A cooperative study between the National Park Service (NPS) and the U.S. Geological Survey (USGS) characterized groundwater quality and hydrogeology in parts of Pinnacles National Park. The water-quality investigation assessed the geochemistry of springs, wells, surface water, and precipitation and analyzed geochemistry of rock formations that affect the water chemistry through water-rock interaction. The hydrogeology investigation used geophysical and groundwater level data to characterize groundwater-flow processes in the alluvial deposits of Bear Valley and the Chalone Creek watershed.
Analysis of aqueous geochemical parameters in water samples from perennial springs, water-supply wells, and surface waters was conducted for samples collected after the dry season (autumnal) and after the wet season (vernal) to assess changes in geochemistry due to changes in groundwater levels or flow resulting from precipitation. The chemistry of bulk precipitation collected during the wet season was also analyzed. Bedrock samples were analyzed for geochemical parameters to help constrain groundwater sources, flow paths, and weathering. The geochemical investigations show a correspondence between the source rock and the spring-water chemistry that can be attributed to the mineralogy of the source rock. The narrow range of strontium isotopes in water samples, sourced in geochemically and mineralogically disparate rocks, indicates that the bedrock groundwater is relatively old and has reached quasi-steady state with respect to weathering of susceptible minerals.
Groundwater-level monitoring indicated that the water table is shallow—from 0 to 10 meters (m) below land surface. In southern Bear Valley and in the Chalone Creek alluvium, water levels rose and declined by several meters over each annual cycle of this study. In northern Bear Valley, water levels rose modestly over two wet seasons but declined during a third wet season. In Bear Valley, groundwater/surface-water interaction occurs along the perennial reach of Sandy Creek. Groundwater discharges to the upstream part of the reach, becomes surface water and is partly consumed by evapotranspiration, and infiltrates farther downstream. In the Chalone Creek alluvium, runoff-generated surface-water flow in intermittent stream reaches is a major component of groundwater recharge. After the onset of significant streamflow, creek water rapidly recharges groundwater until water levels rise to nearly the creek level. Groundwater levels generally remain high throughout the wet season, then gradually decline after the creek becomes dry.
|Title||Aqueous geochemistry of waters and hydrogeology of alluvial deposits, Pinnacles National Park, California|
|Authors||Kathleen Scheiderich, Claire R. Tiedeman, Paul A. Hsieh|
|Publication Subtype||USGS Numbered Series|
|Series Title||Open-File Report|
|Record Source||USGS Publications Warehouse|
|USGS Organization||WMA - Laboratory & Analytical Services Division|
Geochemistry of rocks, precipitation, and water sources from Pinnacles National Park, California, 2016-2017
Streamflow data collected by the wading method, Pinnacles National Park, California, 2018
Passive Seismic Data Collected for the Horizontal-to-Vertical Spectral Ratio (HVSR) Method, Pinnacles National Park, California, 2018-2020
Claire R Tiedeman
Geochemistry of rocks, precipitation, and water sources from Pinnacles National Park, California, 2016-2017Ephemeral springs and other groundwater sources in Pinnacles National Park (San Benito and Monterey Counties, CA) were sample in the Spring and Fall of 2015-2017 during several field visits. Field parameters such as in-situ pH, TDS/conductivity, and temperature were assessed. GPS coordinates for all samples were taken. Comprehensive water chemistry, including major and minor elements, alkalinity,
Streamflow data collected by the wading method, Pinnacles National Park, California, 2018This dataset includes streamflow measurements collected at six sites in Pinnacles National Park during 2018. Data collection occurred at times when the streamflow did not include runoff from precipitation. The wading method was used to measure streamflow (Nolan, K.M. and Shields, R.R., 2000, Measurement of stream discharge by wading, U.S. Geological Survey Water-Resources Investigations Report 200
Passive Seismic Data Collected for the Horizontal-to-Vertical Spectral Ratio (HVSR) Method, Pinnacles National Park, California, 2018-2020This dataset contains passive seismic data collected using a three-component seismometer during 2018-2020 at Pinnacles National Park, California. The data were acquired for the purpose of estimating depth to the bedrock surface underlying alluvial deposits, using the horizontal-to-vertical spectral ratio (HVSR) technique. Data were collected along ten transects, with 3 to 14 points collected along
Claire R Tiedeman