Comprehensive Groundwater Cleanup Strategy for Historical Chromium Discharges from PG&E's Hinkley Compressor Station, San Bernardino County, Final Environmental Impact Report Volume I: Comments on Draft EIR and Responses

California State Water Resources Control Board (SWRCB) | April 20th, 2013

Click here for Volume II

Click here for Volume II

Concentrations for total dissolved solids, arsenic, boron, fluoride, and nitrite-nitrate for wells sampled in the Mojave Water Agency Management Area

U.S. Geological Survey (USGS) | July 1st, 2001

Concentrations for total dissolved solids, arsenic, boron, fluoride, and nitrite-nitrate for wells sampled in the Mojave Water Agency Management Area, California, 1991-97

U.S. Geological Survey (USGS) | January 31st, 2001

Concentrations, Loads, and Associated Trends of Nutrients Entering the Sacramento–San Joaquin Delta, California

University of California, Davis (UC Davis) | December 15th, 2021

Statistical modeling of water-quality data collected at the Sacramento River at Freeport and San Joaquin River near Vernalis, California, USA, was used to examine trends

Statistical modeling of water-quality data collected at the Sacramento River at Freeport and San Joaquin River near Vernalis, California, USA, was used to examine trends in concentrations and loads of various forms of dissolved and particulate nitrogen and phosphorus that entered the Sacramento–San Joaquin River Delta (Delta) from upstream sources between 1970 and 2019. Ammonium concentrations and loads decreased at the Sacramento River site from the mid-1970s through 1990 because of the consolidation of wastewater treatment and continuously reduced from the mid-1970s to 2019 at the San Joaquin River site. Current ammonium concentrations are mostly below 4 µM (0.056 mg N L–1) at both sites, a concentration above which reductions in phytoplankton productivity or changes in algal species composition may occur. The Sacramento River at Freeport site is located upstream of the Sacramento Regional County Sanitation District’s treatment facility’s discharge point; nutrient water quality there is representative of upstream sources. Inorganic nitrogen (nitrate plus ammonium) concentrations and loading differed at both sites. At the Sacramento River location, concentrations decrease in the summer agricultural season, reducing the molar ratios of nitrogen to phosphorus. In contrast, inorganic nitrogen concentrations increase in the San Joaquin River during the agricultural season as a result of irrigation runoff, increasing the molar ratio of nitrogen to phosphorus. This increase suggests a possible nitrogen limitation in the northern Delta and a phosphorus limitation in the southern Delta, as indicated by the molar ratios of bioavailable nitrogen to bioavailable phosphorus. Planned upgrades to the Sacramento Regional Wastewater Treatment Plant (SRWTP) will reduce inorganic nitrogen inputs to the northern Delta. Consequently, the supply of bioavailable nitrogen throughout the upper estuary should diminish. Source modeling of nitrogen and phosphorus identifies agriculture, atmospheric deposition, and wastewater effluent as sources of total nitrogen in the Central Valley. In contrast, geologic sources, agriculture, and wastewater discharge are the primary sources of phosphorus.

Concepts and evolution of urban hydrology

Nature Portfolio (Springer Nature) | October 24th, 2024

Conceptual and Numerical Models of Dissolved Solids in the Colorado River, Hoover Dam to Imperial Dam, and Parker Dam to Imperial Dam, Arizona, California, and Nevada

U.S. Geological Survey (USGS) | August 28th, 2018

Conceptual and numerical models were developed to understand and simulate monthly flow-weighted dissolved-solids concentrations in the Colorado River at Imperial

Conceptual and numerical models were developed to understand and simulate monthly flow-weighted dissolved-solids concentrations in the Colorado River at Imperial Dam. The ability to simulate dissolved-solids concentrations at this location will help the Bureau of Reclamation satisfy the binational agreement on the volume and salinity of Colorado River water delivered to Mexico. A robust spatial- and temporal-resolution dataset that consists of river discharge and dissolved-solids concentration and load information between January 1990 and September 2016 for 10 sites on canals, drains, tributaries, and the main stem of the Colorado River between Hoover and Imperial Dams was generated. Daily mean dissolved-solids concentrations were estimated and monthly mean dissolved-solids loads were computed for each site. Spatial and temporal load patterns, and historical and current controls on loads and concentrations, were analyzed in order to develop a conceptual model of dissolved- solids transport between Hoover and Imperial Dams. Two numerical models describing the relations between dissolved- solids concentrations and components controlling dissolved-solidsconcentrations and loads were developed, calibrated, and verified. Between January 1990 and September 2016, there was a 98.8-million-acre-feet loss of water and a 57.0-million-ton loss of dissolved-solids load from the Colorado River between Hoover and Imperial Dams. Between Hoover and Parker Dams, about 69.0 million acre-feet of water was lost and 51.1 million tons of dissolved solids were lost; between Parker and Imperial Dams, about 29.8 million acre-feet of water was lost and 5.9 million tons of dissolved solids were lost. Water was removed from the river at a relatively consistent rate over the 25-year study period through water transfers to California and Arizona, evapotranspiration from crop irrigation, transpiration processes of riparian vegetation, and evaporation from the river main stem. Dissolved solids were removed from the river between Hoover and Parker Dams at a relatively constant rate through water transfers to California and Arizona, and water pumped from the river for irrigation within the Mohave Valley. A small amount of dissolved solids are gainedby the river from inflow from the Bill Williams River. Between Parker and Imperial Dams, however, dissolved solids were not removed from the river at a consistent rate over the study period. Dissolved solids were generally removed from the river from 1990 to 2012, then gained by the river from 2012 to 2015, and then removed from the river from 2015 through 2016. Dissolved solids are assumed to be removed from the river and accumulated within the floodplain sediments and aquifers during irrigation processes; some dissolved solids may also be removed from the river through uptake by crops and riparian vegetation. Dissolved solids accumulated on the landscape and in the floodplain aquifer during irrigation are transported to the river during periods when the hydraulic gradient between the floodplain aquifer and the river is increased, causing a gain in dissolved solids in the river. Dissolved-solids gains in the river occur during periods of relatively low river discharge, such as during the winter months and during drier climatic conditions. Two numerical models were developed and coefficientswere estimated by using data from a May 2008-September 2016 calibration period. One model simulates concentrations at Imperial Dam based on the Colorado River system downstream from Parker Dam, and the other model simulates concentrations at Imperial Dam based on the Colorado River system downstreamfrom Hoover Dam. Both models simulated monthly flow-weighted concentrations of dissolved solids for the Colorado River at Imperial Dam, which corresponded well with observed concentrations for the entire study period. The models are more sensitive to input variables of monthly discharge of the ColoradoRiver below Parker Dam and monthly flow-weighted dissolved-solids concentrations of the Colorado River below Hoover Dam and Parker Dam than to the rate of change in concentration with respect to time and the combined discharge of the Colorado River Indian Reservation Main Canal and the Palo Verde Canal. The calibrated models can be used to run scenarios of future monthlyflow-weighted dissolved-solids concentrations in the ColoradoRiver at Imperial Dam. Although the models are expected to provide concentration estimates within 18 milligrams per liter (Parker Dam to Imperial Dam model) to 22 milligrams per liter (Hoover Dam to Imperial Dam model), 95 percent of the time, the error of future scenarios increases as uncertainty in the estimated future input variables increases.

Conceptual model for salinity in the Central Valley and Sacramento-San Joaquin Delta

Central Valley Drinking Water Policy Workgroup | July 13th, 2007

This report examines the state of knowledge about the causes of salinity increase in the system and opportunities to improve the Delta as a source of municipal and agricu

This report examines the state of knowledge about the causes of salinity increase in the system and opportunities to improve the Delta as a source of municipal and agricultural water supply. It begins with background information about salinity, its measurement, and its impacts. Following that, we present observed salinity in the Bay-Delta system. The conceptual models section, the core of this report, then seeks to explain the forces and processes (drivers) that cause the salinity patterns we observe. The computational models section introduces some of the tools available to assist with salinity management and planning. The last chapter explores the implications of the conceptual model for monitoring and management of salinity.

Conceptual Model of the Great Basin Carbonate and Alluvial Aquifer System

U.S. Geological Survey (USGS) | September 20th, 2011

Conceptual Model Review of Napa Valley Groundwater Model

Napa County | November 15th, 2010

The purpose of this technical memorandum is to provide a general review of the Napa Valley Groundwater model (groundwater model) produced by DHI Water & Environment (

The purpose of this technical memorandum is to provide a general review of the Napa Valley Groundwater model (groundwater model) produced by DHI Water & Environment (DHI) as part of the 2005 Napa County Baseline Data Report (2005 BDR) (Jones & Stokes et al., 2005). This memorandum is not intended to be a full peer-review in which model code, input/output files, and output results would be analyzed. Opinions stated herein are based solely on a review of the 2006 Final BDR Technical Appendix (DHI, 2006a), which presents the model code, model construction, calibration, and application of modeling efforts introduced in Chapters 15, 16, and 17 of the BDR. Further information on the groundwater model was reviewed from the 2005 BDR and a 2007 technical memorandum Modeling Analysis in Support of Vineyard Development Scenarios Evaluation (DHI, 2007) in which the groundwater model was updated/expanded and applied in evaluating various vineyard development scenarios. The scope of Luhdorff & Scalmanini, Consulting Engineers’ (LSCE) work, described herein, included a review of the conceptual model developed by DHI from which the inputs to the groundwater model were based. In addition, information provided on the model code, construction, and development of the groundwater model and model calibration were also reviewed. The focus of LSCE’s work was to assess whether the information provided in the reviewed documents was complete and whether the model can be used for the stated purpose for which it was developed.

Conceptual Model to Support PCB Management and Monitoring in the Emeryville Crescent Priority Margin Unit

San Francisco Estuary Institute (SFEI) | April 3rd, 2017

The 2014 update of the RMP PCB Strategy called for a multi-year effort to implement the recommendations of the PCB Synthesis Report (Davis et al. 2014) pertaining to: 

The 2014 update of the RMP PCB Strategy called for a multi-year effort to implement the recommendations of the PCB Synthesis Report (Davis et al. 2014) pertaining to:  1. identifying margin units that are high priorities for management and monitoring,  2. development of conceptual models and mass budgets for margin units downstream of watersheds where management actions will occur, and  3. monitoring in these units as a performance measure.  The goal of the effort is to inform the review and possible revision of the PCB TMDL and the reissuance of the Municipal Regional Permit for Stormwater (MRP), both of which are tentatively scheduled to occur in 2020. Conceptual model development for four priority margin units (PMUs) that are high priorities for management and monitoring will provide a foundation for establishing effective and efficient monitoring plans to track responses to load reductions and will also help guide planning of management actions. The Emeryville Crescent (the Crescent) is the subject of this report and the first PMU to be studied.