Studies Related to Nutrients Entering Groundwater From the Heber Valley Sewer Farm and Dairies

Foreword: This report includes the results from a two year study in the Heber Valley to determine amounts of nutrients that are entering the groundwaters of the Heber Valley, and might ultimately enter Deer Creek Reservoir. Since Deer Creek Reservoir in Heber Valley, Utah supplies approximately 65 percent of the water distributed to Salt Lake County, the maintenance of its quality is of considerable importance. To maintain the quality of this reservoir and limit its eutrophication best management practices for surface water have been implemented gradually during the past decade in Heber Valley. These practices have significantly improved the qualities of surface streams flowing into the reservoir. However, data for amounts of phosphorus and nitrogen in groundwater inflows to the reservoir are several times larger than predicted from 1967 data. Concern has been voiced that perhaps cleaning up the surface inflows by spreading treated sewage on land, retaining dairy wastes in lagoon, etc, have only delayed the arrival time of nutrients into Deer Creek Reservoir, and that their transmission through gruondwaters into the reservoir will result in eutrophication unless other measures are implemented. To provide data for better understanding of the processes assocaited with soil sorption and transmission of chemicals (with a focus on phosphorus and nitrogen) into the saturated groundwater and ultimately into Deer Creek Reservoir, a three pronged research program was initiated by Utah State University during the Spring of 1989. This program consisted of: 1. Installation of unsaturated zone (Vandose zone) samples that extract water from the partially saturated soil at 6 sites (with two samplers at different depths at each site) within the land disposal area of the Heber Valley Special Service District (referred to as the sewer farm hereafter), and adjacent to two liquid manure lagoons at dairy farms. 2. Laboratory sorption studies on soil columns that were acquired in an undistrubed state from the 6 sites in the above sewer farm , and 3. Development of computer solutions to estimate the transmission of nutrients through the unsaturated top soil into the groundwater. An earlier 1990 preliminary report Interim Report for Studies related to Nutrients Entering Groundwater from the Heber Valley Sewer Farm and Dairies provided information related to the results of the laboratory sorption studies, and tentative results from the field studies based on the data collected during the summer of 1989. Since the field data given in the earlier report covered only a portion of ayear, and the study was continued for a second year that report is superceded by this report. This report provides the data collected over the two year period of the study, 1989-1990. Included in this report are field data obtained from the most critical spring period of 1990 when the surface soils recieve the relatively large quantities of snow melt water. The 1990 water year was again a dry year in which precipitation was considerably below normal. Thus the field collection period did not include a truly wet condition as will undoubtedly occur during years of above normal precipitation. Above normal rainfall did occur during the months of April and May, 1991. However this was not anticipated and the field samplers were unfortunately removed prior to these occurences to allow more easy working of the farm area. Since only a few copies of the above mentioned interim report were reproduced, this report duplicates the description of the field instrumentation, and the laboratory sorption studies. The data tables contained in that report have been updated to include field data from the second year through 1990. The results from the computer solutions that were contained in the interim report as Appendix A are not included herein, however. That report must be consulted for this detail. Field data collected from the first year indicated that larger quantities of nitrogen in the form of nitrate (NO3) than phophorus were within the unsaturated surface soils of the farm irrigated by the treated sewage, and by the dairy lagoons. Based on this information an additional research program, or changing the emphasis of the research, was directed to studying the nitrogen cycle in the groundwater system of Heber Valley to determine in natural processes reduce the amount of NO3- reaching Deer Creek Reservoir through the Heber Valley aquifers. More specifically the additional emphasis was deirected to determine whether conditions exist that favor denitrification and the extent by which such process might be reducing the amounts of NO3- input to Deer Creek Reservoir from the irrigated farm of the Heber Valley Special Service District, and two dairy lagoons. Denitrification is a process whereby bacteria transfer electrons from compounds, known as electron donors, to NO3-, an electron acceptor. The end products of this reduction are gases of N2O and N2, both of which escape to the atmosphere and thus reduce the amount of nitrogen in the water. The results of this sadditional research will be reported in a forthcoming project report consisting of the Ph.D. dissertation by Scott F. Korom Denitrification in the Unconsolidated Deposits of the Heber Valley Aquifer. This dissertation is being written in the format now allowed by Utah State University where different sections are designed as separate papers for submission to professional journals. Therefore the results of the denitrification phases of the research should also be available in future professional journal papers