MULTILAYER SAMPLING IN THE WATER-TABLE REGION OF A SANDY AQUIFER

Depth profiles of organic pollutants, metals, and anions were obtained using a ground-water multilayer sampler (MLS) in a sandy unconfined aquifer contaminated by liquid fuels. The sampler incorporates dialysis membranes and is capable of obtaining vertical profiles with a resolution on the order of few centimeters. Of the eight solutes examined (metals, organics, and anions), all except sulfate exhibited microscale heterogeneities in their concentration over a vertical interval of 200 cm. Chloride, manganese, and iron showed a long linear concentration gradient versus depth which is probably the result of vertical mixing by rainfall input. Maximum concentrations of toluene, xylene, and xylidine at the water table were 17.1, 8.3, and 17.1 mg/l, respectively, decreasing with depth. For toluene and xylene the maximum concentrations found at the water table with the MLS are 40 and 4 times higher, respectively, than those detected at depths greater than 200 cm in water samples obtained with a pump.