Overview
Senior and colleagues sampled 89 domestic wells in Wayne County, Pennsylvania, to establish a baseline for shallow groundwater quality in bedrock aquifers before potential extensive shale-gas development. This is in-scope as groundwater exposure and source-attribution context, not bottled-water or salt occurrence evidence.
Key numbers
The sampled wells ranged from 85 to 1,300 ft deep, with a median depth of 291 ft. The report states that all groundwater samples were analyzed for bacteria, major ions, nutrients, selected inorganic trace constituents, radon-222, gross alpha and beta activity, selected man-made organic compounds, dissolved gases, and methane isotopes where enough methane was present.
The abstract reports that arsenic concentrations exceeded the 10 µg/L MCL in 4 of 89 samples (4.5%), with concentrations as high as 20 µg/L. Arsenic concentrations exceeded the 2 µg/L Health Advisory level in 27 of 89 samples (30%). Table 4 reports dissolved arsenic above the reporting level in 82 of 89 samples (92%), with minimum <0.010 µg/L, median 0.38 µg/L, and maximum 20.1 µg/L.
Table 4 trace-element summary values include:
| Constituent | Fraction above reporting level | Minimum | Median | Maximum | Standard exceedance |
|---|---|---|---|---|---|
| Aluminum, dissolved | 21 of 89 (24%) | <2.2 µg/L | <2.2 µg/L | 52.3 µg/L | 0 of 89 |
| Antimony, dissolved | 28 of 89 (31%) | <0.027 µg/L | <0.027 µg/L | 0.227 µg/L | 0 of 89 |
| Arsenic, dissolved | 82 of 89 (92%) | <0.010 µg/L | 0.38 µg/L | 20.1 µg/L | 4 of 89 over MCL |
| Cadmium, dissolved | 2 of 89 (2%) | <0.030 µg/L | <0.030 µg/L | 0.132 µg/L | 0 of 89 |
| Copper, dissolved | 80 of 89 (90%) | <0.80 µg/L | 5.8 µg/L | 121 µg/L | 0 of 89 |
| Lead, dissolved | 79 of 89 (89%) | <0.040 µg/L | 0.20 µg/L | 3.06 µg/L | 0 of 89 |
| Nickel, dissolved | 70 of 89 (79%) | <0.20 µg/L | 0.37 µg/L | 1.7 µg/L | 0 of 89 |
| Zinc, dissolved | 69 of 89 (78%) | <2.0 µg/L | 6.6 µg/L | 81.9 µg/L | 0 of 89 |
| Barium, dissolved | 89 of 89 (100%) | 1.26 µg/L | 52.8 µg/L | 803 µg/L | 0 of 89 |
| Iron, total | 70 of 89 (80%) | <1.0 µg/L | 10.6 µg/L | 8,800 µg/L | 9 of 89 over SMCL |
| Manganese, dissolved | 38 of 89 (43%) | <0.40 µg/L | <0.40 µg/L | 246 µg/L | 2 of 89 over SMCL |
| Manganese, total | 33 of 89 (37%) | <0.50 µg/L | 0.8 µg/L | 262 µg/L | 2 of 89 over SMCL |
| Strontium, dissolved | 89 of 89 (100%) | 7.17 µg/L | 144 µg/L | 3,040 µg/L | 0 of 89 |
The report links elevated arsenic to higher-pH groundwater. It states that arsenic concentrations in 2014 and 2013 were generally higher than the 10 µg/L MCL only when pH was greater than 7.8, and higher than the 2 µg/L Health Advisory when pH was greater than 7.2.
Table 3 reports pH from 5.4 to 9.3, median 7.3. Twenty-seven of 89 samples (30%) were outside the EPA SMCL range of 6.5 to 8.5: 20 samples had pH less than 6.5 and 7 samples had pH greater than 8.5. Total dissolved solids ranged from 24 to 370 mg/L, median 120 mg/L, with 0 of 89 above the 500 mg/L SMCL.
Table 5 reports radon-222 in all 89 samples, from 25 to 7,400 pCi/L, median 2,120 pCi/L. Eighty-six of 89 samples (97%) exceeded the proposed 300 pCi/L MCL, and 12 of 89 samples (13%) exceeded the proposed alternative MCL of 4,000 pCi/L.
Methods (brief)
The study sampled domestic wells during July-September 2014. Field parameters included temperature, pH, dissolved oxygen, specific conductance, and alkalinity. Dissolved trace elements were analyzed in filtered samples by the USGS National Water Quality Laboratory; selected total trace constituents were analyzed in unfiltered samples by contract laboratories using drinking-water methods. The page reports total and dissolved forms separately where the source does.
Related evidence
- Irrigation water and soil amendments as anthropogenic inputs to cropland
- Source attribution and environmental burden apportionment
- Arsenic
- Lead
- Cadmium
- Iron
- Manganese
- Uranium
Update history
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