Assessing hydrogeologic controls on dynamic groundwater storage using long-term instrumental records of water table levels

This study analyzes a long-term regional compilation of water table response to climate variability based on 124 long-term groundwater wells distributed across New England, USA, screened in a variety of geologic materials. The New England region of the USA is located in a humid-temperature climate underlain by low-storage-fractured metamorphic and crystalline bedrock dissected by north–south trending valleys filled with glacial and post-glacial valley fill sediments. Uplands are covered by thin glacial till that comprises more than 60% of the total area. Annual and multi-annual responses of the water table to climate variability are assessed to understand how local hydraulic properties and hydrogeologic setting (located in recharge/discharge region) of the aquifer influence the hydrologic sensitivity of the aquifer system to climate variability. This study documents that upland aquifer systems dominated by thin deposits of surface till comprise ~70% of the active and dynamic storage of the region. Total aquifer storage changes of +5 to −7 km³ occur over the region during the study interval. The storage response is dominated by thin and low permeability surficial till aquifer that fills and drains on a multi-annual basis and serves as the main mechanism to deliver water to valley fill aquifers and underlying bedrock aquifers. Whereas the till aquifer system is traditionally neglected as an important storage reservoir, this study highlights the importance of a process-based understanding of how different landscape hydrogeologic units contribute to the overall hydrologic response of a region.