1998 GSA Annual Meeting
Toronto, Ontario

Abstract 50336


Presented by Ayotte, Joseph D..
      Nielsen, Martha G.,
      Robinson, Gilpin R. Jr..

Key words: arsenic, bedrock geology, ground water

In Session 21     T02. Natural Sources of Mercury and Arsenic: Significance in Regional Cycles and Environmental Assessments - IEE Monday, 26-Oct-98 AM in Room: 716B at 9:45 AM for 15 minutes.

Abstract: The concentration of arsenic locally exceeds the U. S. Environmental Protection Agency drinking-water limit of 0.05 mg/L in 10 to 15 percent of private domestic bedrock wells in eastern New England. Data from more than 800 public and 190 privately-owned bedrock wells in New England, analyzed as part of a USGS National Water Quality Assessment study, indicate arsenic levels in 23 percent of the wells exceeded 0.005 mg/L and in 13 percent exceeded 0.01 mg/L. A comparison of arsenic data from these bedrock wells indicates that the frequency of detections of arsenic, at 0.005 mg/L, in the bedrock aquifer is significantly different among major bedrock lithology groups. Bedrock units from state geologic maps were reclassified into five general groups: (1) calcareous metasedimentary rocks, (2) non-calcareous metasedimentary rocks, and (3) felsic igneous rocks, with smaller areas of (4) mafic igneous rocks, and (5) clastic sedimentary rocks. The frequency of detection of arsenic in bedrock aquifer water was 49 percent in the calcareous metasedimentary rocks and less than 25 percent in the other four general groups. Arsenic concentrations from wells completed in rocks of the general groups were ranked, and significance tests were performed on the means of the ranks within each group, followed by pair-wise multiple comparison tests. Results show that arsenic concentrations are significantly higher in calcareous metasedimentary rocks than in lithochemical units containing largely igneous rocks, non-calcareous metasedimentary rocks, and clastic sedimentary rocks. Data for the study were primarily compliance monitoring analyses obtained from the Maine Department of Human Services, New Hampshire Department of Environmental Services, the Massachusetts Department of Environmental Protection, and the Rhode Island Department of Health.

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