Geoscienceshttp://hdl.handle.net/10211.3/10211.4_362024-03-28T11:52:28Z2024-03-28T11:52:28ZShallow subsurface groundwater flow paths and metal contamination in the Malakoff Diggins hydraulic gold mine pitMoore, Travishttp://hdl.handle.net/10211.3/2145842020-01-02T23:37:33Z2020-01-02T00:00:00ZShallow subsurface groundwater flow paths and metal contamination in the Malakoff Diggins hydraulic gold mine pit
Moore, Travis
Malakoff Diggins, in Nevada County, was once the largest hydraulic gold mine in California. Mine drainage still discharges mercury, sediment, and metals to Humbug Creek, degrading downstream habitat. The goals of this study were to (1) characterize the shallow groundwater levels and flow paths in the hydraulically excavated mine pit, (2) compare the distribution of nonfiltered mercury, filtered mercury, and nonfiltered methylmercury in shallow groundwater and surface water drainage from the Pit between saturated and unsaturated conditions, and (3) compare dissolved organic carbon concentrations between saturated and unsaturated conditions in shallow groundwater and surface water drainage from the Pit in water year 2016. Groundwater levels were measured in eight piezometers from November 7, 2015 to October 28, 2016. Mercury samples were collected in piezometers, a pond, and Hiller Tunnel during saturated conditions on May 4, 2016 and unsaturated conditions on July 22, 2016. Dissolved organic carbon samples were collected monthly at all locations from April 25 to October 17, 2016. During saturated and uns aturated conditions, groundwater flow was in two directions, from east to west and north to south towards Hiller Tunnel. During saturated conditions, the nonfiltered mercury concentrations in piezometer P-1, the Pond, and Hiller Tunnel outlet were higher than concentrations measured during unsaturated conditions. Methylmercury concentrations in P-1 and Hiller Tunnel outlet were higher during saturated conditions but higher in the Pond, P-6 and P-7 during unsaturated conditions. Between saturated and unsaturated conditions, the dissolved organic carbon concentrations increased in the piezometers and the Pond but decreased in Hiller Tunnel outlet. The findings presented here suggest that hydrologic condition and dissolved organic carbon concentrations affect the distribution of mercury at Malakoff Diggins.
2020-01-02T00:00:00ZHydraulic mining sedimentation in the Willow Creek Watershed, Yuba County, CA.Kelley, John C.http://hdl.handle.net/10211.3/2145772020-01-02T19:56:48Z2020-01-02T00:00:00ZHydraulic mining sedimentation in the Willow Creek Watershed, Yuba County, CA.
Kelley, John C.
Hydraulic mining is the practice of using high-pressure water to mobilize sediment. In California, historical hydraulic mining mobilized over a billion cubic yards of sediment to work Eocene placer gold deposits in hillsides above modern creek beds of the Western Sierra Nevada Metamorphic Belt. This research utilized sediment mixing ratios to investigate the storage and movement of hydraulic mining sediment (HMS) in the Willow Creek Watershed. The percentage of white quartz was used in the Bear River watershed to determine the percent of hydraulic mining sediment (HMS) in a deposit (James, 1991). Applying sediment mixing ratios to the Willow Creek Watershed, sediment deposits that contained ≥ 50% rounded white quartz pebbles in the 6-64 mm range were considered to be comprised of 100% HMS, Sediment mixing ratios of the hydraulic mining deposits were divided into populations based on their location within the watershed to determine the longitudinal and lateral movement of HMS in the Willow Creek Watershed. Hydraulic mining was shown to increase the white quartz percentage of deposits an average of 7.6% over in-situ auriferous gravels in the Willow Creek Watershed. The sediment mixing ratio varied geomorphically and decreased from mine tailing deposits in high terrace samples (n=12, μ=100%) to gravel bar samples (n=12, μ=49.3%) found in the active channel. Results from this study indicate that sediment mixing ratios can be extended throughout the Western Sierra Nevada metamorphic belt wherever historical hydraulic mining occurred to determine the current location and movement of HMS.
2020-01-02T00:00:00ZEffects of projected land use change on water resources in the California Central ValleyEsposito, Cab M.http://hdl.handle.net/10211.3/2132722019-12-16T22:44:00Z2019-09-13T00:00:00ZEffects of projected land use change on water resources in the California Central Valley
Esposito, Cab M.
With the recent California legislation, SB 1168 (Pavley), SB 1319 (Pavley), and AB 1739 (Dickinson) creating the Sustainable Groundwater Management Act (SGMA), (California Groundwater, 2015) groundwater must be managed sustainably in the future. To accomplish this, a great deal of attention is focused on how groundwater is used, how those uses may change in the future, and what impact climate change and climate variation have on groundwater resources. This research provides a first step into coupling groundwater modeling with land use projections to examine how future water requirements may vary and their corresponding impacts to groundwater and surface water resources. Land use projections from the United States Geological Survey (USGS) are incorporated into the Central Valley Hydrologic Model (CVHM) while controlling for climate. Projected land use from 2090 is compared to land use from 2010 with large shifts to urban areas and agricultural areas shifting from annual to perennial crops. The influence of projected land use change is evaluated through changes in water demand and changes in groundwater elevations. In the Sacramento Valley and Delta regions moderate climate variability is introduced to investigate how both land use and climate change could interact in these regions. This study modeled a decrease of 2 7% in Annual Agriculture, 17% increase in Perennial Agriculture, and a 10% increase in Urban areas across the entire Central Valley study area. These land use projections were examined over two different climate scenarios, an average and a slightly dry of average. In an average climate these land use projections decreased the total required water demand by 13%, with reductions of 6% in surface water demand and 25% reduction in groundwater demand. The groundwater level response in an average climate was variable across the Central Valley with small increases in the northern study area and decreases in the southern study area. When controlling for regional changes in groundwater levels, this study shows that urbanization causes the largest decline in groundwater levels and agricultural expansion into native areas causes the largest increase in groundwater levels. When a dry-of-average climate was modeled in the Sacramento Valley, land use projections caused similar responses in groundwater level changes in some areas as the average year while other areas exhibited higher land use change associated groundwater levels.
2019-09-13T00:00:00ZStructural geology of the Eastern Carrizo Badlands, north of the Coyote Mountains, Southern CaliforniaSmart, Jay W.http://hdl.handle.net/10211.3/2112112019-10-11T22:11:18Z2019-06-27T00:00:00ZStructural geology of the Eastern Carrizo Badlands, north of the Coyote Mountains, Southern California
Smart, Jay W.
The Coyote Mountains in southern California lie within an ~70-km-wide dynamic boundary between the North American and Pacific tectonic plates known as the southern San Andreas fault system. The structure and stratigraphy of the range is the result of two distinct regional episodes of deformation (Dorsey & others, 2012): (1) late Miocene to Pleistocene transtensional faulting accommodated by the West Salton detachment fault in combination with the San Andreas fault to the east, and (2) Pleistocene to Holocene dextral strike-slip transpressional deformation related to the San Andreas, Elsinore and San Jacinto faults and fault zones.
The stratigraphic sequence in the study area depicts a near-continuous depositional history of non-marine and marine sediments into the western Salton Trough between ~8.0 Ma and ~2.8 Ma due to the late Miocene to Pleistocene transtensional faulting. Additionally, evidence of extension-related deformation in the study area may be limited to two faults that show significant normal separation.
Brittle and ductile deformation of sediments in the study area is consistent with prior interpretations of uplift and inversion of the Fish Creek–Vallecito basin as a result of initiation of the Elsinore and other strike-slip faults in the western Salton Trough ~1.2 Ma (Dorsey et al, 2011). The Andradé ladder structure is a previously unmapped and unknown ~7-km-wide ladder-like fault structure similar to the Durmid ladder structure within the San Andreas fault zone documented by Janecke and others (2018). The Andradé ladder structure is consistent with a zone of distributed right-lateral shear and rotation that accommodates the right-lateral deformation between the Elsinore and Painted Gorge faults.
2019-06-27T00:00:00Z