Sources of Metal Loads to the Alamosa River andEstimation of Seasonal and Annual Metal Loads forthe Alamosa River Basin, Colorado, 199597
by Roderick Ortiz, Patrick Edelmann, Sheryl Ferguson, and Robert Stogner, Sr.
Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources Investigations Report 024128, 50 p., 36 figs.
Metal contamination in the upper Alamosa River Basin has occurred for decades from the Summitville Mine site, from other smaller mines, and from natural, metal-enriched acidic drainage in the basin. In 1995, the need to quantify contamination from various source areas in the basin and to quantify the spatial, seasonal, and annual metal loads in the basin was identified. Data collection occurred from 1995 through 1997 at numerous sites to address data gaps. Metal loads were calculated and the percentages of metal load contributions from tributaries to three risk exposure areas were determined. Additionally, a modified time-interval method was used to estimate seasonal and annual metal loads in the Alamosa River and Wightman Fork.
Sources of dissolved and total-recoverable aluminum, copper, iron, and zinc loads were determined for Exposure Areas 3a, 3b, and 3c. Alum Creek is the predominant contributor of aluminum, copper, iron, and zinc loads to Exposure Area 3a. In general, Wightman Fork was the predominant source of metals to Exposure Area 3b, particularly during the snowmelt and summer-flow periods. During the base-flow period, however, aluminum and iron loads from Exposure Area 3a were the dominant source of these metals to Exposure Area 3b. Jasper and Burnt Creeks generally contributed less than 10 percent of the metal loads to Exposure Area 3b. On a few occasions, however, Jasper and Burnt Creeks contributed a substantial percentage of the loads to the Alamosa River. The metal loads calculated for Exposure Area 3c result from upstream sources; the primary upstream sources are Wightman Fork, Alum Creek, and Iron Creek. Tributaries in Exposure Area 3c did not contribute substantially to the metal load in the Alamosa River.
In many instances, the percentage of dissolved and/or total-recoverable metal load contribution from a tributary or the combined percentage of metal load contribution was greater than 100 percent of the metal load at the nearest downstream site on the Alamosa River. These data indicate that metal partitioning and metal deposition from the water column to the streambed may be occurring in Exposure Areas 3a, 3b, and 3c. Metals that are deposited to the streambed probably are resuspended and transported downstream during high streamflow periods such as during snowmelt runoff and rainfall runoff.
Seasonal and annual dissolved and totalrecoverable aluminum, copper, iron, and zinc loads> for 199597 were estimated for Exposure Areas 1, 2, 3a, 3b, and 3c. During 199597, many tons of metals were transported annually through each exposure area. Generally, the largest estimated annual totalrecoverable metal mass for most metals was in 1995. The smallest estimated annual total-recoverable metal mass was in 1996, which also had the smallest annual streamflow. In 1995 and 1997, more than 60 percent of the annual total-recoverable metal loads generally was transported through each exposure area during the snowmelt period. A comparison of the estimated storm load at each site to the corresponding annual load indicated that storms contribute less than 2 percent of the annual load at any site and about 5 to 20 percent of the load during the summer-flow period.
Table of Contents
Purpose and Scope
Description of Study Area
Methods of Data Collection and Analysis
Methods of Collection and Analysis Used to Quantify Contamination from Various Source Areas
Methods of Collection and Analysis Used to Estimate Seasonal and Annual Metal Loads
Sources of Metal Loads to the Alamosa River
Alamosa River Upstream from Wightman Fork (Exposure Area 3a)
Alamosa River from Wightman Fork to Fern Creek (Exposure Area 3b)
Alamosa River from Fern Creek to Terrace Reservoir (Exposure Area 3c)
Estimation of Seasonal and Annual Metal Loads at Selected Sites.
Wightman Fork at WF5.5 (Exposure Area 1)
Wightman Fork at WF0.0 (Exposure Area 2)
Alamosa River at AR45.5 (Exposure Area 3a)
Alamosa River at AR43.6 (Exposure Area 3b)
Alamosa River at AR41.2 and AR34.5 (Exposure Area 3c)
Alamosa River at AR31.0 (Exposure Area 5)
Water Resources of Colorado
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