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Precipitates forming at various stages of acid mine drainage treatment in a high metal load (≈1000 mg L−1 Fe) and low pH (≈3) constructed wetland were characterized by chemical dissolution, x‐ray diffraction, thermal analysis, and scanning electron microscopy. Minerals precipitating in flumes and in entry wetland cells lacking vegetation included poorly crystalline ferrihydrite, lepidocrocite, goethite, possibly an akaganéite‐like mineral, and high Fe/S ratio Fe oxyhydroxysulfates (similar to schwertmannite). Within vegetated wetland cells lined with crushed limestone, well‐crystallized gypsum, lepidocrocite, and Fe‐oxyhydroxysulfate minerals with low Fe/S ratios were accompanied by gradual reductions in ferrihydrite and akaganéite. The Fe/S molar ratios of Fe oxyhydroxysulfates in flume precipitates averaged 5.2 ± 0.3, while those of cell precipitates averaged ≈3.5 ± 0.5. The oxalate‐extractable (Feox) to total (Fet) Fe fraction of the precipitates was considerably higher in wetland cells (1.1 ± 0.3), where organic C was 10‐fold higher than in entry flumes (0.7 ± 0.1). Scanning electron micrographs of flume precipitates showed a fiber‐like morphology of densely aggregated spherical particles, 1.5 to 2.0 mm in diameter, with a closely packed microcrystalline matrix. Precipitates collected from vegetated wetland cells formed aggregates of somewhat smaller diameter spherical particles with grassy surfaces or finger‐like projections entangled with bacterial cells. The overall composition of the precipitates suggested that the Fe chemistry is controlled primarily by the solubility of Fe oxyhydroxides in flumes and by S‐enriched Fe oxyhydroxysulfates inside the wetland cells. Although jarosite and goethite are thermodynamically favored in the wetland cells, their formation appeared to be inhibited by the presence of organics and the precipitation of Fe oxyhydroxysulfates and gypsum.

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The composition of soil solutions and surface waters emanating from unreclaimed or partially reclaimed stripmined watersheds with low buffering capacity in Kentucky were compared with soil solution compositions of unaffected strata in the watershed. The data suggest that almost 20 yr after mining, most soil solutions and surface waters of the disturbed areas still contain high levels of dissolved Al, controlled primarily by the solubilities of a jurbanite‐like mineral (upper limit) and alunite (lower limit). Soluble Al in solutions of undisturbed areas was consistent with the solubility of kaolinite or gibbsite. The absence of jurbanite x‐ray diffraction peaks suggested the presence of an amorphous or a mineral stoichiometrically similar to jurbanite. Despite greater contact times of soil solutions with the soil compared to surface waters, their compositional differences were insignificant. The control of soluble Al by basic aluminum sulfate minerals was not affected by the variable mineralogical and textural composition of soil and geologic strata in the watershed. Apparently, this is the result of low buffering capacity. At pH < 4, pH and sulfate activities can be used to accurately predict the levels of soluble Al3+ in surface and groundwaters of the watersheds. Similar predictions from pH and SO2−4 activities can also be made for dissolved Fe3+ levels, supporting the stoichiometry but a much higher solubility than that of jarosite.

Redox potentials (Eh) were monitored bimonthly and porewater chemistry was analyzed seasonally at three slightly-acidic, high-elevation Kentucky wetlands that differed in hydrology, parent materials, and vegetation. At all sites, Eh values were below 300 mV, which indicated that reducing conditions persisted within the upper 90 cm and fluctuated mainly within the range of iron and sulfate reduction. Significant relationships of Eh values with depth were observed only at the Martins Fork wetland, where precipitation was the primary water source. The strongest and most stable reducing conditions, observed at the Kentenia site, reflected consistently high water levels, which were sustained by ground water. The third wetland (Four Level) was distinguished by irregular Eh fluctuations coinciding with strong seasonal ground-water upwelling. Although Fe 3+ and SO 4 2-were the primary terminal electron acceptors in all wetlands, porewater chemistry also varied significantly by season and soil depth in response to piezometric water level fluctuations. Additional factors that influenced porewater chemistry included: (1) the presence of limestone parent materials that affected porewater pH, Ca 2+ , and Mg 2+ ; and (2) the prevalence of sphagnum moss or graminoid species that influenced dissolved organic carbon, CO 2 , and CH 4 . Results from this study indicated the diverse range and importance of multiple factors in controlling biogeochemical processes and properties in small, highelevation Appalachian wetlands.

This study evaluated the effectiveness of soils with different texture and depth to treat fecal bacteria eluted from a house-hold septic effluent. The assessments were accomplished by leaching undisturbed soil monoliths of 30, 45, and 60cm thickness and 25cm in diameter, representing the four different textural groups and hydraulic loadings recommended by the Kentucky Health Department, with domestic wastewater effluent collected regularly from a house-hold septic system. Eluent concentrations were monitored daily over a 15 day period for fecal coliform and fecal streptococci concentrations. The results of the study indicate an alarming frequency of failure to comply with United States Environmental Protection Agency (USEPA) criteria for depth to groundwater, when using a 30 cm vertical separation distance between the bottom of the drain-field and a limiting soil interface. The treatment performance was especially poor in coarse-textured soils. Although biomat development over time is expected to improve treatment, the high influent levels of fecal bacteria pose great concerns for surface and groundwater contamination. Fine-textured soils generally provided better treatment efficiency and more consistent compliance with EPA standards. Treatment efficiency and compliance usually improved with increasing soil depth, with the 60cm thickness providing the most consistent performance and compliance with maximum discharge limit (MDL) requirements. The findings of this study document a general inadequacy of the 30cm vertical separation distance to provide effective treatment of septic effluents in Kentucky soils, particularly in coarse-textured soils. Considering that increasing the soil depth thickness may be impractical in many marginal soils, complementary or alternative treatment technologies should be adopted to improve treatment efficiency and prevent further deterioration of the quality of water resources.

This study evaluated the effectiveness of soils with different textures and thickness to treat BOD, N and P eluted from household septic effluent. The assessments were accomplished by leaching undisturbed soil monoliths of 30, 45 and 60 cm thickness and 25 cm in diameter, representing the four different textural groups and hydraulic loadings recommended by the Kentucky Health Department, with domestic wastewater effluent collected regularly from a household septic system. Effluent concentrations were monitored daily over a 15d period for biochemical oxygen demand (BOD), total-N, NH4-N, NO3-N and total-P concentrations. The results of the study indicate an alarming frequency of failure to comply with EPA criteria for BOD, total-N and NH4-N concentrations when using a 30 cm vertical separation distance between the bottom of the drain field and a limiting soil interface. The treatment performance was particularly poor in coarse-textured soils, apparently due to insufficient reactive surface area. Although biomat development over time is expected to improve the treatment for some of these parameters, the high influent levels of BOD pose great concerns for surface and groundwater contamination during the early stages of operation. Fine-textured soils generally provided better treatment efficiency and more consistent compliance with EPA standards for BOD, total-N, NH4-N and total-P, as well as greater nitrification/denitrification potential. Treatment efficiency and compliance usually improved with increasing soil depth, with the 60 cm thickness providing the most consistent performance and compliance with MDL requirements. Considering that increasing soil thickness requirements may be impractical in many marginal soils, complementary or alternative treatment technologies should be adopted to improve treatment efficiency and prevent further deterioration of the quality of water resources.

Environmental nanoparticles found in soil systems and biosolids may pose a considerable risk to groundwater quality as contaminant carriers. Little effort has been invested in the characterization of natural nanocolloids compared to corresponding macrocolloids. This study involved physicochemical, mineralogical, and morphological characterizations of nanocolloids and macrocolloids fractionated from three Kentucky soils and one biosolid. Particle size and morphology were investigated using scanning/transmission electron microscopy and dynamic light scattering. Mineralogical composition was determined by X-ray diffraction and thermogravimetric and Fourier-transform infrared spectroscopy analyses. Zeta potentials and cation exchange capacities assessed surface charge and chemical reactivity. The estimated average hydrodynamic diameter of nanoparticles was nearly twice the ideal 100 nm range, apparently due to irregular particle shapes and partial aggregation. Nanoparticles were also found attached to surfaces of macrocolloids, forming macro-nano aggregates and obscuring some of their physical and chemical characteristics. However, nanocolloids exhibited greater surface reactivity, likely due to their smaller size, poor crystallinity, and morphological shape distortions. In spite of some behavior modification due to nanoaggregation phenomena, nanocolloids appeared to be much more potent vectors of contaminant transport in subsurface environments than their macrosize fractions. Nevertheless, their heterogeneous nature brings to light important considerations in addressing pollution prevention and remediation challenges.