Perchlorate in Arizona: Occurrence Study of 2004

1.3 Statement of the Specific ProblemPerchlorate is an oxidizing anion that occurs in ground and surface waters from the dissolutionof ammonium-, potassium-, magnesium- or sodium- perchlorate salts. Perchlorate is very solubleand mobile in aqueous systems and because it degrades very slowly it can persist for many decadesunder typical ground and surface water conditions. Ammonium perchlorate is manufactured foruse as an oxidizer component and primary ingredient in solid propellents for rockets and missiles.Perchlorate is also used in the manufacturing of matches, air bag inflators, and fireworks.Perchlorate has been manufactured at two facilities near Henderson, NV -- PacificEngineering & Production Company of Nevada and Kerr-McGee Chemical Corporation – fromWorld War II to the present. Considerable amounts of process effluents have been dischargedinto unlined surface channels that conveyed the waste to unlined evaporation ponds. As a resultof continuous percolation of perchlorate contaminated water into the underlying aquifer, thegroundwater in the vicinity of the industrial complex has been contaminated. The groundwatercontaminated with soluble ammonium perchlorate has been seeping into the Las Vegas Washwhich drains into Lake Mead, and ultimately into the Colorado River as it flows through HooverDam. Detectable concentrations of perchlorate have been found from Lake Mead to Yuma. Thecontaminated seepage contained perchlorate at 100 mg/L (100,000 ppb); while in the wash, theconcentrations varied from 10 – 750 ppb. Concentrations of 10-20 ppb have been detected inthe water intakes for Las Vegas and at Hoover Dam (EPA, 1999). Both Arizona and Californiawithdraw Colorado River water from Lake Havasu and deliver it inland for use in agriculture,municipal and industrial uses; as well as store it for future use in ADWR permitted undergroundstorage facilities and groundwater savings facilities. Many communities along the river alsowithdraw water directly from the Colorado for domestic and agricultural uses. Concentrations inthe Colorado River below Lake Mead to Yuma have ranged from results at the analytical testdetection limit (usually 4 ppb) to 11 ppb.Studies indicate that perchlorate disrupts iodine uptake in the thyroid gland, which regulateshormone function. Pregnant women and children are most vulnerable to the effects ofperchlorate. In 2003, perchlorate was found in the outer leaves of leafy vegetables grown in theYuma area (e.g., lettuce). A study in Texas revealed concentrations of perchlorate in milk,suggesting that perchlorate may be taken up in feed used for dairy animals.A maximum contaminant level (MCL) has not yet been established by the U.S. EnvironmentalProtection Agency. Arizona has established a Health-based Guidance Level of 14 ppb; Californiahas recently adopted a Public Heath Goal of 6 ppb and Nevada has set its level at 18 ppb.- 34 -