RESUMO
Perchlorate was detected in a municipal wellfield in Evart, Michigan in April 2015. Perchlorate concentrations were detected initially in six of the City's wells at concentrations ranging up to 20 µg/L. An investigation to identify the source determined that the perchlorate was from fireworks launched during the annual 4th of July show held at the fairgrounds located upgradient from the wellfield. The use of approximately 600 kg of fireworks during the annual display resulted in an annual loading of approximately 4 kg of perchlorate to groundwater. An aggressive groundwater extraction system began operation in June 2016 to restore water quality in the affected aquifer, and the 2016 fireworks display was relocated to a location outside the capture zone of the water supply wells. Within 18 months average perchlorate concentrations in the water supply wells had been reduced to about 0.6 µg/L. The extraction system continued to operate through the end of 2019, by which time the average perchlorate concentrations in the water supply wells were reduced to 0.2 µg/L. In 2019, approximately 0.4 kg of perchlorate were removed from the aquifer, about one-half of the amount removed in 2018, reflecting the slow leaching of perchlorate of fireworks residuals from vadose zone soils.
