This project was done in cooperation with
The Pennsylvania Bureau of Radiation Protection.
The Chickies Quartzite, a Lower Cambrian-age formation compromised of quartzite and slate overlying
a basal conglomerate, forms a narrow ridges and crops out discontinuously over 112 square miles in the
Piedmont physiographic province of southeastern Pennsylvania. The formation is a low-yielding, fractured-
rock, water-table aquifer recharged primarily by local precipitation. It is the sole source of water supply for
thousands of domestic users. Ground water in the Chickies Quartzite generally is soft and acidic.
During 1986-88, the U.S. Geological Survey sampled water from 160 wells that penetrate the
Chickies Quartzite to determine the magnitude and distribution of radium-226 (Ra-226), radium-228
(Ra-228), and radon-222 (Rn-222) activities in ground water in the formation and to characterize the
geochemical environmental associated with elevated activities of radium (Ra). In addition, 28 wells
penetrating adjacent geologic units and 1 well in the Hardyston Quartzite were sampled to determine
relative background Ra and Rn-222 activitesin ground water. Analyses included determination of
activities of dissolved Ra-226, Ra-228, and Rn-222, and concentrations of dissolved uranium (U), dissolved
organic carbon (DOC), and major and minor dissolved inorganic ions. Rock samples were analyzed for U
and thorium (Th) and geophysical logs were run to determine sources of Ra and Rn-222 in the Chickies
Quartzite. Activities of up to 41 pCi/L (picocuries per liter) for Ra-226, 160 pCi/L for Ra-228, and
32,300 pCi/L for Rn-222 were measured in ground water in teh Chickies Quartzite. Forty-seven percent of
the samples contained Ra-226 and Ra-228 activities greater than 5 pCi/L. Median activities measured were
1.2 pCi/L for Ra-226, 2.6 pCi/L for Ra-228, 4.2 pCi/L for combined Ra-226 and Ra-228, and 2,400 pCi/L for
Rn-222. Ra-228 activity exceeded Ra-226 activity in about 92 percent of 100 water samples; the median
Ra-228/Ra226 activity ratio was 2.4. Ra-228/Ra-226 activity ratios commonly were greater in ground
water than calculated Th/U ratios in rock samples, suggesting perferential leaching of Ra-228 from aquifer
solids. Of ground water in the adjacent geologic units, the highest activities (up to 2.9 pCi/L for Ra-226,
12 pCi/L for Ra-228, and 25,300 pCi/L for Rn-222) were measured in ground water in the Harpers Phyllite
and Antietam Quartzite.
Nonparametric (Spearman rho test) statistical correlations show that the activity of dissolved Ra is
inversely related to pH and directly related to concentrations of total dissolved solids, DOC, barium, and
sulfate. Low pH decreases absorption of Ra onto the aquifer matrix. The other factors may favor Ra
mobility by enhancing complexation or increasing solubility. Rn-222 activity does not correlate with and is
not supported by the activity of its parent, Ra-226, in solution. Ra-226 activity correlates positively, but
weakly, with U concentrations. Ra-226 does not appear to be supported by its parent, U-238, in solution.
Observed distributions of Ra-228, Ra-226, and Rn-222 activities in ground water in different
lithologies of the Chickies Quartzite reflect different geochemical controls on absorption and distribution of
parent thorium-232 (Th-232) and uranium-238 (U-238) in the formatin. Radium activities were greatest
in acidic ground water in the conglomerate and quartzite (median pH of 5.0 and 5.2, respectively) and least
in the more neutral water in the slate (median pH of 6.4). For ground water in the conglomerate, quartzite,
and slate, respectively, median activities measured were 1.3, 1.5, and .02 pCi/L for Ra-226; and 3.7, 2.5,
and 1.0 pCi/L for Ra-228. Natural-gamma-ray geophysical logs and results of rock analyses indicate that
the conglomerate may contain more Th and U than the quartzite and that the conglomerate may be more
enriched in Th with respect to U than the quartzite; Th and U distribution in both lithogies is variable.
Median Rn-222 activities in ground-water samples generally are greater progressively from teh slate
(1,400 pCi/L) to the quartzite (2,000 pCi/L) to the conglomerate (3,400 pCi/L) and may reflect differences in
U content of the lithologies.
Ra-226, Ra-228, and Rn-222 activities in ground water vary locally and temporally. Lithology
controls the geochmical environment, topography, and ground-water flow, and, therefore, the
spatial distribution of Ra and Rn-222 activities. Temporal variations are seasonal; maximum Ra and
Rn-222 activities in ground wate roccur with water-table lows in autumn and minimum Ra and Rn-222
activities occur with water-table highs in the spring.
Cecil, L.D., Smith, R.C. II, Reilly, M.A., and Rose, A.W., 1987, Radium-228 and radium-226 in
ground water of the Chickies Formation, southeastern Pennsylvania IN Graves, Barbara, ed.,
Radon, radium, and other radioactivity in ground water: Chelsea, Michigan,
Lewis Publishers, p. 437-447.
Cecil, L.D., 1989, Map showing radium concentrations in ground water of the Chickies Formation,
southeastern Pennsylvania, 1986-87:
U.S. Geological Survey Open-File Report 87-232, 1 pl.
Senior, L.A., and Vogel, K.V., 1992, Geochemistry of radium-226 and radium-228, and radon-222
in ground water in the Chickies Quartzite, Southeastern Pennsylvania, in Daniel, C.C. III,
White, R.K., and Stone, P.A., eds., Ground water in the piedmont--Proceedings of a conference
on ground water in the piedmont of the eastern United States, October 16-18, 1989; Clemson,
South Carolina, Clemson University, p. 547-565.
Senior, L.A., and Vogel, K.V., 1995, Radium and radon in ground water in the Chickies Quartzite,
Southeastern Pennsylvania:
U.S. Geological Survey Water-Resources Investigations Report 92-4088, 145 p.
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