Characterization of Groundwater Quality Based on Regional Geologic Setting in the Piedmont and Blue Ridge Physiographic Provinces, North Carolina

Harden, Stephen L.; Chapman, Melinda J.; Harned, Douglas A.

doi:10.3133/sir20095149

Cited by 2 publications

(2 citation statements)

References 21 publications

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“…Importantly, the presence of near-surface sources of Mn to groundwater in the Piedmont does not preclude additional sources of Mn from deeper within profiles. The magmatic-arc and low-grade metamorphic rocks of the Carolina Slate Belt are likely contributors to Mn subsurface cycling, 51 and some of the heterogeneity of Mn within underlying parent material across the NC Piedmont is likely due to the volcanic nature of the region and the diverse and complex geology. 52 topographic-induced groundwater flow patterns may also impact Mn transport and accumulation within oxygenated discharge zones, 24 complicating observed weathering and depletion profiles.…”

Section: Environmental Science and Technologymentioning

confidence: 99%

Soil Weathering as an Engine for Manganese Contamination of Well Water

Gillispie

Austin

Rivera

et al. 2016

Environ. Sci. Technol.

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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.

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Section: Environmental Science and Technologymentioning

confidence: 99%

Soil Weathering as an Engine for Manganese Contamination of Well Water

Gillispie

Austin

Rivera

et al. 2016

Environ. Sci. Technol.

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“…A cluster of geologic units with large As exceedance percentages occurs in the youngest portion of the Carolina Slate belt-the Albemarle arc (Fig 2B )-that lies in a geographic region previous noted as having elevated As concentration in well water [13,14,24]. The Albemarle arc along with the rest of the Carolina Slate belt was a zone of suprasubduction that accreted to North America [29,30]. Other geologic events in these regions included intense metamorphism, folding, faulting, and igneous intrusive activity, resulting from collisions and rifting events associated that contribute to the complex geology of the Albemarle arc [31,32].…”

Section: Plos Watermentioning

confidence: 99%

Geologic predictors of drinking water well contamination in North Carolina

Alvarado,

Austin,

Bradley

et al. 2024

PLOS Water

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More than 200 million people worldwide, including 11 million in the US, are estimated to consume water containing arsenic (As) concentrations that exceed World Health Organization and US EPA standards. In most cases, the As found in drinking water wells results from interactions between groundwater and geologic materials (geogenic contamination). To that end, we used the NCWELL database, which contains chemical information for 117,960 private drinking wells across North Carolina, to determine the spatial distribution of wells containing As contaminated water within geologic units. Specific geologic units had large percentages (up to 1 in 3) of wells with water exceeding the EPA As maximum contaminant level (MCL, 10 μg/L), both revealing significant variation within areas that have been previously associated with As contamination and identifying as yet unidentified problematic geologic units. For the 19 geologic units that have >5% of wells that contain water with As concentrations in exceedance of 10 μg/L, 12 (63%) are lithogenically related to the Albemarle arc, remnants of an ancient volcanic island, indicating the importance of volcanogenic materials, as well as recycled (eroded and deposited) and metamorphosed volcanogenic material. Within geologic units, wells that have As concentrations exceeding 10 μg/L tended to have pH values greater than wells with As concentrations less than 10 μg/L, emphasizing the importance of the extent of interaction between groundwater and geologic materials. Using census information with the geologic-based exceedance percentages revealed the importance of regional geology on estimates of population at risk compared to estimates based on county boundaries. Results illustrate that relating As contamination to geologic units not only helps explain sources of geogenic contamination but sharpens the identification of communities at risk for exposure and further illuminates problematic areas through geologic interpretation.

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Characterization of Groundwater Quality Based on Regional Geologic Setting in the Piedmont and Blue Ridge Physiographic Provinces, North Carolina

Cited by 2 publications

References 21 publications

Soil Weathering as an Engine for Manganese Contamination of Well Water

Soil Weathering as an Engine for Manganese Contamination of Well Water

Geologic predictors of drinking water well contamination in North Carolina

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