Geology Reports⌕ Search

Geology topics

Gregory O. Mendez

Publications and source records attributed to Gregory O. Mendez.

At least 19 recordsLinked to original sources
USGS2018

Geologic, hydrologic, and water-quality data from multiple-well monitoring sites in the Bunker Hill and Yucaipa Groundwater Subbasins, San Bernardino County, California, 1974–2016

In 1974, the U.S. Geological Survey (USGS), in cooperation with the San Bernardino Valley Municipal Water District, initiated a study to assess the regional groundwater resources in the Bunker Hill Subbasin of the Upper Santa Ana Valley Groundwater Basin in San Bernardino County, California. The study area expanded east into the Yucaipa Subbasin in 1996. This report compiles the geologic (borehole lithology and geophysical logs) and hydrologic (water-quality and water-level) data collected from 1974–2016 for 11 multiple-well monitoring sites (48 individual wells) constructed by the USGS in the Bunker Hill (7 sites) and Yucaipa (4 sites) Groundwater Subbasins. Approximately 240 water-quality samples from the 11 sites were analyzed for constituents including major and minor ions, nutrients, selected trace elements, organic wastewater compounds (OWCs), volatile organic compounds (VOCs), pesticides and pesticide degradates, the stable isotopes of hydrogen, oxygen, and nitrogen, and the radiogenic isotopes of tritium and carbon-14. All environmental data associated with these sites are available on the project web page for the San Bernardino Optimal Basin Management study ( https://ca.water.usgs.gov/sanbern/ ) and the Yucaipa Valley Hydrogeology study ( https://ca.water.usgs.gov/yucaipa/ ). Quality-assurance blank samples were processed periodically throughout the study and show that approximately 2.4 percent of the analytical results for major and minor ions, trace elements, and nutrients, and 1.5 percent of the results for VOCs fall below the acceptable study reporting limits and therefore are censored.

California↗
USGS2016

Geologic structure of the Yucaipa area inferred from gravity data, San Bernardino and Riverside Counties, California

In the spring of 2009, the U.S. Geological Survey, in cooperation with the San Bernardino Valley Municipal Water District, began working on a gravity survey in the Yucaipa area to explore the three-dimensional shape of the sedimentary fill (alluvial deposits) and the surface of the underlying crystalline basement rocks. As water use has increased in pace with rapid urbanization, water managers have need for better information about the subsurface geometry and the boundaries of groundwater subbasins in the Yucaipa area. The large density contrast between alluvial deposits and the crystalline basement complex permits using modeling of gravity data to estimate the thickness of alluvial deposits. The bottom of the alluvial deposits is considered to be the top of crystalline basement rocks. The gravity data, integrated with geologic information from surface outcrops and 51 subsurface borings (15 of which penetrated basement rock), indicated a complex basin configuration where steep slopes coincide with mapped faults―such as the Crafton Hills Fault and the eastern section of the Banning Fault―and concealed ridges separate hydrologically defined subbasins. Gravity measurements and well logs were the primary data sets used to define the thickness and structure of the groundwater basin. Gravity measurements were collected at 256 new locations along profiles that totaled approximately 104.6 km (65 mi) in length; these data supplemented previously collected gravity measurements. Gravity data were reduced to isostatic anomalies and separated into an anomaly field representing the valley fill. The ‘valley-fill-deposits gravity anomaly’ was converted to thickness by using an assumed, depth-varying density contrast between the alluvial deposits and the underlying bedrock. To help visualize the basin geometry, an animation of the elevation of the top of the basement-rocks was prepared. The animation “flies over” the Yucaipa groundwater basin, viewing the land surface, geology, faults, and ridges and valleys of the shaded-relief elevation of the top of the basement complex.

California↗
USGS2015

Water- and air-quality and surficial bed-sediment monitoring of the Sweetwater Reservoir watershed, San Diego County, California, 2003-09

In 1998, the U.S. Geological Survey, in cooperation with the Sweetwater Authority, began a study to assess the overall health of the Sweetwater watershed in San Diego County, California. This study was designed to provide a data set that could be used to evaluate potential effects from the construction and operation of State Route 125 within the broader context of the water quality and air quality in the watershed. The study included regular sampling of water, air, and surficial bed sediment at Sweetwater Reservoir (SWR) for chemical constituents, including volatile organic compounds (VOCs), base-neutral and acid- extractable organic compounds (BNAs) that include polycyclic aromatic hydrocarbons (PAHs), pesticides, and metals. Additionally, water samples were collected for anthropogenic organic indicator compounds in and around SWR. Background water samples were collected at Loveland Reservoir for VOCs, BNAs, pesticides, and metals. Surficial bed-sediment samples were collected for PAHs, organochlorine pesticides, and metals at Sweetwater and Loveland Reservoirs. To monitor changes in contaminant concentration in water and air at SWR during the construction and operation of State Route 125, this study was divided into three phases. Phase One sampling (September 1998 to September 2004) was designed to establish baseline conditions for target compounds in terms of detection frequency and concentration in air and water. Phase Two (October 2004 to September 2007) continued sampling at selected monitoring sites during construction of State Route 125 to assess any effect from the construction process and the use of heavy equipment to build the roadway. Phase Three (October 2007 to August 2009) continued sampling for 2 years after the opening of State Route 125 to assess the potential changes in water quality related to vehicle emissions from the roadway alignment. Surficial bed-sediment samples were collected three times during the study—at the beginning of the study, at the start of Phase Two, and at the end of the study. This report describes the study design and the sampling and analytical methods and presents data from water, air, and surficial bed-sediment samples collected from the sixth to eleventh years of the study (October 2003–August 2009), spanning the last year of Phase one and all of Phases Two and Three. Data collected during the first 5 years of sampling have been previously published. Three types of quality-control samples were used in this study—matrix spikes, blanks, and replicates. Matrix-spike data are considered to be adequate if the recovery concentration is within 30 percent of the matrix concentration. Replicate data are considered to be adequate if the replicate sample concentration is within 30 percent of the environmental sample concentration. Additionally, surrogate compounds were added to most samples to monitor sample-specific performance of the analytical method. Most VOC matrix-spike recovery data associated with water samples are within acceptable criteria, but three VOCs had recoveries below the acceptable criteria; these compounds may not have been detected in water samples if they were present at low concentrations. Data for blanks associated with water samples for VOCs and metals showed no detections above their laboratory reporting levels. Most replicate data are within acceptable criteria. Quality-control data for VOC air samples resulted in flagging several reported concentrations for acetone, benzene, ethenylbenzene, and naphthalene because they may be biased high. Acetone, benzene, and toluene were detected at low concentrations in almost every VOC air blank. Some PAH and pesticide concentrations in air samples were designated as estimated because of method performance limitations. PAHs in surficial bed sediment had 83 percent of surrogates below the acceptable criteria. No matrix-spike data for metals in surficial bed sediment were outside the acceptable criteria; only beryllium had a replicate comparison outside the acceptable criteria. Sampling results show concentrations of the gasoline oxygenate methyl tert -butyl ether in water and air samples declined after it was phased out by the State of California in January 2004. The largest concentrations of gasoline hydrocarbons benzene and toluene in water were detected at or near the surface of the SWR. Isophorone and phenol were the two most frequently detected BNA compounds in water. Diuron, prometon, and simazine were the most frequently detected pesticide compounds in water. Concentrations of benzene and toluene in air samples were highest during the cooler months and had a consistent seasonal pattern over time. Ten PAH compounds were detected frequently in air samples. Twelve pesticide compounds were also detected in air samples. Surficial bed-sediment samples were analyzed for 53 PAHs; 22 of the compounds had one or more detections. Surficial bed-sediment samples were analyzed for 22 organic compounds; only 6 compounds had one or more detections. Surficial bed-sediment samples were analyzed for 37 metals.

California↗
USGS2013

A geochemical approach to determine sources and movement of saline groundwater in a coastal aquifer

Geochemical evaluation of the sources and movement of saline groundwater in coastal aquifers can aid in the initial mapping of the subsurface when geological information is unavailable. Chloride concentrations of groundwater in a coastal aquifer near San Diego, California, range from about 57 to 39,400 mg/L. On the basis of relative proportions of major-ions, the chemical composition is classified as Na-Ca-Cl-SO 4 , Na-Cl, or Na-Ca-Cl type water. δ 2 H and δ 18 O values range from −47.7‰ to −12.8‰ and from −7.0‰ to −1.2‰, respectively. The isotopically depleted groundwater occurs in the deeper part of the coastal aquifer, and the isotopically enriched groundwater occurs in zones of sea water intrusion. 87 Sr/ 86 Sr ratios range from about 0.7050 to 0.7090, and differ between shallower and deeper flow paths in the coastal aquifer. 3 H and 14 C analyses indicate that most of the groundwater was recharged many thousands of years ago. The analysis of multiple chemical and isotopic tracers indicates that the sources and movement of saline groundwater in the San Diego coastal aquifer are dominated by: (1) recharge of local precipitation in relatively shallow parts of the flow system; (2) regional flow of recharge of higher-elevation precipitation along deep flow paths that freshen a previously saline aquifer; and (3) intrusion of sea water that entered the aquifer primarily during premodern times. Two northwest-to-southeast trending sections show the spatial distribution of the different geochemical groups and suggest the subsurface in the coastal aquifer can be separated into two predominant hydrostratigraphic layers.

California↗
USGS2011

Application of a watershed model (HSPF) for evaluating sources and transport of pathogen indicators in the Chino Basin drainage area, San Bernardino County, California

A watershed model using Hydrologic Simulation Program-FORTRAN (HSPF) was developed for the urbanized Chino Basin in southern California to simulate the transport of pathogen indicator bacteria, evaluate the flow-component and land-use contributions to bacteria contamination and water-quality degradation throughout the basin, and develop a better understanding of the potential effects of climate and land-use change on water quality. The calibration of the model for indicator bacteria was supported by historical data collected before this study and by samples collected by the U.S. Geological Survey from targeted land-use areas during storms in water-year 2004. The model was successfully calibrated for streamflow at 5 gage locations representing the Chino Creek and Mill Creek drainages. Although representing pathogens as dissolved constituents limits the model's ability to simulate the transport of pathogen indicator bacteria, the bacteria concentrations measured over the period 1998-2004 were well represented by the simulated concentrations for most locations. Hourly concentrations were more difficult to predict because of high variability in measured bacteria concentrations. In general, model simulations indicated that the residential and commercial land uses were the dominant sources for most of the pathogen indicator bacteria during low streamflows. However, simulations indicated that land used for intensive livestock (dairies and feedlots) and mixed agriculture contributed the most bacteria during storms. The calibrated model was used to evaluate how various land use, air temperature, and precipitation scenarios would affect flow and transport of bacteria. Results indicated that snow pack formation and melt were sensitive to changes in air temperature in the northern, mountainous part of the Chino Basin, causing the timing and magnitude of streamflow to shift in the natural drainages and impact the urbanized areas of the central Chino Basin. The relation between bacteria concentrations and air temperature was more complicated, and did not substantially affect the quality of water discharging from the Chino Basin into the Santa Ana River. Changes in precipitation had a greater basin-wide affect on bacteria concentrations than changes in air temperature, and varied according to location. Drainages representing natural conditions had a decrease in bacteria concentrations in correlation with an increase in precipitation, whereas drainages in the central and southern part of the Chino Basin had an increase in bacteria concentrations. Drier climate conditions tended to result in higher sensitivity of simulated bacteria concentrations to changes in precipitation. Simulated bacteria concentrations in wetter climates were usually less sensitive to changes in precipitation because bacteria transport becomes more dependent on the land-use specified bacteria loading rates and the storage limits. Bacteria contamination from impervious-area runoff is affected to a greater degree by drier climates, whereas contamination from pervious-area runoff is affected to a greater degree by wetter climates. Model results indicated that the relation between precipitation, runoff, and bacteria contamination is complicated because after the initial bacteria washoff and transport from the land surfaces during the beginning of a storm period, subsequent runoff has fewer bacteria available for washoff, which then dilutes the concentrations of bacteria in the downstream reach. It was illustrated that pathogen indicator bacteria transport depends most significantly on the relation of imperviousness to runoff, which controls the frequency, and often the magnitude, of transport, and on the contribution of higher bacteria loading rates used for pervious land areas, especially intensive feedlots, to the infrequent, but very high, peaks of bacteria contamination. The indicator bacteria transport model for the Chino Basin was based on the assumption that no

California↗
USGS2010

Water-quality data from storm runoff after the 2007 fires, San Diego County, California

The U.S. Geological Survey collected water-quality samples during the first two storms after the Witch and Harris Fires (October 2007) in southern California. The sampling locations represent an urban area (two residential sites in Rancho Bernardo that were affected by the Witch Fire; a drainage ditch and a storm drain) and a rural area (Cotton-wood Creek, which was downstream of a mobile home park destroyed by the Harris Fire). Fires produce ash and solid residues that contain soluble chemicals that can contaminant runoff. The contaminants, whether sorbed to soil and ash or dissolved, can seriously affect the quality of water supplies and sensitive ecosystems. Stormflow water samples were analyzed for field parameters, optical properties, and for a variety of constituents, including nutrients, dissolved organic carbon (DOC), suspended sediment, and metals. pH values for storm runoff from the urban areas (7.6 to 8.5) were less than pH values for ash and burned soil from previous studies (12.5 to 13). pH values for storm runoff from the rural area (about 7.7) also were less than pH values for ash and burned soil collected from the rural area (8.6 to 11.8), but were similar to pH values for wildland burned soil from previous studies. Turbidity values were much lower for the urban area than for the rural area. Nitrate concentrations in stormflow samples from all sites were less than a quarter of the U.S. Environmental Protection Agency's (2006) maximum allowable contaminant level of 10 milligrams per liter (mg/L) (as nitrogen). Phosphorus concentrations were half as much in filtered samples and two orders of magnitude smaller in unfiltered samples at the urban sites than at the rural site. DOC concentrations in stormflow samples were one order of magnitude lower at the urban sites than at the rural site. Ultraviolet (UV) absorbance at 254 nanometers (UV254) in samples ranged from 0.145 to 0.782 per centimeter (cm-1). UV-absorbance data at the urban sites indicate that the composition of DOC remained similar during both storms even though the DOC concentration changed. Total suspended-sediment concentrations ranged from 0.01 to 0.24 mg/L at the urban area, and were 12 and 45 mg/L at the rural area. Trace metals analyzed in unfiltered water samples had lower concentrations in the urban area than in the rural area. No concentrations of arsenic or mercury measured in the samples were above aquatic-life criteria. In the urban area, most concentrations of aluminum, iron, and lead exceeded aquatic-life criteria. In the rural area, aluminum, cadmium, iron, lead, and zinc exceeded aquatic-life criteria. Concentrations of aluminum and iron were two orders of magnitude larger in the rural area than in the urban area.

Open-File Report↗
USGS2008

Water- and air-quality monitoring of Sweetwater Reservoir watershed, San Diego County, California — Phase one results continued, 2001-2003

In 1998, the U.S. Geological Survey, in cooperation with the Sweetwater Authority, began a study to monitor water, air, and sediment at the Sweetwater and Loveland Reservoirs in San Diego County, California. The study includes regular sampling of water and air at Sweetwater Reservoir for chemical constituents, including volatile organic compounds (VOC), polynuclear aromatic hydrocarbons (PAH), pesticides, and major and trace elements. The purpose of this study is to monitor changes in contaminant composition and concentration during the construction and operation of State Route 125. To accomplish this, the study was divided into two phases. Phase One sampling (water years 1998–2004) determined baseline conditions for the detection frequency and the concentrations of target compounds in air and water. Phase Two sampling (starting water year 2005) continues at selected monitoring sites during and after construction of State Route 125 to assess the chemical impact this roadway alignment may have on water quality in the reservoir. Water samples were collected for VOCs and pesticides at Loveland Reservoir during Phase One and will be collected during Phase Two for comparison purposes. Air samples collected to monitor changes in VOCs, PAHs, and pesticides were analyzed by adapting methods used to analyze water samples. Bed-sediment samples have been and will be collected three times during the study; at the beginning of Phase One, at the start of Phase Two, and near the end of the study. In addition to the ongoing data collection, several special studies were initiated to assess the occurrence of specific chemicals of concern, such as trace metals, anthropogenic indicator compounds, and pharmaceuticals. This report describes the study design, and the sampling and analytical methods, and presents data from water and air samples collected during the fourth and fifth years of Phase One of the study (October 2001 to September 2003). Data collected during the first three years has been previously published. Three types of quality-control samples were used in this study: blanks, spikes, and replicates. Blanks and spikes are used to estimate result bias, and replicates are used to estimate result variability. Additionally, surrogate compounds were added at the laboratory to samples of VOCs, PAHs, pesticides, anthropogenic indicator compounds, and pharmaceuticals to monitor sample-specific performance of the analytical method.

California↗
USGS2007

Water- and air-quality monitoring of the Sweetwater Reservoir Watershed, San Diego County, California-Phase One results, continued, 1999-2001

In 1998, the U.S. Geological Survey, in cooperation with the Sweetwater Authority, began a study to assess the overall health of the Sweetwater watershed with respect to chemical contamination. The study included regular sampling of air and water at Sweetwater Reservoir for chemical contaminants, including volatile organic compounds, polycyclic aromatic hydrocarbons, pesticides, and major and trace elements. Background water samples were collected at Loveland Reservoir for volatile organic compounds and pesticides. The purpose of this study was to monitor changes in contaminant composition and concentration in the air and water resulting from the construction and operation of State Route 125 near Sweetwater Reservoir. To accomplish this, the study was divided into two phases. Phase One sampling was designed to establish baseline conditions for target compounds in terms of detection frequency and concentration in air and water. Phase Two sampling is planned to continue at the established monitoring sites during and after construction of State Route 125 to assess the chemical impact this roadway alignment project may have on the water quality in the reservoir. In addition to the ongoing data collection, several special studies were initiated to assess the occurrence of specific chemicals of concern, such as low-use pesticides, trace metals, and wastewater compounds. This report describes the study design, and the sampling and analytical methods, and presents the results for the second and third years of the study (October 1999 to September 2001). Data collected during the first year of sampling (October 1998 to September 1999) were published in 2002.

California↗
USGS2005

Evaluation of two low-flow releases from Big Tujunga Reservoir, Los Angeles County, California, 2003

Since 1973, the Santa Ana Sucker (Catostomus santaanae) has been listed as a threatened species under the Endangered Species Act. The Lower Big Tujunga Creek, in Los Angeles County, is one of the areas in southern California where the Santa Ana Sucker is still present. This study was designed to assess two flow releases from Big Tujunga Dam that may contribute to favorable habitat conditions for the Santa Ana Sucker. It is important for the Santa Ana Sucker's survival that pools in the lower reach of the study area are replenished periodically. The focus of the study area was on the Lower Big Tujunga Creek within a reach extending approximately 6 miles downstream from the Big Tujunga Reservoir. Six sites were established from the Big Tujunga Dam to Delta Flats day-use area for data collection. This report describes the study design, discharge measurements, and the flow data collected from the two releases. Two scheduled flows (phases 1 and 2) were released from the Big Tujunga Reservoir in August and September 2003. During the first phase, which lasted 50 hours, travel times from the dam to four sites downstream were determined. Arrival times at the four sites were determined on the basis of temperature data. Travel time from the dam to site 6 (the furthest downstream site) was about 51.5 hours. Travel times for subreaches were 3 hours from site 1 to site 2, 6.5 hours from site 2 to site 3, almost 18 hours from site 3 to site 4, and 24 hours from site 4 to site 6. The temperature probe at site 5 was destroyed, and thus the arrival time could not be estimated. A probe that measures stage was placed in one of the many pools downstream from site 4 to evaluate a typical pool response to a low-flow release. Also, discharge measurements were taken at four sites along the study reach. In phase 2, which lasted 5 days (121 hours), flow losses along the 6-mile reach were analyzed. Losses were estimated by measuring difference in flow from the dam to sites 3, 4, 5, and 6, when flow was most stable at each site or when the last measurement made before flow decreased due to flow from dam being shut off. Losses in the plunge pool, directly below the dam were assumed to be negligible for this study. Overall creek loss between the dam and site 6 (the last site) was estimated to be between 4.0 and 4.2 ft3/s (cubic feet per second). Estimated losses between the dam and intermediate sites were about 1.5 ft3/s to site 3; 2.5 ft3/s to site 4; and between 3.7 and 4.1 ft3/s to site 5.

Scientific Investigations Report↗
USGS2005

An assessment of optical properties of dissolved organic material as quantitative source indicators in the Santa Ana River basin, Southern California

The ability to rapidly, reliably, and inexpensively characterize sources of dissolved organic material (DOM) in watersheds would allow water management agencies to more quickly identify problems in water sources, and to more efficiently allocate water resources by, for example, permitting real-time identification of high-quality water suitable for ground-water recharge, or poor-quality water in need of mitigation. This study examined the feasibility of using easily measurable intrinsic optical properties' absorbance and fluorescence spectra, as quantitative indicators of DOM sources and, thus, a predictor of water quality. The study focused on the Santa Ana River Basin, in southern California, USA, which comprises an area of dense urban development and an area of intense dairy production. Base flow in the Santa Ana Basin is primarily tertiary treated wastewater discharge. Available hydrologic data indicate that urban and agricultural runoff degrades water quality during storm events by introducing pathogens, nutrients, and other contaminants, including significant amounts of DOM. These conditions provide the basis for evaluating the use of DOM optical properties as a tracer of DOM from different sources. Sample spectra representing four principal DOM sources were identified among all samples collected in 1999 on the basis of basin hydrology, and the distribution of spectral variability within all the sample data. A linear mixing model provided quantitative estimates of relative endmember contribution to sample spectra for monthly, storm, and diurnal samples. The spectral properties of the four sources (endmembers), Pristine Water, Wastewater, Urban Water, and Dairy Water, accounted for 94 percent of the variability in optical properties observed in the study, suggesting that all important DOM sources were represented. The scale and distribution of the residual spectra, that not explained by the endmembers, suggested that the endmember spectra selected did not adequately represent Urban Water base flow. However, model assignments of sources generally agreed well with those expected, based on sampling location and hydrology. The results suggest that with a fuller characterization of the endmember spectra, analysis of optical properties will provide rapid quantitative estimates of the relative contribution of DOM sources in the Santa Ana Basin.

Scientific Investigations Report↗
USGS2005

Occurrence and distribution of pesticide compounds in surface water of the Santa Ana basin, California, 1998-2001

A study of the occurrence and distribution of pesticide compounds in surface water of the highly urbanized Santa Ana Basin, California, was done as part of the U.S. Geological Survey's National Water-Quality Assessment Program (NAWQA). One-hundred and forty-eight samples were collected from 23 sites, and analyzed for pesticide compounds during the study period from November 1998 to September 2001. Sixty-six different pesticide compounds were detected at varying frequencies and concentrations, and one or more pesticides were detected in 92 percent of the samples. All pesticide concentrations were below maximum levels permitted in drinking water. However, two compounds-diazinon and diuron-exceeded nonenforceable drinking water health-advisory levels in at least one stream sample, and five compounds exceeded guidelines to protect aquatic life-carbaryl, chlorpyrifos, diazinon, lindane, and malathion. Twenty-two pesticide compounds were detected in at least 25 percent of the samples collected from any one fixed site. These are identified as 'major' pesticide compounds and are emphasized in this report. The degree to which pesticides were used in the basin, as well as their physical-chemical properties, are important explanatory factors in stream pesticide occurrence, and most pesticides probably enter streams with urban runoff. Stormflow substantially increases urban runoff, and storm effects on stream pesticide concentrations sometimes persist for several days or weeks after the storm. Water sources other than urban runoff also deliver pesticide compounds to surface water in the basin. For example, atrazine may enter streams in gaining reaches where ground water carries high loads as a result of historical use in the basin. Also, the data suggest that lindane, and perhaps bromacil, are present in treated wastewater, the predominant source of water to streams in the Santa Ana Basin.

Scientific Investigations Report↗
USGS2003

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

The proximity of the Mojave River ground-water basin to the highly urbanized Los Angeles region has resulted in rapid population growth and, consequently, an increase in the demand for water. The Mojave River, the primary source of surface water for the region, normally is dry--except for periods of flow after intense storms; therefore, the region relies almost entirely on ground water to meet its agricultural and municipal needs. The area where the Helendale Fault intersects the Mojave River is of particular hydrogeologic interest because of its importance as a boundary between two water-management subareas of the Mojave Water Agency. The fault is the boundary between the upper Mojave River Basin (Oeste, Alto, and Este subareas) and the lower Mojave River Basin (Centro and Baja subareas); specifically, the fault is the boundary between the Alto and the Centro subareas. To obtain the information necessary to help better understand the hydrogeology of the area near the fault, multiple-well monitoring sites were installed, the surface geology was mapped in detail, and water-level and water-quality data were collected from wells in the study area. Detailed surficial geologic maps and water-level measurements indicate that the Helendale Fault impedes the flow of ground water in the deeper regional aquifer, but not in the overlying floodplain aquifer. Other faults mapped in the area impede the flow of ground water in both aquifers. Evidence of flowing water in the Mojave River upgradient of the Helendale Fault exists in the historical record, suggesting an upward gradient of ground-water flow. However, water-level data from this study indicate that pumping upstream of the Helendale Fault has reversed the vertical gradient of ground-water flow since predevelopment conditions, and the potential now exists for water to flow downward from the floodplain aquifer to the regional aquifer. Sixty-seven ground-water samples were analyzed for major ions, nutrients, and stable isotopes of oxygen and hydrogen from 34 wells within the study area between May 1990 and November 1999. Dissolved-solids concentrations in water samples from 14 wells in the floodplain aquifer ranged from 339 to 2,330 milligrams per liter (mg/L) with a median concentration of 825 mg/L. Concentrations in water from 11 of these wells exceeded the U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Level (SMCL) of 500 mg/L. Dissolved-solids concentrations of water from nine wells sampled in the regional aquifer ranged from 479 to 946 mg/L with a median concentration of 666 mg/L. Concentrations in at least one sample of water from each of the wells in the regional aquifer exceeded the USEPA SMCL for dissolved solids. Arsenic concentrations in water from 14 wells in the floodplain aquifer ranged from less than the detection limit of 2 micrograms per liter (?g/L) to a maximum of 34 ?g/L with a median concentration of 6 ?g/L. Concentrations in water from six of the 14 wells exceeded the USEPA Maximum Contaminant Level (MCL) for arsenic of 10 ?g/L. Arsenic concentrations in water from nine wells in the regional aquifer ranged from less than the detection limit of 2 to 130 ?g/L with a median concentration of 11 ?g/L. Concentrations in water from five of these nine wells exceeded the USEPA MCL for arsenic. Dissolved-solids concentrations in water from seven wells completed in the igneous and metamorphic basement rocks that underlie the floodplain and regional aquifers ranged from 400 to 3,190 mg/L with a median concentration of 1,410 mg/L. Concentrations in water from all but one of the seven wells sampled exceeded the USEPA SMCL for dissolved solids. Concentrations in water from the basement rocks exceeded the USEPA SMCL for arsenic of 10 ?g/L in five of the seven wells. The high concentrations of arsenic, dissolved solids, and other constituents probably occur naturally. Stable isotopes of oxygen and hydrogen indicate that before pumping began in

Water-Resources Investigations Report↗
USGS2003

Evaluation of tracer tests completed in 1999 and 2000 on the upper Santa Clara River, Los Angeles and Ventura Counties, California

The interaction of surface water and hyporheic water along the Santa Clara River in Los Angeles and Ventura Counties, California, was evaluated by conducting tracer tests and analyzing water-quality data under different flow conditions in October 1999 and May 2000. Tracer and water-quality samples were collected at multiple river and hyporheic sites as well as at the Los Angeles County Sanitation Districts Saugus and Valencia Water Reclamation Plants. These water reclamation plants provide the main source of base flow in the river. Rhodamine WT dye was injected into the river to determine river traveltimes and to indicate when Lagrangian water-quality sampling could be performed at each site. Sodium bromide was injected into the river at a constant rate at the water reclamation plants to evaluate the surface-water and shallow ground-water interactions in the hyporheic zone. In the upper reach of the study area, which extends 2.9 river miles downstream from the Saugus Water Reclamation Plant, traveltime was 3.2 hours during May 2000. In the lower reach, which extends 14.1 river miles downstream from the Valencia Water Reclamation Plant, traveltime was 9.6 hours during October 1999 and 7.1 hours during May 2000. The sodium bromide tracer was detected at both hyporheic locations sampled during October 1999, and at two of the three hyporheic locations sampled during May 2000. On the basis of Rhodamine dye tests, flow curves were constructed from the discharge measurements in the Valencia reach. Flow-curve results indicate net gains in flow throughout most, but not all, of the upper parts of the reach and net losses in flow at the lower part of the reach. Lagrangian water-quality sampling provides information on the changes in chemistry as the water flows downstream from the water reclamation plants. Along both reaches there is an increase in sulfate (40-60 mg/L in the Saugus reach and 160 mg/L in the Valencia reach) and a decrease in chloride (about 45 mg/L in the Saugus reach and about 10 mg/L in the Valencia reach). The increasing sulfate concentrations are consistent with discharge of higher sulfate ground water into the river. Along both reaches there is a trend of decreasing ammonia and slightly increasing nitrate concentrations. This trend is consistent with nitrification. Samples were also analyzed for numerous compounds associated with wastewater, but analysis focused on four indicators. Concentrations of wastewater indicators in the Santa Clara River were low and decreased downstream from the reclamation plants. There is general consistency between the chemical and tracer data collected from the hyporheic and the river-aquifer flow regime within a reach. The water quality at the hyporheic site in a gaining reach of the river resembled that of the local ground water and no wastewater indicators or injected tracers were observed; whereas, the water quality at the hyporheic sites in a losing reach of the river resembled the water quality of the river at the corresponding river site, and injected tracers were observed.

California↗
USGS2002

Water quality monitoring of Sweetwater and Loveland reservoirs--Phase one results 1998-1999

In 1998, the U.S. Geological Survey began a study to assess the overall health of the watershed feeding the Sweetwater Reservoir in southern San Diego County, California. The study focussed on monitoring for organic chemical contamination and the effects of construction and operation of State Route 125 on water quality. Three environmental compartments (air, water, and bed sediments) are being sampled regularly for chemical contaminants, including volatile organic compounds, polynuclear aromatic hydrocarbons, polychlorinated biphenyls, pesticides, and major and trace elements. The study is divided into two phases. Phase I sampling is designed to establish baseline conditions for target compounds in terms of detection frequency and concentration in air, water, and bed sediments. Phase II sampling will continue at the established monitoring sites during and after construction of State Route 125 to assess chemical impact on water quality in the reservoir resulting from land-use changes and development in the watershed. This report describes the study design, the sampling and analytical methods, and presents the data results for the first year of the study, September 1998 to September 1999.

Open-File Report↗
USGS2001

Surface-water and ground-water quality in the Yucaipa area, San Bernardino and Riverside counties, California, 1996-98

The quality of surface water and ground water in the Yucaipa area was evaluated to determine general chemical characteristics and to identify areas of recent ground-water recharge. Water samples, collected from 8 sites on 3 creeks and from 25 wells, were analyzed for general chemistry, nutrients, tritium, and stable isotopes of hydrogen and oxygen. At one production well (1S/2W-25R4), water samples were collected at discrete depths during pumping and a continuous profile of the vertical flow rate inside the well casing was recorded. In addition to general-chemistry samples, tritium and carbon-14 samples were collected at this well to interpret the age of water at different depths. Results indicate that most water in the Yucaipa area is a calcium-bicarbonate type. The general chemical composition of surface water resembles that of ground water, although the concentration of most constituents is higher in ground water. The chemical composition of most ground-water samples is similar. Elevated concentrations of nitrate in some ground-water samples may indicate recharge from agricultural areas. In surface water that recharges ground water tritium activity ranged from 7 to 18 picocuries per liter. The range of tritium activity found in ground water indicates different times since recharge and possible mixing along ground-water flow paths. The oldest ground-water sample had a tritium activity less than 0.3 picocuries per liter, indicating more than 50 years since recharge. Water samples that had tritium activity greater than 0.3 picocuries per liter indicate that some of the water was recharged since 1952. The youngest ground water (greater than 7 picocuries per liter) was found near the hills and mountains surrounding the Yucaipa area; the oldest ground water (less than 0.3 picocuries per liter) was found in the Western Heights subbasin. Testing of the vertical contribution of ground water to well 1S/2W-25R4 showed that more than one-half of the water flowed into the well between depths of about 450 and 600 feet below land surface; the rest of the water flowed into the well between 600 and about 850 feet below land surface. At a discharge rate of 750 gallons per minute, virtually no water was contributed to the well below a depth of about 850 feet. The water samples collected at this well ranged in age from less than 50 to less than 400 years before present.

California↗
USGS2000

Stormflow chemistry in the Santa Ana River below Prado Dam and at the diversion downstream from Imperial Highway, southern California, 1995-98

The Santa Ana River drains about 2,670 square miles of the densely populated coastal area of southern California, near Los Angeles. Almost all the flow in the river, more than 200,000 acre-feet annually, is diverted into ponds where it infiltrates and recharges underlying aquifers. About 2 million people are dependent on these aquifers for water supply. Stormflow in the Santa Ana River is considered a source of "high-quality" water suitable for use as a source of ground-water recharge. To test this assumption, stormflow samples were collected at two locations--below Prado Dam and at the diversion point downstream from Imperial Highway--for 12 winter storms between 1995 and 1998. Nitrate concentrations decreased during stormflow from a median concentration of 7.8 milligrams per liter in base flow to concentrations less than 1 milligram per liter in some large storms. Concentrations of chemically reduced forms of nitrogen (nitrite, ammonia, and organic nitrogen) increased during stormflow and are the predominant forms of nitrogen in large stormflows. Dissolved organic carbon (DOC) concentrations increased from a median concentration of 4.6 milligrams per liter in base flow to more than 20 milligrams per liter in some stormflows. Concentrations of DOC were especially high during the first storm of the rainy season, and large increases in DOC concentrations were measured even as a result of small early season storms that did not cause large increases in streamflow. DOC present during early season stormflow had less ultraviolet absorbance at 254 nanometers (UV 254 ) per unit of carbon than did DOC from late season stormflows. DOC in water held in storage behind Prado Dam had the highest UV 254 absorbance per unit of carbon. Maximum pesticide concentrations in stormflow did not exceed U.S. Environmental Protection Agency Maximum Contaminant Levels. Most pesticide concentrations were less than 1 microgram per liter and less than the detection limits obtained using standard drinking water analyses. Increases in concentrations of pesticides such as diazinon, malathion, and chlorpyrifos in stormflow result from runoff from urban areas downstream from Prado Dam. In general, large late season stormflows have the most pesticide detections of all stormflows sampled. Concentrations of methyl tert-butyl ether (MTBE), a gasoline additive, during base flow were as high as 0.9 microgram per liter and concentrations decreased during stormflow. Like pesticides, the concentrations did not exceed the U.S. Environmental Protection Agency Maximum Contaminant Levels for MTBE.

California↗
USGS1998

Chemistry and isotopic composition of ground water along a section near the Newmark area, San Bernardino County, California

Chemical and isotopic analyses and flow-meter measurements in pumped wells were used to determine the source, movement, and age of ground water along a section of the valley-fill aquifer from the San Jacinto Fault to the base of the San Bernardino Mountains near the Newmark area in the Bunker Hill Basin of southern California. Water samples were collected from four multiple-depth well sites, from different depths within three production wells, and from two nearby streams; these samples were analyzed for major ions, selected trace elements, stable isotopes of oxygen and hydrogen (delta oxygen-18 and delta deuterium), tritium, and carbon-14. Within the production wells, variations in vertical flowrate with depth were recorded during pumped conditions using a standard spinner tool. Where saturated, the upper 200 feet of unconsolidated deposits contributed as much as 60 percent of the well discharge; deposits at depths greater than 700 feet contributed less than 10 percent. Chemical analyses indicate that three general zones of ground-water quality are present along a north-south section--an oxygenated zone near the base of the San Bernardino Mountains, an oxygen-depleted zone near the San Jacinto Fault, and a deeper zone characterized by concentrations of fluoride greater than 1 mg/L and by a general water-quality composition similar to that of base flow in East Twin Creek. The presence of tritium in water from wells along the section indicates that post-1952 recharge has moved rapidly through the valley-fill aquifer to depths as great as 800 feet. Carbon-14 data indicate that the maximum age of ground water, sampled at depths ranging from 600 to 1,000 feet, is less than 5,000 years before present. Ground water along the study section is much younger than ground water from similar depths in other nearby basins. Delta oxygen-18 and delta deuterium data indicate that as much as 25 percent of the discharge from some wells near the base of the San Bernardino Mountains is water that was imported from northern California. Improved knowledge of depth-dependent ground-water flow along this section can aid in the design of an effective strategy for basin management, including remediation of the Newmark area, which is designated by the U.S. Environmental Protection Agency as a Superfund cleanup site.

Water-Resources Investigations Report↗