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

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

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.

Geology and Hydrogeology of the Yucaipa Groundwater Subbasin, San Bernardino and Riverside Counties, California

U.S. Geological Survey (USGS) | January 19th, 2022

The Yucaipa groundwater subbasin (referred to in this report as the Yucaipa subbasin) is located about 75 miles (mi) east of of Los Angeles and about 12 mi southeast of t

The Yucaipa groundwater subbasin (referred to in this report as the Yucaipa subbasin) is located about 75 miles (mi) east of of Los Angeles and about 12 mi southeast of the City of San Bernardino. In the Yucaipa subbasin, as in much of southern California, limited annual rainfall and large water demands can strain existing water supplies; therefore, understanding local surface water and groundwater conditions is essential for managing these resources. To better understand the hydrogeology and water resources in the Yucaipa subbasin, especially groundwater, the San Bernardino Valley Municipal Water District and the U.S. Geological Survey initiated a cooperative study to evaluate the hydrogeologic system of the Yucaipa subbasin and the encompassing Yucaipa Valley watershed. Previous studies of the area provided information on general geologic and hydrologic conditions, but this study provides the first comprehensive definition of the hydrogeology of the subsurface throughout the entire subbasin. The Yucaipa subbasin is located between the northwest trending San Andreas fault zone and San Jacinto fault. Several northeast-trending dip-slip faults dissect the Yucaipa subbasin, providing the mechanism for structural relief within the sediment-filled subbasin and between the subbasin and surrounding mountains and highlands. Several of these dip-slip faults have been previously identified as potential barriers to groundwater flow. This report provides a synthesis of previous studies and a discussion of the geologic interpretations that were used as the foundation for hydrogeologic classification of the Yucaipa subbasin. Notably, this report (1) adopts the recently named and classified sedimentary deposits of Live Oak Canyon geologic formation and extends the mapped distribution of the formation into the Yucaipa subbasin, and (2) adopts the interpretation that activity along the Banning fault predates the deposition of most basin-fill sedimentary materials in the Yucaipa subbasin. Four hydrogeologic units were classified in the Yucaipa subbasin: (1) crystalline basement, (2) consolidated sedimentary materials, (3) unconsolidated sediment, and (4) surficial materials. The crystalline basement unit forms the bottom boundary of the aquifer system, and the three other units comprise the basin-fill aquifer system. The four hydrogeologic units vary in extent, thickness, and structural relief across the subbasin, with the unconsolidated sediment unit serving as the primary aquifer unit. A three-dimensional hydrogeologic framework model was developed for the Yucaipa subbasin and surrounding area to characterize the thickness, extent, and hydrogeologic variability of the aquifer system. Geologic maps, borehole geophysical logs, drillers’ lithology logs, and depth-to-basement gravity data were used to map and interpolate the subsurface extent and structure of the hydrogeologic units within the subbasin. Faults and structures of geologic and (or) hydrogeologic importance were included in the model for future evaluation of their potential effects on groundwater flow. The resulting hydrogeologic framework is consistent with existing geologic concepts and the tectonic and structural history of the Yucaipa subbasin and surrounding area. The framework is also suitable for use in basin-scale hydrogeologic investigations.

Geology and Water Resources of Las Vegas, Pahrump, and Indian Spring Valleys, Clark and Nye Counties, Nevada

State of Nevada | July 1st, 1948

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

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

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 a large asymmetric trough that is bounded by granitic, metamorphic, and marine sedimentary rocks of pre-Tertiary age. The trough has been filled with as much as 6 vertical miles of sediment in the San Joaquin Valley and as much as 10 vertical miles of sediment in the Sacramento Valley; these sedi- ments range in age from Jurassic to Holocene. Some volcanic rocks and deposits crop out in the valley, but of those only the Tuscan Formation in the northeastern part of the Sacramento Valley is of major importance to the fresh ground-water basin. Post-Eocene continental rocks and deposits contain most of the fresh water in the Central Valley; they crop out virtually over the whole valley and in most places overlie or contain saline water at depth. Continental rocks and deposits of Tertiary age include the Mehrten Formation. The Mehrten is of great importance to the fresh ground-water basin of the Central Valley and yields large quantities of water to wells.

Geology of the fresh ground‐water basin, Central Valley, California, with texture maps and sections

U.S. Geological Survey (USGS) | July 17th, 1986

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

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 a large asymmetric trough that is bounded by granitic, metamorphic, and marine sedimentary rocks of pre-Tertiary age. The trough has been filled with as much as 6 vertical miles of sediment in the San Joaquin Valley and as much as 10 vertical miles of sediment in the Sacramento Valley; these sedi- ments range in age from Jurassic to Holocene. Some volcanic rocks and deposits crop out in the valley, but of those only the Tuscan Formation in the northeastern part of the Sacramento Valley is of major importance to the fresh ground-water basin. Post-Eocene continental rocks and deposits contain most of the fresh water in the Central Valley; they crop out virtually over the whole valley and in most places overlie or contain saline water at depth. Continental rocks and deposits of Tertiary age include the Mehrten Formation. The Mehrten is of great importance to the fresh ground-water basin of the Central Valley and yields large quantities of water to wells. Although continental rocks and deposits of Tertiary and Quaternary age compose a number of formations and informal deposits, in total they constitute the major aquifer of the Central Valley. In most places, similarity in sediment type between the continental deposits and some underlying rocks and deposits and even between separate units of continental rocks and deposits makes mapping of subsurface geologic contacts difficult if not practically im- possible. In this respect, a unit that can be mapped on the surface is difficult to delineate in the subsurface, and, although such a unit can be called an aquifer, it merges with similar units in the subsurface to form a major, widespread aquifer. Continental rocks and deposits of Tertiary and Quaternary age include (1) the Kern River Formation; (2) the Laguna Formation; (3) the Tulare Formation; (4) the Tehama Formation; and (5) a number of younger formations, as well as some informally named deposits. These deposits and formations also include lacustrine and marsh deposits, which are much thicker and more extensive in the San Joaquin Valley than in the Sacramento Valley. These continental rocks and deposits generally crop out as wide belts along the flanks of the Central Valley and range in thickness from 0 foot along the flanks to about 15,000 feet in the extreme southern part. In general, the rocks and deposits consist of a heterogeneous mixture of generally poorly sorted clay, silt, sand, and gravel; in some places they consist of more consolidated sediments, such as mudstone and sandstone. Yields to wells from these rocks and deposits, except the lacustrine and marsh deposits, range from about 20 gallons per minute to 4,500 gallons per minute. Lacustrine and marsh deposits crop out in the San Joaquin Valley but not in the Sacramento Valley. Beneath Tulare Lake bed in the San Joaquin Valley, the lacustrine and marsh deposits, which constitute a thick plug of clay and silt from which lenses of clay and silt emanate at irregular intervals, are in places more than 3,600 feet thick. The lens mapped as the E Clay in the San Joaquin Valley is the most extensive lacustrine clay in the entire Central Valley and includes the Corcoran Clay Member of the Tulare Formation. More recent mapping has shown that the E Clay in the extreme southern part of the valley is shallower than previous reports had indicated; therefore, in this report the clay is referred to as the modified E Clay. Perhaps the expansion of lakes and the resulting deposition of extensive clays in the San Joaquin Valley occurred principally because of a large downwarping basin beneath an area known as Tulare Lake bed, and perhaps a similar expansion and deposition did not occur in the Sacramento Valley because a similar downwarping basin probably had not developed there. Continental deposits of Quaternary age crop out chiefly along the major rivers and streams of the valley as well as other low-lying areas; the deposits include river deposits, flood-basin deposits, and sand dunes. River deposits, including channel and flood-plain depos- its, are considered to be the most permeable deposits in the valley; in general, they are not tapped by wells. Flood-basin deposits consist largely of fine-grained beds that restrict the vertical movement of water. Sand dunes are not considered important aquifers because they generally lie above the water table. The large, asymmetrical, northwestward-trending structural trough of the Central Valley is the principal structure controlling the occurrence and movement of ground water in the area. Because the flanks of the valley are higher than its axis, recharge from tributary rivers and streams has caused heads in the ground water along the flanks to be higher than those along the axis. Therefore, the overall ground-water movement in the Central Valley is from the flanks toward the axis and from there toward the delta area. Secondary structures in the valley, such as arches and faults, also influence the occurrence and movement of ground water. As it is used in this report, "texture" means the proportion of coarse-grained to fine-grained sediment in sedimentary rocks and deposits. In the Central Valley, most of the deposits for which data are available generally contain no more than 40 to 60 percent of coarse-grained sediment, where coarse-grained sediment includes clayey and silty sand and gravel. Texture columns, maps, and sections, in depth intervals of 300 feet, show that the alluvial deposits of the Central Valley are a heterogeneous mixture whose character ranges over short distances and depths from chiefly fine-grained to chiefly coarse-grained and vice versa. Nevertheless, some areas are underlain chiefly by fine-grained sediment and others by coarse-grained sediment; sediments of like size in an area indicate that sources and depositional environment probably were similar for long periods of time.

Geology of the Northern Sacramento Valley, California

California Department of Water Resources (DWR) | September 22nd, 2014

This study describes the complex geology of the northern Sacramento Valley, focusing on the Late Cenozoic geologic formations and structures that compose or influence the

This study describes the complex geology of the northern Sacramento Valley, focusing on the Late Cenozoic geologic formations and structures that compose or influence the valley’s fresh groundwater aquifer formations. The California Department of Water Resources (DWR) acquired geologic data from groundwater observation well drilling operations that were conducted in the valley over the last 15 years. Using the observation well drilling data, DWR evaluated and classified the lithology of the subsurface sediments, implemented petrographic sand provenance analyses on lithologic sediment samples, and reviewed associated geophysical logs from each bore hole. In addition, DWR conducted an extensive literature review of published and unpublished data and then integrated the data to produce this geologic report, map, and cross sections that describe the geology of the northern Sacramento Valley. Results from the lithologic logging, petrographic analyses, and data review show that the heterogeneous sediments of the northern Sacramento Valley’s most productive groundwater-bearing geologic formations, the Tehama Formation and the Tuscan Formation, intermix in the subsurface in various areas near the center of the valley. The results also show that toward the westward and eastward extents of the valley, the sediments of the formations become more unified in composition due to the proximity of their respective sediment source areas. However, because of the depositional environment of the geologic formations, sediment sizes within the formations can be discontinuous and intermittent in places, resulting in variable groundwater aquifer zones within the geologic formations. Additional data are needed to further define the northern Sacramento Valley aquifer system. Drilling and installing groundwater observation wells in areas of little or no data can provide the information needed to determine the extent and variability of the valley’s groundwater aquifers. Groundwater level data supplied by the observation wells can provide valuable information for monitoring aquifer conditions, for determining the change in groundwater levels over time, and for assessing the ability of groundwater to move through the geologic aquifer sediments. In addition, a textural analysis of formational sediments using lithologic cuttings and/or driller’s well logs could be performed to better identify aquifer production zones. In summary, the geology of the northern Sacramento Valley is diverse and has a widely varied historical sequence of earth-shaping events. It includes periods of time when much of the area was below sea level, multiple and distinct periods of volcanic activity, several periods of mountain building, and intermingled periods of massive erosion and deposition. Analyses of the data illustrate the heterogeneity of the groundwater-bearing geologic formations in the subsurface, and the intermixing of formational sediments toward the center of the northern Sacramento Valley, resulting in a region with great geologic and hydrogeologic complexity.

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

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.

Geology, water resources and usable ground-water storage capacity of part of Solano County, California

U.S. Geological Survey (USGS) | July 1st, 1960

The area described is confined largely to the valley-floor and foothill lands of Solano County, which lies directly between Sacramento, the State capital, and San Franc

The area described is confined largely to the valley-floor and foothill lands of Solano County, which lies directly between Sacramento, the State capital, and San Francisco. The area is considered in two subareas: The Putah area, which extends from Putah Creek southward to the Montezuma Hills and from the foothills of the Coast Ranges eastward to the west edge of the Yolo Bypass; and the Suisun-Fairfield area, which is to the southwest in the notch in the Coast Ranges through which the waters of the Great Central Valley of California reach San Francisco Bay. There are no known hydrologic interconnections between the two subareas, through either surface streams or underground aquifers. The climate of the area is characterized by warm, rainless summers and by cool winters in which temperatures seldom drop much below freezing. The rainfall ranges from about 17 inches per year along the east side to perhaps 24 inches in the foothills to the west, and irrigation is necessary for all crops except dry-farmed grains, pastures, and some orchards.

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

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

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

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. Geological Survey and the Santa Barbara County Water Agency. Between 2008 and 2012, geologic, water-quality, hydrologic and geomechanical data were collected from selected sites throughout the Cuyama Valley groundwater basin.

Geostatistical Mapping of Salinity Conditioned on Borehole Logs, Montebello OilField, California

National Groundwater Association (NGWA) | December 3rd, 2021

We present a geostatistics-based stochastic salinity estimation framework for the Montebello Oil Field that capitalizes on available total dissolved solids (TDS) data fro

We present a geostatistics-based stochastic salinity estimation framework for the Montebello Oil Field that capitalizes on available total dissolved solids (TDS) data from groundwater samples as well as electrical resistivity (ER) data from borehole logging. Data from TDS samples (n = 4924) was coded into an indicator framework based on falling below four selected thresholds (500, 1000, 3000, and 10,000 mg/L). Collocated TDS-ER data from the surrounding groundwater basin were then employed to produce a kernel density estimator to establish conditional probabilities for ER data (n = 8 boreholes) falling below the selected TDS thresholds within the Montebello Oil Field area. Directional variograms were estimated from these indicator coded data, and 500 TDS realizations from conditional indicator simulation were generated for the subsurface region above the Montebello Oil Field reservoir. Simulations were summarized as 3D maps of median TDS, most likely salinity class, and probability for exceeding each of the specified TDS thresholds. Results suggested TDS was below 500 mg/L in most of the study area, with a trend toward higher values (500 to 1000 mg/L) to the southwest; consistent with the average regional groundwater flow direction. Discrete localized zones of TDS greater than 1000 mg/L were observed, with one of these zones in the greater than 10,000 mg/L range; however, these areas were not prevalent. The probabilistic approach used here is adaptable and is readily modified to include additional data and types and can be employed in time-lapse salinity modeling through Bayesian updating.