The Role of Metrology in Monitoring and Preserving the Water Quality in the Edwards Aquifer in Central Texas

摘要

To demonstrate the importance of metrology, this paper will focus on scientific work conducted at Spring Lake in San Marcos, Texas and U.S. Geological Survey (USGS) monitoring of the Edwards Aquifer. Within Spring Lake in San Marcos, Texas, there is an artesian flow of spring water from the Edwards Aquifer along the Balcones Escarpment. The average flow from San Marcos Springs is 192 ft~(3)/sec. and the springs provides most of the water for the San Marcos River. At the research and educational facility at Spring Lake, hydrogeologists monitor water quality. Seven springs in two distinct temperature zones are monitored for pH, conductivity, oxidation-reduction potential (ORP), dissolved oxygen, turbidity, and temperature. The sensors are calibrated monthly. Calibration of the sensors insures that variability between sensor readings is minimized. Accurate sensors are essential because slight differences in water chemistry exist between springs; differences are due to the nature of each spring's hydrology and the unique origin of waters within. The water quality is affected by various environmental conditions, its origin and flow path within the aquifer. Water quality data is collected, recorded, and studied. The data is used to investigate trends and differences between springs and can impact environmental policy, resource management, consumer, and recreational safety. In addition, water samples are taken from 12 springs and six surface sites every two weeks. These samples are tested for all major ions and stable isotopes of Oxygen and Hydrogen. The ratio of these isotopes gives an indication of seasonal weather changes and the evaporative state of water entering the aquifer. Scientists at the U.S. Geological Survey (USGS) and The Edwards Aquifer Authority also monitor aquifer, stream and river water levels as well as water quality throughout the Edwards Aquifer with multi-purpose sensors that include pressure transducers for level measurement. Transducers are calibrated before factory shipment using NIST~(~R) traceable standards. Other means of level measurement, such as tapes, used to measure well depth, are calibrated annually. Locally, The Edwards Aquifer Authority acts to manage, enhance, and protect the Edwards Aquifer system.