Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97
By Roderick Ortiz, Patrick Edelmann, Sheryl Ferguson, and Robert Stogner, Sr.
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 02-4128
Prepared in cooperation with the U.S. ENVIRONMENTAL PROTECTION AGENCY
Denver, Colorado 2002 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary
U.S. GEOLOGICAL SURVEY Charles G. Groat, Director
The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.
For additional information write to: Copies of this report can be purchased from:
District Chief U.S. Geological Survey U.S. Geological Survey Information Services Box 25046, Mail Stop 415 Box 25286 Denver Federal Center Federal Center Denver, CO 80225-0046 Denver, CO 80225 CONTENTS
Abstract...... 1 Introduction...... 1 Purpose and Scope...... 3 Description of Study Area ...... 4 Methods of Data Collection and Analysis ...... 4 Methods of Collection and Analysis Used to Quantify Contamination from Various Source Areas...... 5 Methods of Collection and Analysis Used to Estimate Seasonal and Annual Metal Loads ...... 8 Sources of Metal Loads to the Alamosa River ...... 9 Alamosa River Upstream from Wightman Fork (Exposure Area 3a)...... 10 Alamosa River from Wightman Fork to Fern Creek (Exposure Area 3b)...... 15 Alamosa River from Fern Creek to Terrace Reservoir (Exposure Area 3c)...... 20 Estimation of Seasonal and Annual Metal Loads at Selected Sites...... 20 Wightman Fork at WF5.5 (Exposure Area 1)...... 20 Wightman Fork at WF0.0 (Exposure Area 2)...... 28 Alamosa River at AR45.5 (Exposure Area 3a)...... 31 Alamosa River at AR43.6 (Exposure Area 3b) ...... 32 Alamosa River at AR41.2 and AR34.5 (Exposure Area 3c) ...... 35 Alamosa River at AR31.0 (Exposure Area 5) ...... 39 Summary...... 48 Selected References ...... 49
FIGURES 1. Map showing location of study area, risk assessment exposure areas, and water-quality sampling sites in the Alamosa River Basin...... 2 2. Graph showing daily mean streamflow and number of water-quality samples collected at AR34.5, 1995–97 ..... 5 3. Depiction of hypothetical hydrographs showing selected sample points and estimated traveltime of theoretical parcel of water between downstream sites ...... 7 4. Example diagram of a boxplot...... 10 5–16. Boxplots showing: 5. Percentage of contribution of aluminum load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97...... 11 6. Percentage of contribution of copper load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97...... 12 7. Percentage of contribution of iron load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97...... 13 8. Percentage of contribution of zinc load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97 ...... 14 9. Percentage of contribution of aluminum load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97 ...... 16 10. Percentage of contribution of copper load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97...... 17 11. Percentage of contribution of iron load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97...... 18 12. Percentage of contribution of zinc load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97...... 19 13. Percentage of contribution of aluminum load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97...... 21 14. Percentage of contribution of copper load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97...... 22
CONTENTS III 5–16. Boxplots showing—Continued 15. Percentage of contribution of iron load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97...... 23 16. Percentage of contribution of zinc load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97...... 24 17–36. Graphs showing: 17. Cumulative streamflow for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97 ...... 25 18. Mass of aluminum and copper for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97 ...... 26 19. Mass of iron and zinc for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97 ...... 27 20. Cumulative streamflow for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97 ...... 28 21. Mass of aluminum and copper for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97...... 29 22. Mass of iron and zinc for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97...... 30 23. Cumulative streamflow for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97...... 32 24. Mass of aluminum and copper for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97...... 33 25. Mass of iron and zinc for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97...... 34 26. Cumulative streamflow for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97...... 36 27. Mass of aluminum and copper for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97 ...... 37 28. Mass of iron and zinc for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97 ...... 38 29. Cumulative streamflow for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97 ...... 40 30. Mass of aluminum for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97 ...... 41 31. Mass of copper for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97...... 42 32. Mass of iron for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97 ...... 43 33. Mass of zinc for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97...... 44 34. Cumulative streamflow for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97...... 45 35. Mass of aluminum and copper for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97 ...... 46 36. Mass of iron and zinc for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97 ...... 47
TABLES
1. Ecological risk exposure areas, corresponding stream reach, and U.S. Geological Survey sampling sites ...... 3 2. Flow periods and duration of flow periods in the Alamosa River Basin, 1995–97 ...... 6 3. Approximate periods of operation for streamflow gages on the Alamosa River and Wightman Fork, 1995–97 ...... 9
IV CONTENTS CONVERSION FACTORS, ABBREVIATED UNITS, AND ACRONYMS
Multiply By To obtain cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) foot (ft) 0.3048 meter (m) inch 25.4 millimeter (mm) mile 1.609 kilometer (km) square mile (mi2) 2.590 square kilometer (km2)
Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.
Other abbreviation used in this report:
USGS U.S. Geological Survey USEPA U.S. Environmental Protection Agency ARL Analytical reporting limit
CONTENTS V Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97
By Roderick Ortiz, Patrick Edelmann, Sheryl Ferguson, and Robert Stogner, Sr.
Abstract In many instances, the percentage of dissolved and/or total-recoverable metal load contribution from Metal contamination in the upper Alamosa a tributary or the combined percentage of metal load River Basin has occurred for decades from the contribution was greater than 100 percent of the metal Summitville Mine site, from other smaller mines, and load at the nearest downstream site on the Alamosa from natural, metal-enriched acidic drainage in the River. These data indicate that metal partitioning and basin. In 1995, the need to quantify contamination metal deposition from the water column to the from various source areas in the basin and to quantify streambed may be occurring in Exposure Areas 3a, 3b, the spatial, seasonal, and annual metal loads in the and 3c. Metals that are deposited to the streambed basin was identified. Data collection occurred from probably are resuspended and transported downstream 1995 through 1997 at numerous sites to address data during high streamflow periods such as during snow- gaps. Metal loads were calculated and the percentages melt runoff and rainfall runoff. of metal load contributions from tributaries to three Seasonal and annual dissolved and total- risk exposure areas were determined. Additionally, a recoverable aluminum, copper, iron, and zinc loads modified time-interval method was used to estimate for 1995–97 were estimated for Exposure Areas 1, 2, seasonal and annual metal loads in the Alamosa River 3a, 3b, and 3c. During 1995–97, many tons of metals and Wightman Fork. were transported annually through each exposure Sources of dissolved and total-recoverable area. Generally, the largest estimated annual total- aluminum, copper, iron, and zinc loads were deter- recoverable metal mass for most metals was in 1995. mined for Exposure Areas 3a, 3b, and 3c. Alum Creek The smallest estimated annual total-recoverable metal is the predominant contributor of aluminum, copper, mass was in 1996, which also had the smallest annual iron, and zinc loads to Exposure Area 3a. In general, streamflow. In 1995 and 1997, more than 60 percent of Wightman Fork was the predominant source of metals the annual total-recoverable metal loads generally was to Exposure Area 3b, particularly during the snowmelt transported through each exposure area during the and summer-flow periods. During the base-flow snowmelt period. A comparison of the estimated storm period, however, aluminum and iron loads from Expo- load at each site to the corresponding annual load indi- sure Area 3a were the dominant source of these metals cated that storms contribute less than 2 percent of the to Exposure Area 3b. Jasper and Burnt Creeks gener- annual load at any site and about 5 to 20 percent of the ally contributed less than 10 percent of the metal loads load during the summer-flow period. 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 INTRODUCTION metal loads calculated for Exposure Area 3c result from upstream sources; the primary upstream sources The upper Alamosa River Basin is a heavily are Wightman Fork, Alum Creek, and Iron Creek. mineralized area located in the San Juan Mountains of Tributaries in Exposure Area 3c did not contribute southwestern Colorado (fig. 1). Metal contamination substantially to the metal load in the Alamosa River. has occurred for decades from the Summitville Mine
Abstract 1 TERRACE RESERVOIR Hydrology modified by Denver Water Board, 1998 Water by Denver Hydrology modified C O L O R A D O C O L R
Alamosa River 37'30" ˚
106 Cr Creek Ranger
Lieutenant
Creek
Silver Cr
Water-quality sampling site and Water-quality station streamflow-gaging Water-quality sampling site and number Water-quality Fern
Cr
Spring
Creek
Burnt Gulch an
Creek Castlem EXPLANATION Jasper
Fork 00 1 1 2 2 3 3 4 5 KILOMETERS 4 5 MILES
Cr Wightman Summitville Mine Site Exposure areas Approximate extent of hydrothermal Approximate extent alteration
Bitter Cr Cr
Alum Cropsy 28' ˚ 37 Creek Iron 37'30" ˚ 106 . Location of study area, risk assessment exposure areas, and water-quality sampling sites in the Alamosa River Basin. River Alamosa in the sites sampling and water-quality areas, exposure assessment risk area, of study . Location Base from U.S. Geological Survey Digital Line Graphs, 1:100,000, 1982 Base from U.S. Geological Survey Mercator projection, Zone 13 Transverse Universal 22'30" ˚ Figure 1 Figure 37
2 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 site, from other smaller mines, and from natural, several continuous streamflow gages and water-quality metal-enriched acidic drainage in the basin (Miller and monitors. In addition, periodic water-quality sampling McHugh, 1994). Mining activities have occurred inter- on the Alamosa River, Wightman Fork, and several mittently in the Summitville area since the late 1800’s. other tributaries was established. Data collected from Large-scale open-pit mining began at the Summitville the network from 1995 through 1997 were used to Mine site in the mid-1980’s and continued until the address the data gaps identified in the risk assessment. mine site was suddenly abandoned in late 1992. At that time, the State of Colorado requested the U.S. Environmental Protection Agency (USEPA) to assume Purpose and Scope site-maintenance responsibilities under the emergency response provisions of Superfund. Since 1992, the site has undergone substantial waste-pile consolidation, The purposes of this report are (1) to quantify runoff rerouting, water treatment, and reclamation. In metal contamination and contribution from various 1998, the State of Colorado assumed shared site source areas and (2) to estimate seasonal and annual responsibility of the Summitville site with the USEPA. metal loads at selected sites in the Alamosa River Data-collection activities by the U.S. Geological Basin from 1995 through 1997. Survey (USGS) began in 1993 and included stream- This study was done to address specific data flow measurements and water-quality sampling at gaps identified in the original risk assessment of the several surface-water sites on the Alamosa River and Summitville Superfund site. The risk assessment Wightman Fork. In 1994, investigative work by the addendum (Camp Dresser and McKee Inc., 2000) will USGS was limited to Terrace Reservoir and the inflow provide the results from this and several other studies and outflow sites to the reservoir (fig. 1). In 1995, to the USEPA so that informed decisions regarding the Morrison-Knudsen Corporation and ICF Kaiser need for remedial actions can be made. As part of the Engineers (1995) identified multiple data gaps needed risk assessment addendum, the potentially impacted for ecological risk assessment of the Summitville Superfund site. Two of the data gaps identified were region downstream from the Summitville Mine site the need to quantify metal contamination from various was divided into six exposure areas to address risks source areas in the basin and the need to quantify the related to specific contaminants of concern on an area- spatial, seasonal, and annual metal loads in the basin. by-area basis. The locations of the six exposure areas As a result, the USGS developed a comprehensive are described in table 1 and are shown in figure 1. data-collection plan for the basin to address these data The contaminants of concern addressed in the risk gaps (Patrick Edelmann, U.S. Geological Survey, assessment and in this report are dissolved and total- written commun., 1995). The plan included the use of recoverable aluminum, copper, iron, and zinc.
Table 1. Ecological risk exposure areas, corresponding stream reach, and U.S. Geological Survey sampling sites
[EA, exposure area; USGS, U.S. Geological Survey]
USGS sampling site Exposure area Stream reach within the exposure area (see figure 1) (see figure 1) EA1 Summitville Mine site WF5.5 EA2 Wightman Fork downstream from WF5.5 WF0.0 EA3a Alamosa River upstream from Wightman Fork AR45.5 EA3b Alamosa River from Wightman Fork to Fern Creek AR43.6 EA3c Alamosa River from Fern Creek to Terrace Reservoir AR41.2 and AR34.5 EA4 Terrace Reservoir Not addressed in this report EA5 Alamosa River downstream from Terrace Reservoir AR31.0
INTRODUCTION 3 Description of Study Area the mouth of the Alamosa River. Routine water-quality samples were collected 8 to 12 times per year at these The upper Alamosa River Basin is located in the sites; figure 2 illustrates the temporal distribution of San Juan volcanic fields of southwest Colorado the sampling events over the 3 years of data collection. (fig. 1). The study area has a drainage area of approxi- One additional site on the Alamosa River (AR49.5) mately 110 square miles and extends from near the was designated as a background site. Several other headwaters of the Alamosa River to just above Terrace tributaries were sampled less often, based on their Reservoir (Stogner and others, 1996). Elevations in the potential metal contribution to the Alamosa River. study area range from 8,400 feet to nearly 13,000 feet Tributaries that drain hydrothermally altered areas above sea level. Annual precipitation ranges from were sampled seven to nine times per year from April approximately 12 inches at the lower elevations to as through October. These sites include Iron Creek much as 40 inches at the top of the highest peaks (IC0.0), Alum Creek (AC0.0), Bitter Creek (BI0.0), (Miller and McHugh, 1994). Most of the precipitation Jasper Creek (JC0.0) and Burnt Creek (BC0.0) (fig. 1). is in the form of snowfall. The Alamosa River Other tributaries that drained areas unaffected by upstream from Wightman Fork receives water from mining were sampled four to five times per year, the Iron, Alum, and Bitter Creek drainages, which are primarily during the snowmelt and summer flow. geomorphically degraded and have been for nearly These tributaries were Spring Creek (SC0.0), Fern 5 million years (Bove and others, 1996). Low-pH Creek (FC0.0), Castleman Gulch (CG0.0), Silver water with high concentrations of trace metals from Creek (SI0.0), Lieutenant Creek (LC0.0), and the Summitville Mine site adversely affects Wightman Ranger Creek (RC0.0). The samples were collected Fork and several miles of the Alamosa River down- as described by Horowitz and others (1994) and stream from the confluence with Wightman Fork. The in the USGS comprehensive data-collection plan oxidation of the ubiquitous pyrite stock in the area (Patrick Edelmann, U.S. Geological Survey, written results in acidic water and the release of metals. The commun., 1995). Streamflow measurements were oxidation of pyrite is summarized in Wentz (1974) and done at all tributary sites at the time of sample in Nordstrom (1982). From the mouth of Wightman collection. Fork, the Alamosa River flows east through the The concentration and streamflow data used Alamosa Canyon for about 14 miles before reaching in the analyses of this report are available from Terrace Reservoir. Several small tributary flows enter the Colorado Department of Public Health and the Alamosa River along this reach including Jasper Environment, Hazardous Materials and Waste and Burnt Creeks, which drain hydrothermally altered Management Division, 4300 Cherry Creek Drive areas. Terrace Reservoir is a small irrigation reservoir South, Denver, CO, 80222–1530. The data include that supplies water for agricultural use in the San Luis all instantaneous streamflow values from 1995 valley (Ferguson and Edelmann, 1996). through 1997. In addition, the data include dissolved and total-recoverable metal concentrations for grab samples, discrete samples collected using automatic METHODS OF DATA COLLECTION samplers, and flow-weighted composite samples AND ANALYSIS collected during the same period. Water-quality data collected during storm events also are included. To meet the objectives of this study, the USGS Grab samples (discrete and equal-width increment), collected instantaneous streamflow and periodic composite, and storm samples can be found in the data water-quality data at five sites on the Alamosa River base under the general heading of “sample type.” (AR45.5, AR43.6, AR41.2, AR34.5, and AR31.0) and The annual hydrograph has four distinct two sites on Wightman Fork (WF5.5 and WF0.0) from seasonal flow regimes or flow periods: base flow, early 1995 through 1997 (fig. 1). Site nomenclature uses a snowmelt, snowmelt, and summer flow (fig. 2). The two-letter designation for the stream followed by a timing and duration of these flow periods vary from river mileage (in miles) from the mouth. Hence, year to year depending on the weather conditions and WF5.5 is on Wightman Fork 5.5 miles upstream from the available snowpack at the higher elevations
4 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 LT LT E ELT M W M ME W LO W LOW W LO W OW LT F W O W T F W O E N ELT NO EL L SN LO S LO LO F M ER F M ER F F Y S M ER F E LY W E LY W S R O MM R OW MM SE RL O MM SE A N U AS N A N B EA S S B EA S SU BA E S SU BA 1,000
900
800
700
600
500
400 FEET PER SECOND 300
200 DAILY MEAN STREAMFLOW, IN CUBIC
100
0 JFMAMJ J ASONDJFMAMJJ ASONDJFMAMJJ A SON D 1995 1996 1997
EXPLANATION STREAMFLOW STORM SAMPLE
GRAB SAMPLE COMPOSITE WITH MULTIPLE DISCRETE SAMPLES
Figure 2. Daily mean streamflow and number of water-quality samples collected at AR34.5, 1995–97.
(table 2). The water-quality data were analyzed and prevailing weather patterns. The summer-flow regime summarized for each of these four flow periods. The is delineated by a decrease in streamflow and a gradual base-flow period is characterized by relatively steady- return to base-flow conditions; nearly all significant state low-flow conditions. Typically, base flow extends rainfall events occur during this period. from early October through early April. The early snowmelt flow regime is delineated by a departure Methods of Collection and Analysis Used from base flow as the first substantial snowmelt condi- to Quantify Contamination from Various tions become apparent. This “first flush” period is rela- Source Areas tively short in duration but can be associated with large metal loading to the river. The snowmelt-flow regime Selected water-quality and streamflow data is characterized by the annual peak streamflow and collected from all sites were used to quantify contami- provides the largest percentage of the annual stream- nation and assess the metal contribution from various flow in the river. The extent of the snowmelt period in exposure areas in the basin. Metal concentrations from the basin from 1995 to 1997 was highly variable analysis of water-quality samples and corresponding depending on the amount of snowpack and the streamflow measurements were used to calculate metal
METHODS OF DATA COLLECTION AND ANALYSIS 5 loads at each sampling site for each sampling date. by dividing the metal load at Alum Creek by the metal The following equation was used to compute metal load from the corresponding sample collected at loads: AR45.5. The formula is as follows: []Load() AC0.0 ------× 100 = percentage of metal load Load= () C × Q × M []Load() AR45.5 metal site contribution from Alum Creek where Load is mass of metal, in tons per day, Percentages of metal load contributions were calculated for each tributary and flow period and C is concentration of metal, in micrograms metal grouped by exposure area. per liter, During base-flow conditions, water-quality Qsite is streamflow, in cubic feet per second, samples were collected only once at each site during a and sampling event because relatively little diurnal varia- –7 M is conversion factor of 26.98×10 . tion in metal load was expected between October and Generally, less than 3 percent of the total-recov- March. Water-quality samples generally were erable concentrations at gaged stations were less than collected from all Alamosa River sites, Wightman the reporting limit. Less-than values were more preva- Fork sites, and sites on Iron, Alum, Bitter, Jasper, and lent among dissolved concentrations but most were Burnt Creeks. Instantaneous streamflow measure- associated with aluminum values. If censored concen- ments were done at all sites during base flow. tration data were reported, the reporting limit was Dissolved and total-recoverable aluminum, copper, substituted for the analytical value in the analysis. iron, and zinc loads were calculated and percentage of AR45.5 had the largest overall percentage of less-than contributions to downstream sites were calculated as values among the gaged sites. described previously. During nonsteady-state streamflow conditions, Table 2. Flow periods and duration of flow periods in the Alamosa River Basin, 1995–97 large diurnal variations in streamflow and metal concentrations occur in the Alamosa River and Flow Duration, Wightman Fork (Ortiz and Stogner, 2000). Conse- Date range periods (in days) quently, large variations in metal loads also occur 1995 during these periods. In an effort to collect comparable Base flow January 1–March 20 79 samples, multiple water-quality samples were Early snowmelt March 21–April 29 40 collected at WF5.5, WF0.0, AR45.5, AR43.6, Snowmelt April 30–August 1 94 AR41.2, and AR34.5 using automatic samplers. The Summer flow August 2–October 5 65 automatic samplers were programmed to collect as 1995–1996 Base flow October 6–March 28 175 many as six discrete sample sets at each site during a Early snowmelt March 29–April 25 28 diurnal period (24 hours). The first sample at each Snowmelt April 26–June 20 56 site was collected from the same parcel of water as Summer flow June 21–October 5 107 the parcel moved downstream from the Summitville 1996–1997 Mine to Terrace Reservoir; samples at WF0.0 and Base flow October 6–April 18 195 AR45.5 were collected at the same time because of Early snowmelt April 19–May 5 17 the close proximity of the two sites (fig. 1). The other Snowmelt May 6–July 5 61 sets of samples accomplished in the same manner but Summer flow July 6–October 18 105 on different parts of the hydrograph (fig. 3). The specific timing of the sample collection at each site Percentages of metal load contributions from was determined just prior to the start of sampling by tributaries were determined for each sample collected using satellite-transmitted streamflow data from each by dividing the metal load at the tributary site by the gaging station to compare and determine traveltimes metal load at the nearest downstream Alamosa River between downstream sites. A description of these site. For example, the percentage of metal load contri- methods used can be found in Ortiz and Stogner bution from Alum Creek to AR45.5 was determined (2000).
6 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 Downstream direction SITE 1 SITE 2
SITE 3 C 3
C 2 Travel- time D 3
Travel- C1 time D 2 Stream hydrograph
B 3
D1
B1 B 2 STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW,
E 3 A 3 E2 A 2 A 1
E1
TIME, IN HOURS
Figure 3. Depiction of hypothetical hydrographs showing selected sample points and estimated traveltime of theoretical parcel of water between downstream sites.
Sites AR49.5 and AR31.0 were not equipped located at or near the mouth of (in downstream order) with automatic samplers and were only sampled once Iron Creek, Alum Creek, Bitter Creek, Jasper Creek, during each sampling event. The background site, Burnt Creek, Spring Creek, Fern Creek, Castleman AR49.5, was sampled upstream from its confluence Gulch, Silver Creek, Lieutenant Creek, and Ranger with Iron Creek at approximately the same time as Creek (fig. 1). IC0.0 (Iron Creek). The loads from AR49.5 were used Sources of metals to the Alamosa River were to determine the contribution of metal loads entering evaluated using data collected from a specific parcel of Exposure Area 3a. Hereafter in this report, Exposure water as it flowed through the study area. The specific Area will be designated as “EA.” The metal load at parcel was identified from those sites equipped with AR31.0 (Alamosa River below Terrace Reservoir) was automatic samplers and was chosen to coincide with not expected to change throughout a diurnal cycle and, the approximate traveltime of water sampled at tribu- as such, a single sample was deemed representative of tary sites. Generally, tributary sites were collected the daily mean concentration. within a 6-hour period around noon. Occasionally, Water-quality samples also were collected from tributaries were not sampled on the same day as the tributaries other than Wightman Fork during each sites equipped with automatic samplers. In these cases, sampling event. Typically, only one sample was an effort was made to ensure that the data used from collected at each tributary site. The tributary sites were the automatic samplers were collected at approxi-
METHODS OF DATA COLLECTION AND ANALYSIS 7 mately the same time of day that the tributaries were 1995 through 1997. Methods for processing flow- sampled and that no major changes in streamflow had weighted composite samples were consistent with occurred. Storm samples were not included in the data those described by the USEPA (1991). Appropriate set when evaluating loads and percentage of contribu- concentration data were logarithmically transformed tions from source areas. (log base 10) and averaged. The averages then were Streamflow data accompanied most water- retransformed (antilog of the transformed averages) to quality samples collected during nonsteady-state obtain nonskewed, estimated average metal concentra- periods. Generally, instantaneous data were retrieved tions. This type of data transformation is commonly from the data loggers at gaged sites providing the used with water-quality data because of the generally gage was operational. Streamflow measurements log-normal distribution of the positively skewed data were not made at AR41.2, AR43.6, AR45.5, WF0.0, (Helsel and Hirsch, 1992). However, the statistical and WF5.5 from April through June 1995 because certainties of the average concentrations determined streamflow gages had not been installed and high by this method are unknown because of the small streamflow conditions were unwadeable. As a result, number of samples collected during each flow period load calculations, could not be made for these (fig. 2). samples. Streamflow measurements were done in Streamflow for each flow period was deter- conjunction with water-quality samples collected at mined by summing the reported daily streamflow for tributary sites. the flow period at each gaged site. Streamflow gages at sites AR34.5 and AR31.0 were operated throughout much of the year by the Colorado Division of Water Methods of Collection and Analysis Used Resources (McDonald, 1996, 1997, and 1998). to Estimate Seasonal and Annual Metal Streamflow gages at sites WF5.5, WF0.0, AR45.5, Loads AR43.6, and AR41.2 were installed by the USGS in mid- to late July 1995. The USGS-gaged streamflow Several methods can be used to compute records are reported in the annual water-resources data seasonal and annual metal loads. Estimates using reports for Colorado (Crowfoot and others, 1996, regression equations can be used where there are 1997, and 1998). Table 3 shows the periods of opera- strong correlations between constituents. In the tion for all the gages from 1995 to 1997. Alamosa River, however, relations between the loga- In certain cases, daily streamflow was not avail- rithms of metal concentrations and streamflow able at a site and was estimated by computing the generally were not statistically significant (p<0.10). proportion of instantaneous streamflow measured at Standard time-interval methods divide the data record the site during the flow period to the streamflow into discrete intervals and estimate load as the product measured at AR34.5. Depending on the number of of the concentration for that discrete period and the instantaneous measurements made during the flow sum of the streamflow for that period (Scheider and period, either one proportion or multiple proportions others, 1979). For the purposes of this report, a modi- were used to estimate the cumulative or total stream- fied time-interval method was used to estimate metal flow for the flow period for the ungaged period at the loads. In the modified time-interval method, the data site. record is divided into several discrete time intervals Metal concentrations associated with rainstorm based on changes in streamflow or flow periods. The runoff were not used to compute the average metal mean concentration of the values that occurred during concentrations for the summer-flow period because each flow period was multiplied by the total stream- too few storm samples were collected to adequately flow for the period to determine metal loads for the characterize metal concentrations at each site during flow period. Estimates of the metal loads for each flow storms. As a result, the average metal concentrations period were summed to estimate annual metal loads. and, therefore, loads may be underestimated for the Grab samples collected during steady-state summer-flow period. The available storm data, streamflow conditions and flow-weighted composite however, were analyzed and a semiquantitative discus- samples collected during nonsteady-state streamflow sion of seasonal and annual storm load contribution is conditions were used to compute an average metal presented. First, the storm data were grouped by site concentration at each site for each flow period from and a log-transformed average was computed as
8 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 Table 3. Approximate periods of operation for streamflow gages on the Alamosa River and Wightman Fork, 1995–97
[1234, denotes approximate number of weeks during a month; -, denotes inactive; x, denotes active]
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Site 1234 1234 1234 1234 1234 1234 1234 1234 1234 1234 1234 1234 1995 AR31.0 ------xxxx xxxx xxxx xxxx xxxx xxxx xx------AR34.5 ------xxxx xxxx xxxx xxxx xxxx xxxx xx------AR41.2 ------xxx xxxx xxxx xx------AR43.6 ------xxx xxxx xxxx xx------AR45.5 ------xx xxxx xxxx xx------WF0.0 ------xx xxxx xxxx xx------WF5.5 ------xx xxxx xxxx xx------1996 AR31.0 ------xxxx xxxx xxxx xxxx xxxx xxxx x------AR34.5 ------xxxx xxxx xxxx xxxx xxxx xxxx x------AR41.2 ------xxx xxxx xxxx xxxx xxxx xxxx x------AR43.6 ------xxx xxxx xxxx xxxx xxxx xxxx x------AR45.5 ------xxx xxxx xxxx xxxx xxxx xxxx x------WF0.0 ------xxx xxxx xxxx xxxx xxxx xxxx x------WF5.5 ------xxx xxxx xxxx xxxx xxxx xxxx x------1997 AR31.0 ------xxxx xxxx xxxx xxxx xxxx xxxx xx------AR34.5 ------xxxx xxxx xxxx xxxx xxxx xxxx xx------AR41.2 ------xx xxxx xxxx xxxx xxxx xxxx xx------AR43.6 ------xx xxxx xxxx xxxx xxxx xxxx xx------AR45.5 ------xx xxxx xxxx xxxx xxxx xxxx xx------WF0.0 ------xx xxxx xxxx xxxx xxxx xxxx xx------WF5.5 ------xxxx xxxx xxxx xxxx xxxx xx------
described previously. The average concentrations were odically released water with high metal concentrations multiplied by the median change in streamflow and the and low pH that was not sampled (Rupert, 2001). The median duration of a storm as presented by Rupert releases were generally associated with variations in (2001). The product (load in tons per day) was multi- the operations at the mine site. These releases affect plied by the number of rainstorm runoff events per the accuracy of the estimates of metal loads used in year to estimate the load contributed by storms. this report. Generally, 18 storms were identified during the summer period for each year (Rupert, 2001). A comparison of the estimated storm load at each site to SOURCES OF METAL LOADS TO THE the corresponding annual load indicated that storms ALAMOSA RIVER contribute less than 2 percent of the annual load at any site. When compared to the summer load, storms Sources of dissolved and total-recoverable aluminum, copper, iron, and zinc loads were deter- appeared to contribute from 5 to 20 percent of the mined for Exposure Areas 3a, 3b, and 3c (fig. 1) by load. The highest percentage of contribution was for computing the percentage of contribution of metal total-recoverable aluminum and iron. load for each site relative to the downstream main- In addition to the underestimation of loads due stem site. The equation to calculate the percentage of to storms, the Summitville Mine treatment plant peri- contribution of metal load from each tributary was
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 9 described in a previous section of this report. In addi- boxplots, which show the variation around the median tion, the percentage of contribution of metal load from value of the data. An example of a boxplot is given in the upstream main-stem site to the closest downstream figure 4. main-stem site was calculated in the same manner. This provides a percentage of contribution of the metal load that can be attributed to the Alamosa River Alamosa River Upstream from Wightman upstream from the exposure areas. The percentage of Fork (Exposure Area 3a) contribution of metal loads determined in this manner Sources of metals to the Alamosa River provides an estimate of the contribution of metals from upstream from Wightman Fork, EA3a, were deter- a particular area. In some instances, the percentage of mined for each flow period: base flow, early snowmelt, contribution of metal loads from the tributary site(s) or snowmelt, and summer flow. The source area evalu- the upstream main-stem site is larger than 100 percent ated in EA3a includes the Stunner hydrothermally of the metal load measured at the downstream main- altered area (fig. 1). The water-quality sites evaluated stem site. This indicates that some reaction or process for EA3a were: AR49.5 (Alamosa River upstream occurred within the stream reach that decreased the from Iron Creek), IC0.0 (Iron Creek at the mouth), dissolved and/or total-recoverable metal load in the AC0.0 (Alum Creek at the mouth), and BI0.0 (Bitter water column. Iron and aluminum hydroxide precipi- Creek at the mouth). The percentage of contribution of tates are commonly found on the stream bottom in metal loads from each of these sites is shown in certain areas of the Alamosa River and Wightman figures 5–8. The percentage of contribution of metal Fork. The following sections present the data as loads for AR49.5, IC0.0, AC0.0, and BI0.0 were
Outlier data value greater than 3 times the interquartile range outside the quartile
Outlier data value less than or equal to 3 and more than 1.5 times the interquartile range outside the quartile
Data value less than or equal to 1.5 times the interquartile range outside the quartile
75th percentile (three quarters of data are less than this value)
Interquartile range (one-half of data is 50th percentile (median) within this range)
25th percentile (one quarter of data are less than this value)
Figure 4. Example diagram of a boxplot.
10 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 450 140
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD 400 120
350
100 300
80 250
200 60
150 40
100
20 50 CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT 0 0
3,500 7,000
SNOWMELT PERIOD SUMMER-FLOW PERIOD Maximum total value=7,200 3,000 6,000
2,500 5,000
2,000 4,000
1,500 3,000
1,000 2,000
500 1,000 CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT 0 0 0 AR49.5 IC0.0 AC0.0 BI0.0 AR49.5 IC0.0 AC0.0 BI0.0
EXPLANATION DISSOLVED ALUMINUM INSTANTANEOUS DISSOLVED ALUMINUM
TOTAL-RECOVERABLE ALUMINUM INSTANTANEOUS TOTAL-RECOVERABLE ALUMINUM
Figure 5. Percentage of contribution of aluminum load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 11 160 80 BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
140 70
120 60
100 50
80 40
60 30
40 20
20 10 CONTRIBUTION OF COPPER LOAD, IN PERCENT
0 0
180 350 SNOWMELT PERIOD SUMMER-FLOW PERIOD 160 300
140
250 120
200 100
80 150
60 100
40
50 20 CONTRIBUTION OF COPPER LOAD, IN PERCENT
0 0 AR49.5 IC0.0 AC0.0 BI0.0 AR49.5 IC0.0 AC0.0 BI0.0
EXPLANATION DISSOLVED COPPER INSTANTANEOUS DISSOLVED COPPER
TOTAL-RECOVERABLE COPPER INSTANTANEOUS TOTAL-RECOVERABLE COPPER
Figure 6. Percentage of contribution of copper load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97.
12 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 300 300
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
250 250
200 200
150 150
100 100
50 50 CONTRIBUTION OF IRON LOAD, IN PERCENT
0 0
800 700 SNOWMELT PERIOD SUMMER-FLOW PERIOD
700 600
600 500
500 400
400
300 300
200 200
100 100 CONTRIBUTION OF IRON LOAD, IN PERCENT
0 0 AR49.5 IC0.0 AC0.0 BI0.0 AR49.5 IC0.0 AC0.0 BI0.0
EXPLANATION DISSOLVED IRON INSTANTANEOUS DISSOLVED IRON
TOTAL-RECOVERABLE IRON INSTANTANEOUS TOTAL-RECOVERABLE IRON
Figure 7. Percentage of contribution of iron load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 13 90 50
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD 80 45
40 70
35 60
30 50 25 40 20
30 15
20 10
CONTRIBUTION OF ZINC LOAD, IN PERCENT 10 5
0 0
140 90
SNOWMELT PERIOD SUMMER-FLOW PERIOD 80 120
70
100 60
80 50
40 60
30 40
20
20
CONTRIBUTION OF ZINC LOAD, IN PERCENT 10
0 0 AR49.5 IC0.0 AC0.0 BI0.0 AR49.5 IC0.0 AC0.0 BI0.0
EXPLANATION DISSOLVED ZINC INSTANTANEOUS DISSOLVED ZINC
TOTAL-RECOVERABLE ZINC INSTANTANEOUS TOTAL-RECOVERABLE ZINC
Figure 8. Percentage of contribution of zinc load from Exposure Area 3a (Alamosa River and tributary sites upstream from Wightman Fork), 1995–97.
14 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 computed relative to the metal loads measured at (Wightman Fork at mouth), AR43.6 (Alamosa River AR45.5. upstream from Jasper), JC0.0 (Jasper Creek at the Alum, Iron, and Bitter Creeks contribute mouth), BC0.0 (Burnt Creek at the mouth), and SC0.0 substantially to the metal loads in EA3a. The predomi- (Spring Creek at the mouth). The percentage of contri- nant contributor of dissolved and total-recoverable bution of metal loads from each of these sites are aluminum, copper, iron, and zinc loads to EA3a is shown in figures 9–12. The percentage of contribution Alum Creek. Frequently, the percentage of contribu- of metal loads from AR45.5 and WF0.0 were tion of metal loads from Alum Creek was greater than computed relative to the metal loads measured at the combined metal load contribution from Iron Creek AR43.6, and the percentage of contribution of metal and Bitter Creek. Generally, Iron Creek was a greater loads from AR43.6, JC0.0, BC0.0, and SC0.0 were source of metals to EA3a than Bitter Creek. The computed relative to AR41.2. Alamosa River upstream from Iron Creek (AR49.5) is During the base-flow period, the pH of the shown to contribute a fair percentage of copper and Alamosa River at AR45.5 was at its annual minimum zinc for some flow regimes or periods. It should be and the pH of the Wightman Fork generally was at its noted that much of the copper and zinc concentration annual maximum. During this period, the predominant data at AR49.5 were reported as less than the analyt- contribution of dissolved and total-recoverable ical reporting limit (ARL). A decision was made to use aluminum and iron loads to EA3b was from EA3a, as the ARL when calculating loads because, generally, indicated by the metal loads at AR45.5 (figs. 9 and the ARL was representative of other reported concen- 11). Additionally, EA3a generally contributed more trations. As such, the use of the ARL to calculate loads than 30 percent of the dissolved and total-recoverable at AR49.5 provides a relatively good estimate, albeit a zinc loads to EA3b during base flow (fig. 12). EA3a slightly higher estimate, of the copper and zinc load generally was the predominant contributor of total- contribution to EA3a. recoverable iron load to EA3b during the early snow- As shown in figures 5–8, there were several melt period (fig. 11). instances where the percentage of metal load contribu- During early snowmelt, snowmelt, and summer- tion from a tributary or several tributaries was greater flow periods, Wightman Fork was the predominant than 100 percent of the measured metal load at contributor of dissolved aluminum. Wightman Fork AR45.5. This indicates that, with respect to dissolved was the predominant contributor of dissolved iron load metal loads, the dissolved metal partitioned to the to AR43.6 during snowmelt periods. During base flow, suspended or particulate phase within the exposure early snowmelt, snowmelt, and summer flow, area; and with respect to total-recoverable metal loads, Wightman Fork was the predominant contributor of the suspended or particulate metal settled from the dissolved and total-recoverable copper loads. water column to the streambed within the exposure Throughout the year, Wightman Fork was the predom- area. Metals that are deposited to the streambed are inant contributor of dissolved and total-recoverable probably resuspended and transported downstream zinc loads. There were several instances where the during high streamflow associated with snowmelt percentages of dissolved aluminum, copper, iron, and runoff and during rainfall runoff in the summer. zinc loads and total-recoverable copper and zinc loads from Wightman Fork were greater than 100 percent of the metal load at AR43.6. Additionally, there were Alamosa River from Wightman Fork to occurrences where the dissolved and total-recoverable Fern Creek (Exposure Area 3b) aluminum and iron loads at AR45.5 were greater than 100 percent of the metal load at AR43.6. These data Sources of metals to the Alamosa River from indicate that, during certain times, metal partitioning Wightman Fork to Fern Creek, EA3b, were deter- and metal deposition from the water column to the mined for each flow period: base flow, early snowmelt, streambed may be occurring in the reach between snowmelt, and summer flow. The source areas evalu- Wightman Fork and AR43.6, a distance of 2.1 miles. ated in EA3b include Wightman Fork and the Jasper Downstream from AR43.6, Jasper and Burnt hydrothermally altered area (fig. 1). The water-quality Creeks generally contributed less than 10 percent of sites evaluated for EA3b were: AR45.5 (Alamosa the metal loads relative to AR41.2. However, on a few River upstream from Wightman Fork), WF0.0 occasions, Burnt Creek contributed a substantial
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 15 700 600
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
600 500
500 400
400
300
300
200 200
100 100 CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT NO DATA NO DATA NO DATA 0 0
1,000 1,000
SNOWMELT PERIOD SUMMER-FLOW PERIOD
Maximum dissolved 800 800 value=1,850
600 600
400 400
200 200 CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA 0 0 AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0 AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0
EXPLANATION DISSOLVED ALUMINUM INSTANTANEOUS DISSOLVED ALUMINUM
TOTAL-RECOVERABLE ALUMINUM INSTANTANEOUS TOTAL-RECOVERABLE ALUMINUM
Figure 9. Percentage of contribution of aluminum load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97.
16 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 200 150
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD 180
125 160
140 100
120
100 75
80
50 60
40 25
20 CONTRIBUTION OF COPPER LOAD, IN PERCENT NO DATA NO DATA NO DATA 0 0
400 350
SNOWMELT PERIOD SUMMER-FLOW PERIOD 350 Maximum Maximum dissolved 300 dissolved value = 1,250 value = 1,040
300 250
250
200
200
150 150
100 100
50 50 NO DATA NO DATA NO DATA NO DATA CONTRIBUTION OF COPPER LOAD, IN PERCENT
0 0 AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0 AR45.5 WF0.0 AR43.6 JC0.0 BC0.0 SC0.0
EXPLANATION DISSOLVED COPPER INSTANTANEOUS DISSOLVED COPPER
TOTAL-RECOVERABLE COPPER INSTANTANEOUS TOTAL-RECOVERABLE COPPER
Figure 10. Percentage of contribution of copper load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 17 300 150 BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
250 125 Maximum dissolved Maximum value = 596 dissolved value = 355
200 100
150 75
100 50
50 25 CONTRIBUTION OF IRON LOAD, IN PERCENT NO DATA NO DATA NO DATA
0 0
700 700
SNOWMELT PERIOD SUMMER-FLOW PERIOD
600 600
500 500 Maximum dissolved value = 8,850 400 400 Maximum dissolved value = 1,780 300 300
200 200
100 100 NO DATA NO DATA NO DATA NO DATA CONTRIBUTION OF IRON LOAD, IN PERCENT
0 0 AR45. 5 WF0.0 AR43. 6 JC0. 0 BC0.0 SC0.0 AR45.5 WF0.0 AR43. 6 JC0.0 BC0.0 SC0.0
EXPLANATION DISSOLVED IRON INSTANTANEOUS DISSOLVED IRON
TOTAL-RECOVERABLE IRON INSTANTANEOUS TOTAL-RECOVERABLE IRON
Figure 11. Percentage of contribution of iron load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97.
18 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 160 140 BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
140 120
120 100
100 80
80
60 60
40 40
20 20 CONTRIBUTION OF ZINC LOAD, IN PERCENT NO DATA NO DATA NO DATA
0 0
150 200 SNOWMELT PERIOD SUMMER-FLOW PERIOD
175 125
150
100 125
75 100
75 50
50
25 25 CONTRIBUTION OF ZINC LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA 0 0 AR45. 5 WF0. 0 AR43. 6 JC0.0 BC0.0 SC0.0 AR45. 5 WF0. 0 AR43. 6 JC0. 0 BC0.0 SC0.0
EXPLANATION DISSOLVED ZINC INSTANTANEOUS DISSOLVED ZINC
TOTAL-RECOVERABLE ZINC INSTANTANEOUS TOTAL-RECOVERABLE ZINC
Figure 12. Percentage of contribution of zinc load from Exposure Area 3b (Alamosa River and tributary sites from Wightman Fork to Fern Creek), 1995–97.
SOURCES OF METAL LOADS TO THE ALAMOSA RIVER 19 percentage of the dissolved aluminum load and the column to the streambed may be occurring in the last dissolved and total-recoverable iron loads to the 8.5 miles of EA3c. Alamosa River in EA3b. Also, on a few occasions, Jasper Creek contributed a substantial percentage of the dissolved and total-recoverable iron loads to the ESTIMATION OF SEASONAL AND Alamosa River in EA3b. Spring Creek did not ANNUAL METAL LOADS AT SELECTED contribute substantially to the metal loading of the SITES Alamosa River in EA3b. Seasonal and annual dissolved and total-recov- erable aluminum, copper, iron, and zinc loads for Alamosa River from Fern Creek to Terrace 1995–97 were estimated for Exposure Areas 1, 2, 3a, Reservoir (Exposure Area 3c) 3b, and 3c. As indicated in table 2, the duration of flow varied from year to year for the same flow period. For Sources of metals to the Alamosa River from example, the base-flow period for 1995 had a duration Fern Creek to Terrace Reservoir, EA3c, were deter- of 79 days, the base-flow period for 1996 had a dura- mined for each flow period—base flow, early snow- tion of 175 days, and the base-flow period for 1997 melt, snowmelt, and summer flow. The tributaries had a duration of 195 days. The duration of the flow evaluated in EA3c do not drain any hydrothermally period affects the mass of metals estimated for each altered areas (fig. 1). The water-quality sites evaluated flow period. Therefore, it is important to remember for EA3c are FC0.0 (Fern Creek at mouth), CG0.0 this when making year-to-year comparisons of metal (Castleman Gulch at the mouth), AR41.2 (Alamosa loads for the same flow period. Additionally, the River downstream from Castleman Gulch), SI0.0 magnitude of streamflow varied from year to year; (Silver Creek at the mouth), LC0.0 (Lieutenant Creek 1995 and 1997 were above-normal flow years, at the mouth), and RC0.0 (Ranger Creek at the mouth). whereas 1996 was a below-normal flow year. The The percentages of contribution of metal loads from streamflow in 1995 had the highest total flow with a each of these sites are shown in figures 13–16. The 94-day snowmelt period, and the streamflow in 1996 percentage of contribution of metal loads from FC0.0 had the lowest total flow with a 56-day snowmelt and CG0.0 were computed relative to the metal loads period. measured at AR41.2, and the percentage of contribu- tion of metal loads from AR41.2, SI0.0, LC0.0, and RC0.0 were computed relative to AR34.5. Wightman Fork at WF5.5 (Exposure None of the five tributaries sampled in EA3c Area 1) contributed substantially to dissolved or total- recoverable aluminum, copper, iron, and zinc loads. The cumulative streamflow and estimates of the The combined streamflow for these tributaries contrib- mass of dissolved and total-recoverable aluminum, uted less than 2 percent of the streamflow to EA3c. copper, iron, and zinc for each of the four seasonal Therefore, the tributaries do not provide substantial flow regimes (flow periods) and the annual streamflow dilution to the metal loads measured in EA3c. The and metal mass for 1995–97 at WF5.5 are presented in metal loads in EA3c result from upstream sources; the figures 17–19. In 1995, streamflow measurements and primary upstream sources are Wightman Fork in EA1 water-quality samples were not collected from WF5.5 and Alum and Iron Creeks in EA3a. until the snowmelt period. Therefore, metal loads were Throughout the year, the contributions of not estimated for the 1995 base flow and early snow- dissolved aluminum, copper, iron, and zinc loads and melt periods. The annual streamflow and estimates of total-recoverable copper and iron loads at AR41.2 metal mass shown for 1995 in figures 17–19 were were frequently greater than 100 percent of the respec- based on partial year records and included estimates tive metal loads at AR34.5. Except during the early only for the snowmelt and summer-flow periods. snowmelt period, total-recoverable zinc loads (fig. 16) Many tons of metals were transported past were frequently greater than 100 percent of the respec- WF5.5 from 1995 through 1997. Between 49 and tive metal loads at AR34.5. These data indicate that 246 tons of total-recoverable aluminum (fig. 18), metal partitioning and metal deposition from the water between 6 and 44 tons of total-recoverable copper
20 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 14,000 4,000
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
3,500 12,000
3,000 10,000
2,500 8,000
2,000
6,000 1,500
4,000 1,000
2,000 500 CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 0 0
800 8,000 SNOWMELT PERIOD SUMMER-FLOW PERIOD
700 7,000
600 6,000
500 5,000
400 4,000
300 3,000
200 2,000
100 1,000 CONTRIBUTION OF ALUMINUM LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 0 0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0
EXPLANATION DISSOLVED ALUMINUM INSTANTANEOUS DISSOLVED ALUMINUM
TOTAL-RECOVERABLE ALUMINUM INSTANTANEOUS TOTAL-RECOVERABLE ALUMINUM
Figure 13. Percentage of contribution of aluminum load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 21 1,250 1,000
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
1,000 800
750 600
500 400
250 200 CONTRIBUTION OF COPPER LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 0 0
500 1,000 SNOWMELT PERIOD SUMMER-FLOW PERIOD
400 800
300 600
200 400
100 200 CONTRIBUTION OF COPPER LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 0 0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0
EXPLANATION DISSOLVED COPPER INSTANTANEOUS DISSOLVED COPPER
TOTAL-RECOVERABLE COPPER INSTANTANEOUS TOTAL-RECOVERABLE COPPER
Figure 14. Percentage of contribution of copper load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97.
22 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 1,200 4,000
BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
3,500 1,000
3,000
800 2,500
600 2,000
1,500 400
1,000
200 500 CONTRIBUTION OF IRON LOAD, IIN PERCENT NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 0 NO DATA 0
2,000 20,000 SNOWMELT PERIOD SUMMER-FLOW PERIOD 18,000 Maximum 1,750 dissolved Maximum value=47,000 dissolved 16,000 value=3,400 1,500 14,000
1,250 12,000
1,000 10,000
8,000 750
6,000 500 4,000
250 CONTRIBUTION OF IRON LOAD, IN PERCENT 2,000 NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA
0 0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0
EXPLANATION DISSOLVED IRON INSTANTANEOUS DISSOLVED IRON
TOTAL-RECOVERABLE IRON INSTANTANEOUS TOTAL-RECOVERABLE IRON
Figure 15. Percentage of contribution of iron load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 23 400 120 BASE-FLOW PERIOD EARLY SNOWMELT PERIOD
350 100
300 80
250
60
200
40 150
20 100 CONTRIBUTION OF ZINC LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA 50 0
320 300 SNOWMELT PERIOD SUMMER-FLOW PERIOD
280 250
240
200 200
160 150
120 100
80
50 40 CONTRIBUTION OF ZINC LOAD, IN PERCENT NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA NO DATA
0 0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0 FC0.0 CG0.0 AR41.2 SI0.0 LC0.0 RC0.0
EXPLANATION DISSOLVED ZINC INSTANTANEOUS DISSOLVED ZINC
TOTAL-RECOVERABLE ZINC INSTANTANEOUS TOTAL-RECOVERABLE ZINC
Figure 16. Percentage of contribution of zinc load from Exposure Area 3c (Alamosa River and tributary sites from Fern Creek to Terrace Reservoir), 1995–97.
24 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 10,000
1995 9,000 1996 1997
8,000
7,000
6,000
Based on partial year records 5,000
4,000
3,000
2,000
CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND 1,000 No data collected No data collected 0 BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL
Figure 17. Cumulative streamflow for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97.
(fig. 18), between 39 and 342 tons of total-recoverable iron, and zinc transported during the snowmelt period iron (fig. 19), and between 4 and 20 tons of total- generally constituted between about 70 and 90 percent recoverable zinc (fig. 19) were estimated to have been of the corresponding annual metal mass. During 1996, transported annually past WF5.5 from 1995 through the metal mass transported during the snowmelt period 1997. The largest estimated annual mass for dissolved generally constituted between 25 and 50 percent of the and total-recoverable aluminum, copper, iron, and zinc annual metal mass. occurred in 1995. The annual metal mass estimated for From 1995 through 1997, generally more than 1995 was between 5 and 10 times larger than the 95 percent of the annual copper and zinc mass was annual metal mass estimated for 1996 and about transported past WF5.5 in the dissolved fraction. In 2 times the annual metal mass estimated for 1997. The 1995 and 1997, 85 percent of the annual aluminum annual mass of dissolved aluminum, copper, iron, and mass was transported past WF5.5 in the dissolved zinc substantially decreased after 1995. fraction; in 1996, about 40 percent of the annual More than 60 percent of the annual streamflow aluminum mass was transported past WF5.5 in the occurred during the 8 to 13 weeks of the snowmelt dissolved fraction. Between 1995 and 1997, between period (fig. 17). For 1995 and 1997, the mass of 40 and 60 percent of the annual iron mass was trans- dissolved and total-recoverable aluminum, copper, ported past WF5.5 in the dissolved fraction.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 25 250 250
1995 Based on partial year 1996 Based on partial year 1997 200 200
150 150
100 100 DISSOLVED ALUMINUM, IN TONS
50 50 TOTAL-RECOVERABLE ALUMINUM, IN TONS No data collected No data collected No data collected No data collected No data collected 0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT 45 45
Based on partial year Based on partial year 40 40
35 35
30 30
25 25
20 20
15 15 DISSOLVED COPPER, IN TONS 10 10 TOTAL-RECOVERABLE COPPER, IN TONS
5 5 No data collected No data collected No data collected No data collected 0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 18. Mass of aluminum and copper for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97.
26 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 350 350
1995 Based on partial year 1996 300 300 1997
250 250
200 Based on partial year 200
150 150
100 100 DISSOLVED IRON, IN TONS TOTAL-RECOVERABLE IRON, IN TONS 50 50 No data collected No data collected No data collected No data collected 0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
25 25
Based on partial year Based on partial year
20 20
15 15
10 10 DISSOLVED ZINC, IN TONS
5 5 TOTAL-RECOVERABLE ZINC, IN TONS No data collected No data collected No data collected No data collected 0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 19. Mass of iron and zinc for selected flow periods, Exposure Area 1 (site WF5.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 27 Wightman Fork at WF0.0 (Exposure copper (fig. 21), between 40 and 240 tons of total- Area 2) recoverable iron (fig. 22), and between about 5 and 19 tons of total-recoverable zinc (fig. 22) were esti- The cumulative streamflow and estimates of the mated to have been transported annually past WF0.0 mass of dissolved and total-recoverable aluminum, from 1995 through 1997. The largest estimated annual copper, iron, and zinc for each of the four seasonal mass for dissolved and total-recoverable aluminum, flow regimes (flow periods) and the annual streamflow copper, iron, and zinc occurred in 1995. The annual and metal mass for 1995–97 at WF0.0 are presented in metal mass estimated for 1995 was between 3 and 6 figures 20–22. times larger than the annual metal mass estimated for Many tons of metals were transported past 1996 and generally was between about 1 and 2 times WF0.0 from 1995 through 1997. Between 55 and the annual metal mass estimated for 1997. The annual 220 tons of total-recoverable aluminum (fig. 21), mass of dissolved copper, iron, and zinc substantially between about 8 and 42 tons of total-recoverable decreased after 1995. However, the estimated annual
10,000
1995
9,000 1996
1997
8,000
7,000
6,000
5,000
4,000
3,000
2,000 CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND
1,000
0 BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL
Figure 20. Cumulative streamflow for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97.
28 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 250 250
1995 1996 1997 200 200
150 150
100 100 DISSOLVED ALUMINUM, IN TONS 50 50 TOTAL-RECOVERABLE ALUMINUM, IN TONS
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
45 45
40 40
35 35
30 30
25 25
20 20
15 15 DISSOLVED COPPER, IN TONS 10 10 TOTAL-RECOVERABLE COPPER, IN TONS 5 5
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 21. Mass of aluminum and copper for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 29 350 350
1995 1996 300 1997 300
250 250
200 200
150 150
100 100 DISSOLVED IRON, IN TONS TOTAL-RECOVERABLE IRON, IN TONS 50 50
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
25 25
20 20
15 15
10 10 DISSOLVED ZINC, IN TONS
5 5 TOTAL-RECOVERABLE ZINC, IN TONS
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 22. Mass of iron and zinc for selected flow periods, Exposure Area 2 (site WF0.0), 1995–97.
30 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 mass of dissolved aluminum was similar in 1995 and that these metals partitioned to the solid phase. How- 1997. ever, the annual dissolved copper and zinc masses More than 60 percent of the annual streamflow were smaller at WF5.5 than at WF0.0, indicating that occurred during the snowmelt period (fig. 20). For other sources of metals contributed to the metal mass 1995 and 1997, the mass of aluminum, copper, iron, at WF0.0 during 1996. A plausible explanation is that and zinc transported during the snowmelt period metal loads associated with instream sources or storm generally constituted between 50 and 90 percent of the runoff during 1996 contributed to the increases in esti- annual metal mass. During 1996, the metal mass trans- mated metal mass at WF0.0. Also, potential estimation ported during the snowmelt period constituted errors could account for the estimated differences in between 14 and 56 percent of the annual metal mass. metal loads. From 1995 through 1997, between 10 and approximately 45 percent of the annual aluminum mass, between 60 and 90 percent of the annual copper Alamosa River at AR45.5 (Exposure mass, between 17 and 25 percent of the annual iron Area 3a) mass, and between 90 and 100 percent of the annual zinc mass were transported past WF0.0 in the The cumulative streamflow and estimates of the dissolved fraction. The dissolved fraction of mass of dissolved and total-recoverable aluminum, aluminum, copper, and iron mass tended to be smaller copper, iron, and zinc for each of the four seasonal at WF0.0 than the dissolved-metal mass fraction at flow regimes and the annual streamflow and metal WF5.5, indicating that the dissolved fraction of mass for 1995–97 at AR45.5 are presented in aluminum, copper, and iron partitioned to the solid figures 23–25. phase in the intervening reach between WF5.5 and Many tons of total-recoverable aluminum and WF0.0. There was no appreciable change to the iron were transported past AR45.5 between 1995 and dissolved zinc fraction between WF5.5 and WF0.0, 1997. Between 120 and 185 tons of total-recoverable indicating that little metal partitioning of zinc aluminum (fig. 24), and between 230 and 400 tons of occurred. total-recoverable iron (fig. 25) were estimated to have A comparison of the annual streamflow at been transported annually past AR45.5 from 1995 WF0.0 to the annual streamflow at WF5.5 showed that through 1997. A relatively small mass of total- about 40 percent of the annual streamflow at WF0.0 recoverable copper and zinc was transported past was attributable to WF5.5, indicating that the inter- AR45.5 during 1995–97. Less than 1 ton of total- vening 11.7 square miles of drainage between WF5.5 recoverable copper (fig. 24) and less than 2 tons of and WF0.0 contributed about 60 percent of the annual total-recoverable zinc (fig. 25) were estimated to have streamflow. However, a comparison of the annual been transported annually past AR45.5 from 1995 metal mass at WF0.0 and WF5.5 in 1995 and 1997 through 1997. The estimated annual mass for total- indicated that estimates of annual mass of total- recoverable aluminum, copper, iron, and zinc was recoverable aluminum, copper, iron, and zinc were similar in 1995 and 1997; the estimated annual mass generally equivalent. Based on data collected from for total-recoverable aluminum, copper, and iron in tributaries to the Wightman Fork in the reach between 1996 was about 60 to 70 percent of the respective WF5.5 and WF0.0 during 1998 and 1999 annual metal mass estimated for 1995 and 1997. The (K. Nordstrom, U.S. Geological Survey, written estimated annual mass of dissolved copper, iron, and commun., 2000), it appears unlikely that there are any zinc substantially decreased after 1995. appreciable sources of metals downstream from Less than 14 percent of the annual streamflow WF5.5 along Wightman Fork. In 1996, however, the occurred during the base flow period. However, during estimates of annual mass of total-recoverable metals at this flow regime, the pH of the Alamosa River at WF5.5 were 84 percent (aluminum), 75 percent AR45.5 generally is at its annual minimum and most (copper), 95 percent (iron), and 69 percent (zinc) of of the annual dissolved aluminum and iron, and a the annual mass of metals estimated at WF0.0. Addi- considerable portion of the annual dissolved copper tionally, the annual dissolved aluminum and iron and zinc, were transported during the 1996 and 1997 masses were larger at WF5.5 than at WF0.0, indicating base-flow period. More than 65 percent of the annual
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 31 32,000
1995 1996 28,000 1997
24,000
20,000
16,000
12,000
8,000
4,000 CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND
0 BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL
Figure 23. Cumulative streamflow for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97.
streamflow occurred during the snowmelt period majority of metals transported past AR45.5 was in the (fig. 23), and the largest mass of total-recoverable particulate or suspended fraction. However, as stated aluminum, copper, iron, and zinc generally was trans- earlier, a large dissolved metal fraction was trans- ported during this period. However in 1996, the mass ported during the base-flow period. of total-recoverable aluminum, copper, iron, and zinc transported during the snowmelt period constituted of less than one-third of the annual metal mass. In 1995 Alamosa River at AR43.6 (Exposure and 1997, the mass of total-recoverable aluminum, Area 3b) copper, iron, and zinc transported during the snowmelt period constituted between about 40 and 71 percent of The cumulative streamflow and estimates of the the annual metal mass. mass of dissolved and total-recoverable aluminum, copper, iron, and zinc for each of the four seasonal From 1995 through 1997, between 15 and about flow regimes and the annual streamflow and metal 30 percent of the annual aluminum mass and between mass for 1995–97 at AR43.6 are presented in about 15 and 25 percent of the annual iron mass was figures 26–28. In 1995, streamflow measurements and transported past AR45.5 in the dissolved fraction. water-quality samples were not collected from AR43.6 More than 50 percent of the annual copper and zinc until the snowmelt period. Therefore, metal loads were mass was in the dissolved fraction. This indicated that, not estimated for the 1995 base-flow and early snow- with the exception of zinc and copper, the vast melt periods. The annual streamflow and estimates of
32 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 200 200
1995 180 180 1996 1997 160 160
140 140
120 120
100 100
80 80
60 60 DISSOLVED ALUMINUM, IN TONS 40 40 TOTAL-RECOVERABLE ALUMINUM, IN TONS 20 20
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
0.8 0.8
0.7 0.7
0.6 0.6
0.5 0.5
0.4 0.4
0.3 0.3
DISSOLVED COPPER, IN TONS 0.2 0.2
0.1 TOTAL-RECOVERABLE COPPER, IN TONS 0.1
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 24. Mass of aluminum and copper for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 33 450 450
1995 400 1996 400 1997
350 350
300 300
250 250
200 200
150 150 DISSOLVED IRON, IN TONS
100 TOTAL-RECOVERABLE IRON, IN TONS 100
50 50
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
2.5 2.5
2.0 2.0
1.5 1.5
1.0 1.0 DISSOLVED ZINC, IN TONS
0.5 0.5 TOTAL-RECOVERABLE ZINC, IN TONS
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 25. Mass of iron and zinc for selected flow periods, Exposure Area 3a (site AR45.5), 1995–97.
34 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 metal mass shown for 1995 in figures 26–28 were AR45.5 and WF0.0 indicated that 45–65 percent of the based on partial year records and included estimates annual total-recoverable aluminum mass at AR43.6 only for the snowmelt and summer-flow periods. may be attributed to EA3a (AR45.5) and about Many tons of metals were transported past 30–55 percent may be attributed to contributions from AR43.6 between 1995 and 1997. Between 185 and Wightman Fork. Less than 4 percent of the annual 415 tons of total-recoverable aluminum (fig. 27), total-recoverable copper mass at AR43.6 may be between 7 and 40 tons of total-recoverable copper attributed to EA3a (AR45.5) and more than 85 percent (fig. 27), between 285 and 760 tons of total- of the annual total-recoverable copper mass at AR43.6 recoverable iron (fig. 28), and between 6 and 20 tons may be attributed to contributions from Wightman of total-recoverable zinc (fig. 28) were estimated to Fork. About 50–80 percent of the annual total-recover- have been transported annually past AR43.6 from able iron mass at AR43.6 may be attributed to EA3a 1995 through 1997. The largest estimated annual mass (AR45.5) and about 15–40 percent of the annual total- for dissolved aluminum, dissolved and total- recoverable iron mass at AR43.6 may be attributed to recoverable copper, dissolved iron, and dissolved and contributions from Wightman Fork. About 10–25 total-recoverable zinc occurred in 1995. The smallest percent of the annual total-recoverable zinc mass at annual mass, with the exception of dissolved AR43.6 may be attributed to EA3a (AR45.5) and aluminum, occurred in 1996. The annual total- about 80-90 percent of the annual total-recoverable recoverable metal mass estimated for 1995 was zinc mass at AR43.6 may be attributed to contributions between 2 and 5 times larger than the annual metal from Wightman Fork. mass estimated for 1996 and about the same or just slightly larger than the annual metal mass estimated for 1997. The annual mass of dissolved aluminum, Alamosa River at AR41.2 and AR34.5 copper, iron, and zinc substantially decreased after (Exposure Area 3c) 1995. More than 60 percent of the annual streamflow The cumulative streamflow and estimates of the occurred during the snowmelt period (fig. 26). For mass of dissolved and total-recoverable aluminum, 1995 and 1997, the mass of total-recoverable copper, iron, and zinc for each of the four seasonal aluminum, copper, iron, and zinc transported during flow regimes and the annual streamflow and metal the snowmelt period constituted between about 70 and mass for 1995–97 at AR41.2 and AR34.5 are 90 percent of the annual metal mass. However during presented in figures 29–33. 1996, the total-recoverable metal mass transported Many tons of metals were transported past during the snowmelt period was between about 25 and AR41.2 and AR34.5 between 1995 and 1997. Between 42 percent of the annual total-recoverable metal mass. 180 and 500 tons of total-recoverable aluminum During 1996, a large percentage of the dissolved (fig. 30) were estimated to have been transported aluminum (92 percent), copper (85 percent), iron annually past AR41.2, and between 170 and 670 tons (80 percent), and zinc (59 percent) for the year was of total-recoverable aluminum (fig. 30) were estimated transported past AR43.6 during the base-flow period. to have been transported annually past AR34.5. From 1995 through 1997, between 8 and Between 7 and 36 tons of total-recoverable copper 25 percent of the annual aluminum mass, between 60 (fig. 31) were estimated to have been transported and 75 percent of the annual copper mass, between 12 annually past AR41.2, and between 7 and 32 tons of and 22 percent of the annual iron mass, and between total-recoverable copper (fig. 31) were estimated to 85 and 100 percent of the annual zinc mass was trans- have been transported annually past AR34.5. Between ported past AR43.6 in the dissolved fraction. 320 and 880 tons of total-recoverable iron (fig. 32) A comparison of the annual streamflow at were estimated to have been transported annually past AR43.6 to the annual streamflow at AR45.5 and AR41.2, and between 280 and 1,140 tons of total- WF0.0 indicated that about 75 percent of the annual recoverable iron (fig. 32) were estimated to have been streamflow at AR43.6 was attributable to streamflow transported annually past AR34.5. Between 6 and upstream from AR45.5 (EA3a), and about 25 percent 20 tons of total-recoverable zinc (fig. 33) were esti- from Wightman Fork (EA2). A comparison of the mated to have been transported annually past AR41.2, annual metal mass at AR43.6 to the annual mass at and 5 and 18 tons of total-recoverable zinc (fig. 33)
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 35 40,000
Based on partial year record 1995 1996 35,000 1997
30,000
25,000
20,000
15,000
10,000
5,000 CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND No data collected No data collected
0 BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL
Figure 26. Cumulative streamflow for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97.
were estimated to have been transported annually past More than 58 percent of the annual streamflow AR34.5. occurred during the snowmelt period (fig. 29). The mass of total-recoverable aluminum, copper, iron, and The largest estimated annual mass for dissolved zinc transported during the snowmelt period in 1995 aluminum, copper, iron, and zinc and total-recoverable and 1997 constituted between about 70 and 85 percent copper and zinc was measured in 1995. The smallest of the annual metal mass at AR41.2 and AR34.5. annual mass for all dissolved and total-recoverable During 1996, the total-recoverable metal mass trans- constituents was measured in 1996. The annual total- ported during the snowmelt period was between about recoverable metal mass estimated for 1995 was 30 and 45 percent of the annual total-recoverable between 2 and 5 times larger than the annual total- metal mass at AR41.2 and between about 45 and recoverable metal mass estimated for 1996 and just 60 percent of the annual total-recoverable metal mass slightly larger than the annual total-recoverable metal at AR34.5. mass estimated for 1997; total-recoverable aluminum From 1995 through 1997, between 6 and 16 and iron were larger in 1997. The annual mass of percent of the annual aluminum mass, between about dissolved aluminum, copper, iron, and zinc at AR41.2 55 and 61 percent of the annual copper mass, between substantially decreased after 1995. The annual mass of about 12 and 26 percent of the annual iron mass, and dissolved aluminum, copper, and iron at AR34.5 between about 88 and 94 percent of the annual zinc substantially decreased after 1995. mass was transported past AR41.2 in the dissolved
36 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 450 450 Based on partial year 1995 400 1996 400 1997
350 350
300 300
250 250
200 200
150 Based on partial year 150
100 100 DISSOLVED ALUMINUM, IN TONS TOTAL-RECOVERABLE ALUMINUM, IN TONS 50 50 No data collected No data collected No data collected No data collected 0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
40 40
Based on partial year Based on partial year 35 35
30 30
25 25
20 20
15 15
10 10 DISSOLVED COPPER, IN TONS TOTAL-RECOVERABLE COPPER, IN TONS 5 5 No data collected No data collected No data collected No data collected 0 0 UAL BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANN SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 27. Mass of aluminum and copper for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 37 900 800
1995 800 1996 700 1997 Based on partial year
700 600
600 500
500
400 400
Based on partial year 300 300 DISSOLVED IRON, IN TONS 200 200 TOTAL-RECOVERABLE IRON, IN TONS
100 100 No data collected No data collected No data collected No data collected 0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
25 25
Based on partial year Based on partial year
20 20
15 15
10 10 DISSOLVED ZINC, IN TONS
5 5 TOTAL-RECOVERABLE ZINC, IN TONS No data collected No data collected No data collected No data collected 0 0 UAL BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANN SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 28. Mass of iron and zinc for selected flow periods, Exposure Area 3b (site AR43.6), 1995–97.
38 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 fraction. From 1995 through 1997, less than 2 percent Alamosa River at AR31.0 (Exposure of the annual aluminum mass, between about 14 and Area 5) 32 percent of the annual copper mass, between about 3 and 8 percent of the annual iron mass, and between 55 The cumulative streamflow and estimates of and 80 percent of the annual zinc mass were trans- the mass of dissolved and total-recoverable aluminum, ported past AR34.5 in the dissolved fraction. The copper, iron, and zinc for each of the four seasonal smaller dissolved-metal mass fraction at AR34.5 rela- flow regimes and the annual streamflow and metal tive to AR41.2, which is located in the upper part of mass for 1995–97 at AR31.0 are presented in figures 34–36. Estimates of metal mass presented in EA3c (fig. 1), indicates that a large portion of the this section of the report represent: (1) the mass of dissolved aluminum, copper, iron and, to a lesser metals being transported past AR31.0 and the mass of extent, zinc mass (figs. 30, 31, 32, and 33) is parti- metals available for risk exposure in EA5, and (2) the tioned to the particulate or suspended fraction in the mass of metals being transported out of Terrace Reser- stream reach. voir that were available for risk exposure in EA4. A comparison of the annual streamflow at Terrace Reservoir has a capacity of about AR41.2 to the annual streamflow at AR43.6 (EA3b) 17,000 acre-ft (Watts, 1996) and is primarily used as indicated that about 80 to 90 percent of the annual storage for irrigation water. Streamflow at AR31.0 is streamflow at AR41.2 was attributable to streamflow lowest between November and about mid-April. when upstream from AR43.6. A comparison of the annual the outlet works are closed. During this time, storage metal mass at AR41.2 to the mass at AR43.6 indicated is gradually increased in the reservoir. From May that the total-recoverable metal mass at AR41.2 was through June, reservoir releases for downstream irriga- approximately equivalent to the total-recoverable tion users generally match reservoir inflow. From July through October, reservoir releases are generally metal mass at AR43.6. The only exceptions were for greater than the reservoir inflow (as measured at the total-recoverable aluminum mass in 1997 and the AR34.5) thus reducing the reservoir storage substan- total-recoverable iron mass in 1995, 1996, and 1997. tially. This comparison indicates that there were no appre- Many tons of metals were transported past ciable sources of total-recoverable metals entering the AR31.0 between 1995 and 1997. Between 25 and intervening drainage area between AR43.6 and 85 tons of total-recoverable aluminum (fig. 35), AR41.2. between about 2 and 25 tons of total-recoverable A comparison of the annual streamflow at copper (fig. 35), between about 80 and 170 tons of AR34.5 and AR41.2 indicated that between 88 and total-recoverable iron (fig. 36), and between about 3 100 percent of the annual streamflow at AR34.5 was and 20 tons of total-recoverable zinc (fig. 36) were attributable to streamflow upstream from AR41.2 estimated to have been transported annually past (fig. 29). A comparison of the annual metal masses at AR31.0 from 1995 through 1997. AR34.5 and AR41.2 indicated that the annual total- The largest estimated annual mass for dissolved and total-recoverable aluminum, copper, iron, and zinc recoverable copper and zinc mass at AR34.5 was was in 1995, and the smallest annual mass was in similar to the annual mass at AR41.2. This comparison 1996. The annual total-recoverable metal mass esti- indicated there were no appreciable sources of total- mated for 1995 was between about 2 and 12 times recoverable copper and zinc entering the intervening larger than the annual metal mass estimated for 1996 drainage area between AR41.2 and AR34.5. In 1995 and was less than 4 times the annual metal mass esti- and 1997, however, the annual total-recoverable mated for 1997. The annual mass of dissolved aluminum and iron mass at AR34.5 was about aluminum, copper, iron, and zinc substantially 30 percent greater than the annual total-recoverable decreased after 1995. aluminum and iron mass at AR41.2. A plausible expla- Between 70 and 85 percent of the annual nation for these increases is that aluminum and iron streamflow at AR31.0 occurred during the snowmelt deposited in the streambed were resuspended and period (fig. 34). From 1995 through 1997, between 87 contributed to the increases in estimated aluminum and 94 percent of the total-recoverable aluminum and iron mass estimated at AR34.5. mass, between 55 and 70 percent of the total-
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 39 60,000 AR41.2 1995 1996 50,000 1997
40,000
30,000
20,000
10,000
0 60,000 AR34.5
50,000
40,000
30,000 CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND
20,000
10,000
0 BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL
Figure 29. Cumulative streamflow for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.
40 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 700 700 AR41.2 AR41.2 1995 1996 600 1997 600
500 500
400 400
300 300
200 200 DISSOLVED ALUMINUM, IN TONS
100 100 TOTAL-RECOVERABLE ALUMINUM, IN TONS
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
700 700 AR34.5 AR34.5
600 600
500 500
400 400
300 300
200 200 DISSOLVED ALUMINUM, IN TONS
100 100 TOTAL-RECOVERABLE ALUMINUM, IN TONS
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 30. Mass of aluminum for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 41 40 40 AR41.2 AR41.2 1995 35 1996 35 1997
30 30
25 25
20 20
15 15
10 10 DISSOLVED COPPER, IN TONS
5 TOTAL-RECOVERABLE COPPER, IN TONS 5
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
40 40 AR34.5 AR34.5
35 35
30 30
25 25
20 20
15 15
10 10 DISSOLVED COPPER, IN TONS
5 TOTAL-RECOVERABLE COPPER, IN TONS 5
0 0 UAL BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANN SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 31. Mass of copper for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.
42 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 1,200 1,200 AR41.2 AR41.2 1995 1996 1997 1,000 1,000
800 800
600 600
400 400 DISSOLVED IRON, IN TONS
200 TOTAL-RECOVERABLE IRON, IN TONS 200
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
1,200 1,200 AR34.5 AR34.5
1,000 1,000
800 800
600 600
400 400 DISSOLVED IRON, IN TONS
200 TOTAL-RECOVERABLE IRON, IN TONS 200
0 0 UAL BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANN SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 32. Mass of iron for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 43 25 25 AR41.2 AR41.2 1995 1996 1997 20 20
15 15
10 10 DISSOLVED ZINC, IN TONS
5 TOTAL-RECOVERABLE ZINC, IN TONS 5
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
25 25 AR34.5 AR34.5
20 20
15 15
10 10 DISSOLVED ZINC,IN TONS
5 TOTAL-RECOVERABLE ZINC, IN TONS 5
0 0 UAL BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANN SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 33. Mass of zinc for selected flow periods, Exposure Area 3c (sites AR41.2 and AR34.5), 1995–97.
44 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 60,000
1995 1996 1997
50,000
40,000
30,000
20,000
10,000 CUMULATIVE STREAMFLOW, IN CUBIC FEET PER SECOND
0 BASE FLOW EARLY SNOWMELT SNOWMELT SUMMER FLOW TOTAL ANNUAL
Figure 34. Cumulative streamflow for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97. recoverable copper mass, between 63 and 91 percent Terrace Reservoir drive the operation of the reservoir. of the total-recoverable iron mass, and between 48 and A comparison of the annual metal mass at AR31.0 to 71 percent of the total-recoverable zinc mass were the annual metal mass at AR34.5 indicated that transported during the snowmelt period. between 1995 and 1997, the annual total-recoverable From 1995 through 1997, between 5 and aluminum mass at AR31.0 was about 15 percent of 23 percent of the annual aluminum mass, between annual total-recoverable aluminum mass at AR34.5, about 40 and 66 percent of the annual copper mass, the annual total-recoverable copper mass at AR31.0 between about 3 and 16 percent of the annual iron was between about 25 and 75 percent of annual total- mass, and between 78 and 95 percent of the annual recoverable copper mass at AR34.5, the annual total- zinc mass were transported past AR31.0 in the recoverable iron mass at AR31.0 was between 13 and dissolved fraction. 28 percent of annual total-recoverable iron mass at A comparison of the annual streamflow at AR34.5, and the annual total-recoverable zinc mass at AR31.0 to the annual streamflow at AR34.5 (EA3c) AR31.0 was between about 50 and 100 percent of indicated that about 85 to more than 100 percent of the annual total-recoverable zinc mass at AR34.5. These annual streamflow at AR31.0 was attributable from data indicate that Terrace Reservoir serves as a sink for streamflow upstream from Terrace Reservoir. Down- metals. This conclusion is consistent with a previous stream irrigation needs and storage limitations in report by Ferguson and Edelmann (1996).
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 45 100 100
1995 1996 1997 80 80
60 60
40 40 DISSOLVED ALUMINUM, IN TONS 20 20 TOTAL-RECOVERABLE ALUMINUM, IN TONS
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
25 25
20 20
15 15
10 10 DISSOLVED COPPER, IN TONS 5 5 TOTAL-RECOVERABLE COPPER, IN TONS
0 0 UAL BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANN SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 35. Mass of aluminum and copper for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97.
46 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 200 200
1995 180 180 1996 1997 160 160
140 140
120 120
100 100
80 80
DISSOLVED IRON, IN TONS 60 60
40 TOTAL-RECOVERABLE IRON, IN TONS 40
20 20
0 0
BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANNUAL SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
20 20
18 18
16 16
14 14
12 12
10 10
8 8
DISSOLVED ZINC, IN TONS 6 6
4 TOTAL-RECOVERABLE ZINC, IN TONS 4
2 2
0 0 UAL BASE FLOW SNOWMELT BASE FLOW SNOWMELT SUMMER FLOWTOTAL ANN SUMMER FLOWTOTAL ANNUAL EARLY SNOWMELT EARLY SNOWMELT
Figure 36. Mass of iron and zinc for selected flow periods, Exposure Area 5 (site AR31.0), 1995–97.
ESTIMATION OF SEASONAL AND ANNUAL METAL LOADS AT SELECTED SITES 47 SUMMARY Creeks contributed a substantial percentage of the iron loads to the Alamosa River in EA3b. The metal loads The upper Alamosa River Basin is a heavily observed in EA3c result from upstream sources; the mineralized area located in the San Juan Mountains of primary upstream sources are Wightman Fork in EA1 southwestern Colorado. Metal contamination has and Alum and Iron Creeks in EA3a. Tributaries in occurred for decades from the Summitville Mine site, EA3c did not contribute substantially to the metal load from other smaller mines, and from natural, metal- in the Alamosa River. enriched acidic drainage in the basin. In 1995, In many instances, the percentage of dissolved multiple gaps in data needed for an ecological risk and/or total-recoverable metal load contribution from assessment of the Summitville Superfund site were a tributary or the combined percentage of metal load identified. Specifically, the need to quantify contami- contribution was greater than 100 percent of the metal nation from various source areas in the basin and the load at the nearest downstream site on the Alamosa need to quantify the spatial, seasonal, and annual River. These data indicate that metal partitioning and metal loads in the basin was identified. As a result, the metal deposition from the water column to the USGS developed a comprehensive data-collection streambed may be occurring in Exposure Areas 3a, 3b, plan for the basin to address these data gaps. and 3c. Metals that are deposited to the streambed To meet the objectives of this study, instanta- probably are resuspended and transported downstream neous streamflow data and periodic water-quality data during high-streamflow periods such as during snow- were collected from 1995 through 1997 at 6 sites on melt runoff and rainfall runoff. the Alamosa River, 2 sites on Wightman Fork, and 11 Seasonal and annual dissolved and total- other tributary sites. Concentrations of metals and recoverable aluminum, copper, iron, and zinc loads for values of streamflow measurements were used to 1995–97 were estimated for Exposure Areas 1, 2, 3a, determine metal loads for each sampling date. Percent- 3b, and 3c. EA1 incorporates the Summitville Mine ages of metal load contributions from tributaries were site, and EA2 extends along Wightman Fork. During determined for each sample collected. A modified 1995–97, many tons of metals were transported annu- time-interval method was used to estimate seasonal ally through each exposure area. Generally, the largest and annual metal loads in the Alamosa River and estimated annual total-recoverable metal mass for Wightman Fork. most metals was in 1995. The smallest estimated Sources of dissolved and total-recoverable annual total-recoverable metal mass was in 1996, aluminum, copper, iron, and zinc loads were deter- which also coincided with the smallest annual stream- mined for three risk exposure areas. EA3a extends flow. In 1995 and 1997, more than 60 percent of the upstream from Wightman Fork along the Alamosa annual total-recoverable metal loads generally was River. EA3b extends along the Alamosa River from transported through each exposure area during the Wightman Fork to Fern Creek. EA3c extends along snowmelt period; however, in 1996, generally less than the Alamosa River from Fern Creek to Terrace Reser- 40 percent of the annual total-recoverable metal loads voir. Alum Creek is the predominant contributor of was transported through the exposure areas during the aluminum, copper, iron, and zinc loads to EA3a. The snowmelt period. A comparison of the estimated storm percentage of contribution of metal loads from Alum load at each site to the corresponding annual load indi- Creek was often greater than the combined metal load cated that storms contribute less than contribution from Iron and Bitter Creeks. In general, 2 percent of the annual load at any site and about 5 to Wightman Fork was the predominant source of metals 20 percent of the load during the summer-flow period. to EA3b particularly during the snowmelt and summer The highest percentage of contribution was observed flow periods. During the base-flow period, however, for total-recoverable aluminum and iron. aluminum and iron loads from EA3a were the domi- A comparison of the annual metal mass at nant source of these metals to EA3b. Jasper and Burnt WF5.5 (EA1) to annual metal mass estimated at Creeks generally contributed less than 10 percent of WF0.0 (EA2) indicated that estimates of total- the metal loads to EA3b. On a few occasions, however, recoverable metal mass for the two exposure areas Burnt Creek contributed a substantial percentage of were approximately equivalent in 1995 and 1997. The the dissolved aluminum load, and Jasper and Burnt annual dissolved aluminum and iron mass was larger
48 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97 at WF5.5 (EA1) than at WF0.0 (EA2), indicating these ———1998, Water resources data, Colorado, water year metals partitioned to the solid phase. Between 1995 1997: U.S. Geological Survey Water–Data Report and 1997, many tons of total-recoverable aluminum CO–97–1, v. 1. Missouri River Basin, Arkansas River Basin and Rio Grande Basin, 513 p. and iron were transported past AR45.5, whereas only a Crowfoot, R.M., Ugland, R.C., Maura, W.S., Steger, R.D., relatively small mass of total-recoverable copper and and O’Neill, G.B., 1996, Water resources data, zinc was transported past AR45.5. Most of the Colorado, water year 1995: U.S. Geological Survey dissolved metals transported past AR45.5 occurred Water-Data Report CO–95–1, v. 1. Missouri River during base flow even though only 14 percent of the Basin, Arkansas River Basin and Rio Grande Basin, annual streamflow occurred during this period. A 506 p. comparison of the annual metal mass at AR43.6 to the Ferguson, S.A., and Edelmann, Patrick, 1996, Assessment annual mass at AR45.5 and WF0.0 indicated that most of metal transport into and out of Terrace Reservoir, Conejos County, Colorado, April 1994 through March of the annual total-recoverable aluminum and iron 1995: U.S. Geological Survey Water-Resources mass may be attributed to EA3a (AR45.5) and most of Investigations Report 96–4151, 77 p. the annual total-recoverable copper and zinc mass may Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in be attributed to contributions from Wightman Fork. A water resources: New York, Elsevier, Studies in comparison of the annual metal masses at AR34.5 and Environmental Science 49, 522 p. AR41.2 indicated that the annual total-recoverable Hirsch, R.M., Slack, J.R., and Smith, R.A., 1982, Tech- copper and zinc mass was similar, which indicated that niques of trend analysis for monthly water-quality data: Water Resources Research, v. 18, no. 1, there were no appreciable sources of total-recoverable p. 107–121. copper and zinc entering the intervening drainage area. Hirsch, R.M., Alexander, R.B., and Smith, R.A., 1991, A comparison of the annual metal mass at AR31.0 to Selection of methods for the detection and estimation the annual metal mass at AR34.5 indicated that the of trends in water quality: Water Resources Research, annual total-recoverable aluminum and iron mass at v. 27, no. 5, p. 803–813. AR31.0 was about 15–30 percent of annual total- Horowitz, A.J., Demas, C.R., Fitzgerald, K.K., Miller, T.L., recoverable mass at AR34.5, which indicated that and Rickert, D.A., 1994, U.S. Geological Survey protocol for the collection and processing of surface- Terrace Reservoir served as a sink for most contami- water samples for the subsequent determination of nants of concern. inorganic constituents in filtered water: U.S. Geological Survey Open–File Report 94–539, 57 p. McDonald, J., ed., 1996, Streamflow data for Colorado, SELECTED REFERENCES water year 1995: Colorado Department of Natural Resources, Division of Water Resources, Office of Bove, D.J., Wilson, A.B., and Barry, T.H., Hon, K., State Engineer, 204 p. Kurtz, J., Van Loenen, R.E., and Calkin, W.S., 1996, McDonald, J., ed.,1997, Streamflow data for Colorado, Geology, alteration, and rock and water chemistry of water year 1996: Colorado Department of Natural the Iron, Alum, and Bitter Creek area, upper Alamos Resources, Division of Water Resources, Office of River, southwestern Colorado: U.S. Geological Survey State Engineer, 203 p. Open–File Report 96–0039, 34 p. ———1998, Streamflow data for Colorado, water year Camp Dresser and McKee Inc., 2000, Final report- Tier 2 1997: Colorado Department of Natural Resources, Summitville Ecological Risk Assessment addendum Division of Water Resources, Office of State Engineer, for Summitville Mine Superfund site, Rio Grande, 202 p. Conejos, and Alamosa counties, Colorado: prepared Miller, W.M., and McHugh, J.B., 1994, Natural acid for the U.S. Environmental Protection Agency, drainage from altered areas within and adjacent to the November 2000. upper Alamosa River basin, Colorado: U.S. Geological Crowfoot, R.M., Paillet, A.V., Ritz, G.F., Smith, M.E., Survey Open–File Report 94–144, 47 p. Steger, R.D., and O’Neill, G.B., 1997, Water resources Morrison-Knudsen Corporation and ICF Kaiser Engineers, data, Colorado, water year 1996: U.S. Geological 1995, Tier I Ecological Risk Assessment, Summitville Survey Water–Data Report CO–96–1, Mine Site: Prepared under contract to U.S. Environ- v. 1. Missouri River Basin, Arkansas River Basin and mental Protection Agency, ARC contract number Rio Grande Basin, 512 p. 68–W9–0025, July 1995.
SELECTED REFERENCES 49 Nordstrom, D.K., 1982, Aqueous pyrite oxidation and the Stogner, R.W., Edelmann, Patrick, and Walton-Day, consequent formation of secondary iron minerals in Katherine, 1996, Physical and chemical characteristics Acid Sulfate Weathering: Soil Science Society of of Terrace Reservoir, Conejos County, Colorado, May American, Special Publication 10, 1994 through May 1995: U.S. Geological Survey p. 37–56. Water-Resources Investigations Report 96–4150, 34 p. Ortiz, R.F., and Stogner, Sr., R.W., 2000, Diurnal variations in metal concentrations in the Alamosa River and U.S. Environmental Protection Agency, 1991, Guidance Wightman Fork, southwestern Colorado, 1995–97: manual for the preparation of NPDES permit applica- U.S. Geological Survey Water-Resources tions for storm water discharges associated with indus- Investigations Report 00-–4160, 14 p. trial activity: U.S. Environmental Protection Agency Rupert, M.G., 2001, Relations among rainstorm runoff, report EPA–505/8–91–002, 81 p. streamflow, pH, and metal concentrations, Summitville Watts, K.R., 1996, Bathymetric surface and storage capacity Mine area, upper Alamosa River Basin, southwest of Terrace Reservoir, Conejos County, Colorado, Colorado, 1995–97: U.S. Geological Survey Water- July-August 1994: U.S. Geological Survey Water- Resources Investigations Report 01–4027, 33 p. Resources Investigations Report 96–4027, map report, Scheider, W.A., Moss, J.J., and Dillon, P.J., 1979, Measure- 1 sheet. ment and uses of hydraulic and nutrient budgets—Proceedings, national conference on lake Wentz, D.A., 1974, Effect of mine drainage on the quality of restoration, Minneapolis, Minnesota, August 22-24, streams in Colorado, 1971–1972: Colorado Water 1978: U.S. Environmental Protection Agency Report Conservation Board, Water-Resources Circular 21, EPA 440/5–79–001, p. 77–83. 117 p.
50 Sources of Metal Loads to the Alamosa River and Estimation of Seasonal and Annual Metal Loads for the Alamosa River Basin, Colorado, 1995–97