Geochemistry of nitrate in ground water in Kansas.

Abstract

Ground water pollution in Kansas by nitrate has occurred for many years, but its chemistry in aquifers is still not well known. Some wells in Nemaha, Chase and Harvey Counties have shown a disappearance in nitrate accompanied by an increase in dissolved iron, suggesting a natural nitrate reduction process. The main purposes of this study are to describe the chemical reactions of nitrate in ground water and to identify the geological factors controlling the reactions. In order to examine the purposes of this study both Flow tests and Beaker tests were carried out with the minerals pyrite and siderite with nitrate and synthetic ground water solutions. The Beaker tests revealed reduction of nitrate by pyrite. The tests indicated that pyrite particle <0.125 mm size are able to reduce nitrate. The tests also revealed that after 74 and 51 days, total reduction of nitrate in Preliminary beaker test no. 2 and Final beaker test no. 2 were 78.6 %and 10 %respectively. The reaction between N03and FeS2 mineral is not a direct one. It took place after a lag time. The reaction is most possibly catalyzed either by bacteria or by freshly precipitated Fe(OH)3. The nature of the reduction of n1trate by pyrite closely corresponds to the iron and nitrate relationship in alluvial aquifer in Harvey County, glacial drift aquifer in Nemaha County, High Plains aquifer in Harvey County, Chase and Council Grove Group aquifer in Chase County and Pleistocene aquifer in Nemaha and Chase Counties. This phenomenon suggests that the reduction of nitrate in ground water in Kansas is also controlled by pyrite. The presence of pyrite in aquifers in Kansas can be supported by two indirect evidences: pyrite occurs in rocks of all ages in Kansas (Buchanan, 1989) and the variation of SO4² -concentrations in relation to iron and nitrate concentrations in the aquifers of the study areas. The reduction of nitrate by pyrite in ground water conditions can not be fully justified because the tests were carried out by pure minerals. In order to obtain detailed information regarding the rate of reduction of nitrate and reaction between nitrate and pyrite in actual ground water conditions, a scheme of experiments has been proposed.