Adit Water Research Articles

Determination of contamination sources and geochemical reactions in groundwater of a mine area using Cu, Zn, and S–O isotopes

To determine contamination sources and pathways, the use of multiple isotopes, including metal isotopes, can increase the reliability of environmental forensic techniques. This study differentiated contamination sources in groundwater of a mine area and elucidated geochemical processes using Cu, Zn, S–O, and O–H isotopes. Sulfate reduction and sulfide precipitation were elucidated using concentrations of dissolved sulfides, δ34SSO4, δ18OSO4, and δ66Zn. The overlying contaminated soil was possibly responsible for the contamination of groundwater at <5 mbgl, which was suggested by low δ65Cu values (0.419–1.120‰) reflecting those of soil (0.279–1.115‰). The existence of dissolved Cu as Cu(I) may prevent the increase in δ65Cu during leaching of contaminated soil in the sulfate-reducing environment. In contrast, the groundwater at >5 mbgl seemed to be highly affected by the contamination plume from the adit water, which was suggested by high SO42− concentrations (407–447 mg L−1) and δ65Cu (0.252–2.275‰) and δ66Zn (−0.105‰–0.362‰) values at a multilevel sampler approaching those of the adit seepages. Additionally, the O–H isotopic ratios were distinguished between <5 mbgl and >5 mbgl. Using δ65Cu and δ66Zn to support the determination of groundwater contamination sources may be encouraged, particularly where the isotopic signatures are distinct for each source.

Determination of soil contamination sources in mining area using Zn/Cd ratios with mobile Cd.

Paddy fields near metalliferous mining area are sometimes contaminated by tailings or mine water. In the contaminated paddy fields around the abandoned Seoseong mine, South Korea, groundwater, surface water, and soil samples were assessed to infer sources (tailings and/or mine water) of soil contamination. Major contaminants in the soil included As and Pb which were not detected in the adit water. Moreover, δ34SSO4 values of groundwater at contaminated downstream paddy fields were higher than those of ground and surface water in the mining area, which indicated water-derived contamination is not evident. The Zn/Cd ratios of soil were assessed to verify the source (tailings) of soil contamination. Plots of the Zn/Cd ratio against Zn and As contents showed that soil samples contaminated from tailings had Zn/Cd ratios (108-247) which were similar with the Zn/Cd range of the tailings. In contrast, the ratios of the soil samples were different from the Zn/Cd range of contaminated water samples. The Zn/Cd ratios were determined using 0.1M HCl-extractable Cd, and the fraction of 0.1M HCl-extractable Cd in aqua regia-digestible Cd increased with increasing aqua regia-digestible Cd content. These observations suggest that Zn/Cd ratios in contaminated soil are primarily controlled by 0.1M HCl-extractable Cd, possibly due to the greater exchangeability of 0.1M HCl-extractable Cd than that of total Cd. This suggests that Zn/Cd ratios determined using 0.1M HCl-extractable Cd can be especially sensitive and useful for determining sources of soil contamination in mining areas such as tailings or contaminated water.

Physical and chemical properties of natural and anthropogenic groundwater outflows in the cieszyn foothills

The purpose of this article is to present the hydrographic and hydrochemical properties of the waters of old adits, which drained excavations after exploitation of iron ores. For this research, both the natural springs and control object have been identified. These are located in the Cieszyn Foothills. It has been shown that adit water has a higher average electrolytic conductivity (> 600 µS/cm) than natural spring water (<300 µS/cm). The increase in conductivity is undoubtedly influenced by the air supply to the excavations, which accelerates the rock weathering process. However, the increase in water mineralisation has no effect on the hydrochemical type of water. Adit waters and spring waters represent the same bicarbonate calcium (HCO3− - Ca2+) hydrochemical type. Adit waters show a small variation in water temperature in the annual cycle (Cv < 8%) compared to a natural spring (Cv -18%). Changes in the water temperature in the adits and the spring show high synchronism (r> 0.7).

Source and pathway determination of mine seepages using sulfate and Pb isotopes at the Daema and Okdong mines, South Korea

Utilization of multiple stable isotopes including metal isotopes have been useful to trace sources and pathways of contamination. Contaminated seepages flow out from tailings dumps at the Daema gold-silver mine and the Okdong copper mine in South Korea. Ion concentrations, δ34SSO4, δ18OSO4, and Pb isotopes, as well as leaching tests were used to evaluate the sources and pathways of seepages from tailings dumps at the Daema and Okdong mines. The δ34SSO4 and δ18OSO4 values of the seepage were similar to that of the groundwater at the tailings layer and differed from that of the groundwater at the coal shale layer of the tailings dump at the Daema mine. The Pb isotopic ratios of groundwater at the tailings layer also approached those of the tailings, although the Pb concentration in the seepage that was too low (0.559 μg L−1) did not indicate isotopic signatures of tailings. This suggests that the source of contaminants in the seepage is the tailings of the Daema mine rather than waste rocks (coal shale) of an adjacent mine in the tailings dump. In the Okdong mine, the contamination of seepage may be a result of a 67–71% contribution of groundwater from the northern side of the dump through buried waste rock (OD-T2) and a 19–23% contribution of groundwater from the eastern valley (OD-T3), as calculated by the isotopic mixing of δ34SSO4 and δ18OSO4. Adit water is not considered to be the major source of the seepage because of the large difference in Mn concentrations (22.0 mg L−1 and 0.10 mg L−1 in adit water and seepage, respectively) and the undersaturation with respect to Mn phases before and after mixing with tailings water. To reduce the contamination load of seepage in a tailings dump, we should prevent water inflow not only from the surface but also from the side of the tailings dump. Both studied areas suggest that a dual isotopic approach using δ34SSO4 and δ18OSO4 is especially useful in identifying the contamination sources and pathways. Additionally, a leaching test for waste evaluation proved helpful in qualitatively simulating the composition of leachate from the tailings at the Daema mine and adit water from ore rocks at the Okdong mine. Dissolved Pb isotopic ratios were effective in determining the solid sources of dissolved Pb, if the Pb concentration is greater than 0.6–1.8 μg L−1 in the cases of the studied mines. Pb isotopic ratios at five sites including Nakdong mine and two other sites suggest that dissolved Pb with too low concentration may have isotopic signature of atmospheric input. Pb concentrations above threshold values may be required to reflect contamination sources other than atmospheric contribution.

Geochemical behaviors of antimony in mining-affected water environment (Southwest China)

Antimony (Sb) is a harmful element, and Sb pollution is one of the typical environmental issues in China, meaning that understanding of the geochemical behaviors of Sb is the key to control the fate of environmental Sb pollution. Sb tends to migrate in soluble form in the water-sediment system, but the fate of dissolved Sb is poorly known. Duliujiang river basin, located in southwest China, provided us with a natural aqueous environment to study the transport of Sb because of its unique geological and geographical characteristics. Physicochemical properties (pH, EC, Eh, DO, Flux), trace elements (Sb, As, Sr) and main ions (Ca2+, Mg2+, SO42-) concentrations in mining-impacted waters were measured in order to determine their distribution and migration potential. There are three types of water samples; they are main stream waters (pH of 7.33-8.43), tributary waters (pH of 6.85-9.12) and adit waters with pH values ranging from 7.57 to 9.76, respectively. Results showed that adit waters contained elevated concentrations of Sb reaching up to 13350µgL-1 from the abandoned Sb mines, and mine wastes contained up to 8792mgkg-1 Sb from the historical mine dumps are the important sources of Sb pollution in the Duliujiang river basin. Dissolved Sb had strong migration ability in streams, while its attenuation mainly depended on the dilution of tributary water with large flow rate. In the exit section of the Duliujiang river basin, which had only 10µgL-1 of average Sb concentration. The simple deionized water extraction was designed to investigate the ability of Sb likely to dissolve from the mine wastes. The results indicated that a greater solubility of Sb in alkaline (pH of 7.11-8.16) than in acid (pH of 3.03-4.45) mine wastes, suggesting that mine wastes contained high Sb concentrations, could release Sb into solution in the natural river waters. Furthermore, the fate of Sb pollution depends on the comprehensive treatment of abandoned adit waters and mine wastes in the upper reaches of the drainage basin.

Signature of oxygen and sulfur isotopes of sulfate in ground and surface water reflecting enhanced sulfide oxidation in mine areas

Aqueous geochemistry data together with sulfur and oxygen isotope ratios of minerals and dissolved sulfate in ground and surface water were assessed in six mining areas including five metalliferous mines and one coal mine in various regions in South Korea. The δ34Ssulfate values effectively reflected characteristic sulfur isotopic ratios of minerals in each mine area, and the δ18Osulfate values of mining-affected water (adit water and leachate) were depleted than those of background water. A plot of δ18Osulfate values versus the logarithmic sulfate concentration revealed a good linear negative relationship (R2 = 0.78) for 219 samples spanning six mines in different regions. The observed range of δ18Osulfate values spanned the region where most of oxygen is derived from molecular oxygen for samples with low sulfate concentrations and the region of 100% oxygen derived from water molecules when sulfate concentrations were highest. This suggests that enhanced sulfide oxidation by ferric iron incorporating water-derived oxygen exponentially increases sulfate concentrations in mining areas. In addition, the lower and upper limits of sulfate in the plot could be defined as the atmospheric sulfate input and saturation of gypsum, respectively. The observed relationship between δ18Osulfate and sulfate concentration based on field data can further be used for semi-quantitative interpretation of oxygen isotopic ratios of sulfate in mine areas in terms of pyrite oxidation pathways.

Distribution and migration of antimony and other trace elements in a Karstic river system, Southwest China.

Antimony (Sb) usually occurs associated with arsenic, lead, and other metal elements in sulfide deposits, and most is currently being extracted from the Karst areas, southwest China. In these areas, the acid generated from the oxidative dissolution of sulfide minerals is neutralized by the abundant carbonates but little is known about the effect of this process on the geochemical behavior of Sb and other contaminants. In this study, physicochemical properties (pH, EC) and the trace elements (Sb, As, Cu, Pb, Zn, Sr, etc.) concentrations in waters from mining-impacted Karstic environments were determined in order to determine their distribution and migration potential. It was found that pH values ranged from 6.51 to 9.82, and EC values varied from 369 to 1705μs·cm-1 in river water samples. Waters of various types such as adit waters, flotation drainage, leaching waters, and river waters all contained high concentrations of dissolved trace elements, reaching up to 5475μg·L-1Sb, 1877μg·L-1As, 10,371μg·L-1Zn, 1309μg·L-1 Pb, 46μg·L-1 Cu, and 1757μg·L-1 Sr. The elevated concentrations of dissolved Sr indicated that Sr could be considered as an indicator of oxidative dissolution of sulfide minerals in the Karst rivers. A proportion of the trace elements were removed in the streams in the vicinity of the mine due to adsorption onto particulate matter, whereas migration of trace elements in the downstream of mine area was attributed to dispersion in dissolved forms. Strontium and Sb have a strong hydrophilicity compared to the other elements analyzed; in contrast, Pb had a high affinity for suspended particulate matter (SPM). It was also found that downstream sediments had elevated concentrations of mining-derived trace elements, but there was a significant decrease in concentration of contaminants in aqueous phase, suggesting that contaminant behavior was conservative in the water-sediment systems under the oxic conditions prevailing in these waters. There was a good correlation between Sb and As in water-SPM-sediment system, indicating that Sb and As are homologous in water environment of the study area.

CONCENTRATION OF HEAVY METALS IN WATER FLOWS IN THE AREA OF UNALSKY TAILING DUMP AND ARDON RIVER

The long history of development of deposits of lead-zinc ores of the Sadonsky mining region led to the formation of extensive halos of chemical pollution of surface watercourses. Aim. The aim of this study is to monitor surface watercourses in the area of the Unalsky tailing dumps and the Kholst deposit by points of sampling of 1992-2004. Sampling was conducted in the summer of 2016. Methods. The content of heavy metals of 2 and 3 hazard classes (Pb, Cd, Ni, Zn and Cu) was studied by atomic absorption. The contribution of the Unaldon River and Unalsky tailing dump to the pollution of the Ardon River. Results. The highest content of cadmium, lead and zinc, significantly exceeding the maximum permissible concentrations (MPC) in the water bodies of cultural and domestic use is found in the Ardon River down from the Unalsky tailing dump. The flow of heavy metals into the Unaldon River with adit waters compared with the observation period of 1992-2004 decreased noticeably. In conditions of a reduction in the production capacity of mining and processing enterprises, the leaching of heavy metals from mountain dumps and excavations make an insignificant contribution to the pollution of the Ardon River in comparison with the Unalsky tailing dump. Conclusion. The state of the Ardon River down from the discharge from the tailing dump corresponds to the "environmental disaster" category. The condition of the rivers Mayramdon and Unaldon according to the content of heavy metals corresponds to a "relatively satisfactory" type.

Assessment of Heavy Metal Contamination in Surface and Ground Water Resources around Udege Mbeki Mining District, North-Central Nigeria

The study assessed the surface water and groundwater chemistry with special concern to heavy metal contaminations/pollution in Udege Mbeki mining district. A total of eight mine ponds, eight hands – dog wells, three streams and one adit water samples were analysed for their heavy metals contents. The heavy metal concentrations ranged as follows: Cd (0.000-0.110 mg/L), Cr (0.003-0.146 mg/L), Co (0.110-1.260 mg/L), Cu (0.000-0.260 mg/L), Fe (0.015-8.398 mg/L), Pb (0.0001-1.853 mg/L) and Ni (0.001.112 mg/L). Concentrations of Cr, Cu and Ni are generally within the maximum permissible limit of the WHO (2006) guideline, whereas concentrations of Fe, Co, Pb and Cd are above the maximum permissible limit. The contamination/pollution level was estimated based on the geoaccumulation index (Ige0), enrichment factor (EF) and heavy metal pollution index (HPI). Sources of the heavy metals in the waters of the area are mainly anthropogenic. The heavy metal pollution index (HPI) calculated was 559.12, which is far above the critically pollution index value of 100 and therefore depict that the waters of the area are critically polluted with regards to heavy metals.

Influence of Radionuclides on Farmland Soil and Creek Sediment around a Uranium Mine in the Southwest of China

The farmland soil and creek sediments in different depth in the mining area were sampled, and their content of 238U,226Ra and 232Th were determined by gamma spectrometric method to assess the impact of the soil environment by single index method. The result shows 232Th was not influenced on soil in survey area. 226Ra influenced more seriously than 238U on farmland soil, meanwhile, the farmland soil at downstream of tailings dam was contaminated seriously by radionuclides than at other places. For creak sediments ,adit water resulted in more serious pollution by 238U than 226Ra, however, tailings erosion resulted in more serious pollution by 226Ra than 238U.

Arsenic speciation and mobility in surface water at Lucky Shot Gold Mine, Alaska

Historical mining in Alaska has created a legacy of approximately 6,830 abandoned mine sites which include adits, tailing piles and contaminated land that continue to impact surface and groundwater quality through run-off and leaching of potentially toxic metals, especially arsenic (As). One such site is the Lucky Shot Gold Mine in Hatcher Pass, south-central Alaska, which operated from 1920 until 1942, mining gold-bearing quartz veins hosted in a Cretaceous tonalite intrusion. Arsenopyrite (FeAsS) and pyrite (FeS(2)) present in the quartz veins contribute to elevated As levels in water draining, abandoned mine adits. As future underground mining at Lucky Shot may further adversely impact water quality, baseline geochemical studies were undertaken to assess As mobility in the vicinity of the mine adits. Water samples were collected from streams, adits and boreholes around the mine and analysed for major and minor elements using inductively coupled plasma-mass spectrometry (ICP-MS) and for anions by ion chromatography (IC). Arsenic species separation was performed in the field to determine the ratio of inorganic As(III)/As(V) using anion-exchange chromatography, following established methods. It was determined that water draining the adits had elevated levels of As roughly seventy times the United States Environmental Protection Agency Drinking Water Standard of 10 μg L(-1), although this was rapidly diluted downstream in Craigie Creek to <2 μg L(-1). Adit and surface water pH was circum-neutral and displayed no characteristics of acid mine drainage. Despite being well oxygenated, As(III) is the dominant As species in adit water, accounting for close to 100 % of total As. The proportion of As(V) increases downstream of the adits, as some As(III) is oxidized, but the speciation enhances arsenic mobility at the site. The δ(18)O measurements indicate that the water in the system has a short residence time as it is very similar to meteoric water, supporting the observation that the predominance of As(III) in adit water results from the lack of thermodynamical equilibrium being attained and preferential absorbance of As(V).

Assessment of environmental hazards at abandoned mining sites: A case study in Sardinia, Italy

In the last two centuries, several Pb–Zn mines were active in the Rio Mannu basin near Narcao (SW Sardinia, Italy), but are now abandoned. These abandoned mines pose a serious risk to the population and required an assessment of the hazard sources and the contaminant pathways in the area. The characterization plan of the Rio Mannu basin was carried out according to Italian protocols. Specifically, samples of soil, stream sediment, fine-grained ore-processing waste (from washery and flotation processes), surface water and groundwater have been analyzed in order to assess the levels of contamination in each mine area and the risks in the plains surrounding the site. Several potential chemical contaminants were considered both in solid materials and water samples. The Rosas mine was recognized as the most contaminated area in the basin, due to the presence of a large tailing pond, some fine-grained waste piles and two mine adits with concentrations of the toxic elements As, Cd, Cu, Pb, Sb and Zn exceeding Italian regulatory standards. The dispersion of contaminants occurs downstream from the small stream draining the area. In case of heavy rain the runoff into the streamlet transports the contaminated material far into the plain. The results of this study show that the characterization plan is a relatively cheap tool for establishing mitigation actions, prior to the realization of a complete, and usually expensive, remediation project at abandoned mine sites. Urgent recommended actions in the Rio Mannu basin include the treatment of the adit water prior to its discharge into the Rio Barisonis; the construction of drainage barriers on waste piles to reduce runoff and solid transport into the Rio Barisonis; the consolidation of the earthen dam containing the tailing pond of Rosas to avoid the deepening of erosion furrows that may threaten its stability.

English

Spreadsheets can be used to provide an accurate and straightforward method of modeling the effects resulting from the disposal of treated and untreated mine wastewaters using percolation and land application disposal on surface and ground water quality. Spreadsheets are more user-friendly than many ground water modeling programs. Spreadsheet models are a valuable tool that can be used to evaluate the potential effects of a new mine, proposed revisions to a mine's operating permit throughout mine life, water disposal options in preparation for closing tailings impoundments, and for disposal of adit water. As mining progresses, adjustments may be made to the formulas and input values to reflect changes in water quality and quantity, hydrogeologic data, mine wastewater treatment efficiency, method or volume requiring disposal (water balance), and other changes that may occur in the composition of the mine wastewater streams. The spreadsheet models are constructed using basic data (e.g., hydrogeologic, wastewater quality and quantity, treatment, storage, and disposal system capacities, etc.), Darcy's equation, standard mixing zone calculations, and weighted-average equations. The calculations used are consistent with those of the National Pollutant Discharge Elimination System (NPDES) permitting for discharges to surface water and to ground waters that discharge to surface water. The use of spreadsheets is an innovative approach to identify water disposal requirements and the more critical elements of a water management system so that the most effective capital investment can be made during operations, and to identify operational mitigations that should be implemented to avoid costly issues during closure.

Arsenic species in weathering mine tailings and biogenic solids at the Lava Cap Mine Superfund Site, Nevada City, CA

BackgroundA realistic estimation of the health risk of human exposure to solid-phase arsenic (As) derived from historic mining operations is a major challenge to redevelopment of California's famed "Mother Lode" region. Arsenic, a known carcinogen, occurs in multiple solid forms that vary in bioaccessibility. X-ray absorption fine-structure spectroscopy (XAFS) was used to identify and quantify the forms of As in mine wastes and biogenic solids at the Lava Cap Mine Superfund (LCMS) site, a historic "Mother Lode" gold mine. Principal component analysis (PCA) was used to assess variance within water chemistry, solids chemistry, and XAFS spectral datasets. Linear combination, least-squares fits constrained in part by PCA results were then used to quantify arsenic speciation in XAFS spectra of tailings and biogenic solids.ResultsThe highest dissolved arsenic concentrations were found in Lost Lake porewater and in a groundwater-fed pond in the tailings deposition area. Iron, dissolved oxygen, alkalinity, specific conductivity, and As were the major variables in the water chemistry PCA. Arsenic was, on average, 14 times more concentrated in biologically-produced iron (hydr)oxide than in mine tailings. Phosphorous, manganese, calcium, aluminum, and As were the major variables in the solids chemistry PCA. Linear combination fits to XAFS spectra indicate that arsenopyrite (FeAsS), the dominant form of As in ore material, remains abundant (average: 65%) in minimally-weathered ore samples and water-saturated tailings at the bottom of Lost Lake. However, tailings that underwent drying and wetting cycles contain an average of only 30% arsenopyrite. The predominant products of arsenopyrite weathering were identified by XAFS to be As-bearing Fe (hydr)oxide and arseniosiderite (Ca2Fe(AsO4)3O3•3H2O). Existence of the former species is not in question, but the presence of the latter species was not confirmed by additional measurements, so its identification is less certain. The linear combination, least-squares fits totals of several samples deviate by more than ± 20% from 100%, suggesting that additional phases may be present that were not identified or evaluated in this study.ConclusionsSub- to anoxic conditions minimize dissolution of arsenopyrite at the LCMS site, but may accelerate the dissolution of As-bearing secondary iron phases such as Fe3+-oxyhydroxides and arseniosiderite, if sufficient organic matter is present to spur anaerobic microbial activity. Oxidizing, dry conditions favor the stabilization of secondary phases, while promoting oxidative breakdown of the primary sulfides. The stability of both primary and secondary As phases is likely to be at a minimum under cyclic wet-dry conditions. Biogenic iron (hydr)oxide flocs can sequester significant amounts of arsenic; this property may be useful for treatment of perpetual sources of As such as mine adit water, but the fate of As associated with natural accumulations of floc material needs to be assessed.

Evaluation of the water quality related to the acid mine drainage of an abandoned mercury mine (Alaşehir, Turkey)

Mobility of metals in water, mine wastes, and stream sediments around the abandoned Alaşehir mercury mine was investigated to evaluate the environmental effects around the area. Mine waters are dominantly acidic with pH values of 2.55 in arid season and 2.70 in wet season and are sulfate rich. Acidity is caused mainly by the oxidation of sulfide minerals. Pyrite is the main acid-producing mineral in the Alaşehir area. Of the major ions, SO(4) shows a notable increase reaching 3981 mg/l, which exceeds the WHO (WHO guidelines for drinking water quality, vol. 2. Health criteria and other supporting information, 1993) and TS (Sular-Içme ve kullanma sulari. Ankara: Türk Standartlari Enstitüsü, 1997) drinking water standard of 250 mg/L. Mine waters have As, Fe, Mn, Ni, and Al with concentrations higher than drinking water standards. Hg concentrations of adit water samples and surface waters draining the mine area are between 0.25 and 0.274 microg/L and are below the WHO (WHO guidelines for drinking water quality, vol. 2. Health criteria and other supporting information, 1993) drinking water standard of 1.0 microg/L. However, the concentrations are above the 0.012 microg/L standard (EPA, Water quality standards. Establishment of numeric criteria for priority toxic pollutants, states' compliance, final rule. Fed. Reg., 40 CFR, Part 131, 57/246, 60847-60916, 1992) used to protect aquatic life. Stream sediment samples have abnormally high values of especially Hg, As, Ni, and Cr metals. Geoaccumulation (Igeo) and pollution index (PI) values are significantly high and denote heavy contamination in stream sediments. The stream sediments derived from the mining area with the surface waters are potentially hazardous to the environment adjacent to the abandoned Hg mine and are in need of remediation.

Radionuclides and metals in freshwater mussels of the upper South Alligator River, Australia

During an inspection of the old Rockhole Mine area in Kakadu National Park in 1999, it was found that a small amount of tailings from the former South Alligator uranium (U) mill had been uncovered by wet season rain and road works. Samples of sediment, water and freshwater mussels, Velesunio angasi, were collected from the South Alligator River, near and at the confluence of Rockhole Mine Creek, and adjacent to the exposed tailings. The 228Ra/ 226Ra activity ratios in sediments and mussel tissue indicate a small influence from the tailings and from Rockhole Mine adit water on 226Ra concentrations. The uptake of 226Ra in mussels does not correlate with other alkaline-earth metals. Mussel U concentrations are higher immediately downstream of Rockhole Mine Creek, but there is no noticeable increase in the immediate vicinity of the tailings area. A hypothetical ingestion of 2 kg of mussels from the sites was used to estimate the committed effective dose for a 10-year-old child resulting in a figure of 0.23 mSv per annum, of this total dose, 69% is attributed to 210Po. Only 0.03 mSv per annum can be directly linked to impacts of the tailings.

English

Aquatic biological data have been collected from the upper Arkansas River since 1994 to monitor aquatic biological conditions in the river relative to historic mining and recent remediation activities in the California Gulch drainage. California Gulch flows directly into the Arkansas River and has historically contained elevated levels of several metals. Reclamation efforts (capping of waste rock piles, interception and treatment of adit water, etc.) have eliminated surge flows from the adits and lowered concentrations of metals entering the Arkansas River. Monitoring of brown trout populations has shown increasing trends in both density and biomass since 1994. Brown trout density and biomass were historically low downstream of California Gulch. However, trout density and biomass have been comparable or better than the reference condition upstream of California Gulch since 2002. Numbers of young-of-year brown trout have also improved. For macroinvertebrates, density, total number of taxa, number of mayfly taxa, and number of metal intolerant taxa have shown increasing trends downstream of California Gulch since 1994. The percent of total density as heptageniid mayflies is still somewhat lower than the reference sites, indicating some residual effects of California Gulch are still occurring. These data indicate reclamation efforts have improved conditions for the aquatic biota in the Arkansas River downstream of California Gulch. Additional

English

The Tip Top Mine in Gamble Gulch, Colorado is a high mountain site where the stream above the mine is pristine and below the influx of acid rock drainage, the aquatic ecosystem appears to be impacted. An aquatic toxicity assessment study was carried out to determine the impact of contaminants on the stream and to test the leaching methods and simple toxicity tests that have been developed at the Colorado School of Mines. All tests show that the stream water above the adit inflow is pristine. However, the stream below shows concentrations of Al, Cu and Zn that are slightly above acute aquatic toxicity limits. Leaching tests on stream sediment samples taken below the adit entrance show concentrations of contaminants that are on the borderline of being toxic. Physical and chemical assessments of the mine waste piles on the site show that they are not impairing the immediate vicinity or the stream. It appears that the cause of any aquatic toxicity is the adit water entering the gulch or the heavy oxyhydroxide precipitates lining the streambed below the mine site.

Scavenging and immobilization of trace contaminants by colloids in the waters of abandoned ore mines

The occurrence of mine water colloids mainly results from the formation of oxyhydroxides and hydroxysulfates of Fe(III) and Al. In acid rock drainage solutions As and Pb are strongly associated with the colloids. In the near-neutral bulk waters of mines, as for instance in adit waters, trace elements such as As, Pb, Cu and the rare earth elements are sorbed. These trace contaminants can be scavenged by the colloids in the near-neutral mine waters and can be immobilized due to colloid coagulation and aggregate precipitation (‘natural attenuation’). In the pH range of 4–6, a pH range that must be passed through during the flooding of a mine, also U(VI) is adsorbed to the colloids and can be temporarily immobilized by precipitating colloids. The latter can result in a delay of the uranium release of a uranium mine and thus in a flattening and broadening of the uranium concentration profiles during the mine's ‘first flush’.

Mobilisation and attenuation of arsenic around gold mines, east Otago, New Zealand

Arsenic is released into the environment by decomposition of natural arsenopyrite in gold‐bearing veins in east Otago. Natural release is slow, but is accelerated by mining activity. Waters from old mine adits have pH of 6–7, compared to normal groundwater pH of 7–8, and adit waters have arsenic concentrations up to 4 ppm compared to background levels of c. 0.01 ppm. Tailings disposed about 80–90 years ago into what is now a wetland at Barewood have arsenic concentrations of up to 33 000 ppm, principally in the form of the secondary arsenic mineral scorodite. The maximum dissolved arsenic concentration in the Barewood tailings is 0.75 ppm at pH of c. 5.5. Dissolved arsenic release at that pH may be restricted to levels near 1 ppm by the formation of scorodite with solubility and/or kinetic controls on scorodite redissolution. Modern mining activity in the Macraes area has resulted in localised dissolved arsenic concentrations in excess of 200 ppm at pH near 10. Evaporation of this water produces scorodite precipitates. Dissolved arsenic released from arsenopyrite decomposition is attenuated by fine‐grained minerals, predominantly phyllosilicates, in soils around weathered veins, and in wetlands downstream from mine workings. Lithic soils can hold at least 50–100 ppm As on the fine fraction (c. 1 μ,m), and wetland soils can hold hundreds to thousands of parts per million on their fine fractions. Both soil adsorption and scorodite mediation slow the release of arsenic into the environment, allowing more effective dilution by downstream waters to safe arsenic levels.