Creation of passive biobarriers using emulsified oil: a summary of multiple field applications
Emulsified vegetable oil (EVO) was successfully used as a long-term electron donor for stimulation of bioremediation of chlorinated chemicals in four field trials completed under a variety of site conditions. During the field trials, a number of factors impacting the successful application of EVO were evaluated, including: (i) the achievable radius of injection and vertical distribution of the EVO around the point of injection; (ii) potential for sustained oil mobility; (iii) EVO injection method; (iv) impacts to secondary groundwater quality; (v) oil longevity and associated breakdown products; and (vi) the effectiveness of the EVO at achieving complete dechlorination of all contaminants present under varying geochemical conditions. From the trials, it was concluded that EVO is an effective electron donor for chlorinated methanes, ethanes and ethenes, where the required microorganisms are present, in a wide range of geochemical environments. Effective distribution of EVO was found to be impacted by soil permeability, soil heterogeneity, nearby extraction of groundwater, and use of injection wells with proper seals and of sufficient diameter. Hydrolysis of the EVO resulted in transient formation of elevated organic concentrations in the groundwater; however, the formed organic constituents readily biodegraded once sufficient biomass developed, thus mitigating the impact to secondary groundwater quality. Methane formation is variable, and sulfate reduction may be stimulated in some environments. Longevity of the EVO has been demonstrated to be a minimum of 12 months, even where high contaminant mass flux and groundwater velocity result in a higher electron donor demand.