05/31/2000 Env Bd Packet - Laserfiche WebLink

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it.,Z$ Minnesota Pollution Control Agency Environmental Outcomes Division Ground Water Monitoring & Assessment Program Monitoring and Assessment Program (GWMAP) statewide baseline network of 954 wells. Inorganic phosphorus (phosphates) accounted for about 80 percent of the total phosphorus and organic phosphorus about 20 percent of the total phosphorus and organic phosphorus about 20 percent, assuming that 0.05 percent of organic matter is phosphorus. There was considerable variability between aquifers. The highest median concentrations occurred in the Cedar Valley (median = 203 pg/L), Cretaceous (140 pg/L) and buried Quaternary (124 pg/L) aquifers. Lowest concentrations occurred in the Jordan (25 pg/L), Prairie du Chien (34 pg/L) and Precambrian (35 µg/L) aquifers. The median concentration in the surficial Quaternary aquifer was 561.1g/L. Although the distribution of phosphorus is somewhat complicated, concentrations are highest in aquifers with large natural inputs. Concentrations increase as residence time increases, probably because of increased association with iron and manganese. Which aquifers are most sensitive to contamination with phosphorus? Contamination is difficult to define for phosphorus, since surface water is the primary concern. Aquifers that are most likely to impact surface water do not appear to be sensitive to contamination with phosphorus. Nevertheless, shallow ground water is likely to show some impacts from human activity. The baseline study does not provide good information for assessing phosphorus inputs to shallow ground water. Why is it important to measure phosphorus concentrations in ground water? Phosphorus should be sampled in aquifer systems that discharge to surface water and in which there are potentially large anthropogenic inputs. Along with sampling for phosphorus, sampling includes an assessment of the attenuation properties of the aquifer. This includes differentiation of phosphorus species, pH and concentrations of iron, manganese and aluminum. May 1999 What are some management strategies for reducing risks from phosphorus? Despite the large anthropogenic inputs to soil, phosphorus will not be a contaminant of concern in most aquifers because of limited mobility. Excessive use of fertilizer and poor waste management, particularly on sandy soils with low organic matter content, are most likely to lead to high phosphorus concentrations in shallow ground water. Implementation of best management practices for agriculture and disposal of human and animal wastes represent the best mechanisms for limiting phosphorus inputs to ground and surface waters. Additional information, including reports and distribution maps, can be found the Minnesota Pollution Control Agency's Internet site at http://www.pea.state.mn.us/water/groundwater/gwm ap /index.html. Phosphorus in Minnesotat Ground Water Page 2