APPLICATION OF A GEOCHEMICAL FRAMEWORK FOR WATER RESOURCE MANAGEMENT IN A SEMI-ARID, KARST LANDSCAPE: SAN SOLOMON SPRINGS AND COMANCHE SPRINGS, TEXAS, USA

Effective water management requires that source areas to springs in arid and semi-arid environments be characterized well enough to assess impacts on flow from changes in recharge and groundwater withdrawals. Geochemical signatures of groundwater can be used as indicators of different components of flow to springs and can be especially useful for characterizing different sources that contribute to multi-outlet spring systems. The San Solomon and Comanche Springs systems in Trans-Pecos Texas provide examples of multi-outlet spring systems in a karstic landscape with potentially different source areas. Samples from each of the six named orifices at San Solomon Springs and three named orifices at Comanche Springs were collected in 2022 and 2023 and combined with historical data to assess the geochemical signatures of the spring systems. Results of analyses of field parameters, ions and trace elements, and multiple stable and radiogenic isotopes were combined with multivariate statistical analyses to investigate the hydraulic relationships among the individual springs and surrounding wells in the study area.

Results indicate that most samples are fed by a regional flow system that conveys submodern (i.e., Pleistocene age) waters to springs and wells in the study area. Most springs and wells have similar ionic and isotopic assemblages, although a few locations stand out. Saragosa Spring consistently exhibits modern behavior, which suggests that it is likely fed from a near-surface component. Diamond Y Spring, Euphrasia Spring, and possibly Saragosa Spring may be recharged by precipitation that has a significant component of evaporation. This recharge mechanism may also impact East Sandia and West Sandia springs but to a lesser extent. Moreover, hydrochemical signatures of local recharge derived from precipitation events are present in most samples. Most notably, significant rainfall that preceded the 2022 sample collection by 45 days appears to have impacted all of the samples collected. The 2022 response to rainfall is noticeably different than the response from 2004 in San Solomon, Giffin, Phantom Lake, and East Sandia springs. Additional samples will allow the Project Team to better constrain geochemical endmembers and mixing amongst these waters throughout the study area.