Nutrient Reduction by Year Round Land Application of Secondary Effluent

Penn State conducted its land application research project during 1963-1974 using 20 percent of its secondary effluent and up to15,141 m³/d by 1983 at a design rate of 5.0 cm/wk. Some groundwater nitrate values exceeded the 10 mg/l limit within a 2-to 6-year period. An interdisciplinary committee was appointed to develop a management strategy to bring nitrate into compliance. This required a 2-to 10-year period. Four methods were used to document nitrate removal. 1. Reductions in nitrate concentrations in stormwater runoff. 2. Comparison of applied effluent v nitrate concentrations in up-and down- gradient monitoring wells. 3. Flow and transport simulations. 4. Lysimeter studies in woodlots that showed that 90.72 kg of N could be removed within irrigated woodland given a 4-month rest period. Monitoring well v applied effluent (9.99 mg/l mean) data showed nitrate reduction of 2.47 to 4.17 mg/l for woodlots and 1.70 to 13.5 mg/l for a combination of cropland and woodlots. Nitrate was reduced by 21.4 to 58.7 percent and phosphorous (3.25 mg/l mean) by 14.8 to 99.3 percent. Transport model simulations predicted nitrate concentrations of 4 to 16 mg/l depending upon input values assumed.

Multiple lines of evidence indicate that groundwater nitrate concentration can be maintained at < 10 mg/l under the current management strategy provided that total N in applied effluent does not exceed 20 mg/l, the 5.0 cm/wk application rate is maintained on a year around basis, biomass is removed, and physical-chemical soil properties are maintained.