 |
|
|
||||
| Publications— Scientific Investigations Reports |
In cooperation with the U.S. Environmental Protection Agency
U.S. Geological Survey Scientific Investigations Report 2006-5261
By Lisa A. Senior and Ronald A. Sloto
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
View the full report in PDF 11.7 MB
View the plate in PDF 5.0 MB
During an investigation in 2000 by the U.S. Environmental Protection Agency (USEPA) of possible contaminant releases
from an industrial facility on Congo Road near Gilbertsville in Berks and Montgomery Counties, southeastern Pennsylvania,
concentrations of arsenic and fluoride above USEPA drinking-water standards of 10 µg/L and 4 mg/L, respectively, and of
boron above the USEPA health advisory level of 600 µg/L were measured in ground water in an area along the northwestern
edge of the Newark Basin. In 2003, the USEPA requested technical assistance from the U.S. Geological Survey (USGS) to
help identify sources of arsenic, boron, and fluoride in the ground water in the Congo Road area, which included possible
anthropogenic releases and naturally occurring mineralization in the local bedrock aquifer, and to identify other areas
in the Newark Basin of southeastern Pennsylvania with similarly elevated concentrations of these constituents. The USGS
reviewed available data and collected additional ground-water samples in the Congo Road area and four similar
hydrogeologic settings.
The Newark Basin is the largest of the 13 major exposed Mesozoic rift basins that stretch from
Nova Scotia to South Carolina. Rocks in the Newark Basin include Triassic through Jurassic-age sedimentary sequences of
sandstones and shales that were intruded by diabase. Mineral deposits of hydrothermal origin are associated with alteration
zones bordering intrusions of diabase and also occur as strata-bound replacement deposits of copper and zinc in sedimentary
rocks.
The USGS review of data available in 2003 showed that water from about 10 percent of wells throughout the Newark
Basin of southeastern Pennsylvania had concentrations of arsenic greater than the USEPA maximum contaminant level
(MCL) of 10 µg/L; the highest reported arsenic concentration was at about 70 µg/L. Few data on boron were available, and
the highest reported boron concentration in well-water samples was 60 µg/L in contrast to concentrations over 5,000 µg/L
in the Congo Road area. Although concentrations of fluoride up to 4 mg/L were reported for a few well-water samples
collected throughout the Newark Basin, about 90 percent of the samples had concentrations of 0.5 mg/L or less.
The USGS sampled 58 wells primarily in 5 areas in the Newark Basin, southeastern Pennsylvania, from February 2004
through April 2005 to identify other possible areas of elevated arsenic, boron, and fluoride and to characterize the
geochemical environment associated with elevated concentrations of these constituents. Sampled wells included 12 monitor
wells at an industrial facility near Congo Road, 45 private-supply wells in Berks, Montgomery, and Bucks Counties, and 1
private-supply well near Dillsburg, York County, an area where elevated fluoride in ground water had been reported in the
adjacent Gettysburg Basin. Wells were sampled in transects from the diabase through the adjacent hornfels and into the
unaltered shales of the Brunswick Group. Field measurements were made of pH, temperature, dissolved oxygen concentration,
and specific conductance. Samples were analyzed in the laboratory for major ions, nutrients, total organic carbon,
dissolved and total concentrations of selected trace elements, and boron isotopic composition.
Generally, the ground water from the 46 private-supply wells had relatively neutral to alkaline pH (ranging from 6.1 to
9.1) and moderate concentrations of dissolved oxygen. Most water samples were of the calcium-bicarbonate type.
Concentrations of arsenic up to 60 µg/L, boron up to 3,950 µg/L, and fluoride up to 0.70 mg/L were measured.
Drinking-water standards or health advisories (for constituents that do not have standards established) were exceeded most
frequently (about 20 percent of samples) for arsenic and boron and less frequently (6 percent or less of samples) for total
iron, manganese, sulfate, nitrate, lead, molybdenum, and strontium. In water from 12 monitor wells at the industrial
facility on Congo Road, concentrations of arsenic up to 61 µg/L, boron up to 5,240 µg/L, and fluoride up to 6.51 mg/L were
measured, and drinking-water standards or health advisories were exceeded most frequently (more than 30 percent of samples)
for manganese, boron, strontium, and arsenic and less frequently (8 to 25 percent of samples) for chloride, sulfate,
fluoride, ammonia, iron, and selenium.
Statistical comparisons of constituent concentrations in five sampling areas (including the Congo Road area) and three main
lithologies using the nonparametric Kruskal-Wallis test found few statistically significant differences for water from
private-supply wells in the five sampling areas, but those differences included arsenic and boron concentrations. Arsenic concentrations
were lowest in the Jacksonwald area of Berks County, and boron concentrations were lowest in the Quakertown
area of Bucks County. Many differences in water quality were found in the comparison of private-supply and monitor-well
samples; water from the monitor wells had higher concentrations of numerous constituents, including major cations,
chloride, fluoride, ammonia, total organic carbon, barium, cobalt, iron, lithium, manganese, nickel, selenium, strontium,
and uranium.
Statistically significant differences were not found in arsenic and boron concentrations when water from the
private-supply wells and monitor wells were compared, suggesting that elevated arsenic and boron concentrations are not
restricted to the industrial site and can occur naturally in ground water elsewhere in the Newark Basin.
Statistically significant differences in concentrations of some major ions and trace elements and for boron isotopic compositions
were found when water from wells in the three main lithologies--diabase, hornfels, and unaltered shales--was compared,
although significant differences were not found in concentrations of arsenic, boron, or fluoride. Concentrations of
most constituents tended to be lowest in water from wells in diabase and highest in water from wells in the shales and generally
intermediate in water from wells in the hornfels, but water from wells in the diabase and hornfels tended to have higher concentrations
of silica and vanadium than water from wells in the unaltered shales. Water from wells in the diabase tended to have
water most enriched in the heavier isotope of boron, 11B. The boron isotope compositions of most water samples from
private-supply wells in all the sampled areas indicate natural mineral sources, such as datolite, for boron.
Relations between chemical constituents were explored using the nonparametric Spearman rho correlation test. In water
samples from 46 private-supply wells, arsenic correlated most strongly and positively with pH, boron, and molybdenum.
Arsenic also correlated positively with selenium, uranium, nickel, lithium, fluoride, and strontium, and negatively with
total organic carbon, copper, and dissolved oxygen. Arsenic concentrations may be controlled partly by pH affecting adsorption
of the anion arsenate. All samples with pH of 8 or higher had arsenic concentrations greater than the MCL of 10 µg/L,
whereas no sample with pH of 7 or lower had arsenic concentrations that exceeded the MCL. The correlation of arsenic with
many of the other trace elements suggests similar geochemical controls and (or) distribution in the aquifer materials.
For wells completed in and near diabase, the percentage of wells with ground-water concentrations of arsenic above the
MCL of 10 µg/L appears to be greater than for the Newark Basin as a whole (about 20 percent compared to 10 percent),
suggesting some arsenic enrichment in the rocks and (or) a favorable geochemical environment to mobilize arsenic. Also,
the amount of boron in and near diabase intrusions probably is higher than in the Newark Basin as a whole. Boron may have
been introduced or remobilized during the intrusion of diabase in the basin, especially where connate brines or residual brines
associated with evaporites may have been present. Only a few elevated fluoride concentrations, other than those related to
anthropogenic sources at the industrial facility near Congo Road, were measured in samples from wells in and near diabase,
indicating limited local natural fluoride enrichment. Possible natural sources of arsenic, boron, and fluoride in the rocks
include minerals deposits associated with the diabase intrusions and minerals in unaltered shales.
Abstract
Introduction
Background
Purpose and Scope
Study Area
Previous Investigations
Hydrogeologic Setting
Geology
Geologic Structure
Geologic Units
Precambrian and Paleozoic Rocks
Mesozoic Rocks
Effects of Thermal Metamorphism
Mineral Deposits in the Newark Basin
Magnetite Skarn and Skarn/Replacement Deposits
Hornfels Copper Deposits
Diabase-Hosted Vein and Late-Stage Igneous Segregation Deposits
Sediment-Hosted and Stratabound Replacement Deposits
Evaporites
Ground-Water System
Arsenic, Boron, and Fluoride in Ground Water
Geochemical Controls on Arsenic, Boron, and Fluoride in Ground Water
Review of Available Data
Arsenic
Boron
Fluoride
Methods of Data Collection and Analysis
Ground-Water Sample Collection
Sample Analysis
Summary of Ground-Water Composition
Major Ions and Characteristics
Trace Elements
Boron Isotopes
Relation to Hydrogeologic Setting
Congo Road Area
Jacksonwald Area
Kibblehouse Quarry Area
New Hope Area
Quakertown ARea
Comparison of Sampling Areas and Lithologies
Relation to Trace Elements and Other Chemical Constituents
Hydrogeochemical Controls on the Distribution of Arsenic, Boron, and Fluoride in Ground Water
Summary and Conclusions
Acknowledgments
References Cited
Appendix 1--Mines and Prospects in the Newark Basin
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
View the full report in PDF 11.7MB
For more information about USGS activities in Pennsylvania contact:
Director
USGS Pennsylvania Water Science Center
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: (717) 730-6960
Fax: (717) 730-6997
or access the USGS Water Resources of Pennsylvania home page at:
http://pa.water.usgs.gov/.
U.S. Department of the Interior | U.S. Geological Survey
Persistent URL: https://pubs.water.usgs.gov/sir20065261
Page Contact Information: USGS Publishing Network
Page Last Modified: Thursday, 01-Dec-2016 19:32:44 EST