Aziz Amoozegar

Influence of Natural Organic Matter on Colloid Transport Through Saprolite

Mobile colloids in soils and their underlying strata may play an important role in the translocation of some contaminants from surface sources to groundwater. This study was conducted to evaluate the role of adsorbed natural organic matter (NOM) in the transport of submicron soil colloids through a commonly occurring type of saprolite in North Carolina. Intact saprolite columns from 4 m below the soil surface were used to study the movement of a conservative tracer (3H2O) and of soil colloids with and without adsorbed NOM. For natural (i.e., untreated) soil colloids having high colloidal stability due to adsorbed NOM, the filier efficiency of the saprolite decreased rapidly to zero as increasing amounts of colloids were deposited on the pore walls in the saprolite (blocking effect). Colloid breakthrough curves exhibited little tailing, indicating that colloid deposition was largely irreversible. The colloids were excluded from about 33% of the water-filled pore space, resulting in faster transport of colloids as compared to 3H2O. When the colloids were treated with NaOCl to remove adsorbed NOM, colloidal stability and mobility were strongly decreased. For these suspensions the filter efficiency of the columns increased as increasing amounts of colloids were deposited in the saprolite (filter ripening). After addition of small amounts of humic acid (1 mg L−1) to the NaOCl-treated colloids, they exhibited very similar transport behavior as the untreated soil colloids. Stabilization of colloids by NOM and the possible occurrence of the blocking effect or filter ripening must be considered in future models of subsurface colloid transport.

Biotite alteration to halloysite and kaolinite in soil-saprolite profiles developed from mica schist and granite gneiss

Abstract The chemical weathering of biotite and associated formation of secondary minerals has important implications for the genesis, mineralogy, chemical properties, and physical properties of soils and saprolites developed from biotite-rich parent rocks. In this study, we used a combination of X-ray diffraction, micromorphological, and scanning electron microscopy techniques to investigate biotite weathering in two soil-saprolite profiles (Typic Kanhapludults) developed from granite gneiss and mica schist in the Piedmont region of North Carolina, USA. In both profiles, sand-sized biotite grains appeared to be transformed directly into kaolinized pseudomorphs of biotite without going through a detectable vermiculite or interstratified biotite-vermiculite intermediate weathering stage. Minerals with biotite-vermiculite mixed layers were only detected in small amounts in the clay- and silt-sized fractions of the saprolite. Weathering sand-sized biotite grains exhibited expanded edges, exfoliation, and cleavage along (001) planes. In the saprolite developed from granite gneiss, kaolin intergrowths within weathering biotite grains were observed. The edges of weathering biotite grains were densely covered with tubular halloysite, suggesting a complex transformation of biotite to halloysite. Halloysite was the dominant clay mineral in the saprolite, but the halloysite content in the clay fractions diminished towards the soil surface.

Directional saturated hydraulic conductivity and macropore morphology of a soil-saprolite sequence

Abstract The soils in the Piedmont and Mountain regions of the southeastern United States are characterized by the presence of saprolite at or near the soil surface. This study was conducted to describe the macropore network of a representative soil-saprolite sequence and to relate the directional saturated hydraulic conductivity of the soil profile to water flow through macropores. Large observation pits were constructed at three geomorphic positions (ridge top, shoulder and ridge nose). Soil-saprolite macropores and their morphology were described in the field. Triplicate intact soil cores were collected in five orientations: one vertical, two horizontals (perpendicular to one another) and two diagonals (perpendicular to one another) from the Bt, B/C and C (massive saprolite) horizons at each of the geomorphic positions. The saturated hydraulic conductivity (Ka) of each intact core sample was determined in the laboratory. In situ Ka of each horizon was also determined near the three observation pits. Mean Ka values for the five orientations, three horizons and three geomorphic positions ranged from 8.20×10−8 m s−1 to 2.75×10−6 m s−1. Mean in situ Ka values ranged from 7.50×10−8 m s−1 to 2.66×10−6 m s−1. The results indicated that no significant differences existed among the Ka values in different orientations for each horizon-landscape combination, with no exceptionally high conductivity value. The in situ Ka results generally agree with the results for the core samples.

Filter efficiency of three saprolites for natural clay and iron oxide colloids.

The mobility of natural soil colloids during saturated low through undisturbed saprolite columns was studied. The colloids were isolated from a surface soil and consisted of clay and iron oxide particles (<0.2 μm) partially coated with adsorbed natural organic matter. Seventy-five intact saprolite columns (7.7 cm length, 6.6 cm diameter) were collected at three field sites, and each column was characterized with respect to chemical and physical properties. Dilute colloidal suspensions were passed through the saprolite columns, and the efluents were analyzed for colloidal Fe, Al, and Si. The results demonstrate that colloids can be rather mobile in some saprolites, whereas other saprolites are efficient filters for colloidal particles

The impact of co-contaminants and septic system effluent quality on the transport of estrogens and nonylphenols through soil.

The impact that varying qualities of wastewater may have on the movement of steroid estrogens through soils into groundwater is little understood. In this study, the steroid estrogens 17beta-estradiol (E2) and estrone (E1) were followed through batch and column studies to examine the impact that organic wastewater constituents from on-site wastewater treatment systems (i.e., septic systems or decentralized systems) may have on influencing the rate of transport of estrogens through soils. Total organic carbon (TOC) content (as a surrogate indicator of overall wastewater quality) and the presence of nonyl-phenol polyethoxylate surfactants (NPEO) at concentrations well below the critical micelle concentration were independently shown to be indicative of earlier breakthrough and less partitioning to soil in batch and column experiments. Both NPEO and wastewater with increasing TOC concentrations led to shifts in the equilibrium of E1 and E2 towards the aqueous phase and caused the analytes to have an earlier breakthrough than in control experiments. The presence of nonylphenols, on the other hand, did not appreciably impact partitioning of E1 or E2. Biodegradation of the steroids in soil was also lower in the presence of septic tank effluents than in an organic-free control water. Furthermore, the data indicate that the rate of movement of E1 and E2 present in septic tank effluent through soils and into groundwater can be decreased by removing the NPEOs and TOC through wastewater treatment prior to sub-surface disposal. This study offers some insights into mechanisms which impact degradation, transformation, and retardation, and shows that TOC and NPEO surfactants play a role in estrogen transport.

Turbidimetric Determination of Anionic Polyacrylamide in Low Carbon Soil Extracts

Concerns over runoff water quality from agricultural lands and construction sites have led to the development of improved erosion control practices, including application of polyacrylamide (PAM). We developed a quick and reliable method for quantifying PAM in soil extracts at low carbon content by using a turbidimetric reagent, Hyamine 1622. Three high-molecular weight anionic PAMs differing in charge density (7, 20, and 50 mol%) and five water matrices, deionized (DI) water and extracts from four different soils, were used to construct PAM calibration curves by reacting PAM solutions with hyamine and measuring turbidity development from the PAM-hyamine complex. The PAM calibration curve with DI water showed a strong linear relationship ( = 0.99), and the sensitivity (slope) of calibration curves increased with increasing PAM charge density with a detection limit of 0.4 to 0.9 mg L. Identical tests with soil extracts showed the sensitivity of the hyamine method was dependent on the properties of the soil extract, primarily organic carbon concentration. Although the method was effective in mineral soils, the highest charge density PAM yielded a more reliable linear relationship ( > 0.97) and lowest detection limit (0.3 to 1.2 mg L), compared with those of the lower charge density PAMs (0.7 to 23 mg L). Our results suggest that the hyamine test could be an efficient method for quantifying PAM in environmental soil water samples as long as the organic carbon in the sample is low, such as in subsurface soil material often exposed at construction sites.

Granular and Dissolved Polyacrylamide Effects on Erosion and Runoff under Simulated Rainfall.

Polyacrylamide (PAM) has been demonstrated to reduce erosion under many conditions, but less is known about the effects of its application method on erosion and concentrations in the runoff water. A rainfall simulation study was conducted to evaluate the performance of an excelsior erosion control blanket (cover) and two PAM application methods. The treatments were (i) no cover + no PAM (control), (ii) cover + no PAM, (iii) cover + granular PAM (GPAM), and (iv) cover + dissolved PAM (DPAM) applied to soil packed in wooden runoff boxes. The GPAM or DPAM (500 mg L) was surface-applied at a rate of 30 kg ha 1 d before rainfall simulation. Rainfall was applied at 83 mm h for 50 min and then repeated for another 20 min after a 30-min rest period. Runoff samples were analyzed for volume, turbidity in nephelometric turbidity units (NTU), total suspended solids (TSS), sediment particle size distribution, and PAM concentration. The cover alone reduced turbidity and TSS in runoff by >60% compared with the control (2315 NTU, 2777 mg TSS L). The PAM further reduced turbidity and TSS by >30% regardless of the application method. The median particle diameter of eroded sediments for PAM treatments was seven to nine times that of the control (12.4 μm). Loss of applied PAM in the runoff water (not sediment) was 19% for the GPAM treatment but only 2% for the DPAM treatment. Both GPAM and DPAM were effective at improving groundcover performance, but DPAM resulted in much less PAM loss.

Soil Weathering as an Engine for Manganese Contamination of Well Water

Manganese (Mn) contamination of well water is recognized as an environmental health concern. In the southeastern Piedmont region of the United States, well water Mn concentrations can be >2 orders of magnitude above health limits, but the specific sources and causes of elevated Mn in groundwater are generally unknown. Here, using field, laboratory, spectroscopic, and geospatial analyses, we propose that natural pedogenetic and hydrogeochemical processes couple to export Mn from the near-surface to fractured-bedrock aquifers within the Piedmont. Dissolved Mn concentrations are greatest just below the water table and decrease with depth. Solid-phase concentration, chemical extraction, and X-ray absorption spectroscopy data show that secondary Mn oxides accumulate near the water table within the chemically weathering saprolite, whereas less-reactive, primary Mn-bearing minerals dominate Mn speciation within the physically weathered transition zone and bedrock. Mass-balance calculations indicate soil weathering has depleted over 40% of the original solid-phase Mn from the near-surface, and hydrologic gradients provide a driving force for downward delivery of Mn. Overall, we estimate that >1 million people in the southeastern Piedmont consume well water containing Mn at concentrations exceeding recommended standards, and collectively, these results suggest that integrated soil-bedrock-system analyses are needed to predict and manage Mn in drinking-water wells.

Applying Soil Morphology to Long Term Acceptance Rate Determination

Abstract: Soil morphology and site conditions are used in many states to determine the suitability of a building lot for a decentralized wastewater treatment and dispersal system. Although rules in many states mention site and soil conditions, they are at times ambiguous or only assess whether the site can or can not be used for wastewater treatment and dispersal. Often the rules provide little guidance on the specific procedure for determining a final long term acceptance rate (LTAR) based on multiple soil and site conditions, relying on the discretion and experience of the field practitioner to determine the final LTAR. The end result is that two site evaluators can come up with vastly differing LTARs on the same site. Using the North Carolina rules for wastewater treatment and dispersal as a starting point we developed a standardized procedure to assign an LTAR. This procedure is based on principles of water and air movement in soil as well as expected treatment capacity. Each section of the rules that deals with a specific soil or site parameter was rated. The result is a step-by-step procedure that includes each parameter in the final LTAR determination. The procedure is reproducible from site to site and from practitioner to practitioner. Once the LTAR for the soil/site is determined it can be further adjusted based on wastewater strength, flows and other applicable factors related to expected performance.

Wastewater Infiltration and Water Movement Around Trenches of Septic Systems

In designing septic systems it is often assumed that wastewater infiltration from the trenches into the soil and water movement away from the drainfield occurs uniformly through the soil in all directions. Soils, however, are heterogeneous and vary spatially in all directions. Wastewater infiltration and movement of water through the soil in the drainfield area of a number of actual and simulated septic systems with gravel-filled trenches installed in different soils were assessed. In one study, 56 tensiometers were installed on a 20- by 20-cm grid system perpendicular to the middle trench of three low-pressure pipe septic systems. The distance between the tensiometers in both horizontal and vertical directions was 20 cm. A series of observation wells were also installed in the trenches of these systems to evaluate infiltration rate. In another study, using a tracer dye and bromide, movement of water through the soil around the trenches of four simulated septic systems installed at three sites were assessed. Wastewater infiltration from the trenches into the soil varied along the length of the trenches as well as among different trenches. The equipotential lines generated from the tensiometer readings around the trenches showed that water flow from the trenches through the soil is neither symmetrical nor uniform. Assessment of the distribution patterns of tracer dye and bromide under the trenches of the four simulated drainfields indicated that preferential flow is the main mechanism for water movement when trenches are installed in a structured clayey Bt horizon. When trenches are installed in coarse textured materials above a clayey horizon in sloping areas, most of the water applied to the trenches move away from the area above the clayey Bt layer.