| Abstract: | 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.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. 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. |
| Genre: | Article |
| ProdID: | 70020680 |
| Citation Author: | Johnston, C. T.; Cook, P. G.; Frape, S. K.; Plummer, L. N.; Busenberg, E.; Blackport, R. J. |
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| Citation End Page: | 180 |
| Citation Issue: | 1 |
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| Citation Language: | English |
| Citation Larger Work Title: | Ground Water |
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| Citation Number Of Pages: | 10 |
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| Citation Publisher: | Ground Water Publ Co |
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| Citation Search Results Text: | Ground water age and nitrate distribution within a glacial aquifer beneath a thick unsaturated zone; 1998; Article; Journal; Ground Water; Johnston, C. T.; Cook, P. G.; Frape, S. K.; Plummer, L. N.; Busenberg, E.; Blackport, R. J. |
| Citation Start Page: | 171 |
| Citation Volume: | 36 |
| Citation Year: | 1998 |
| Type: | citation/reference |
| Text: | Ground water age and nitrate distribution within a glacial aquifer beneath a thick unsaturated zone; 1998; Article; Journal; Ground Water; Johnston, C. T.; Cook, P. G.; Frape, S. K.; Plummer, L. N.; Busenberg, E.; Blackport, R. J. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Thu, 1 Jan 1998 00:00 -0600 |
| Publisher: | Ground Water Publ Co |
