CAN SLUG TESTING DETECT BIOFOULING IN BIOSTIMULATION WELLS?

Accretion of biofouling materials in biostimulation injection wells can decrease the transmissivity (T) of an aquifer. Slug testing is a simple method commonly used for T estimation, and may be useful for identifying T decreases associated with biofouling. Six wells utilized during biostimulation of a trichloroethylene-contaminated fractured sedimentary rock aquifer were slug tested pre- and post-injection for comparison. Slug tests at five of six wells indicated no or negligible T change after biostimulation, while T at one well decreased at least two orders of magnitude. Routine groundwater chemistry sampling indicates this decrease coincided with the onset of dominant sulfate-reducing groundwater conditions in that well following biostimulation. Growth of biomass and precipitation of sulfide mineral byproducts often result from enhanced sulfate-reducing bacteria activity, so accumulation of these materials in fractures can clog the primary groundwater flow conduit to the well and cause the observed T decrease. The effectiveness of slug tests to recognize T decreases developed from biofouling is confirmed by identification of clogging materials in fractures through visual geophysical borehole logging methods. Verification furthers understanding of the resultant side effects of biostimulation.