Lessons Learned as the Result of Completing 200 Microcosm Studies

Samuel Fogel, Ph.D., Donna Smoler, Margaret Findlay, Ph.D. (Bioremediation Consulting Inc., Watertown MA)

Microcosm testing procedures have been recommended by the U.S. Air Force and Bioremediation Consulting (BCI), as a method for evaluating a site’s potential for in situ remediation by enhanced natural attenuation, and for documenting natural attenuation of chlorinated solvent in groundwater. Using procedures similar to those of the U.S. Air Force, BCI has, over the past 10 years, conducted approximately 200 such tests on groundwaters and soils representing 125 locations throughout the U.S. The majority of such tests have been done to evaluate a site’s potential for in situ remediation. The purpose of this presentation is to share some of the important information learned from conducting such tests.

Since microcosms constructed with site soil and groundwater theoretically contain all the relevant site bacteria needed for judging the effectiveness of reductive dechlorination, including Dehalococcoides species, sulfate reducers, acetogens and fermentors, the results from a properly run microcosm test should approximate that obtained under field conditions or from a properly run pilot test, or full scale remediation. For example, when pH of groundwater in a microcosm becomes acidic as a result of donor utilization, the same effect can be expected to occur in the field.

Topics to be discussed include the following:

Microcosm testing also offers for those engaged in site cleanup, the possibility to replacing high cost pilot tests with low cost microcosm tests. We will discuss how results from microcosm tests can be used directly for full-scale design. The cost implications of such a decision are very large since microcosm tests costs are relatively low ($ 6,000 to $ 12,000 per well sample) versus costs for pilot tests ($ 50,000 to $ 150,000). Furthermore, the time required for a microcosm test is 2 to 3 month versus 12 to 18 months for a pilot test.

The importance of these topics will be discussed in terms of their implications for field practices.