Tuesday, March 13, 2012

Soil Rehabilitation Not Capping

Soil Safety protocol and licensing procedures should emphasize rehabilitation rather than capping. Thus, require all soils to be tested rather than allow barrier and soil replacement on untested sites. Soils with low or medium levels of lead and other contaminants should be remediated by phytoremediation or soil replacement without a barrier. Only very toxic sites should be required to use the geotextile and new soil remediation procedure.

The preliminary “Soil Safety” recommendation for Boston provides two options for urban agriculture on sites over 5000 square feet: 1) barrier and new soil (presented first, and in some detail) or 2) “provid[ing] results of testing by a Licensed Site Professional (LSP) demonstrating that the existing soil is safe for growing. The specific protocols and licensing procedures for such testing will be developed concurrently with the draft Urban Agriculture rezoning recommendations.” It seems misguided to emphasize capping with geotextiles and new soil. This system just defers resolution of the toxic problem on our grandchildren or great-grandchildren. Although I could not quickly find life expectancies for the recommended geotextiles (I have an email enquiry pending to a manufacturer), it is clear that they will not last more than a generation or two. Unfortunately, the U.S. continually approves technologies and kicks the can down the road as far as longevity and remediation. Just think of all the leaking buried oil tanks being removed from homes (often with strict liability for current owners) and of the remediation of buried gas and diesel tanks at former gas stations. These were installed with the same mentality that the geotextile solution is being touted – “the present” is what matters and the future can take care of the problems we create by developing new technologies. Unfortunately, the current global warming crisis is demonstrating that the synergies between all these deferred solutions and ignored externalities have damaged the environment and ultimately ourselves. Sustainable thinking requires that we think in the long term, for “seven generations,” and solve problems now when possible.

In the instance of remediating contaminated urban soils for agriculture, this means that phytoremediation and other solutions that actually clean up the site for the long term should be emphasized, rather than short-term solutions. This is especially true for the soils with low and medium levels of lead. For example, the UMass Extension Center for Agriculture flyer, issued by the Soil and Plant Tissue Testing Laboratory, entitled “Soil Lead: Testing, Interpretation and Recommendations” recommends that farmers growing in soil with “Low” levels of lead contamination (less than 22 mg/kg extracted lead/less than 299 mg/kg estimated total load) should follow “good gardening practices” to reduce lead exposure. At this minimum level of contamination, the danger is more to the gardener/farmer than to the consumers of the crop. Consequently, a “low” level of lead in soil is particularly suited to phytoremediation rather than capping and new soil. Moreover, lead contamination is typically present only in the top few layers of soil. As a result, the preliminary “Soil Safety” recommendation for Boston should be amended to separate out soil tested at low levels of lead from the requirement for geotextile barrier and new soil and instead require phytoremediation and/or new soil without a barrier. This process can still be overseen by a Licensed Site Professional to ensure that the produce is safe for consumption, but this emphasis gives the signal that remediation is the preferred option, where possible. As the proposed ordinance now reads, it emphasizes barrier and soil as the preferred options for all soil types and will result in the capping of soils that could easily be rehabilitated.

Phytoremediation should be emphasized over soil replacement, where possible. Phytoremediation is a proven technology that produces less volume of contaminated materials (plant residue) that can be buried rather than soil replacement at much more volume of landfill. In addition, soil replacement merely shuffles the lack of good soil around, taking soil from one place and moving it to another rather than rehabilitating existing soil. It is my understanding that the contaminated plant materials can also be incinerated under special conditions, and the toxic metals recovered in a pure state, so that there is very little volume of toxic residue to be disposed of or reused in manufacturing processes. It seems that city, state and federal money would be better spent creating these types of incinerators, or discovering other solutions to disposal of small amounts of toxic materials, rather than emphasizing capping and new soil as the favored solution in all instances.

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