PUBLIC HEALTH ASSESSMENT
DEL NORTE, RIO GRANDE COUNTY, COLORADO
Selection of Contaminants
ATSDR considers the following factors in selecting contaminants for further evaluation (19):
- comparison of concentrations of contaminants on and off site with values for noncarcinogenic and carcinogenic endpoints,
- sampling plan, and field and laboratory data quality, and
- community health concerns.
Identification of a contaminant in the On-Site and Off-Site Contamination sections does not mean that exposure will result in adverse health effects, only that there is a need for additional evaluation. Subsequent sections of this public health assessment contain evaluations of the public health significance, if any, of exposure to the contaminants.
EPA's contractor, Morrison Knudsen, provided environmental data for Summitville Mine (1986-1995) to ATSDR in a master database (9). The master database contained information through April 1995. Additionally, ATSDR obtained US Geological Survey surface water data through November 1995 (21). Evaluators used these data in this assessment.
The preparers of this document searched EPA's Toxic Chemical Release Inventory database (self-reports from chemical manufacturers and other companies throughout the United States) but found no reported releases for Summitville Mine (22). There are no industrial sources near the mine site or contributing to rivers affected by Summitville Mine drainage.
Contamination at the mine includes cyanide and cyanide compounds in the heap leach system and french drain and heavy metals (aluminum, cadmium, copper, iron, lead, manganese, and zinc) in those systems and in acid drainage (8,9) [Figure 3]. Mining activities at Summitville increased the release of acid water and metals to surface water. The open-pit mining of sulfide-bearing rocks and the storage of these rocks in waste dumps throughout the mine site lead to their weathering and oxidation. Snowmelt and rain water reacted with the sulfide minerals to form waters with high contents of sulfuric acid and metals. There are relatively small amounts of carbonate and other acid-consuming rocks at Summitville Mine to buffer the acid drainage naturally (3).
EPA's remedial actions at the site have reduced the amount of metals and other contaminants entering surface waters. Because of the remote location of the mine site, human exposure is unlikely. Current workers use personal protective equipment and have health and safety plans. Summitville mine workers used a well north of the mine site for drinking water in the early 1980s. It drew water from a saturated zone 185 feet deep in the volcanic bedrock (23). The maximum concentrations of detected metals except arsenic are below ATSDR comparison values. The maximum arsenic concentration was 2 parts per billion (ppb), and the comparison value, based on cancer risk, is 0.02 ppb (8). The hydrogeology suggests that arsenic in this well was not contamination from the mine site. Cyanide, which is not naturally occurring was also detected (23) but the results are suspected to be erroneous because of poor quality control (11). The current drinking water source at the mine site is bottled water (24).
On October 15, 1987, SCMCI, Inc. requested that NIOSH evaluate cyanide exposures among heavy equipment operators working on the heap leach pad. Several workers had symptoms consistent with diagnoses of cyanide poisoning. However, no health hazard from cyanide exposure could be documented at the time of the survey (25). Exposures to cyanide on the heap leach pad are unlikely to occur now or in the future because mining activities have ceased.
The Heap Leach System
Contaminants associated with the leaching process were detected in the water of the french drain system in August 1986. The process solution used in ore leaching had a pH value near 10 to 11, total dissolved solids of about 1,000 parts per million (ppm), and cyanide concentrations of around 100 to 300 ppm (26). The original concentration of cyanide sprayed on the heap leach pile was about 500 ppm (6). The french drain system was set up so that drainage from the Cropsy waste pile area (highly acidic at pH around 3) flowed below the heap leach pad (highly basic at pH around 9 to 11). Some mixing of these waters occurred because of leaks in the liner system's seal, resulting in cyanide concentrations of 1 to 2 ppm in the french drain system. SCMCI designed its mining operation to have no wastewater discharge; however, problems occurred that required the company to obtain a state wastewater treatment plant operating permit. A wastewater treatment plant began operating in June 1989 to process excess water from the heap leach system.
The heap leaching system initially (in 1992) contained approximately 150 million gallons of water contaminated with cyanide and metals (cadmium, copper, lead, and zinc) . EPA pumped this contaminated water from the french drain sump back to the leach pad to prevent releases. Before EPA's involvement, the french drain sump often overflowed and spilled contaminated water into Cropsy Creek. Since the pond containing the heap was almost full when SCMCI abandoned the site in 1992, a release could have occurred during spring runoff if conditions were not altered. Basically, EPA prevented a major release of cyanide- and metal-laden water to local streams (7).
Since mining ended, some of the cyanide in the heap leach pad has degraded, and some of the high pH waters have been diluted from melt water and Cropsy waste pile water. Additionally, the heap leach pad/french drain is a controlled system. Excess water from the heap leach system goes to a water treatment plant.
Adits and waste piles
In addition to the contaminated water from the heap leach system and french drain, contaminated water (acid mine drainage) has also been released from the Reynolds Adit and the associated Dexter, Iowa, and Chandler adits . Before the mine pit was capped and the adits were plugged, precipitation entered the pit above the underground workings and discharged through Reynolds Adit. Beginning in August 1992, the water from the adit was treated to reduce heavy metal content before its release into Wightman Fork. After the adit was plugged in January 1994, treatment of the water ceased. In addition to plugging the Reynolds Adit, EPA has filled the mine pit and channeled runoff around the pit (12). Through remedial measures such as these, EPA has reduced acid mine drainage and the release of water containing heavy metals.
Waste piles such as the Cropsy Waste Pile, Summitville Dam Impoundment (formerly the Cleveland Cliffs Tailings Pond), and Beaver Mud Dump have been moved to the mine pits and mixed with a buffer agent (lime kiln dust) to reduce acidity of any infiltrating waters [Figure 3](12). Waste piles (mine tailings) at the mine site were moved to reduce heavy metal and acidity levels reaching surface waters. The Cropsy Waste Pile, the Summitville Dam Impoundment, and Beaver Mud Dump were located on or near former stream beds and, therefore, were associated with considerable acid mine drainage (8). Surface runoff from the waste piles and land application of wastes caused additional drainage problems. The mine pit was covered with a vegetative cap to lessen infiltration of waters and contoured to enhance surface runoff (27).
The Summitville Mine site is a major source of metals to Wightman Fork and the Alamosa River. The metals contamination (aluminum, copper, cadmium, iron, lead, manganese, and zinc) results primarily from water flow through former waste piles such as the Cropsy Waste Pile, the Summitville Dam Impoundment, and the Beaver Mud Dump, and adits. Contaminants enter the streams through surface water runoff and groundwater seeps. Spring runoff resulting from snowmelt usually occurs in May and June and increases metal loading to streams. Storms, common in July and August, also contribute to runoff and metal loading in surface water. Table 1 presents data for selected locations downstream of the mine site. Figures 1 and 2 show surface water sampling locations.
High acidity or low pH, elevated dissolved solids, and elevated heavy metal concentrations have degraded surface water quality downstream of the mine. The sediment and water downstream of the Summitville mining site have become more acidic. River water in the Wightman Fork of the Alamosa changed from pH 6 or 7 in the 1970s/1980s to pH 5 or less in the 1990s (28) [Table 1]. The pH of river water tends to increase downstream along the Alamosa to about pH 6 near Terrace Reservoir (23) [Table 1]. Although most of the metal and acid loading to the Alamosa River comes from Wightman Fork, which receives drainage from the mine site, some of this acidity comes from naturally occurring acid metal seeps upstream of the mine. Aluminum, iron, and manganese tend to be elevated even in tributaries unaffected by Summitville Mine (23). Source areas downstream of Wightman Fork have affected water quality in Terrace Reservoir during storms (29).
Table 1 presents a summary of metals in selected downstream locations [Figures 1 and 2]. The data indicate that heavy metals concentrations are highest just downstream of the mine site in Wightman Fork. Concentrations of metals in the Alamosa River--especially, copper, iron, manganese, and zinc--have increased since mining operations began at Summitville Mine (9, 28). Concentrations of copper are elevated above drinking water standards in the Alamosa River as far as Terrace Reservoir. Manganese is elevated beyond Terrace Reservoir (data for Station AR-31) (Table 1). Wightman Fork was the source of most of the copper, manganese, and zinc discharged to the Alamosa River in 1993 (29). From May 1994 through March 1995, most of the total aluminum and iron that entered Terrace Reservoir remained there, while the majority of copper, manganese, and zinc was transported out of the reservoir (30).
Table 1 also presents data for cyanide in the Alamosa River. Cyanide concentrations in the Alamosa River are below federal drinking water standards (Table 1). Cyanide in the Wightman Fork or Alamosa River tends to volatilize, to form temporary metal cyanide complexes, and to react with sulfur species to form thiocyanate (31). Most of the cyanide in surface water does not remain as free cyanide. EPA's drinking water standard for free cyanide is 200 ppb. Free cyanide for Wightman Fork waters was below the detection level in all samples but one (900 ppb at WF-6 on 11/11/91). The 1990-1991 cyanide data for surface water samples indicate that concentrations of several thousand ppb total or weak acid dissociable cyanide were released periodically from the mine site but did not appear to persist downstream much beyond the confluence with the Alamosa River.
Historical data suggest that sulfate concentrations in Wightman Fork commonly exceeded 500 ppm, EPA's proposed maximum contaminant level (MCL) (9). The maximum at WF-6 was 1,462 ppm, recorded in March 1992. The levels of sulfate in the Alamosa River were below 500 ppm, usually 30 to 350 ppm.
- Surface Water Compliance Data
In July 1992, the Colorado Department of Health and SCMCI/Galactic Resources entered a Settlement Agreement and Amended Compliance Plan. This plan established the compliance criteria for the mine site, which will be used in the evaluation of the impact of contamination on surface water. The compliance criteria concept provides that protection of human health and the environment can be demonstrated through attainment of numeric criteria levels (NCLs) at one compliance point (32). The compliance point, WF-5.5 or WF-6, is on Wightman Fork downstream of the Summitville Mine site and below the confluence of Wightman Fork and Cropsy Creek. NCLs were established for total recoverable zinc, copper, lead, silver, cadmium, manganese, and iron, and for total mercury, weak acid dissociable cyanide, and pH. Compliance with NCLs is determined based on the 30-day average concentrations of the parameters at the compliance point.
Copper is the key indicator species with respect to achieving compliance with all the NCL parameters (33). It is an excellent predictor of the concentrations of cadmium, iron, lead, manganese, and zinc. Copper concentrations are being used to evaluate current loadings to the surface and groundwater systems and to predict improvements in water quality as a result of potential remedial actions (33). The July 1991 through November 1995 compliance data suggest that maximum metal concentrations at the compliance point tend to occur May through September during months of higher precipitation and peak streamflow. The monthly maximum copper concentrations for this period occurred each July. The average copper concentrations for July 1993, July 1994, and July 1995 are 21.4, 39.2, and 7.8 ppm respectively. The maximum copper concentrations and loading occurred in July 1994. Copper concentrations at the compliance point for July 1991 through November 1995 suggest that water quality improved during treatment of the Reynolds Adit water and other sources and then degraded again during problems with adit plugging in 1994 (34). The compliance point data for 1995 indicate that concentrations and loads of copper have been substantially reduced. Further remedial activities, particularly capping of the pit, have contributed to copper load reductions. EPA is continuing work to bring the concentrations of copper and other metals (such as manganese, cadmium, and zinc) low enough to meet the NCLs. Plans call for sitewide reclamation and revegetation.
Private Well Water
A number of San Luis Valley residents use private wells that receive groundwater from shallow aquifers in the alluvium of the Alamosa River or shallow unconfined aquifers in the Valley. Private wells may be located near irrigation ditches or irrigated fields that receive Alamosa River water. Private wells in the San Luis Valley have been sampled to determine whether heavy metals or low pH of the Alamosa River water have affected water quality. Although Summitville mine has affected water quality in the Alamosa River, ATSDR acknowledges that other abandoned mines and naturally occurring acid metal seeps may also degrade water quality of streams and groundwater affected by the mine site.
Private well samplings in the San Luis Valley (January 1993 through June 1995) suggest that well water quality has suffered no widespread effect from mine drainage. Most private wells in the San Luis Valley have concentrations of metals below federal drinking water standards, as discussed below. Based on private well water results through 1995, adverse human health effects from drinking water are not anticipated.
EPA's Technical Assistance Team sampled 31 residential wells along the lower Alamosa River Basin in January 1993. Most of these residential wells are below Terrace Reservoir along the Alamosa River and along drainage ditches receiving Alamosa River water. Most water samples came from kitchen faucets. Heavy metal analysis included testing for cadmium, copper, and zinc (35). None of the metal concentrations were at levels approaching federal drinking water standards.
A water testing program for private wells in the Capulin area began in March 1993. Colorado State University (CSU) Extension Studies staff analyzed about 75 samples of domestic, stock water, and irrigation water wells. Landowners collected these samples and delivered them to the extension office in La Jara. Concentrations in most wells did not exceed federal drinking water standards [Table 2]. Two wells contained lead exceeding 15 ppb, EPA's action level (may be attributable to lead solder or lead pipe). One well contained copper exceeding 400 ppb which was attributed by the State of Colorado to copper plumbing. One well contained cadmium exceeding 5 ppb, EPA's MCL (36). Although manganese was elevated (above 50 ppb) in about eight wells (some of them were control wells that were not influenced by Alamosa River water), there is no federal drinking water standard. Sulfate levels were far below EPA's drinking water standard of 500 ppm (37).
A follow up to this initial spring/summer testing began in September 1993. Only about half of the landowners submitted samples for the second testing. Once again, most wells did not have metals exceeding federal drinking water standards. However, metals requiring further evaluation based on screening values included cadmium (exceeding 5 ppb in three domestic wells) and lead (exceeding 50 ppb in one well) [Table 2] (38). Manganese appeared to be elevated (exceeded 50 ppb) in three wells.
The State of Colorado Division of Minerals and Geology sampled 5 private wells in November 1993 in a resampling followup to the fall CSU extension study. Staff members retested wells that showed elevated cadmium in the fall sampling. Although the fall 1993 samples showed high cadmium levels, this later sampling did not show cadmium or other metals at levels exceeding federal drinking water standards (39).
EPA contractor Morrison Knudsen took three rounds of private wells samples during March through June 1995, sampling approximately 30 private wells in the San Luis Valley for heavy metals. Arsenic above the federal drinking water standard of 50 ppb was detected in one control well (a well not influenced by Alamosa River water) (40). After the Colorado Department of Public Health and Environment informed them of their test results, residents formerly using water from the well are using bottled water (41). Other metals in drinking water wells were not above federal drinking water standards.
The source or sources of elevated metals concentrations in private wells have not been identified. Elevated cadmium apparently occurs in a few wells on what may be a seasonal basis. Manganese in well water may be elevated on a regional basis because of background concentrations in soils (and possibly because of the increased mobility of manganese due to acidic Alamosa River water). Lead and copper concentrations may be elevated in private wells because of leaching of metals from pipes by acidic waters. Alamosa River water could also contribute to leaching of metals from naturally occurring metals in soil.
Private well samplings in the San Luis Valley through June 1995 show that most private wells have concentrations of metals below federal drinking water standards. Based on private well water results through June 1995, adverse human health effects from metals in drinking water are unlikely. However, monitoring of Alamosa River water quality should continue so that its long-term effects on groundwater can be evaluated. Private wells should be sampled again to confirm 1995 results. We recommend sampling private wells during surface water sampling.
Soils in fields irrigated by contaminated Alamosa River water have lower pH than those in nonirrigated fields (42). The lower pH could result in easier uptake of some metals by some crops. Soil tests taken from farms irrigated with Alamosa River water have shown elevated levels of zinc, iron and copper compared with samples from nonirrigated areas (42). However, the metal concentrations for soils irrigated with Alamosa River water are within acceptable ranges for Western U.S. soils (43).
The Colorado School of Mines and Agro-Engineering of Alamosa, Colorado, and Colorado State University Department of Soil and Crop Sciences are cooperating on further studies (44).
Agro Engineering collected soil samples from March 19 to 21, 1996, for the Phase I soil study (45). Fields irrigated with Alamosa River water currently were compared with fields irrigated with water from other sources--Rio Grande River water and/or deep groundwater and fields irrigated with Alamosa River water prior to 1984, for instance--and with undeveloped land. The fields currently irrigated with Alamosa River water show higher levels of cadmium, copper, iron, manganese, nickel, and zinc compared with fields irrigated with water from the other water sources. The concentrations of copper and iron are higher within the study area than in areas outside it. Although the results of the Phase I sampling fall within acceptable ranges for agricultural soil in the San Luis Valley, they indicate increased overall metal loads and solubility and possibly bioavailablity of metals in fields irrigated with Alamosa River water. Analysis of the data has not been completed.
None of the metal concentrations in the March 1996 soil data exceed screening criteria for ingestion of soil; there is no indication of human health effects. Therefore, no further analysis was conducted.
Results to date indicate that acidic metal-laden Alamosa River water has increased some metal concentrations in some crops in the San Luis Valley. However, most crops still have metal concentrations within the ranges reported for crops grown in other regions of the U.S. An agricultural study indicates that alfalfa irrigated exclusively with water from the Alamosa River contains higher concentrations of copper than alfalfa watered from other sources (42). Copper occurs naturally in plants and animals and is an essential nutrient for all living organisms. The Colorado Department of Agriculture has researched the question of copper accumulation in plants and animals. The staff concluded that reported copper levels in the Alamosa River pose no threat to the food supply (46). Manganese concentrations in alfalfa, which is used as livestock feed for sheep and cattle, climbed during the 1993 through 1995 sampling period and are beyond the concentrations reported in alfalfa grown in other parts of the West (47). Although manganese concentrations are elevated in alfalfa, the maximum concentration (150 ppm) is well below the maximum tolerable level of 1,000 ppm for sheep and cattle (47). These manganese concentrations in alfalfa are not a threat to sheep or cattle or their food supply. Studies on barley grown in 1993 indicate that irrigation with Alamosa River water resulted in higher concentrations of some metals (48). However, the 1993 concentrations were within ranges reported for barley grown in other regions of the U.S. (48). The metal content in wheat and potatoes grown in 1993 was within normal ranges for US produce (49).
Analyses from 1993/1994 indicate there are no mineral toxicities in beef cattle or sheep herds that were watered with or fed crops grown with contaminated Alamosa River water (50). Although manganese concentrations are elevated in alfalfa, the maximum concentration of 150 ppm manganese in alfalfa is well below the maximum tolerable level of 1,000 ppm for sheep and cattle (47).
The potential for bioaccumulation of metals in muscle tissue consumed as meat is relatively low, because metals are more likely to accumulate in tissues of organs (kidneys or livers, for example) or bones (46). Studies were conducted during the summers of 1995 and 1996 on domestic sheep, which are very sensitive to elevated copper in their diet (51). The results summarized here are tentative pending the final analyses and report.
The 1995 field exposure study reported on maximally exposed sheep (those that drank Alamosa River water and grazed in pastures watered by it) under a reasonable exposure scenario of 116 days. Tests evaluated 18 sheep from the contaminated site and 23 from the uncontaminated (control) site. Sheep at the contaminated site had elevated copper in their liver tissue (211 to 635 ppm on a dry weight basis compared with 87.5 to 331 ppm in the control group). Copper was not detected (detection limit of 24.6 ppm on a wet weight basis) in blood, muscle or kidney samples from either exposed or unexposed (control group) sheep. No mortality attributable to contaminants was observed at the contaminated site.
The 1996 dosing study of sheep showed a strong correlation between amount of copper ingested and amount of copper accumulated in the liver. Copper sulfate was provided in a feed supplement, and two groups received drinking water containing copper acetate (designed to replicate average metal concentrations in Alamosa River water). Copper levels were below 1,000 ppm copper in dry weight tissue, the concentration associated with hemolytic crisis of copper toxicosis in sheep, which leads to death. No mortality or overt clinical signs of copper toxicosis was observed during the study. Human health effects from eating sheep with contaminated livers are very unlikely because doses of copper would be within the range for normal human ingestion of copper (52). Additional analyses of copper levels in other tissues (such as muscle) and blood from these sheep are in progress, and the conclusions from the 1995 and 1996 studies are tentative pending the final report.
There are no fish in or upstream of Terrace Reservoir on the Alamosa River or in Wightman Fork downstream of the mine site (17). There are some fish in headwaters of rivers above the mine. Although fish were present in Terrace Reservoir in the late 1970s, no fish were found in these areas in 1990 and 1993 (17). The absence of fish downstream of the mine site through Terrace Reservoir is attributable primarily to metals and acid levels that are elevated because of drainage from the mine site (18). There were no data on contamination in fish. There may be fish in some farm ponds irrigated with contaminated surface water.
As the metal and acidity levels are reduced, it may be feasible to reestablish a fishery in Terrace Reservoir (18). The Use Attainability Assessment, prepared by the state and EPA, addresses the water quality and its ability to support aquatic life in stream segments near Summitville Mine. Segments of the Alamosa River may be reclassified from Class I cold water fishery to class 2. The reclassification would be from a river that should support fish to one that can support agriculture and aquatic life but not necessarily fish.
Mallard ducks collected at Terrace Reservoir in 1995 had elevated copper concentrations in their livers (328 to 428 ppm) compared with duck livers from habitats such as Alamosa National Wildlife Refuge, which were described as not contaminated (5.4 to 137 ppm) (51). Mallard ducks (two juveniles) near Terrace Reservoir had accumulated copper in their livers, probably because of elevated copper in the environment. Media samples obtained at duck collection sites in 1995 indicated a mean value of around 0.37 ppm copper in water. The highest concentrations of copper (463 ppm) were found in unwashed vegetation near Terrace Reservoir.
The 1996 laboratory duck study used commercially produced mallard ducklings. Copper sulfate was provided in the feed at 200, 400, and 800 ppm concentrations. Liver copper concentrations were not significantly higher in any of the dosing groups (51).
Additional information from field studies of a greater number of ducks in their natural habitat would be helpful to determine their main sources of exposure and to have reasonable scenarios for bioavailability of the metals. Consumption of duck, including the liver, is not anticipated to result in adverse human health effects.
The quality assurance project plan (QAPP) for Summitville Mine (January 1988) requires that chemical analyses follow the procedures in EPA Methods for Chemical Analysis of Water and Wastes. In-stream biological assessments follow the EPA's Rapid Bioassessment Protocols For Use in Streams and Rivers (53). The QAPP outlines the use of duplicates and field blanks. ATSDR received an electronic copy of the pre-1993 quality assurance/quality control (QA/QC) data. The QA/QC of on-site samples is explicit. The EPA Technical Assistance Team collected quality control samples. However, there was no QA/QC for cyanide analysis in surface water because this sampling was for screening purposes only. ATSDR used data in the Morrison Knudsen database, some of which have not been validated. The data are a collection from numerous studies requiring varying protocols. We tried to draw general conclusions from these data.
ATSDR did not receive information on private well locations. Because of the lack of consistent identifiers for each well, ATSDR could not evaluate seasonal changes in water quality on a per well basis. Therefore, staff could draw only general conclusions from the private well data such as the absence of a widespread effect on private well water from Alamosa River water.
Hazards that may be encountered on site include those typically found in chemical processing areas and associated with soil removal activities: hazards associated with motorized equipment and movement of heavy equipment used in soil excavation; chemicals in storage tanks and storage areas, particularly in treatment plant areas; and wastes in ponds, drains, sumps, piles, and dumps.
This section of the public health assessment contains evaluations of the possible exposure pathways that help determine whether persons have been, are being, or will be exposed to contaminants associated with the site. Pathway analysis consists of five elements (19):
- identifying contaminants of possible concern;
- determining that contaminants have been, are being, or will be transported
through an environmental medium;
- identifying a point of exposure (i.e., a place or situation where humans might be
exposed to the contaminated media);
- determining that there is a plausible route of human exposure (i.e., whether the
contaminant can enter the body?); and
- identifying an exposed population (i.e., how many people, if any, are at the point of exposure).
An exposure pathway is considered complete when there is good evidence that all five elements exist. The presence of a completed pathway indicates that human exposure to contaminants has occurred, is occurring, or will occur. When one or more of the five elements of an exposure pathway are missing, the pathway is considered potential. The presence of a potential exposure pathway indicates that human exposure to contaminants could have occurred, could be occurring, or could occur. An exposure pathway can be eliminated if at least one of the five elements is missing and will never be present. If there is uncertainty about the site-relatedness of the contaminants of concern in an exposure pathway, this uncertainty will be mentioned but the pathway will be evaluated as if it were site related.
Contaminants from the Summitville Mine site include cyanide, heavy metals, sulfates, and acidic waters. A brief description of the fate of cyanide and heavy metals in the environment is presented below. Sulfates were not considered further because their concentrations were not at levels of public health concern.
EPA has also considered pathways that could lead to human exposure (1). Their Baseline Human Health Risk Assessment evaluates pathways using a quantitative approach where applicable. In general, ATSDR evaluates pathways using a qualitative approach such as presented in this pathways section.
Cyanide has the tendency to volatilize and biodegrade (54). The fate of cyanide in water and soil is pH dependent. Cyanide commonly occurs as hydrogen cyanide, alkali metal cyanides (such as sodium cyanide), or other metallocyanide complexes. The environmental fates of cyanide compounds vary. Biomagnification of cyanide in animals is not anticipated, because high doses are toxic and low doses are metabolized rapidly. Hydrogen cyanide and simple metal cyanides do not bioaccumulate in most aquatic organisms; however, fish can store metal cyanides, such as silver and copper cyanide, in their tissues. Although cyanide is found in foods such as peas, nuts, spices, and dried beans, there is no evidence of biomagnification of cyanide in the food chain (54). Cyanide is being diluted by groundwater at Summitville Mine and it would be further diluted if released to nearby streams. Given the dilution of cyanide and the distance to the nearest private well user (several miles downstream), cyanide does not pose a human health threat for groundwater users downstream of the mine.
Metallic ores at Summitville would primarily be insoluble sulfides except where acid mine drainage has solubilized the metals. Acid mine drainage will leach heavy metals and enhance their mobility particularly through surface water transport. Most metals will be strongly adsorbed to soil under normal conditions. At Summitville, heavy metals have leached into local creeks.
The Summitville mine site is not the only mineralized area contributing heavy metals to local streams. The Alum, Bitter, and Iron Creek watersheds, which are upstream of drainage from the mine site, also contribute metals to the Alamosa River [Figure 1]. There is also an altered area near Jasper, downstream of the mine site, which contributes metals to the Alamosa River and Terrace Reservoir [Figures 1 and 2].
The information available to ATSDR suggests one site-related completed exposure pathway: the air pathway for heavy equipment operators on the site because of cyanide exposures (Table 3).
ATSDR considers the air pathway to be a past completed exposure pathway because of cyanide exposures in operators on the heap leach pad (25). As long as workers wear personal protective equipment, cyanide concentrations in the processing plant and other enclosed areas should not pose health problems. Past mining operations used a water truck to hose down areas needing dust suppression. Exposure to metals during ore processing could have occurred if mine workers breathed ore dust or handled ore (dermal exposure). There are no residences or businesses within several miles of the site, so this pathway can basically be eliminated for people off site.
Potential exposure pathways are indicated if exposure to a contaminant could have occurred, could be occurring, or could occur. Potential exposure pathways are discussed below.
Most private wells in the San Luis Valley have concentrations of metals below federal drinking water standards. A few wells have occasionally contained one to several elevated metals. Since private well locations were not specified in 1993 through 1995 samplings (because landowners wished to remain anonymous), ATSDR could not evaluate whether or not some of the contamination was related to Alamosa River water quality. Shallow wells near the Alamosa River waters may be influenced directly by contamination in these waters. The lower pH of Alamosa River water may raise the concentration of naturally occurring metals or metals from other sources (pipes) in well water. ATSDR recommends that remediation at the Summitville Mine site continue so that environmental impacts from metal and hydrogen ion loading to the Alamosa River are lessened. ATSDR also recommends monitoring of Alamosa River water quality so that its long-term effects on groundwater can be evaluated. A private well sampling program is recommended to confirm 1995 results and assure residents that their drinking water is safe.
Crops grown for human consumption in the San Luis Valley (wheat, barley, potatoes) have metal concentrations within the ranges reported for crops grown in other regions of the U.S. (48, 49). However, 1993 results indicate that acidic metal-laden Alamosa River water has increased some metal concentrations in some crops, such as barley, in the San Luis Valley. The increased availability of metals to some crops means a greater potential for metals intake by humans and animals through the food chain. However, it is unlikely that metal concentrations would increase enough to result in human health effects, because it would be difficult to get a harmful dose of the metals through crops or animals.
Surface Water/ Sediment
Humans could be exposed to heavy metals and cyanide from the site through contact with contaminated sediments and surface water from Wightman Fork. Heavy metals have been transported beyond Terrace Reservoir on the Alamosa River. Heavy metals will accumulate in sediments and be transported downstream along the Alamosa. Cyanide in acidic river water will tend to volatilize to a gas and become diluted as it progresses downstream. Signs warn against drinking the contaminated water.
People who swim or wade in the Alamosa River or irrigation ditches or laterals receiving Alamosa River water may be exposed to metals in surface water or sediment. However, since the skin is fairly impermeable to metals (1), no adverse health effects are anticipated from absorption of metals from surface water or sediment. Recreational users are unlikely to ingest surface water to any significant degree while swimming or wading. People swimming or wading in the Alamosa River even above Terrace Reservoir (such as at the Phillips University Camp) are unlikely to be affected by metals in surface water.
Workers excavating soil and conducting other removal activities may inhale dust containing heavy metals or breathe cyanide that has volatilized from the heap leach pile or treatment systems. However, if workers use personal protective equipment in appropriate areas, exposure will be unlikely. Soil irrigated with water from Terrace Reservoir or other contaminated Alamosa River water may contain elevated levels of metals and be more acidic. The impact of irrigating soil with Alamosa River water is still being investigated. It is unlikely that the quantity of soil or dust ingested incidentally would contain enough contamination to cause adverse health effects.
Humans could have been or could be exposed to contaminants from the site through eating contaminated fish. This pathway is considered potential because reestablishment of a fishery may occur in the future even though fish do not currently live in drainage from the Summitville mine. However, bioaccumulation of heavy metals in edible portions of the fish is unlikely. ATSDR staff are not aware of data on analysis of fish tissue from contaminated portions of the Alamosa River, especially because fish no longer exist in these waters. However, fishing did occur in the past at Terrace Reservoir (7) and may occur in the future.
Livestock could be or could have been exposed to heavy metals from the site by drinking contaminated water or eating contaminated crops. Metals may accumulate in organs such as the kidney and liver of the livestock. Humans could be exposed by eating those livestock. However, since the potential for metal accumulation in muscle tissue consumed as meat is low, it is unlikely that human health effects will occur.
Wildlife (game animals such as deer, ducks, etc.) could be or could have been exposed to heavy metals from the site by drinking contaminated water, eating contaminated vegetation, or ingesting contaminated sediment. Game animals could also be exposed by eating contaminated crops, native shrubs and grasses, or other contaminated animals. Although minor impacts to a specific group of localized individuals, such as some ducks at Terrace Reservoir, may occur, the limited potential for accumulation of metals in edible portions of wildlife indicates that adverse human health effects are not likely.
As discussed in the Pathways Analyses Section, air was the only completed exposure pathway identified for the Summitville NPL site, and heavy-equipment operators on the site were exposed to cyanide through that pathway. The Health Outcome Data Evaluation Section contains a discussion of possible health consequences of this past exposure, how health outcome data are evaluated in a public health assessment, and the NIOSH report on Summitville. San Luis Valley residents did not report any community health concerns to ATSDR; therefore, there are no community health concerns to evaluate.
Even though there are many potential exposure pathways, ATSDR concludes that health effects are unlikely. Our rationale for this conclusion is given on a pathway-by-pathway basis in this public health assessment's Potential Exposure Pathways Section. Human exposure to metals from contaminants from the Summitville site could occur through surface water/sediment, groundwater, soil, crops, fish, livestock, and wild game. As indicated in the Off-site Contamination Section, some of the soil, barley, sheep, and ducks from the areas receiving contaminated Alamosa River water have higher concentrations of metals than those from other areas of the San Luis Valley. As discussed in the Potential Exposure Pathways Section, the available data generally indicate that humans are not being exposed or are experiencing infrequent exposure and are not at risk of health problems from metals in any of the pathways. Though there is a need for additional sampling, ATSDR concludes that human exposure to metals in more than one pathway is also unlikely to be a health risk.
HEALTH OUTCOME DATA EVALUATION
This section contains a review of the guidelines that ATSDR follows for evaluating information from health outcome databases and a discussion of the NIOSH health hazard evaluation.
Guidance on Health Outcome Data Evaluation
A public health assessment, identifies available health outcome databases for the area near the site. From those data, ATSDR selects health outcomes for further evaluation based on whether there is a completed exposure pathway. If a community has concerns about specific health outcomes, ATSDR may evaluate health outcomes if there is a potential exposure pathway.
For the Summitville NPL site, there are no completed exposure pathways other than the worker exposure described next nor were there any community concerns about health outcomes. Therefore, no health outcomes were evaluated.
NIOSH Health Hazard Evaluation
NIOSH investigated an incident at the Summitville Mine in which a heavy-equipment operator experienced symptoms suggestive of cyanide poisoning (25). After the initial incident, two other workers reported similar symptoms. The investigation included air sampling, analysis of urine and serum, and medical interviews. Air levels of cyanide were well below permissible exposure levels. The individual reporting the cyanide-like symptoms had a slightly elevated level of a marker of cyanide exposure in his urine. NIOSH concluded that exposure to cyanide probably did occur but that exposure was limited to a relatively short period. The individuals reporting the symptoms suggestive of cyanide poisoning recovered quickly and appeared to suffer no long-term effects. Since EPA is dewatering and detoxifying the heap leach pile, such exposures to cyanide are unlikely to occur again now or in the future.