Applied Geochemistry (v.20, #8)

Changes in precipitate mineralogy, morphology, and major and trace element concentrations and associations throughout 5 coal mine drainage (CMD) remediation systems treating discharges of varying chemistries were investigated in order to determine the factors that influence the characteristics of precipitates formed in passive systems. The 5 passive treatment systems sampled in this study are located in the bituminous coal fields of western Pennsylvania and northern Maryland, and treat discharges from Pennsylvanian age coals. The precipitates are dominantly (>70%) goethite. Crystallinity varies throughout an individual system, and lower crystallinity is associated with enhanced sorption of trace metals. Degree of crystallinity (and subsequently morphology and trace metal associations) is a function of the treatment system and how rapidly Fe(II) is oxidized, forms precipitates, aggregates and settles. Precipitates formed earlier in the passive treatment systems tend to have the highest crystallinity and the lowest concentrations of trace metal cations. High surface area and cation vacancies within the goethite structure enable sorption and incorporation of metals from coal mine drainage-polluted waters. Sorption affinities follow the order of Zn > Co ≈ Ni > Mn. Cobalt and Ni are preferentially sorbed to Mn oxide phases when these phases are present. As pH increases in the individual CMD treatment systems toward the pHpzc of goethite, As sorption decreases and transition metal (Co, Mn, Ni and Zn) sorption increases. Sulfate, Na and Fe(II) concentrations may all influence the sorption of trace metals to the Fe hydroxide surface. Results of this study have implications not only for solids disposal and resource recovery but also for the optimization of passive CMD treatment systems.

Near-conservative behavior of 129I in the orange county aquifer system, California by Kathleen A. Schwehr; Peter H. Santschi; J.E. Moran; David Elmore (1461-1472).
Iodine is a biophilic element, with one stable isotope, 127I, and one long-lived radioisotope, 129I. Radioiodine originates in the surface environment almost entirely from anthropogenic activities such as nuclear fuel reprocessing in Europe and thus provides a unique point source tracer. Very few studies have evaluated the geochemical behavior of I isotopes in the subsurface. In this study, the concentrations of 129I and 127I were measured in wells fed by a series of artificial recharge ponds in the Forebay Area of the Orange County ground water basin (California, USA) to evaluate their potential use as hydrological tracers. To substantiate interpretation of 129I and 127I concentration data, the aquifer system was evaluated using the literature values of aquifer water mass age based on 3H/3He, Xe and δ 18O tracer data. The aquifer data demonstrate the nearly conservative behavior of 129I with 129I/127I ratios likely reflecting variations in source functions as well as climatic conditions, and with inferred particle-water partition coefficients (K d) of 0.1 cm3 g−1 or less.

Fertiliser characterisation: Major, trace and rare earth elements by N. Otero; L. Vitòria; A. Soler; A. Canals (1473-1488).
In recent years, there has been increasing concern regarding the chemical impact of agricultural activities on the environment so it is necessary to identify contaminants, and/or characterise the sources of contamination. In this study, a comprehensive chemical characterisation of 27 fertilisers of different types used in Spain has been conducted; major, minor and trace elements were determined, including rare earth elements. Results show that compound fertilisers used for fertigation or foliar application have low content of heavy metals, whereas fertilisers used for basal and top dressing have the highest content of both REE and other heavy metals. REE patterns of fertilisers have been determined in order for them to be used as tracers of fertilisers in future environmental studies. Furthermore in this work REE patterns of fertilisers are used as tracers of the source of phosphate in compound fertilisers, distinguishing between phosphorite and carbonatite derived fertilisers. Fertilisers from carbonatites have higher contents of REE, Sr, Ba and Th whereas fertilisers from phosphorites have higher contents of metals of environmental concern, such as Cd, U and As; and the sum of the heavy metals is higher. Some of the analysed fertilisers have Cd concentrations that exceed maximum values established in some countries and can be expected to produce long-term soil accumulation. Furthermore, other elements such as U, As and Cr are 10–50 times higher in concentration than those of Cd, but there is no legislation regarding them, therefore it is necessary to regulate fertiliser compositions in order to achieve environmental protection of soils and waters.

Application of geochemical ratios for delineating gem-bearing areas in high grade metamorphic terrains by P.N. Ranasinghe; C.B. Dissanayake; M.S. Rupasinghe (1489-1495).
Trace element data for stream sediment samples collected from 6 river basins situated in geomorphologically and climatologically different terrains of Sri Lanka were analyzed to identify a suitable geochemical ratio to delineate potential areas for gems. All the areas are located in high grade metamorphic terrains with different lithologies. Correlations between different elements were studied using Spearman rank correlation and elements showing consistent high correlations were selected to calculate element ratios that can be used to discriminate areas with different potentials for gems. It was noted that the Rb, Ba, Sr, and the Ti, Nb, Zr element groups have high correlations between them. From the calculated ratios Ba/Sr, Rb/Sr and RbxBa/Sr2 were identified as being useful. The best ratio was determined considering the discrimination %, and representation of within category gem potential variation.Results show that RbxBa/Sr2 is the best ratio and a value greater than 4 represents gem potential areas while a ratio less than 1 represents low/no potential areas. Application of these results to the locations where test gem pits were validated this empirical rule.

Inorganic, isotopic, and organic composition of high-chloride water from wells in a coastal southern California aquifer by John A. Izbicki; Allen H. Christensen; Mark W. Newhouse; George R. Aiken (1496-1517).
Chloride concentrations were as high as 230 mg/L in water from the surface discharge of long-screened production wells in Pleasant Valley, Calif., about 100 km NW of Los Angeles. Wells with the higher Cl concentrations were near faults that bound the valley. Depending on well construction, high-Clwater from different sources may enter a well at different depths. For example, Cl concentration in the upper part of some wells completed in overlying aquifers influenced by irrigation return were as high as 220 mg/L, and Cl concentrations in water sampled within wells at depths greater than 450 m were as high as 500 mg/L. These high-Cl waters mix within the well during pumping and produce the water sampled at the surface discharge. Changes in the major ion, minor ion, trace element, and δ 34S and δ 13C isotopic composition of water in wells with depth were consistent with changes resulting from SO4 reduction, precipitation of calcite, and cation exchange. The chemical and isotopic composition of high-Cl water from deep wells trends towards the composition of oil-field production water from the study area. Chloride concentrations in oil-field production water present at depths 150 m beneath freshwater aquifers were 2200 mg/L, and Cl concentrations in underlying marine rock were as high as 4400 mg/L. High-Cl concentrations in water from deeper parts of wells were associated with dissolved organic C composed primarily of hydrophobic neutral compounds believed to be similar to those associated with petroleum in underlying deposits. These compounds would not be apparent using traditional sampling techniques and would not be detected using analytical methods intended to measure contamination.

Water mass transfer can occur between water and petroleum during changes in pressure and temperature. This process can result in the dilution or concentration of dissolved ions in the water phase of oilfield petroleum–water samples. In this study, PVT simulations were undertaken for 4 petroleum–water systems covering a range of reservoir conditions (80–185 °C; 300–1000 bar) and a range of water-petroleum mixtures (volume ratios of 1:1000–300:1000) to quantify the extent of H2O mass transfer as a result of pressure and temperature changes. Conditions were selected to be relevant to different types of oilfield water sample (i.e. surface, downhole and core samples). The main variables determining the extent of dilution and concentration were found to be: (a) reservoir pressure and temperature, (b) pressure and temperature of separation of water and petroleum, (c) petroleum composition, and (d) petroleum:water ratio (PWR). The results showed that significant dilution and concentration of water samples could occur, particularly at high PWR. It was not possible to establish simple guidelines for identifying good and poor quality samples due to the interplay of the above variables. Sample quality is best investigated using PVT software of the type used in this study.

Spring waters were analysed in the field by anodic stripping voltammetry, using equipment which is sufficiently portable to be useful in a remote heavily forested area accessible by foot only. The equipment and techniques are capable of producing analyses on site to the μg/L level for labile metals. Field analysis avoids issues of sample storage and transport protocols that limit confidence in laboratory measurements of labile elements. Samples were taken as a feedback to immediate analysis resulting in a fine grid map of the geological site. Acid rock drainage emanates from a New Zealand historic mine site, with elevated concentrations of metals. However, ground water and surface water discharging naturally from mineralised rocks in the same area also have elevated levels of metals. This study quantifies natural metalliferous discharges from a single site, and compares this to the overall metal flux from the mine area. Acid (pH 3) metalliferous springs emanate from colluvium and bedrock in a young (months-old) landslide. Labile Cu, Pb, Zn and Cd are the environmentally most significant metals in the studied area. Labile metal concentrations observed in the natural springs are up to 24 μg/L Cu, up to 50 μg/L Pb, up to 5 μg/L Cd and up to 9 mg/L Zn. Labile Cu and Zn concentrations are similar to laboratory-determined total concentrations, whereas labile Pb and Cd concentrations are generally distinctly lower than total Pb and Cd concentrations. Four different spring water compositions occur within metres of each other: acid metalliferous water with high Pb, acid metalliferous water with low Pb, high Cu, Pb, Zn acid water and high pH water with elevated Cu. High metal concentrations in these waters are readily attenuated by adsorption to Fe oxyhydroxides (HFO), especially when rain raises spring water pH at the surface. Copper, Pb and Cd are >99% adsorbed, and Zn >95% adsorbed, during this rainfall dilution. Natural spring waters have potential to contribute up to 10% of the total Zn flux from the catchment, but negligible proportions of Cu, Pb and Cd.

Total Hg concentrations and Hg speciation were determined in bottom sediments of Marano lagoon to investigate the consequences of Hg phases on fish farms and shellfish cultivation areas. Mercury phases were separated into cinnabar (HgS) and non-cinnabar compounds, via a thermo-desorption technique, in surface and core sediments; both of which had been contaminated by industrial wastes and mining activity residues. The former are due to an industrial complex, which has been producing cellulose, chlor-alkali and textile artificial fibres since 1940. Processing and seepage wastewaters, which were historically discharged into the Aussa-Corno river system and therefore into the lagoon, have been significantly reduced since 1984 due to the construction of wastewater treatment facilities. The second source is the Isonzo River, which has been the largest contributor of Hg into the northern Adriatic Sea since the 16th century due to Hg mining at the Idrija mine (western Slovenia). Red cinnabar (HgS) derived from the mining area is mostly stable and insoluble under current environmental conditions. In contrast, organically bound Hg, such as Hg bound to humic acids, has the potential to be transformed into bioavailable Hg compounds (for example, methylmercury). The presence of the two Hg forms permitted each Hg source to be quantified. It also allowed the areas with the highest risk of Hg contamination from Hg-rich sediment to be identified; thus potentially avoiding the transfer of Hg from the sediment into the water column and eventually into living biota. The results show that Hg Enrichment Factors in bottom sediments exceed values of 10 and cinnabar dominates the central sector near the main tidal channel where tidal flux is more effective. Non-cinnabar compounds were found to be enriched in fine grained material and organic matter. In fact, up to 98% of total Hg at the Aussa-Corno river mouth and in the inner margin of the basin occurred in an organic form. This evidence, combined with the high contents of total Hg (4.1–6.6 μg g−1 and EF > 10) measured in surface sediments, suggest that Hg in Marano lagoon is involved in biogeochemical transformations (e.g., methylation).

Trace-element concentrations in baseline samples from a survey of aquifers used as potable-water supplies in the United States are summarized using methods appropriate for data with multiple detection limits. The resulting statistical distribution models are used to develop summary statistics and estimate probabilities of exceeding water-quality standards.The models are based on data from the major aquifer studies of the USGS National Water Quality Assessment (NAWQA) Program. These data were produced with a nationally-consistent sampling and analytical framework specifically designed to determine the quality of the most important potable groundwater resources during the years 1991–2001.The analytical data for all elements surveyed contain values that were below several detection limits. Such datasets are referred to as multiply-censored data. To address this issue, a robust semi-parametric statistical method called regression on order statistics (ROS) is employed.Utilizing the 90th–95th percentile as an arbitrary range for the upper limits of expected baseline concentrations, the models show that baseline concentrations of dissolved Ba and Zn are below 500 μg/L. For the same percentile range, dissolved As, Cu and Mo concentrations are below 10 μg/L, and dissolved Ag, Be, Cd, Co, Cr, Ni, Pb, Sb and Se are below 1–5 μg/L.These models are also used to determine the probabilities that potable ground waters exceed drinking water standards. For dissolved Ba, Cr, Cu, Pb, Ni, Mo and Se, the likelihood of exceeding the US Environmental Protection Agency standards at the well-head is less than 1–1.5%. A notable exception is As, which has approximately a 7% chance of exceeding the maximum contaminant level (10 μg/L) at the well head.

87Sr/86Sr ratio variations were analyzed in rainfall, shallow ground water and base flow collected from 4 Piedmont streams within the Middle Oconee River basin in northeastern Georgia during the period between March, 2003 and March, 2004. They Sr isotope ratio analyses were accompanied by measurements of stream discharge, rainfall, stable O isotope ratios and major ion and 3H concentrations. The average Sr ion concentration and 87Sr/86Sr ratio for the terminal stream basin (the Middle Oconee River) were 23.6 μg/L and 0.7172, respectively. The average 87Sr/86Sr ratios of the rainwater and shallow ground water were below 0.7125, indicating that most of the Sr in this stream water is input by weathering reactions in deeper ground water, rather than by ion exchange in shallow soil horizons. This is consistent with the higher alkalinity concentrations (∼23–47 mg/L) and specific conductance values (60–113 μS/cm) that characterize stream base flow. Piedmont streams are characterized by lower concentrations of Sr and higher 87Sr/86Sr ratios than average global stream flow.Base flow rates decreased by a factor of 2–3 during the summer months and this is accompanied by increased alkalinity concentrations. 87Sr/86Sr ratios, however, were temporally invariant for a given stream basin and were independent of season, antecedent rainfall, and discharge. 87Sr/86Sr ratios were unique for each of the 4 basins and a general trend toward higher ratios with increasing basin area was apparent. The inferred contribution from minerals with high Rb contents such as K feldspar and muscovite may have resulted from the greater integration of flow from mineralogically diverse pathways afforded by a larger basin area. The basin specificity and temporal or seasonal invariability make 87Sr/86Sr ratios an invaluable hydrological tracer that can be readily employed in mass balance studies of stream flow within the Piedmont Province.

Deciphering the presence of wastewater in a medium-sized Mediterranean catchment using a multitracer approach by Marion Rabiet; François Brissaud; Jean-Luc Seidel; Séverin Pistre; Françoise Elbaz-Poulichet (1587-1596).
The impact of wastewater disposal on the water resource in a medium-sized Mediterranean watershed, the Hérault River basin, has been studied using a multitracer approach including NO 3 - , Cl - , B concentrations and the Gd anomaly. The Hérault watershed supplies drinking water to approximately 300,000 inhabitants and receives the effluents of 96 sewage treatment plants. The geological context is heterogeneous with 4 main lithologies: a Palaeozoic basement in the north, a karstified Mesozoic cover in the middle, an evaporite layer in the western part of the basin and alluvial deposits in the southern plain. The concentration of major ( Ca 2 + , Cl - , NO 3 - ) and trace elements (B, Sr and rare earth elements) has been monitored in streams, aquifers and sewage treatment plant effluents. Because of the particularly heterogeneous and rich geological context of the Hérault basin, the challenge of using NO 3 - , Cl - and B as wastewater tracers was to distinguish their natural and anthropogenic origins. Indeed, none of these wastewater borne elements can be considered as a highly reliable tracer by itself because they are ubiquitous in water where they can be supplied by both natural (evaporite dissolution, rainfall) and anthropogenic sources (wastewater or agriculture). However, the respective contributions of different sources of candidate tracers, NO 3 - , Cl - and B could be roughly assessed using Sr/Ca, B/Sr and Cl/B ratios which, combined with the information provided by each tracer, allowed the ascertainment of the presence of wastewater in two tributaries of the Hérault River and in a few wells tapped for drinking water in the alluvial plain.

Behaviour of sulphur during diagenesis of a maritime ombrotrophic peat from Yell, Shetland Islands, UK by Rebecca Bartlett; Simon Bottrell; Jonathan Coulson (1597-1605).
Surface water, pore water, vegetation and peat cores were sampled from a waterlogged ombrotrophic peat bog on the Shetland Isles, UK and analysed for different S forms and their isotopic composition, in an attempt to elucidate the biogeochemical processes affecting S during peat diagenesis. Surface waters show that inputs of S to the peat have a maritime-dominated isotopic composition close to +20‰CDT. Uptake of S by vegetation introduces a −10‰ shift in δ 34S from these input values.Below the vegetation layer and down to 18 cm depth, bacterial SO 4 2 - reduction is the major control on S species distribution and isotopic composition within the solid peat and pore waters. In this part of the peat, preferential reduction of 32SO4 in pore water during metabolism produces isotopically light sulphide, which is incorporated into the solid phase in both inorganic and organic forms, while pore water SO 4 2 - becomes enriched in 34S. From 18 to 28 cm, organic S content falls relative to C and residual organic S becomes 34S-enriched, indicative of mineralization of organic S, a process which releases isotopically light S to the pore waters. Still deeper in the core (28 to ∼50 cm), bacterial reduction of pore-water SO 4 2 - , now enriched in 34S, results in addition of isotopically heavy S to the solid phase. Limited pore water data suggest that below 50 cm mineralization reactions again release S from the organic fraction of the peat.