Potential Effects of a Large-Scale Housing Development and Associated Golf Course on the Edwards Aquifer in San Marcos, Texas
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A large-scale housing development, Paso Robles, is planned for construction in the southwest outskirts of San Marcos, Texas, and will result in the placement of residential homes, small commercial businesses, new roads, and a golf course adjacent to and on the sensitive Edwards Aquifer recharge zone where surface water enters the aquifer system. There is concern that the construction process and subsequent residential use of lawn chemicals such as herbicides and insecticides will adversely influence the water quality of surrounding areas. Further concern lies with the planned application of effluent, or reclaimed wastewater, from the San Marcos Wastewater Treatment Plant for irrigation of the golf course. This research sought to establish a pre-construction baseline understanding of water quality conditions in the region around the future Paso Robles development and associated golf course. To accomplish this, water samples from nine groundwater wells in the vicinity of the future development were monitored bimonthly, beginning in January 2011 and continuing through July 2012. GC-MS-MS (gas chromatography-mass spectrometry-mass spectrometry) analysis of groundwater samples detected the presence of select compounds typically found to persist in treated wastewater: triclosan (11% detection frequency), triethyl citrate (4%), and TCEP (2%). Common insecticides and herbicides detected with this method include DEET (28%), malathion (4%), permethrin (1%), and atrazine (2%). The use of passive sampling semi-permeable membranes assisted the sampling for and analysis of volatile and semi-volatile organic compounds at select wells. Detections through this method included the following: total petroleum hydrocarbons (73%), PCE (12%), undecane (10%), benzene (5%), fluorine (5%), and tridecane (2%). Although these detections occurred at extremely low levels (ppb and ppt), their presence in the Edwards Aquifer groundwater supports the need for continuous monitoring of well water samples; particularly during the construction process and upon completion of the Paso Robles housing development and associated golf course.