Res 2011-037 (2) - Laserfiche WebLink

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Water Quality of the Balcones Fault Zone Edwards Aquifer: potential effects of the Paso Robles housing development and associated golf course March 7, 2011 Abstract A 1,300-acre housing development, Paso Robles (Carma Developers), and an associated golf course are planned for construction just north of Hunter Road (FM 2439) in the southwestern outskirts of San Marcos, Texas (Figure 5). The housing development and golf course will span environmentally sensitive recharge and contributing zones of the Edwards Aquifer within the structurally complex Balcones Fault Zone in Hays County, south central Texas. Reuse water, or effluent, from the City of San Marcos Wastewater Treatment Plant will be used to irrigate the golf course. There is concern over the potential effects the construction process, residential use of pesticides and herbicides, and use of treated effluent on the golf course will have on the underlying groundwater within the Edwards Aquifer. This thesis project will monitor nine wells, located both up gradient and down gradient from the future Paso Robles development (Figure 6), that are inferred to be in hydrologic connectivity with the Edwards Aquifer. This supposition is based on dye tracing and the use of optical brighteners in previous studies (Murray, Straud, Hammond, 2007; Schindel et al., 2009). Each monitoring well will be sampled prior to construction in order to obtain baseline water quality data. Further water quality analysis will continue throughout construction. As a result, this project will compare acquired baseline data with that obtained throughout construction to assess impacts on the underlying groundwater of the Edwards Aquifer, and aid in the timely identification of potential contamination as a result of the Paso Robles development and associated golf course. In partnership with the San Marcos National Fish Hatchery and Technology Center, a systematic water quality monitoring program for their two wells, located immediately down gradient to the Paso Robles development site, will also be established and will continue upon the completion of this project. Executive Summary The Edwards Aquifer, which encompasses a total area of approximately 4,350 square miles (Figure 1), is a karst aquifer composed of faulted and fractured Cretaceous -age dolomite and limestone (Smith, Hunt, Schindel, 2005). Over an extended period of time, flowing water containing carbon dioxide can chemically dissolve carbonate rocks, such as limestone and dolomite. This creates pipe -like channels called conduits, as well as pores and fractures through which water gravitationally flows. This structuring allows the karstic Edwards Aquifer to be highly porous and permeable in nature (Abbott, 1977; Schindel et al., 2009). In an unconfined aquifer setting, or one that possesses no upper, impervious confining layer, as with some sections of the Edwards Aquifer (Figure 2); water infiltrates the surface soil layers and moves vertically downward through rocks that are only partially occupied by water. This unsaturated area is referred to as the vadose zone, and is relatively in free contact with the surface (Ford, Williams, 2007). Over time, the permeability and porosity of karst will increase, allowing for the formation of more - 1 -