Dissolved Radon'' and, lJ 

Ground,-Water be 
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY 

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year 

issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that may be listed in various U.S. 

Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" may no longer be 

available. 

Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of 

Commerce, Springfield, VA 22161 ; please include NTIS report number with inquiry. 

Order U.S. Geological Survey publications by mail or over the counter from the offices listed below. 

BY MAIL 

Books 

Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications of 

general interest (such as leaflets, pamphlets, booklets), single copies 

of Earthquakes & Volcanoes, Preliminary Determination of Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone out of print at the Superintendent of 

Documents, are obtainable by mail from 

U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Determination of Epicenters) can be obtained ONLY 

from the 

Superintendent of Documents 

Government Printing Office 

Washington, DC 20402 

(Check or money order must be payable to Superintendent of 

Documents.) 

Maps 

For maps, address mail orders to 

U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

Residents of Alaska may order maps from 

U.S. Geological Survey, Earth Science Information Center 

101 Twelfth Ave., Box 12 

Fairbanks, AK 99701 

OVER THE COUNTER 

Books and Maps 

Books and maps of the U.S. Geological Survey are available 

over the counter at the following U.S. Geological Survey offices, all 

of which are authorized agents of the Superintendent of Documents. 

• ANCHORAGE,Alaska-Rm. 101,4230 University Dr. 

• LAKEWOOD, Colorado-Federal Center, Bldg. 810 

• MENLO PARK, California-Bldg. 3, Rm. 3128, 

345 Middlefield Rd. 

• RESTON, Virginia-USGS National Center, Rm. 1C402, 

12201 Sunrise Valley Dr. 

• SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105, 

125 South State St. 

• SPOKANE, Washington-U.S. Post Office Bldg., Rm. 135, 

West 904 Riverside Ave. 

• WASHINGTON, D.C.-Main Interior Bldg., Rm. 2650, 

18th and C Sts., NW. 

Maps Only 

Maps may be purchased over the counter at the following 

U.S. Geological Survey offices: 

• FAIRBANKS, Alaska-New Federal Bldg, 101 Twelfth Ave. 

• ROLLA, Missouri-1400 Independence Rd. 

• STENNIS SPACE CENTER, Mississippi-Bldg. 3101 
Dissolved Radon and Uranium, and 

Ground-Water Geochemistry in 

an Area near Hylas, Virginia 

By Mark R. Stanton, Richard B. Wanty, Errol P. Lawrence, and Paul H. Briggs 

U.S. GEOLOGICAL SURVEY BULLETIN 2070 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1996 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director 

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government 

Library of Congress Cataloging-in-Publication Data 

Dissolved radon and uranium, and ground-water geochemistry in an area near Hylas, 

Virginia I by Mark R. Stanton ... [et. al.]. 

p. em.- (U.S. Geological Survey Bulletin: 2070) 

Includes bibliography references (p. - ). 

Supt, of Docs. no.: I 19013:B2070 

1. Radioactive pollution of water-Virginia-Hylas region. 2. RadonEnvironmental aspects. 3. Uranium-Environmental aspects. 4. GroundwaterPollution-Virginia-Hylas Region. 5. Mylonite-Virginia-Hylas Region. 

I. Stanton, Mark R. II. Series. 

[QE75.B9 TD427.R3] 

557 .3s-dc20 

[363.73'8] 95-35262 

CIP 
CONTENTS 

Abstract. ................................................................................................................... :...... 1 

Introduction ................................................................................................................... . 

Geology.......................................................................................................................... 2 

Field and Laboratory Methods . . . . . . . . .. ... .. . . . . . . . . . . . . . . . .. . . ..... ....... .. . . .. . . . . ... ... . . . . . ............ .... ... . 4 

Description of Well Types...................................................................................... 4 

Sampling and Analytical Methods . .. . . . . . . . . . . . . . . . . . . . . .... ................ ... . .. .. . . . . . .. ........ ... . ... 4 

Statistical Procedures.............................................................................................. 5 

Results............................................................................................................................ 8 

Ground-water Quality............................................................................................. 8 

Major Ions and Elements........................................................................................ 8 

Trace Elements . .. .. . . .. ... . . . . . . .. . .................. ... . ..................... .. ... .. ... . . . . . .. . . .. ... . . ... . .. ... . . . . 12 

Dissolved Uranium and Radon Abundances.......................................................... 12 

Discussion....................................................................................................................... 13 

Comparison of Ground-water Chemistry to Well Type or Depth.......................... 13 

Comparison of Ground-water Chemistry of Saprolite and Bedrock...................... 13 

Statistical Comparison of Water Chemistries......................................................... 14 

Major Ions and Elements................................................................................ 14 

Trace Elements . . . . . ..... ... .. . . . ...... ... .. . ..... .. . . . . . . . . . . .... ... .... ... . . . . . .. ... ... . . . . . . .. .......... .. . 15 

Dissolved Uranium and Radon....................................................................... 16 

Processes Affecting Uranium Concentrations in Ground Water............................ 16 

Whole Rock Uranium Abundance and Distribution....................................... 16 

Water Chemistry............................................................................................. 18 

Processes Affecting Radon Concentrations in Ground Water................................ 18 

Secular Equilibrium........................................................................................ 18 

Transfer of Radon from Aquifer Rocks to Ground Water.............................. 19 

Conclusions . . . . . . .. . . ............... ... .. . .. . . . . . ... ... . .. .. . . .. . . . . .. . . . . . . . .... ... ............. ... . .. . . . . . . . . . . . ....... .. .... 19 

Controls on Uranium and Radon Dissolved in Ground Water............................... 19 

Rock Chemistry and Mineralogy.................................................................... 19 

Water Chemistry............................................................................................. 19 

Fractures and Surface Area............................................................................. 21 

Summary ......................................................................................................................... 21 

Acknowledgments.......................................................................................................... 22 

References Cited............................................................................................................. 22 

FIGURES 

1. Generalized geologic map of the Hylas, Virginia, study area, showing locations of 52 ground-water samples........ 3 

2. Trilinear (Piper) diagram for ground-water samples from Petersburg Granite, shear zone mylonite, 

and metamorphic rocks (including amphibolites within the Maidens Gneiss)........................................................... 11 

3. Cumulative frequency plot of 222Rn concentrations in ground water......................................................................... 12 

4. Total dissolved uranium (measured) versus concentration of LCO/·- (calculated by PHREEQE) in ground water... 13 

5. Radioactivities (in pCi/L) of dissolved U versus dissolved 222Rn in ground water.................................................... 13 

6. Average dissolved U versus average whole rock eU (equivalent uranium)................................................................ 17 

7. Average dissolved 222Rn versus average whole rock eU (equivalent uranium).......................................................... 18 

III 
IV CONTENTS 

TABLES 

1. Results of chemical analyses for ground-water samples from the Hylas, Virginia, study area................................... 5 

2. Analytical results for radionuclides and trace elements in ground water from the Hylas, Virginia, study area.......... 8 

3. Statistical comparison of pH, HC03, TDS, DO, and dissolved U and 222Rn (log-transformed) in 

ground-water samples from granitic, mylonitic, and metamorphic rocks in the Hylas area, Virginia........................ 17 

4. Results of saturation index for selected common uranium minerals .......... ................ ............. ............ ...... .............. .... 20 
Dissolved Radon and Uranium, and Ground-Water 

Geochemistry in an Area near Hylas, Virginia 

By Mark R. Stanton, 1 Richard B. Wanty, 1 Errol P. Lawrence,2 and Paul H. Briggs3 

ABSTRACT 

Radon gas (222Rn) dissolved in domestic well water is 

a potential source of indoor radon. Recent evidence suggests 

that ground water in contact with rocks deformed by shear 

may contain higher concentrations of 222Rn than ground 

water from adjacent unsheared rocks. Fifty-two groundwater samples from crystalline-rock aquifers in and near the 

Hylas shear zone of central Virginia were analyzed to investigate the relationship between water chemistry, dissolved 

222Rn and uranium (U), and aquifer type. Forty-four samples have concentrations of dissolved 222Rn that exceed the 

recently proposed United States Environmental Protection 

Agency (EPA) maximum contaminant level (MCL) of 300 

pCi/L (picocuries per liter). Eighteen ground-water samples 

from mylonite of the Hylas shear zone range from 360 to 

32,000 pCi/L 222Rn (average=5,800 pCi/L). Twelve 

ground-water samples from adjacent granitic intrusive rocks 

range from 400 to 81,000 pCi/L 222Rn (average=14,900 pCi/ 

L). Dissolved 222Rn values are significantly lower in the 22 

ground-water samples from metamorphic rocks located west 

of the shear zone and range from 80 to 2,300 pCi/L 222Rn 

(average=550 pCi/L). In all samples, dissolved 222Rn is 

unsupported by dissolved U, suggesting that excess 222Rn is 

provided by emanation from aquifer rocks. 

Mineral-solution equilibria calculations using the 

measured chemistry of the waters indicate that all waters are 

greatly undersaturated with respect to some common uranium 

minerals. Only 3 of the 49 water samples analyzed for U have 

concentrations greater than 1 part per billion (ppb). 

Adsorption of uranium onto mineral surfaces is probably the 

key process that limits dissolved U concentrations to such low 

levels. Ground waters from mylonite have higher average pH, 

total carbonate (L.C03

2-), and dissolved U concentrations, 

1U.S. Geological Survey, Mail Stop 916, Denver Federal Center, Denver, CO 80225. 

2Geraghty and Miller, Inc., Denver, CO 80202. 

3U.S. Geological Survey, Mail Stop 973, Denver Federal Center, Denver, CO 80225. 

suggesting the formation of uranyl-carbonate complexes 

(UQ22+(C03)0 2-2n) as a means for solubilizing or mobilizing 

U from these rocks. Uranyl ion (U02

2+) or uranyl-carbonate 

complexes dissolved in ground water may be transported via 

fractures and adsorbed onto ferric oxides that coat grains and 

fracture surfaces, where U eventually decays to produce 

aqueous 222Rn. Lower average pH, L.C03

2-, and dissolved U 

concentrations in ground waters from granitic and 

metamorphic rocks suggest that U-C03 complexing occurs to 

a lesser extent in these aquifers and that adsorption and 

retention of U on mineral surfaces of these rocks is more 

effective than on mineral surfaces of the mylonite. Lower 

dissolved U may also be the result of less abundant labile U 

in primary minerals of the granitic and metamorphic rocks. 

The high concentrations of 222Rn in ground waters from 

granite and mylonite are due to greater abundances of 

uranium and radium (Ra) at grain surfaces in contact with 

ground water. According to this model, the mobility and 

enrichment of 222Rn in these ground waters is largely a 

function of the location of U and Ra near the mineral/water 

interface in the aquifer rocks. 

INTRODUCTION 

Ground water used for domestic supply may contribute 

radon gas e22Rn) to indoor air (Hess and others, 1990; 

Lawrence and others, 1991; Nazaroff and others; 1988). 

Radon-rich ground water brought into enclosed living areas 

can release dissolved 222Rn into indoor air when the water is 

used for household purposes. Degassing, combined with 

other processes such as soil gas leakage into basements, 

could lead to an increase in the airborne 222Rn concentration 

in homes and buildings (Crawford-Brown, 1990). 

The original accumulation of 222Rn in domestic well 

water supplies and the subsequent contribution of 222Rn to 

indoor air in homes through degassing depends on the distribution, mobility, and contrasting chemical behavior of 

222Rn, its immediate parent radium (226Ra), and its ultimate 

parent uranium e38U) (Brutsaert and others, 1981; Nazaroff 

and Nero, 1988). Because U can exist in several oxidation 
2 RADON AND URANIUM IN GROUND WATER: HYLAS, VIRGINIA 

states (usually reduced U(IV) or oxidized U(VI)) and form 

complexes with different aqueous ions, U solubility is 

strongly influenced by changes in solution chemistry, Eh, 

and pH (Langmuir, 1978). Aqueous sulfate and carbonate 

complexes of radium (as Ra2+) that form in natural waters 

are usually adsorbed onto mineral surfaces or coprecipitated 

with sulfate minerals, such as barite, or carbonate minerals, 

such as calcite (Ames and others, 1983). As a result, the 

abundance of dissolved Rain natural waters rarely exceeds 

10-12 M (Langmuir and Melchior, 1985). 222Rn possesses a 

noble gas configuration and is chemically unreactive; 222Rn 

mobility is therefore controlled primarily by physical factors, especially its contrasting solubility in water and air. 

Abundances of U, Ra, and Rn in ground water may depend 

on related factors such as U and Ra content of parent rock, 

accessibility of ground water to U- and Ra-bearing minerals, 

solubility of U and Ra in local ground water, and soil moisture regime (LeGrand, 1987). 

The present study compares radionuclide concentrations (U and 222Rn) and geochemistry of ground waters 

obtained from sheared mylonitic rocks, unsheared granitic 

and metamorphic rocks, and weathered saprolite overlying 

these rocks, to examine the effect of rock composition and 

texture on dissolved 222Rn concentrations. Specific hydrologic properties of aquifer materials (for example, hydraulic 

conductivity and porosity) that might affect radionuclide 

abundances were not examined in this study. Increased levels of aqueous 222Rn should be facilitated by enrichment of 

U and Ra at the mineral-water interface. Such enrichment is 

produced by weathering, alteration, and shear processes 

(brittle and/or ductile) that can redistribute U and Ra and perhaps increase permeability and surface area of host rocks. 

Differences in ground-water chemistry and radionuclide (U 

and 222Rn) content in the study area do not correlate with 

well depth or well type, and water chemistry is controlled 

primarily by the interaction of ground water with the rock or 

saprolite. The results lend support to the hypothesis that 

222Rn emanation is enhanced in high-U rocks that have 

experienced extensive oxidative weathering and shearing. 

GEOLOGY 

The study area is located in central Virginia approximately 10 km northwest of the Richmond metropolitan area 

in Goochland, Hanover, and Henrico Counties (fig. 1). This 

region is part of the Piedmont Province of the Appalachian 

orogenic belt. Surficial aquifers in the study area include 

deeply weathered saprolite zones above fractured bedrock, 

and Quaternary sediments along stream drainages and other 

low-lying areas (Gates and Gundersen, 1992). Crystalline 

bedrock units include Precambrian metamorphic rocks and 

Paleozoic granites, pegmatites, and mylonites. Water is 

obtained from both the weathered (saprolitic) and unweathered (but apparently fracture permeable) crystalline rocks, 

although the water-bearing horizons vary with depth and 

geographic location. The most transmissive horizons are usually in the basal saprolite, an iron- and clay-rich assemblage 

produced by extensive chemical weathering of underlying 

crystalline bedrock. Atlantic Coastal Plain sediments 

(located east of the area of figure 1} and Triassic sedimentary 

rocks were not investigated. Geologic contacts are simplified 

on the geologic-sample locality map to accentuate the contacts of the granitic and metamorphic rocks with the mylonite 

(shear) zone. A more detailed description of the local geology 

and mineralogy is given in Gates and Gundersen (1992). 

Twenty-two water samples were obtained from Middle 

Proterozoic metamorphic rocks of the Eastern gneiss complex that are present west of the Hylas shear zone (fig. 1). 

The Maidens Gneiss, which constitutes most of the mapped 

gneiss complex in the study area, is composed of several 

mineralogically distinct units presumed to have been derived 

from igneous and volcanic precursors (Goodwin, 1970); 

some units are interpreted as metamorphosed sediments (for 

example, metapelite). One well water sample was obtained 

from the Sabot Amphibolite in the western portion of the 

study area (fig. 1); this amphibolite represents metamorphosed lava flows and pyroclastic debris and is composed of 

hornblende, plagioclase, quartz, K-feldspar, pyroxene, 

sphene, apatite, and secondary calcite (Goodwin, 1970). 

Three additional water samples were taken from wells in an 

unnamed amphibolite in the Maidens Gneiss. The remaining 

18 ground-water samples from metamorphic rocks were 

drawn from undifferentiated units of the Eastern gneiss complex. These undifferentiated units (not mapped separately in 

figure 1) include metapelite, hornblende-biotite gneiss, garnet-biotite gneiss, and granite gneiss (Gates and Gundersen, 

1992). For purposes of this report, the amphibolites plus 

other metamorphic rocks are generally treated as a single 

rock type; in a few instances, the amphibolites are discussed 

separately from the other metamorphic units. 

Eleven ground-water samples were taken from wells in 

the Petersburg Granite of Mississippian age that is present 

east of the Hylas shear zone and composed, on average, of 38 

percent orthoclase, 35 percent plagioclase, 25 percent quartz, 

and 2 percent mafic minerals (Ellison and Masiello, 1979). 

Several small pegmatites (0.5-300 m wide) are present near 

the contact between the granite and mylonite; only one well 

within pegmatite was sampled in this study. On the basis of 

similar mineralogical composition and probable genetic relationships, the sample from the pegmatite (88V A-7) is 

grouped with samples from the granitic rocks. 

The Hylas mylonite is a cataclastic unit composed 

primarily of quartz, potassium and plagioclase feldspars, and 

muscovite (sericite); 18 ground-water samples were collected 

from wells located within this lithologic unit. Mylonite and 

ultramylonite have been identified in the shear zone, but both 

are referred to here as mylonite since the primary difference 

is one of grain size rather than mineralogical composition. 

Shearing generally does not result in the growth of new or 
GEOLOGY 

3]037'30" 

.. 

Richmond 

VIRGINIA 

Location of Study Area 

Hylas zone 

mylonite 

Pegmatite 

Mississippian 

Petersburg 

Granite 

Middle Proterozoic 

~ Eastern gneiss 

~ complex. Includes 

Maidens Gneiss 

0 1 KILOMETER 

L.....J 

3 

Figure 1. Generalized geologic map of the study area showing locations of ground-water samples. The geologic map base is from Gates 

and Gundersen ( 1992). Geology north of approximately 37°4 7 '00" is inferred from mapped units in the remainder of the study area. Sample numbers correspond to those in tables 1 and 2. Filled diamonds represent samples with prefix "88VA," collected in June 1988; open 

diamonds represent samples with prefix "90V A," collected in May 1990. 
4 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

different minerals, rather only a reduction in grain size of 

existing minerals (Jackson, 1970). The mylonites were 

formed during several periods of brittle, brittle-ductile, and 

ductile shearing and faulting of adjacent rocks; the last 

episode of deformation in the Hylas zone was of the brittle 

type and produced cataclasite and gouge (Gates and 

Gundersen, 1992). The deformations could have produced a 

greater mineral surface area in the mylonites relative to 

adjacent rocks. Petrographic evidence indicates that most 

mylonite within the Hylas zone was derived from Petersburg 

Granite, pelitic units of the Maidens Gneiss (Gates and 

Gundersen, 1992), and volcanic rocks (Goodwin, 1970). 

Shear zone boundaries are characterized by heterogeneous 

rock assemblages and irregular contacts, and samples from 

these areas may encompass multiple lithologies. 

Quaternary alluvial and fluvial deposits are largely 

confined to the margins of streams and rivers in the region. 

Saprolite ranges up to approximately 30 meters thick and is 

usually thickest in highly weathered, topographically low 

ground between drainages. To show bedrock geology more 

clearly, surficial deposits are not illustrated in figure 1. 

FIELD AND LABORATORY METHODS 

DESCRIPTION OF WELL TYPES 

Water samples were obtained from both augered (or 

bored) and drilled wells. Available drilling records for the 

study area indicated augered wells generally penetrated the 

full thickness of the saprolite but did not extend into unweathered bedrock. Lithologic logs placed the depth of the saprolite (weathered) to bedrock (unweathered) transition at 

approximately 25 to 30 meters. Augered wells were consistently shallower than this maximum depth to saprolite; that 

is, all wells above the 30-meter depth are the augered type. 

Augered wells were lined with circular, !-meter-diameter 

terra cotta tiles for their entire depth with pump placement 

commonly at the bottom of the well. 

Drilled wells were as deep as 120 meters and therefore 

provided water from unweathered crystalline rocks. Drilling 

records were unavailable for the wells that were sampled, but 

records from other wells in the study area identified as many 

as 3 water-producing zones in crystalline rocks; the number 

of water-bearing zones intersected by a well depended on 

depth. Screening and the length of open intervals for drilled 

wells was variable. Wells were usually cased to approximately 10 meters, and generally, the water-bearing fracture 

zones were screened but the non-producing sections through 

bedrock were unscreened. Materials used for casing and 

screening were not identified on all records and grouting was 

not used in every well. Location of the pump in the drilled 

wells was not always known with certainty but was usually 

deeper than 30 meters (that is, below the saprolite zone). The 

nine wells ( 4 augered, 5 drilled) whose depths were 

unknown were not used in the evaluation of changes in water 

chemistry with depth. 

SAMPLING AND ANALYTICAL METHODS 

Fifty-one well-water samples and one spring-water 

sample were collected from an area of approximately 230 

km2 (fig. 1). Sampling was conducted during the first two 

weeks of June 1988, and the last two weeks of May 1990; 

both periods were characterized by stable, dry weather. 

Water was allowed to flow for sufficient time to empty 

stored water to obtain as fresh a sample as possible and to 

permit stabilization of temperature (T°C) and conductivity 

(SpC), which were monitored before sampling. Samples 

were withdrawn into a gastight syringe from a hose connected to a spigot as close to the wellhead as possible, but 

before the water entered any treatment system; turbulence 

and possible 222Rn loss by degassing were minimized by 

using a slow flow rate through the hose during the entire 

sampling operation. 

Dissolved oxygen (DO), alkalinity (as bicarbonate, 

HC03), and pH were determined at the time of sampling in 

addition to T°C and SpC; these results appear in table 1 (the 

electronic charges carried by dissolved ions are not shown in 

this report unless needed for clarity). Three aliquots were filtered through a 0.45 f..liil membrane filter for subsequent 

anion, cation, and uranium analyses. Microbes that might 

utilize and thus alter the concentrations of certain dissolved 

constituents, such as nitrate (N03), are removed by filtration; 

in addition, concentrated reagent-grade nitric acid (HN03) 

was added to the cation and uranium samples to prevent 

adsorption and precipitation during transportation and storage. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES; Lichte and others, 1987) was used to 

determine concentrations of major and trace cations to 

within ±10%. Major anions-sulfate, nitrate, phosphate, 

chloride, and fluoride-were determined by ion chromatography (Fishman and Pyen, 1979) to within ±10%. TDS (total 

dissolved solids) was calculated for each sample as the sum 

of cations and anions (Hem, 1989). Individual sample cation 

+anion (C+A) balances agreed to within ±10%, but ten samples were outside of these limits; these samples generally 

had low total cations and anions, and low pH and HC03; lack 

of buffering capacity may have resulted in chemical changes 

that produced the larger analytical error. The mean for all 

C+A balances was -4.9%. Uranium was determined by 

laser-induced fluorescence with standard addition; replicate 

analyses agreed to within ±15%. The method determines 

total u only; u isotopes and oxidation states (U4+ and u6+) 

are not differentiated. 222Rn was determined by liquid scintillation within 48 hours of sampling on duplicate samples, 

and a correction factor was applied for the amount of 222Rn 

that decayed between the time of sampling and counting. 
FIELD AND LABORATORY METHODS 5 

Table 1. Results of chemical analyses for ground-water samples from the Hylas, Virginia, study area. 

[Units are as follows: pH (dimensionless), Temperature (

0

C), Specific Conductivity (SpC,!J.S/cm), all others, (ppm). Phosphate was below detection in all samples (<0.1 ppm). 

ND, not detected. Well depths in meters; UNK, unknown. TDS was calculated as the sum of dissolved cations and anions (in ppm)] 

SAMPLES OF GROUND WATER FROM GRANITES 

Sample No. pH [1) Temp. 

88VA-7 5.3 1 .3 1 5 

88VA-23 5.6 2.8 1 6 

90VA-5 7.3 8.4 1 5 

90VA-7 4.4 7.4 1 7 

90VA-8 6.4 1 .5 1 5 

90VA-9 5.6 2.9 1 4 

90VA-10 4.8 6.4 1 5 

90VA-11 5.6 9.3 1 7 

90VA-12 5.7 6.0 1 7 

90VA-13 6.0 8.4 1 5 

90VA-14 5.3 3.3 1 5 

90VA-15 6.6 0.9 1 7 

Mean 5.7 4.9 15.7 

Std. Dev. 0.8 3.1 1 . 1 

Sample No. K HC03 S04 

88VA-7 1 46. 2.7 

88VA-23 1 26 6.0 

90VA-5 15. 95 2.9 

90VA-7 1. 7 25 NO 

90VA-8 3.2 130 12. 

90VA-9 1 .5 62 2.4 

90VA-10 1 .3 27 0.3 

90VA-11 2.2 21 NO 

90VA-12 2.4 59 0.4 

90VA-13 NO 75 1 .5 

90VA-14 1 .4 48 1 .8 

90VA-15 3.8 130 4.7 

Mean 3.1 62. 3.5 

Std. Dev. 4.0 39. 3.4 

The 222Rn value in table 2 is the average of these two analyses. In nearly every case, the duplicates agreed to within 5%. 

STATISTICAL PROCEDURES 

Ground waters from the three rock types were compared 

using average values (arithmetic means) in a single-factor 

analysis of variance (ANOV A) when values for a geochemical parameter were available, or above the lower limit of 

detection (LLD), in at least 90 percent of the samples. The 

ground-water parameters subjected to statistical treatment 

include pH, DO, SpC, TDS, Hardness, 222Rn, U, Ca, Mg, Na, 

K, HC03, S04, Cl, Mn, Si (reported as Si02), Ti, Sr, Ba, and 

~ ca Mg Na TDS 

74 11 . 1 .5 9.3 105 

79 7.1 1 .6 1 9. 1 1 9 

50 1 7. 0.4 4.8 143 

54 1 .5 0.4 4.8 51 

53 1 .4 1 .9 45. 226 

51 9.3 0.8 7.3 1 01 

48 6.2 0.19 2.1 47 

50 3.3 1 .0 7.9 72 

52 13. 0.4 4.9 94 

51 1 2. 1 .9 7.2 1 21 

47 8.9 1 .0 5.3 85 

49 23. 4.0 9.8 198 

54.8 9.4 1 .3 10.6 113.5 

10.4 6.2 1 . 1 11 .5 54.1 

Cl NOJ F Si Depth 

11 . 3.0 0.2 18. 1 1 

12. 22. NO 25. 58 

2.3 NO NO 6.1 1 1 

2.1 NO NO 15. 63 

9.3 NO 2.4 18. 91 

13. 0.6 NO 4.7 1 0 

3.4 0.2 NO 6.0 9 

3.6 18. NO 15. UNK 

2.3 0.2 NO 12. 1 0 

2 NO NO 21. 9 1 

4.4 NO NO 1 4 9 

2.4 NO 0.2 21. 93 

5.6 7.3 0.70 14.7 

4.3 9.9 1 . 1 6.4 

Zn. e22Rn was log10-transformed to more closely approximate a normal distribution). Appropriate values greater than 

zero and below the LLD (O<X<LLD) were substituted in the 

two cases (U, S04) where slightly less than 90 percent of the 

measurements were above the LLD. Because there were 

insufficient numbers of samples above the LLD for other 

trace elements, no statistical or correlative analyses were performed; therefore, most discussions that follow are concerned with major elements and ions, and the radionuclides 

U and 222Rn. However, some elements or ions are discussed 

in terms of whether or not they were detected in a groundwater sample (N03, Li, Fe). The Scheffe F-test, a conservative estimator of sample variances in 3-group tests, was 

applied to determine if the means were significantly different 
6 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

Table 1. Results of chemical analyses for ground-water samples from the Hylas, Virginia, study area.-Continued 

SAMPLES OF GROUND WATER FROM MYLONITES 

Sample No. pH [l) Temp. 

88VA-1 6.9 8.8 4 

88VA-2 6.6 6.2 1 9 

88VA-4 6.9 2.1 1 5 

88VA-6 6.1 7.6 1 9 

88VA-8 7.2 0.3 1 6 

88VA-9 5.6 1 .5 1 9 

88VA-10 5.7 8.8 1 6 

88VA-12 6.5 0.3 1 7 

88VA-13 6.7 9.0 1 5 

88VA-14 6.5 3.0 1 5 

88VA-16 5.6 5.3 1 5 

88VA-17 6.6 4.8 1 8 

88VA-20 6.0 3.4 1 6 

88VA-21 6.6 0.3 1 8 

88VA-29 6.0 0.4 1 8 

88VA-35 7.0 0.4 1 5 

88VA-36 7.1 2.7 1 9 

90VA-3 6.5 1 .8 1 6 

Mean 6.5 3.7 1 6.1 

Std. Dev. 0.5 3.2 3.4 

Sample No. K HC03 S04 

88VA-1 2 25. 2.7 

88VA-2 1 42. 1 . 1 

88VA-4 2 31. NO 

88VA-6 2 33. 0.1 

88VA-8 1 190 11. 

88VA-9 2 130 5.3 

88VA-10 2 15. 0.2 

88VA-12 2 1 70 2.4 

88VA-13 3 11 0 2.3 

88VA-14 2 150 3.3 

88VA-16 2 29. 0.7 

88VA-17 1 82. 1 1 . 

88VA-20 1 75. 0.7 

88VA-21 3 150 6.0 

88VA-29 2 85. 8.6 

88VA-35 3 170 5.4 

88VA-36 1 130 20. 

90VA-3 6 1 60 7.8 

Mean 2.11 99.3 4. 91 

Std. Dev. 1.1 8 59.6 5.17 

(Scheffe, 1933). In all statistical analyses, a 95 percent confidence level was employed. In addition, the nonparametric 

Kruskal-Wallis test, which is often applied to data sets con-

~ ca Mg Na IDS 

68 6.0 2.3 8.1 87 

67 5.9 2.8 11 . 99 

55 6.3 0.8 7.1 78 

38 3.4 0.4 4.1 62 

74 42. 9.9 15. 285 

90 33. 7.2 1 0. 225 

24 2.3 0.5 1. 9 34 

84 26. 7.2 20 251 

82 26. 2.1 8.4 175 

82 30. 5.6 1 5. 235 

81 8.6 2.3 1 0. 102 

84 18. 3.2 15. 155 

82 12. 2.7 1 8 148 

8 1 47. 3.8 15. 264 

87 16. 3.6 1 9. 175 

56 37. 6.8 1 5 264 

72 33. 5.8 24. 256 

45 23. 4.9 23. 255 

69.6 20.9 4.00 13.3 175 

18.7 14.1 2.64 6.17 82.2 

Cl NOJ F Si Depth 

6.4 1 9. NO 16. UNK 

7.7 5.8 0.5 20. 38 

9.9 5.8 NO 15. 1 4 

3.0 4.1 ND 12. 1 1 

7.7 NO 0.2 13. 69 

8.4 1 .5 0.2 23. 11 6 

2.5 2.9 NO 6.7 1 2 

2.6 0.4 0.2 24 8 1 

2.2 0.8 NO 1 9 1 2 

6.4 NO 0.4 23. 37 

1 0. 22. NO 1 8. 9 

3.9 NO 0.4 19. 88 

11 . NO 0.1 28. 1 2 

13. 1 .6 0.1 21. 9 

13. 0.5 0.5 27. 70 

2.4 NO 0.2 20. UNK 

14.0 13. 0.2 11 . UNK 

9.3 NO 0.3 21. 6 1 

7.36 4.58 0.18 18.7 

3.91 6.93 0.1 8 5.69 

taining mainly qualified (below the LLD) values (Till, 1974), 

corroborated the results and conclusions obtained from the 

parametric Scheffe method. 
FIELD AND LABORATORY METHODS 7 

Table 1. Results of chemical analyses for ground-water samples from the Hylas, Virginia, study area.--Continued 

SAMPLES OF GROUND WATER FROM METAMORPHIC ROCKS(*= AMPHIBOLITE) 

Sample No. pH m Temp. ~ ca Mg Na TDS 

88VA-3 7.1 7.4 1 8 56 6.4 3.4 5.3 89 

88VA-5 6.7 0.5 1 7 120 19. 3.7 8.9 1 51 

88VA-11 6.5 1 .9 1 6 83 20. 6.8 1 0. 174 

88VA-15 6.4 6.7 1 6 54 6.5 2.1 7.5 102 

88VA-18 5.5 5.6 1 7 62 7.7 1 .2 7.6 80 

88VA-19 5.3 2.9 1 7 74 16. 9.7 1 8. 158 

88VA-22 5.6 7.7 1 5 63 16. 0.9 1 .3 82 

88VA-24 5.9 6.3 1 9 92 7.1 3.9 8.2 11 5 

88VA-25 6.4 0.2 1 6 82 8.3 4.6 1 9. 1 61 

88VA-26 4.8 7.0 1 7 38 4.7 1 .8 2.8 53 

88VA-27* 5.5 8.6 1 8 32 2.3 1 .3 2.8 38 

88VA-28 5.7 9.0 1 6 85 1 4 4.7 5.4 120 

88VA-30 5.8 9.4 1 8 63 7.9 3.0 4.9 94 

88VA-31* 5.6 8.0 1 6 63 6.4 1. 7 3.4 78 

88VA-32 4.6 11 .4 1 6 27 1 .6 0.3 1 .2 1 6 

88VA-33 5.8 4.9 1 4 35 4.9 0.7 2.7 45 

88VA-34 5.6 8.2 1 8 52 7.7 1 .8 3.5 66 

90VA-1 5.9 9.8 1 7 44 8.6 0.9 1. 7 58 

90VA-2* 6.7 4.3 1 6 43 15. 5.3 1 0. 166 

90VA-4 3.8 9.2 1 6 48 1 .6 2.6 5.0 52 

90VA-6* 7.2 1 .9 1 5 51 25 7.4 25. 246 

90VA-16 6.6 8.2 1 6 54 31. 0.8 2.0 158 

Mean 5.9 6.3 16.6 60.1 11 . 3.1 7.1 11 0. 7 

Std. Dev. 0.8 3.2 1 .2 22.3 7.7 2.5 6.3 62.9 

Sample No. K HC0.3 S04 Cl NOJ F Si Depth 

88VA-3 1 48. NO 3.9 0.9 0.2 19. 100 

88VA-5 2 90. 7.4 1 .5 NO 0.1 1 9. 9 1 

88VA-11 1 1 1 0 2.3 5.3 NO 0.2 20. 11 0 

88VA-15 2 51. 0.6 2.6 4.6 NO 24. UNK 

88VA-18 1 31. 2.0 7.3 3.8 NO 18. 9 

88VA-19 1 31. 3.8 58. 3.1 NO 18. 8 

88VA-22 2 54. 1 . 1 1 . 1 0.6 NO 5.6 9 

88VA-24 2 57. 12. 1 .6 NO 0.4 23. UNK 

88VA-25 4 98. 3.6 1 .6 0.1 0.2 22. 122 

88VA-26 1 29. 0.2 1 .6 1. 9 NO 10. 1 1 

88VA-27* 2 15. NO 3.8 3.3 0.1 6.9 43 

88VA-28 1 75. 0.2 3.2 0.2 NO 17. 20 

88VA-30 46. 0.7 1 .8 13.9 NO 15. 1 1 1 

88VA-31* 41. 0.3 6.0 12.9 NO 5 1 2 

88VA-32 7.2 0.4 1 .4 NO NO 2.6 UNK 

88VA-33 1 25. 0.2 1 .5 NO NO 9.2 UNK 

88VA-34 38. 0.5 1 .6 0.7 NO 11 . UNK 

90VA-1 1 . 1 32 NO 5.7 4.2 NO 3.8 9 

90VA-2* 3.4 1 1 0 6.4 2.3 NO NO 1 4. 6 1 

90VA-4 2 4.6 1.2 5.4 30 NO 4.6 5 

90VA-6* 3.7 120 30.4 21. NO NO 14. 30 

90VA-16 3.3 1 1 0 1 .3 3.4 NO NO 6.4 1 0 

Mean 1. 75 55.5 3.57 6.46 4.22 0.07 13.0 

Std. Dev. 1 .00 35.7 6.88 12.3 7.45 0.12 6.80 
8 RADON AND URANIUM IN GROUND WATER: HYLAS, VIRGINIA 

Table 2. Analytical results for radionuclides and trace elements in ground water from the Hylas, Virginia, study area. 

[Concentration units are as follows: Rn (pCi/L); U. B. Ba, Cr, Cu. Li, Mn, Sr, Ti, Zn (ppb); AI, Fe (ppm). NA, not analyzed; NO, not detected. Other elements sought but below the 

limit of detection (in ppb, shown in parentheses after element name) were Ag (2); Be (1), except 88VA-19, 2 ppb; Bi (10); Cd (1), except 90VA-9, 1 ppb; Co (3), except 88VA-4, 3 

ppb, and 88VA-19, 4 ppb; Ga (5); Mo (10); Ni (5). except 88VA-19, 45 ppb, and 90VA-4, 5 ppb; Pb (10) except 88VA-26, 10 ppb; Sn (6); V (6); and Zr (1), except 88VA-16, 2 ppb] 

SAMPLES OF GROUND WATER FROM GRANITES 

Sample No. Rn u AI 

88VA-7 8900 0.3 <0.1 

88VA-23 81000 4.4 <0.1 

90VA-5 740 ~ 0.23 

90VA-7 16000 <0.05 <0.1 

90VA-8 5900 <0.05 <0.1 

90VA-9 1200 ~ 0.11 

90VA-10 1600 <0.05 0.11 

90VA-11 28000 0.06 <0.1 

90VA-12 1600 <0.05 <0.1 

90VA-13 30000 <0.05 <0.1 

90VA-14 390 <0.05 <0.1 

90VA-15 2800 <0.05 <0.1 

Mean 14900 0.5 0.1 5 

Std. Dev. 23400 1 .4 0.07 

Sample No. Fe Li Mn 

88VA-7 <0.05 1 2 21 

88VA-23 <0.05 1 6 1 3 

90VA-5 <0.05 1 4 1. 7 

90VA-7 <0.05 <4 3.1 

90VA-8 1.05 51 40. 

90VA-9 3.3 <4 120 

90VA-10 0.08 <4 4.5 

90VA-11 0.08 <4 2.4 

90VA-12 0.08 <4 8.7 

90VA-13 <0.05 1 6 1 4 

90VA-14 0.08 5 1 2. 

90VA-15 0.32 46 140 

Mean 0.71 23. 32. 

Std. Dev. 1. 1 9 18. 48. 

RESULTS 

GROUND-WATER QUALITY 

Ground water in the Hylas study area is generally of 

good quality for domestic consumption. The U.S. Environmental Protection Agency (EPA) standard for drinking water 

is exceeded only by dissolved Fe (8 samples) and Mn (15 

samples); for other dissolved components for which standards exist or are proposed, the concentrations are below the 

recommended value (U.S. Environmental Protection 

Agency, 1976). e22Rn, however, exceeds the proposed standard in nearly all samples; this is discussed below). The maximum total dissolved solids (TDS) is 285 ppm (parts per 

B Ba Cr Cu 

<10 1 8 <1 310 

<10 37 <1 120 

<10 1 5 <1 1 7 

<10 62 <1 <10 

<10 3 <1 <10 

<10 48 <1 <10 

<10 44 <1 1 6 

<10 82 <1 1 8 

<10 40 <1 25 

<10 1 2 <1 <10 

<10 36 <1 1 3 

<10 1 9 <1 <10 

35. 74. 

23. 11 0 

Si Sr Ti Zn 

1 8. 49. <1 9 

25. 55. 4 7 

6.1 160 6.3 9 

15. 35. 6.1 7 

18. 1 1 4.9 1000 

4.7 69 4.9 74 

6.0 8.3 6.1 1 6 

15. 59. 4.8 1 1 

12. 57. 6.2 6 

21. 40. 4.9 1 1 

1 4 30. 4.8 9 

21. 120 4.8 <3 

15. 58. 5.3 11 0 

6.4 43. 0.77 310 

million) and the maximum total hardness (Ca + Mg) is 50 

ppm (table 1). The pH range in ground water from mylonites 

is 5.6-7 .2, pH in the granite-hosted ground water ranges from 

4.4 to 7 .3, and pH in ground water from metamorphic rocks 

ranges from 3.8 to 7 .2. The pH range for drinking water recommended by EPA is 6.5-8.5. Corrosion of pipes and staining of porcelain fixtures may result from low (acidic) pH; 

both were observed in some water delivery systems. 

MAJOR IONS AND ELEMENTS 

The concentrations of major dissolved ions and elements are summarized in table 1. The water samples are 

dominated by Ca-Mg/HC03 types. As seen in the summary 
RESULTS 9 

Table 2. Analytical results for radionuclides and trace elements in ground water from the Hylas, Virginia, study area.-Continued 

SAMPLES OF GROUND WATER FROM MYLONITES 

Sample No. Rn u AI 

88VA-1 12000 0.24 <0.1 

88VA-2 32000 0.58 <0.1 

88VA-4 3700 0.34 <0.1 

88VA-6 4700 0.2 <0.1 

88VA-8 2400 2.9 <0.1 

88VA-9 600 0.47 <0.1 

88VA-1 0 460 0.14 <0.1 

88VA-12 2400 0.21 <0.1 

88VA-13 850 0.42 <0.1 

88VA-14 3400 0.07 <0.1 

88VA-16 113 00 <0.05 <0.1 

88VA-17 1900 0.34 <0.1 

88VA-20 360 0.13 <0.1 

88VA-21 1600 0.28 <0.1 

88VA-29 20000 0.98 <0.1 

88VA-35 2500 2.29 <0.1 

88VA-36 750 0.63 <0.1 

90VA-3 3900 0.05 <0.1 

Mean 5800 0.6 

·std. Dev. 8300 0.8 

Sample No. Fe Li Mn 

88VA-1 0.59 6 120 

88VA-2 <0.05 1 8 5 

88VA-4 0.08 <4 67 

88VA-6 <0.05 <4 5 

88VA-8 0.09 1 6 120 

88VA-9 <0.05 56 160 

88VA-1 0 <0.05 <4 24 

88VA-12 1 .38 39 140 

88VA-13 <0.05 1 2 1 

88VA-14 2.34 60 370 

88VA-16 <0.05 7 3 

88VA-17 <0.05 7 4 

88VA-20 <0.05 1 0 2 

88VA-21 <0.05 28 5 

88VA-29 0.06 62 55 

88VA-35 0.2 37 100 

88VA-36 <0.05 6 43 

90VA-3 0.1 46 230 

Mean 0.61 27. 80. 

Std. Dev. 0.83 21. 99. 

Piper diagram (fig. 2), the fields encompassing ground-water 

compositions of each rock type overlap significantly. The 

lobes that extend from the main group of water compositions 

B Ba Cr OJ 

<10 50 <1 <10 

<10 1 0 <1 50 

<10 1 1 0 <1 1 0 

<10 47 <1 30 

<10 7 <1 <10 

<10 4 <1 <10 

<10 36 2 40 

<10 28 <1 <10 

<10 72 1 20 

<10 1 3 <1 <10 

<10 93 <1 <10 

<10 3 <1 <10 

<10 53 <1 <10 

<10 75 <1 <10 

<10 6 <1 50 

1 0 77 <1 <10 

1 0 1 4 <1 <10 

<10 7 <1 <10 

39. 

35. 

Si Sr Ti Zn 

16. 83. <1 20 

20. 66 4 1 8 

15. 83. 3 9 1 

12. 25. <1 1 3 

13. 95. 4 1 4 

23. 94. <1 1 9 

6.7 12. 6 1 1 

24 1 20 7 9 

1 9 1 70 7 2 1 

23. 120 6 32 

1 8. 140 6 1 5 

1 9. 39. 7 25 

28. 72. 4 5 

21. 240 7 7 

27. 54 5 6 

20. 300 7 230 

1 1 . 90. 6 2200 

21. 80. 3.6 220 

19. 105 5.5 1 70 

5.7 73. 1 .4 520 

on the Piper plot are due to six outlying samples-two from 

metamorphic rock-hosted ground water and four from granite-hosted ground water. The sample with the second-highest 
10 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

Table 2. Analytical results for radionuclides and trace elements in ground water from the Hylas, Virginia, study area.-Continued 

SAMPLES OF GROUND WATER FROM METAMORPHIC ROCKS(*= AMPHIBOLITE) 

Sample No. Rn u AI 8 Ba Cr Cu 

88VA-3 1400 0.2 <0.1 <10 7 2 <10 

88VA-5 1000 0.3 <0.1 <10 7 <1 <10 

88VA-11 2300 0.3 <0.1 <10 3 <1 <10 

88VA-15 800 0.1 <0.1 <10 35 1 <10 

88VA-18 1 70 0.1 <0.1 <10 5 1 100 

88VA-19 320 0.2 <0.1 <10 130 1 2 1 0 

88VA-22 200 0.1 <0.1 <10 46 <10 

88VA-24 320 0.3 <0.1 <10 36 <1 <10 

88VA-25 510 <0.05 <0.1 30 8 <1 <10 

88VA-26 270 0.2 <0.1 <10 30 2 140 

88VA-27* 450 0.1 <0.1 <10 30 <1 50 

88VA-28 230 0.1 <0.1 <10 26 2 70 

88VA-30 1300 0.1 <0.1 <10 9 <10 

88VA-31 * 200 0.1 <0.1 <10 46 <1 20 

88VA-32 190 0.1 <0.1 <10 6 <1 <10 

88VA-33 470 <0.05 <0.1 <10 26 1 1 0 

88VA-34 740 0.1 <0.1 <10 1 8 1 0 

90VA-1 350 <0.05 0.14 <10 59 <1 1 9 

90VA-2* 390 <0.05 <0.1 <10 52 <1 <10 

90VA-4 80 NA. <0.1 <10 160 <1 854 

90VA-6* 300 <0.05 <0.1 1 2 7 <1 <10 

90VA-16 90 0.05 0.16 <10 46 <1 1 8 

Mean 550 0.13 38. 120 

Std. Dev. 530 0.08 39. 250 

Sample No. Fe Li Mn Si Sr Ti Zn 

88VA-3 <0.05 <4 <1 19. 91. 3 7 

88VA-5 <0.05 <4 59 19. 51. 6 3 

88VA-11 <0.05 <4 1 1 20. 71. 4 770 

88VA-15 <0.05 <4 2 24. 43. 6 6 

88VA-18 <0.05 <4 2 18. 44. 6 7 

88VA-19 <0.05 5 31 18. 85. 6 7 

88VA-22 <0.05 <4 7 5.6 33. 6 <3 

88VA-24 '3.0 <4 69 23. 70. 3 6 

88VA-25 0.8 <4 54 22. 47. 4 140 

88VA-26 <0.05 <4 2 1 0. 21. 7 1 2 

88VA-27* <0.05 <4 3 6.9 25. 3 6 1 

88VA-28 <0.05 <4 1 17. 58. 5 <3 

88VA-30 <0.05 <4 2 15. 41 4 1 3 

88VA-31 * <0.05 <4 1 2 5.0 22. <1 100 

88VA-32 <0.05 <4 3 2.6 6.3 3 4 

88VA-33 0.08 <4 6 9.2 30. 3 360 

88VA-34 <0.05 <4 1 11 . 37. 6 6 

90VA-1 <0.05 <4 1 5 3.8 73. 11 . 20 

90VA-2* 0.06 6 57 14. 46. 6.4 <3 

90VA-4 0.16 <4 43 4.6 22. 4.8 44 

90VA-6* 0.12 5 94 14. 79. 3.6 <3 

90VA-16 <0.05 4 9.6 6.4 67. 2 4 

Mean 0.71 23. 13. 48. 4.9 88. 

Std. Dev. 1 .2 28. 6.8 23. 2.0 190 
RESULTS 11 

Ca Cl 

/ ---- o Granitic 

---,,----- o Mylonitic 

~ o Metamorphic 

Figure 2. Trilinear (Piper) diagram for ground-water samples from Petersburg Granite, shear zone mylonite, and metamorphic rocks (including amphibolites within the Maidens Gneiss) of the Hylas study area. Lines show approximate fields of water composition for the three 

rock types. 

chloride content from the granite-hosted waters (88V A-23; 

Cl=12 ppm) is located near a rock quarry that has been active 

for several decades. It is possible that the prolonged effects 

of quarrying have led to an alteration, although not necessarily a deterioration, of water quality in the immediate area. 

Several of the other "outlying" samples, including the one 

near the quarry, have high N03 concentrations, suggesting 

leakage from septic systems or input from fertilizers. 

Ground-water chemistry throughout the study area 

suggests a limited degree of water-rock interaction. Some 

wells may sample more than one lithology, but the similarity 

of water composition from all wells suggests that minerals 

controlling the chemical composition of the waters (quartz, 

feldspar) are present in all rock types. Results of chemical 

modelling using the program PHREEQE (Parkhurst and 

others, 1980) show that the only major rock-forming mineral 

to approach saturation in these waters is quartz. Because most 

aluminum values were below detection, the saturation state 

was not calculated for common aluminosilicates that might 

be expected to form (clays, feldspars). Generally, the major 

mineral classes for which saturation states were calculable 

were carbonates, sulfates, oxides, and oxyhydroxides. 
12 RADON AND URANIUM IN GROUND WATER: HYLAS, VIRGINIA 

Ground water in the study area is dilute (defined as having TDS of less than 500 ppm), indicating that it has not had 

a long history of contact with the rocks. A high recharge rate 

may also be responsible for the low TDS. Because TDS is 

strongly controlled by the calcium and magnesium concentrations (r2 = 0.76 for TDS vs Ca+Mg), this indicates that the 

water has not evolved chemically to any great degree. CaMg/HC03 (fresh) waters are dominant in the earliest stages 

of ground-water evolution but are altered over time to waters 

having much higher TDS values and containing primarily 

Na, K, Cl, and S04 (Davis and DeWiest, 1966). 

TRACE ELEMENTS 

Data for dissolved trace elements are summarized in 

table 2. Abundances of most dissolved trace elements vary 

only slightly with host lithology, and as noted, statistical 

analyses were not performed when qualified values were 

present in more than 10 percent of the samples. Trace elements below detection in every sample include Ag, Bi, Ga, 

Mo, Sn, and V. Comparative statistics were not computed for 

the following nine trace elements because of insufficient 

numbers of samples above detection: Be, Cd, Pb, and Zr 

were above detection in only one sample each (four separate 

samples); Co and Ni were found in only 2 samples; AI and B 

were present in detectable amounts in only 4 samples; Cr 

was detected in no granite-hosted samples and in only 2 

mylonite-hosted samples. 

DISSOLVED URANIUM AND RADON 

ABUNDANCES 

Results of radionuclide analyses are also summarized 

in table 2. Average 222Rn values for ground waters from the 

Petersburg Granite and mylonite of the Hylas shear zone 

are 14,900 and 5,800 pCi/L (picocuries per liter), respectively (table 2; fig. 3). 222Rn ranges from 360 to 32,000 

pCi/L in water samples from mylonite and from 400 to 

81,000 pCi/L in water samples from granite. Thus, all 

ground waters from granitic and mylonitic samples have 

222Rn values above the recently proposed EPA maximum 

contaminant level (MCL) for drinking water of 300 pCi/L 

(U.S. Environmental Protection Agency, 1991). Significantly lower 222Rn values are associated with the Maidens 

or Eastern gneiss complex. The average value for 222Rn in 

ground-water samples from the metamorphic rocks is 550 

pCi/L, with a maximum concentration of 2,300 pCi/L. The 

8 water samples with 222Rn concentrations below the proposed MCL of 300 pCi/L are all from metamorphic rocks. 

The cumulative frequency plot of figure 3 illustrates that 

the range of 222Rn concentrations in water samples from 

mylonitic and granitic units are similar but much higher 

compared to the metamorphic units. The median 222Rn 

value (50th percentile in figure 3) in water samples from 

mylonite is 2,500 pCi/L and 4,400 pCi/L for water samples 

from granite, but in waters from metamorphic units, the 

median 222Rn value is only 330 pCi/L. · 

Aqueous U concentrations from all samples are generally above the lower limit of detection (0.05 ppb) and as high 

as 4 ppb (table 2). Virtually all of the water samples contain 

measurable dissolved oxygen and can therefore be considered to be oxidizing. The dominant form of dissolved U 

under these conditions is U(VI), as the uranyl ion, U022+. 

Uranyl forms a series of strong complexes with carbonate, 

represented by the general formula U02(C03)n2·

2n. As 

shown in figure 4, ground waters from mylonitic rocks generally have higher :EC03 compared to samples from granitic 

and metamorphic rocks. The formation of uranyl-carbonate 

complexes stabilizes u in solution and inhibits uo2 adsorption onto mineral surfaces (Wanty and others, 1991a). 

Average U concentrations are higher in ground water 

from mylonite (0.6 ppb) and granite (0.5 ppb) compared to 

metamorphic rocks (0.1 ppb ), similar to the results for 222Rn. 

However, no correlation exists between dissolved U and dissolved 222Rn activities in the water samples (r2 = 0.024, fig. 

5). A primary drinking water standard for dissolved U of 20 

ppb U (30 pCi/L) has been recently proposed by the EPA 

(U.S. Environmental Protection Agency, 1991); all ground 

waters that were sampled are well below the 20 ppb level. In 

addition to the proposed standards for aqueous 222Rn and U, 

the EPA has proposed an MCL for 226Ra in drinking water 

100,000:::r---------r---------::----, 

. Average dissolved Rn, pCi/L C 

Granitic - 14900 

Mylonitic - 5800 

Metamorphic - 550 [] 

[] [] 0 

0 

=::! 10,000 ~ [] 0 0 

0 

~ [] 0 

c oOO 

a: oE:bo • 

'C [] [f) <a •• ~ 1,000; • 

o . ~oo •• 0 . 0 ••• 

0 Q!. - - - - - - ......... _ ..... ·- - - - - - - - - - - - C • • • • e proposed MCL (300 pCi/L) 

100: •• 

0 Mylonitic l

c Granitic 

10 +---~.---,.~--~.~-~·-M~e-ta_m_o~rp_h~ic 

0 ~ ~ 00 ~ 100 

Percentile 

Figure 3. Cumulative frequency plot of 222Rn concentrations in 

ground-water samples from granitic, mylonitic, and metamorphic 

rocks in the Hylas area. Average and median values (50th percentile) respectively, are 14,900 and 4,400 pCi/L from granitic rocks, 

5,800 and 2,500 pCi/L from mylonitic rocks, and 550 and 330 pCi/ 

L from metamorphic rocks. Dashed horizontal line indicates the 

U.S. Environmental Protection Agency's proposed maximum contaminant level (MCL) of 300 pCi/L as dissolved 222Rn. 
DISCUSSION 13 

'ii 

0 

:!! 

c= 

Ia ;J._ 

10"7 ~-------------------, 

10 "

8 -

10.9 -

• • 

10·10_ D D 

10·11 I 

10·10 10"9 

D 

00 

0 

0 0 0 

0 

D 

~ 0~. 0 

0 

.. ~ .. • Oe 

D 

D 

• • D 

D 

• 

1

1

0"8 I 

10"7 

2- L.C03, Molal 

• 

0 

•o 

cc• • 

D Granitic 

0 Mylonitic 

• Metamorphic 

1

1

0"6 10"5 

Figure 4. Total dissolved uranium (measured) versus concentration ofl:C032- (calculated by PHREEQE) in ground water samples 

from granitic, mylonitic, and metamorphic rocks in the Hylas area. 

of 20 pCi/L (U.S. Environmental Protection Agency, 1991). 

Although 226Ra concentrations were not measured in the 

Hylas water samples, most values reported for 226Ra in 

ground water are on the order of 10-2 to 101 pCi/L (Wanty 

and Gundersen, 1991, and references therein). Below pH 

values of approximately 5.5, aqueous 226Ra concentrations 

may be higher than the upper limit for the range listed above 

(Szabo and Zapecza, 1987; Zapecza and Szabo, 1987; Cecil 

and others, 1987), but as discussed later, it is unlikely that the 

standard for aqueous 226Ra would be exceeded in most samples from the Hylas area. 

DISCUSSION 

COMPARISON OF GROUND-WATER 

CHEMISTRY TO WELL TYPE OR DEPTH 

Samples from wells within both saprolite and crystalline rocks generally showed variable and broad ranges of 

dissolved constituents; no systematic relationships of 

ground-water chemistry and radionuclide content dependent 

on well depth or well type were observed. For example, TDS 

varies widely regardless of well depth or type. In ground 

waters from crystalline rocks, 222Rn in metamorphic units 

does show an increase with well depth, but only below the 

saprolite zone (r2=0.64); no depth-related trends in 222Rn 

concentrations (or other parameters), either within or 

beneath the saprolite, were observed in water samples from 

mylonite (r2=0.02) or granite (r2=0.03). Nonetheless, some 

differences in ground-water chemistry were observed; the 

100,000 ,....------------------D---, 

.:::::! 10,000 

0 

c. 

c 

a: 

, 

~ 1,000 

0 

Ill 

Ill 

c 

100 

D 

[] 

0 0 [] 

[] [] 

• 

I [] 

• 

0 

0 

0 [] 

0 0 

0 

• ~0 

• 0 0 • 0 

a. . .. . • 

0.1 

Dissolved U, pCi/L 

oo 

D Granitic 

o Mylonitic 

• Metamorphic 

Figure 5. Radioactivities (in pCi!L) of dissolved U versus dissolved 222Rn in ground water. The line drawn across the lower right 

comer of the diagram represents radioactivity of 222Rn that is approximately 1,000 times that of uranium (assuming secular equilibrium 

238U and 234U; U activity calculated using the conversion 1 ppb U = 

0.68 pCi). All samples plot above this line, indicating that at least 

99.9% of the dissolved 222Rn is unsuppoprted by dissolved U. 

remainder of this report examines some possible reasons for 

these differences in ground waters from the 3 major rock 

types in the Hylas area. 

COMPARISON OF GROUND-WATER 

CHEMISTRY OF SAPROLITE 

AND BEDROCK 

When all 52 ground-water samples are examined solely 

on the basis of whether they originate from saprolite or bedrock (but without regard to the type of bedrock), only average DO and Cl were significantly higher in the saprolite than 

in the bedrock. No significance can be attached to Cl 

because of the conservative nature of this anion. The higher 

DO in saprolite undoubtedly reflects its close proximity to 

the atmosphere, where oxygenated meteoric waters can 

readily infiltrate the saprolite and continually replenish 02 

that may be consumed by near-surface weathering reactions. 

Dissolved 0 2 in ground water in the crystalline units tends to 

decrease with increasing depth, although DO was detected in 

every sample. Lower DO in the deeper crystalline units may 

result from multiple causes: (1) 0 2 does not reach these 

depths because of slow recharge or recharge with poorlyoxygenated meteoric waters, (2) 0 2 is rapidly consumed by 

weathering reactions as oxygenated recharge water percolates through the saprolite, or (3) 02 carried in ground water 

reaches lower depths but is quickly used up by weathering 
14 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

reactions within the crystalline rocks. It is likely that all 

three processes are operating in the ground-water system, 

but the relative magnitude or importance of each process is 

unknown. 

In comparing saprolite to its underlying parent bedrock 

(and distinguishing among bedrock types), some geochemical differences in ground waters are more noticeable, particularly for waters from the mylonitic and metamorphic rocks. 

It is assumed that the saprolite was derived from the crystalline rocks directly beneath the saprolite. Because the area is 

tectonically stable and has low relief, it is less likely that geological processes have caused large vertical or horizontal 

displacements of the surficial layers away from the parent 

bedrock. 

Granite-hosted ground waters showed the fewest number of geochemical differences; only SpC, 222Rn, Si (as 

Si02), Mg, and N03 were significantly higher in the 

unweathered granitic rock compared to the weathered saprolite. The higher concentration of 222Rn in bedrock ground 

waters, even though U(aq) shows no differences in ground 

water from rock or saprolite, suggests that U is more strongly 

retained by mineral surfaces in the bedrock. Alternatively, 

these results may merely be an indication of the higher abundance of U in the bedrock; as noted later, however, U within 

minerals would have to be ideally sited at the rock-water 

interface to support the observed 222Rn abundances. Similarly, higher Si and Mg may merely reflect the higher abundances of these elements in granitic rocks, or that crystalline 

rock weathering is proceeding to a greater degree than in the 

saprolite. Which of these 2 possibilities accounts for the 

observed Si and Mg concentrations could not be determined 

with the available data. Higher N03 in waters from the 

deeper crystalline rock is difficult to explain, but it may be 

that some surface N03 does indeed infiltrate to deeper 

ground waters, whereas the bulk of N03 is consumed by biological processes in the shallow saprolite. 

Ca, Mg, Na, HC03, S04, TDS, U, and Hardness 

(=Ca+Mg) were significantly higher in waters from the 

mylonitic bedrock than in the saprolite derived from this 

rock. These parameters, especially the higher TDS and major 

cations, and the lower DO of the crystalline rocks, suggest 

that the mylonitic rocks may be undergoing weathering with 

release of cations to a greater degree than the granitic rocks. 

N03 and Ba contents were significantly lower in the crystalline rock, and all other parameters showed no differences 

between saprolite and bedrock. The high U may be indicative of mobile dissolved U, which is not held as tightly on 

mineral surfaces as in the other two rock types. 

Samples from metamorphic-hosted ground waters 

exhibited the greatest number of differences in saprolitic versus bedrock ground waters. The pH, SpC, 222Rn, K, HC03, 

TDS, Mn, Si, Sr, Na, S04, and Hardness are all higher in the 

bedrock; only DO is higher in the saprolite. Again, the dissolved elements could result from ferromagnesian and silicate mineral weathering (K, Mn, Si, Sr, Na), while the higher 

SpC, TDS, HC03, S04, and Hardness simply reflect 

increased abundances of dissolved species from the weathering process. U(aq) is probably adsorbed more strongly to 

mineral surfaces within the metamorphic rocks than in the 

saprolite derived from these rocks, as indicated by the 

observed 222Rn being higher in ground waters from bedrock, 

while U(aq) shows no differences in waters from either bedrock or saprolite. 

STATISTICAL COMPARISON OF WATER 

CHEMISTRIES 

MAJOR IONS AND ELEMENTS 

Bicarbonate (HC03) is the dominant anion in most 

ground-water samples; its significance in the observed U and 

222Rn abundances is discussed in a later section. Average 

sulfate (S04) concentrations are similar for ground-water 

samples from granitic and metamorphic samples (3.5 ppm) 

and slightly higher in the mylonitic samples ( 4.9 ppm), but 

these so4 values are indistinguishable at the 95% confidence 

level. Sulfate can be produced by oxidative weathering of 

sulfide minerals, such as pyrite (FeS2), that have been noted 

in some of the aquifer rocks (Ellison and Masiello, 1979). 

Although no relationship of dissolved Fe and S04 was 

observed (,.2 = 0.01), weathering of pyrite and mafic minerals is a potential source of dissolved and solid forms of iron 

in the aquifers. Average chloride (Cl) in ground waters from 

the 3 rock types does not exceed 8 ppm; the maximum abundance of Cl was 58 ppm and only one other sample had Cl 

higher than 20 ppm. Phosphate (P04) and fluoride (F) form 

complexes with U and could potentially enhance the abundance of soluble U (Langmuir, 1978); however, P04 is 

below the detection limit ( <0.1 ppm) in all samples and F is 

below the detection limit ( <0.1 ppm) in 31 samples; no statistics were computed for P04 or F. The Environmental Protection Agency's MCL of 45 ppm as nitrate (N03) was not 

exceeded in any sample. N03 was not detected in 20 samples, and only 8 samples have N03 concentrations greater 

than 10 ppm. Samples with the highest N03 values are from 

areas where fertilizers are used, such as golf courses or agricultural fields. 

Major dissolved species in ground water are Si (Si02), 

Ca, Mg, and Na, but the abundance of dissolved K is generally low (1-2 ppm) despite the fact that alkali feldspar is a 

component of most aquifer rocks; this lack of dissolved K 

probably reflects the formation of K-bearing weathering 

products, such as clay minerals, or the resistance of the feldspars to weathering (Busenberg and Clemency, 1976). Ca, 

Mg, and Na are major constituents of aquifer minerals, such 

as hornblende, pyroxene, and plagioclase feldspars, and their 

dominance in the aqueous phase is consistent with the 

weathering of crystalline silicate rocks in a humid environment (Garrels and MacKenzie, 1967). Dissolved Ca, Na, and 
DISCUSSION 15 

K are not statistically different among the three groundwater types; only dissolved Mg showed some variation. Mg 

was lower in the granite-hosted waters (1.2 ppm) but the 

same in metamorphic- and mylonitic-hosted waters (3.7 

ppm). On a mass basis, the sum of the major cations (Ca, Mg, 

Na, and K) comprises up to 26 percent ofTDS in some samples while the major anion HC03 constitutes as much as 70 

percent of TDS in other samples. 

Average dissolved Si values are 19 ppm from mylonite, 

15 ppm from granite, and 13 ppm from metamorphics; the 

metamorphic units are significantly lower in Si compared to 

the mylonite. The higher Si concentrations from mylonite 

samples suggests more extensive weathering or alteration of 

silicate minerals, but the extent of weathering or alteration 

and types of minerals involved is unknown. Si may also be 

controlled or limited by mineral precipitation reactions, for 

example, the formation of clays or other secondary silicates 

(Garrels and MacKenzie, 1967). Ion ratios that have been 

used as indicators of weathering reactions (for example, Si/ 

TDS or Na/total cations; see Hem, 1989, and Garrels and 

MacKenzie, 1967) did not provide any insight into the types 

of minerals undergoing weathering or processes that might 

be involved. 

TRACE ELEMENTS 

Quantitative comparisons were made for the following 

trace elements that were above detection in 90 percent of the 

ground-water samples: Ba, Mn, Sr, Ti, and Zn. However, the 

mean values of Ba, Ti, and Zn are not significantly different 

among ground waters from the three rock types. It should be 

noted that the Zn and Cu detected in some samples could 

arise from solubilization of these metals by acidic waters 

from galvanized or copper pipe that is commonly used in 

well-water delivery systems. 

Average dissolved Mn concentrations are 80.3 ppb 

from mylonite, 31.8 ppb from granite, and 23 ppb from metamorphics. The metamorphic units are significantly lower in 

Mn compared to the mylonite. Mn often behaves chemically-similar to Fe in that both are generally more soluble in 

reduced form and less soluble in oxidized form, but the correlation of these two elements was weak (,.2 = 0.27). A weak 

negative correlation of higher dissolved Mn versus lower 

dissolved 0 2 was observed in all water samples (,.2 = 0.21); 

this trend was slightly stronger in waters from metamorphic 

(,.2 = 0.36) and granitic (,.2 = 0.36) rocks. The increase in dissolved Mn concentrations with higher dissolved 02 values 

seems inconsistent with the known geochemistry of Mn and 

could be due to mixing of waters from different aquifers. 

Nonetheless, the higher Mn concentrations from mylonitehosted water samples suggest more extensive weathering or 

alteration of Fe- and Mn-bearing silicate minerals in this 

unit, but as noted with silica, the possible weathering mechanisms are not known. 

Sr is significantly higher in water samples from both 

mylonite (105 ppb) and granite (58 ppb) compared to the 

metamorphics (48 ppb). The most likely explanation for the 

observed values is that Sr is more abundant in granitic rocks 

and less abundant in basic (ultramafic) crystalline rocks 

(Turekian and Wedepohl, 1961); weathering and dissolution 

of plagioclase feldspars, apatite, or calcite, where Sr readily 

substitutes for Ca, could lead to higher dissolved Sr. 

Although Li was detected in only 4 water samples from 

metamorphic rocks, it was detected in 7 granite-hosted and 

15 mylonite-hosted water samples. The presence of detectable Li in waters from granites and mylonites, like Sr, probably reflects a greater original abundance of this element in 

micaceous minerals from granitic or volcanic rocks (Hem, 

1989) that were precursors to mylonite. 

The distribution of the 20 water samples that contain 

measurable dissolved iron is approximately equal among all 

three rock types. Average Fe concentrations in filtered water 

samples from mylonite (0.27 ppb), granite (0.42 ppb), and 

metamorphics (0.2 ppb) are not significantly different. Six 

freshly collected water samples from the mylonitic rocks and 

three water samples from the metamorphic rocks contained 

suspended rust-colored particles, assumed to be amorphous 

iron oxyhydroxides (and hereafter referred to as ferric oxides 

or iron oxides); water samples from granitic rocks contained 

no visible iron oxide. The presence of suspended iron oxides 

does not correlate with dissolved oxygen (,.2 = 0.04) or 

dissolved iron concentrations (,.2 = 0.1). An increase in 

dissolved iron with decreasing pH was observed in those 

samples with iron concentrations above the detection limit. 

Consistent with the known geochemistry of iron, a rise in pH 

and aeration during sampling would favor oxidation of 

dissolved Fe(II) to form insoluble Fe(III) oxides. 

Alternatively, the wells may sample several of the waterbearing horizons (as noted in some drilling logs) with 

different redox potentials and dissolved Fe and 02 

concentrations. Mixing of these waters may produce changes 

in water chemistry that lead to in situ iron oxide precipitation 

(Hem, 1989). Although the presence of some iron oxides 

may be due to corrosion (formation of soluble Fe2+) of steel 

well casings, iron oxides were also observed in samples from 

the augered wells lined with terra cotta tiles. A newly drilled 

flowing well (in operation 1 week; 120 meters deep) within 

the Maidens Gneiss had deposited a 1-2 mm thick layer of 

fresh iron oxide precipitate on the ground surface, 

suggesting that mobile Fe2+ is present in the waters tapped by 

this well. In the active quarries in the area, abundant iron 

oxides were observed on fresh rock surfaces and throughout 

the overlying saprolite. Additionally, autoradioluxographs 

of shear zone mylonites show that abundant ferric oxides are 

located along shear planes and that radioactive elements are 

concentrated within these ferric oxides (L.C. Gundersen, 

oral commun., 1992). These observations suggest, but do not 

necessarily confirm, that iron oxides may be suspended in 

ground waters or are precipitating in these rocks. The 
16 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

presence of abundant iron oxide sorbents could be important 

in limiting the concentrations of dissolved trace elements 

and radionuclides. 

DISSOLVED URANIUM AND RADON 

Although the major and minor element chemistry of 

ground water in the study area does not differ markedly from 

one rock type to another, analysis of variance suggests that 

there are differences with respect to key geochemical parameters that may influence 222Rn and U abundances and mobilities in the ground waters. These parameters (pH, HC03, 

DO, and TDS) indicate that ground waters from the mylonitic, granitic, and metamorphic rocks are sufficiently different to account for some of the variation in the U and 222Rn 

abundances and distributions. 

Ground water from mylonite within the Hylas zone is 

characterized by a narrower range of pH (5.6-7 .2), higher 

average pH (6.4), and higher HC03 (average=99.3 ppm). 

These values are significantly different (95% confidence 

level) compared to values from the Petersburg Granite and 

metamorphic units (table 1). 

The correlation of (calculated) total carbonate (.LC03) 

with dissolved U in mylonite ground waters seems quite 

strong (r2= 0.7, fig. 4) but should be viewed with caution due 

to the few data points at higher values. The average U value 

from the mylonite ground waters is not significantly different 

from the granite-hosted group of samples. However, both are 

higher in U (0.5 ppb) than ground waters from the metamorphic rocks (0.1 ppb ). Most samples analyzed for dissolved U 

from Petersburg Granite were below detection, and the high 

average value is primarily caused by sample 88V A-23 ( 4.4 

ppb). As mentioned earlier, this high U sample is located next 

to an active quarry near the contact of granite and mylonite 

and may be influenced by anthropogenic activities (fracturing by explosives) to a larger extent than other samples. This 

sample also has the highest measured 222Rn value (81 ,000 

pCi/L) and is anomalous in many other ways (high Cl and 

N03, see earlier discussion of Piper diagram). If 88V A-23 is 

excluded from statistical calculations, the average U from 

granite-hosted water samples is only 0.1 ppb, the same as 

water samples from the metamorphic rocks. (Similarly, average 222Rn from granite-hosted water drops to 8,800 pCi/L, 

still higher than the mylonite but almost one-half the value 

when 88V A-23 is included). However, because all but three 

uranium values are below detection in the granitic samples, 

statistical calculations involving U from these samples may 

not be reliable. In contrast, nearly all mylonite samples show 

U values well above detection (table 2). The lower pH and 

lower abundance of aqueous U (but nonetheless high 222Rn 

values) in the granite-hosted water samples suggest that U 

and Ra may be adsorbed onto mineral surfaces in these rocks 

to a greater extent than in the mylonite. 

The metamorphic samples are uniformly low in aqueous U and HC03, suggesting that low whole-rock U abundance, decreased co3 complexation, or adsorption act to 

produce low aqueous U values. In summary, data for pH, 

.LC03, and U in mylonite ground water suggest that there is 

greater potential for co3 complexing to stabilize u in solution relative to sorptive mineral surfaces. 

Individual water samples from the mylonites generally 

contain lower DO and higher TDS than samples from the 

metamorphic and granitic units. The average DO content of 

samples from mylonite (3.7 ppm) is not statistically different 

from the granite-hosted samples ( 4.9 ppm) but is lower than 

the metamorphic samples (6.3 ppm). Average TDS from 

mylonite samples (175 ppm) is significantly higher than 

samples from granites (113 ppm) or metamorphic units (1 05 

ppm). The differences in DO and TDS suggest that the 

mylonite reacts with ground water to a greater extent or at a 

faster rate than the other rock units, perhaps because of 

greater permeability and/or greater surface area available to 

the ground water. 0 2 in ground water is efficiently consumed during oxidative weathering of fine-grained mafic 

minerals. These reactions promote oxidation of iron and 

release of other cations and silica. An example of such a 

reaction is the weathering of pyroxene: 

{ 1} 2CaFeSi206 + 11202 + 10H20 + 4C02 ---7 

Fe20 3+4H4Si04 + 2Ca2+ + 4C03-

0ther reactions (such as organic carbon oxidation) may also 

consume 02, but the extent of any of these 02-consuming 

reactions is not known. 

Exclusion of the anomalous granitic water sample 

88V A-23 from the statistical calculations produced a significant decrease in average dissolved U in granites (discussed 

above) and equalized the average dissolved HC03 in mylonite and granite. These changes did not greatly alter the conclusions derived from the analysis of variance. Summary 

statistical comparisons for major ground-water parameters 

from the three 3 rock types is presented in table 3. 

PROCESSES AFFECTING URANIUM 

CONCENTRATIONS IN GROUND WATER 

WHOLE ROCK URANIUM ABUNDANCE AND 

DISTRIBUTION 

Figure 6 compares the average abundance of whole 

rock eU to the average concentration of ground-water U 

from four rock types. The minimum amount of U present is 

2.2 ppm in amphibolite, the rock type most likely have the 

lowest U abundance. The eU analyses (Gates and Gundersen, 1992) show only slightly higher average U concentrations for metamorphic rocks of increasingly granitic 

composition, as with granite gneiss (2.8 ppm); all metamorphic rocks are lower in total U (as eU) than the granitic or 

mylonitic rocks. A likely explanation for these differences in 
DISCUSSION 17 

Table 3. Statistical comparison of pH, HC03, TDS, DO, and dissolved U and 222Rn (logtransformed) in ground water samples from granitic, mylonitic, and metamorphic rocks in the 

Hylas area, Virginia. 

[Mean values compared using Scheffe F-test for one-factor analysis of variance. In general, water samples from 

mylonitic rocks are significantly different from metamorphic and granitic water samples at the 95% confidence level. 

See text for detailed discussion of differences in ground water chemistry. (+)=Significant at 95% confidence level; 

sample 88V A-23 included. (*) = Significant at the 95% confidence level; sample 88VA-23 not included. (#) = Not 

significant at the 95% confidence level; sample 88V A-23 not included] 

P1 HCOJ 

MYLONITIC vs 

MET Al\t10RPHIC • • 

MYLONITIC vs • +,# 

GRANITIC 

METAMORPHIC vs 

GRANITIC 

U abundances is that mylonitization is a kinetic metamorphic 

process that does not involve greatly elevated temperatures 

or recrystallization (Jackson, 1970); U is not highly mobile 

under these conditions, so the shear zone mylonites probably 

did not suffer a significant loss of primary U (U present in 

precursor rocks) during deformation (Gundersen, 1989). On 

the other hand, at least some of the Maidens Gneiss units 

formed under medium-grade (amphibolite facies) metamorphic conditions (Goodwin, 1970). With increasing metamorphic grade, U is less compatible in new mineral lattices and 

may escape with volatiles (H20 + C02) along pressure 

release conduits, such as shear zone boundaries; U may ultimately be lost from the precursor rocks (Heier and Adams, 

1965; Yermolayev, 1971). Thus, U either is no longer 

present or is present at reduced levels in minerals of the 

Maidens Gneiss rocks. U in all rocks is not limited to the 

parts per billion (ppb) levels found in the ground waters, and 

the strong correlation of dissolved U with whole rock eU (,-'2 

= 0.96) in figure 6 initially suggests that the concentration of 

U in ground water might be controlled by the original abundance of U in the rocks. If an assumption is made that all dissolved U was derived from crystalline-rock U, the 

percentage of "labile" U from the rocks, calculated as 

[average dissolved U(ppb)l *100 

[average whole rock eU(ppb)l 

is only 0.005 to 0.01 for all four rock types. Therefore, only 

a small fraction of total U in the rock is available to the 

ground water at the rock-water interface. Because dissolved 

U varies over large ranges for each rock type (fig. 4; table 

2), it would be an oversimplification to use whole-rock U 

abundances as a primary predictor of dissolved U 

abundances. 

The parent radionuclides are available from the 

aqueous or solid (crystalline and adsorbed) phases within the 

aquifer units. In figure 7, the graph of dissolved 222Rn versus 

[X) 

• 

.c 

a. 

a. 

:j 

"C 

(I) 

> 

0 

Ill 

Ill 

:0 

(I) 

C) 

ca 

.... 

(I) 

> <( 

TDS 

• 

• 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0 

2.0 

u log 222Rn 

• • 

* 

.,# • 

2.5 3.0 3.5 4.0 

r 2 = 0.96 

c Granitic 

0 Mylonitic 

• Metamorphic* 

~ Amphibolitic 

4.5 5.0 

Average whole rock eU, ppm 

(*Metamorphic rocks do not include four rocks of amphibolite composition) 

Figure 6. Average dissolved U in ground water versus average 

whole rock eU (equivalent uranium) in four major rock types in the 

Hylas area. Error bars are standard deviations for dissolved U analyses. Amphibolites are plotted separately to show the range of 

whole rock eU and dissolved U for rock compositions ranging from 

ultamafic to granitic. The group denoted as "metamorphic" does 

not include the four rocks of amphibolite composition. 

whole rock U (eU) for the four rock types shows that 

dissolved 222Rn is not derived wholly from U within the 

crystalline rocks. Figure 7 also indicates that approximately 

60 percent (r'l = 0.61) of the variation in observed average 

222Rn abundances is attributable to variation of parent 

radionuclides in the whole rock. Meanwhile, figure 5 shows 

that dissolved 222Rn is also unsupported by dissolved U 

because U radioactivity is much less than that of its daughter, 
18 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

100,000 r----------------::----, r 2 = 0.61 

...J 

:::::: 

0 

Q. 

c 10,000 a: 

, 

Q) 

> 0 

U) 

U) 

:c 

8, 1,000 m 

~ <C c Granitic 

0 Mylonitic 

e Metamorphic* 

e Amphibolitic 

100+---~--~--~--~--~--~ 

2.0 2.5 3.0 3.5 4.0 4.5 5.0 

Average whole rock eU, ppm 

(*Metamorphic rocks do not include four rocks of amphibolite composition) 

Figure 7. Average dissolved 222Rn in ground water versus average whole rock eU (equivalent uranium) in four major rock types in 

the Hylas area. Error bars are standard deviations for dissolved 

222Rn analyses. Amphibolites are plotted separately to show the 

range of whole rock eU and dissolved 222Rn for rock compositions 

ranging from ultamafic to granitic. The group denoted as "metamorphic" does not include the four rocks of amphibolite composition. 

222Rn. (An element produced by radioactive decay is said to 

be unsupported by its parent element if the radioactivity of 

the parent is less than that of its daughter). Thus, figures 5 

and 7 demonstrate that another source of the parent 

radionuclide(s) in the aquifer must be present. This 

additional source is the U or Ra (which ultimately decay to 

produce dissolved 222Rn) adsorbed onto the solid mineral 

surfaces in the aquifers. Variations of 222Rn in ground water 

are due to differing contributions of the three sources to the 

total U or Ra abundances. 

WATER CHEMISTRY 

Ground-water analyses in tables 1 and 2 were used to 

calculate saturation indexes (SI) for some of the more common uranium minerals; the Sl values are compiled in table 4. 

The Sl of a mineral is defined as the base-l 0 logarithm of the 

ion activity product (lAP) of dissolved mineral constituents 

divided by the equilibrium constant (solubility product, Ksp) 

for the mineral: 

lAP Sl = log 10K 

sp 

A positive Sl indicates that mineral precipitation from 

the solution may occur (supersaturation), while a negative Sl 

indicates mineral dissolution may occur (undersaturation) if 

the mineral is present. All of these oxygen-bearing groundwater samples were highly undersaturated with respect to the 

major oxidized U(VI) minerals, usually by many orders of 

magnitude. Measurable uranium concentrations in ground 

water from the three rock types are generally limited to the 

range of 0.1 to 1.0 ppb. These concentrations are far below 

those predicted by the solubility of insoluble U (VI) minerals, 

such as schoepite (U02(0Hh·H20) or rutherfordine 

(U02C03). The observed U concentrations are not limited 

by the solubility of discrete U minerals; rather, the data suggest that some other process, such as adsorption, plays a role 

in limiting U concentrations. 

Ferric oxide minerals are the most likely sorbents for U 

because of their observed abundance in the host rocks, high 

specific surface area, and recognized ability to adsorb a variety of dissolved constituents including U (Hsi, 1981; 

Wathen, 1987). Ferric oxides are able to adsorb U about 105-

106 times more efficiently than most aluminosilicates (Langmuir, 1978; Wanty and others, 199lb), and amorphous ferric 

oxides are more effective adsorbents than crystalline forms 

like hematite. Adsorption of U onto ferric oxides is most 

complete over the pH range 5-8.5, and increasing C03 concentration leads to desorption of the U species; Ca and Mg 

have little influence on the adsorption process (Hsi and Langmuir, 1985). Ferric oxides are also effective adsorbents for 

226Ra, the immediate parent of 222Rn (Ames and others, 

1983), although below pH 5.5, ferric oxides begin to dissolve 

and thus become less effective adsorbents (Szabo and 

Zapecza, 1987). Nonetheless, a small mass of ferric oxide can 

be a particularly important adsorbent when it is present as 

fracture or grain coatings in direct contact with coexisting 

water. Chemical weathering of ferromagnesian minerals in a 

humid climate leaches Ca and Mg, but Fe generally remains 

as an oxide (equation 1 ); thus, the rocks and residual saprolite 

are enriched in iron oxides and oxyhydroxides. Shear zones 

in other regions of the Eastern United States are recognized 

by their characteristic red staining caused by abundant Feoxides and Fe-oxyhydroxides (Gundersen, 1989). Further, 

ferric oxides collected on the 0.45J.Lm filter suggest that soluble forms of iron and perhaps iron oxides are present in the 

local aquifers. 

PROCESSES AFFECTING RADON 

CONCENTRATIONS IN GROUND WATER 

SECULAR EQUILIBRIUM 

222Rn is produced by the a-decay of 226Ra; both are 

daughters in the 238u decay series. With the passage of time, 

a condition known as secular equilibrium may be attained in 

a closed system. Secular equilibrium is reached when the 

rate of decay of all nuclides in a decay series is equal. 

Attainment of secular equilibrium occurs independently of 
CONCLUSIONS 19 

the system's tendency to attain chemical equilibrium. In fact, 

deviations from secular equilibrium may yield valuable 

clues to active chemical processes, as will be demonstrated. 

To determine whether secular equilibrium is attained in a 

system, the radioactivity of all nuclides must be measured 

and compared. Uranium is easily measured in terms of mass 

and can be converted to radioactivity units assuming that 

235u activity is small and that 234u and 238u are in secular 

equilibrium. The first assumption has been shown to be generally correct but the second may be a poor one, as 234u :238u 

a-activity ratios over 10:1 have been observed (Szabo, 

1982). However, most water samples have 234U:238U activity ratios of 1 to 2 (Osmond and Cowart, 1976). Even considering the uncertainty in the 234U:238U ratio, the dissolved 

U a-activities in solution are at least three orders of magnitude less than that required to sustain the observed activities 

of dissolved 222Rn (fig. 5) and thus indicate a dramatic 

departure from secular equilibrium between U and 222Rn. 

TRANSFER OF RADON FROM AQUIFER ROCKS TO 

GROUND WATER 

The a-decay of 226Ra causes a recoil of the daughter 

222Rn according to the laws of conservation of momentum. 

This a-recoil effect has been described recently by Semkow 

(1990, and references therein) and is thought to be the principal mechanism for transferring 222Rn from mineral surfaces to coexisting pore water. It is unlikely that 222Rn 

produced deep within mineral grains could diffuse to mineral 

surfaces within the short (3.8 days) half-life of 222Rn. Therefore, 222Rn in solution is probably derived from the parent 

226Ra (and 238U) located very near the water-rock interface 

(Torgersen and others, 1990). After entering the aqueous 

phase, 222Rn is probably not far removed from its original 

source (U and Ra in the rocks) because of its fast decay rate 

relative to probable ground-water flow rates. 

226Ra concentrations were not measured in this study, 

but as noted, most reported values for ground water are in the 

range of 10-2 to 101 pCi/L, well below the range of 222Rn 

concentrations observed in the Hylas ground waters (1 02-104 

pCi/L). Therefore, 222Rn concentrations in the water are 

almost certainly unsupported by dissolved 226Ra. Rather, 

222Rn is transferred to the solution via a-decay and recoil 

from 226Ra located in the solid phase. This condition 

requires that some portion of the parent Ra (and perhaps 

associated U precursor) be located within an a-recoil distance of the water-rock interface, a distance on the order of 

hundredths of micrometers (Torgersen and others, 1990). 

If efficient transfer of 222Rn from solid to solution 

occurs at grain surfaces, then processes that increase the specific surface area of the aquifer rock should lead to greater 

concentrations of dissolved 222Rn, and this has been 

observed (Torgersen and others, 1990; Wanty and others, 

1991b; Wanty and others, 1992). This argument generally 

applies to all rocks in the study area, and especially to the 

mylonitized rocks, which probably have a greater specific 

surface area and a larger number of fractures per unit area 

than the other rocks (Bobyarchick and Glover, 1979; Gates 

and Gundersen, 1992), and have 222Rn-enriched ground 

water. 

222Rn values show that water samples from mylonitic 

and granitic rocks are similar with respect to average 

dissolved 222Rn but that metamorphic rocks produce 

significantly lower average dissolved 222Rn; this is perhaps 

one of the more important observations in the Hylas area. An 

initial screening for areas of high dissolved 222Rn in the 

Hylas region should be based on the geographic distribution 

of underlying rock types. In a companion study of the Hylas 

area (Gates and Gundersen, 1992), similar positive 

relationships of soil gas and indoor 222Rn values to rock type 

were found. With the proposed 222Rn drinking water 

standard in mind, screening measurements in the Hylas area 

should be directed initially to wells tapping mylonitic and 

granitic rocks. 

CONCLUSIONS 

CONTROLS ON URANIUM AND RADON 

DISSOLVED IN GROUND WATER 

ROCK CHEMISTRY AND MINERALOGY 

The concentrations of solid phase U (eU) indicate that 

the abundance of U (and Ra) located at the rock-water 

interface differs among the mylonitic, granitic, and metamorphic rocks. The observed abundances of dissolved U 

are probably controlled, in part, by labile U in these aquifers. High abundances of U in ground water from mylonite 

suggests that U is not strongly adsorbed onto mineral surfaces or that U-bearing minerals are more susceptible to 

release of U; thus, more U is present in solution. In contrast, low U in ground water from granite suggests that U 

is held more strongly to mineral surfaces or that U-bearing 

minerals are less susceptible to release of U; thus, less U is 

present in solution. In contrast to both mylonite and granite, the metamorphic units are uniformly low in solid-phase 

U and dissolved U, indicating that low U (and Ra) abundances limit dissolved 222Rn to a much greater extent than 

in the mylonite or granite. 

WATER CHEMISTRY 

Abundances of most dissolved species in ground-water 

samples in the Hylas area do not change dramatically despite 

the fact that aquifer lithologies vary in composition from 

granitic to ultramafic. This observation, combined with the 

fact that ground water generally contains low total dissolved 
20 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

Table 4. Results of saturation index for selected common uranium minerals. 

[The computer program PHREEQE (Parkhurst and others, 1980) was used along with thermodynamic data for aqueous uranium species and minerals from 

Langmuir (1978). "ND" means that uranium was not detected in the sample and no SI values were calculated. For samples with U below the detection 

limit (<0.05 ppb), 0.05 ppb was used to calculate a maximum SI. Uraninite + (UOz); coffinite= (USi04); schoepite = (U03(0H)z*2Hz0); rutherfordine 

= (UOzC03)] 

Sample No. 

88VA-7 

88VA-23 

90VA-5 

90VA-7 

90VA-8 

90VA-9 

90VA-10 

90VA-11 

90VA-12 

90VA-13 

90VA-14 

90VA-15 

Sample Number 

88VA-1 

88VA-2 

88VA-4 

88VA-6 

88VA-8 

88VA-9 

88VA-10 

88VA-12 

88VA-13 

88VA-14 

88VA-16 

88VA-17 

88VA-20 

88VA-21 

88VA-29 

88VA-35 

88VA-36 

90VA-3 

SAMPLES OF GROUND WATER FROM GRANITES 

Uraninite Coffinite Schoepite Rutherfordine 

-2.5 -2.8 -5.9 -4.6 

-1 . 4 - 1 . 6 -4. 1 -3.4 

ND ND ND ND 

-2 7 -27 -7.7 -5.8 

-7.7 - 8 -7. 1 -6.5 

ND ND ND ND 

- 1 7 - 1 8 -7.3 -5.7 

- 1 2 - 1 3 -5.9 -5.3 

- 1 2 - 1 3 -6.4 -5.5 

- 1 6 - 1 6 -6.2 -5.3 

- 1 4 - 1 5 -6.8 -5.6 

-7.5 -7.8 -6.7 -6.3 

SAMPLES OF GROUND WATER FROM MYLONITES 

Uraninite Coffinite Schoepite Rutherfordine 

- 3 -3.2 -4.6 - 5 

-3.9 -4.3 -4.4 -4.5 

-5. 1 -5.5 -4.3 -4.8 

-3.6 -4.2 - 5 -4.8 

-4.3 -4.8 -4.8 -4.9 

-3.3 -3.6 -5.8 -4.4 

-2.8 -3.6 -5.2 -4.9 

-5.8 -6. 1 -5.8 -5.3 

-4.6 -4.9 -5.2 -4.9 

-5.8 - 6 -6.3 -5.7 

ND ND ND ND 

-4.5 -4.8 -5. 1 -4.9 

-3.9 - 4 -5.8 - 5 

-5. 1 -5.4 -5.6 -5.2 

-9.5 -9.8 -4.9 -4.2 

-4.4 -4.7 -4.8 -4.7 

-5.6 -6.2 -5. 1 -5.2 

-8.8 -9. 1 -6.6 - 6 

solids, is consistent with relatively rapid recharge attendant 

in a moist climate. Apparently, dissolution of rock-forming 

minerals in the different lithologic units that serve as aquifers has not proceeded to a great enough extent to impart a 

distinctive chemical signature to the various aquifer waters. 

As noted, the only major rock-forming mineral to approach 

saturation is quartz. 

aquifer lithology. In some areas, the concentrations of 

dissolved 222Rn may exceed the newly proposed MCL of 

300 pCi/L as 222Rn, especially in ground waters from 

granitic and mylonitic rocks. Although 222Rn concentrations 

in ground-water samples from the granite and mylonite 

encompass a fairly wide range and are not readily 

distinguishable, the 222Rn concentrations in ground water 

from these two aquifers are much higher than in ground 

water obtained from the low-U metamorphic rocks. 

In contrast to major dissolved species, dissolved U and 

particularly dissolved 222Rn, show a greater variation with 
SUMMARY 21 

Table 4. Results of saturation index for selected common uranium minerals. -Continued 

SAMPLES OF GROUND WATER FROM METAMORPHIC ROCKS{*= AMPHIBOLITE) 

Sample No. Uraninite Coffinite Schoepite Rutherfordine 

88VA-3 -5.3 -5.7 -4.9 -5.4 

88VA-5 -4.8 -5.2 -5.3 -5. 1 

88VA-11 -4.5 -4.8 -5.4 - 5 

88VA-15 -4. 1 -4.3 -5.3 -5. 1 

88VA-18 -2.9 -3.2 -5.8 -4.9 

88VA-19 -2.7 -3. 1 -5.9 -4.9 

88VA-22 -3. 1 - 4 - 6 -4.9 

88VA-24 -6.8 - 7. 1 -5.3 -4.7 

88VA-25 NO ND NO NO 

88VA-26 -2.2 -2.8 -6.4 -4.9 

88VA-27* -8.7 -9.5 -5.4 -4.9 

88VA-28 -3.5 -3.9 - 6 -4.9 

88VA-30 -3.7 -4.2 - 6 -5.2 

88VA-31 * -9.2 - 1 0. -5.9 -5.0 

88VA-32 - 1 . 6 -2.8 -6.3 -5.2 

88VA-33 ND NO NO NO 

88VA-34 -3. 1 -3.7 -5.8 -4.9 

90VA-1 - 1 6 - 1 7 -6.2 -5.7 

90VA-2* -8.2 -8.7 -6.5 -6.3 

90VA-4 ND NO NO NO 

90VA-6* -5.8 -6.3 -6.5 -6.8 

90VA-16 - 1 7 - 1 8 -6.2 -5.9 

U and Ra solubility and adsorption at the rock-water 

interface are strongly influenced by ground-water chemistry, 

particularly pH, Eh (DO), and the concentration of C03

2-

ions that form soluble complexes with U. The lower pH and 

lower alkalinity (as :LC03) of ground water from metamorphic and granitic rocks favors adsorption of U (as U02) on 

mineral surfaces. Thus, the variation of dissolved U within 

and between different aquifers is also influenced by water 

chemistry that determines the importance of adsorptive 

uptake on mineral surfaces. Increased solubility and adsorption of U and Ra at the rock-water interface enhances the 

emanation of 222Rn into ground water. 

FRACTURESANDSURFACEAREA 

Differences between mylonitic and granitic ground 

waters with respect to pH, :LC03, U, TDS, and DO suggest 

that dissolved U may increase as a result of shearing and 

chemical weathering processes. Shearing and weathering 

of the mylonitic rocks increase the surface area that is 

available for reaction with ground water. Fracturing of 

anthropogenic or geological origin acts to increase the efficiency of rock-water interaction and the efficiency of 

222Rn emanation to pore water and needs to be investigated in greater detail. 

SUMMARY 

In general, ground water in the vicinity of Hylas, Virginia, is of good quality for domestic consumption and major 

and trace element chemistry does not vary greatly with host 

lithology. However, greater abundances of U and certain 

ions and trace elements in ground waters from mylonite indicate that weathering and probable increased surface area due 

to shearing enhances U release into ground water (and perhaps U- and Ra-siting at the rock-water interface), and thus 

222Rn emanation into ground water. Adsorption probably 

limits dissolved U (but not 222Rn) to the lower levels 

observed in water samples from granitic rocks. Both dissolved U and 222Rn in ground waters from metamorphic 

rocks appear to be limited by the low abundance of U. In 

areas where crystalline rocks are dominant, determination of 

lithologies would be a logical first step prior to examining 

ground-water supplies thought to have elevated levels of dissolved 222Rn. 
22 RADON AND URANIUM IN GROUNDWATER: HYLAS, VIRGINIA 

ACKNOWLEDGMENTS 

This work was performed as part of the Uranium and 

Radon Investigations Program of the U.S. Geological Survey and supported by the U.S. Department of Energy. We 

thank Jim Otton, Mike Reimer, and Bob Zielinski for technical reviews that improved the content of this manuscript. 

Kris Kranbis assisted with the May 1990 portion of field 

work. We also thank Ann Mullin and Greg Brown of the 

USGS National Water Quality Lab for the 222Rn analyses. 

REFERENCES CITED 

Ames, L.L., McGarrah, J.E., Walker, B.A., and Salter, P.F., 1983, 

Uranium and radium sorption on amorphous ferric oxyhydroxide: Chemical Geology, v. 40, p. 135-148. 

Bobyarchick, A.R., and Glover, L., III, 1979, Deformation and 

metamorphism in the Hylas zone and adjacent parts ofthe eastem Piedmont in Virginia: Geological Society of America Bulletin, v. 90, p. 739-752. 

Brutsaert, W.F., Norton, S.A., Hess, C.T., and Williams, J.S., 1981, 

Geologic and hydrologic factors controlling radon-222 in 

ground water in Maine: Ground Water, v. 19, p. 407-417. 

Busenberg, E., and Clemency, C.V., 1976, The dissolution kinetics 

of feldspars at 25 oc and 1 atm C02 partial pressure: Geochimica et Cosmochimica Acta, v. 40, p. 41-50. 

Cecil, L. DeWayne, Smith, Robert 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, Radon, radium, and other radioactivity in ground 

water: Chelsea, Michigan, Lewis Publishers, Inc., p. 437-447. 

Crawford-Brown, D.J., 1990, Analysis of the health risk from 

ingested radon, in Cothern, C.R., and Rebers, P.A., Radon, 

radium, and uranium in drinking water: Chelsea, Michigan, 

Lewis Publishers, Inc., p. 17-26. 

Davis, S.N., and DeWiest, R.J.M., 1966, Hydrogeology: New 

York, John Wiley and Sons, 463 p. 

Ellison, R.P., III, and Masiello, R.A., 1979, Groundwater resources 

of Hanover County, Virginia: Virginia State Water Control 

Board, Planning Bulletin 314, 127 p. 

Fishman, M.J., and Pyen, G.S., 1979, Determination of selected 

anions in water by ion chromatography: U.S. Geological Survey Water-Resources Investigations Report 79-101, 30 p. 

Garrels, R.M., and MacKenzie, F.T., 1967, Origin ofthe chemical 

compositions of some springs and lakes, in Equilibrium concepts in natural-water chemistry: Advances in Chemistry 

Series, no. 67, Washington, D.C., American Chemical Society, 

p. 222-242. 

Gates, A.E., and Gundersen, L.C.S., 1992, Sensitivity of soil radon 

to geology and the distribution of radon and uranium in the 

Hylas zone area, Virginia, in Gates, A., and Gundersen, L.C.S., 

eds., Geological Society of America Special Paper no. 271, p. 

17-27. 

Goodwin, B.K., 1970, Geology ofthe Hylas and Midlothian quadrangles, Virginia: Virginia Division of Mineral Resources, 

Report of Investigations 23, Charlottesville, Virginia, 51 p. 

Gundersen, L.C.S., 1989, Anomalously high radon in shear zones, 

in Osborne, M.C., and Harrison, J., The 1988 Symposium on 

Radon and Radon Reduction Technology, Proceedings: U.S. 

Environmental Protection Agency Publication EP N600/9-89/ 

006a, v. 1, p. V27-V44. 

Heier, K.S., and Adams, J.A.S., 1965, Concentration of radioactive 

elements in deep crustal material: Geochimica et Cosmochimica Acta, v. 29, p. 53-61. 

Hem, J.D., 1989, Study and interpretation of the chemical characteristics of natural water, 3rd ed., U.S. Geological Survey 

Water-Supply Paper no. 2254, 263 p. 

Hess, C.T., Vietti, M.A., Lachapelle, E.B., and Guillemette, J.F., 

1990, Radon transferred from drinking water into house air, in 

Cothern, C.R., and Rebers, P.A., Radon, radium, and uranium 

in drinking water: Chelsea, Michigan, Lewis Publishers, Inc., 

p. 51-68. 

Hsi, C.-K.D., 1981, Sorption of uranium(VI) by iron oxides: Colorado School of Mines, unpublished Ph. D. thesis, 154 p. 

Hsi, C.-K.D., and Langmuir, Donald, 1985, Adsorption of uranyl 

onto ferric oxyhydroxides: Application ofthe surface complexation site-binding model: Geochimica et Cosmochimica Acta, 

v.49,p. 1931-1941. 

Jackson, K.C., 1970, Textbook of Lithology: New York, McGrawHill, 552 p. 

Langmuir, Donald, 1978, Uranium solution-mineral equilibria at 

low temperatures with applications to sedimentary ore deposits: Geochimica et Cosmochimica Acta, v. 42, p. 547-569. 

Langmuir, Donald, and Melchior, Daniel, 1985, The geochemistry 

of Ca, Sr, B a, and Ra sulfates in some deep brines from the Palo 

Duro Basin, Texas: Geochimica et Cosmochimica Acta, v. 49, 

p. 2423-2432. 

Lawrence, E.P., Wanty, R.B., and Nyberg, P.A., 1991, Contribution 

of 222Rn in domestic water supplies to 222Rn in indoor air in 

homes in Colorado: Health Physics, v. 62, p. 171-177. 

LeGrand, H.E., 1987, A predictive model for indoor radon occurrence - a first approximation, in Graves, Barbara, Radon, radium, and other radioactivity in ground water: Chelsea, 

Michigan, Lewis Publishers, Inc., p. 477-487. 

Lichte, F.E., Golightly, D.W., and Lamothe, P.J., 1987, Inductively 

coupled plasma-atomic emission spectrometry, in Baedecker, 

P.A., Geochemical Methods of Analysis: U.S. Geological Survey Bulletin 1770: p. B 1-B 10. 

Nazaroff, W.W., and Nero, A.V., Jr., 1988, Radon and its decay 

products in indoor air: New York, John Wiley and Sons, 518 p. 

Nazaroff, W.W., Doyle, S.M., Nero, A.V., Jr., and Sextro, R.G., 

1988, Radon entry via potable water, in Nazaroff, W.W., and 

Nero, A.V., Jr., Radon and its decay products in indoor air: 

New York, John Wiley and Sons, p. 131-160. 

Osmond, J.K., and Cowart, J.B., 1976, The theory and uses of natural uranium isotopic variations in hydrology: Atomic Energy 

Review, v. 14, p. 621-679. 

Parkhurst, D.L., Thorstenson, D.C., and Plummer, L.N., 1980, 

PHREEQE- A computer program for geochemical calculations: U.S. Geological Survey Water-Resources Investigations 

80-96, 210 p. 

Scheffe, Henry, 1933, A method for judging all contrasts in the 

analysis of variance: Biometrika, v. 40, p. 87-104. 

Semkow, T.M., 1990, Recoil-emanation theory applied to radon 

release from mineral grains: Geochimica et Cosmochimica 

Acta, v. 54, p. 425-440. 
REFERENCES CITED 23 

Szabo, B.J., 1982, Extreme fractionation of 234Uf238U and 23D-fhl 

234U in spring waters, sediments, and fossils at the Pomme de 

Terre Valley, southwestern Missouri: Geochimica et Cosmochimica Acta, v. 46, p. 1675-1679. 

Szabo, Zoltan, and Zapecza, O.S., 1987, Relation between natural 

radionuclide activities and chemical constituents in ground 

water in the Newark Basin, New Jersey, in Graves, Barbara, 

Radon, radium, and other radioactivity in ground water: 

Chelse~, Michigan, Lewis Publishers, Inc., p. 283-308. 

Till, Roger, 1974, Statistical methods for the earth scientist: New 

York, Halsted Press, 154 p. 

Torgersen, Thomas, Benoit, Janina, and Mackie, David, 1990, Controls on groundwater Rn-222 concentrations in fractured rock: 

Geophysical Research Letters, v. 17, no. 6, p. 845-848. 

Turekian, K.K., and Wedepohl, K.H., 1961, Distribution of the elements in some major units of the Earth's crust: Geological 

Society of America Bulletin, v. 72, p. 175-182. 

U.S. Environmental Protection Agency, 1976, Washington, D.C., 

National Interim Primary Drinking Water Regulations: EPA570/9-76-003, 163 p. 

U.S. Environmental Protection Agency, 1991, National Primary 

Drinking Water Regulations; Radionuclides; Proposed Rule: 

Federal Register, Part II, v. 56, no. 138, July 18, p. 33050-

33127. 

Wanty, R.B., and Gundersen, L.C.S., 1991, Field studies of radon 

in rocks, soils, and water: U.S. Geological Survey Bulletin 

1971, 334 p. 

Manuscript approved for publication September 7, 1993. 

Published in the Central Region, Denver, Colorado 

Edited by Thomas Kohnen 

Photocomposition by Denny Welp 

Figures drafted by the author 

Wanty, R.B., Johnson, S.L., and Briggs, P.H., 1991a, Radon-222 

and its parent radionuclides in groundwater from two study 

areas in New Jersey and Maryland, USA: Applied Geochemistry, v. 6, no. 3, p. 305-318. 

Wanty, R.B., Lawrence, E.P., and Gundersen, L.C.S., 1992, A theoretical model for the flux of radon-222 from rock to ground 

water, in Gates, A., and Gundersen, L.C.S., eds., Geological 

Society of America Special Paper no. 271, p. 73-78. 

Wanty, R.B., Rice, C.A., Langmuir, D., Briggs, P.H., and 

Lawrence, E.P., 1991b, Prediction of uranium adsorption by 

crystalline rocks: The key role of reactive surface area, in 

Materials Research Society Symposium Proceedings Volume: 

Boston, Massachusetts, Materials Research Society, v. 212, p. 

695-702. 

Wathen, J.B., 1987, The effect of uranium siting in two-mica granites on uranium concentrations and radon activity in ground 

water, in Graves, Barbara, Radon, radium, and other radioactivity in ground water: Chelsea, Michigan, Lewis Publishers, 

Inc., p. 31-46. 

Yerrnolayev, N.P., 1971, Processes of redistribution and extraction 

of uranium in progressive metamorphism: Geochemistry International, v. 8, p. 599-609. 

Zapecza, O.S., and Szabo, Zoltan, 1987, Source and distribution of 

natural radioactivity in ground water in the Newark Basin, new 

Jersey, in Graves, Barbara, Radon, radium, and other radioactivity in ground water: Chelsea, Michigan, Lewis Publishers, 

Inc., p. 47-68. 

i:r U.S. GOVERNMENT PRINTING OFFICE: 1996 - 774-045 / 20023 REGION NO. 8 

SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly). 

Technical Books and Reports 

Professional Papers are mainly comprehensive scientific reports 

)f wide and lasting interest and importance to professional scientists and 

!ngineers. Included are reports on the results of resource studies and of 

opographic, hydrologic, and geologic investigations. They also include 

;ollections of related papers addressing different aspects of a single sci-

!ntific topic. _ 

Bulletins contain significant data and interpretations that are of 

asting scientific interest but are generally more limited in scope or geo-

~raphic coverage than Professional Papers. They include the results of re-

;ource studies and of geologic and topographic investigations; as well as 

:ollections of short papers related to a specific topic. 

Water-Supply Papers are comprehensive reports that present siglificant interpretive results of hydrologic investigations of wide interest 

o professional geologists, hydrologists, and engineers. The series covers 

nvestigations in all phases of hydrology, including hydrology, availabilty of water, quality of water, and use of water. 

Circulars present administrative information or important scientifc information of wide popular interest in a format designed for distribuion at no cost to the public. Information is usually of short-term interest. 

Water-Resources Investigations Reports are papers of an intertretive nature made available to the public outside the formal USGS pubications series. Copies are reproduced on request unlike formal USGS 

•ublications, and they are also available for public inspection at deposiJries indicated in USGS catalogs. 

Open-File Reports include unpublished manuscript reports, maps, 

nd other material that are made available for public consultation at de-

·ositories. They are a nonpermanent form of publication that may be citd in other publications as sources of information. 

naps 

Geologic Quadrangle Maps are multicolor geologic maps on toagraphic bases in 7 112- or 15-minute quadrangle formats (scales main-

{ 1:24,000 or 1 :62,500) showing bedrock, surficial, or engineering 

eology. Maps generally include brief texts; some maps include structure 

nd columnar sections only. 

Geophysical Investigations Maps are on topographic or planimetc bases at various scales, they show results of surveys using geophysical 

:chniques, such as gravity, magnetic, seismic, or radioactivity, which reect subsurface structures that are of economic or geologic significance. 

1any maps include correlations with the geology. 

Miscellaneous Investigations Series Maps are on planimetric or 

>pographic bases of regular and irregular areas at various scales; they 

resent a wide variety of format and subject matter. The series also intudes 7 1/2-minute quadrangle photogeologic maps on planimetric 

ases which show geology as interpreted from aerial photographs. The 

!ries also includes maps of Mars and the Moon. 

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, 

stratigraphy, and structural relations in certain coal-resource areas. 

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum potential. 

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology in relation to specific mining or mineral-deposit problems; post-1971 maps 

are primarily black-and-white maps on various subjects such as environmental studies or wilderness mineral investigations. 

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wid~ ra~ge 

of geohydrologic data of both regular and irregular areas; the pnnc1pal 

scale is 1:24,000, and regional studies are at 1:250,000 scale or smaller. 

Catalogs 

Permanent catalogs, as well as some others, giving comprehensive 

listings of U.S. Geological Survey publications are available under the 

conditions indicated below from USGS Map Distribution, Box 25286, 

Building 810, Denver Federal Center, Denver, CO 80225. (See latest 

Price and Availability List.) 

"Publications of the Geological Survey, 1879-1961"may be purchased by mail and over the counter in paperback book form and as a set 

microfiche. 

"Publications of the Geological Survey, 1962-1970"may be purchased by mail and over the counter in paperback book form and as a set 

of microfiche. 

"Publications of the U.S. Geological Survey, 1971-1981"may be 

purchased by mail and over the counter in paperback b~ok form (two volumes, publications listing and index) and as a set of microfiche. 

Supplements for 1982, 1983, 1984, 1985, 1986, and for subs~­

quent years since the last permanent catalog may be purchased by ma1l 

and over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic and Water-Supply Reports and Maps For (State)," may be purchased by mail and 

over the counter in paperback booklet form only. 

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet 

form only. 

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" is available free of charge by mail or rna~ b~ obtained over the counter in paperback booklet form only. Those wtshmg a 

free subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 National Center, Reston, VA 22092. 

Note.-Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the prices 

charged may differ from the prices in catalogs, announcements, and publications.