Soil Chemistry Changes at Rapid Infiltration Site

Unchlorinated primary effluent has been applied to the land for rapid infiltration treatment at Hollister, Calif. for 30 yr. Domestic wastewater has been used on the site for about 50 yr so that accumulations of wastewater constituents in the soil should have occurred. Nitrogen and organic matter did not accumulate significantly compared with offsite control soils. Phosphorus adsorption is still occurring and the onsite soils retained 64% of their original sorption capacity. Seven of the nine monitored heavy metals showed significant concentration increases in the soil. Despite these increases, the rapid infiltration site could potentially be converted to agricultural use because the soil concentrations of heavy metals were not outside the normal range for soils.