Rory Doherty

Microbial analysis of soil and groundwater from a gasworks site and comparison with a sequenced biological reactive barrier remediation process

Aims:  To investigate the distribution of a polymicrobial community of biodegradative bacteria in (i) soil and groundwater at a former manufactured gas plant (FMGP) site and (ii) in a novel SEquential REactive BARrier (SEREBAR) bioremediation process designed to bioremediate the contaminated groundwater.

A microbial fuel cell in contaminated ground delineated by electrical self-potential and normalized induced polarization data

There is a growing interest in the use of geophysical methods to aid investigation and monitoring of complex biogeochemical environments, for example delineation of contaminants and microbial activity related to land contamination. We combined geophysical monitoring with chemical and microbiological analysis to create a conceptual biogeochemical model of processes around a contaminant plume within a manufactured gas plant site. Self-potential, induced polarization and electrical resistivity techniques were used to monitor the plume. We propose that an exceptionally strong (>800 mV peak to peak) dipolar SP anomaly represents a microbial fuel cell operating in the subsurface. The electromagnetic and electrical geophysical data delineated a shallow aerobic perched water body containing conductive gasworks waste which acts as the abiotic cathode of microbial fuel cell. This is separated from the plume below by a thin clay layer across the site. Microbiological evidence suggests that degradation of organic contaminants in the plume is dominated by the presence of ammonium and its subsequent degradation. We propose that the degradation of contaminants by microbial communities at the edge of the plume provides a source of electrons and acts as the anode of the fuel cell. We hypothesize that ions and electrons are transferred through the clay layer that was punctured during the trial pitting phase of the investigation. This is inferred to act as an electronic conductor connecting the biologically mediated anode to the abiotic cathode. Integrated electrical geophysical techniques appear well suited to act as rapid, low cost sustainable tools to monitor biodegradation.

Spectral induced polarization signatures of abiotic FeS precipitation

In recent years, geophysical methods have been shown to be sensitive to microbial-induced mineralization processes. The spectral induced-polarization (SIP) method appears to be very promising for monitoring mineralization and microbial processes. With this work, we study the links of mineralization and SIP signals, in the absence of microbial activity. We recorded the SIP response during abiotic FeS precipitation. We show that the SIP signals are diagnostic of FeS mineralization and can be differentiated from SIP signals from biomineralization processes. More specifically, the imaginary conductivity shows almost linear dependence on the amount of FeS precipitating out of solution, above the threshold value 0.006 gr under our experimental conditions. This research has direct implications for the use of the SIP method as a monitoring and decision-making tool for sustainable remediation of metals in contaminated soils and groundwater.

Comparison of methods used to calculate typical threshold values for potentially toxic elements in soil

The environmental quality of land can be assessed by calculating relevant threshold values, which differentiate between concentrations of elements resulting from geogenic and diffuse anthropogenic sources and concentrations generated by point sources of elements. A simple process allowing the calculation of these typical threshold values (TTVs) was applied across a region of highly complex geology (Northern Ireland) to six elements of interest; arsenic, chromium, copper, lead, nickel and vanadium. Three methods for identifying domains (areas where a readily identifiable factor can be shown to control the concentration of an element) were used: k-means cluster analysis, boxplots and empirical cumulative distribution functions (ECDF). The ECDF method was most efficient at determining areas of both elevated and reduced concentrations and was used to identify domains in this investigation. Two statistical methods for calculating normal background concentrations (NBCs) and upper limits of geochemical baseline variation (ULBLs), currently used in conjunction with legislative regimes in the UK and Finland respectively, were applied within each domain. The NBC methodology was constructed to run within a specific legislative framework, and its use on this soil geochemical data set was influenced by the presence of skewed distributions and outliers. In contrast, the ULBL methodology was found to calculate more appropriate TTVs that were generally more conservative than the NBCs. TTVs indicate what a “typical” concentration of an element would be within a defined geographical area and should be considered alongside the risk that each of the elements pose in these areas to determine potential risk to receptors.

The effects of lead sources on oral bioaccessibility in soil and implications for contaminated land risk management.

Lead (Pb) is a non-threshold toxin capable of inducing toxic effects at any blood level but availability of soil screening criteria for assessing potential health risks is limited. The oral bioaccessibility of Pb in 163 soil samples was attributed to sources through solubility estimation and domain identification. Samples were extracted following the Unified BARGE Method. Urban, mineralisation, peat and granite domains accounted for elevated Pb concentrations compared to rural samples. High Pb solubility explained moderate-high gastric (G) bioaccessible fractions throughout the study area. Higher maximum G concentrations were measured in urban (97.6 mg kg(-1)) and mineralisation (199.8 mg kg(-1)) domains. Higher average G concentrations occurred in mineralisation (36.4 mg kg(-1)) and granite (36.0 mg kg(-1)) domains. Findings suggest diffuse anthropogenic and widespread geogenic contamination could be capable of presenting health risks, having implications for land management decisions in jurisdictions where guidance advises these forms of pollution should not be regarded as contaminated land.

Integrated earth resistivity tomography (ERT) and multilevel sampling gas: a tool to map geogenic and anthropogenic methane accumulation on brownfield sites

Soil gas emissions of methane and carbon dioxide on brownfield sites are usually attributed to anthropogenic activities; however geogenic sources of soil gas are often not considered during site investigation and risk management strategies. This paper presents a field study at a redeveloped brownfield site on a flood plain to identify accumulations of methane biogas trapped in underlying sediments. The investigation is based on a multidisciplinary approach using direct multi-level sampling measurements and Earth resistivity tomography . Resistivity imaging was applied to evaluate the feasibility of identifying the size and spatial continuity of soil gas accumulations in anthropogenic and naturally occurring deposits. As a result, biogas accumulations are described within both anthropogenic deposits and pristine organic sediments. This result is important to identify the correct approaches to identify and manage risks associated with soil gas emissions on brownfield and pristine sites. The organic-rich sediments in Quaternary fluvial environments of São Paulo Basin in particular the Tietê River, biogas reservoirs can be generated and trapped beneath geogenic and anthropogenic layers, potentially requiring the management of brownfield developments across this region.

Organic composition and multiphase stable isotope analysis of active, degrading and restored blanket bog

Here we used organic composition and stable isotopic analysis to evaluate the effects of drainage and restoration at an ombrotrophic peatland, to assess whether rewetting of blanket bogs will reverse degradation. The organic composition of the peat and the isotopic fractionation between the solid (peat), liquid (pore water) and gas (soil gas) phases on actively accumulating, degrading and restored locations are compared. Fourier Transform Infrared Spectroscopy (FTIR) analysis of the organic material has shown a high level of humification (low decomposition) in the active peat. Stable isotope analysis in the solid, liquid and gas phases has corresponded with this and indicated that the active location is enriched in 13C in the solid and gas phases, 15N in the solid phase, 18O in the liquid and gas phases and D in the liquid phase, suggesting a closed system with limited isotopic fractionation and thus limited water movement and decomposition. The degrading location has a lower level of humification, and is depleted in 13C in the solid phase due to ingression of vascular plants. The restored location has high humification and enrichment of 13C and 15N in the solid phase, and D in the liquid phase suggesting increased microbial activity. 13C and 18O in the gas phase and 18O in the liquid phase are depleted, as a result of microbial mediated gas production and rewetting. FTIR analysis has also indicated a subsurface zone of increased decomposition between the acrotelm and catotelm in both the active and degrading peat. This is due to a stable water table and is not present within the restored location, which we attribute to water table fluctuation associated with rewetting. This zone of increased decomposition adds to the complexity of blanket bog peatlands and the assumption that all systems can be generalized under one conceptual model.

Resistivity and induced polarization monitoring of biogas combined with microbial ecology at a brownfield site

AbstractThe accumulation of biogenic greenhouse gases (methane, carbon dioxide) in organic sediments is an important factor in the redevelopment and risk management of many brownfield sites. Good practice with brownfield site characterization requires the identification of free-gas phases and pathways that allow its migration and release at the ground surface. Gas pockets trapped in the subsurface have contrasting properties with the surrounding porous media that favor their detection using geophysical methods. We have developed a case study in which pockets of gas were intercepted with multilevel monitoring wells, and their lateral continuity was monitored over time using resistivity. We have developed a novel interpretation procedure based on Archie’s law to evaluate changes in water and gas content with respect to a mean background medium. We have used induced polarization data to account for errors in applying Archie’s law due to the contribution of surface conductivity effects. Mosaics defined by cha...

From raw materials to NORM by-products

Abstract Naturally occurring radionuclides are present in the Earth crust; however, their distribution is not homogeneous. When primary or secondary raw materials containing relatively low concentrations of naturally occurring radionuclides are introduced in an industrial process then the radionuclides can become more concentrated in the produced (by-)products. For example, during the production of purified metals, throughout the purification process, also other elements, such as naturally occurring radionuclides, become concentrated in the by-products. In order to assure radiation protection of the population, it is important to map the potential exposure for workers and the general public. There is an extensive literature available regarding the presence of naturally occurring radionuclides in various by-products; however, it can be hard to review and even to interpret for the regulators and members of the industry in order to assure the safe use of by-products for example in construction. To solve this problem data mining and text processing have been applied to the ever-increasing numbers of publications (More than 39,000 filtered publications have been processed up to the Jan. 6, 2017), and the NORM4Building database has been compiled based on the analysis of the collected data. Based on this database using text analysis methods the most NORM prone raw materials and industries have been identified. This chapter gives a concise overview on the parameters to be considered during the selection of NORM by-products as feedstock for the construction industry, specifically for the production of cement, concrete, and ceramics. In the frame of this chapter the technical and radiological properties of the most representative industrial processes (such as coal mining and combustion; iron and steel production; the alumina, the zirconia, and the phosphate industry; etc.) and their by-products are discussed, especially considering the needs of the construction industry and the new European Basic Safety Standards.

Combined use of geophysical and geochemical methods to assess areas of active, degrading and restored blanket bog

Here we combine the use of geo-electrical techniques with geochemical analysis of the solid and liquid phase to determine subsurface properties and general peatland health. Active, degrading and restored peat locations were analysed from the same blanket bog site (ensuring they were under the same environmental conditions, such as rainfall and temperature) at the Garron Plateau, Northern Ireland. A normalized chargeability (ratio of resistivity (inverse of conductivity) and chargeability) profile was compared with organic composition analysis of the solid and liquid phases from active, degrading and restored locations. Results show that the degrading location is undergoing high rates of decomposition and loss of organic matter into the interstitial water, whereas the opposite is true for the active location. The restored peat is showing low rates of decomposition however has a high concentration of organic material in the porewater, primarily composing long chain aliphatic compounds, sourced from vascular plants. The ingression of vascular plants permits the diffusion of oxygen via roots into the subsurface and supports the oxidation of phenols by phenol oxidase, which produces phenoxy radicals and quinones (CO double bonds). This production of conjugated quinones, which are characterized by a CO double bond, in the aerated degrading and restored locations, increase the polarity, cation exchange capacity, and the normalized chargeability of the peat. This higher chargeability is not evident in the active peat due to decreased aerobic decomposition and a domination of sphagnum mosses.