A Comprehensive Approach for Evaluation of Groundwater Vulnerability to Contamination
Groundwater vulnerability to contamination from surface sources was evaluated for Nottawa Creek Watershed, Calhoun County Michigan using AQUIPRO and DRASTIC vulnerability methods. A geographic information system (GIS) was used to analyze and map the data. Forty groundwater samples were collected following a statistical sampling protocol from private wells. Samples were analyzed for nitrate-N and atrazine. Atrazine was not detected ( detection limit 0.1 ppb) in any of the samples. Five samples contained detectable nitrate-N (detection limit 0.05 mg/L). Due to insufficient chemical data, the relative AQUIPRO and DRASTIC vulnerability scores could not be compared with the frequency of occurrences of groundwater contamination. The wells with detectable nitrate-N have indicated that the shallow glacial drift aquifers with low AQUIPRO scores and high DRASTIC scores are susceptible to contamination from surface sources.
In addition, AQUIPRO was used to evaluate groundwater vulnerability to contamination in Kalamazoo County, Michigan. Computerized water well records of 2,653 wells with partial chemistry data were utilized for this site. A previously prepared DRASTIC map of Kalamazoo County was utilized to obtain the DRASTIC scores of the wells used in AQUIPRO. The relative AQUIPRO and DRASTIC vulnerability scores were compared with the frequency of occurrences of nitrate-N in groundwater wells. The average nitrate-N concentrations within each relative AQUIPRO and DRASTIC vulnerability category were also compared. The results indicated that the groundwater wells containing 5 mg/L or more nitrate-N showed a positive correlation between the frequency of occurrences of nitrate-N and relative increase of AQUIPRO (r2 = 0.98) and DRASTIC (r2 = 0.46) vulnerability. The results also showed that as the relative AQUIPRO (r2 = 0.99) and DRASTIC (r2 = 0.33) vulnerability increases the mean nitrate-N concentration also increases. Overall, the aquifer vulnerability prediction by AQUIPRO and DRASTIC methods were valid. However, the results also indicated that the vulnerability prediction by AQUIPRO proved superior to DRASTIC in this particular hydrogeologic setting.