This study combined national and state household water databases with new field sampling to describe manganese in 1815 wells and 119 springs in the Shenandoah Valley, Virginia. Wells in sandstone and shale aquifers exceeded 100 ppb (µg/L) far more often than wells in limestone and dolostone karst aquifers. Soil chemistry and X-ray spectroscopy pointed to redox conditions as the main control on dissolved manganese.
Key numbers
- Wells exceeding 100 ppb: all wells 7.0% (n = 1815); dolostone 1.0% (n = 687); limestone 2.6% (n = 541); metamorphic 10.4% (n = 193); sandstone 26.8% (n = 41); shale 21.2% (n = 353) (Table 1, p. 10).
- Springs exceeding 100 ppb: all 4% (n = 119); shale 9.4% (n = 32); limestone 4.9% (n = 41); dolostone 0% (Table 1).
- Well water: average 37 ppb, median below the 1 ppb detection limit, 90th percentile 41.5 ppb; springs average 32 ppb, maximum 1348 ppb (Results, p. 8; Table 1).
- Table 1 gives a well maximum of 7100 ppb while the text gives 1926 ppb (pp. 8 and 10).
- Guidance values as reported by the paper: World Health Organization provisional guideline 80 ppb (2021) and US EPA lifetime health advisory 300 ppb; the authors also use 100 ppb as a chronic exposure threshold drawn from health studies (Introduction, pp. 2 to 3).
Methods (brief)
Well and spring records came from the USGS National Water Information System and the Virginia Household Water Quality Program, supplemented by field sampling of springs and soils in June to August 2021. Water was analyzed by ICP-MS with a 1 ppb detection limit. Soils were analyzed by X-ray fluorescence and manganese K-edge X-ray absorption spectroscopy. Each site was assigned a most likely aquifer rock type.
Evidence fitness
The paper supports occurrence data for manganese in private well and spring drinking water in a karst and non-karst region and the influence of aquifer type. It does not measure intake or health effects and does not cover treated public supplies.
Limitations
Database samples span many years and lack winter field sampling. Aquifer assignment from surface lithology is approximate in folded terrain. Most values are below detection, so medians are uninformative, and the table and text disagree on the well maximum.
Related evidence
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