Thursday, May 19, 2016

Biochar to Improve Soil Drainage and Save the Bay

In Maryland, the Environmental Site Design (ESD) standard for water runoff is that it should mimic woods in good condition. This is difficult when impervious surfaces are being added, since the water collected and treated in stormwater management devices must then exceed what would be impeded and filtered if woodlands completely covered the unbuilt portions of the site, i.e. the additional effectiveness required increases with the amount of impervious surface introduced. The Design Manual qualifies the standard to require that it be achieved to the Maximum Extent Practicable (MEP). This is not as big of an escape clause as it may appear, since the manual also includes a checklist that helps determine whether the design process demonstrates a sincere MEP effort.

The idea of using wooded areas as the standard for all sites is very suitable for Maryland, as a glance at Google Earth will show how very wooded our state is. Yet, rumor has it that the next update to the manual will not be so stringent. As it is, the absolute minimum standard already obviates the wooded area criteria, if it turns out to be impractical on any given site. That minimum standard in the eastern part of Maryland is to design stormwater devices to hold an amount based on 1" of rainfall, ensuring that a specified portion of that water volume drains into the ground to recharge the aquifer. I hope they hold to the more rigorous ESD standard because the Chesapeake Bay will flourish if we can insulate it from the effects of our exploits on the land.

Photo by Birgit Speulman (CC BY-NC-SA 2.0)
Deep biochar-soil mixtures in planting beds would be an effective way to improve drainage, thus helping to meet the recharge volume requirement. Wet ponds are preferred to dry ponds, but you get less aquifer recharging since the water drains slowly in a wet pond. What you could do is use biochar to improve drainage of combination pond forebays, possibly allowing smaller overall pond size.

Here in Southern Maryland, we have a lot of Beltsville soils which are typified by a fragipan layer that is practically impenetrable. It may even reform after being broken up. Here again, biochar could help if it could be injected in fragipan layer breaches, preventing it from reforming. For the gardener, this might involve digging with a post hole digger and dropping biochar into smaller holes that have been chiseled through the fragipan. This would improve drainage considerably and, if the biochar was inoculated first and enough added, eventually eliminate the fragipan through microbial action.

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