Ground water age and nitrate distribution within a glacial aquifer beneath a thick unsaturated zone

• Published in: Ground water 1998-01, Vol.36 (1), p.171-180
• Main Authors: Johnston, C.T. (University of Waterloo, Waterloo, Ontario, Canada.), Cook, P.G, Frape, S.K, Plummer, L.N, Busenberg, E, Blackport, R.J
• Format: Article
• Language: English
• Subjects: ABONOS NITROGENADOS; AGE DETERMINATION; AGUAS SUBTERRANEAS; Aquifers; CAPA FREATICA; CARACTERISTICAS MORFOLOGICAS SUELO; CHLORIDES; CHLOROFLUOROCARBONS; CHLORURE; CLORUROS; COMPOSE ORGANOHALOGENE; Composition; COMPUESTO ORGANICO HALOGENO; DETERMINACION DE LA EDAD; DETERMINATION DE L'AGE; DISSOLVED OXYGEN; EAU SOUTERRAINE; ENGRAIS AZOTE; Environmental aspects; EPAISSEUR; ESPESOR; Fertilizers; FLUVIOGLACIAL SOILS; GROUNDWATER; GROUNDWATER RECHARGE; GROUNDWATER TABLE; HELIUM; Hydrology; LEACHING; LESSIVAGE DU SOL; LITHOLOGICAL SOIL TYPES; LIXIVIACION; METALLOIDE; NAPPE SOUTERRAINE; Nitrates; NITROGEN FERTILIZERS; NO METALES; NONMETALS; ONTARIO; ORGANIC HALOGEN COMPOUNDS; OXIGENO EN DISOLUCION; OXYGENE EN DISSOLUTION; POLLUTION DE L'EAU; POLUCION DEL AGUA; RECARGA DE AGUAS SUBTERRANEAS; RECHARGE DE LA NAPPE; SOIL MORPHOLOGICAL FEATURES; SURFACE LAYERS; THICKNESS; TIPOS LITOLOGICOS DE SUELO; TRAIT MORPHOLOGIQUE DU SOL; TRITIO; TRITIUM; TYPE DE SOL LITHOLOGIQUE; WATER POLLUTION; Water, Underground
• ISSN: 0017-467X; 1745-6584
• DOI: 10.1111/j.1745-6584.1998.tb01078.x

The impact on ground water quality from increasing fertilizer application rates over the past 40 years is evaluated within a glacial aquifer system beneath a thick unsaturated zone. Ground water ages within the aquifer could not be accurately determined from the measured distribution of 3H and as a result, chlorofluorocarbon (CFC) and 3H/3He dating techniques were applied. Beneath a 25 m thick unsaturated zone, ground water ages based on CFC-11 concentrations were greater than 3H/3He ground water ages by 6 to 10 years, due to the time lag associated with the diffusion of CFCs through the unsaturated zone. Using the corrected CFC-11 and 3H/3He ground water ages and the estimated travel time of 3H within the unsaturated zone, the approximate position of ground water recharged since the mid-1960s was determined. Nitrate concentrations within post mid-1960s recharge were generally elevated and near or above the drinking water limit of 10 mg-N/L. In comparison, pre mid-1960s recharge had nitrate concentrations 2.5 mg-N/L. The elevated NO3- concentrations in post mid-1960s recharge are attributed mainly to increasing fertilizer application rates between 1970 and the mid- to late 1980s. Anaerobic conditions suitable for denitrification are present within pre mid-1960s recharge indicating that removal of DO is a slow process taking tens of years. Over the next 10 to 20 years, nitrate concentrations at municipal well fields that are currently capturing aerobic ground water recharged near the mid-1960s are expected to increase because of the higher fertilizer application rates beginning in the 1970s and 1980s