A FIELD STUDY TO ASSESS THE RISK OF USING REUSE WATER TO IRRIGATE TURF-COVERED SOIL

In arid and semi-arid regions, reuse water for landscape irrigation is becoming a significant asset to conserve potable water supplies. Currently, Texas has nearly 500,000 acre-feet of reuse supply and this is expected to increase to over 600,000 acre-feet by 2060 (TWDB, 2012). Reuse water could reduce pressures on potable supplies if used as an irrigation source. However, small amounts of pharmaceutical compounds can remain in the waste water. Long-term, field-scale data are generally unavailable to show their fate and transport. Recently, a 2-yr experiment was conducted where reuse water was the sole source of non-ambient water input. We studied 13 compounds, all originating in irrigation water, ranging from anti-convulsants to anti-inflammatories to tranquilizers. Goals of the study were to assess fate and transport of these compounds in turfgrass/soil systems, and to use these data to assess potential health risk from using this reuse water. Experiments were conducted at lysimeter-scale and field-scale. The 24 drainage lysimeters (120 cm thick) varied by soil type (two types), soil cover (bare- versus turf-covered) and leaching fraction (5% and 25%). Upper and lower boundaries were monitored throughout the study, and water samples were collected periodically after water breakthrough. After the study, soil samples were analyzed for compound mass to assess mass balance. At the field-scale, drain gages were installed in fairways at 4 operating golf courses, one in NV and three in CA, all with histories of using treated wastewater. Irrigation and draining waters were sampled and analyzed for mass, so removal efficiencies could also be assessed. Results of the lysimeter study showed that mass fluxes were reduced to less than 1 g/ha/yr for all compounds (sulfamethoxazole was highest at 0.25 g/ha/yr). Solute breakthrough was concentrated during fall and winter periods during overseeding. Results of the golf course study showed total mass fluxes of <0.1 g/ha for all compounds. The preliminary risk assessment used mass fluxes and acceptable daily input levels for each compound, and showed substantial margins of safety when reuse water is used for irrigation. Nonetheless, irrigation regimes not based on an evapotranspiration feedback approach should be avoided in sandy soils.