Dr Sreenivasulu Chadalavada

Study region: Toowoomba, Queensland, Australia Study focus: In this study we derive loss model parameters suitable for use in the dynamic loss Australian Representative Basin Model (ARBM) through the calibration of a continuous simulation hydrologic model. We compare the derived parameters to those published in the literature, and our results highlight the need to develop a database of calibrated loss parameters for urban catchments. New hydrological insights: The development of design storms for flood modelling commonly uses the initial loss/continuous loss model to estimate the conversion of rainfall to runoff. This loss model, when applied to pervious areas, uses parameters that have been calibrated for gauged rural catchments. These same parameters are often applied to the pervious component of ungauged urban catchments with minimal understanding of the resulting impact on runoff. This research uses a continuous simulation modelling approach to calibrate parameters suitable for use in the ARBM loss model built into the hydrological modelling software XPRAFTS. Through a two-stage calibration approach, the model offered a satisfactory fit (Nash Sutcliffe Efficiency > 0.5) for 9 of the 11 selected storm events, with seven events exceeding a Nash Sutcliffe Efficiency of 0.75. Events used in the calibration/validation included peak flows as low as 9 m3/s and as high as 600 m3/s. Developing these loss model parameters offers new insights into the suitability of a dynamic loss model approach in an urban catchment in regional Australia and provides an alternative to the parameters already available in the literature which were found to overestimate the peak flow in frequent events.

Green roofs are becoming increasingly popular in urban construction due to their wide array of benefits for creating a sustainable ecosystem. Many stakeholders invest in green roofs in the 21st century to enhance the environmental quality and mitigate urban ecological pollution. The substrate layer is the most important and critical component of green roof systems. The objective of the review study is to present the important information regarding the required elements that need to be considered for substrate selection of green roofs by critically reviewing the scientifically published articles. Research findings from past studies relevant to green roofs, vegetation and selective substrate parameters were extensively discussed under different topics related to water retention, drought resistance and related physico-chemical parameters. The generalities in past research articles were presented and special focus was provided on specific research articles those presented novelty regarding green roof substrates. Furthermore, the hotspots in all the considered research articles were commentatively identified and the appropriate solutions were evaluated. The critical review of published research articles indicates that most of the research on green roof substrates was conducted in either controlled laboratories or greenhouses and did not provide much importance to actual field tests. Therefore, these research findings are not sufficient to obtain the realistic field outcomes of the research. Future studies on green roof substrates should need to incorporate field experiments along with classical controlled tests by adhering to standard guidelines for assimilating climatic influences in substrates. Few studies have focused on dry climates, and further research needs to be conducted on dry climates due to their high susceptibility to drought and evapotranspiration. This manuscript would be the first review article that mainly focuses on substrates for green roofs, which is a novel aspect.

The application of portable chromatography¿mass spectrometer (GC¿MS) is restrained by its detection limits without the development of proper sample pre-concentration methods. The primary focus of this paper is to introduce a practical field measurement methodology for the analysis of volatile organic compounds (VOCs) in soil vapour and groundwater using a portable gas (GC¿MS)system for application to in situ assessment of vapour intrusion from VOC contamination. A solid-phase micro-extraction (SPME) technique was applied for sample pre-concentration before the GC¿MS¿ measurement. Practical in-field soil gas SPME sampling methods have been developed to optimise the SPME extraction efficiency to then ultimately improve the detection limits of portable GC¿MS. An Australian site impacted by a chlorinated VOC, trichloroethylene (TCE), was the subject of the case study. To rapidly assess soil vapour samples in subsurface soil, in-house-developed retractable soil vapour sampling probes (SVSPs) were installed at the site in clusters at depths of 1 m, 2 m and 3 m below ground level at each sampling location. Use of the SVSPs for sampling enabled the generation of a three-dimensional map and distribution contours for TCE concentrations using the in situ measurement results of a portable GC¿MS analysis for vapour intrusion investigation. The results of the portable GC¿MS¿ analysis were compared with the results from conventional USEPA methods, such as TO-15 and Method 8265 for soil vapour and groundwater samples, respectively. This work demonstrates that the developed methodology of using a portable GC¿MS system has the capability for in-field quantitative analysis of VOCs for rapid contaminated site vapour intrusion assessment.

In the urban environment, anthropogenic activities provide numerous potential sources of contamination, which can often lead to difficulties in identifying the processes impacting groundwater quality (natural and anthropogenic). This is particularly relevant at Wastewater Treatment Plants (WWTPs) that are often subject to changes in land use and composition of contaminant sources over time and space, as well as multiple potential hydrogeochemical interactions. To help address this issue, we demonstrate how long-term time-series analysis of major ions and key contaminants of concern, which are routinely collected by WWTP operators, can be analysed using hydrogeochemical plotting tools, multivariate statistics and targeted isotopic analysis, to provide a means of better characterising key hydrogeochemical influences and anthropogenic inputs. Application of this approach to a WWTP in south-eastern Australia indicated that anthropogenic impacts were the primary driver influencing the local hydrogeochemical environment and groundwater quality. However, secondary processes, including mineral (particularly calcite) dissolution, ion exchange and possible dedolomitisation, as well as natural degradation/transformation of contaminants were also important. Long-term, time-series analysis of trends in NO3-N, NH4-N, Ca2+, SO42-, HCO3- and K+ in conjunction with the other lines of evidence, allowed for enhanced separation between individual contaminant sources, particularly when paired with a detailed site history and Conceptual Site Model (CSM). This indicated that off-site agricultural impacts post-date most site derived impacts, and to date, have not significantly added to the identified contaminant plume. The outcomes of this work have significant global application in the identification, assessment, and control of environmental and health risks at complex sites and show how significant value (rarely obtained) can be derived from the analysis of routine monitoring datasets, particularly when analysed using a multiple lines of evidence approach.

The influence of soil properties on PFOS sorption are not fully understood, particularly for variable charge soils. PFOS batch sorption isotherms were conducted for 114 temperate and tropical soils from Australia and Fiji, that were well-characterized for their soil properties, including total organic carbon (TOC), anion exchange capacity, and surface charge. In most soils, PFOS sorption isotherms were nonlinear. PFOS sorption distribution coefficients (Kd) ranged from 5 to 229 mL/g (median: 28 mL/g), with 63% of the Fijian soils and 35% of the Australian soils showing Kd values that exceeded the observed median Kd. Multiple linear regression showed that TOC, amorphous aluminum and iron oxides contents, anion exchange capacity, pH, and silt content, jointly explained about 53% of the variance in PFOS Kd in soils. Variable charge soils with net positive surface charges, and moderate to elevated TOC content, generally displayed enhanced PFOS sorption than in temperate or tropical soils with TOC as the only sorbent phase, especially at acidic pH ranges. For the first time, two artificial neural networks were developed to predict the measured PFOS Kd (R2 = 0.80) in the soils. Overall, both TOC and surface charge characteristics of soils are important for describing PFOS sorption.

Vapour intrusion (VI) is the phenomenon by which volatile organic compounds (VOCs) migrate from the subsurface source through the soil and enter into the overlying buildings, affecting the indoor air quality and ultimately causing health hazards to the occupants. Health risk assessments associated with hydrocarbon contaminated sites and recommendations of site closure are often made by quantifying the VI risks using mathematical models known as ¿vapour intrusion models¿ (VIM). In order to predict the health risk, various factors such as the lithological and geochemical conditions of the subsurface, environmental conditions, building operational conditions etc. are commonly evaluated using VIMs. Use of these models can overlook the role of preferential pathways like highly permeable subsurface layers and utility lines which act as the path of least resistance for vapour transport, which can increase the VI risks. The extensive networks of utility lines and sanitary sewer systems in urban areas can significantly exacerbate the uncertainty of VI investigations. The backfill materials like sand and gravel surrounding the utility lines can allow the vapours to easily pass through due to their high porosity as compared to natural formations. Hence, failure to understand the role of preferential pathways on the fate and transport of VOC in the vadose zone can result in more conservative predictions of indoor air vapour concentrations and wrong clean up approaches. This comprehensive review outlines the vapour transport mechanisms, factors influencing VI, VIMs and the role of preferential pathways in predicting indoor air vapour concentrations.

The remediation of petroleum hydrocarbons (TPH) in a contaminated soil by electrokinetic (EK) treatment was studied in the laboratory. The effects of applying a constant electrical current on soil pH, moisture content, electrical conductivity (EC), temperature, and the concentrations of three fractions of TPH (C10¿C16, C17¿C34 and C35¿C40) were investigated. The experiment was run for seven days and soil samples were collected at the end of the 7 day period for analysis of soil pH and TPH concentration. There were extreme pH conditions near the electrodes. At the end of the experiment there was around a 37% reduction of C10¿C16 chain compounds compared to the initial concentration of 164 ± 18 mg/kg. The study investigated TPH remediation to a depth of 24 cm, which is significantly more than most studies of EK remediation of TPH-contaminated soils. We observed reductions in TPH concentrations even at a depth of 24 cm. The spatial distribution of reductions in TPH concentrations was also studied and it was observed that more remediation occurred near the cathodes than near the anodes. Further, the greatest reductions in TPH concentrations were recorded near the electrodes in the lowest and middle parts of the experimental set-up. The application of electrokinetics to remediate TPH-contaminatedsoils could be a viable option as an in situ remediation technology.

Current practices in health risk assessment from vapor intrusion (VI) using mathematical models are based on assumptions that the subsurface sorption equilibrium is attained. The time required for sorption to reach near-steady-state conditions at sites may take months or years to achieve. This study investigated the vapor phase attenuation of trichloroethylene (TCE) in five soils varying widely in clay and organic matter content using repacked columns. The primary indicators of TCE sorption were vapor retardation rate (Rt), the time required for the TCE vapor to pass through the soil column, and specific volume of retention (VR), and total volume of TCE retained in soil. Results show TCE vapor retardation is mainly due to the rapid partitioning of the compound to SOM. However, the specific volume of retention of clayey soils with secondary mineral particles was higher. Linear regression analyses of the SOM and clay fraction with VR show that a unit increase in clay fraction results in higher sorption of TCE (VR) than the SOM. However, partitioning of TCE vapor was not consistent with the samples' surface areas but was mainly a function of the type of secondary minerals present in soils.

A feedback-based methodology has been developed for identifying the unknown pollution sources in groundwater-contaminated aquifers. The methodology consists of models within an iterative feedback system, with the capacity of feeding back real-time measurements of pollutant concentrations for the sequential optimal designs and characterization of the contaminated aquifer study area. The resulting linked-simulation optimization model considers the delineation of the contaminant plume, optimally characterizing the site in terms of pollutant sources and the optimal monitoring network leading to the remediation and/or management of the contaminated aquifer. As part of the methodology, a simulation-optimization code was developed by linking a groundwater flow and transport model with an optimization code for the purpose of identifying the unknown pollution sources. The proposed methodology addresses the source identification process with very limited information available regarding the observed contamination data for the identification of unknown pollution sources. This methodology is applied to a chlorinated hydrocarbon contaminated site for the identification of unknown pollution sources. Information regarding the sources such as the magnitude, location and the duration of contamination activity were not known for the study area considered in this work except the information regarding the likely activities that led to its contamination. Developed methodology is applied to choose the optimal source locations from the identified potential locations. Depending on the availability of observed contaminant concentration values the domain for the methodology application is divided into three different management periods. The optimal source estimates obtained at the end of the third management period suggests that only one potential source location, S2, confirms to be the source and active. The qualitative assessment of the results also performed utilizing the contamination information obtained during the field investigations. The results demonstrate the practicability of the feedback-based methodology in identifying the unknown pollution sources in groundwater. © 2012 Copyright Taylor and Francis Group, LLC.

Groundwater pollution occurs from different anthropogenic sources like leakage from Underground Storage Tanks (USTs) and depositories, leakage from hazardous waste dump sites and soak pits. Remediation of these contaminated sites requires optimal decision-making system so that the remediation is done in a cost-effective and efficient manner. Identification of unknown pollution sources plays an important role in remediation and containment of contaminant plume in a hazardous site. This paper reviews different optimisation algorithms like classical, nonclassical such as Genetic Algorithm, Artificial Neural Network and Simulated Annealing and hybrid methods, which can be applied for optimal identification of unknown groundwater pollution sources. Copyright © 2011 Inderscience Enterprises Ltd.