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Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California By

U.S. Geological Survey (USGS) | January 3rd, 2003

Summary

Historical ground-water development of the Central and West Coast Basins in Los Angeles County, California through the first half of the 20th century caused large water-l

Historical ground-water development of the Central and West Coast Basins in Los Angeles County, California through the first half of the 20th century caused large water-level declines and induced seawater intrusion. Because of this, the basins were adjudicated and numerous groundwater management activities were implemented, including increased water spreading, construction of injection barriers, increased delivery of imported water, and increased use of reclaimed water. In order to improve the scientific basis for these water management activities, an extensive data collection program was undertaken, geohydrological and geochemical analyses were conducted, and ground-water flow simulation and optimization models were developed. In this project, extensive hydraulic, geologic, and chemical data were collected from new multiple-well monitoring sites. On the basis of these data and data compiled and collected from existing wells, the regional geohydrologic framework was characterized. For the purposes of modeling, the three-dimensional aquifer system was divided into four aquifer systems—the Recent, Lakewood, Upper San Pedro, and Lower San Pedro aquifer systems. Most pumpage in the two basins is from the Upper San Pedro aquifer system. Assessment of the three-dimensional geochemical data provides insight into the sources of recharge and the movement and age of ground water in the study area. Major-ion data indicate the chemical character of water containing less than 500 mg/L dissolved solids generally grades from calcium-bicarbonate/sulfate to sodium bicarbonate. Sodium-chloride water, high in dissolved solids, is present in wells near the coast. Stable isotopes of oxygen and hydrogen provide information on sources of recharge to the basin, including imported water and water originating in the San Fernando Valley, San Gabriel Valley, and the coastal plain and surrounding hills. Tritium and carbon-14 data provide information on relative ground-water ages. Water with abundant tritium (greater than 8 tritium units) is found in and downgradient from the Montebello Forebay and near the seawater barrier projects, indicating recent recharge. Water with less than measurable tritium is present in, and downgradient from, the Los Angeles Forebay and in most wells in the West Coast Basin. Water from several deep wells was analyzed for carbon-14. Uncorrected estimates of age for these samples range from 600 to more than 20,000 years before present. Chemical and isotopic data are combined to evaluate changes in chemical character along flow paths emanating from the Montebello and Los Angeles Forebays.

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Geohydrology, Simulation of Regional Groundwater Flow, and Assessment of Water-Management Strategies, Twentynine Palms Area, California

U.S. Geological Survey (USGS) | June 28th, 2011

Summary

The Marine Corps Air Ground Combat Center (MCAGCC) Twentynine Palms, California, overlies the Surprise Spring, Deadman, Mesquite, and Mainside subbasins of the Morongo gr

The Marine Corps Air Ground Combat Center (MCAGCC) Twentynine Palms, California, overlies the Surprise Spring, Deadman, Mesquite, and Mainside subbasins of the Morongo groundwater basin in the southern Mojave Desert. Historically, the MCAGCC has relied on groundwater pumped from the Surprise Spring subbasin to provide all of its potable water supply. Groundwater pumpage in the Surprise Spring subbasin has caused groundwater levels in the subbasin to decline by as much as 190 feet (ft) from 1953 through 2007. Groundwater from the other subbasins contains relatively high concentrations of fluoride, arsenic, and (or) dissolved solids, making it unsuitable for potable uses without treatment. The potable groundwater supply in Surprise Spring subbasin is diminishing because of pumping-induced overdraft and because of more restrictive Federal drinking-water standards on arsenic concentrations. The U.S. Geological Survey, in cooperation with the MCAGCC, completed this study to better understand groundwater resources in the area and to help establish a long-term strategy for regional water-resource development. The Surprise Spring, Deadman, Mesquite, and Mainside subbasins are filled with sedimentary deposits of Tertiary age, alluvial fan deposits of Quaternary-Tertiary age, and younger alluvial and playa deposits of Quaternary age. Combined, this sedimentary sequence reaches a maximum thickness of more than 16,000 ft in the Deadman and Mesquite subbasins. The sedimentary deposits of Tertiary age yield a small amount of water to wells, and this water commonly contains high concentrations of fluoride, arsenic, and dissolved solids. The alluvial fan deposits form the principal water-bearing unit in the study area and have a combined thickness of 250 to more than 1,000 ft. The younger alluvial and playa deposits are unsaturated throughout most of the study area. Lithologic and downhole geophysical logs were used to divide the Quaternary/ Tertiary alluvial fan deposits into two aquifers (referred to as the upper and the middle aquifers) and the Tertiary sedimentary deposits into a single aquifer (referred to as the lower aquifer). In general, wells perforated in the upper aquifer yield more water than wells perforated in the middle and lower aquifers. The study area is dominated by extensive faulting and moderate to intense folding that has displaced or deformed the pre-Tertiary basement complex as well as the overlying Tertiary and Quaternary deposits. Many of these faults act as barriers to the lateral movement of groundwater flow and form many of the boundaries of the groundwater subbasins. The principal recharge to the study area is groundwater underflow across the western and southern boundaries that originates as runoff in the surrounding mountains. Groundwater discharges naturally from the study area as spring flow, as groundwater underflow to downstream basins, and as water vapor to the atmosphere by transpiration of phreatophytes and direct evaporation from moist soil. The annual volume of water that naturally recharged to or discharged from the groundwater flow system in the study area during predevelopment conditions was estimated to be 1,010 acre-feet per year (acre-ft/yr). About 90 percent of this recharge originated as runoff from the Little San Bernardino and the Pinto Mountains to the south, and the remainder originated as runoff from the San Bernardino Mountains to the west. Evapotranspiration by phreatophytes near Mesquite Lake (dry) was the primary form of predevelopment groundwater discharge. From 1953 through 2007, approximately 139,400 acre-feet (acre-ft) of groundwater was pumped by the MCAGCC from the Surprise Spring subbasin. A regional-scale numerical groundwater flow model was developed using MODFLOW–2000 for the Surprise Spring, Deadman, Mesquite, and Mainside subbasins. The aquifer system was simulated by using three model layers representing the upper, middle, and lower aquifers. Measured groundwater levels for predevelopment conditions (before 1953) and for the period 1953 through 2007 were used to calibrate the groundwater- flow model. The simulated steady-state (predevelopment) recharge was about 980 acre-ft/yr; about 90 percent of the recharge was in the Mesquite subbasin. Most of the simulated steady-state discharge occurred as evapotranspiration at the Mesquite Lake (dry). A total of about 145,450 acre-ft of groundwater was simulated as being pumped from the model domain during the transient simulation period (1953–2007); about 139,400 acre-ft of the total was extracted from the Surprise Spring subbasin. The transient simulation indicates that almost all of the groundwater pumped in the Surprise Spring subbasin comes from groundwater storage, which is consistent with the measured long-term declines in groundwater levels. The calibrated groundwater model was used to evaluate the potential effects on water levels and aquifer conditions in the Surprise Spring, Deadman, Mesquite, and Mainside subbasins for water-management strategies being considered by the MCAGCC to meet the projected water demand at the base for 2008–2017. One of the main objectives of the water-management strategies is to reduce pumpage from the Surprise Spring subbasin. Reducing groundwater pumpage in the Surprise Spring subbasin by about 38 percent (about 1,345 acre-ft/yr) substantially decreased or reversed simulated hydraulic-head declines in the subbasin. Redistributing about 15 percent of the 2007 groundwater pumpage (about 550 acre-ft/yr) from the Surprise Spring to the Mainside subbasin resulted in more than 60 ft of simulated declines in hydraulic head in the Mainside subbasin by 2017; however, redistributing about 22 percent of the 2007 pumpage (about 800 acre-ft/yr) from the Surprise Spring subbasin to the Deadman subbasin resulted in 5–10 ft of simulated hydraulic-head decline in the Deadman subbasin. The water-management scenarios simulated for this study demonstrate how the calibrated regional model can be utilized to evaluate the hydrologic effects of a water-management strategy.

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Geohydrology, Water Quality, and Estimation of Ground-Water Recharge In San Francisco, California, 1987-92

U.S. Geological Survey (USGS) | January 14th, 1993

Summary

The city of San Francisco is considering further development of local ground-water resources as a supplemental source of water for potable or non-potable use. By the y

The city of San Francisco is considering further development of local ground-water resources as a supplemental source of water for potable or non-potable use. By the year 2010, further water demand is projected to exceed the delivery capacity of the existing supply system, from which San Francisco draws most of its water. The existing system is fed by surfacewater sources; thus, supplies are susceptible to drought conditions and damage to conveyance lines by earthquakes. The primary purpose of this study is to describe local geohydrology and water quality, and to estimate ground-water recharge in the area of the city of San Francisco. Seven ground-water basins were identified in San Francisco on the basis of geologic and geophysical data. Basins on the east side of the city are relatively thin and contain a greater percentage of fine-grained sediments than those on the west side. The relatively small capacity of the basins and greater potential for contamination from sewer sources may limit the potential for ground-water development on the east side. Basins on the west side of the city have a relatively large capacity and low density sewer network. Water-level data indicate that the southern part of the largest basin on the west side of the city (Westside basin) probably cannot accommodate additional ground-water development without adversely affecting water levels and water quality in Lake Merced; however, the remainder of the basin, which is largely undeveloped, could be developed further. A hydrologic routing model was developed for estimating ground-water recharge throughout San Francisco. The model takes into account climatic factors, land and water use, irrigation, leakage from underground pipes, rainfall runoff, evapotranspiration, and other factors associated with an urban environment. Results indicate that areal recharge rates for water years 1987-88 for the seven ground-water basins range from 0.32 to 0.78 foot per year. Recharge for the Westside basin was estimated at 0.51 foot per year. Average annual ground-water recharge represents the maximum annual long-term yield of the basin. Attainable yield may be less than the volume of ground-water recharge because interception of all discharge from the basin may not be feasible without inducing seawater intrusion or causing other undesirable effects.

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Geologic Setting, Geohydrology, and Ground-Water Quality near the Helendale Fault in the Mojave River Basin, San Bernardino County, California

U.S. Geological Survey (USGS) | July 15th, 2003

Summary

The proximity of the Moja ve River groundwater basin to the highly urbanized Los Angeles region has resulted in rapid population growth and, consequently, an increase in

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Geology and Ground Water Features of the Butte Valley Region Siskiyou County California

U.S. Geological Survey (USGS) | January 14th, 1960

Summary

The Butte Valley region includes an area of about 600 square miles, between long 121°37' and 122°10' W. and lat 41°38' and 42° N., in northern Siskiyou County, Cali

The Butte Valley region includes an area of about 600 square miles, between long 121°37' and 122°10' W. and lat 41°38' and 42° N., in northern Siskiyou County, Calif. U.S. Highway 97, connecting Weed with Klamath Falls, traverses the region in a northeasterly direction, and the Southern Pacific railroad serves several small farming communities in Butte Valley. The region is near the west edge of the Modoc plateau. It includes along its western border a part of the Cascade Range, Butte and Red Rock Valleys, the Oklahoma district, and a prominent northwestward-trending fault block (the Mahogany Mountain ridge) which separates Butte Valley fro-n the Oklahoma district and the Lower Klamath Lake marshland. Geologic units have been divided into two groups: Volcanic rocks which range in age from Eocene to Recent; and sedimentary rocks which range in age from Pliocene to Recent. From oldest to youngest the volcanic rocks include: (a) Predominantly andesitic lavas and pyroclastic rocks comprising the volcanic rocks of the "Western Cascades"; (b) older volcanic rocks of the "High Cascades"; (c) basaltic flows and pyroclastic rocks east of the Cascade Rang; and (d) younger volcanic rocks of the "High Cascades." Volcanic rocks of the "Western Cascades" are the oldest rocks in the region. They range in age from late Eocene to late Miocene. These rocks are chiefly pyroxene andesite, and andesitic tuff-breccia, but include lesser amounts of basalt, rhyolite, and associated pyroclastic rocks. In most places they are badly decomposed and less permeable than the younger volcanic rocks. They are best exposed in the Klamath River canyon, where the prevailing dips are to the east and northeast. The angle of dip diminishes in these directions from about 15° near the base of the series to nearly zero where the rocks disappear beneath a younger series of volcanic rocks designated on plate 1 as the older volcanic rocks of the "High Cascades." The volcanic rocks of the "Western Cascades" are at least 12,000 feet thick. The older volcanic rocks of the "High Cascades," which UE conformably overlie the volcanic rocks of the "Western Cascades," are Pliocene and Pleistocene (?) in age. They consist chiefly of basalt and basaltic andesite that spread out in successive sheets from a chain of northward-trendinr shield volcanoes built along the crest of the Cascade Range. Here the topography is almost wholly constructional, and even the oldest cones retain much of their original shape. East of the Cascade Range several large dome-shaped lava cones and most of the northwestward-trending fault block called Mahogany. Mountain ridge are composed of volcanic rocks of similar lithology. In most places the older volcanic rocks of the "High Cascades" are highly fractured and moderately permeable; they serve as a large intake area and groundwater reservoir. East of the Cascade Range, basalt of Pleistocene and Recent age issued from vents and fissures and spread out over alluvial deposits and lava sediments in the southern parts of Butte and Red Rock Valleys and the Lover Klamath Lake marshland. One of these flows the Butte Valley basalt forms the most productive water-bearing formation in the region. In the southwestern part of Butte Valley, where it is overlain by about 20 to 60 feet; of alluvial materials and lake deposits, this basaltic flow is an excellent aquifer. Yields of more than 100 gpm (gallons per minute) for each foot of drawdown are common and yields of 1,000 gpm for each foot of drawdown have been recorded. Late Pleistocene and Recent lava flows and cinder cones in the Cascade Range and extensive basaltic extrusions near Sharp Mountain are important chiefly as recharge (intake) areas for ground water. Sedimentary deposits range in age from Pliocene to Recent. The oldest of these deposits is a massive fresh-water diatomite which underlies a large part of the Oklahoma district. The diatomite is impermeable, but wells penetrating interbedded sand or cindery lapilli lenses in the diatomite may yield moderate quantities of water. Glacial moraines and fluvioglacial outwash deposits of late Pleistocene age occur near the mouth of Butte Creek canyon. These deposits are unstratified or poorly sorted and commonly are only slightly permeable. Semi-consolidated lake deposits, ranging in age from Pleistocene to Recent, underlie most of the Butte Valley plain. West of U.S. Highway 97 these deposits are composed principally of impermeable layers of clay, diatomaceous clay, and volcanic ash. However, east of U.S. Highway 97, and especially near the eastern border of the valley, the lake deposits contain a larger percentage of sand, and permeabilities range from about 50 to 230 gpd per square foot as determined from tests made in 3 pumped wells. Alluvial-fan deposits on the west side of Butte Valley range from Pleistocene to Recent in age. They are composed of poorly sorted rock debris derived from the Cascade Range and are only slightly permeable. Areas mapped as alluvium include thin beds of gravel, sand, dry, and peat covering older lake deposits in Butte Valley and the area around Lower Klamath Lake. They include also small playa deposits, poorly sorted alluvium collected in broad, shallow basins and depressions, and alluvluir in present intermittent stream channels. In most places alluvium forms a thin cover resting on lava flows or lake deposits. In general the alluviuir is slightly permeable and of little hydrologic importance except in the southwestern part of Butte Valley, where it consists of sand and gravel, ranging in thickness from 20 to 60 feet and rests on the Butte Valley basalt. In this area the alluvium probably yields moderate quantities of water to wells. Elsewhere the alluvium is largely above the saturated zone and is important chiefly because of its ability to absorb precipitation and surface runoff which percolate through it into underlying rocks. Linear wedge-shaped talus strips, formed at the foot of precipitous fault scarps, are partly concealed beneath and probably interfinger with alluvium and lake deposits. The blocky talus debris is very permeable and, where saturated, yields water readily to wells. East of the Cascade Range, block faulting is the dominant structural feature. The faults are normal and displacement is almost wholly vertical. Vertical displacements range from a few feet along minor faults to perhaps several thousand feet along major faults; there are no appreciable horizontal displacements. Butte Valley is a complexly downfaulted basin nearly surrounded by well-preserved fault scarps of late Pleistocene and Recent age. Groundwater moves eastward and northeastward across the valley into the buried talus and volcanic rocks that compose the Mahogany Mountain ridge, and may flow through that ridge to supply recharge to the area to the east. Th« direction of water movement in Red Rock Valley and in the Oklahoma district was not determined. Records of water-level fluctuations in observation wells show that water levels recover each winter, and during the period 1951-54 there was little overall change in the height of yearly recovery. Ground-water recharge in the southern part of the region occurs mainly by seepage loss from perennial spring-fed streams and unlined canals along the western margin of Butte Valley, by seepage loss from small spring-fed streams that discharge onto alluvial fans, and along the north, west, and south sides of the valley by lateral movement from the volcanic rocks. In irrigated tracts throughout the area some recharge probably occurs by deep percolation of irrigation water. Ground water is discharged by natural means and by pumping. In Butte Valley about 21,000 acre-feet of ground water was used for irrigation in 1953. In Red Rock Valley pumping of ground water for irrigation purposes was negligible. In the Oklahoma district ground water for irrigation and domestic requirements is supplied by springs and flowing and pumped wells. The quality of most of the ground water in the region is satisfactory for most uses, but in the east-central part of Butte Valley some wells yield water containing high percentages of sodium, probably derived from buried playa deposits. The chemical quality of the surface water is such that it can be used for most purposes. However, analyses of water from Meiss Lake show high concentrations of dissolved solids, ranging from 473 to 1,380 ppm, and high percentages of sodium, ranging from 75 to 91. Here the salts have been concentrated by evaporation of the lake water.

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Geology and Ground-Water Features of Shasta Valley, Siskiyou County California

U.S. Geological Survey (USGS) | January 15th, 1959

Summary

Shasta Valley is in the central part of Siskiyou County, Calif., and about 12 miles south of the Oregon border. It lies between the Klamath Mountains on the west and th

Shasta Valley is in the central part of Siskiyou County, Calif., and about 12 miles south of the Oregon border. It lies between the Klamath Mountains on the west and the Cascade Range 011 the east. The valley has an area of about 250 square miles; the north-south length is about 30 miles and the maximum width is about 15 miles. The average precipitation from July 1 to June 30 at Yreka and Montague is about 17 and 12 inches, respectively, and the average annual temperature at Yreka is 51.5°F. The area has a population of about 12,000, most of whom are employed in farming, cattle raising, and lumbering. The farm income is derived chiefly from livestock, principally beef cattle, hogs, and sheep. Alfalfa, wheat, barley, oats, and rye are the main crops grown in the valley. The Klamath Mountains are underlain by metamorphic and sedimentary rocks of Paleozoic age and by intrusive rocks of Mesozoic age that form the basement complex. Near Yreka the Chico formation of Late Cretaceous age, which is composed of shale, sandstone, and some conglomerate, overlies the older rocks with profound unconformity. The Chico formation in turn is overlain disconformably by the Umpqua formation of Eocene age, which consists mainly of black shale. These rocks are covered by a thin veneer of older alluvium which floors much of the northern part of the valley. Volcanic rocks make up much of the valley floor from Montague southward to Edgewood. The southeastern, flatter part of the valley is occupied by the Plutos Cave basalt, which is a relatively large single flow erupted from the northeast flank of Mount Shasta within the last few thousand years. The western half of the valley floor is occupied largely by the older volcanic rocks of the western Cascades, which range in age from Eocene to Miocene and which have been eroded into hillocks that range in height from a few feet to as much as 300 feet. Between these hillocks lie many small ponds and marshes and the alluvial flats formed by slow, winding streams. The valley is drained principally by the Shasta River and Parks Creek, which rise in the Klamath Mountains, and the Little Shasta River, which rises in the high Cascades. The volcanic rocks of the high Cascades were built by eruptions that commenced at the close of the Miocene epoch and continued intermittently to Recent time. Mount Shasta was built mainly during the Pleistocene epoch. Morainal and fluvioglacial deposits, which are concentrated at the south end of the valley, were formed mainly during Pleistocene time by glaciers that descended the northwest flanks of Mount Shasta. Glaciers still remain on Mount Shasta and have supplied fluvioglacial debris to the valley during Recent time. The Plutos Cave basalt constitutes the principal aquifer in the valley, yielding abundant water for irrigation, stock, and domestic wells in the vicinity of Big Springs. Yields of irrigation wells in the basalt average about 1,300 gpm (gallons per minute). The andesitic lavas of the western Cascades supply sufficient water for domestic and stock uses. Yields of wells tapping the andesites vary greatly because of rapid changes in lateral and vertical permeability. Abundant water for irrigation is yielded from fractures in the volcanic rocks of the western Cascades in the Gazelle-Grenada area. The basement complex and the Chico and Umpqua formations are tapped by relatively few wells in the area, although locally these wells seem to yield sufficient water for domestic and stock uses. The basement complex yields water from joints, faults, shear zones, and openings along foliation planes. The morainal and fluvioglacial deposits generally yield sufficient water for domestic and stock uses. Several irrigation wells tapping glacial materials east of Edgewood yield 600 to 1,500 gpm. The younger and older alluviums of Recent and Pleistocene age yield water sufficient for domestic and stock uses. Along the west side of the valley the younger alluvium yields sufficient water for irrigation and supplies Yreka with abundant water for municipal uses. Ground water moves generally northward in the southern part of Shasta Valley and troughward from the east and west, converging toward the Shasta River along the valley axis. At the north end of the valley an eastward-trending divide separates the ground water that moves north to Willow Creek from ground water that moves south to the Shasta River. Recharge to ground water is effected by deep infiltration of precipitation that falls on the tributary drainage area, principally the western slopes of Mount Shasta, and by seepage from streams. The mean annual precipitation on the valley floor of 12-15 inches probably is not sufficient to contribute much recharge to ground water, but during years of above-average precipitation some deep penetration probably occurs. Recharge from irrigation water in 1953 was about 15,000 acre-feet from a total surface-water diversion of 58,000 acre-feet, and recharge from ground water pumped for irrigation was about 2,000 acre-feet. Ground-water discharge in Shasta Valley occurs principally by seepage into streams, which is estimated crudely to have been 70,000 acre-feet in 1953. Big Springs has an annual discharge of about 30,000 acre-feet. Evapotranspiration from subirrigated crops is estimated to have been 28,000 acre-feet in 1953. Pumpage for all uses in 1953 was approximately 6,000 acre-feet, and net draft was about 4,000 acre-feet. Ground-water discharge in 1953 by all these principal means was about 130,000 acre-feet. In addition, there was minor discharge from flowing wells, unestimated discharge from small springs on the valley floor, and evapotranspiration losses from relatively small areas of phreatophytes. Because of the relatively small pumpage in the valley, water levels in wells show declines of only 5-10 feet during the summer and autumn. So far as is known, the levels each winter and spring recover nearly completely, and as of 1953 there had been no indication of a long-term decline of water levels in the valley. Surface water and ground water are generally low in dissolved mineral content and with few exceptions meet minimum standards for irrigation and domestic use. A close correlation exists between the composition of the various rock types in the area and the mineralization of surface and ground waters in areas adjacent to each rock type.

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Geology of the Fresh Ground‐water Basin of the Central Valley, California, with Texture Maps and Sections

U.S. Geological Survey (USGS) | December 1st, 1986

Summary

The Central Valley of California, which is about 400 miles long and averages about 50 miles wide, comprises about 20,000 square miles. Geologically, the valley is

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Geology, Ground-Water Hydrology, Geochemistry, and Ground-Water Simulation of the Beaumont and Banning Storage Units, San Gorgonio Pass Area, Riverside County, California

U.S. Geological Survey (USGS) | December 14th, 2006

Summary

Ground-water has been the only source of potable water supply for residential, industrial, and agricultural users in the Beaumont and Banning storage units of the San Gor

Ground-water has been the only source of potable water supply for residential, industrial, and agricultural users in the Beaumont and Banning storage units of the San Gorgonio Pass area, Riverside County, California. Ground-water levels in the Beaumont area have declined as much as 100 feet between the early 1920s and early 2000s, and numerous natural springs have stopped flowing. In 1961, the San Gorgonio Pass Water Agency (SGPWA) entered into a contract with the California State Department of Water Resources to receive 17,300 acre-feet per year of water to be delivered by the California State Water Project (SWP) to supplement natural recharge. Currently (2005), a pipeline is delivering SWP water into the area, and the SGPWA is artificially recharging the ground-water system using recharge ponds located along Little San Gorgonio Creek in Cherry Valley with the SWP water. In addition to artificial recharge, SGPWA is considering the direct delivery of SWP water for the irrigation of local golf courses and for agricultural supply in lieu of ground-water pumpage. To better understand the potential hydrologic effects of different water-management alternatives on ground-water levels and movement in the Beaumont and Banning storage units, existing geohydrologic and geochemical data were compiled, new data from a basin-wide ground-water level and water-quality monitoring network were collected, monitoring wells were installed near the Little San Gorgonio Creek recharge ponds, geohydrologic and geochemical analyses were completed, and a ground-water flow simulation model was developed. The San Gorgonio Pass area was divided into several storage units on the basis of mapped or inferred faults. This study addresses primarily the Beaumont and Banning storage units. The geologic units in the study area were generalized into crystalline basement rocks and sedimentary deposits. The younger sedimentary deposits and the surficial deposits are the main water-bearing deposits in the San Gorgonio Pass area. The water-bearing deposits were divided into three aquifers: (1) the perched aquifer, (2) the upper aquifer, and (3) the lower aquifer based on lithologic and downhole geophysical logs. Natural recharge in the San Gorgonio Pass area was estimated using INFILv3, a deterministic distributed- parameter precipitation-runoff model. The INFILv3 model simulated that the potential recharge of precipitation and runoff in the Beaumont and Banning storage units was about 3,710 acre-feet per year and that the potential recharge in 28 sub-drainage basins upstream of the storage units was about 6,180 acre-feet per year. The water supply for the Beaumont and Banning storage units is supplied by pumping ground water from wells in the Canyon (Edgar and Banning Canyons), Banning Bench, Beaumont, and Banning storage units. Total annual pumpage from the Beaumont and Banning storage units ranged from about 1,630 acre-feet in 1936 to about 20,000 acre-feet in 2003. Ground-water levels declined by as much as 100 feet in the Beaumont storage unit from 1926–2003 in response to ground-water pumping of about 450,160 acre-feet during this period. Since ground-water development began in the San Gorgonio Pass area, there have been several sources of artificial recharge to the basin including return flow from applied water on crops, golf courses, and landscape; septic-tank seepage; and infiltration of storm runoff diversions and imported water into recharge ponds. Return flow from applied water and septic-tank seepage was estimated to reach a maximum of about 8,100 acre-feet per year in 2003. Owing to the great depth of water in much of study area (in excess of 150 feet), the return flow and septic-tank seepage takes years to decades to reach the water table. Stable-isotope data indicate that the source of ground-water recharge was precipitation from storms passing through the San Gorgonio Pass as opposed to runoff from the higher altitudes of the San Bernardino Mountains. In addition, these data indicate that little if any of the ground water in the fractured crystalline rocks flows across the Banning Fault into the Beaumont storage unit. Tritium concentrations indicate that little to no recharge has reached the water table since 1952 in most areas of the Beaumont and Banning storage units. In general, the uncorrected carbon-14 ages of ground water sampled from wells in the Beaumont, Banning, and surrounding storage units ranged from about 400 to 17,500 years before present. The older water was sampled in southeastern part of Beaumont storage unit and in the Banning storage unit, and ranged from 1,900 to 17,500 years before present. To better understand the dynamics of ground-water flow and the potential effects of water-level changes resulting from artificial recharge in the San Gorgonio Pass area, a regional-scale, numerical ground-water flow model was developed using MODFLOW-96. This model will be used by water managers to help manage the ground-water resources in the San Gorgonio Pass area. Results of the steady-state simulation indicate that the total inflow rate, or recharge, was about 6,590 acre-feet per year with about 3,710 acre-feet per year from areal recharge, about 2,670 acre-feet per year from mountain-front recharge, and about 210 acre-feet per year from the surrounding older sedimentary deposits. The simulated water budget for 1926–2003 indicates that of the total simulated volume of water pumped from the aquifer (450,160 acre-feet), about 50 percent was derived from depletion of ground-water storage (222,660 acre-feet), about 21 percent was derived from the reduction of underflow to the Cabazon and San Timoteo storage units (about 96,280 acre-feet), about 19 percent was derived from a reduction of ground-water outflow to the stream channels draining the San Timoteo storage unit (about 86,030 acre-feet), about 8 percent was derived from irrigation return flows and septic-tank seepage (about 36,780 acre-feet), and about 2 percent was derived from an increase in ground-water underflow from the surrounding older sedimentary deposits (about 8,410 acre-feet). The calibrated ground-water flow model was used to simulate the effects of four water-management scenarios being considered by SGPWA for the period 2004–13. In general, the results of the water-management scenarios indicate that artificial recharge in the Little San Gorgonio Creek recharge ponds primarily benefits the area north of the Cherry Valley Fault. For the scenario that used SWP water in lieu of ground water for golf course irrigation and for agricultural use, hydraulic heads increased by about 50 feet. None of the water-management scenarios significantly benefited the Banning storage unit.

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Geology, Water-Quality, Hydrology, and Geomechanics of the Cuyama Valley Groundwater Basin, California, 2008–12

U.S. Geological Survey (USGS) | July 11th, 2013

Summary

To assess the water resources of the Cuyama Valley groundwater basin in Santa Barbara County, California, a series of cooperative studies were undertaken by the U.S. Geol

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Getting Involved in Groundwater: A Guide to California's Groundwater Sustainability Plans

Union of Concerned Scientists | September 1st, 2017

Summary

Using this guide and online toolkit, a diverse range of people can equip themselves to effectively participate in shaping the vision and plan for their community around m

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Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization of the Central and West Coast Basins, Los Angeles County, California By

Geohydrology, Simulation of Regional Groundwater Flow, and Assessment of Water-Management Strategies, Twentynine Palms Area, California

Geohydrology, Water Quality, and Estimation of Ground-Water Recharge In San Francisco, California, 1987-92

Geologic Setting, Geohydrology, and Ground-Water Quality near the Helendale Fault in the Mojave River Basin, San Bernardino County, California

Geology and Ground Water Features of the Butte Valley Region Siskiyou County California

Geology and Ground-Water Features of Shasta Valley, Siskiyou County California

Geology of the Fresh Ground‐water Basin of the Central Valley, California, with Texture Maps and Sections

Geology, Ground-Water Hydrology, Geochemistry, and Ground-Water Simulation of the Beaumont and Banning Storage Units, San Gorgonio Pass Area, Riverside County, California

Geology, Water-Quality, Hydrology, and Geomechanics of the Cuyama Valley Groundwater Basin, California, 2008–12

Getting Involved in Groundwater: A Guide to California's Groundwater Sustainability Plans

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