SECURING WATER FOR MOAB, UTAH: THE ROLE OF HESA AND DETAILED CONCEPTUAL MODEL DEVELOPMENT IN ASSESSING SURFACE WATER AND GROUNDWATER RESOURCES AFFECTING THE SPRINGS AND WELLS OF THE CITY OF MOAB, UT, AND THE IMPORTANCE OF AQUIFER TESTS TO CONFIRM FRACTURE AND FAULT ZONE CONNECTIVITY

Hydrologic and Environmental Systems Analysis (HESA) is an approach used to conceptualize and characterize relevant features of hydrologic and environmental systems, integrating relevant considerations of climate, topography, geomorphology, groundwater and surface water hydrology, geology, ecosystem structure and function, hydrochemistry/water quality, and the human activities associated with these systems into a holistic, three-dimensional dynamic conceptual site model (CSM). This watershed-based, hierarchical and iterative approach is codified in ASTM D5979 - 96(2019) Standard Guide for Conceptualization and Characterization of Ground Water Systems.

The Case History presented, the complex La Sal Mountain/Spanish Valley hydrologic systems serving as the water supply for the Moab, Utah region, demonstrates the value of a HESA derived CSM to develop a comprehensive and updated understanding of hydrogeologic and hydrologic characteristics of the interconnected surface and groundwater systems. The CSM is used to: 1) identify and characterize the major local hydrologic components, and estimate their quantitative contribution to relevant water budgets; 2) update drinking water source protection plans and the delineations of the drinking water source protection zones for the City’s springs and wells; 3) evaluate the Safe Yield of the hydrologic systems given extensive human development and climate change in this arid-land region; and 4) design, implement, and evaluate drilling and aquifer test results. The resulting updated CSM shows how the mountain/plateau hydrologic systems are structured and function with respect to subregional and local fracture and fault zones acting as French drains, as opposed to primarily matrix flow as earlier studies suggested. These fracture and fault zones control the surface water and groundwater flowpaths and interactions, recharge, and subsurface storage capacity. The resulting water budgets more accurately represent the properties of the complex hydrologic systems and provide guidance for water rights, water management, surface water and groundwater monitoring and aquifer testing, and modeling purposes and ultimately support understanding and assuring water supply sustainability for the City of Moab.