Column methodologies for determining sorption and biotransformation potential for chlorinated aliphatic compounds in aquifers

A method is described to measure the potential for sorption and biotransformation of halogenated compounds in aquifers. Glass columns, 40 cm in length and with a volume of 130 ml, were filled with aquifer material under conditions to avoid contamination from surface bacteria. Poorly sorted fluvial aquifer soils from three locations in the Bay area of San Francisco were used for evaluation. Gravel larger than 5 mm in diameter and a portion of the clay and silt fraction were removed during column filling. The columns were operated aerobically or anaerobically. The fluid within a column was periodically replaced within 15 minutes with new fluid of defined composition by syringe pump at time intervals of days to weeks. Initially, bromide was used to characterize flow through properties and to determine pore volume. Break-through curves for chlorinated aliphatic compounds allowed determination of sorption behaviour during fluid exchange.During the first several exchanges, and in the absence of biotransformation, added chlorinated aliphatics were removed significantly by sorption until a steady state was achieved. Through mass balance, the extent of sorption could be estimated. The ratio of sorbed mass to solution mass for the aquifer materials evaluated were 2.2 ± 1.0 for 1,1,1-trichloroethane (TCA) and 4.5 ± 1.5 for 1,1-dichloroethane (DCA) in the chloroorganic concentration range used of 50–150 μg/l. In an anaerobic column, biotransformation of TCA to DCA was demonstrated.