Jeffery Chanton

Submarine ground water discharge driven by tidal pumping in a heterogeneous Aquifer

Submarine ground water discharge (SGD) is now recognized as an important water pathway between land and sea. It is difficult to quantitatively predict SGD owing to its significant spatial and temporal variability. This study focuses on quantitative estimation of SGD caused by tidally induced sea water recirculation and a terrestrial hydraulic gradient. A two-dimensional hydrogeological model was developed to simulate SGD from a coastal unconfined aquifer in the northeastern Gulf of Mexico, where previous SGD studies were performed. A density-variable numerical code, SEAWAT2000, was applied to simulate SGD. To accurately predict discharge, various influencing factors such as heterogeneity in conductivity, uncertain boundary conditions, and tidal pumping were systematically assessed. The tidally influenced sea water recirculation zone and the fresh water-salt water mixing zone under various tidal patterns, tidal ranges, and water table heights were also investigated. The model was calibrated and validated from long-term, intensive measurements at the study site. The percentage of fresh SGD relative to total SGD ranged from 4% to 50% under normal conditions. Based on simulations of two field measurements in summer and spring, respectively, the fresh water ratios were 9% and 15%, respectively. These results support the hypothesis that the SGD induced by tidally driven sea water recirculation is much larger than terrestrial fresh ground water discharge at this site. The estimates of total and fresh SGD are at the low and high ends, respectively, of the estimation ranges obtained from geochemical tracers (e.g., (222)Rn).

New evidence for the geological origins of the ancient Delphic oracle (Greece)

Ancient tradition linked the Delphic oracle in Greece to specific geological phenomena, including a fissure in the bedrock, intoxicating gaseous emissions, and a spring. Despite testimony by ancient authors, many modern scholars have dismissed these traditional accounts as mistaken or fraudulent. This paper presents the results of an interdisciplinary study that has succeeded in locating young faults at the oracle site and has also identified the prophetic vapor as an emission of light hydrocarbon gases generated in the underlying strata of bituminous limestone.

Methane oxidation in water-spreading and compost biofilters

This study evaluated two biofilter designs to mitigate methane emissions from landfill vents. Water-spreading biofilters were designed to use the capillarity of coarse sand overlain by a finer sand to increase the active depth for methane oxidation. Compost biofilters consisted of 238-L barrels containing a 1: 1 mixture (by volume) of compost to expanded polystyrene pellets. Two replicates of each type of biofilter were tested at an outdoor facility. Gas inflow consisted of an approximately 1: 1 mixture (by volume) of CH4 and CO2. Methane output rates (J out; g m-2 day-1) were measured using the static chamber technique and the Pedersen et al. (2001) diffusion model. Methane oxidation rate (J ox; g m-2 day-1) and fraction of methane oxidized (f ox) were determined by mass balance. For methane inflow rates (J in) between 250 and 500 g m-2 day-1, the compost biofilter J ox, 242 g m-2 day-1, was not significantly different (P = 0.0647) than the water-spreading biofilter J ox, 203 g m-2 day-1; and the compost f ox, 69%, was not significantly different (P = 0.7354) than water-spreading f ox, 63%. The water-spreading biofilter was shown to generally perform as well as the compost biofilter, and it may be easier to implement at a landfill and require less maintenance.

Comment on “A Persistent Oxygen Anomaly Reveals the Fate of Spilled Methane in the Deep Gulf of Mexico”

Kessler et al. (Reports, 21 January 2011, p. 312) reported that methane released from the 2010 Deepwater Horizon blowout, approximately 40% of the total hydrocarbon discharge, was consumed quantitatively by methanotrophic bacteria in Gulf of Mexico deep waters over a 4-month period. We find the evidence explicitly linking observed oxygen anomalies to methane consumption ambiguous and extension of these observations to hydrate-derived methane climate forcing premature.

ESTIMATING METHANE EMISSION AND OXIDATION FROM EARTHEN LANDFILL COVERS

Measuring methane emission and oxidation through landfill covers has been well studied. However, numerical methods to estimate methane emission and oxidation are very limited. A simulation model was developed that combined water and heat flow model and a gas transport and oxidation model. The gas transport and oxidation model is able to use dynamic parameters associated with water content and temperature and incorporate into dynamic methanotrophic activity. Four sites were selected to showcase how emissions and oxidation can be estimated knowing cover design, management practices, and climatic conditions. Simulations were performed for scenarios with and without an active gas collection system. Different simulations were performed with and without organic amendments to the soil cover. Thirty-two simulations were conducted under different locations, climate conditions, bottom pressure boundaries, and soil oxidation capacities. Simulations showed that soil covers in subhumid areas can prevent high methane emission with blockage and decent oxidation capacity. In semiarid sites, higher emission was obtained due to the higher air filled void space of the soil. Oxidation capacities in semiarid sites are higher than those in subhumid sites since influxes of methane are higher in semiarid sites. High pressure underneath the cover caused higher emission in all sites. Even with active gas collection system (vacuum pressure), emissions were significant in semiarid climates. Soil oxidation is not only dependent on the potential methane oxidation capacity (Vmaxmax), but also depends on methane availability.

Uncertainties associated with the use of optical remote sensing technique to estimate surface emissions in landfill applications.

Abstract Landfills represent a source of distributed emissions source over an irregular and heterogeneous surface. In the method termed “Other Test Method-10” (OTM-10), the U.S. Environmental Protection Agency (EPA) has proposed a method to quantify emissions from such sources by the use of vertical radial plume mapping (VRPM) techniques combined with measurement of wind speed to determine the average emission flux per unit area per time from nonpoint sources. In such application, the VRPM is used as a tool to estimate the mass of the gas of interest crossing a vertical plane. This estimation is done by fitting the field-measured concentration spatial data to a Gaussian or some other distribution to define a plume crossing the vertical plane. When this technique is applied to landfill surfaces, the VRPM plane may be within the emitting source area itself. The objective of this study was to investigate uncertainties associated with using OTM-10 for landfills. The spatial variability of emission in the emitting domain can lead to uncertainties of –34 to 190% in the measured flux value when idealistic scenarios were simulated. The level of uncertainty might be higher when the number and locations of emitting sources are not known (typical field conditions). The level of uncertainty can be reduced by improving the layout of the VRPM plane in the field in accordance with an initial survey of the emission patterns. The change in wind direction during an OTM-10 testing setup can introduce an uncertainty of 20% of the measured flux value. This study also provides estimates of the area contributing to flux (ACF) to be used in conjunction with OTM-10 procedures. The estimate of ACF is a function of the atmospheric stability class and has an uncertainty of 10–30%.

A new approach to characterize emission contributions from area sources during optical remote sensing technique testing

In the method termed “Other Test Method-10,” the U.S. Environmental Protection Agency has proposed a method to quantify emissions from nonpoint sources by the use of vertical radial plume mapping (VRPM) technique. The surface area of the emitting source and the degree to which the different zones of the emitting source are contributing to the VRPM computed emissions are often unknown. The objective of this study was to investigate and present an approach to quantify the unknown emitting surface area that is contributing to VRPM measured emissions. Currently a preexisting model known as the “multiple linear regression model,” which is described in Thoma et al. (2009), is used for quantifying the unknown surface area. The method investigated and presented in this paper utilized tracer tests to collect data and develop a model much like that described in Thoma et al. (2009). However, unlike the study used for development of the multiple linear regression model, this study is considered a very limited study due to the low number of pollutant releases performed (seven total releases). It was found through this limited study that the location of an emitting source impacts VRPM computed emissions exponentially, rather than linearly (i.e., the impact that an emitting source has on VRPM measurements decreases exponentially with increasing distances between the emitting source and the VRPM plane). The data from the field tracer tests were used to suggest a multiple exponential regression model. The findings of this study, however, are based on a very small number of tracer tests. More tracer tests performed during all types of climatic conditions, terrain conditions, and different emissions geometries are still needed to better understand the variation of capture efficiency with emitting source location. This study provides a step toward such an objective. Implications The findings of this study will aid in the advancement of the VRPM technique. In particular, the contribution of this study is to propose a slight improvement in how the area contributing to flux is determined during VRPM campaigns. This will reduce some of the techniques inherent uncertainties when it is employed to estimate emissions from an area source under nonideal conditions.

A Rapid Response Study of the Hercules Gas Well Blowout

On 20 April 2010, the Deepwater Horizon drilling rig lost well control while drilling at the Macondo prospect in the Gulf of Mexico. At the time of the Macondo blowout, the academic scientific community was ill prepared to initiate and rapidly conduct the necessary coordinated interdisciplinary studies of the environments around the discharge area.

Tire-Derived Steel for Hydrogen Sulfide Removal in Landfill Cover

The use of tire-derived steel, a by-product of tire recycling, for removal of H2 S in landfill cover systems was examined through a laboratory study. Experiments under both static and dynamic conditions were conducted. Results demonstrated that tire-derived steel removed H2 S to a greater extent relative to a control landfill cover material consisting of sandy soil. In batch experiments, over 98% H2 S [550 parts per million (ppm) initial concentration] was removed in 2 min by 20 g of tire-derived steel, compared to only 50% H2 S removal in 60 min by the same amount of soil. In column experiments using 100 ppm inlet H2 S gas concentrations, after 24-h continuous operation, the outlet H2 S concentration increased to over 90 ppm in the sandy soil columns, while it was less than 1 ppm in the tire-derived steel columns. The experimental results showed that the outlet H2 S concentrations from the closed columns were higher than that from the open columns, indicating a potential role of oxygen in creating or reg...

Mitigating methane emissions from passive landfill vents: a viable option for older closed landfills

This study investigated the use of biofilters to reduce methane emissions from landfill passive gas vents. Two biofilter designs were evaluated. The two filter designs achieved similar percent oxidation averages. The radial biofilter design, however, obtained a much higher methane oxidation rate. The higher surface area of flow in the radial biofilters decreased the methane influx leading to greater oxygen penetration into the biofilters. An average percent oxidation of 20% and higher were obtained when air temperature was 20-36°C, indicating the optimal soil temperature for methanotrophs to oxidise methane.