USING TIME SERIES DATA TO EVALUATE BAROMETRIC EFFICIENCY AND THE ROLE OF EARTH TIDES IN SPRING WATER LEVELS: NACIMIENTO FAULT ZONE, NEW MEXICO

At San Ysidro, NM, numerous travertine-forming springs discharge along a major north/south trending structure, the Nacimiento fault. The springs form artesian, CO₂ charged pools that range from 10s of centimeters to meters in depth. To evaluate controls on hydrology and circulation within the fault zone, 4 springs were instrumented over a two-year period. We present the results of time series data including water level, temperature and specific conductance.

Monitoring resolution was set at 5-minute intervals, and data were downloaded bimonthly. Anomalous readings were removed and water depth was corrected for altitude and barometric pressure. Springs have depth variations from 10 cm to over 60 cm. As each spring pool varies in size, higher depth variations are not directly related to greater variations in water volume between spring pools. Water temperature tracks air temperature, and specific conductance is correlated with higher temperature and exhibits a response to precipitation events.

Barometric pressure analysis indicates barometric efficiency is close to zero, an uncommon feature in wells, but can occur in confined/semi-confined aquifers with horizontal fractures that extend great distances, suggesting fluid movement along the fault zone and a connected nature to the springs.

Spectral analysis shows water depth frequencies at 1 and 2 cycles/day, coinciding with known diurnal and semi-diurnal Earth tides, while pumping tests highlight the recharge nature of the springs, and help to refine the hydrogeologic relationship between springs. Taken together, these data provide a means to analyze subsurface properties, such as storativity and transmissivity, can be used to compare and contrast the hydrogeologic character of the springs, as well as indicating how the character of the fault changes along its axis.

Hydrologic drivers influencing water depth include local precipitation events, potential recharge driven by monsoonal precipitation in the nearby Jemez Mountains, well pumping and Earth tides. The data provide a baseline against which future variation can be compared, provide indications of the hydrogeologic character of large a fault/fracture system, and enable more accurate construction of management practices, leading to more effective resource management.