Applied Geochemistry (v.25, #9)

Estimating specific surface area of fine stream bed sediments from geochemistry by B.G. Rawlins; G. Turner; I. Mounteney; G. Wildman (1291-1300).
Specific surface area (SSA) of headwater stream bed sediments is a fundamental property which determines the nature of sediment surface reactions and influences ecosystem-level, biological processes. Measurements of SSA – commonly undertaken by BET nitrogen adsorption – are relatively costly in terms of instrumentation and operator time. A novel approach is presented for estimating fine (<150 μm) stream bed sediment SSA from their geochemistry – after removal of organic matter – for agricultural headwater catchments across 15,400 km2 of central England, UK. From a regional set of 1972 stream bed sediment sites with common characteristics for which geochemical data were available, 60 samples were selected – based on maximising their variation in Al concentrations – and their BET SSA measured by N2 adsorption. After careful selection of potential regression predictors following a principal component analysis and removal of a subset of samples with the largest Mo concentrations (>2.5 mg kg−1), four elements were identified as significant predictors of SSA (ordered by decreasing predictive power): V > Ca > Al > Rb. The optimum model from these four elements accounted for 73% of the variation in bed sediment SSA (range 6–46 m2  g−1) with a root mean squared error of prediction – based on leave-one-out cross-validation – of 6.3 m2  g−1. It is believed that V is the most significant predictor because its concentration is strongly correlated both with the quantity of Fe-oxides and clay minerals in the stream bed sediments, which dominate sediment SSA. Sample heterogeneity in SSA – based on triplicate measurements of sub-samples – was a substantial source of variation (standard error = 2.2 m2  g−1) which cannot be accounted for in the regression model.The model was used to estimate bed sediment SSA at the other 1792 sites and at 30 duplicate sites where an extra sediment sample had been collected, 25 m from the original site. By delineating sub-catchments for the headwater sediment sites only those sub-catchments were selected with a dominant (>50% of the sub-catchment area) bedrock formation and land use type; the bedrock and land use classes accounted for 39% and 7% of the variation in bed sediment SSA, respectively. Variation in estimated, fine bed sediment SSA from the paired, duplicate sediment sites was small (2.7 m2  g−1), showing that local variation in SSA at stream sites is modest when compared to that between catchments. How the approach might be applied in other environments and its potential limitations are discussed.

Chlorine isotope evidence for the anthropogenic origin of tris-(4-chlorophenyl)methane by Henry Holmstrand; Zdenek Zencak; Manolis Mandalakis; Per Andersson; Örjan Gustafsson (1301-1306).
► TCPMe is a bioaccumulating organochlorine found at significant levels in organisms at high trophic levels, e.g. birds and mammals. ► Previous investigations have suggested TCPMe being co-released as a trace byproduct in pesticides such as DDT. ► The results from compound-specific chlorine isotope analysis of TCPMe supports the hypothesis that the source of TCPMe is indeed the extensive historical use of DDT.Compound-specific Cl-isotope analysis was performed on the persistent and bioaccumulating compound tris-(4-chlorophenyl)methane (4,4′,4″-TCPMe, referred to as TCPMe in this study) to elucidate whether its main source is natural or anthropogenic. Blubber from the Baltic grey seal (Halichoerus grypus) was extracted by continuous acetonitrile partitioning, and the TCPMe was isolated from the extract by preparative-capillary gas chromatography. Chlorine isotope analysis was subsequently performed by sealed-tube combustion in conjunction with thermal-ionization mass spectrometry (TIMS). The δ 37Cl of TCPMe was −3.5 ± 0.5‰, similar to the previously reported δ 37Cl of technical grade p,p′-DDT (referred to as DDT in this study). The data is not consistent with a putative marine natural source of TCPMe, as enzymatic (biotic) production is reported to give values of δ 37Cl < −10‰. The δ 37Cl–TCPMe data thus supports the hypothesis that TCPMe is produced as a byproduct during DDT synthesis and is released to the environment through the same pathways as DDT. It is also consistent with tris-(4-chlorophenyl)methanol as the primary biotransformation product of TCPMe.

Major ion and isotope geochemistry of fluids and gases from coalbed methane and shallow groundwater wells in Alberta, Canada by Katrina Cheung; Patrick Klassen; Bernhard Mayer; Fariborz Goodarzi; Ramon Aravena (1307-1329).
The production of coalbed methane (CBM) represents a vital new source of natural gas supply in Western Canada. There are, however, concerns over potential negative environmental impacts on shallow groundwater resources in the hypothetical case that leakage of fluids and gases from CBM operations occurs. This paper compares major ion and isotope geochemistry data for produced fluids or gases from two major coal deposits in Western Canada (Mannville Formation and the Horseshoe Canyon/Belly River Group) with similar data collected for shallow groundwater in south-central Alberta. The objective was to generate comprehensive baseline geochemical data to determine the key geochemical characteristics and differences of produced fluids and gases from two coal deposits and shallow groundwater in Alberta and to find parameters that are suitable for identifying potential leakage of fluids or gases into shallow groundwater. Shallow groundwater had average total dissolved solids (TDS) of 1037 mg/L. Most samples belonged to the Na–HCO3–SO4 water type and average SO 4 2 - concentrations were 185 mg/L. The Horseshoe Canyon/Belly River Group swabbing fluids had average TDS of 5427 mg/L, a Na–HCO3 water type, and average SO 4 2 - concentrations of 47.7 mg/L. The produced fluids from the Mannville Formation had average TDS contents of 74,500 mg/L, negligible SO 4 2 - and a Na–Cl water type. Shallow groundwater and produced fluids from the Horseshoe Canyon Formation and the Mannville group had distinct δ 2H and δ 18O values and plotting δ 18O values versus total dissolved solids was found to be an effective approach to distinguish the waters. Sulfur isotope data revealed the occurrence of bacterial (dissimilatory) SO4 reduction in some shallow groundwater samples and in the produced fluids from the Horseshoe Canyon/Belly River Group.Methane was found in several shallow groundwater samples and its average δ 13C (−72.1 ± 6.8‰) and δ 2H values (−297 ± 17‰) indicated a biogenic origin predominantly from CO2 reduction. Dissolved gases from the Horseshoe Canyon Formation fluids with average δ 13C values of methane of −54.0 ± 4.1‰ and ethane of −36.5 ± 2.4‰ and traces of higher alkanes suggest a mixture of predominantly biogenic and some thermogenic gas. Dissolved hydrocarbon gas from the Mannville Formation had the highest average δ 13C values of −49.4 ± 3.6‰ for methane, −28.8 ± 2.1‰ for ethane and −26.9 ± 1.1‰ for propane. The presence of higher alkanes suggests that the Mannville produced fluids contain an appreciable thermogenic gas component. The biogenic gas component in the Horseshoe Canyon and the Mannville Formation was mainly formed via acetate fermentation according to α CO2–CH4 values between 1.02 and 1.07.It is concluded that δ 18O values of the fluids in concert with total dissolved solids, and the isotopic compositions of methane and ethane are sufficiently distinct in shallow groundwater and produced fluids from the Horseshoe Canyon and the Mannville Formations that they may serve as tracers for evaluating potential contamination of shallow groundwater with produced fluids or gases.

Comparative studies on compounds occluded inside asphaltenes hierarchically released by increasing amounts of H2O2/CH3COOH by Jing Zhao; Zewen Liao; Lühui Zhang; Patrice Creux; Chupeng Yang; Anna Chrostowska; Haizu Zhang; Alain Graciaa (1330-1338).
► Some other molecules are occluded inside asphaltenes ► These occluded molecules can be released from asphaltenes by H2O2/CH3COOH oxidation ► These occluded molecules are representatives of the original oils from kerogensBeing the heaviest fraction of crude oils, asphaltenes are liable to aggregate, and other molecules in the oils can be steadily adsorbed onto, and even occluded inside the macromolecular structures of the asphaltenes. These occluded compounds inside the asphaltenes can survive over geological time in oil reservoirs owing to effective protection by the macromolecular structures of the asphaltenes. The asphaltenes of a crude oil (ZG31) from the central Tarim Basin, NW China, were hierarchically degraded by increasing the amount of H2O2/CH3COOH to release the occluded compounds. Besides the common components, series of even numbered n-alk-1-enes and 3-ethylalkanes were detected among the occluded compounds. Comparison of the biomarker distributions and the compound-specific C isotopic results between the compounds from the maltenes and those from the occluded fraction, the ZG31 reservoir was suggested to have been charged multiple times, with different charges being derived from different strata of source rocks.

13C of indoor CO2 indicates proportion of C4-derived carbon in occupants’ diet. ► Flux balance model for ventilated rooms shows rapid approach to CO2 steady-state. ► From extant indoor CO2 data more dietary C4 carbon in American than European diets. ► Local outdoor urban CO2 increase of 17 ppm in ten years, no change in average 13C.From July to November 2009, concentrations of CO2 in 78 samples of ambient air collected in 18 different interior spaces on a university campus in Dallas, Texas (USA) ranged from 386 to 1980 ppm. Corresponding δ 13C values varied from −8.9‰ to −19.4‰. The CO2 from 22 samples of outdoor air (also collected on campus) had a more limited range of concentrations from 385 to 447 ppm (avg. = 408 ppm), while δ 13C values varied from −10.1‰ to −8.4‰ (avg.=-9.0‰). In contrast to ambient indoor and outdoor air, the concentrations of CO2 exhaled by 38 different individuals ranged from 38,300 to 76,200 ppm (avg. = 55,100 ppm), while δ 13C values ranged from −24.8‰ to −17.7‰ (avg. = −21.8‰). The residence times of the total air in the interior spaces of this study appear to have been on the order of 10 min with relatively rapid approaches (∼30 min) to steady-state concentrations of ambient CO2 gas. Collectively, the δ 13C values of the indoor CO2 samples were linearly correlated with the reciprocal of CO2 concentration, exhibiting an intercept of −21.8‰, with r 2  = 0.99 and p  < 0.001 (n  = 78). This high degree of linearity for CO2 data representing 18 interior spaces (with varying numbers of occupants), and the coincidence of the intercept (−21.8‰) with the average δ 13C value for human-exhaled CO2 demonstrates simple mixing between two inputs: (1) outdoor CO2 introduced to the interior spaces by ventilation systems, and (2) CO2 exhaled by human occupants of those spaces. If such simple binary mixing is a common feature of interior spaces, it suggests that the intercept of a mixing line defined by two data points (CO2 input from the local ventilation system and CO2 in the ambient air of the room) could be a reasonable estimate of the average δ 13C value of the CO2 exhaled by the human occupants. Thus, such indoor spaces appear to constitute effective “sample vessels” for collection of CO2 that can be used to determine the average proportions of C3 and C4-derived C in the diets of the occupants. For the various groups occupying the rooms sampled in this study, C4-derived C appears to have constituted ∼40% of the average diet.The average concentration of outdoor Dallas atmospheric CO2 was ∼17 ppm higher than the average of CO2 concentrations measured on the same campus 10 a ago. In addition, Dallas outdoor CO2 concentrations at both times were higher than the contemporaneous global atmospheric CO2 concentrations. This observation, plus the fact that the increase of ∼17 ppm in the average concentration of Dallas outdoor CO2 was comparable to the global increase of ∼18 ppm over the same 10-a interval, is consistent with a significant role for urban CO2 “factories” in the global atmospheric CO2 budget.

Managed aquifer recharge (MAR) is increasingly being considered as a means of reusing urban stormwater and wastewater to supplement the available water resources. Subsurface storage is advantageous as it does not impact on the area available for urban development, while the aquifer also provides natural treatment. However, subsurface storage can also have deleterious effects on the recovered water quality through water–rock interactions which can also impact on the integrity of the aquifer matrix. A recent investigation into the potential for stormwater recycling via Aquifer Storage Transfer and Recovery (ASTR) in a carbonate aquifer is used to determine the important hydrogeochemical processes that impact on the recovered water quality. An extensive period of aquifer flushing allows observation of water quality changes under two operating scenarios: (1) separate wells for injection and recovery, representing ASTR; and (2) a single well for injection and recovery, representing Aquifer Storage and Recovery (ASR).Calcite dissolution produces the dominant inorganic chemical change to the quality of stormwater following storage in the carbonate aquifer; independent of the mode of MAR operation (ASTR or ASR). The magnitude of calcite dissolution in response to the injection of urban stormwater exceeds that previously reported within the same aquifer using both stormwater and reclaimed wastewater. While some dissolution is induced in response to redox processes, the primary influence on dissolution is the reactivity of the source water itself as indicated by the sub-saturation with respect to calcite. Cation exchange is evident through the ASTR mode of operation, producing a marginal increase in the Na concentration during freshening of the storage zone. This increase in Na concentration is not evident in the ASR mode as cation exchange is limited to the initial pore flushes of the storage zone.Aquifer storage provides some treatment through nutrient removal, mainly through removal of ∼35% of the dissolved organic C (DOC). DOC removal is greatest when the MAR operation involves separate injection and recovery wells as ASTR allows enhanced removal by sorption. ASR can lead to nutrient recycling around the injection well which can produce water quality that is atypical of the quality in the bulk of the storage zone. Water recovered from ASR shows some removal of DOC through microbial oxidation coincident with removal of O2 from the source water, which is considered to be a sustainable process during subsurface treatment. During ASTR, enhanced DOC removal is attributed to adsorption, but as with cation exchange, this removal may be limited to the initial period of aquifer conditioning. Oxidation of pyrite is evident during the initial stages of injection until the pool of reactive pyrite within the storage zone is consumed, affecting the quality of water recovered via the ASTR mode only.

On metal diagenesis in contaminated sediments of the Deûle river (northern France) by L. Lesven; B. Lourino-Cabana; G. Billon; P. Recourt; B. Ouddane; O. Mikkelsen; A. Boughriet (1361-1373).
► Behaviour and fate of metal contaminants in sediments (remobilisation, dredging ...). ► Implication of metal contaminations on biogeochemical processes in anoxic sediments. ► Impacts on the distribution of anthropogenic metal in sediments.The objective of the present work was to assess depth-related variations in the (bio)geochemical processes involved in anoxic sediments from the Deûle river, and to examine particularly their impacts on the distribution of anthropogenically sourced metals. Anoxic sediment samples were sliced and analyzed to determine total concentrations vs. depth of elements and corresponding pore waters were analyzed to determine concentration profiles with depth of pH, Eh, alkalinity, O2, dissolved organic carbon (DOC), and main inorganic anions and cations present in the medium. It was shown that rapid depletions of O2, NO 3 - and SO 4 2 - , accompanied with HCO 3 - generation and a sharp decrease in the redox potential occurred within the first centimeters of the surface sediment as a consequence of early diagenesis. Bacterial reductive dissolution of Mn(III and IV) and Fe(III) oxides/hydroxides to Mn(II) and Fe(II) accompanied by microbial degradation of organic matter took place as well, and resulted in trace metal increases in the pore water at levels that raised the possibility of mineral generation. Thermodynamic calculations predicted removal of metals from interstitial waters through combinations with carbonates and/or sulfides. These took place either by direct precipitation to form pure crystals, or by coprecipitation/sorption with/into calcite and with pyritic compounds. Chemical sequential extraction data were useful in this work to support, at least partially, some thermodynamic predictions concerning the existence of interactions between trace metals and carbonate and sulfide ions to generate (co)precipitates. Electron paramagnetic resonance (EPR) studies on Deûle sediments revealed the presence of Mn(II) adsorbed onto sedimentary calcite surfaces. X-ray diffractograms of heavy minerals from Deûle sediments extracted with CHBr3 by density separation exhibited peaks ascribed to galena, sphalerite and pyrite. In addition to these compounds, using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS), micro-analyses of sedimentary heavy minerals confirmed successfully the existence of other thermodynamically predicted associations: covellite; chalcopyrite, greenockite and/or amorphous CdS.

Significance of polycyclic aromatic hydrocarbons (PAHs) in Permian/Triassic boundary sections by Birgit Nabbefeld; Kliti Grice; Roger E. Summons; Lindsay E. Hays; Changqun Cao (1374-1382).
► Detailed study of PAHs across several P/Tr sample sets. ► Significance of perylene and its association with fungal spike. ► Significance of combustion-dervied PAHs in ash beds at GSSP, South China.In this study the abundances of several polycyclic aromatic hydrocarbons (PAHs Table 1, I–XXI) have been measured throughout three Permian/Triassic (P/Tr) sections from Meishan (South China), Kap Stosch area (East Greenland) and Peace River Basin (Western Canada). Dibenzothiophene (I) and dibenzofuran (II) were found to decrease in abundance just before or shortly after the P/Tr transition in all three sections while perylene (III) was observed to increase in abundance at the onset of the main extinction horizon (bed 25) in Meishan. Perylene has been attributed to a wood degrading fungal source and, therefore, it seems possible these phenomena are related to the demise of land plants. Further, distinct patterns of various combustion-derived PAHs occurring in each section imply that forest fire events occurred within the Late Permian and Early Triassic. In the Meishan section high amounts of combustion-derived PAHs [pyrene (IV), fluoranthene (V), benzo[a]anthracene (VI), benzofluoranthenes (sum, i.e. VII), benzo[a]pyrene (VIII), benzo[e]pyrene (IX) and coronene (X)] occur within bed 25, also containing ash attributed to the fallout from massive volcanic eruptions in Siberia and/or China.

Experiments and geochemical modelling of CO2 sequestration by olivine: Potential, quantification by B. Garcia; V. Beaumont; E. Perfetti; V. Rouchon; D. Blanchet; P. Oger; G. Dromart; A.-Y. Huc; F. Haeseler (1383-1396).
Aqueous solutions equilibrated with supercritical CO2 (150 °C and total pressure of 150 bar) were investigated in order to characterize their respective conditions of carbonation. Dissolution of olivine and subsequent precipitation of magnesite with a net consumption of CO2 were expected. A quantified pure mineral phase (powders with different olivine grain diameter [20–80 μm], [80–125 μm], [125–200 μm] and [>200 μm]), and CO2 (as dried ice) were placed in closed-batch reactors (soft Au tubes) in the presence of solutions. Different salinities (from 0 to 3400 mM) and different ratios of solution/solid (mineral phase) (from 0.1 to 10) were investigated. Experiments were performed over periods from 2 to 8 weeks. Final solid products were quantified by the Rock-Eval 6 technique, and identified using X-ray diffraction, Raman spectroscopy, electron microprobe and scanning electron microscopy. Gaseous compounds were quantified by a vacuum line equipped with a Toepler pump and identified and measured by gas chromatography (GC). Carbon mass balances were calculated.Olivine reacted completely with CO2, trapping up to 57 ± 2% (eqC of initial CO2) as magnesite; some amorphous silica also formed. Olivine grain diameter and solution/mineral ratios appeared to be the primary controls on the reaction, salinity acting as a second order parameter. During the experiments, fluid analyses may not be performed with approach adopted but, geochemical modelling was attempted to give information about the solution composition. This showed an interesting mineral matrix evolution. Under the experimental conditions, olivine appeared to be a good candidate for CO2 trapping into a geologically stable carbonate, magnesite. The possible use of mafic and ultramafic rocks for CO2 sequestration is discussed.

► Groundwater table rebound in aquifer containing sulfide ore. ► Degradation of water quality causes by the significant increase in sulfate concentrations. ► Isotopic examinations of sulfate and sulfate concentrations along flow path. ► Sulfate concentrations as a result of binary mixing of sources (sulfide and evaporate). ► Changes in isotopic composition of sulfide in extended vadose zone.The objective of this study was to determine the sources of SO 4 2 - in groundwater of the Olkusz–Zawiercie Major Groundwater Body. The quality of groundwater was relatively good in the past, but fluctuations of the water table level have caused degradation of water quality. Variations in the water table level and the formation of the depression cone have resulted from both groundwater withdrawal and Zn–Pb mine dewatering. As a result within the extended vadose zone of the aquifer, weathering of pyrite and accompanying sulfides has taken place. Since 1992 the water table has risen and this process has been associated with an increase in concentrations of SO 4 2 - , Ca and Mg. At the same time, the pH has decreased and periodically high Fe concentrations have been detected. High concentrations of Mg and Sr have been observed and, since gypsum layers are known to be present, a de-dolomitisation process has been hypothesized. The PHREEQC program for Windows was used to estimate saturation indices for calcite, dolomite, gypsum and epsomite. Isotopic data for SO 4 2 - dissolved in the groundwater and archival data on isotopic composition of ore sulfides were used to solve the isotope balance equation and to estimate the fraction of dissolved SO 4 2 - that originated from pyrite oxidation and gypsum dissolution. The results have shown that dissolution of pyrite oxidation products has a significant influence on chemical composition of groundwater, especially in the southern part of the cone of depression. By solving the additional, combined mass transfer and isotope balance equations it was inferred that a variation in isotopic composition of weathered sulfides must also occur.

Atmospheric wet deposition of trace elements to central Tibetan Plateau by Zhiyuan Cong; Shichang Kang; Yulan Zhang; Xiangdong Li (1415-1421).
► Long-term study of trace elements in wet precipitation shows anthropogenic pollutants have affected the pristine Tibetan Plateau by long-range transport, especially in summer.To investigate trace elements in wet precipitation over the Tibetan Plateau (TP), a total of 79 event-based precipitation samples were collected from September 2007 to September 2008 at Nam Co Station. Samples were analyzed for concentrations of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb using inductively coupled plasma-mass spectrometry (ICP-MS). The annual volume-weighted concentrations of elements were generally comparable to other background sites, and much lower than urban areas. The enrichment factors (EF) showed that, in comparison with the Tibetan soils, the wet precipitation had elevated concentrations of Cr, Co, Ni, Cu, Zn, Cd and Pb, probably indicating their anthropogenic origins. Other elements (Al, Fe, Mn and V) with enrichment factor value of <10 may derive mainly from crustal sources. The principal component analysis further confirmed the two different groups of elements in wet deposition samples. The backward trajectories were calculated for each precipitation event using the NOAA HYSPLIT model. The results indicated significant differences of EF for trace elements of anthropogenic origin between the summer monsoon and non-monsoon seasons. The data obtained in the present study indicated that pollutants can affect remote high altitude regions like the Tibetan Plateau through long-range transport, especially in the summer monsoon season.

► Arsenic (As) retention by soil constituents vary with time. ► Soluble and exchangeable forms of As decreased after 6 months. ► Arsenic bioaccessibility was high all throughout the study period. ► Aging had an impact on the geochemical forms of As. ► Gastric pH was the sole important factor effecting As bioaccessibility.Ingestion of As – contaminated soil by children is a growing concern in former agricultural lands converted to residential or recreational land use areas. The mobility and bioavailability of As is controlled by its reactions with soil particles. The degree and strength of As retention by soil constituents may vary greatly with time. The present authors hypothesize that aging results in reduced mobility of As thereby decreasing As release and its bioavailability. The present study is aimed at evaluating the effect of aging on soil As fractionation and bioaccessibility in a temperature and humidity-controlled greenhouse setting. The design allowed the evaluation of dynamic interactions between soils, pesticides, water, and plants. Therefore, 4 soil types (Immokalee, Millhopper, Pahokee Muck, and Orelia) were selected based on their potential differences in As reactivity. The soils were amended with the pesticide Na arsenate at two rates. Rice was used as the test crop. Soil samples collected after different time periods (0, 6 months, 1 a and 3 a) were extracted for soil-As forms via a sequential extraction technique. Bioaccessible As was extracted via an in vitro gastrointestinal method. At time 0, most of the extractable As in soil was in the soluble form, resulting in high bioaccessibility. As expected, soluble and exchangeable fractions decreased with time for up to 6 months, but remained constant thereafter. After 3 a of soil–pesticide equilibration, As bioaccessibility was still high in all the soils except for the Pahokee Muck. No significant difference in As bioaccessibility was observed between the soils. Arsenic was present predominantly as As(V) with 5–10% of the total dissolved As being present as As(III). Data obtained suggest that although aging had an impact on the geochemical forms, gastric pH was the sole important factor effecting As bioaccessibility.

► With small amounts (1 mM) of pyrite, more water can be extracted than was injected. ► Formation of goethite during injection caused more Fe sorption during extraction. ► With more pyrite, there was more acidity, less goethite formed, more dissolved Fe. ► Dissolved Fe in extracted water increased with smaller amounts of injectate buffer. ► Addition of a buffer to the injectate increased the recovery efficiency of ASR.The effects of injecting oxic water from the New York city (NYC) drinking-water supply and distribution system into a nearby anoxic coastal plain aquifer for later recovery during periods of water shortage (aquifer storage and recovery, or ASR) were simulated by a 3-dimensional, reactive-solute transport model. The Cretaceous aquifer system in the NYC area of New York and New Jersey, USA contains pyrite, goethite, locally occurring siderite, lignite, and locally varying amounts of dissolved Fe and salinity. Sediment from cores drilled on Staten Island and western Long Island had high extractable concentrations of Fe, Mn, and acid volatile sulfides (AVS) plus chromium-reducible sulfides (CRS) and low concentrations of As, Pb, Cd, Cr, Cu and U. Similarly, water samples from the Lloyd aquifer (Cretaceous) in western Long Island generally contained high concentrations of Fe and Mn and low concentrations of other trace elements such as As, Pb, Cd, Cr, Cu and U, all of which were below US Environmental Protection Agency (USEPA) and NY maximum contaminant levels (MCLs). In such aquifer settings, ASR operations can be complicated by the oxidative dissolution of pyrite, low pH, and high concentrations of dissolved Fe in extracted water.The simulated injection of buffered, oxic city water into a hypothetical ASR well increased the hydraulic head at the well, displaced the ambient groundwater, and formed a spheroid of injected water with lower concentrations of Fe, Mn and major ions in water surrounding the ASR well, than in ambient water. Both the dissolved O2 concentrations and the pH of water near the well generally increased in magnitude during the simulated 5-a injection phase. The resultant oxidation of Fe2+ and attendant precipitation of goethite during injection provided a substrate for sorption of dissolved Fe during the 8-a extraction phase. The baseline scenario with a low (0.001 M) concentration of pyrite in aquifer sediments, indicated that nearly 190% more water with acceptably low concentrations of dissolved Fe could be extracted than was injected. Scenarios with larger amounts of pyrite in aquifer sediments generally resulted in less goethite precipitation, increased acidity, and increased concentrations of dissolved Fe in extracted water. In these pyritic scenarios, the lower amounts of goethite precipitated and the lower pH during the extraction phase resulted in decreased sorption of Fe2+ and a decreased amount of extractable water with acceptably low concentrations of dissolved Fe (5.4 × 10−6  M). A linear decrease in recovery efficiency with respect to dissolved Fe concentrations is caused by pyrite dissolution and the associated depletion of dissolved O2 (DO) and increase in acidity. Simulations with more than 0.0037 M of pyrite, which is the maximum amount dissolved in the baseline scenario, had just over a 50% recovery efficiency. The precipitation of ferric hydroxide minerals (goethite) at the well screen, and a possible associated decrease in specific capacity of the ASR well, was not apparent during the extraction phase of ASR simulations, but the model does not incorporate the microbial effects and biofouling associated with ferric hydroxide precipitation.The host groundwater chemistry in calcite-poor Cretaceous aquifers of the NYC area consists of low alkalinity and moderate to low pH. The dissolution of goethite in scenarios with unbuffered injectate indicates that corrosion of the well could occur if the injectate is not buffered. Simulations with buffered injectate resulted in greater precipitation of goethite, and lower concentrations of dissolved Fe, in the extracted water. Dissolved Fe concentrations in extracted water were highest in simulations of aquifers (1) in which pyrite and siderite in the aquifer were in equilibrium, and (2) in coastal areas affected by saltwater intrusion, where high dissolved-cation concentrations provide a greater exchange of Fe2+ (FeX2). Results indicate that ASR in pyrite-bearing, Cretaceous aquifers of the NYC area can be a cost effective way to both store drinking water supplies and significantly reduce ambient concentrations of dissolved Fe.

Long term measurements of NO 3 - concentrations in two estuaries on Buzzards Bay, Massachusetts, USA, coupled with a large, step-wise increase in the groundwater NO 3 - to one of those estuaries, have allowed the effects on the estuary to be isolated and quantified. The results show that prior to the abrupt increase, the estuary responded in a linear manner to NO 3 - input, as suggested in the literature. After the abrupt increase, the estuary initially absorbed the greatly increased groundwater input, and after a year the response became a fluctuating variable with periods of less than 1 year. It is proposed that this indicates increased recycling from the sediments. This behavior is consistent with models of nutrient-induced regime shift in its early stages, as described in the literature. Future isotopic analysis is suggested as a means to confirm the estuary mechanism.