Methods to Reduce Infiltration Rates
Methods to Reduce Infiltration Rates
(OP)
Greetings. I'm interested in reducing the natural infiltration rate of sandy soils from several feet per day to say 2 inches per day. The only idea we have come up with is to amend the sandy soils with bentonite at a very low ratio...perhaps only 1% bentonite by dry weight. Our thinking is that with some combination of low bentonite addition and compaction, we can get rates reduced to the desired range.
We are dealing with existing stormwater dry retention areas and wastewater rapid infiltration basins. By design and siting, they currently have high infiltration rates. We would like to convert those basins to wetland treatment systems that discharge to groundwater (no surface outfall). In order to create an appropriate wetland hydroperiod with the available water (either stormwater or reclaimed water), we need to slow down, but not stop the infiltration. Without modification, the water will infiltrate too quickly and we will not be able support the desired wetland plant community. To be clear, we do not want to seal the bottoms of the basins. We've already demonstrated that these infiltrating wetland cells work in areas where soil modification was not needed. What we really want is the ability to engineer a natural sandy soil to give us a specific "approximate" infiltration rate.
Can anyone offer any recommendations or alternatives? Thanks.
We are dealing with existing stormwater dry retention areas and wastewater rapid infiltration basins. By design and siting, they currently have high infiltration rates. We would like to convert those basins to wetland treatment systems that discharge to groundwater (no surface outfall). In order to create an appropriate wetland hydroperiod with the available water (either stormwater or reclaimed water), we need to slow down, but not stop the infiltration. Without modification, the water will infiltrate too quickly and we will not be able support the desired wetland plant community. To be clear, we do not want to seal the bottoms of the basins. We've already demonstrated that these infiltrating wetland cells work in areas where soil modification was not needed. What we really want is the ability to engineer a natural sandy soil to give us a specific "approximate" infiltration rate.
Can anyone offer any recommendations or alternatives? Thanks.





RE: Methods to Reduce Infiltration Rates
RE: Methods to Reduce Infiltration Rates
RE: Methods to Reduce Infiltration Rates
Most of the references we have found regarding bentonite addition are for pond sealing or liner applications where the goal is near-zero infiltration. We've been having difficulty finding references that give useful design guidance for slowing versus stopping downward flow.
Thanks again for your comments.
RE: Methods to Reduce Infiltration Rates
RE: Methods to Reduce Infiltration Rates
You can also do blending as suggested. I don't think recompaction would return too great a value, but there is certainly some benefit. When considering the affect of recompaction, target compaction water contents at or greater than 90 percent saturation. I'm not saying, "Wet of optimum." As optimum water content for 95 percent compaction is not the same as optimum water content for 95 percent compaction. Refer to the Mitchell, Hooper and Campanerlla, ASCE 1965 for more information on permeability and compaction water content.
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