Geology topics
Francis H. Chapelle
Publications and source records attributed to Francis H. Chapelle.
Relative vulnerability of public supply wells to VOC contamination in hydrologically distinct regional aquifers
A process-based methodology was used to compare the vulnerability of public supply wells tapping seven study areas in four hydrologically distinct regional aquifers to volatile organic compound (VOC) contamination. This method considers (1) contributing areas and travel times of groundwater flowpaths converging at individual supply wells, (2) the oxic and/or anoxic conditions encountered along each flowpath, and (3) the combined effects of hydrodynamic dispersion and contaminant- and oxic/anoxic-specific biodegradation. Contributing areas and travel times were assessed using particle tracks generated from calibrated regional groundwater flow models. These results were then used to estimate VOC concentrations relative to an unspecified initial concentration (C/C0) at individual public supply wells. The results show that the vulnerability of public supply wells to VOC contamination varies widely between different regional aquifers. Low-recharge rates, long travel times, and the predominantly oxic conditions characteristic of Basin and Range aquifers in the western United States leads to lower vulnerability to VOCs, particularly to petroleum hydrocarbons such as benzene and toluene. On the other hand, high recharge rates and short residence times characteristic of the glacial aquifers of the eastern United States leads to greater vulnerability to VOCs. These differences lead to distinct patterns of C/C0 values estimated for public supply wells characteristic of each aquifer, information that can be used by resource managers to develop monitoring plans based on relative vulnerability, to locate new public supply wells, or to make land-use management decisions.
Deducing the distribution of terminal electron-accepting processes in hydrologically diverse groundwater systems
The distribution of microbially mediated terminal electron-accepting processes (TEAPs( was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor (nitrate, sulfate) consumption, intermediate product (hydrogen (H 2 )) concentrations, and final product (ferrous iron, sulfide, and methane) production. In each hydrologic system a determination of predominant TEAPs could be arrived at, but the level of confidence appropriate for each determination differed. In a portion of the lacustrine aquifer of the San Joaquin Valley, for example, all three indicators (sulfate concentrations decreasing, H 2 concentrations in the 1–2 nmol range, and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant TEAP, leading to a high degree of confidence in the determination. In portions of the Floridan aquifer and a petroleum hydrocarbon-contaminated aquifer, sulfate reduction and methanogenesis are indicated by production of sulfide and methane, and hydrogen oncentrations in the 1–4 nmol and 5–14 nmol range, respectively. However, because electron acceptor consumption could not be documented in these systems, less confidence is warranted in the TEAP determination. In the Black Creek aquifer, no pattern of sulfate consumption and sulfide production were observed, but H2 concentrations indicated sulfate reduction as the predominant TEAP. In this case, where just a single line of evidence is available, the least confidence in the TEAP diagnosis is justified. Because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes, it provides a better description of predominant redox processes in groundwater systems than more traditional Eh-based methods.
Biodegration of chlorinated ethenes
Biodegradation of chlorinated ethenes by naturally occurring or artificially enhanced processes is an important component of current site remediation strategies. At this writing, several microbial mechanisms for chlorinated ethene transformation and degradation have been identified. The purpose of this chapter is to briefly summarize the current understanding of those processes that lead to the biodegradation of chlorinated ethenes.
Total mercury, methylmercury, and selected elements in soils of the Fishing Brook watershed, Hamilton County, New York, and the McTier Creek watershed, Aiken County, South Carolina, 2008
Mercury is an element of on-going concern for human and aquatic health. Mercury sequestered in upland and wetland soils represents a source that may contribute to mercury contamination in sensitive ecosystems. An improved understanding of mercury cycling in stream ecosystems requires identification and quantification of mercury speciation and transport dynamics in upland and wetland soils within a watershed. This report presents data for soils collected in 2008 from two small watersheds in New York and South Carolina. In New York, 163 samples were taken from multiple depths or soil horizons at 70 separate locations near Fishing Brook, located in Hamilton County. At McTier Creek, in Aiken County, South Carolina, 81 samples from various soil horizons or soil depths were collected from 24 locations. Sample locations within each watershed were selected to characterize soil geochemistry in distinct land-cover compartments. Soils were analyzed for total mercury, selenium, total and carbonate carbon, and 42 other elements. A subset of the samples was also analyzed for methylmercury.
Fate of sulfamethoxazole, 4-nonylphenol, and 17β-estradiol in groundwater contaminated by wastewater treatment plant effluent
Organic wastewater contaminants (OWCs) were measured in samples collected from monitoring wells located along a 4.5-km transect of a plume of groundwater contaminated by 60 years of continuous rapid infiltration disposal of wastewater treatment plant effluent. Fifteen percent of the 212 OWCs analyzed were detected, including the antibiotic sulfamethoxazole (SX), the nonionic surfactant degradation product 4-nonylphenol (NP), the solvent tetrachloroethene (PCE), and the disinfectant 1,4-dichlorobenzene (DCB). Comparison of the 2005 sampling results to data collected from the same wells in 1985 indicates that PCE and DCB are transported more rapidly in the aquifer than NP, consistent with predictions based on compound hydrophobicity. Natural gradient in situ tracer experiments were conducted to evaluate the subsurface behavior of SX, NP, and the female sex hormone 17β-estradiol (E2) in two oxic zones in the aquifer: (1) a downgradient transition zone at the interface between the contamination plume and the overlying uncontaminated groundwater and (2) a contaminated zone located beneath the infiltration beds, which have not been loaded for 10 years. In both zones, breakthrough curves for the conservative tracer bromide (Br − ) and SX were nearly coincident, whereas NP and E2 were retarded relative to Br − and showed mass loss. Retardation was greater in the contaminated zone than in the transition zone. Attenuation of NP and E2 in the aquifer was attributed to biotransformation, and oxic laboratory microcosm experiments using sediments from the transition and contaminated zones show that uniform-ring-labeled 14 C 4-normal-NP was biodegraded more rapidly (30−60% recovered as 14 CO 2 in 13 days) than 4- 14 C E2 (20−90% recovered as 14 CO 2 in 54 days). There was little difference in mineralization potential between sites.
Biodegradation of 17β-estradiol, estrone and testosterone in stream sediments
Biodegradation of 17β-estradiol (E2), estrone (E1), and testosterone (T) was investigated in three wastewater treatment plant (WWTP) affected streams in the United States. Relative differences in the mineralization of [4- 14 C] substrates were assessed in oxic microcosms containing saturated sediment or water-only from locations upstream and downstream of the WWTP outfall in each system. Upstream sediment demonstrated significant mineralization of the “A” ring of E2, E1, and T, with biodegradation of T consistently greater than that of E2 and no systematic difference in E2 and E1 biodegradation. “A” ring mineralization also was observed in downstream sediment, with E1 and T mineralization being substantially depressed relative to upstream samples. In marked contrast, E2 mineralization in sediment immediately downstream from the WWTP outfalls was more than double that in upstream sediment. E2 mineralization was observed in water, albeit at insufficient rate to prevent substantial downstream transport. The results indicate that, in combination with sediment sorption processes which effectively scavenge hydrophobic contaminants from the water column and immobilize them in the vicinity of the WWTP outfall, aerobic biodegradation of reproductive hormones can be an environmentally important mechanism for nonconservative (destructive) attenuation of hormonal endocrine disruptors in effluent-affected streams.
An Excel Workbook for Identifying Redox Processes in Ground Water
The reduction/oxidation (redox) condition of ground water affects the concentration, transport, and fate of many anthropogenic and natural contaminants. The redox state of a ground-water sample is defined by the dominant type of reduction/oxidation reaction, or redox process, occurring in the sample, as inferred from water-quality data. However, because of the difficulty in defining and applying a systematic redox framework to samples from diverse hydrogeologic settings, many regional water-quality investigations do not attempt to determine the predominant redox process in ground water. Recently, McMahon and Chapelle (2008) devised a redox framework that was applied to a large number of samples from 15 principal aquifer systems in the United States to examine the effect of redox processes on water quality. This framework was expanded by Chapelle and others (in press) to use measured sulfide data to differentiate between iron(III)- and sulfate-reducing conditions. These investigations showed that a systematic approach to characterize redox conditions in ground water could be applied to datasets from diverse hydrogeologic settings using water-quality data routinely collected in regional water-quality investigations. This report describes the Microsoft Excel workbook, RedoxAssignment_McMahon&Chapelle.xls, that assigns the predominant redox process to samples using the framework created by McMahon and Chapelle (2008) and expanded by Chapelle and others (in press). Assignment of redox conditions is based on concentrations of dissolved oxygen (O2), nitrate (NO3-), manganese (Mn2+), iron (Fe2+), sulfate (SO42-), and sulfide (sum of dihydrogen sulfide [aqueous H2S], hydrogen sulfide [HS-], and sulfide [S2-]). The logical arguments for assigning the predominant redox process to each sample are performed by a program written in Microsoft Visual Basic for Applications (VBA). The program is called from buttons on the main worksheet. The number of samples that can be analyzed is only limited by the number of rows in Excel (65,536 for Excel 2003 and XP; and 1,048,576 for Excel 2007), and is therefore appropriate for large datasets.
Comparison of Methylmercury Production and Accumulation in Sediments of the Congaree and Edisto River Basins, South Carolina, 2004-06
Fish-tissue mercury concentrations (approximately 2 micrograms per gram) in the Edisto River basin of South Carolina are among the highest recorded in the United States. Substantially lower mercury concentrations (approximately 0.2 microgram per gram) are reported in fish from the adjacent (about 30 kilometer) Congaree River basin and the Congaree National Park. In contrast, concentrations of total mercury were statistically higher in sediments from the Congaree River compared with those in sediments from the Edisto River. Furthermore, no statistically significant difference was observed in concentrations of methylmercury or net methylation potential in sediments collected from various Edisto and Congaree hydrologic settings. In both systems, the net methylation potential was low (0-0.17 nanogram per gram per day) for in-stream sediments exposed to continuously flowing water but substantially higher (about 1.8 nanograms per gram per day) in wetland sediments exposed to standing water. These results are not consistent with the hypothesis that differences in fish-tissue mercury between the Edisto and Congaree basins reflect fundamental differences in the potential for each system to methylate mercury. Rather, the significantly higher ratios of methylmercury to total mercury observed in the Edisto system suggest that the net accumulation and(or) preservation of methylmercury are greater in the Edisto system. The marked differences in net methylation potential observed between the wetland and in-stream settings suggest the hypothesis that methylmercury transport from zones of production (wetlands) to points of entry into the food chain (channels) may contribute to the observed differences in fish-tissue mercury concentrations between the two river systems.
Selecting remediation goals by assessing the natural attenuation capacity of groundwater systems
Remediation goals for the source areas of a chlorinated ethene‐contaminated groundwater plume were identified by assessing the natural attenuation capacity of the aquifer system. The redox chemistry of the site indicates that sulfate‐reducing (H 2 ∼ 2 nanomoles [nM]) per liter conditions near the contaminant source grade to Fe(III)‐reducing conditions (H 2 ∼ 0.5 nM) downgradient of the source. Sulfate‐reducing conditions facilitate the initial reduction of perchloroethene (PCE) to trichloroethene (TCE), cis ‐dichloroethene ( cis ‐DCE), and vinyl chloride (VC). Subsequently, the Fe(III)‐reducing conditions drive the oxidation of cis ‐DCE and VC to carbon dioxide and chloride. This sequence gives the aquifer a substantial capacity for biodegrading chlorinated ethenes. Natural attenuation capacity (the slope of the steady‐state contaminant concentration profile along a groundwater flowpath) is a function of biodegradation rates, aquifer dispersive characteristics, and groundwater flow velocity. The natural attenuation capacity at the Kings Bay, Georgia site was assessed by estimating groundwater flowrates (∼0.23 ± 0.12 m/d) and aquifer dispersivity (∼1 m) from hydrologic and scale considerations. Apparent biodegradation rate constants (PCE and TCE ∼ 0.01 d −1 ; cis ‐DCE and VC ∼ 0.025 d −1 ) were estimated from observed contaminant concentration changes along aquifer flowpaths. A boundary‐value problem approach was used to estimate levels to which contaminant concentrations in the source areas must be lowered (by engineered removal), or groundwater flow velocities lowered (by pumping) for the natural attenuation capacity to achieve maximum concentration limits (MCLs) prior to reaching a predetermined regulatory point of compliance.
Anoxic mineralization: Environmental reality or experimental artifact?
No abstract available.
Chloroethene dechlorination in acidic groundwater: Implications for combining fenton's treatment with natural attenuation
A sulfuric acid leak in 1988 at a chloroethene-contaminated groundwater site at the Naval Air Station Pensacola has resulted in a long-term record of the behavior of chloroethene contaminants at low pH and a unique opportunity to assess the potential impact of source area treatment technologies, which involve acidification of the groundwater environment (e.g., Fenton's-based in situ chemical oxidation), on downgradient natural attenuation processes. The greater than 75 percent decrease in trichloroethene (TCE) concentrations and the shift in contaminant composition toward predominantly reduced daughter products (dichloroethene [DCE] and vinyl chloride [VC]) that were observed along a 30-m groundwater flow path characterized by highly acidic conditions (pH = 3.5 ± 0.4) demonstrated that chloroethene reductive dechlorination can continue to be efficient under persistent acidic conditions. The detection of Dehalococcoides -type bacteria within the sulfuric acid/chloroethene co-contaminant plume was consistent with biotic chloroethene reductive dechlorination. Microcosm studies conducted with 14 C-TCE and 14 C-VC confirmed biotic reductive dechlorination in sediment collected from within the sulfuric acid/chloroethene co-contaminant plume. Microcosms prepared with sediment from two other locations within the acid plume, however, demonstrated only a limited mineralization to 14 CO 2 and 14 CO, which was attributed to abiotic degradation because no significant differences were observed between experimental and autoclaved control treatments. These results indicated that biotic and abiotic mechanisms contributed to chloroethene attenuation in the acid plume at NAS Pensacola and that remediation techniques involving acidification of the groundwater environment (e.g., Fenton's-based source area treatment) do not necessarily preclude efficient chloroethene degradation.
Investigation of reductive dechlorination supported by natural organic carbon
Because remediation timeframes using monitored natural attenuation may span decades or even centuries at chlorinated solvent sites, new approaches are needed to assess the long-term sustainability of reductive dechlorination in ground water systems. In this study, extraction procedures were used to investigate the mass of indigenous organic carbon in aquifer sediment, and experiments were conducted to determine if the extracted carbon could support reductive dechlorination of chloroethenes. Aquifer sediment cores were collected from a site without an anthropogenic source of organic carbon where organic carbon varied from 0.02% to 0.12%. Single extraction results showed that 1% to 28% of sediment-associated organic carbon and 2% to 36% of the soft carbon were removed depending on nature and concentration of the extracting solution (Nanopure water; 0.1%, 0.5%, and 1.0% sodium pyrophosphate; and 0.5 N sodium hydroxide). Soft carbon is defined as organic carbon oxidized with potassium persulfate and is assumed to serve as a source of biodegradable carbon within the aquifer. Biodegradability studies demonstrated that 20% to 40% of extracted organic carbon was biodegraded aerobically and anaerobically by soil microorganisms in relatively brief tests (45 d). A five-step extraction procedure consisting of 0.1% pyrophosphate and base solutions was investigated to quantify bioavailable organic carbon. Using the extracted carbon as the sole electron donor source, tetrachloroethene was transformed to cis-1,2- dichloroethene and vinyl chloride in anaerobic enrichment culture experiments. Hydrogen gas was produced at levels necessary to sustain reductive dechlorination (>1 nM).
A simple pore water hydrogen diffusion syringe sampler
Molecular hydrogen (H2) is an important intermediate product and electron donor in microbial metabolism. Concentrations of dissolved H 2 are often diagnostic of the predominant terminal electron-accepting processes in ground water systems or aquatic sediments. H2 concentrations are routinely measured in ground water monitoring wells but are rarely measured in saturated aquatic sediments due to a lack of simple and practical sampling methods. This report describes the design and development (including laboratory and field testing) of a simple, syringe-based H 2 sampler in (1) saturated, riparian sediments, (2) surface water bed sediments, and (3) packed intervals of a fractured bedrock borehole that are inaccessible by standard pumped methods.
Biotransformation of caffeine, cotinine, and nicotine in stream sediments: Implications for use as wastewater indicators
Microbially catalyzed cleavage of the imadazole ring of caffeine was observed in stream sediments collected upstream and downstream of municipal wastewater treatment plants (WWTP) in three geographically separate stream systems. Microbial demethylation of the N -methyl component of cotinine and its metabolic precursor, nicotine, also was observed in these sediments. These findings indicate that stream sediment microorganisms are able to substantially alter the chemical structure and thus the analytical signatures of these candidate waste indicator compounds. The potential for in situ biotransformation must be considered if these compounds are employed as markers to identify the sources and track the fate of wastewater compounds in surface-water systems.
Hydrologic significance of carbon monoxide concentrations in ground water
Dissolved carbon monoxide (CO) is present in ground water produced from a variety of aquifer systems at concentrations ranging from 0.2 to 20 nanomoles per liter (0.0056 to 0.56 μg/L). In two shallow aquifers, one an unconsolidated coastal plain aquifer in Kings Bay, Georgia, and the other a fractured‐bedrock aquifer in West Trenton, New Jersey, long‐term monitoring showed that CO concentrations varied over time by as much as a factor of 10. Field and laboratory evidence suggests that the delivery of dissolved oxygen to the soil zone and underlying aquifers by periodic recharge events stimulates oxic metabolism and produces transiently high CO concentrations. In between recharge events, the aquifers become anoxic and more substrate limited, CO is consumed as a carbon source, and CO concentrations decrease. According to this model, CO concentrations provide a transient record of oxic metabolism affecting ground water systems after dissolved oxygen has been fully consumed. Because the delivery of oxygen affects the fate and transport of natural and anthropogenic contaminants in ground water, CO concentration changes may be useful for identifying predominantly anoxic ground water systems subject to periodic oxic or microaerophilic conditions.
Fate of MTBE relative to benzene in a gasoline-contaminated aquifer (1993-98):
Methyl tert -butyl ether (MTBE) and benzene have been measured since 1993 in a shallow, sandy aquifer contaminated by a mid-1980s release of gasoline containing fuel oxygenates. In wells downgradient of the release area, MTBK was detected before benzene, reflecting a chromatographic-like separation of these compounds in the direction of ground water flow. Higher concentrations of MTBE and benzene were measured in the deeper sampling ports of multilevel sampling wells located near the release area, and also up to 10 feet (3 m) below the water table surface in nested wells located farther from the release area. This distribution of higher concentrations at depth is caused by recharge events that deflect originally horizontal ground water flowlines. In the laboratory, microcosms containing aquifer material incubated with uniformly labeled 14 C-MTBE under aerobic and anaerobic. Fe(III)-reducing conditions indicated a low but measurable biodegradation potential (<3% 14 C-MTBW as 14 CO 2 ) after a seven-month incubation period, Tert -butyl alcohol (TBA), a proposed microbial-MTBE transformation intermediate, was detected in MTBE-contaminated wells, but TBA was also measured in unsaturated release area sediments. This suggests that TBA may have been present in the original fuel spilled and does not necessarily reflect microbial degradation of MTBE. Combined, these data suggest that milligram per liter to microgram per liter decreases in MTBE concentrations relative to benzene are caused by the natural attenuation processes of dilution and dispersion with less-contaminated ground water in the direction of flow rather than biodegradation at this point source gasoline release site.