Nitrate Contamination from Dairy Lagoons Constructed in Coarse Alluvial Deposits

In an effort to reduce surface inflows of nutrients to Deer Creek Reservoir in north central Utah, several dairies in Heber Valley constructed unlined lagoons to store wastes for later application onto fields as fertilizer. Previous research indicated that dairy lagoons sealed with use and were not significant sources of contamination; however, the soils in Heber Valley are coarser than in the literature. Therefore, two of Heber Valley's dairy lagoons were studied as sources of NO^- ₃ -N to the groundwater system. One lagoon was constructed on Holmes subsoils (loamy-skeletal, mixed, frigid Typin Argixerolls); its seepage rate was estimated at 13 to 91 mm/d, which is as high or higher than any of the rates reported in the literature. The other lagoon was constructed on Deer Creek subsoils (fine, montmorillonitic, frigid Typic Palexerolls). Leachate quality from both lagoons typically exceeded the drinking water standard of 10 mg NO^- ₃ -N/L and sometimes exceeded 100 mg NO^- ₃ -N/L. The likely reason for the high NO^- ₃ -N concentrations was that the coarse soils in Heber Valley sometimes permitted the aerobic conditions necessary for nitrification of immobile NH⁺ ₄ to mobile NO^- ₃ . We concluded that the unlined dairy lagoons were significant sources of N (as NO^- ₃ ) contamination to the Heber Valley aquifer.