May 6 engineered media meeting notes

May 6, 2020, Engineered Media meeting notes

• Attendees
  • Andy Erickson
  • Dwayne Stenlund
  • Jessica Kozarek
  • David Fairbairn
  • Erin Anderson Wenz
  • Keith Pilgrim
  • Beth Fisher
  • Mike Isensee
  • Curt Coudron
  • Mike Findorff
  • Todd Smith
  • Lynn Duijndam
  • Linnea Savereide
  • Carlee Kjeldahl
  • Kayla Walsh
  • Brandon Smith
  • Britt Faucette
  • Greg Wilson
  • Josh Hull
  • Kerry Glader
  • Jay Michels

Andy Erickson provided an overview of his recent research on bioretention media and an overview of planned research in 2020-2022. Because of the COVID-19 situation, these projects have experienced temporary delays. If restrictions are eased in the coming weeks, Andy anticipates completing a final report for the recent work by the end of June and starting work on the new project later this year. The recording of Andy's presentation and a link to his slide show are below.

• Meeting recording
• Andy's presentation - File:2020-05-06 AJE Biofiltration.pdf

There was a lot of discussion following Andy's presentation. Below is a general summary of the discussion topics. To see the discussion, go to the Youtube link of the recording (above).

Caution: Andy indicated his analysis has not been completed yet and any references to his work below are preliminary

• There are questions about the use of compost in biofiltration systems. Note that these are underdrained systems. There are generally no concerns with bioinfiltration systems as phosphorus is generally attenuated in the soil zone below the infiltration practice and phosphorus is typically not a concern in groundwater, except possibly when infiltration systems are located adjacent to waters impaired for or sensitive to eutrophication.
• Although Andy's results are preliminary at this point, it appears that there is some phosphorus leaching even for a 10% compost mix. Andy indicated leaching appears to be roughly linear with the compost percentage in the bioretention mix over the compost range used in these experiments (10 and 20%).
• Mixing iron in the media appeared to give good results. This was corroborated by Stephanie Hurley in her presentation as part of the St. Anthony Falls Speaker Series on Thursday, May 7.
• Vegetative growth in Andy's experiment was disappointing, but again, this was corroborated by Dr. Hurley's presentation on May 7. Dr. Hurley suggested the main role of compost may be related to water-holding capacity rather than nutrient supply and she suggested spot use of compost rather than mixing compost throughout the engineered media.
• In general, iron appears to offer good potential for minimizing phosphorus leaching, results are unclear for spent lime, and biochar does not appear effective in retaining phosphorus, though it is not a source of phosphorus leaching.
• Regarding spent lime, we have limited information on levels of spent lime needed to be most effective in attenuating phosphorus. It was suggested that 5% lime, as used in Andy's experiment, may not be enough to raise the pH to a level that would maximize phosphorus attenuation.
• In general, this is a complicated issue. For example, some questions that arose during the discussion include the following.
  • Do iron-chloride relationships vary seasonally?
  • Are there effects of microbial function that would decrease pH in spent lime systems, thus making it less effective at attenuating phosphorus?
  • How important is particle size for the organic media?
• There were some questions about sources of material and variability within a specific product delivered to a site. Perhaps there could be information/guidance developed to assist in sampling material to ensure product consistency and quality.
• Dwayne Stenlund mentioned he has used taconite as an iron source and preliminary testing indicates metal leaching has not been a concern.
• Some changes to the manual were suggested.
  • Can the manual provide better guidance or a range for iron in an iron mix?
  • Can the manual provide testing guidance?
  • Should there be more information on the use of topsoil in engineered media?
  • Are there some examples of standard specifications that can be incorporated into the manual?
  • Should the manual be less rigid in media mix specifications?