Exploring the Relationship of Groundwater Exploitation and Variability in Chemical Composition in Bristol, Cadiz, and Danby Dry Lakes, California

Abstract:

Field investigations of Bristol, Cadiz, and Danby Dry Lakes in southeastern California have shown different chemical compositions despite their proximity and similar geographic setting. These three playas are in topographically closed basins in the same extensional trough, but calcium concentrations in the three dry lakes vary from 56 g/L in Bristol Dry Lake to near 0 in Danby Dry Lake, decreasing progressively from northwest to southeast. Historical groundwater data in the basins indicate a non-saline groundwater source for at least some of these brines, probably from the alluvial fans feeding the basins. All three dry lakes have been mined for halite, gypsum, and dense brines since the early 1900s, with operations at Bristol and Cadiz Dry Lakes currently pumping brines from the shallow subsurface to the surface evaporation pools. Historical data also indicate that the elevation of the dry lakes may have changed by as much as 4.6 m over the past 100 years, raising the question of whether the long-term mining operations may have changed the hydrology of the region, and therefore influenced the flow of water between the lakes and their relative composition.

We have performed preliminary analysis of contemporary surface deformation from 2014-2020 using synthetic aperture radar small baseline (SBAS) interferometry time series methods to see if any subsidence or uplift can be detected in this area, following Zebker 2017 (DOI: 10.1109/LGRS.2017.2753580). The European Union Copernicus Sentinel-1 radar satellite has been acquiring image data over this region every 12 days since 2014, allowing a dense time series of deformation.

This region is typically quite dry but rain events and water pooling in the basins can create correlation challenges for the interferometric analysis, principally phase unwrapping errors in particular temporal pairs. Nonetheless, there is a clear subsidence signature localized around the pumping station at Bristol Dry Lake, and each of the dry lakes has distinct signatures of both subsidence and potential uplift relative to the surrounding regions, which are quite stable. Optimizing the selection of the over 7000 available interferometric pairs will lead to improved confidence in the interpretation in the basins themselves.