Sulfate Land Application Enhances Biodegradation in a Petroleum Hydrocarbon Smear Zone

Delivery of sulfate to petroleum hydrocarbons (PHCs) source zones and groundwater plumes is desirable to enhance biodegradation rates when treatment has become limited due to depletion of sulfate. Sulfate land application involves spreading sulfate salts on ground surface and allowing their dissolution and infiltration of sulfate into subsurface. The objectives of this pilot-scale investigation were to capture the vertical transport of sulfate beneath an application area, confirm that sulfate reduction was occurring, and explore how the added sulfate affected biodegradation of benzene and toluene. Approximately 4000 kg of gypsum was spread over a 30 m × 30 m study area above a smear zone located approximately 2 m below-ground surface. Precipitation was augmented by two irrigation events. Groundwater samples, collected over 1058 days from multilevel wells and a conventional long-screened monitoring well, were analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX), sulfate, bromide, dissolved inorganic carbon (DIC) and methane. Compound-specific isotope analyses (CSIA) for benzene and toluene, and isotope analyses of ¹³C-DIC and ³⁴S-SO₄²⁻ were performed. Following application, an increase in sulfate concentration was noted in the smear zone. ³⁴S-SO₄²⁻ enrichment and ¹³C-DIC depletion indicated that sulfate reduction and mineralization of PHCs were enhanced. CSIA results provided unequivocal evidence of anaerobic biodegradation of benzene and toluene. After 1058 days when sulfate was depleted, methane concentrations were about three times greater than baseline conditions suggesting syntrophic benefit of the delivered sulfate. Observations from this investigation support the viability of sulfate land application to enhance biodegradation rates in shallow PHC smear zones.     

Estimation of a non-stationary prior covariance from seismic data

Non-stationarity in statistical properties of the subsurface is often ignored. In a classical linear Bayesian inversion setting of seismic data, the prior distribution of physical parameters is often assumed to be stationary. Here we propose a new method of handling non-stationarity in the variance of physical parameters in seismic data. We propose to infer the model variance prior to inversion using maximum likelihood estimators in a sliding window approach. A traditional, and a localized shrinkage estimator is defined for inferring the prior model variance. The estimators are assessed in a synthetic base case with heterogeneous variance of the acoustic impedance in a zero-offset seismic cross section. Subsequently, this data is inverted for acoustic impedance using a non-stationary model set up with the inferred variances. Results indicate that prediction as well as posterior resolution is greatly improved using the non-stationary model compared with a common prior model with stationary variance. The localized shrinkage predictor is shown to be slightly more robust than the traditional estimator in terms of amplitude differences in the variance of acoustic impedance and size of local neighbourhood. Finally, we apply the methodology to a real data set from the North Sea basin. Inversion results show a more realistic posterior model than using a conventional approach with stationary variance.     

Correction of precipitation based on off-site weather information

Owing to aerodynamic errors, correction of precipitation measurements, liquid, mixed or solid, is often carried out by means of an explicit mathematical statistical model. The magnitude of correction, e.g., calculated as a correction factor to the observed amount of precipitation, is the dependent variable, and wind speed, temperature and a measure of precipitation intensity are independent variables entering the correction model. Usually these independent variables are accessible on site where the precipitation measurements are recorded. However, in many standard precipitation networks the gauge measurements are not accompanied by on site information of these variables, and information from remote stations must be used. The aim of the paper is to describe how the statistical models can be used in evaluating if the set of remote information of the independent variables can be used for the estimation of a reliable correction factor on site. The technique is then applied to an example of precipitation network in Denmark where the typical situation for the standard gauges is that only the amount of precipitation is available. It is expected that not only can the methods be adapted to other countries, but for landscapes similar to Denmark even the conclusions can be applied directly: extrapolation of all independent variables from remote sites should be conducted with caution, wind speed information can be extrapolated from remote sites not farther away than approximately 50 km, while information on rain intensity and temperature can be safely extrapolated across longer distances.     

Investigation of Kinnekulle K-bentonite aimed at assessing the long-term stability of bentonites under repository conditions

Müller-Vonmoos, M., Kahr, G., Bucher, F. and Madsen, F.T., 1990. Investigation of Kinnekulle K. bentonite aimed at assessing the long-term stability of bentonites under repository conditions. Eng. Geol., 28: 269–280.

The mineral formula, the content of fixed potassium and the average interlayer charge of the montmorillonite–illite mixed layer part of four Ordovician K-bentonite samples from Kinnekulle (Sweden) were investigated. The content of fixed potassium was found to decrease from 84% to 50% with increasing depth and distance from the Permian basalt intrusion about 100 m above the bentonite beds. The interlayer charge of the mixed layer is smectitic, i.e. below 0.5 charges per formula unit. The swelling pressures of air-dried, gently grinded and uniaxially compressed specimens with dry densities between 1.5 Mg/m³ and 2 Mg/m³ range from 1 N/mm² to 15 N/mm². This is about 20% of the swelling pressure values of identically treated Ca-montmorillonite. Following ultrasonic treatment, air-drying, gently grinding and compaction, increased swelling pressures of of about 70% of those Ca-montmorillonite were obtained. The reason for this increase in swelling pressure was investigated by dispersion experiments and determinations of water vapour adsorption isotherms of ultrasonically treated and untreated material.     

The luminescence dating chronology of a deep core from Bosten Lake (NW China) in arid central Asia reveals lake evolution over the last 220 ka

The lacustrine deposits of lakes in arid central Asia (ACA) potentially record palaeoclimatic changes on orbital and suborbital time scales, but such changes are still poorly understood due to the lack of reliable chronologies. Bosten Lake, the largest freshwater inland lake in China, is located in the southern Tianshan Mountains in central ACA. A 51.6‐m‐deep lacustrine succession was retrieved from the lake and 30 samples from the succession were used for luminescence dating to establish a chronology based on multi‐grain quartz OSL and K‐feldspar post‐IR IRSL (pIRIR₂₉₀) dating. Quartz OSL ages were only used for samples from the upper part of the core. The K‐feldspar luminescence characteristics (dose recovery test, anomalous fading test, first IR stimulation temperature plateau test) are satisfactory and from the relationship amongst the quartz OSL, IR₅₀ and pIRIR₂₉₀ doses we infer that the feldspar signals are likely to be well bleached at deposition. Bacon age‐depth modelling was used to derive a chronology spanning the last c. 220 ka. The chronology, lithology and grain‐size proxy record indicate that Bosten Lake formed at least c. 220 ka ago and that lake levels fluctuated frequently thereafter. A stable deep lake occurred at c. 220, 210–180, c. 165, 70–60, 40–30 and 20–5 ka, while shallow levels occurred at c. 215, 180–165, 100–70, 60–40 and 30–20 ka. Bosten Lake levels decreased by at least ~29 m and possibly the lake even dried up between c. 160 and c. 100 ka. We suggest that the water‐level fluctuations in the lakes of ACA may not respond directly to climatic changes and may be affected by a number of complex factors.     

Scalar fields,fluids and exact Bianchi type-V solutions

A photometric study of a large sample of Be stars is reported. Infrared homogeneous observational data in theJHKL system are used to derive some photometric characteristics of Be stars, as a class. New infrared observations of 34 Be stars are included in the present paper. Infrared two-colour diagrams are used to investigate the presence of in frared emission in Be stars. The origin of infrared excess in relation to Balmer line emission in Be stars is discussed.