Geosyntec, a thought leader among environmental science and engineering firms, recently devised an innovative approach to rescue a client from a long-standing site condition where dissolved fluoride impacted groundwater at high enough levels to impair water quality and require cleanup.
Fluoride releases are uncommon, but when this does occur the solubility of fluoride often results in groundwater contamination. Led by Chris Herin, the Geosyntec project team recognized that soil excavation was too disruptive to site operations and a public roadway, was complicated by buried utilities, and the contaminated aquifer matrix extended well below the water table. With no cost-effective conventional removal options, groundwater extraction seemed like the default alternative, but this was projected to take many years of costly operation to remediate the site. As part of the remedial options evaluation, Geosyntec's Technology Evaluation Lab in Knoxville collaborated with the project team for innovative ideas.
Taking hints from modern dentistry, Geosyntec's Technology Evaluation Lab staff in Tennessee, Linxi Chen, Jacques Smith, and Duane Graves, worked with the project team to devise an in situ treatment strategy which is related to fluoride treatment for tooth enamel. By combining calcium and phosphate injection fluids in carefully developed ratios and concentrations, soluble fluoride can be crystalized into very insoluble calcium fluorapatite, which is the desired end product of fluoride tooth treatments. Testing in Geosyntec's Technology Evaluation Lab of a number of possible sequestration approaches using soil and groundwater from the Site showed that the use of calcium/phosphate reduced soluble fluoride concentrations from tens of mg/L to non-detect levels less than 0.1 mg/L, far below the MCL.
When lightheartedly asked if Geosyntec would be growing teeth in the subsurface, Duane Graves, the lab's director who oversaw development of this novel application, said "No, but the thin mineral layer formed in the surface of our teeth from using fluoridated toothpaste is essentially the same chemical as the insoluble, microscopic fluorapatite crystals we intend to form during in-situ treatment of the fluoride impacts to soil and groundwater. Additionally, this sequestration technology can be easily implemented by direct injection into the subsurface. This avoids the problems associated with excavation and is predicted to dramatically shorten the time and reduce the cost to achieve regulatory closure compared to conventional groundwater and soil remedial methods.
Geosyntec's innovative thinking and ability to devise and demonstrate novel and cost-saving approaches exemplifies the value we bring to each of our clients. This is just one of the reasons clients turn to us when they need fresh solutions to solve their most challenging environmental and engineering problems and manage their costs and environmental liabilities.