Petroleum mass removal from low permeability sediment using air sparging/soil vapor extraction: impact of continuous or pulsed operation

Air sparging and soil vapor extraction (AS/SVE) are innovative remediation techniques that utilize volatilization and microbial degradation to remediate petroleum spills from soils and groundwater. This in situ study investigated the use of AS/SVE to remediate a gasoline spill from a leaking underground storage tank (UST) in the low permeability, clayey soil of the Appalachian Piedmont. The objectives of this study were to evaluate AS/SVE in low permeability soils by quantifying petroleum mass removal rates, monitoring vadose zone contaminant levels, and comparing the mass extraction rates of continuous AS/SVE to 8 and 24 h pulsed operation. The objectives were met by collecting AS/SVE exhaust gas samples and vadose zone air from multi-depth soil vapor probes. Samples were analyzed for O₂, CO₂, BTEX (benzene, toluene, ethylbenzene, xylene), and total combustible hydrocarbon (TCH) concentrations using portable hand meters and gas chromatography. Continuous AS/SVE was effective in removing 608 kg of petroleum hydrocarbons from low permeability soil in 44 days (14.3 kg day⁻¹). Mass removal rates ranged from 2.6 times higher to 5.1 times lower than other AS/SVE studies performed in sandy sediments. BTEX levels in the vadose zone were reduced from about 5 ppm to 1 ppm. Ten pulsed AS/SVE tests removed 78 kg in 23 days and the mean mass removal rate (17.6 kg day⁻¹) was significantly higher than the last 15 days of continuous extraction. Pulsed operation may be preferable to continuous operation because of increased mass removal and decreased energy consumption.     

Generalised linear modelling of fecundity at length in southern rock lobsters, <Emphasis Type="Italic">Jasus edwardsii</Emphasis>

Accurate fecundity estimates are central to population modelling of reproductive status and egg production in a fishery. Southern rock lobster (Jasus edwardsii) fisheries are managed with the consideration of performance measures based on the level of current egg production relative to the unfished stock. Egg production is a function of the size at the onset of maturity, the size structure of the stock, and the fecundity at length of lobsters. Fecundity at length of the Tasmania stock of J. edwardsii has not been reported previously and was estimated from seven sites around Tasmania. Data were analysed by classical linear regression and also generalised linear models (GLM) with gamma and Poisson distributions. GLM with a gamma distribution produced the best fit and did not require a correction factor to generate a model on the linear scale. Individual fecundity ranged from 43,918 to 660,156 and could be predicted from carapace length according to the equation F = −1.707 + 2.969 (log length). The coefficient of length approximated three, implying the fecundity at length relationship is cuboidal. Despite the spatial heterogeneity in reproductive parameters in this fishery, the inclusion of spatial information and egg development stage into the analysis only explained an additional 1% of the variance in fecundity. Thus, it appears valid to apply the relationship across the fishery without spatial separation.     

Contrasting behaviour of cadmium and zinc in a soil-plant-arthropod system

This study investigates the transfer of Cd and Zn from a soil amended with sewage sludge at rates up to 100 t ha(-1) through a multi-trophic system consisting of barley, the aphid Sitobion avenae and the larvae of the lacewing Chrysoperla carnae. Results show marked differences in the transfer of the two metals. Cadmium was freely accumulated in barley roots, but accumulation in the shoot was restricted to a concentration of around 0.22 mg kg(-1) (dry weight). This limited the transfer of Cd to higher trophic levels and resulted in no significant accumulation of Cd in S. avenae or in C. carnae. Zinc transfer in the system was largely unrestricted, resulting in significant accumulation in roots and shoots, in S. avenae and in C. carnae. Cadmium biomagnification occurred in lacewing pupae, with concentrations up to 3.6 times greater than in aphids. S. avenae biomagnified Zn by a factor of ca. 2.5 at low sludge amendment rates, but biomagnification decreased to a factor of 1.4 at the highest amendment rate. Biomagnification of Zn did not occur in C. carnae, but concentrations were up to 3.5 time higher than in soil. Results are discussed in light of the mechanisms regulating transfer of the two metals in the system.     

The statistical merits of various methods of calculating transfer coefficients between environmental media--development of the ideal formula for data-sets with a log-normal distribution

The statistical treatment of data-sets from environmental pollutant studies in which different measurements are combined to produce averages or comparative factors (e.g., transfer coefficients (TCs), input-output balance values) are considered here, with particular reference to the analysis of data from input-output balance studies of pollutants such as PCBs in animals and humans. Many methods of statistical analysis ignore the fact that all measurements are subject to error, and generally assume that the normal distribution applies to all data-sets, which is commonly inappropriate for environmental (and particularly biological system) data. Considerably different estimations can be obtained by applying different, commonly used, statistical methods, as shown in a simulation study presented here and when applied to data from an input-output balance study of PCBs in humans. Alternative average and combined factor estimators for the treatment of data from these types of studies that give considerable advantages in terms of bias and the ease of assessment of accuracy are proposed.     

Regional transport and urban contributions to fine particle concentrations in southeastern Canada

The impact of various atmospheric transport directions on ambient fine particle (PM2.5) concentrations at several sites in southeastern Canada was estimated (for May-September) using back-trajectory analysis. Three-day back trajectories (four per day) were paired with 6-hr average PM2.5 mass concentrations measured using tapered element oscillating microbalances (TEOM). PM2.5 concentrations at rural locations in the region were affected by nonlocal sources originating in both Canada and the United States. Comparison of sites revealed that, on average, the local contribution to total PM2.5 in the greater Toronto area (GTA) is approximately 30-35%. At each location, average PM2.5 concentrations under south/southwesterly flow conditions were 2-4 times higher than under the corresponding northerly flow conditions. The chemical composition of both urban and rural PM2.5 was determined during two separate 2-week spring/summer measurement campaigns. Components identified included SO4(2-) NO3-, NH4+, black carbon and organic carbon (OC), and trace elements. Higher particle mass at the urban Toronto site was composed of a higher proportion of all components. However, black carbon, NO3-, NaCl, and trace elements were found to be the most enriched over the rural/regional background levels.     

Airborne measurements of peroxy radicals using the PERCA technique

The Peroxy Radical Chemical Amplifier (PERCA) technique is a proven method for measurement of ambient levels of peroxy radicals at ground level, but there are no published instances of the technique being used on an aerial platform. Here we describe deployment of a PERCA on the former UK Meteorological Office C-130 Hercules research aircraft. The instrument uses the established method of chemical amplification and conversion of peroxy radicals to nitrogen dioxide (NO2) by doping the sample air-flow matrix with CO and NO, subsequently measuring the NO2 yield with an improved 'Luminox' LMA-3 NO2 detector. NO2 from the amplification chemistry is distinguished from other sources of NO2 reaching the detector by periodically injecting CO approximately 1 s downstream of the NO injection point (termination mode). Chain lengths (CL's) for the amplification chemistry were typically approximately 260 (ground level) to approximately 200 (7,000 m). This variation with altitude is less than the variation associated with the 'age' of the PFA inlet material where the amplification chemistry occurs; CL's of approximately 200 with old tubing to approximately 300 with new clean tubing were typical (ground level values). The CL determinations were made in-flight using an onboard calibration unit based on the 254 nm photolysis of 7.5 to 10 parts per billion (by volume, ppbv) of CH3I in air, producing CH3O2 in a quantitative manner. The noise-equivalent detection limit for peroxy radicals (HO2 + RO2) is 2 parts per trillion (by volume, pptv) at 3,650 m when the background ambient ozone levels are stable, based on a 5 min average of five 30 s amplification cycles and five 30 s termination cycles. This detection limit is a function of several factors but is most seriously degraded when there is large variability in the ambient ozone concentration. This paper describes the instrument design, considers its performance and proposes design improvements. It concludes that the performance of an airborne PERCA in the free troposphere can be superior to that of ground-based instruments when similar sampling frequencies are compared.     

Solubilization of manganese and trace metals in soils affected by acid mine runoff

Manganese solubility has become a primary concern in the soils and water supplies in the Alamosa River basin, Colorado due to both crop toxicity problems and concentrations that exceed water quality standards. Some of the land in this region has received inputs of acid and trace metals as a result of irrigation with water affected by acid mine drainage and naturally occurring acid mineral seeps. The release of Mn, Zn, Ni, and Cu following saturation with water was studied in four soils from the Alamosa River basin. Redox potentials decreased to values adequate for dissolution of Mn oxides within 24 h following saturation. Soluble Mn concentrations were increased to levels exceeding water quality standards within 84 h. Soluble concentrations of Zn and Ni correlated positively with Mn following reduction for all four soils studied. The correlation between Cu and Mn was significant for only one of the soils studied. The soluble concentrations of Zn and Ni were greater than predicted based on the content of each of these metals in the Mn oxide fraction only. Increases in total electrolyte concentration during reduction indicate that this may be the result of displacement of exchangeable metals by Mn following reductive dissolution of Mn oxides.