Geochemical transformations during artificial groundwater recharge: soil–water interactions of inorganic constituents

Six soils from two vadose-zone injection wells were used in conjunction with three types of recharge waters (microfiltered reclaimed wastewater; reverse osmosis-treated reclaimed wastewater and membrane-filtered Colorado River water) to evaluate soil–water chemical processes that may alter water quality during recharge of these waters. Batch studies (soil–water slurries; 30-day contact time) and flow-through column studies (upflow mode columns; 100 pore volumes over 30 to 100 days) showed that F, Ba and As were leached in appreciable concentrations, whereas leaching of B, Cr, Pb and Se was minimal. In the column study, concentrations often peaked during the first few days of operation (a “washout” phenomenon) and then declined. Precipitation and dissolution reactions may be important from a standpoint of sustained infiltration rates.