In-Situ Remediation Practice Leader
Woodard & Curran
Dan is the In-Situ Remediation Practice Leader for Woodard & Curran. Dan holds bachelor's and master's degrees in geology from the University of Florida, and a Ph.D. in geochemistry from Columbia University. He has over 20 years of experience and 3 patents in the field of in-situ remediation, including oxidation and reduction technologies and bioremediation technologies for a wide range of organic and inorganic contaminants.
Activated Potassium Persulfate for In-Situ Remediation of Chemically-Diverse Contaminant Plumes
Groundwater plumes comprised of a diverse mixture of contaminants pose special challenges for in-situ remediation. Compounds that are primarily susceptible to oxidation or aerobic biodegradation (such as aromatic hydrocarbons) are commonly encountered intermingled with compounds that are primarily susceptible to the opposing conditions of chemical reduction or anaerobic bioremediation (such as chlorinated aliphatic hydrocarbons). These opposing treatment conditions introduce a significant complexity for design and implementation of in-situ chemical or biological remedies. This challenge can be magnified with emerging contaminants, which often are found as secondary contaminants associated with other compounds, and which are not readily treated by remedies targeting the primary contaminants. One option is to develop chemically- or biologically-discrete treatment zones separated spatially within a plume, for example an initial anaerobic bioremediation zone to address chlorinated solvents coupled with a second treatment zone under aerobic conditions to subsequently address aromatic hydrocarbons such as BTEX that are not degraded in the first treatment zone. This approach has been effective at some sites, but requires large shifts in groundwater geochemical conditions that are generally difficult to maintain and achieve. A promising, long-lifetime solution may be afforded by alkaline-activated potassium persulfate. Persulfate is usually considered a chemical oxidant due to formation of hydroxyl radicals and sulfate radicals. However, under highly alkaline conditions (pH approximately 12 or above), persulfate activation produces superoxide radicals in addition to hydroxyl radicals and sulfate radicals. Superoxide radical is a nucleophile and chemical reductant able to destroy a wide range of compounds not reactive with strong oxidants, including chlorofluorocarbons, highly halogenated aliphatics such as hexachloroethane, chloromethanes, and emerging contaminants potentially including PFAS compounds. Bench test batch and soil column test results demonstrate that potassium persulfate blended with metal bases such as calcium hydroxide may be able to provide effective treatment of groundwater impacted by a complex blend of contaminants from a DNAPL site, primarily chlorobenzene (susceptible to oxidative degradation) and Freon 113 (susceptible to nucleophilic attack). The sparingly soluble nature of potassium persulfate and calcium hydroxide requires injection as solid reagents, which in turn are then expected to slowly dissolve over a long time period (many years). This approach offers the promise of long-term treatment of large plume areas, and to address back-diffusion and other challenges requiring longer treatment periods than commonly achieved by single applications of in-situ reagents.