Hydrogeologic Characterization Using a Shallow Seismic Reflection Survey at Fort Ord, California

Merey, Carlene; Miller, R. Drew; Ticken, Edward J.; Lewis, J. Scott

doi:10.4133/1.2922027

Cited by 1 publication

(1 citation statement)

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“…Interpretation of hydrogeologic data in this area is difficult and has resulted in conflicting interpretations of local lithology even when using data from the same boreholes (Yates et al 2005). This is likely a result of several factors including, the complex depositional nature of the subsurface geology; the highly heterogeneous nature of the subsurface, making interpretation of the continuity of layers based on well data difficult and prone to error; and the vertical and horizontal displacement of layers resulting from faults (Merey et al 1992).…”

Section: Study Areamentioning

confidence: 99%

Electrical Resistivity Imaging of Seawater Intrusion into the Monterey Bay Aquifer System

Pidlisecky¹,

Moran

Hansen

et al. 2015

Groundwater

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We use electrical resistivity tomography to obtain a 6.8-km electrical resistivity image to a depth of approximately 150 m.b.s.l. along the coast of Monterey Bay. The resulting image is used to determine the subsurface distribution of saltwater- and freshwater-saturated sediments and the geologic controls on fluid distributions in the region. Data acquisition took place over two field seasons in 2011 and 2012. To maximize our ability to image both vertical and horizontal variations in the subsurface, a combination of dipole-dipole, Wenner, Wenner-gamma, and gradient measurements were made, resulting in a large final dataset of approximately 139,000 data points. The resulting resistivity section extends to a depth of 150 m.b.s.l., and is used, in conjunction with the gamma logs from four coastal monitoring wells to identify four dominant lithologic units. From these data, we are able to infer the existence of a contiguous clay layer in the southern portion of our transect, which prevents downward migration of the saltwater observed in the upper 25 m of the subsurface to the underlying freshwater aquifer. The saltwater and brackish water in the northern portion of the transect introduce the potential for seawater intrusion into the hydraulically connected freshwater aquifer to the south, not just from the ocean, but also laterally from north to south.

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Section: Study Areamentioning

confidence: 99%