NITRATE CONTAMINATION FROM DAIRY LAGOONS CONSTRUCTED IN COARSE ALLUVIAL DEPOSITS

In an effort to reduce surface inflows of nutrients to Deer Creek Rese rvoir in north central Utah, several dairies in Heber Valley construct ed unlined lagoons to store wastes for later application onto fields a s fertilizer. Previous research indicated that dairy lagoons sealed wi th 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 NO3--N to the groundwater system. One lagoon was constructed on Holmes subsoi ls (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 o f the rates reported in the literature. The other lagoon was construct ed on Deer Creek subsoils (fine, montmorillonitic, frigid Typic Palexe rolls). Leachate quality from both lagoons typically exceeded the drin king water standard of 10 mg NO3--N/L and sometimes exceeded 100 mg NO 3--N/L. The likely reason for the high NO3--N concentrations was that the coarse soils in Heber Valley sometimes permitted the aerobic condi tions necessary for nitrification of immobile NH4+ to mobile NO3-. We concluded that the unlined dairy lagoons were significant sources of N (as NO3-) contamination to the Heber Valley aquifer.