Groundwater Chemistry and Hexavalent Chromium

Professional Paper 1885-E
Prepared in cooperation with the Lahontan Regional Water Quality Control Board
By: , and 



Water samples collected by the U.S. Geological Survey from more than 100 wells between March 2015 and November 2017 in Hinkley and Water Valleys, in the Mojave Desert 80 miles northeast of Los Angeles, California, were analyzed for field parameters, major ions, nutrients, and selected trace elements, including hexavalent chromium, Cr(VI). Water from most wells was alkaline and oxic. The pH ranged from 6.9 in water-table wells near recharge areas along the Mojave River to 9.4 in deeper wells farther downgradient in the northern subarea.

Hexavalent chromium concentrations measured by ion chromatography using U.S. Environmental Protection Agency Method 218.6 and a version of that method used for detection of Cr(VI) concentrations as low as 0.06 micrograms per liter (μg/L), produced results comparable to field speciation with subsequent analyses by graphite furnace atomic absorption spectroscopy (coefficient of determination, R2, of 0.97). Hexavalent chromium concentrations ranged from less than the study reporting level of 0.10 to 2,500 μg/L. The highest concentrations were within the October–December 2015 (Q4 2015) regulatory Cr(VI) plume downgradient from the Hinkley compressor station. Hexavalent chromium concentrations outside the Q4 2015 regulatory Cr(VI) plume were as high as 11 μg/L. Hexavalent chromium concentrations in water from most wells were distributed in a narrow redox potential and pH band within the overlapping chromate ion, CrO42−(aqueous), and manganese-3, Mn(III)(solid), stability fields. The redox potential of water from some wells completed in carbonate-rich mudflat/playa deposits approached the more oxic manganese-4, Mn(IV)(solid), stability field. However, Cr(VI) concentrations in porewater pressure-extracted from Mn(IV)-containing deposits in the eastern subarea did not exceed 3.3 μg/L, and porewater does not appear to be a source of Cr(VI) concentrations greater than this concentration in water from wells in the eastern subarea.

On the basis of comparison with California-wide data, Cr(VI) concentrations at the measured pH were higher than expected for uncontaminated water from wells (1) within the Q4 2015 regulatory Cr(VI) plume, (2) within the eastern subarea nominally crossgradient from the Hinkley compressor station and upgradient from the Q4 2015 regulatory Cr(VI) plume, and (3) from shallow wells in the northern subarea downgradient from the leading edge of the Q4 2015 regulatory Cr(VI) plume. Hexavalent chromium concentrations in alkaline water from wells in the northern subarea of Hinkley Valley and in Water Valley were within ranges expected for uncontaminated water elsewhere in California given their pH and trace-element composition. Hexavalent chromium concentrations were higher than expected on the basis of selected trace-element concentrations that co-occur with Cr(VI) in water from wells within the Q4 2015 regulatory Cr(VI) plume and from wells in the eastern and northern subareas near the plume margins. Hexavalent chromium concentrations did not exceed 4 μg/L in water from domestic wells sampled in Hinkley and Water Valleys and were generally within ranges expected for uncontaminated groundwater given their pH and trace-element composition.

Interpretations derived from Cr(VI) and pH, and from Cr(VI) and selected trace-element concentrations collected between March 2015 and November 2017 were used within a summative-scale analysis to determine the Cr(VI) plume extent (chapter G). However, Cr(VI) background concentrations (chapter G) were calculated from regulatory data collected from selected wells between April 2017 and January 2018.

Suggested Citation

Izbicki, J.A., McCleskey, R.B., Burton, C.A., Clark, D.A., and Smith, G.A., 2023, Groundwater chemistry and hexavalent chromium, Chapter E of Natural and anthropogenic (human-made) hexavalent chromium, Cr(VI), in groundwater near a mapped plume, Hinkley, California: U.S. Geological Survey Professional Paper 1885-E, 63 p.,

ISSN: 2330-7102 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • E.1. Introduction
  • E.2. Field and Laboratory Methods and Quality-Assurance Data
  • E.3. Groundwater Chemistry
  • E.4. Porewater
  • E.5. Water from Domestic Wells
  • E.6. Conclusions
  • E.7. References Cited
  • Appendix E.1. Water Chemistry and Isotope Data Collected by the U.S. Geological Survey in Hinkley and Water Valleys, Western Mojave Desert, California, March 2015 through November 2017
Publication type Report
Publication Subtype USGS Numbered Series
Title Groundwater chemistry and hexavalent chromium
Series title Professional Paper
Series number 1885
Chapter E
DOI 10.3133/pp1885E
Year Published 2023
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) California Water Science Center
Description Report: x, 63 p.; Data Release; 3 Appendixes
Country United States
State California
City Hinkley
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
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