| In Door County, the Wisconsin DNR recently found lead in house water-supply wells with concentrations greater than the health advisory limit of 50 {dollar}mu{dollar}g/l. In addition, a total of 35 abandoned lead-arsenate mixing facilities were identified around the county with significant contamination of soils by lead and arsenic. Although lead contamination was more significant along the northwestern part of the County, detections were irregular both temporally and spatially.; A study was initiated to identify the extent, source and the transport mechanisms of lead, and to develop a predictive model for lead in ground water in Door County. Statistics were performed among lead indicators in ground water (frequency of detection, mean and maximum concentrations) and other variables, such as well design, geology and site hydrogeology to determine their relation to lead arsenate mixing sites. The mixing sites were found to be significantly related to lead indicators in ground water, and are the source of the observed lead contamination.; A total of 136 ground-water samples and 86 filter cakes were collected from five house water-supply wells and two monitoring wells in Sturgeon Bay and Sevastopol Townships in the County, during the 1991 spring recharge. Lead was found only on particles larger than 0.45 {dollar}mu{dollar}m, and seems to be carried in ground water sorbed onto Fe-oxyhydroxide coatings on alumino-silicate minerals. Arsenic was not detected in any water or filter samples. The detection limit for arsenic was 10 {dollar}mu{dollar}g/l.; Recharge events were simulated in the laboratory with intact Longrie loam soil columns of 30 cm x 30 cm x 30 cm in size to identify the effects of such events on particle concentrations in the recharge water. Particle concentrations increased as recharge intensity increased. The initial moisture content of soil did not significantly affect particle concentration in the recharge water.; From field study and column experiments results, a model was developed to predict the highest likely lead concentrations in ground water from recharge events. The model requires information on local soil type, well casing and total depth, distance to the nearest upgradient mixing site, and depth to water level at the site. The model works for the spring and fall seasons. The model can effectively be used during the spring and fall (1) to alert residents to dangerous lead levels in ground water used for drinking, and (2) to develop a ground-water monitoring scheme for lead contamination. |
