Ground-Water Quality at Rapid Infiltration Site

The ground water quality beneath a 30-yr old rapid infiltration was studied over a 12-month period. The system receives primary effluent and treats it to a very high quality through the land treatment process. The flow of treated water passes through 10 m to 20 m of permeable sands and then moves laterally off the site. This shallow ground water is not used as a water supply and does not affect the deeper, separate aquifers. A 96% BOD and TOC removal was achieved. Because of the high BOD to nitrogen ratio, the relatively low loading rate of 15.4 m/yr, and the moderate climate, nitrogen was removed by nitrification and denitrification in the soil. The average nitrogen removal was 93%. Phosphorus removal was 30%. Trace element removal varied, but shallow ground-water levels were generally lower than guidelines established for unrestricted irrigation.