Dr. Michael Lee, Ph.D.

Permeable Reactive Barriers: In-Situ Treatment Strategies to Mitigate Nitrate and Phosphate Discharge to Surface Water

Dr. Michael Lee, Ph.D., Vice President of Research and Development, Terra Systems, Inc.

Background/Objectives. 

Eutrophication due to excessive nutrient loadings to surface water bodies is a global environmental issue. High concentrations of nitrate and phosphate in groundwater can occur from fertilizer usage, manufacturing, agriculture, or septic systems. On Cape Cod in Massachusetts and eastern Long Island in New York, septic systems are the leading contributor of nitrate to the groundwater and manage 60% to more than 80% of wastewater. Eutrophication results in health, environmental and financial impacts where it occurs, including drinking water, recreation, tourism, property valuation, and fisheries.

Approach/Activities. 

Denitrification permeable reactive barriers (PRBs) can enhance the activity of naturally occurring soil bacteria that remove nitrate from groundwater prior to discharging to surface water through the addition of an organic carbon substrate to the subsurface. Organic carbon can be applied as a solid (e.g., wood chips) or as a liquid solution. Various methods of PRB construction can be used including injection wells, temporary injection points, trenching, large diameter boreholes, and as part of bulkhead replacement. Key factors for selecting the type of denitrification PRB and design parameters include depth of nitrate impacted groundwater, soil type, groundwater velocity, nitrogen concentrations, and distance to surface water. Batch and column studies were also conducted to evaluate phosphate adsorption using three commercial products. 

Results/Lessons Learned. 

Permeable reactive barriers for in-situ denitrification have been implemented using wood chips and emulsified vegetable oil (EVO), including using an EVO formulated for increasing retention to soil in sandy aquifers with fast groundwater velocity. Pilot test PRBs have been implemented for a range of nitrate concentrations and hydrogeologic conditions. Field applications of denitrification PRBs demonstrate treatment of nitrate to very low concentrations with sustained denitrification over multiple years. Bench-scale batch and column studies and field demonstration tests continue to inform PRB design, refinement of lifetime cost estimates, and future full-scale implementation. Adsorption may be used to remove phosphate from groundwater before it discharges to surface waters or applied to the water column in the surface water.

Dr. Michael D. Lee is Vice-President of Research and Development at Terra Systems. He has Ph.D (1986) and MS (1983) degrees in Environmental Science and Engineering from Rice University and a BS in Biology from University of Louisiana at Monroe (1980). Dr. Lee has over 30 years of experience in the field of bioremediation, with expertise in applying in-situ anaerobic bioremediation of chlorinated solvents and metals, implementing in-situ aerobic bioremediation of hydrocarbons and other contaminants in groundwater and waste impoundments, conducting biodegradation and chemical oxidation treatability studies, and assessing natural attenuation of organic contaminants. He has been HAZWOPER certified since 1988. He was a technical lead for the first successful demonstration of bioaugmentation to promote the complete anaerobic biodegradation of trichloroethene and cis-1,2-dichloroethene for the Remediation Technologies Development Forum at Dover Air Force Base. Terra Systems was a participant in the Source Area BioREmediation (SABRE) project in the United Kingdom that demonstrated in the laboratory and field the anaerobic bioremediation of dense non-aqueous phase trichloroethene. Dr. Lee has conducted laboratory microcosm, column studies, and field demonstrations of the anaerobic bioremediation of chlorinated solvents and chemical oxidation at over two hundred sites. He jointly holds the patent on the use of emulsified soybean oil to support complete reductive dechlorination of chlorinated solvents. Dr. Lee has published over 100 articles in peer-reviewed journals, conference proceedings, or books. He develops new products in support of our customers’ needs. They includes SRS®-M for abiotic degradation of hexavalent chromium and other reducible metals; SRS®-Z combining SRS® and zero valent iron; SRS®-STA with a shear thickening agent for increased distribution in heterogeneous aquifers; SRS®-NR with an anionic surfactant mixture for greater retention in a high groundwater flow rate aquifers.