In Situ Determination of the Rate of Unassisted Degradation of Saturated-Zone Hydrocarbon Contamination

Abstract

A method to measure the in situ degradation rate of dissolved hydrocarbon contamination has been developed and applied at two locations at a field site. The method uses the rates of downward diffusion of oxygen and upward diffusion of carbon dioxide through the unsaturated zone, as calculated from vertical soil-gas concentration gradients, combined with stoichiometry to obtain two degradation rates in hydrocarbon mass per water table surface area per time. Values of 0.385 gram per m² per day and 0.52 gram per m² per day (based upon oxygen data) and 0.056 gram per m² per day and 0.12 gram per m² per day (based upon carbon dioxide data) were calculated at a field site with dissolved fuel contamination. This result of lower values from ground-air carbon dioxide concentrations is consistent with a significant fraction of the carbon dioxide produced being lost to the aqueous phase. Based upon a single-stage equilibrium phase-transfer model, gas/water volume ratios of 0.02 and 0.2 for the capillary fringe were calculated. Groundwater carbon dioxide fugacities and soil-gas carbon dioxide concentrations were used at the two locations and a third to determine whether the source of elevated soil carbon dioxide concentrations were unsaturated-zone hydrocarbon degradation or a saturated-zone process. This technique has potential applicability in setting risk-based remedial criteria and in allowing inclusion of the contribution of in situ degradation in remedial design. This can result in major remedial cost savings.     

Defining contamination limits with pneumatic hammer soil probes

There have been more than 100,000 confirmed releases of petroleum from underground storage tanks (USTs) in the United States and its territories. The 10,000-gallon spill and cleanup of unleaded gasoline, detailed in this article, that occurred from 1988 to 1990 on Cape Cod, Massachusetts, illustrates the author's argument that electric pneumatic-hammer soil probes are the fastest, most convenient, and least costly way of performing the soil-gas surveys needed to locate spilled petroleum product, evaluate vapor intrusion into basements, and determine the extent of groundwater contamination for remediation purposes. Current state soil-gas requirements are also included.     

Predator choice in the field; grouping guppies, Poecilia reticulata, receive more attacks

Capture success of many predator species has been shown to decrease with increasing prey group size and it is therefore suggested that predators should choose to attack stragglers and/or small groups. Predator choice in the laboratory has shown mixed results with some species preferentially attacking large groups and others preferring to attack stragglers over groups. Such predator choices have not been tested in the field. In our study we presented a binary choice between a shoal of guppies and a single guppy to predators in pools in the Arima river, Trinidad. We observed attacks in 11 different pools from a total of 53 predators (20 acara cichlids, Aequidens pulcher, 32 pike cichlids, Crenicichla frenata, and one wolf-fish, Hoplias malabaricus) and found that all predators showed a strong preference for the shoal of guppies in terms of both first choice and total number of attacks. We discuss the implications of these preferences with regards to predator–prey interactions.     

Landfill Gas Effects on Groundwater Samples at a Municipal Solid Waste Facility

A study was performed to determine the source of low concentrations of volatile organic compounds (VOCs) detected in groundwater samples at a solid waste management facility. The affected wells were identified as hydraulically upgradient of an old unlined facility, but downgradient of a new clay-lined landfill. These monitoring wells are close to both sites. Subsurface landfill gas migration was identified after a low permeability cap was installed on the older site. Subsurface gas pressure was monitored to identify horizontal landfill gas migration. Monitoring well headspace gases were evaluated to identify depressed oxygen concentrations and methane because of landfill gas migration into the well. Monitoring well headspace gas VOC concentrations were compared to groundwater VOC concentrations to determine the direction of phase transfer. A ratio above 1.0 of the observed well headspace gas concentration of a VOC to the concentration that would be in equilibrium with the groundwater concentration indicates gas-to-water phase transfer within the well. For the major gas-phase and aqueous-phase VOC, cis-1,2-dichloroethene, gas-to-water phase transfer is clearly indicated from the data for two of the four wells. Fifteen other VOCs were detected in monitoring well headspace gases but not in groundwater samples from the four wells studied. Only one compound in one well was detected in the groundwater sample but not in the headspace gases, and only one compound in one well was detected in both matrices at concentrations that suggested water-to-gas phase transfer. This study suggests that if landfill gas is suspected as the source of detected VOCs, monitoring well construction and stratigraphy are important considerations when attempting to differentiate between groundwater contamination by landfill gas and contamination from other sources.     

Analytical Performance of Four Portable Gas Chromatographs Under Field Conditions

A field evaluation of the performance of four portable gas chromatographs was conducted at two field sites, one in the Pacific Northwest (chlorinated solvent contamination) and one in the Desert Southwest (primarily jet fuel contamination). The purpose of the study was to compare the performance of four portable GCs under the same conditions. The gas chromatographs had either electron-capture detectors or photoionization detectors. The study evaluated instrument linearity, instrument detection limits, retention time stabilities, response factor stability, and chromatographic performance. Standards and samples contained 1, 1, 2, 2-tetrachloroethane, trichloroethene, tetrachloroethane, 1, 1, 1-trichloroethane, benzene, toluene, and ethylbenzene. In order to ensure data comparability, the same model wide-bore column and computing integrator were used with each instrument, where possible. Significant differences in the performance of the four models were detected under the specific conditions used for this study. The results indicate the need to fully characterize the performance of portable instruments before field use so that appropriate quality control measures can be planned and implemented based on the performance of a specific analytical system.     

The use of isotopes to identify landfill gas effects on groundwater

An evaluation of the source of volatile organic compounds in groundwater samples was performed at a landfill in southern California. The 3H (tritium) content of the water in leachate and water from the gas-collection system (condensed water and entrained water droplets) and the delta 13C and 14C content of the inorganic carbon in landfill gas CO2, leachate, and gas-collection system water were used to characterize the dissolved inorganic carbon (DIC) inside the landfill, while the same parameters were monitored in groundwater samples from affected monitoring wells and an unaffected well. Tritium levels from leachate and gas-collection system condensate ranged from approximately 2000 TU to over 4000 TU, orders of magnitude higher than unaffected groundwater. The average 14C content of DIC in the landfill pore-water samples was 121 pMC and the 14C content of unaffected groundwater DIC was 93 pMC, while the 14C content of the dissolved inorganic carbon in groundwater with VOC detections ranged from 105 to 119 pMC. The delta 13C of DIC in pore water was consistently above 0 per thousand and the delta 13C of unaffected groundwater DIC was -20.3 per thousand, while the delta 13C of DIC in affected groundwater samples was increased from -17.3 to -13.2 per thousand. The increases in both delta 13C and 14C in landfill gas-impacted groundwater DIC generally correlated with the number of volatile organic compounds detected and their concentrations. Based on the tritium and DIC 14C levels in leachate and water from the gas-collection system compared to those of unaffected water, significant increases in the tritium content of the water would be expected to accompany VOC detections and increases in delta 13C and 14C caused by landfill water. The results rule out landfill water as the VOC source, leaving landfill gas as the source. The identities and concentrations of the specific VOCs in affected groundwater samples varied among wells as well as between two leachate samples, ruling out the use of a VOC "fingerprint" for leachate or landfill gas to be compared to groundwater VOC concentrations.     

Pre-Colombian Mercury Pollution Associated with the Smelting of Argentiferous Ores in the Bolivian Andes

The development of the mercury (Hg) amalgamation process in the mid-sixteenth century triggered the onset of large-scale Hg mining in both the Old and New Worlds. However, ancient Hg emissions associated with amalgamation and earlier mining efforts remain poorly constrained. Using a geochemical time-series generated from lake sediments near Cerro Rico de Potosí, once the world’s largest silver deposit, we demonstrate that pre-Colonial smelting of Andean silver ores generated substantial Hg emissions as early as the twelfth century. Peak sediment Hg concentrations and fluxes are associated with smelting and exceed background values by approximately 20-fold and 22-fold, respectively. The sediment inventory of this early Hg pollution more than doubles that associated with extensive amalgamation following Spanish control of the mine (1574–1900 AD). Global measurements of [Hg] from economic ores sampled world-wide indicate that the phenomenon of Hg enrichment in non-ferrous ores is widespread. The results presented here imply that indigenous smelting constitutes a previously unrecognized source of early Hg pollution, given naturally elevated [Hg] in economic silver deposits.     

The effects of different predator species on antipredator behavior in the Trinidadian guppy, Poecilia reticulata

Different types of predators often elicit different antipredator responses in a common type of prey. Alternatively, some prey species may adopt a general response, which provides limited protection from many different types of predator. The Trinidadian guppy, Poecilia reticulata, is faced with a wide range of different predators throughout its range and is known to display varying levels of antipredator behavior depending on the predator assemblage. Pike cichlids, Crenicichla frenata, are regarded as the primary aquatic guppy predator in streams in the northern mountain range in Trinidad. As such, they are seen to be responsible for many of the differences in morphology, life history traits, and behavior between guppy populations from areas with few predators and those from areas with many pike cichlids. In this study we investigated how guppies responded when faced with different predator species using three common aquatic predators. We exposed shoals of ten guppies to one out of four treatments: no predator (control), pike cichlid, acara cichlid (Aequidens pulcher), and wolf fish (Hoplias malabaricus); and we made behavioral observations on both focal individuals and the shoal as a whole. Guppies showed significantly greater levels of predator inspection and shoaling behavior, foraged less, spent more time in the surface water, and stayed in significantly larger shoals when faced with pike cichlids than in other treatments. We discuss these results in the context of multiple predator effects.     

Achieving competitive advantage through product stewardship and LCA

Companies have achieved competitive advantage by expanding the boundaries of their concern beyond the product life-cycle stage that they directly control. By using product stewardship and life-cycle information, coupled with business analysis, companies can successfully outperform their competitors by improving their product or product system by reducing costs, increasing revenue, reducing liabilities, and enhancing their image. Life-cycle information and its use within a product stewardship management framework goes beyond traditional life-cycle applications. Used wisely, it can help companies establish a sustainable framework for long-term success.