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Sep 10

Filtering for the Future

Posted on September 10, 2018 at 5:40 PM by Ryan Hiniker

Drainage update 9/10/2018


Upcoming Drainage Hearings or Meetings:

  • CD56 Branch 18 (Lincoln Twp.)  We received a winning bid for a major repair to replace two tile branches.  This official awarding will be part of the September 11 Board of Commissioners' meeting.
  • CD28 (Lincoln Twp.)  We are hosting a repair petition hearing on September 11 as part of the Blue Earth County Board of Commissioners' meeting.  Affected landowners received notice by mail.  Please call or email for additional details if needed.

Project Updates:


  • JD09 (Le Ray Twp.)  Heavy rains from the week before slowed the two contractors down for a few days, but it did not stop them from installing pipe last week in some very muddy conditions.  The southern portion of this improvement project has roughly another 20-25 days left.  The northern portion of this improvement has about another 30-35 days.  These are rough guesses and weather can change those approximations quickly.  Below is updated map showing areas of new tile installed. JD09 south improvement map update
  • CD48 (Cambria Twp.)   No specific start date has been decided as of yet, but the contractor still plans on completing yet this year.
  • CD35 (Mapleton Twp.)  We should see the contractor starting this repair project fairly soon.  I would imagine in the next week or two we should see this project done, as September 30 is the scheduled deadline for completion.
  • CD56 (Lincoln Twp.)  Heavy rains from a week ago slowed things down on completing some punch-list items for this repair.  Hopefully the nicer weather this week will help the contractor on this project finish up.

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. 

iron sand filter

Recent Drainage Inspections – week of September 3 – September 7:

  • CD35 (Mapleton Twp.)  Very high-water conditions from last week’s heavy storms.  Hopefully the heavy rains stay away so we can make much needed repairs to the township road issues.
  • CD86 (Beauford Twp.)  Our Alternative Side Intake, or ASI project, had been going well until the rains came last week.  Rain events like we just had are the reasons why we are installing these ASI’s.  They filter the sediment and other debris in the water before it’s released into the open ditch.  The old style, pass-through intakes as I call them, would just shoot straight into the ditch and suck all the soil and other debris with it in heavy storms.  These new ASI’s should help cut maintenance costs by reducing the sediment loading into the open ditch.
  • JD48 (Butternut Valley Twp.)  I inspected yet another area with a sink hole starting from a collapsed tile.  This is the second collapse in one year and third collapse in two years.  I plan to have this branch fully televised this fall after harvest is completed.
  • CD56 (Garden City & Lincoln Twps) The wet weather last week prevented the contractor from finishing the check-list items left for this repair.
  • CD41 (Vernon Center Twp.)  We will be doing an open ditch cleaning which will include sediment cleaning of the ditch, straightening alignment and tree removal along the ditch.
  • CD95 (Mapleton Twp.)  Inspected an area of a smaller slough starting along a portion of the open ditch.  With high flood stage water conditions at the moment, I anticipate that there will be more issues after waters recede.
  • CD96 (Danville Twp.)  Our concrete weir structure is holding back water perfectly just like it was designed to do.  This project turned out really well and now is a new wetland conservation area.


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.




Ryan Hiniker

Drainage Management Specialist