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 14C‐MTBE under aerobic and anaerobic. Fe(III)‐reducing conditions indicated a low but measurable biodegradation potential (<3%14C‐MTBW as 14CO2) 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.

Sediments recovered from the flooded mine workings of the Penn Mine, a Cu-Zn mine abandoned since the early 1960s, were cultured for anaerobic bacteria over a range of pH (4.0 to 7.5). The molecular biology of sediments and cultures was studied to determine whether sulfate-reducing bacteria (SRB) were active in moderately acidic conditions present in the underground mine workings. Here we document multiple, independent analyses and show evidence that sulfate reduction and associated metal attenuation are occurring in the pH-4 mine environment. Waterchemistry analyses of the mine water reveal: (1) preferential complexation and precipitation by H 2 S of Cu and Cd, relative to Zn; (2) stable isotope ratios of 34 S/ 32 S and 18 O/ 16 O in dissolved SO 4 that are 2-3 ‰ heavier in the mine water, relative to those in surface waters; (3) reduction/oxidation conditions and dissolved gas concentrations consistent with conditions to support anaerobic processes such as sulfate reduction. Scanning electron microscope (SEM) analyses of sediment show 1.5-micrometer, spherical ZnS precipitates. Phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analyses of Penn Mine sediment show a high biomass level with a moderately diverse community structure composed primarily of iron-and sulfate-reducing bacteria. Cultures of sediment from the mine produced dissolved sulfide at pH values near 7 and near 4, forming precipitates of either iron sulfide or elemental sulfur. DGGE coupled with sequence and phylogenetic analysis of 16S rDNA gene segments showed populations of Desulfosporosinus and Desulfitobacterium in Penn Mine sediment and laboratory cultures.

Leaching of phosphorus (P) mobilizes edaphic and applied sources of P and is a primary pathway of concern in agricultural soils of the Delmarva Peninsula, which defines the eastern boundary of the eutrophic Chesapeake Bay. We evaluated P leaching before and after poultry litter application from intact soil columns (30 cm diameter × 50 cm depth) obtained from low- and high-P members of four dominant Delmarva Peninsula soils. Surface soil textures ranged from fine sand to silt loam, and Mehlich-3 soil P ranged from 64 to 628 mg kg. Irrigation of soil columns before litter application pointed to surface soil P controls on dissolved P in leachate (with soil P sorption saturation providing a stronger relationship than Mehlich-3 P); however, strong relationships between P in the subsoil (45-50 cm) and leachate P concentrations were also observed ( = 0.61-0.73). After poultry litter application (4.5 Mg ha), leachate P concentrations and loads increased significantly for the finest-textured soils, consistent with observations that well-structured soils have the greatest propensity to transmit applied P. Phosphorus derived from poultry litter appeared to contribute 41 and 76% of total P loss in leachate from the two soils with the finest textures. Results point to soil P, including P sorption saturation, as a sound metric of P loss potential in leachate when manure is not an acute source of P but highlight the need to factor in macropore transport potential to predict leaching losses from applied P sources.

An analytical method is described that can detect the major alkyl ether compounds that are used as gasoline oxygenates (methyl tert-butyl ether, MTBE; ethyl tert-butyl ether, ETBE; and tert-amyl methyl ether, TAME) and their most characteristic degradation products (tert-butyl alcohol, TBA; tert-butyl formate, TBF; and tert-amyl alcohol, TAA) in water at sub-ppb concentrations. The new method involves gas chromatography (GC) with direct aqueous injection (DAI) onto a polar column via a splitless injector, coupled with detection by mass spectrometry (MS). DAI-GC/MS gives excellent agreement with conventional purgeand-trap methods for MTBE over a wide range of environmentally relevant concentrations. The new method can also give simultaneous identification of polar compounds that might occur as degradation products of gasoline oxygenates, such as TBA, TBF, TAA, methyl acetate, and acetone. When the method was applied to effluent from a column microcosm prepared with core material from an urban site in New Jersey, conversion of MTBE to TBA was observed after a lag period of 35 days. However, to date, analyses of water samples from six field sites using the DAI-GC/MS method have not produced evidence for the expected products of in situ degradation of MTBE.

High levels of accumulated phosphorus (P) in soils of the Delmarva Peninsula are a major source of dissolved P entering drainage ditches that empty into the Chesapeake Bay. Th e objective of this study was to design, construct, and monitor a within-ditch fi lter to remove dissolved P, thereby protecting receiving waters against P losses from upstream areas. In April 2007, 110 Mg of fl ue gas desulfurization (FGD) gypsum, a low-cost coal combustion product, was used as the reactive ingredient in a ditch fi lter. Th e ditch fi lter was monitored from 2007 to 2010, during which time 29 storm-induced fl ow events were characterized. For storm-induced fl ow, the event mean concentration effi ciency for total dissolved P (TDP) removal for water passing through the gypsum bed was 73 ± 27% confi dence interval (α = 0.05). Th e removal effi ciency for storm-induced fl ow by the summation of load method was 65 ± 27% confi dence interval (α = 0.05). Although chemically eff ective, the maximum observed hydraulic conductivity of FGD gypsum was 4 L s −1 , but it decreased over time to <1 L s −1 . When bypass fl ow and base fl ow were taken into consideration, the ditch fi lter removed approximately 22% of the TDP load over the 3.6-yr monitoring period. Due to maintenance and clean-out requirements, we conclude that ditch fi ltration using FGD gypsum is not practical at a farm scale. However, we propose an alternate design consisting of FGD gypsum-fi lled trenches parallel to the ditch to intercept and treat groundwater before it enters the ditch.

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The 420 km2 Mahantango Creek Watershed, within the Northern Appalachian Ridges and Valleys Province, is a subwatershed of the Susquehanna River, which flows to the Chesapeake Bay. Research on agricultural management and hydrologic processes controlling nonpoint source nutrient loss is conducted within a 7.3 km2 subwatershed designated WE‐38. The physical watershed description and history of monitoring and research activities contained herein and the data discussed in three companion papers are intended to facilitate the use and interpretation of archived databases on the U.S. Department of Agriculture Agricultural Research Service's Sustaining the Earth's Watersheds—Agricultural Research Data System (STEWARDS) Web site. Sources for regional geospatial data not maintained on STEWARDS are also identified.

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