Publication Summary

The Department of Ecology's Environmental Investigations and Laboratory Services Program monitored ground water quality for one year at a new two-stage dairy lagoon (two settling ponds and a main lagoon) in Yakima County. This study was conducted at the request of the Ecology's Water Quality Program as part of a larger effort to define the impact of dairy lagoons on ground water quality at several locations in Washington State. The results of these studies will be used to augment existing dairy waste management programs.

The Department of Ecology's Environmental Investigations and Laboratory Services Program monitored ground water quality for one year at a new two-stage dairy lagoon (two settling ponds and a main lagoon) in Yakima County. This study was conducted at the request of Ecology′s Water Quality Program as part of a larger effort to define the impact of dairy lagoons on ground water quality at several locations in Washington State. The results of these studies will be used to augment existing dairy waste management programs.

Monitoring wells were installed and sampled quarterly beginning about three months after initial placement of liquid manure. Analytes included chloride, total dissolved solids, total organic carbon, chemical oxygen demand, total phosphate-P, ammonia-N, and nitrate+nitrite-N. The estimated ambient ground water flow velocity ranged from 0.0009 to 0.08 feet per day (0.3 to 29 feet/year) with a geometric mean of about 0.005 feet per day (1.8 feet/year). Chloride concentrations in all wells downgradient of the main lagoon increased after the second and third quarters of monitoring (between four and ten months after the main lagoon received wastewater) probably due to leakage from the lagoon. At the onset of monitoring, one well downgradient of the settling ponds showed elevated concentrations of most parameters relative to the upgradient well. Two potential sources for the elevated concentrations are the settling ponds and an old lagoon that was replaced by the new lagoons. The closest water-supply well (located about 200 feet downgradient of the main lagoon) was unaffected during the course of the study. Based on the estimated ground water velocities, the long-term effects of lagoon leakage on ground water quality were probably not observed in the first year of sampling. For this reason, additional monitoring is recommended to determine if concentrations for other parameters increase downgradient of the main lagoon and to determine if chloride concentrations decrease. This continued monitoring would require authorization by the Water Quality Program based on alignment with their priorities.