IMPACT OF RECYCLED WATER USE AT MAMMOTH GOLF COURSES ON BASIN GROUNDWATER QUALITY

The Mammoth Community Water District's proposed plan for recycled water use in golf course irrigation as a solution to the district's water shortage problem develops concerns over protecting its basin groundwater quality. A detailed assessment through model development, and monitoring and testing is done in this study to determine the fate and transport of concerned pollutants in the recycled water in the two golf course system, Sierra Star and Snow Creek and their potential impact on the groundwater quality. The results showed that if recycled water had been used in place of groundwater between 2002 and 2005, average additional nitrogen supply of 77 percent and 47 percent would have occurred for Sierra Star and Snow Creek, respectively, and would have infiltrated nitrogen in the same order of magnitude (440 lbs and 430 lbs of nitrogen per season at Lysimeters level for Sierra Star and Snow Creek, respectively) as that from current chemical fertilization practices. The higher removal of nitrogen in the golf course system in case of recycled water use was attributed to a higher nitrogen loss through volatilization of ammonia-nitrogen fraction, and higher turf growth in presence of more plant available nitrogen and likely assimilation within the vadose zone through the natural nitrogen cycle. Phosphorus application rates using recycled water were found to be similar to that from the current operation. Monitoring data and model results on the fate of DBPs in the percolation pond system facilitated to conclude that DBPs released from the recycled water to the golf course system would be reduced through biotransformation in vardose zone to non-detectable levels in the groundwater. Infiltrated TDS from the recycled water was estimated to be about 50 percent lower than the current golf course operation due to the lower TDS concentration in the recycled water than that contributed by current fertilization practices. Groundwater chloride concentration due to recycled water use was estimated to be about 2.5 mg/L, in the same range of 0 to 2.7 mg/L as observed now. No adverse impacts on the basin groundwater quality are expected from the use of the recycled water for the golf course irrigation.