Metals Transport in the Sacramento River, California, 1996-1997.
Volume 2: Interpretation of Metal Loads

By Charles N. Alpers, Ronald C. Antweiler Howard E. Taylor, Peter D. Dileanis, and Joseph L. Domagalski, editors


Water-Resources Investigations Report 00-4002

Prepared in cooperation with the

Sacramento Regional County Sanitation District

California State Water Resources Control Board

U.S. Environmental Protection Agency

U.S. Department of Commerce, National Marine Fisheries Service


Sacramento, California 2001

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Front matter and contents (252 KB) - 10 pages

Text pages 1-21 (2.4 MB) -21 pages

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Metals transport in the Sacramento River, northern California, from July 1996 to June 1997 was evaluated in terms of metal loads from samples of water and suspended colloids that were collected on up to six occasions at 13 sites in the Sacramento River Basin. Four of the sampling periods (July, September, and November 1996; and May-June 1997) took place during relatively low-flow conditions and two sampling periods (December 1996 and January 1997) took place during high-flow and flooding conditions, respectively. This study focused primarily on loads of cadmium, copper, lead, and zinc, with secondary emphasis on loads of aluminum, iron, and mercury.

Trace metals in acid mine drainage from abandoned and inactive base-metal mines, in the East and West Shasta mining districts, enter the Sacramento River system in predominantly dissolved form into both Shasta Lake and Keswick Reservoir. The proportion of trace metals that was dissolved (as opposed to colloidal) in samples collected at Shasta and Keswick dams decreased in the order zinc ≈ cadmium > copper > lead. At four sampling sites on the Sacramento River--71, 256, 360, and 412 kilometers downstream of Keswick Dam--trace-metal loads were predominantly colloidal during both high- and low-flow conditions. The proportion of total cadmium, copper, lead, and zinc loads transported to San Francisco Bay and the Sacramento-San Joaquin Delta estuary (referred to as the Bay-Delta) that is associated with mineralized areas was estimated by dividing loads at Keswick Dam by loads 412 kilometers downstream at Freeport and the Yolo Bypass. During moderately high flows in December 1996, mineralization-related total (dissolved + colloidal) trace-metal loads to the Bay-Delta (as a percentage of total loads measured downstream) were cadmium, 87 percent; copper, 35 percent; lead, 10 percent; and zinc, 51 percent. During flood conditions in January 1997 loads were cadmium, 22 percent; copper, 11 percent; lead, 2 percent; and zinc, 15 percent. During irrigation drainage season from rice fields (May-June 1997) loads were cadmium, 53 percent; copper, 42 percent; lead, 20 percent; and zinc, 75 percent. These estimates must be qualified by the following factors: (1) metal loads at Colusa in December 1996 and at Verona in May-June 1997 generally exceeded those determined at Freeport during those sampling periods. Therefore, the above percentages represent maximum estimates of the apparent total proportion of metals from mineralized areas upstream of Keswick Dam; and (2) for logistics reasons, the Sacramento River was sampled at Tower Bridge instead of at Freeport during January 1997.

Available data suggest that trace metal loads from agricultural drainage may be significant during certain flow conditions in areas where metals such as copper and zinc are added as agricultural amendments. Copper loads for sampling periods in July and September 1996 and in May-June 1997 show increases of dissolved and colloidal copper and in colloidal zinc between Colusa and Verona, the reach of the Sacramento River along which the Colusa Basin Drain, the Sacramento Slough, and other agricultural return flows are tributaries. Monthly sampling of these two agricultural drains by the USGS National Water-Quality Assessment Program shows seasonal variations in metal concentrations, reaching maximum concentrations of 4 to 6 micrograms per liter in "dissolved" (0.45-micrometer filtrate) copper concentrations in May 1996, December 1996, and June 1997. The total (dissolved plus colloidal) load of copper from the Colusa Basin Drain in June 1997 was 18 kilograms per day, whereas the copper load in Spring Creek, which drains the inactive mines on Iron Mountain, was 20 kilograms per day during the same sampling period. For comparison, during the January 1997 flood, the copper load in Spring Creek was about 1,100 kilograms per day and the copper load in the Yolo Bypass was about 7,300 kilograms per day. The data clearly indicate that most copper and zinc loads during the January 1997 flood entered the Sacramento River upstream of Colusa, and upstream of the influence of the most intense agricultural drainage return flows in the Sacramento River watershed.

This study has demonstrated that some trace metals of environmental significance (cadmium, copper, and zinc) in the Sacramento River are transported largely in dissolved form at upstream sites (below Shasta Dam, below Keswick Dam, and at Bend Bridge) proximal to the mineralized areas of the West Shasta and East Shasta mining districts. In contrast, these trace metals are transported largely in colloidal form at downstream sites (Colusa, Verona, Freeport, and Yolo Bypass). Aluminum, iron, and lead were observed to be transported predominantly in the colloidal phase at all mainstem Sacramento River sampling sites during all sampling periods in this study. Despite continuous water treatment, which has removed 85 to 90 percent of the cadmium, copper, and zinc from the mine drainage at Iron Mountain, Spring Creek remains a significant source of these metals to the Sacramento River system.


Executive Summary



Previous Work and Related Ongoing Studies

Purpose and Scope


Computation of Metal Loads


Dissolved Loads

Colloidal Loads

Transport Plots

Total Recoverable Loads

Colloid Speciation Data

Uncertainties in Metal Loads

Discussion of Spatial and Temporal Variations in Metal Loads

Temporal Variations in Dissolved and Colloidal Loads

Cadmium, Copper, and Zinc

Lead, Aluminum, and Iron

Discussion of Transport and Fate of Metals from Various Sources

Copper-Zinc-Lead Mines in the Shasta Region

Mines Draining into Shasta Lake and Its Tributaries

Mines Draining into Keswick Reservoir and Its Tributaries

Mass Balance and Metal Transport in Keswick Reservoir

Mass Balance in the Spring Creek Arm of Keswick Reservoir

Overall Mass Balance in Keswick Reservoir

Metal Sources Downstream of Keswick Dam

Tributaries Between Keswick Dam and Colusa

Tributaries Between Colusa and Freeport

Agricultural Drainage

Urban Runoff

Summary and Conclusions

Appendix 1. Tables of Data Comparing Metal Loads in Dissolved Form, Colloidal Form, and Whole Water

Appendix 2. Tables of Data Comparing Metal Loads Relative to Loads at Freeport and in the Yolo Bypass

Appendix 3. Tables of Data Comparing Metal Loads Used in Mass Balance Calculations for the

Spring Creek Arm of Keswick Reservoir

Appendix 4. Tables of Data Comparing Metal Loads Used in Mass Balance Calculations for Keswick Reservoir

Appendix 5. Plots of Metal Loads in Dissolved and Colloidal Forms for Miscellaneous Trace Metals in Water

Appendix 6. Hydrographs Showing Daily Mean Discharge and Time of Sampling

Water Resources of California

U.S. Department of the Interior, U.S. Geological Survey
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