Ground-water Quality in the Lompoc Plain, Santa Barbara County, California, 1983

U.S. Geological Survey (USGS) | June 13th, 1988

This report summarizes the results of a comprehensive study of ground-water quality in the Lompoc plain in western Santa Barbara County. Water-quality characteristics

This report summarizes the results of a comprehensive study of ground-water quality in the Lompoc plain in western Santa Barbara County. Water-quality characteristics in 1983 are described, and changes in water quality since the last comprehensive study in the early 1970's are documented. Ground water is the main source of water in the Lompoc plain. The younger alluvium is the major aquifer and consists predominantly of unconsolidated deposits of sand and gravel. The younger alluvium is as much as 180 feet thick and is divided into an upper member and a lower member throughout most of the plain. The lower member is the main water-bearing zone in the Lompoc plain. Long-term ground-water levels in most of the plain have not changed significantly since the 1940's. A seasonal water-level decline of about 15 feet in 1982 in the central part of the plain may be attributed to nearby military and agricultural pumping. Ground-water quality in the plain in 1983 tended to deteriorate from east to west. Dissolved-solids concentrations throughout the plain exceeded the U.S. Environmental Protection Agency secondary maximum contaminant level of 500 milligrams per liter for drinking water; in most of the plain, concentrations exceeded 1,000 milligrams per liter. In samples from some wells, concentrations of one or more of the following constituents sodium, chloride, nitrate, and iron exceeded primary or secondary maximum contaminant levels for drinking water. Concentrations of constituents in some samples also exceeded recommended levels for irrigation water. The predominant ions generally were calcium, magnesium, sulfate, and bicarbonate - except in the western part, where sodium and chloride were the predominant dissolved ions. From 1972 to 1983, dissolved-solids concentrations in the main water-bearing zone generally decreased in the central part of the plain but increased throughout most of the study area. The largest increases, greater than 1,000 milligrams per liter, were in the extreme western part of the plain.

Ground-Water Recharge from Small Intermittent Streams in the Western Mojave Desert, California

U.S. Geological Survey (USGS) | July 15th, 2007

Population growth has impacted ground-water resources in the western Mojave Desert, where declining water levels suggest that recharge rates have not kept pace with withd

Population growth has impacted ground-water resources in the western Mojave Desert, where declining water levels suggest that recharge rates have not kept pace with withdrawals. Recharge from the Mojave River, the largest hydrographic feature in the study area, is relatively well characterized. In contrast, recharge from numerous smaller streams that convey runoff from the bounding mountains is poorly characterized. The current study examined four representative streams to assess recharge from these intermittent sources. Hydraulic, thermal, geomorphic, chemical, and isotopic data were used to study recharge processes, from streamflow generation and infiltration to percolation through the unsaturated zone. Ground-water movement away from recharge areas was also assessed.

Ground-Water Resources of Honey Lake Valley, Lassen County, California, and Washoe County, Nevada

U.S. Geological Survey (USGS) | January 8th, 1990

Honey Lake Valley is a 2,200-square-mile, northwest-trending, topographically closed basin about 35 miles northwest of Reno, Nevada. Unconsolidated basin-fill deposits o

Honey Lake Valley is a 2,200-square-mile, northwest-trending, topographically closed basin about 35 miles northwest of Reno, Nevada. Unconsolidated basin-fill deposits on the valley floor and fractured volcanic rocks in the northern and eastern uplands are the principal aquifers. Ground water in the Nevada part of the basin is being considered as a potential source of public supply to the Reno area. This report describes the ground-water resources of the basin and the potential hydrologic effects of ground-water development in its eastern part. During an average year, about 1.1 million acre-feet of precipitation falls on the 1,700-square-mile study area within the valley, and an estimated 86,000 acre-feet enters the study area as streamflow in the Susan River and Long Valley Creek. Almost 90 percent of this water runs off, evaporates, or is transpired by plants before it can infiltrate and become ground-water recharge; this includes about 130,000 acre-feet per year that reaches Honey Lake as surface-water inflow. About 130,000 acre-feet recharges the aquifer system annually, about 40 percent by direct infiltration of precipitation over the study area and about 60 percent by infiltration of streamflow and irrigation water. Balancing this is an equal amount of ground-water discharge, of which about 65 percent evaporates from the water table or is transpired by phreatophytes, about 30 percent is withdrawn from wells, and about 5 percent leaves the basin as subsurface outflow to the east. A ground-water flow model of the eastern part of the study area, where withdrawals for public supply have been proposed, was used to evaluate components of the water budget and to estimate the long-term hydrologic effects of hypothetical increased development. Results of the evaluation indicate conditions under which a new equilibrium would be established if 15,000 acre-feet of water were withdrawn from the Fish Springs Ranch area annually. The model indicates that, as a result of such an increase in pumpage, water levels would decline more than 100 feet from present (1988) levels in the vicinity of the pumping, and as much as 40 feet at the California-Nevada State line. Evapotranspiration and subsurface outflow to the east would each be reduced by about 60 percent, but hydrologic effects would be minimal at the western boundary of the flow-model area (just east of Honey Lake). Within the modeled area, the simulation indicates that the increased withdrawals would cause the net flow of ground water eastward across the State line to increase from about 700 acre-feet per year to about 2,300 acre-feet per year.

Ground-Water Resources of Honey Lake Valley, Lassen County, California, and Washoe County, Nevada

U.S. Geological Survey (USGS) | December 15th, 1990

Honey Lake Valley is a 2,200-square-mile, northwest-trending, topographically closed basin about 35 miles northwest of Reno, Nevada. Unconsolidated basin-fill deposits on

Honey Lake Valley is a 2,200-square-mile, northwest-trending, topographically closed basin about 35 miles northwest of Reno, Nevada. Unconsolidated basin-fill deposits on the valley floor and fractured volcanic rocks in the northern and eastern uplands are the principal aquifers. Ground water in the Nevada part of the basin is being considered as a potential source of public supply to the Reno area. This report describes the ground-water resources of the basin and the potential hydrologic effects of ground-water development in its eastern part. During an average year, about 1.1 million acre-feet of precipitation falls on the 1,700-square-mile study area within the valley, and an estimated 86,000 acre-feet enters the study area as streamflow in the Susan River and Long Valley Creek. Almost 90 percent of this water runs off, evaporates, or is transpired by plants before it can infiltrate and become ground-water recharge; this includes about 130,000 acre-feet per year that reaches Honey Lake as surface-water inflow. About 130,000 acre-feet recharges the aquifer system annually, about 40 percent by direct infiltration of precipitation over the study area and about 60 percent by infiltration of streamflow and irrigation water. Balancing this is an equal amount of ground-water discharge, of which about 65 percent evaporates from the water table or is transpired by phreatophytes, about 30 percent is withdrawn from wells, and about 5 percent leaves the basin as subsurface outflow to the east. A ground-water flow model of the eastern part of the study area, where withdrawals for public supply have been proposed, was used to evaluate components of the water budget and to estimate the long-term hydrologic effects of hypothetical increased development. Results of the evaluation indicate conditions under which a new equilibrium would be established if 15,000 acre-feet of water were withdrawn from the Fish Springs Ranch area annually. The model indicates that, as a result of such an increase in pumpage, water levels would decline more than 100 feet from present (1988) levels in the vicinity of the pumping, and as much as 40 feet at the California-Nevada State line. Evapotranspiration and subsurface outflow to the east would each be reduced by about 60 percent, but hydrologic effects would be minimal at the western boundary of the flow-model area (just east of Honey Lake). Within the modeled area, the simulation indicates that the increased withdrawals would cause the net flow of ground water eastward across the State line to increase from about 700 acre-feet per year to about 2,300 acre-feet per year.

Ground-water storage depletion in Pahrump Valley, Nevada-California, 1962-1975

U.S. Geological Survey (USGS) | July 1st, 1982

Ground-Water-Level Monitoring and the Importance of Long-Term Water-Level Data

U.S. Geological Survey (USGS) | July 12th, 2001

Ground-water is among the Nation’s most precious natural resources. Measurements of water levels in wells provide the most fundamental indicator of the status of this r

Ground-water is among the Nation’s most precious natural resources. Measurements of water levels in wells provide the most fundamental indicator of the status of this resource and are critical to meaningful evaluations of the quantity and quality of ground water and its interaction with surface water. Water-level measurements are made by many Federal, State, and local agencies. It is the intent of this report to high-light the importance of measurements of ground-water levels and to foster a more comprehensive and systematic approach to the long-term collection of these essential data. Through such mutual efforts, the Nation will be better positioned in coming decades to make wise use of its extensive ground-water resources. - Robert M. Hirsch, Associate Director for Water

Groundwater and Stream Interaction in California's Central Valley: Insights for Sustainable Groundwater Management

Nature Conservancy | June 16th, 2016

Sustainable water management requires ensuring ecosystem water needs are met in balance with water needs for people. The Nature Conservancy (TNC) is working across Califo

Sustainable water management requires ensuring ecosystem water needs are met in balance with water needs for people. The Nature Conservancy (TNC) is working across California to demonstrate how to achieve this balance in the context of integrated water management programs. Sustainable water management must also recognize that surface water and groundwater resources are interconnected and that proper management of these resources includes understanding this interaction and managing the resources accordingly. Management of groundwater and surface water systems in an integrated manner is impeded by California water law and policy, which has separate rules and regulations for managing groundwater and surface water resources. The Central Valley of California is the hub of the state’s water supply system. An extensive network of dams and canals supplies surface water to users within the Central Valley as well as to the San Francisco Bay Area, the Central Coast, and Southern California. Analysis of information collected in this study reveals that just within the Central Valley, agricultural and urban sectors use an average of 13 million acre-feet (MAF) of surface water and over 8 MAF of groundwater per year. Approximately 2 MAF of water is exported annually to areas outside the Central Valley. Because the availability of surface water supplies varies significantly from year to year, groundwater use also varies considerably on annual basis. In an average year, groundwater meets about 40% of the state’s water demand and up to 60% or more during droughts, when groundwater provides a water supply buffer against economic and environmental harm from water scarcity (DWR, 2014). In some areas, groundwater provides 100% of the supply, even in wetter years, and then is heavily pumped during drought. In other locations, where surface water supplies are reasonably abundant, groundwater use may be relatively light during wetter years, but more heavily pumped during drier years when surface water supplies are cut back. Accordingly, the impact of groundwater use is much more evident during dry years, and especially in drought conditions. A case in point is the drought condition of 2013-15. This drought is exerting significant stress on the state’s water supply. The surface water deliveries have been reduced dramatically, to near zero in many regions; therefore, agricultural and municipal water users in the Central Valley and other parts of the state that normally rely on surface water for much of their supplies, are now greatly increasing their use of groundwater to meet their needs. A 2014 UC Davis report indicates that expected increase in Central Valley groundwater pumping would be in the range of 20% to 25%, during the 2014 irrigation season. To the authors’ knowledge, there are no reports of actual estimates of increase in groundwater use for the recent drought conditions. The long-term increase in groundwater pumping and especially recent drought related increases in pumping would translate into significantly more adverse impacts on the surface water and stream systems, as well as groundwater dependent ecosystems. In addition, this increase in groundwater pumping could potentially result in more land subsidence throughout the valley. The drought has also affected the irrigated lands under cultivation. A November 2014 DWR publication “Public Update for Drought Response” 3 reported that based on NASA satellite imagery, approximately 700,000 acres of land were estimated idled between 2011 and 2014. Majority of these acreages idled are reported to be due to the drought conditions, although, some were also due to normal agronomic practices, crop markets, and other reasons. This report provides the results of a number of analyses and evaluations of Central Valley hydrologic conditions using the California Central Valley Groundwater-Surface Water Simulation Model (C2VSim). The study examines important hydrologic and operational characteristics and behaviors of the California’s Central Valley water system during the historical development in the Valley. In addition, the study presents results of model simulations conducted to assess potential impacts of several water management scenarios. The results of this study contribute significantly to the understanding of how management of groundwater and surface water are interrelated and will inform the development of more effective integrated water management in the Central Valley and throughout California. The interaction between groundwater and surface water resources has been evaluated and illustrated by many researchers. As early as 1941, Theis (1941) documented the hydraulic connection between stream and aquifer systems and quantitatively described the general behavior of stream-groundwater systems. Many others, including Glover & Balmer (1954) and Hantush (1965) built on Theis’ work, which demonstrated and confirmed the basic principles of hydraulic connection between stream and aquifer systems. In recent years, significant work has been conducted regarding regional impacts of groundwater pumping and operation on regional surface water systems. For example, the recent USGS study (Barlow & Leake, 2012) presents original findings of the stream-aquifer interaction in the context of sustainable groundwater management. In an effort to quantify the interaction between the groundwater and the surface water system, DWR’s C2VSim model was employed in this study. The C2VSim model was originally developed in 1990 for DWR, U. S. Bureau of Reclamation (USBR), and California State Water Resources Control Board (SWRCB) as the Central Valley Groundwater and Surface water Model (CVGSM) (James M. Montgomery Consulting Engineers, 1990a). Subsequently, the model was enhanced through numerous key applications, including the Central Valley Project Improvement Act – Programmatic Environmental Impact Statement (CVPIA-PEIS). In 2005, the CVGSM model was upgraded to the newly developed Integrated Water Flow Model (IWFM) platform, and was renamed the C2VSim model. The detailed features of the model are described and presented in Section 2 of this report. The C2VSim model is a leading Central Valley-wide integrated hydrologic model adopted by DWR and many other regional and state-wide agencies, as well as non-governmental organizations (NGOs) to evaluate various water management scenarios throughout the Valley. This report is organized in six sections: Section 1: Provides the background information and lays out the goals and objectives of this study. Section 2: Provides information on the status of C2VSim model, refinements made during this study, and assumptions on the modeling analysis. Section 3: Discusses simulation of the historical hydrologic conditions in the Central Valley. Section 4: Provides the assumptions and results of the existing baseline conditions, assuming that no changes to the facilities and their operations, as well as water management actions, take place over the course of a predetermined hydrologic condition. Section 5: Provides a description of three water management scenarios that may have major impacts on the future of surface water and groundwater interaction in Central Valley. Results of simulation of these management scenarios are presented and discussed in detail. Section 6: Provides conclusions from this study and a list of recommendations for future work.

Groundwater Characterization and Effects of Pumping in the Death Valley Regional Groundwater Flow System, Nevada and California, with Special Reference to Devils Hole

U.S. Geological Survey (USGS) | March 5th, 2020

Groundwater flow and development were characterized in four groundwater basins of the Death Valley regional flow system in Nevada and California with calibrated, groundwa

Groundwater flow and development were characterized in four groundwater basins of the Death Valley regional flow system in Nevada and California with calibrated, groundwater-flow models. Natural groundwater discharges in the Furnace Creek, Lower Amargosa, and Saratoga Spring areas were defined and distributed consistently with a revised hydrogeologic framework. This simplified hydrogeologic framework was limited to four hydraulically unique, hydrogeologic units: (1) basin fill; (2) carbonate rocks; (3) volcanic rocks; and (4) low-permeability granitic and siliciclastic rocks. Hydrogeologic units and division of carbonate and volcanic rocks between shallow and deep were supported by results from 271 aquifer tests and specific-capacity estimates. Greater than 90 percent of field-estimated transmissivity occurred within 1,600 feet (ft) of the water table. Pumping in the study area from 1960 to 2010 averaged 46,000 acre-feet per year (acre-ft/yr), which is 80 percent of the predevelopment discharge. The central Amargosa Desert and Pahrump Valley were the two primary pumping centers and measurably affected water levels across 900 square miles in 2018. Water levels in Devils Hole were a special focus because endangered Devils Hole pupfish (Cyprinodon diabolis) are affected by water-level declines. Pumping 42,100 acre-ft by Cappaert Enterprises, formerly Spring Meadows, Inc., caused a 2.3-ft water-level decline in Devils Hole, which temporarily reduced habitat of Devils Hole pupfish by 85 percent in 1972. If no pumping occurred, water levels in Devils Hole would have risen naturally about 1 ft between 1973 and 2018 from temporal variations in recharge. The 2.6-ft range of measured water-level changes in Devils Hole was simulated with a root-mean-square error of 0.2 ft during the 70-year period of record. Simulated water-level declines from pumping totaled 1.4 ft in 2018, with 25 and 34 percent attributed to pumping by Cappaert Enterprises and the central Amargosa Desert, respectively. Water levels in Devils Hole will decline at rates of 0.1–0.2 ft per decade if pumping from Ash Meadows groundwater basin and the central Amargosa Desert continue at current rates. Effects of future natural water-level fluctuations remain unknown. Ash Meadows and Alkali Flat–Furnace Creek Ranch groundwater basins are hydraulically connected near well AD-4, about 5 miles south of the town of Amargosa Valley, Nevada. About 40 percent of the discharge from the Furnace Creek area is recharged in the Ash Meadows groundwater basin. Basin fill in the central Amargosa Desert hydraulically connects carbonate rocks east of well AD-4 with saturated carbonate rocks in the Funeral Range. About 7 percent of the 960,000 acre-ft pumped from Ash Meadows and Alkali Flat–Furnace Creek Ranch groundwater basins prior to 2019 was captured discharge from springs and phreatophytes. Greater than 40 percent of the 2,080,000 acre-ft pumped from Pahrump Valley between 1910 and 2019 was capture that primarily discharged from Bennetts and Manse Springs. Simulated advective-flow distances and velocities from underground nuclear tests are within the range of advective transport calculations from tritium data and previous radionuclide transport investigations. Boundary conditions and flow rates from the regional model in this study are plausible for local-scale flow and radionuclide transport models. Simulated 165-year groundwater-flow paths do not extend into pumping areas and effects of regional pumping on advective transport are negligible.

Groundwater Contributions of Flow, Nitrate, and Dissolved Organic Carbon to the Lower San Joaquin River, California, 2006–08

U.S. Geological Survey (USGS) | October 8th, 2013

The influence of groundwater on surface-water quality in the San Joaquin River, California, was examined for a 59-mile reach from the confluence with Salt Slough to Verna

The influence of groundwater on surface-water quality in the San Joaquin River, California, was examined for a 59-mile reach from the confluence with Salt Slough to Vernalis. The primary objective of this study was to quantify the rate of groundwater discharged to the lower San Joaquin River and the contribution of nitrate and dissolved organic carbon concentrations to the river. Multiple lines of evidence from four independent approaches were used to characterize groundwater contributions of nitrogen and dissolved organic carbon. Monitoring wells (in-stream and bank wells), streambed synoptic surveys (stream water and shallow groundwater), longitudinal profile surveys by boat (continuous water-quality parameters in the stream), and modeling (MODFLOW and VS2DH) provided a combination of temporal, spatial, quantitative, and qualitative evidence of groundwater contributions to the river and the associated quality. Monitoring wells in nested clusters in the streambed (in-stream wells) and on both banks (bank wells) along the river were monitored monthly from September 2006 to January 2009. Nitrate concentrations in the bank wells ranged from less than detection—that is, less than 0.01 milligrams per liter (mg/L) as nitrogen (N)—to approximately 13 mg/L as N. Nitrate was not detected at 17 of 26 monitoring wells during the study period. Dissolved organic carbon concentrations among monitoring wells were highly variable, but they generally ranged from 1 to 4 mg/L. In a previous study, 14 bank wells were sampled once in 1988 following their original installation. With few exceptions, specific conductivity and nitrate concentrations measured in this study were virtually identical to those measured 20 years ago. Streambed synoptic measurements were made by using a temporarily installed drive-point piezometer at 113 distinct transects across the stream during 4 sampling events. Nitrate concentrations exceeded the detection limit of 0.01 mg/L as N in 5 percent of groundwater samples collected from the in-stream wells as part of the synoptic surveys. Only 7 of the 113 cross-sectional transects had nitrate concentrations greater than 1 mg/L as N. In contrast, surface waters in the San Joaquin River tended to have nitrate concentrations in the 1–3 mg/L as N range. A zone of lower oxygen (less than 2 mg/L) in the streambed could limit nitrate contributions from regional groundwater flow because nitrate can be converted to nitrogen gas within this zone. Appreciable concentrations of ammonium (average concentration was 1.92 mg/L as N, and 95th percentile was 10.34 mg/L as N) in the shallow groundwater, believed to originate from anoxic mineralization of streambed sediments, could contribute nitrogen to the overlying stream as nitrate following in-stream nitrification, however. Dissolved organic carbon concentrations were highly variable in the shallow groundwater below the river (1 to 6 ft below streambed) and generally ranged between 1 and 5 mg/L, but had maximum concentrations in the 15–25 mg/L range. The longitudinal profile surveys were not particularly useful in identifying groundwater discharge areas. However, the longitudinal approach described in this report was useful as a baseline survey of measured water-quality parameters and for identifying tributary inflows that affect surface-water concentrations of nitrate. Results of the calibrated MODFLOW model indicated that the simulated groundwater discharge rate was approximately 1.0 cubic foot per second per mile (cfs/mi), and the predominant horizontal groundwater flow direction between the deep bank wells was westward beneath the river. The modeled (VS2DH) flux values (river gain versus river loss) were calculated for the irrigation and non-irrigation season, and these fluxes were an order of magnitude less than those from MODFLOW. During the irrigation season, the average river gain was 0.11 cfs/mi, and the average river loss was ?0.05 cfs/mi. During the non-irrigation season, the average river gain was 0.10 cfs/mi, and the average river loss was 0.08 cfs/mi.

Groundwater deeper than 500 m contributes less than 0.1% of global river discharge

Nature Portfolio (Springer Nature) | February 23rd, 2023

Groundwater is one of the largest reservoirs of water on Earth but has relatively small fluxes compared to its volume. This behavior is exaggerated at depths below 500 

Groundwater is one of the largest reservoirs of water on Earth but has relatively small fluxes compared to its volume. This behavior is exaggerated at depths below 500 m, where the majority of groundwater exists and where residence times of millions to even a billion years have been documented. However, the extent of interactions between deep groundwater (>500 m) and the rest of the terrestrial water cycle at a global scale are unclear because of challenges in detecting their contributions to streamflow. Here, we use a chloride mass balance approach to quantify the contribution of deep groundwater to global streamflow. Deep groundwater likely contributes