GROUNDWATER AGE DETERMINATION USING CFCS IN A NITRATE CONTAMINATED AGRICULTURAL SITE IN STRATHROY, ONTARIO

CFCs, specifically CFC-12 and CFC-11, were used to determine the age of groundwater at a nitrate-contaminated agricultural site in Strathroy, Ontario with an unconfined fine to medium sand aquifer and a horizontal flow system. The aquifer has a 3-meter thick unsaturated zone and has been investigated to a depth of 15 meters via a fence of 60 nested piezometers. The upper aquifer is oxic, and apparently becomes nitrate reducing at about 6 meters below ground surface, and then iron and manganese reducing at about 7 meters. Tritium was detected in the entire 15 meters. Degradation of both CFC-12 and CFC-11 were observed to occur where the aquifer is apparently iron and manganese reducing, but not at shallower depths where it was oxic or nitrate reducing. To date, no other studies have been published showing degradation of CFCs in iron and manganese reducing aquifer conditions. Further study is underway using other age determination tracers to corroborate the ages determined with CFCs and to determine the age of groundwater at depths where CFCs were degraded.