Estimating contamination potential at waste-disposal sites using a natural tracer

Chloride is a conservative, natural tracer found in precipitation, soil water, and groundwater. The chloride mass-balance approach, long used to estimate groundwater recharge, also provides a downward flux of moisture and solute at sites where there is a potential for groundwater contamination. The flux is obtained by dividing the product of the mean annual precipitation and total annual chloride input (via precipitation and dust) by the mean soil-water chloride content. Chlorideversusdepth profiles can also be used to determine optimum depth of waste burial to minimize deterioration of waste containers. The method has been applied to three sites in arid alluvial-basin settings in New Mexico, U.S.A.: a proposed landfill, a battery recycling plant, and a hazardous-waste disposal facility. It is concluded that the method is reliable, economical, and practical. Furthermore, it can be applied at any stage in the development of a site. The chloride method should apply in any recharge area where the base of the root zone is separated from the water table by at least 3 m or so and chloride in soil water comes only from precipitation and dust.