Drinking Water Engineering and Science Discussions www.drink-water-eng-sci-discuss.net 1996-9473 1996-9481 3 1 2010 10.5194/dwesd-3-177-2010 http://www.drink-water-eng-sci-discuss.net/3/177/2010/ http://www.drink-water-eng-sci-discuss.net/3/177/2010/dwesd-3-177-2010.html http://www.drink-water-eng-sci-discuss.net/3/177/2010/dwesd-3-177-2010.pdf 177 198 2010-06-04 Metals releases and disinfection byproduct formation in domestic wells following shock chlorination M. Walker mwalker@cabnr.unr.edu J. Newman University of Nevada, Department of Natural Resources and Environmental Science, MS 370/FA 132, 1664 N. Virginia Street, Reno, NV 89557, USA Shock chlorination is used for rapid disinfection to control pathogens and nuisance bacteria in domestic wells. A typical shock chlorination procedure involves adding sodium hypochlorite in liquid bleach solutions to achieve concentrations of free chlorine of up to 200 ppm in the standing water of a well. The change in pH and oxidation potential may bring trace metals from aquifer materials into solution and chlorine may react with dissolved organic carbon to form disinfection byproducts. We carried out experiments with four wells to observe and determine the persistence of increased concentrations of metals and disinfection byproducts. Water samples from shock chlorinated wells were analyzed for Pb, Cu, As, radionuclides and disinfection byproducts (haloacetic acids and trihalomethanes), immediately prior to treatment, after sufficient contact time with chlorine had elapsed, and at intervals determined by the number of casing volumes purged, for up to four times the well casing volume. <br><br> Elevated concentrations of lead and copper dissipated in proportion to free chlorine (measured semi-quantitatively) during the purging process. Trihalomethanes and haloacetic acids were formed in wells during disinfection. In one of two wells tested, disinfection byproducts dissipated in proportion to free chlorine during purging. However, one well retained disinfection byproducts and free chlorine after four well volumes had been purged. Although metals returned to background concentrations in this well, disinfection byproducts remained elevated, though below the MCL, likely because purging volume was insufficient. Simple chlorine test strips may be a useful method for indicating when purging is adequate to remove metals and disinfection by-products mobilized and formed by shock chlorination. Amoore, J. E. and Hautala, E.: Odor as an ald to chemical safety: Odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution, J. Appl. Toxicol., 3(6), 272–290, 1983. Driscoll, F. G.: Groundwater and Wells, 2nd Edn., Johnson Division, St. Paul, MN, 1108~pp., 1986. Fram, M. S., Maurer, D. K., and Lico, M. S.: Potential for formation of disinfection by-products from storage of chlorinated surface water in the basalt aquifer near Fallon, Nevada, US~Geological Survey, Carson City, NV, 23~pp., 2005. Glancy, P.: Geohydrology of the Basalt and Unconsolidated Sedimentary Aquifers in the Fallon Area, Churchill County, Nevada, Institution, Alexandria, Va., US~Geological Survey Water Supply Paper 2263, 60~pp., 1986 Gotkowitz, M., Ellickson, K., Clary, A., Bowman, G., Standridge, J., and Sonzogni, W.: Effect of well disinfection on arsenic in ground water, Ground Water Monit. R., 28(2), 60–67, 2008. Llopis, J. L.: The effects of well casing material on ground water quality, US~Environmental Protection Agency, Washington, D.C., Ground-Water Issue, 15~pp., 1991. McCaulou, D. R., Jewett, D. G., and Huling, S.: Nonaqueous phase liquids compatibility with materials used in well construction, sampling and remediation, US~Environmental Protection Agency, Washington, D.C., Ground Water Issue, 14~pp., 1995. Schnieders, J. H.: Use of Chlorine to Disinfect Water Wells, Water Well Journal, 7, 52–53, 2005. Seiler, R. L.: Mobilization of lead and other trace elements following shock chlorination of wells, Sci. Total Environ., 367(2–3), 757–768, 2006. Walker, M. J., Benson, M., and Shaw, W. D.: Significance of private water supply wells as a route of exposure to aqueous arsenic, J. Water Health, 3(3), 305–312, 2005. Welch, A. H. and Lico, M. S.: Factors controlling As and U in shallow ground water, southern Carson Desert, Nevada, Appl. Geochem., 13(4), 521–539, 1998. Westerhoff, P., Chao, P., and Mash, H.: Reactivity of natural organic matter with aqueous chlorine and bromine, Water Res., 38(6), 1502–1513, 2004.