In-situ bioremediation is not an elusive process where we must hold our breath to see if it will work. The fundamental processes are well established. The required ratios and calculations for electron acceptors or electron donors are not a mystery. If we could have 100% confidence that all the inputs and assumptions are correct, we would have 100% confidence in a quick and complete cleanup. The challenge with any site is overcoming the unknowns.
Over the past 30-plus years, we’ve noticed that the challenges seem to fall into just a few categories. Some of these are specific to groundwater bioremediation, and others are relevant for any in-situ method. Below we’ve outlined the top five reasons that bioremediation can come up short, and what steps should be taken from the beginning to minimize the unknowns and meet your goals every time.
Planning for incorrect contaminant mass
One of the most common errors when planning a bioremediation project is calculating contaminant mass based solely on testing of the contaminant of concern. Bacteria are opportunistic. If another compound is present that is easier to break down, the microbes will focus there first. So, we can’t test only for the contaminant of concern. For calculating the electron acceptor needs for bioremediation of petroleum, a much better test would be for total petroleum hydrocarbons (TPH). For calculating substrate dosing in anaerobic bioremediation, testing should include all solvents plus any additional electron acceptors (sulfate, manganese, nitrate, iron, etc.). Using these inputs, we can much more confidently calculate how much product is required to meet the site goals.
Skipping the nutrients
Microbes use nutrients for cell walls, cell structures, and DNA/RNA. In fact, nutrients make up around 25% of the mass of these microorganisms. In bioremediation, we want to build up the contaminant-degrading microbial population as much as possible. If the site is amended only with an electron acceptor/donor, the microbes will always be limited by the available nutrients, and it should be no surprise when the progress is stalled.
Distribution #1: Geology and other subsurface unknowns
Nothing is more frustrating than feeling blind to the subsurface geology of a challenging site. Because geologic barriers can have such a profound effect on distribution, it is typically worth the effort and cost to eliminate this unknown. Hi-res site characterization tools are always helpful. Quality and accurate boring logs are essential. Look for utility lines to anticipate preferential pathways. All of these steps reduce the unknowns and increase the confidence of success.
Distribution #2: Wrong delivery method
In addition to geology, the product delivery method can also significantly affect distribution. It is important is to match the delivery method to the characteristics of the site and the chosen product. This requires careful planning of the well placement and design as well as the field application. If performing an injection event, is extraction being used to ensure breakthrough distribution across the target area? If direct push is being used, are you confident of the radius of influence for the chosen injection points? There are many factors to consider, and every site requires unique planning. However, the challenges related to distribution are partly why we prefer fully soluble amendments as well as groundwater recirculation.
Not performing regular check and adjustment
Quarterly sampling events are a fantastic opportunity for all parties involved to evaluate and adjust the site plan. Even under the best conditions, there are usually improvements that can be made throughout the project. Regular site performance reviews can mean the difference between struggling on a site for years versus making the right adjustment at the right time to rapidly meet your site goals. We highly encourage our clients to reach out, provide data, and let us provide recommendations. We love to be involved throughout the life of a project.