work and also drastically cut the life expectancy of the filter.
I can hear the question coming already, why would you only filter during major rain events or wait until a peak flow to clean up the phosphorus? Current and past studies show that the major movement of phosphorus and other sediment and nutrients comes at the major rain event times, when there is a large and sudden surge of water movement both surface water and subsurface. Like I mentioned before, these current system designs aren’t made to be constantly wet, but instead will filter in the peak flow times when there is a large influx of nutrient movement in the water.
Many people have probably heard of the bioreactor or may remember me speaking about them in past blogs. Bioreactors are specifically designed to collect nitrates from water. Iron sand filters are specially-designed to collect phosphorus and phosphates from water. There is currently research being done to combine the two-collection processes into what they are now calling a super bioreactor. The super bioreactor is being tested on a small scale so far at the U of M. To my knowledge, no large scale outside testing has been conducted on these super bioreactors. I mentioned a few weeks ago about these next-generation bioreactors and how they are testing many different mediums for collecting sediment. Some of the new mediums being tested include concrete, crushed limestone, corn cobs and some others.
Hopefully we can get these iron sand filter projects moving yet this year, and I will keep everyone posted if we do. I’m very excited to try these as I’ve read and heard about the outstanding results. For more reading about these filters click the link provided.
Shown above is an example of the iron sand bench filter. Below is the basin and tank style iron sand filter. Photos courtesy of MPCA Storm Water Manual.
Recent Drainage Inspections – week of September 3 – September 7:
We require that all repairs to a county drainage system (tile or open ditch) be authorized by one us in the drainage office, either Craig or myself, before any repairs are made.
Drainage Management Specialist