Thus far, in all cases where subaqueous sulphide tailings have been studied, no signs of oxidation have been observed. However, a far more sensitive, effective and elegant approach is to look for direct effects of sulphide oxidation such as a drop in pH, an increase in sulphate or the most direct indicator of all, an increase in dissolved metals. The distribution of dissolved metals in porewaters has been determined by two proven approaches. Sampling porewaters by core involves the collection of sediment with a specialized, light-weight, gravity corer. Peepers sample porewaters much more passively.
Peepers consist of an array of depressions or wells in a plexiglas plate.
The wells are filled with ultra-pure water and covered with a filtration membrane. The peeper is inserted vertically into the sediments and allowed to equilibrate within the sediments for 10 to 14 days. During that period, dissolved metals move across the membrane into the sample wells while the solids are excluded. In order to avoid oxidizing the samples by allowing them to contact the atmosphere, all sample handling of both cores and peepers after collection is carried out in nitrogen-filled, plastic glove bags. Release or consumption of dissolved metals results in the formation of adjacent zones of differing concentrations.