J.F. Devlin

The effects of electron donor and granular iron on nitrate transformation rates in sediments from a municipal water supply aquifer

Abstract A municipal water supply well for the town of Baden, located about 10 km southwest of Waterloo, ON, Canada, was forced to close due to unacceptably high concentrations of nitrate in the groundwater. Stimulated in situ denitrification was considered a possible solution to the problem. In advance of a planned field test, the effectiveness of various electron donors (acetate, hydrogen gas, elemental sulphur, thiosulphate, aqueous ferrous iron and pyrite) at stimulating denitrification was compared in microcosm experiments involving sediment from the Baden aquifer. All electron donors tested, with the possible exception of pyrite, stimulated nitrate removal from solution. Acetate was found to be the substance that stimulated the quickest initial removal rates, and denitrification was confirmed as the mechanism using the acetylene block technique. Nitrite accumulation was minimal in most systems, although the local water quality guideline limit of 1.0 mg/l NO 2 − –N was briefly and temporarily exceeded (maximum value was 1.2 mg/l) in some of the acetate amended microcosms. Granular iron was also considered as an electron donor or abiotic reducing agent, but was found to reduce nitrate predominantly to ammonium, in a neutral pH solution buffered with pyrite. In mixed granular iron aquifer sediment systems, where several electron donors were present (hydrogen, ferrous iron and pyrite) that could have supported denitrification, the abiotic reaction with the granular iron appeared to dominate other transformation pathways, and ammonium was again the major product. Based on the testing completed as part of this project, the aquifer at Baden is considered a good candidate for acetate-stimulated in situ denitrification for the removal of nitrate from the groundwater near the municipal water supply well.

Migration and natural fate of a coal tar creosote plume. 2. Mass balance and biodegradation indicators

Abstract A source of coal tar creosote was emplaced below the water table at CFB Borden to investigate natural attenuation processes for complex biodegradable mixtures. A mass balance indicated that ongoing transformation occurred for seven study compounds. Phenol migrated as a discrete slug plume and almost completely disappeared after 2 years, after being completely leached from the source early in the study. The m -xylene plume migrated outward to a maximum distance at approximately 2 years, and then receded back towards the source as the rate of mass flux out of the source decreased to below the overall rate of plume transformation. Carbazole showed similar behaviour, although the reversal in plume development occurred more slowly. The dibenzofuran plume remained relatively constant in extent and mass over the last 2 years of monitoring, despite constant source input over this period, providing evidence that the dibenzofuran plume was at steady state. Meanwhile, the naphthalene and 1-methylnaphthalene plumes continued to advance and increase in mass over the observation period, although at a decreasing rate. The phenanthrene plume was also subject to transformation, although measurement of the rate was less conclusive due to the higher proportion of sorbed mass for this compound. Three lines of evidence are presented to evaluate whether the observed plume mass loss was due to microbial biodegradation. Measurement of redox-sensitive parameters in the vicinity of the plume showed the types of changes that would be expected to occur due to plume biodegradation: dissolved oxygen and SO 4 2− decreased in groundwater within the plume while significant increases were noted for Fe 2+ , Mn 2+ and methane. Further evidence that plume mass loss was microbially-mediated was provided by the accumulation of aromatic acids within the plume. Measurements of phospholipid fatty acids (PLFA) in aquifer material indicated that microbial biomass and turnover rate were greater within the plume than outside: also consistent with biodegradation. Study results highlight the potential for utilizing natural attenuation as a site cleanup approach for dissolved phase plumes from complex organic mixture like coal tar creosote.

A sequential zero valent iron and aerobic biodegradation treatment system for nitrobenzene

The remediation of nitroaromatic contaminated groundwater is sometimes difficult because nitroaromatic compounds are resistant to biodegradation and, when they do transform, the degradation of the products may also be incomplete. A simple nitroaromatic compound, nitrobenzene, was chosen to assess the feasibility of an in situ multi-zone treatment system at the laboratory scale. The proposed treatment system consists of a zero valent granular iron zone to reduce nitrobenzene to aniline, followed by a passive oxygen release zone for the aerobic biodegradation of the aniline daughter product using pristine aquifer material from Canadian Forces Base (CFB) Borden, Ontario, as an initial microbial source. In laboratory batch experiments, nitrobenzene was found to reduce quickly in the presence of granular iron forming aniline, which was not further degraded but remained partially sorbed onto the granular iron surface. Aniline was found to be readily biodegraded with little metabolic lag under aerobic conditions using the pristine aquifer material. A sequential column experiment, containing a granular iron reducing zone and an aerobic biodegradation zone, successively degraded nitrobenzene and then aniline to below detection limits (0.5 microM) without any noticeable reduction in hydraulic conductivity from biofouling, or through the formation of precipitates.

In situ sequential treatment of a mixed contaminant plume

Groundwater plumes often contain a mixture of contaminants that cannot easily be remediated in situ using a single technology. The purpose of this research was to evaluate an in situ treatment sequence for the control of a mixed organic plume chlorinated ethenes and petroleum hydrocar- . bons within a Funnel-and-Gate. A shallow plume located in the unconfined aquifer at Alameda .

In situ sequenced bioremediation of mixed contaminants in groundwater.

A mixture of chlorinated solvents (about 0.5-10 mg/l), including tetrachloroethene (PCE) and carbon tetrachloride (CT), together with a petroleum hydrocarbon, toluene (TOL), were introduced into a 24 m long x 2 m wide x 3 m deep isolated section (henceforth called a gate) of the Borden aquifer and subjected to sequential in situ treatment. An identical section of aquifer was similarly contaminated and allowed to self-remediate by natural attenuation, thus serving as a control. The control presents a rare opportunity to critically assess the performance of the treatment systems, and represents the first such study for sequenced in situ remediation. The first treatment step was anaerobic bioremediation. This was accomplished using a modified nutrient injection wall (NIW) to pulse benzoate and a nutrient solution into the aquifer, maximizing mixing by dispersion and minimizing fouling near the injection wells. In the anaerobic bioactive zone that developed, PCE, CT and chloroform (CF), a degradation product of CT, degraded with a half-lives of about 59, 5.9 and 1.7 days, respectively. The second step was aerobic bioremediation, using a biosparge system. TOL and cis-1,2 dichloroethene (cDCE), from PCE degradation, were found to degrade aerobically with half-lives of 17 and 15 days, respectively. Compared to natural attenuation, PCE and TOL removal rates were significantly better in the sequenced treatment gate. However, CT and CF were similarly and completely attenuated in both gates. It is believed that the presence of TOL helped sustain the reducing environment needed for the reduction of these two compounds.

Field investigation of nutrient pulse mixing in an in situ biostimulation experiment

This research was funded by the Ontario Ministry of Environment and Energy. Additional support from the University Consortium Solvents-in-Groundwater Research Program is also gratefully acknowledged. Sponsors of the program have included The Boeing Company, Ciba-Geigy, Dow Chemical, Eastman Kodak, General Electric, Mitretek Systems, Motorola, PPG Industries, United Technologies Corporation, the Natural Sciences and Engineering Research Council of Canada, and the Ontario Research University Fund.

Field comparison of the point velocity probe with other groundwater velocity measurement methods

1 meter tests returned average velocity magnitudes of 30.2 ± 7.7 to 34.7 ± 13.1 cm/d (depending on prior knowledge of flow direction in PVP tests) and 36.5 ± 10.6, respectively, which were near the estimated bulk velocity (20 cm/d). The other direct velocity measurement techniques yielded velocity estimates 5 to 12 times the bulk velocity. Best results with the PVP instrument were obtained by jetting the instrument into place, though this method may have introduced a slight positive bias to the measured velocities. The individual estimates of point velocity direction varied, but the average of the point velocity directions agreed quite well with the expected bulk flow direction. It was concluded that the PVP method is a viable technique for use in the field, where high-resolution velocity data are required.

Applications and implications of direct groundwater velocity measurement at the centimetre scale.

Three projects involving point velocity probes (PVPs) illustrate the advantages of direct groundwater velocity measurements. In the first, a glacial till and outwash aquifer was characterized using conventional methods and multilevel PVPs for designing a bioremediation program. The PVPs revealed a highly conductive zone that dominated the transport of injected substances. These findings were later confirmed with a natural gradient tracer test. In the second, PVPs were used to map a groundwater velocity field around a dipole recirculation well. The PVPs showed higher than expected velocities near the well, assuming homogeneity in the aquifer, leading to improved representations of the aquifer heterogeneity in a 3D flow model, and an improved match between the modelled and experimental tracer breakthrough curves. In the third study, PVPs detected subtle changes in aquifer permeability downgradient of a biostimulation experiment. The changes were apparently reversible once the oxygen source was depleted, but in locations where the oxygen source lingered, velocities remained low. PVPs can be a useful addition to the hydrogeologists toolbox, because they can be constructed inexpensively, they provide data in support of models, and they can provide information on flow in unprecedented detail.

Hydrogeologic assessment of in situ natural attenuation in a controlled field experiment

Financial support for this research was provided by the Advanced Alternative Technology Demonstration Facility, funded by the Department of Defense and administered by Rice University. Additional support was provided by the NSERC/Motorolla/ETI Industrial Research Chair in Groundwater Remediation and the Solvents in Groundwater Consortium, University of Waterloo. T. Anderson of the University of Massachusetts assisted with hydrogen measurements, while Susan Froud and Dennis Katic assisted with all other aspects of the fieldwork and participated in discussions of the data. Mike Brown is acknowledged for his contribution to the installation of the gate, and Stephanie Fiorenza is acknowledged for her comments and assistance liaising with AATDF.

HydrogeoSieveXL: an Excel-based tool to estimate hydraulic conductivity from grain-size analysis

For over a century, hydrogeologists have estimated hydraulic conductivity (K) from grain-size distribution curves. The benefits of the practice are simplicity, cost, and a means of identifying spatial variations in K. Many techniques have been developed over the years, but all suffer from similar shortcomings: no accounting of heterogeneity within samples (i.e., aquifer structure is lost), loss of grain packing characteristics, and failure to account for the effects of overburden pressure on K. In addition, K estimates can vary by an order of magnitude between the various methods, and it is not generally possible to identify the best method for a given sample. The drawbacks are serious, but the advantages have seen the use of grain-size distribution curves for K estimation continue, often using a single selected method to estimate K in a given project. In most cases, this restriction results from convenience. It is proposed here that extending the analysis to include several methods would be beneficial since it would provide a better indication of the range of K that might apply. To overcome the convenience limitation, an Excel-based spreadsheet program, HydrogeoSieveXL, is introduced here. HydrogeoSieveXL is a freely available program that calculates K from grain-size distribution curves using 15 different methods. HydrogeoSieveXL was found to calculate K values essentially identical to those reported in the literature, using the published grain-size distribution curves.RésuméDepuis plus d’un siècle, les hydrogéologues ont estimé la conductivité hydraulique (K) à partir des courbes de distribution de la granulométrie. Les bénéfices de cette pratique sont la simplicité, le coût, et les moyens d’identifier les variations spatiales de K. Plusieurs techniques ont été développées au cours des années, mais toutes souffrent des raccourcis similaires : pas de prise en compte de l’hétérogénéité au sein des échantillons (par ex. la structure de l’aquifère est perdue), perte des caractéristiques de l’arrangement des grains, et manque de prise en compte des effets de la pression de charge sur K. De plus, les estimations de K peuvent varier d’un ordre de grandeur selon les différentes méthodes, et il n’est généralement pas possible d’identifier la meilleure méthode pour un exemple donné. Les inconvénients sont importants, mais les avantages ont vu l’utilisation de courbes de distribution de la granulométrie pour une estimation continue de K, souvent en utilisant une méthode unique sélectionnée pour estimer K dans un projet donné. Dans la plupart des cas, cette restriction résulte de la commodité. Il est proposé ici que l’extension de l’analyse en introduisant plusieurs méthodes serait bénéfique, car elle fournirait une meilleure indication de la gamme de K qui pourrait être appliquée. Pour surmonter la limitation de commodité, un programme développé à l’aide de feuilles de calcul sous Excel, HydrogeoSieveXL, est introduit dans cet article. HydrogeoSieveXL est un programme disponible gratuitement qui calcule K à partir des courbes de granulométrie en utilisant 15 méthodes différentes. HydrogeoSieveXL permet de calculer des valeurs de K sensiblement identiques à celles rapportées dans la littérature, en utilisant des courbes de distribution de granulométrie publiées.ResumenDurante más de un siglo, los hidrogeólogos estimaron la conductividad hidráulica (K) a partir de las curvas de distribución del tamaño de grano. Los beneficios de esta práctica son la simplicidad, el costo y un medio para identificar las variaciones espaciales de K. Se han desarrollado muchas técnicas a lo largo de los años, pero todas adolecen de carencias similares: no tener en cuenta la heterogeneidad dentro de las muestras (es decir, se pierde la estructura del acuífero), la pérdida de las características del empaquetamiento de granos, y la falla en considerar los efectos de la sobrepresión sobre K. Además, las estimaciones de K pueden variar en un orden de magnitud entre los distintos métodos, y generalmente no es posible identificar el mejor método para una muestra dada. Los inconvenientes son serios, pero las ventajas en el uso de curvas de distribución de tamaño de grano para las estimaciones de K continúan, a menudo utilizando un único método seleccionado para estimar K en un proyecto determinado. En la mayoría de los casos, esta restricción proviene de la conveniencia. Aquí se propone extender el análisis para incluir varios métodos lo cual sería beneficioso ya que proporcionaría una mejor indicación del rango de K que sería aplicable. Para superar la limitación de la conveniencia, se introduce aquí un programa de hoja de cálculo, HydrogeoSieveXL, basado en Excel. HydrogeoSieveXL es un programa de libre acceso que calcula K a partir de curvas de distribución de tamaño de grano utilizando 15 métodos diferentes. Se encontró que los valores de K calculados por HydrogeoSieveXL son esencialmente idénticos a los reportados en la literatura, utilizando las curvas publicadas de distribución de tamaño de grano.摘要一百多年来,水文地质学家都是通过粒径分布曲线估算水力传导率(K)的。这种做法的好处就是简单、成本低,也是确定k 值空间变化的一种手段。多年以来,开发了许多技术,但都有类似的缺点:没有解释样品(即:含水层结构丢失)内的非均质性,颗粒排列特征的缺失及无法解释覆盖层压力对k值的影响。另外,k估算值在不同的方法之间有数量级的变化,通常不能确定针对某一样品的最好方法。弊端非常严重,但优势就是用于估算k值的粒径分布曲线继续在使用,常常在某一项目中采用单一选择的方法估算k值。在大部分情况下,这个限制起因于便利。在此提出,拓展包含几种方法的分析将是有益的,因为这会提供更好的可能应用的k值范围。为了克服便利上的局限性,这里介绍了一种基于Excel电子指标程序—水文筛网程序XL。水文筛网程序XL是一个可免费获取的程序,采用15种不同的方法通过粒径分布曲线计算k值。发现水文筛网程序XL计算的k值和文献记载的、采用公布的粒径分布曲线得到的k值基本相同。ResumoPor mais de um século, hidrogeólogos têm estimado a condutividade hidráulica (K) por curvas de distribuição do tamanho de partículas. Os benefícios dessa prática são simplicidade, custo, e uma maneira de identificar variações espaciais na K. Muitas técnicas têm sido desenvolvidas ao longo dos anos, mas todas sofrem da mesma deficiência: não consideram a heterogeneidade entre amostras (por exemplo, a estrutura do aquífero é perdida), a perda de características de arranjo das partículas, e falham ao considerar os efeitos de sobrecargas de pressão na K. Além disso, estimativas de K podem variar em uma ordem de grandeza entre vários métodos, e geralmente não é possível de se identificar o melhor método para uma determinada amostra. Os inconvenientes são sérios, mas as vantagens que permitiram o uso de curvas de distribuição do tamanho de partículas para estimar K continuam, frequentemente utilizando um único método selecionado para estimar K em um determinado projeto. Na maioria dos casos, essa restrição é resultado da conveniência. É proposto aqui que a extensão das análises para que se incluam vários métodos seria benéfico, desde que isso fornecesse uma melhor indicação do intervalo de K que se ajuste à realidade. Para superar a limitação da conveniência, é aqui introduzido um programa baseado em planilha eletrônica Excel, HydrogeoSieveXL. HydrogeoSieveXL é um programa disponível de forma livre, que calcula K a partir de curvas de distribuição do tamanho de partículas utilizando 15 métodos diferentes. HydrogeoSieveXL foi instaurado para calcular valores K essencialmente idênticos àqueles descritos na literatura, utilizando as curvas de distribuição do tamanho de partículas anteriormente publicadas.