U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2008–5205

In Cooperation With the Miami Conservancy District 

Relation Between Solid-Phase and Dissolved Arsenic in the 

Ground-Water System Underlying Northern Preble County, Ohio

Dolomite

Nickel, arsenic,

iron sulfides

Clay

100 micrometers
Cover image. Micrograph of a sample from the unconsolidated bedrock zone at site 1, Preble County, Ohio, showing 

etched dolomite rhombs in a clay matrix. (Image produced by Sharon Diehl, U.S. Geological Survey.)
Relation Between Solid-Phase and Dissolved 

Arsenic in the Ground-Water System 

Underlying Northern Preble County, Ohio

By Mary Ann Thomas, Sharon F. Diehl, Bruce A. Pletsch, Thomas L. Schumann, 

Richard R. Pavey, and E. Mac Swinford

In cooperation with the Miami Conservancy District

Scientific Investigations Report 2008–5205

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Thomas, M.A., Diehl, S.F., Pletsch, B.A., Schumann, T.L., Pavey, R.R., and Swinford, E.M., 2008, Relation between 

solid-phase and dissolved arsenic in the ground-water system underlying northern Preble County, Ohio: U.S. 

Geological Survey Scientific Investigations Report 2008-5205, 56 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Description of Study Area ...................................................................................................................2

Background............................................................................................................................................4

Methods...........................................................................................................................................................6

Solid-Phase Characteristics ........................................................................................................................8

Stratigraphy ...........................................................................................................................................8

Site 1. ...........................................................................................................................................8

Site 2. .........................................................................................................................................10

Bulk Elemental Composition .............................................................................................................12

Site 1. .........................................................................................................................................12

Site 2. .........................................................................................................................................12

Residence of Arsenic in Sulfide Minerals ......................................................................................15

Ground-Water Quality .................................................................................................................................18

Site 1. ..................................................................................................................................................20

Site 2. ..................................................................................................................................................20

Relation Between Arsenic in Ground Water and the Solid Phase......................................................22

Glacial Deposits ..................................................................................................................................23

Carbonate Bedrock.............................................................................................................................24

Summary and Conclusions.........................................................................................................................25

References Cited..........................................................................................................................................26

Appendix 1. Core log description for site 1, glacial deposits and bedrock....................................... 30

Appendix 2. Core log description for site 2............................................................................................. 65

Appendix 3. Bulk elemental composition of solid phase samples, sites 1 and 2 ..............................38

Appendix 4. Mineralogical description of seven solid-phase samples............................................. 50

Appendix 5. Results of inverse mass-balance modeling ......................................................................53

Figures

1. Map showing location of study sites in northern Preble County, Ohio ..................................3

2. Simplified stratigraphic column, site 1 in northern Preble County, Ohio ................................9

3. Simplified stratigraphic column, site 2 in northern Preble County, Ohio ..............................11

4. Graphs showing solid-phase concentrations of arsenic, iron, sufur, and organic 

carbon at sites 1 and 2 in nothern Preble County, Ohio .......................................................13 

5–9. Micrographs of selected samples from— 

5. Horizon 1A ............................................................................................................................14

6. Horizon 1B ............................................................................................................................15

7. Unconsolidated bedrock zone at site 1 .............................................................................16

8. Horizon 2B ............................................................................................................................17

9. Horizon 2C...............................................................................................................................17
iv

10. Graphs showing concentrations of dissolved arsenic, iron, sulfate, sulfide and 

organic carbon at sites 1 and 2 in nothern Preble County, Ohio........................................21

11. Graph showing relation between arsenic concentrations in the solid phase and 

ground water ..............................................................................................................................22

Tables

1. Arsenic concentrations for selected geologic materials...................................................... 4

2. Simplified conceptual model of the interaction between arsenic-bearing minerals 

and ground water under different redox conditions ..............................................................5

3. Characteristics of sampled wells .................................................................................................6

4. Threshold concentrations of water-quality constituents for assessing redox 

processes.......................................................................................................................................7

5. Arsenic concentrations in solid-phase samples, northern Preble County, Ohio ...............12

6. Selected water-quality constituents and properties from six horizons ...............................19

Conversion Factors

Multiply By To obtain

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L)

Concentrations of chemical constituents in solid-phase samples are given in milligrams per 

kilogram (mg/kg), which is equivalent to parts per million (ppm). 
Relation Between Solid Phase and Dissolved Arsenic 

in the Ground-Water System Underlying Northern 

Preble County, Ohio

By Mary Ann Thomas1, Sharon F. Diehl2, Bruce A. Pletsch3, Thomas L. Schumann4, Richard R. Pavey5,

and E. Mac Swinford5

Abstract

The U.S. Geological Survey (USGS), in cooperation 

with the Miami Conservancy District, collected and analyzed 

samples of the aquifer materials and ground water from 

multiple depths at two sites in northern Preble County, Ohio. 

The aquifer materials included glacial deposits and Silurian 

carbonate bedrock. In the study area, elevated arsenic concentrations have been detected in ground water from both types of 

aquifers. 

The aquifer materials were described in terms of the stratigraphy and the bulk elemental composition of 70 samples. In 

addition, six water-producing horizons were selected for more 

detailed study; ground-water quality was analyzed, microanalytical techniques were used to examine thin sections of the 

aquifer materials, and simplified geochemical modeling was 

done to identify plausible reactions between the ground water 

and aquifer materials. 

At both study sites, the highest solid-phase arsenic 

concentrations were from a roughly similar stratigraphic 

position—a transition zone that extends from just above the 

Wisconsinan/Illinoian contact to just below the Pleistocene/

Silurian contact. 

For carbonate bedrock, the solid-phase arsenic concentrations were generally low (<1 to 4 mg/kg (milligrams per 

kilogram)). The one notable exception was a thin horizon 

about 10 feet below the top of bedrock, which had an arsenic 

concentration of 42 mg/kg. This horizon showed some textural 

and compositional evidence of alteration by geothermal fluids. 

Additional study might be warranted to investigate whether 

arsenic concentrations in ground water from carbonate bedrock could be decreased by excluding discrete horizons from 

the open intervals of wells. 

For glacial deposits, solid-phase arsenic concentrations were slightly higher in fine-grained deposits (2 to 20 

mg/kg) than in coarse-grained deposits (2 to 9 mg/kg). In 

ground water, arsenic concentrations ranged from <1 to 51 

μg/L (micrograms per liter); samples from two horizons had 

concentrations greater than the U.S. Environmental Protection 

Agency Maximum Contaminant Level (MCL) of 10 μg/L. 

Dissolved arsenic concentrations appear to be more closely 

related to redox conditions of the ground water than to the 

arsenic content of the aquifer materials. Geochemical modeling and thin-section analysis were generally consistent with 

the idea that arsenic was released to water from iron oxides 

under iron-reducing conditions. In addition, there was some 

evidence in support of the idea that arsenic can be removed 

from ground water by precipitation of sulfide minerals, which 

occurs under sulfate-reducing conditions. At one site, the dissolved arsenic concentrations in two water-bearing horizons 

increased from <1 to 51 μg/L over a depth of 15 feet. The 

large increase might be due to a shift from sulfate-reducing to 

methanogenic conditions; in the absence of sulfate reduction, 

arsenic is not sequestered in sulfide minerals and may accumulate in the ground water.

1

 USGS Ohio Water Science Center, Columbus, Ohio.

2

 USGS Geologic Discipline, Lakewood, Colo.

3

Miami Conservancy District, Dayton, Ohio.

4

Formerly with the USGS Ohio Water Science Center, Columbus, Ohio.

5

Ohio Department of Natural Resources, Division of Geological Survey, 

Columbus, Ohio.
2 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Introduction

Drinking water is the primary source of human exposure 

to arsenic. Long-term exposure to arsenic in drinking water 

has been linked to cancers of the bladder, skin, lungs and prostate; diabetes; cardiovascular disease; neurological dysfunction; and eye disease (National Research Council, 1999, 2001; 

Chen and others, 2007; Benbrahim-Tallaa and others, 2007; 

Lin and others, 2008). Arsenic is a potent endocrine disruptor, which might be why it influences multiple diverse disease 

processes (Davey and others, 2007). 

The U.S. Environmental Protection (USEPA) Maximum 

Contaminant Level (MCL) for arsenic is 10 micrograms per 

liter (μg/L) (U.S. Environmental Protection Agency, 2006). 

The MCL is applicable to public water systems but not to 

domestic wells. Domestic wells are not routinely tested for 

arsenic in most parts of the country, so homeowners may not 

know whether their well water has arsenic concentrations 

greater than the MCL. Moreover, arsenic concentrations in 

ground water have considerable spatial variability and are 

difficult to predict on a well-by-well basis. However, the 

risk of high arsenic concentrations is greater in some areas 

than in others (Smedley and Kinniburgh, 2002). If the most 

susceptible aquifers (or parts of aquifers) could be identified, 

efforts related to monitoring, education, or mitigation could be 

targeted to areas of greatest need. 

In ground water of southwestern Ohio, arsenic concentrations 2 to 5 times the MCL have been reported by the Ohio 

Environmental Protection Agency (Bendula and Khoury, 1998; 

Ohio Environmental Protection Agency, 2000, 2002), the 

Miami Conservancy District (2001, 2004, 2005), and the U.S. 

Geological Survey (Dumouchelle, 1998; Rowe and others, 

2004; Thomas and others, 2005). Elevated arsenic concentrations have been detected at a range of depths in both bedrock 

and glacial aquifers. It is not clear which combinations of 

geologic, hydrologic, or chemical factors are responsible for 

the spotty elevated arsenic concentrations that were detected. 

In 2002, the U.S. Geological Survey (USGS), in cooperation with the Miami Conservancy District, began an 

investigation of arsenic in ground water of the Great Miami 

River Basin in southwest Ohio. The goal was to determine 

which parts of the aquifer system are most (and least) likely 

to produce water with elevated arsenic concentrations. The 

investigation was designed in a stepwise fashion so that results 

from one year’s study guided the design of the next. During 

2002, ground-water samples were analyzed from 29 domestic 

wells in selected areas of Preble, Miami, and Shelby Counties. During 2003, study areas in Preble and Shelby Counties 

were revisited, and ground-water samples from 28 additional 

domestic wells were analyzed. Data from both years were used 

to relate arsenic concentrations in the ground water to redox 

conditions, aquifer type, and geologic setting (Thomas and 

others, 2005). The current study, which began in 2004, focused 

on a smaller geographic area, but it involved more detailed 

analyses of both arsenic in the solid phase—that is, in the 

aquifer materials themselves—and dissolved arsenic. Northern 

Preble County was chosen for study because elevated arsenic 

concentrations were known to exist in glacial deposits and carbonate bedrock at sites near the recharge and discharge areas 

of a single watershed. 

Purpose and Scope 

This report summarizes the findings of the cooperative 

study by the USGS and the Miami Conservancy District, 

which also involved collaborators from the Ohio Department 

of Natural Resources, Division of Geological Survey. The 

study area includes two sites in the Price Creek watershed 

in northern Preble County (fig. 1). In 2004, five monitor 

wells were installed, and cores of the aquifer materials were 

retrieved. The stratigraphy was documented, and 70 solidphase samples were analyzed for bulk elemental composition. 

Samples from selected horizons were analyzed for groundwater chemistry and solid-phase mineralogy. 

The purpose of this report is to (1) document characteristics of solid-phase aquifer materials, including stratigraphy, 

bulk elemental composition, and mineralogy; (2) document 

the ground-water chemistry of six water-producing horizons; 

and (3) relate arsenic concentrations in ground water to solidphase characteristics in order to increase understanding of 

susceptibility of the ground water in the study area to arsenic 

contamination. 

Description of Study Area

The study area is in northern Preble County, Ohio, which 

is part of the Till Plains section of the Central Lowlands Physiographic Province (Fenneman and Johnson, 1946). Landsurface elevations are 1,125 to 1,200 ft, and the water table is 

typically 9 to 60 ft below land surface. Land use is primarily 

agricultural and rural-residential. The area is near the broad 

axis of the Cincinnati Arch, which separates the Illinois and 

Appalachian Basins. 

Pleistocene glacial deposits mantle the bedrock and 

extend to land surface. The glacial deposits are 35 to 120 ft 

thick and are composed predominantly of fine-grained till. 

Coarse-grained sediment is present as layers or lenses within 

the till and as valley-fill deposits. Beneath the glacial deposits 

is the Silurian Lockport Dolomite, which is 30 to 200 ft thick 

and typically vuggy and porous. A relatively shallow buried 

valley cuts across bedrock in the southeastern corner of the 

study area (Ohio Department of Natural Resources, Division of Geological Survey, 2004). The glacial deposits and 

bedrock are hydraulically connected and are considered to be 

part of the same regional aquifer system (Eberts and George, 
Introduction 3

EXPLANATION

 Well locations

Site 1

Site 2

84 ̊ 42’ 84 ̊ 41’ 84 ̊ 40’

39 ̊ 54’

39 ̊ 53’

Base from U.S. Geological Survey, New Madison, 1960, 1:24,000

Photoinspected 1984

Figure 1. Location of study sites in northern Preble County, Ohio.

Preble County

Figure 1. Location of study sites in northern Preble County, Ohio.
4 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

2000). Both units are used as a source of water to domestic 

and public-supply wells. Wells completed in bedrock typically 

produce water from uncased boreholes that start at the top of 

bedrock and extend 30 to 100 ft into the formation. In contrast, 

wells completed in glacial deposits typically produce water 

from well screens less than 10 ft long. 

The study area consists of two sites in the Price Creek 

watershed (fig. 1). Site 1 is near the surface- and ground-water 

divides of the Great Miami River Basin and the surface-water 

divide of the Price Creek watershed and is therefore considered to be a recharge area in relation to regional and local 

ground-water flow systems. At site 1, elevated arsenic concentrations have been detected in water samples from domestic 

wells that tap carbonate bedrock and coarse-grained lenses 

within glacial till (Thomas and others, 2005). Site 2 is 2.4 mi 

southeast of site 1, in the direction of regional ground-water 

flow (Eberts and George, 2000). It is near a small tributary to 

Price Creek and a buried bedrock valley. At site 2, elevated 

arsenic concentrations have been detected in a domestic well 

that taps glacial valley-fill deposits (Thomas and others, 2005). 

Background

For most cases of widespread arsenic contamination 

of ground water, the source of arsenic is naturally occurring 

minerals in the aquifer materials (Welch and others, 2000; 

Smedley and Kinniburgh, 2002). High concentrations of 

arsenic can occur in sulfide minerals, especially pyrite (FeS2), 

and hydrous metal oxides, especially iron oxyhydroxides 

(FeOOH) (table 1). In sulfide minerals, arsenic can substitute 

for sulfur, and this substitution can increase the susceptibility of arsenic-bearing sulfides to weathering and dissolution 

(Savage and others, 2000). In iron oxides, arsenic can be part 

Table 1. Arsenic concentrations for selected geologic materials.

[From Smedley and Kinniburgh (2002) and references therein; ppm, parts per milion (equivalent to 

milligrams per kilogram); --, not reported]

Solid-phase material Average, in ppm Range, in ppm

Sulfide minerals:

 Pyrite -- 100–77,000

 Sphalerite -- 5–17,000

Oxides:

 Fe oxide (Undifferentiated) -- Up to 2,000

 Fe(III) oxyhydroxide -- Up to 76,000

Soils (various) 7.2 <1–55

 Peaty and bog soils 13 2–36

Unconsolidated sediments (various) 3 <1–50

 Alluvial sands (Bangladesh) 2.9 1.0–6.2

 Alluvial mud/clay (Bangladesh) 6.5 2.7–14.7

 Till (British Columbia) 9.2 1.9–170

 Lake sediments (British Columbia) 5.5 0.9–44

Sedimentary rocks -- 5–10

 Limestone/dolomite <3 <1–20

 Sandstone 4 <1–120

 Shale 13 <1–490

 Bituminous shale (Germany) -- 100–900

Igneous rocks 1.5 <1–113

Metamorphic rocks <5 <1–143
Introduction 5

of the mineral structure or sorbed onto the surface. In general, 

fine-grained deposits tend to have higher arsenic contents 

than coarse-grained sediment, owing to higher proportions of 

colloid-size iron oxides, pyrite, and organic matter (Smedley 

and Kinniburgh, 2002). 

In the study area, sulfides and iron oxides are common 

components of the glacial deposits and bedrock (Stout, 1941; 

Gerrard, 1959; Blackman, 1970; Botomon and Stieglitz, 1978; 

core descriptions on file at the Columbus, Ohio, offices of the 

Ohio Department of Natural Resources, Division of Geological Survey). However, not much is known about the concentration, distribution, or residence of arsenic associated with the 

sulfide minerals and iron oxides within aquifer materials of the 

study area. 

Arsenic concentrations in ground water are controlled 

largely by redox processes, pH, and (or) competitive sorption 

with other anions (Smedley and Kinniburgh, 2002). In the 

study area, concentrations of dissolved arsenic are not strongly 

correlated with pH—probably because pH does not vary much, 

owing to buffering by carbonate minerals in aquifer materials. 

However, there is a significant correlation between elevated 

arsenic concentrations and redox conditions, and the predominant mechanism for mobilizing arsenic appears to be the 

release of arsenic from iron oxides under reducing conditions 

(Thomas and others, 2005). The same mechanism has been 

proposed for aquifers in other areas, including other parts of 

Ohio (Matisoff and others, 1982; Bendula and Khoury, 1998; 

Slattery and others, 2000), central Illinois (Kirk and others, 

2004; Kelly and others, 2005), the midwestern United States 

(Welch and others, 2000; Thomas, 2003; Thomas, 2007), and 

Bangladesh (Smedley and Kinniburgh, 2002). 

However, the relation between dissolved arsenic concentrations and redox conditions can be complex (table 2). Under 

oxic conditions, arsenic can be released to ground water by 

dissolution of pyrite and (or) removed from the ground water 

by precipitation of iron oxides. The opposite can occur under 

reducing conditions: arsenic can be released from iron oxides 

under iron-reducing conditions and (or) removed from the 

ground water by precipitation of pyrite under sulfate-reducing 

conditions. 

Changes in redox conditions can cause arsenic to cycle 

back and forth between pyrite and iron oxides. Elevated arsenic concentrations in reducing ground water have been linked 

to a multistep process: (1) Arsenic-bearing pyrite is subjected 

to oxidation, and arsenic released from the pyrite is incorporated into the newly formed iron oxides. (2) A shift from oxic 

to iron-reducing conditions causes the arsenic associated with 

iron oxides to be released to the ground water. Changes in geochemical environments can be the result of fluctuations of sea 

level, cycles of erosion and burial, or land use (Breit and others, 2001). Land-use effects of possible consequence include 

the exposure of geologic materials to oxidizing conditions by 

mining or water extraction, or the creation of anaerobic conditions within shallow aquifers by waste disposal (Smedley and 

Kinniburgh, 2002; Chapelle and others, 2002). 

Table 2. Simplified conceptual model of the interaction between arsenic-bearing minerals and ground water 

under various redox conditions.

[Gray shading indicates that a process is active] 

Redox conditions

Processes that add arsenic to 

the ground water—

dissolution of or desorption 

from:

Processes that remove 

arsenic from the ground 

water—precipitation of or 

sorption to:

Oxidizing → Reducing Sulfide 

minerals

Iron oxyhydroxidesSulfide 

minerals

Iron oxyhydroxides

Oxic

Iron reducing

Sulfate reducing
6 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Methods

Boreholes were drilled to retrieve samples of the aquifer 

materials (solid phase). At site 1, three boreholes were drilled 

by personnel from the USGS Wisconsin Water Science Center. 

A 4 1/4-in. hollow-stem auger was used to drill through the 

glacial material, and split-spoon samples were collected from 

land surface to about 65 ft (Appendix 1A). A 3-in. continuous 

core of bedrock from 73 to 177 ft was retrieved by use of a 

wireline core-barrel system (Appendix 1B). At site 2, drilling was done by a rotosonic rig by personnel from a consulting engineering firm. A 4-in.-diameter continuous core was 

retrieved from land surface to 119 ft (Appendix 2). Cores of 

carbonate bedrock and split-spoon samples of glacial deposits were described in the field by geologists from the Ohio 

Department of Natural Resources, Division of Geological 

Survey. Subsamples of the solid phase were collected approximately every foot. Samples were preserved by air drying, 

and the sample containers were purged with nitrogen gas and 

sealed with tape for storage and shipment. 

In all, 70 solid-phase samples were analyzed for bulk 

composition of 42 major, minor, and trace elements at a 

contract laboratory used by the USGS Geologic Discipline. 

Samples were ground, digested with multiple acids, and 

analyzed by inductively coupled plasma-atomic emission 

spectrometry (ICP-AES) and inductively coupled plasma-mass 

spectrometry (ICP-MS) (Briggs and Meier, 2002). Samples 

also were analyzed for total sulfur and total carbon by use 

of automated analyzers and for carbonate carbon by use of 

coulometric titration. Four replicate solid-phase samples were 

analyzed for bulk elemental composition, and concentrations 

of arsenic, iron, sulfate, and organic carbon were judged to be 

similar to those of the environmental samples. 

The mineralogy of selected horizons was analyzed from 

polished thin sections. Transmitted and reflected light microscopy were used to make mineral point counts. In addition, 

polished thin sections of core samples were examined with a 

JOEL 5800LV scanning electron microscope (SEM) equipped 

with an Oxford ISIS energy-dispersive X-ray (EDS) detector 

to determine basic mineralogy, identify textural features, and 

obtain qualitative to semiquantitative analyses of trace- and 

minor-element content and distribution in minerals, especially 

pyrite. Element distribution maps of the thin sections, which 

show the spatial distribution and intensity of individual elements, were generated from both the SEM and a JEOL JXA8900 electron probe microanalyzer (EPMA). Warm colors (red 

to yellow) in the element distribution maps indicate relative 

high concentrations of an element, and cool colors (green to 

blue) indicate lower concentrations. The SEM and EPMA both 

have excellent spatial resolution (better than a few micrometers), but differ in terms of detection limits for arsenic and 

other heavy trace elements, such as nickel; the EPMA has a 

detection limit of 500–1,000 ppm, and the SEM has a detection limit of 1,000 ppm. 

Six water-producing horizons were selected for further 

analysis on the basis of visual inspection of the solid-phase 

cores and split-spoon samples. Water samples from these six 

horizons were collected from five 2-in. monitor wells installed 

for this study and one domestic well installed in 1977 (table 3); 

sampling the domestic well was not optimal but was considered acceptable because the well was within 150 ft of the coresample collection site. 

Table 3. Characteristics of sampled wells. 

 [BLS, below land surface; NA, not available]

Well identifier Horizon; aquifer 

type 

Screened 

interval, 

in feet BLS

Water level, 

in feet BLS

Date water level 

measured

Well type; 

installation

method

Site 1, land surface altitude = 1,147 feet

395430084415400 1A; glacial 30–35 24.29 09-02-2004 Monitor; auger

395429084415500 1B; glacial 47–52 25.34 09-01-2004 Monitor; auger

395429084415600 1C; carbonate 83–88 25.79 09-02-2004 Monitor; rotary

Site 2, land-surface altitude = 1,132 feet

395236084403600 2A; glacial 32–37 16.64 08-31-2004 Monitor; rotosonic

395236084403601 2B; glacial 75–80 17.48 08-31-2004 Monitor; rotosonic

395237084403600 2C; glacial 90–931 17.18 09-01-2004 Domestic; NA

1

 Estimate based on driller’s log for domestic well.
Methods 7

Ground-water samples were collected in late August and 

early September 2004. Procedures for well purging, sample 

collection and preservation, and quality assurance were consistent with standard protocols of the USGS (U.S. Geological 

Survey, variously dated). Field determinations were made for 

pH, dissolved oxygen, specific conductance, and temperature 

(with a multiparameter instrument and a flowthrough chamber), alkalinity (by titration), turbidity (with a turbidimeter), 

and sulfide and ferrous iron (with a field spectrophotometer). 

Samples were sent to the USGS National Water-Quality Laboratory for analysis of major ions, trace elements, nutrients, 

dissolved organic carbon, and arsenic speciation (Fishman, 

1993; Brenton and Arnette, 1993; Garbarino, 1999; Garbarino 

and others, 2002). The water-quality data were published in 

the USGS annual water-data report for Ohio (Shindel and others, 2005).

Four quality-control ground-water samples were collected and analyzed. An equipment blank was collected just 

before sampling and was analyzed for major ions, nutrients, 

and trace elements. During sampling, a field blank and replicate were analyzed for total arsenic. A field spike and replicate 

were analyzed for arsenic species. None of the blanks showed 

any indication of contamination. Replicates were within 

acceptable limits (1–6 percent). Field-spike results showed 

recoveries of 80 to 83 percent for arsenic species, which was 

considered acceptable. 

Redox processes were assessed by means of a framework 

of threshold concentrations of five commonly measured waterquality constituents considered to be redox indicator species—

dissolved oxygen, nitrate, manganese, iron, and sulfate (table 

4) (Paschke, 2007; McMahon and Chapelle, 2008). In addition, for samples classified as “iron or sulfate reducing,” concentration ratios of dissolved ferrous iron to sulfide were used 

to estimate the relative predominance of iron reduction and 

sulfate reduction. Fe/S mass ratios less than 0.3 indicate that 

sulfate reduction is predominant, whereas Fe/S ratios greater 

than 10 indicate that (1) iron reduction is predominant or (2) 

conditions have shifted from iron reduction to sulfate reduction even though iron has not been removed from solution 

(Chapelle and others, in press).

Chemical-equilibrium modeling was used to test hypotheses about interactions between the ground water and the solid 

phase. Speciation and mass-balance modeling were done by 

use of PHREEQC version 2 (Parkhurst and Appelo, 1999). 

Speciation modeling requires input of ground-water composition, including temperature, pH, concentrations of elements 

and (or) element valence states, and a redox indicator. The 

model calculates the distribution of aqueous species and mineral saturation indices. Saturation indices (SI) are used to indicate the saturation state of a ground-water sample with respect 

to a particular set of minerals. When the ion activity product 

(IAP) of a ground-water sample is equal to the solubility product (Ksp) of a given mineral at a given temperature, SI equals 

zero, meaning that the water is in thermodynamic equilibrium 

with respect to the mineral. If SI is greater than zero, the mineral might precipitate, but it cannot dissolve. If SI is less than 

zero, the mineral might dissolve but it cannot precipitate. 

Mass-balance modeling was done by use of the inverse 

modeling module of PHREEQC, version 2. Input to the model 

includes (1) the water chemistry of two or more ground-water 

samples assumed to be from the same flow path and (2) the presumed composition of the solid phase and gases. Results from 

the model show the mass transfer among solid and gas reactants 

that can account for the observed difference in ground-water 

composition. Positive mass transfers indicate mineral dissolution, and negative mass transfers indicate mineral precipitation. 

Table 4. Threshold concentrations of water-quality constituents for assessing redox processes. 

[Modified from Paschke, 2007, and McMahon and Chapelle, 2008; <, less than; >, greater than or equal to; --, constituent concentration not specified]

Redox process

Concentration, in milligrams per liter

Dissolved oxygen (O2

)

Nitrate

(NO3

-

-N)

Manganese

(Mn2+) 

Iron 

(Fe2+)

Sulfate

(SO4

2-)

Oxygen reduction >0.5 -- <0.5 <0.1 --

Nitrate reduction <0.5 >0.5 <0.5 <0.1 --

Manganese reduction <0.5 <0.5 >0.5 <0.1 --

Iron or sulfate reduction 

(Fe(III)/SO4

2-)

<0.5 <0.5 -- >0.1 >0.5

Methanogenesis <0.5 <0.5 -- >0.1 <0.5

Mixed Criteria for more than one redox processes are met
8 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Solid-Phase Characteristics

The term “solid phase” refers to the aquifer materials, either unconsolidated glacial 

deposits or bedrock. Characteristics of the solid phase were described at several scales: 

visual descriptions of cores, the elemental composition of ground-up samples, and microscopic analysis of polished thin sections. Figures in this report show data from a limited 

depth interval (20 to 120 ft) to facilitate visual comparisons between the two study sites. 

However, the appendixes include data from the entire range of depths sampled. 

Stratigraphy

Simplified stratigraphic columns for sites 1 and 2 are presented in figures 2 and 3, 

respectively. The figures are based on detailed core descriptions (Appendixes 1 and 2), 

supplemented by drillers’ notes and core photographs. 

Site 1

Glacial deposits at site 1 were about 68 ft thick. Deposits to a depth of 57.5 ft were 

silty, sandy till with interbeds of sand and (or) gravel. The sediments were calcareous and 

were predominantly gray, grayish-brown, or brownish-gray. The coarse-grained deposits 

were predominantly carbonate rock fragments, along with a complex mix of igneous and 

sedimentary rock fragments and quartz and feldspar grains. 

Deposits from 57.5 to 59 ft were fine-grained, noncalcareous, and yellow- or orangebrown with some gray mottles. This is a probable paleosol at the contact between Wisconsinan and Illinoian glacial deposits. The contact between glacial deposits and bedrock 

was estimated to be at about 68 ft. There was some evidence that this zone was enriched in 

organic carbon; the last sample of glacial material (from 67 ft) was dark gray, and the first 

piece of bedrock (from 73 ft) had petroleum tar stains. 

Bedrock was cored from 73 ft to 177 ft, which accounts for almost the entire section 

of the Lockport Dolomite (73–156 ft) and Laurel Dolomite (156–177 ft) (Slucher and others, 2006). The Lockport Dolomite was pale gray to pale yellow dolomite with vuggy or 

intercrystalline porosity and fine to coarse texture. Also noted were argillaceous laminae 

and high-angle fractures. The Laurel Dolomite was predominantly limestone with dolomite with chert. At 77 ft was a 6-in. zone of unconsolidated material composed of clay and 

clasts of dolomite. The deposits appeared to be cavity fill because competent bedrock was 

above and below the unconsolidated material. 

Report coauthors Tom Schumann (center) and Bruce Pletsch (right) cut rock cores while 

USGS hydrologic technician Brent Olson (left) looks on. (Phototograph by Mary Ann Thomas, 

U.S. Geolgocal Survey.)
Solid-Phase Characteristics 9

 

Yellow-orange brown, gray mottles 

Sandy, silty till with clay 

Gray 

Gray brown

Brown Dry 

Clayey silt till 

Horizon 1B 

Horizon 1C 

Mottled brown and gray 

SITE 1

 Stratigraphy

 Silt, till or clay Clay and carbonate fragments

 

 Sand or gravel No sample recovered

 Carbonate bedrock 

Texture Color Other characteristics Interpreted age

120 

DEPTH, IN FEET BELOW 

LAND SURFACE 

20 

40 

80 

100 

60 

90 

30 

110 

70 

Silty, sandy till 

with interbeds of 

silt, sand, or gravel 

Gray brown 

Noncalcareous 

 Wisconsinan 

Illinoian 

Silurian 

Calcareous 

Calcareous 

Tar 

Gray 

Carbonate bedrock

Carbonate bedrock 

Clay, carbonate fragments 

Light gray to pale yellow 

Light gray with black

Dark olive gray 

Light gray to pale yellow 

Light gray 

Silty clay Dark gray 

Horizon 1A 

50 

 EXPLANATION

Figure 2. Simplified stratigraphic column, site 1 in northern Preble County, Ohio.
10 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Site 2

At site 2, the glacial deposits were 110 ft thick. From 20 to 60 ft, the glacial deposits 

were predominantly silty, sandy till with interbeds of sand and gravel. The sediments were 

calcareous and were predominantly gray, brown, or grayish-brown; coarse-grained deposits 

were predominantly carbonate bedrock fragments. From 60 to about 80 ft was well-sorted 

sand, presumably valley fill. A sample from 77 ft had a higher proportion of quartz and 

feldspar grains than carbonate rock fragments. From about 80 to 90 ft, the deposits were 

clayey silt that is presumed to be lacustrine. 

From about 90 to 92 ft, the glacial deposits were organic-rich silt and gravel, which is 

a probable paleosol near the boundary between Wisconsinan and Illinoian deposits. Hard, 

dry, dark reddish-brown sediment at 103 to 107 ft was interpreted as a second Illinoian 

paleosol. Altered bedrock was at 107 to 110 ft, and competent Lockport Dolomite bedrock 

was cored from 110 to 120 ft. 

The resident dog at site 1 scans split-spoon samples of glacial deposits that have been boxed for 

shipment to the Ohio Department of Natural Resources, Division of Geological Survey’s Horace 

R. Collins Laboratory near Columbus for archiving. (Photo by Mary Ann Thomas, U.S. Geological 

Survey.)
Solid-Phase Characteristics 11

Figure 3. Simplified stratigraphic column, site 2 in northern Preble County, Ohio.

 Stratigraphy

 Silt, till or clay Silt and gravel 

 

 Sand or gravel Fine sand, silt, clay, and carbonate fragments 

 Carbonate bedrock No sample recovered 

 

50 

SITE 2

 Texture Color Other characteristics Interpreted age

DEPTH, IN FT BELOW 

LAND SURFACE 

20 

40 

80 

100 

120 

60 

90 

30 

110 

70 

Silty sandy till 

with interbeds of 

silt, sand, or gravel 

Weakly calcareous 

Mottled dark gray and brown 

Wisconsinan 

Sulfur odor 

Organic odor 

Gray 

Carbonate bedrock 

Brown or gray brown 

Silt and gravel 

Sand, well sorted 

Fine sand, silt, clay, 

and carbonate fragments 

 Clayey silt 

Clayey silt till 

Illinoian 

Silurian 

Calcareous 

Brown 

Brown or gray brown 

Dark brown with black 

Tan 

Dark reddish brown

Calcareous 

Noncalcareous 

Dry

Plastic

Dry

Light gray to pale yellow 

 Calcareous 

Very calcareous 

Horizon 2A 

Horizon 2B 

Horizon 2C 

 EXPLANATION
12 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Bulk Elemental Composition

Samples of the solid-phase materials were ground, treated 

with acid, and analyzed for bulk concentrations of 42 inorganic constituents and organic carbon (Appendix 3). Arsenic 

concentrations ranged from less than 1 to 42 mg/kg (table 5). 

The median arsenic concentration for glacial deposits (6 mg/

kg) was higher than for bedrock (<l mg/kg). For glacial deposits, the median arsenic concentration of fine-grained material 

(8.5 mg/kg) was higher than for coarse-grained (4.5 mg/kg). 

In general, arsenic concentrations from the study area were 

within the range of typical values for unconsolidated deposits 

and limestone/dolomite listed in table 1. 

At both sites, the highest solid-phase arsenic concentrations were from a roughly similar stratigraphic position, a 

transition zone that extends from just above the Wisconsinan/

Illinoian contact to just below the Pleistocene/Silurian contact 

(fig. 4). Also, at both sites, the concentrations of arsenic and 

iron show similar patterns of variation. This is consistent with 

the idea that the major sources of arsenic are pyrite and iron 

oxides, both of which contain iron. Comparison of depth relations with sulfur and organic carbon yield additional qualitative clues as to the mineral source of arsenic. 

Site 1 

From site 1, 16 samples of glacial deposits were analyzed 

for bulk composition (Appendix 3A). Wisconsinan deposits 

had arsenic concentrations of 2 to 6 mg/kg. Illinoian deposits, 

all of which were fine-grained, had arsenic concentrations 

of 9 to 20 mg/kg. For glacial deposits, the highest arsenic 

concentrations were from the leached paleosol just below the 

Wisconsinan/Illinoian contact. In this horizon, the concentration of iron was relatively high and concentrations of sulfur 

and organic carbon were relatively low, indicating that arsenic 

might be associated with iron oxides within this weathered 

horizon. 

Twenty samples of carbonate bedrock were analyzed 

between 73 and 177 ft (Appendix 3A). Seventy-five percent 

of samples had arsenic concentrations less than 1 mg/kg, and 

95 percent had concentrations less than or equal to 4 mg/kg. 

Arsenic concentrations in carbonate bedrock were generally 

lower than in glacial deposits, as were concentrations of iron, 

sulfur, and organic carbon. One very high concentration of 

arsenic was detected in the unconsolidated horizon within bedrock at 77 ft. This zone had extreme outlier concentrations of 

arsenic (42 mg/kg), as well as zinc (571 mg/kg), lead (47 mg/

kg), nickel (64 mg/kg), and strontium (657 mg/kg). This zone 

is hereafter referred to as the “unconsolidated bedrock zone.”

Site 2 

From site 2, 26 samples of glacial deposits were analyzed 

for bulk composition (Appendix 3B). Arsenic concentrations 

were 4 to 14 mg/kg in Wisconsinan deposits and 5 to 11 mg/

kg in Illinoian deposits. At this site, the maximum arsenic 

concentration was detected in fine-grained glacial deposits just 

above the Wisconsinan/Illinoian contact. This horizon also had 

relatively high concentrations of sulfur and organic carbon. 

The second highest arsenic concentration was just above the 

Illinoian/Silurian contact, in a leached paleosol. High concentrations of iron and low concentrations of sulfur and organic 

carbon suggest that this might be a weathered zone in which 

arsenic is associated with iron oxides. Four samples of carbonate bedrock were analyzed between 110 and 120 ft, and all had 

arsenic concentrations less than 1 mg/kg. 

At both sites, the highest solid-phase arsenic concentrations were from a roughly similar stratigraphic position, a transition zone that extends from just above the Wisconsinan/Illinoian contact to just below the Pleistocene/Silurian contact. At 

both sites, the transition zone included (1) a leached paleosol 

where arsenic might be associated with iron oxides and (2) a 

horizon with relatively high concentrations of organic carbon. 

Table 5. Arsenic concentrations in solid-phase samples, northern Preble County, Ohio. 

[mg/kg, milligrams per kilogram (equivalent to parts per million)]

Type of solid-phase material Number of 

samples

Solid-phase arsenic concentration 

(mg/kg)

Median Range

Glacial deposits, all samples 42 6 2–20

Predominantly coarse grained 20 4.5 2–9

Predominantly fine grained 22 8.5 2–20

Lockport Dolomite, all samples 24 <1 <1–42

Unconsolidated bedrock zone, site 1 1 - 42

Excluding unconsolidated bedrock zone, site 1 23 <1 <1–4
Solid-Phase Characteristics 13 Figure 4. Solid-phase concentrations of arsenic, iron, sulfur, and organic carbon at sites 1 and 2 in northern Preble County, Ohio.
14 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Red, yellow, and yellow-green colors 

indicate relatively high concentration of 

an element; blue colors indicate lower

concentration.

A B

C

D E

Coarse-grained 

pyrite

Iron oxide 

rims

Calcite

Pyrite Pyrite

Calcite

Pyrite Pyrite

Calcite

Pyrite Pyrite

Calcite

Iron oxide 

rims

Arsenic-bearing 

pyrite

Figure 5. Micrograph of a sample from horizon 1A (small scale bars in lower left corners of images 

represent 20 micrometers). A, Backscatter image of a calcite clast with partially dissolved pyrite. Remant 

iron-oxide rims outline the former extent of the pyrite grains. B, Element distribution map of calcium 

showing that pyrite occurs within a carbonate clast. C, Element distribution map of sulfur showing pyrite 

distribution. D, Element distribution map of iron showing pyrite and remnant iron-oxide rims. E, Element 

distribution map of arsenic showing that arsenic is not evenly distributed; higher concentrations are in 

core areas of pyrite grains. Arsenic was also detected in the iron-oxide rims.
Solid-Phase Characteristics 15

Residence of Arsenic in Sulfide Minerals

Microanalytical techniques were used to examine the 

mineralogy of seven samples—six samples from the waterproducing horizons and one sample from the unconsolidated 

bedrock zone (Appendix 4). The emphasis was on examining 

the residence of arsenic in sulfide minerals. There were several 

morphological forms of sulfide minerals, indicating multiple 

generations of formation. The sulfide minerals also displayed 

multiple textures, indicating varied weathering intensities. 

The most abundant sulfide mineral was framboidal pyrite, a 

spheroidal form composed of aggregates of microcrystalline 

pyrite. Framboidal pyrite was found in every thin section, but 

arsenic was not detected in framboidal pyrite at concentrations 

above the detection limit of the SEM. However, other types of 

sulfide minerals had arsenic concentrations that ranged from 

0.3 to 4.0 weight percent. 

A sample from horizon 1A was examined with the SEM 

and EPMA. The sample was composed primarily of carbonate fragments, along with igneous rock fragments and liberated grains of quartz, feldspar, and pyroxene (Appendix 4). 

A clast of micritic carbonate rock contained coarse-grained 

pyrite in which arsenic was detected at a concentration of up 

to 2.6 weight percent (fig. 5, facing page). Pyrite within the 

rock fragment showed signs of weathering; the arsenic-bearing 

pyrite was partially dissolved, and the former boundaries of 

the pyrite grains were outlined by skeletal iron oxides. The 

iron-oxide rims also contained arsenic (although it is difficult 

to see them in figure 5E) and showed evidence of partial dissolution. 

A sample from horizon 1B was examined with the SEM 

and EPMA. The sample was composed mainly of carbonate 

rock fragments, along with igneous and sedimentary rock fragments and liberated grains of quartz and feldspar (Appendix 

4). A clast of quartz siltstone included two forms of arsenicbearing sulfide minerals: (1) coarsely crystalline pyrite with 

an arsenic concentration of up to 0.4 weight percent and 

(2) a very fine-grained nickel-arsenic sulfide mineral, possibly 

gersdorffite (fig. 6). Sphalerite, a zinc sulfide mineral, also 

was noted. Iron oxides were not detected in association with 

the arsenic-bearing sulfide minerals. 

A sample of the Lockport Dolomite from horizon 1C was 

examined with the SEM. The sample contained both ironbearing and nonferroan dolomite (Appendix 4). Pyrite was 

found as microcrystalline cubes and as spheroidal framboids. 

It appears that iron oxides replaced a coarsely crystalline 

sulfide mineral within the dolomite. Arsenic was not detected 

at the limits of the SEM. 

Pyrite

Quartz

A

B

Nickel, arsenic

sulfides

Arsenic-rich

 core of pyrite

10 micrometers

(10 micrometers)

Figure 6. Micrograph of a sample from horizon 1B. A, Coarse-grained pyrite in a clast of quartz siltstone. B, Element distribution map 

of arsenic showing two forms of arsenic-bearing sulfide minerals: coarse-grained pyrite and fine-grained arsenic-nickel sulfides. Reds, 

yellows, and greens indicate relatively high concentration of arsenic, and blues indicate lower concentration.
16 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

A sample from the unconsolidated bedrock zone at 

77 ft at site 1 was examined with the SEM. The sample was 

composed of dolomite and illitic clay, with a minor amount of 

igneous rock fragments (Appendix 4). The dolomite rhombs 

were deeply embayed and etched, and they floated in a clay 

matrix (fig. 7). Arsenic was detected at a concentration of up 

to 4 weight percent in a nickel-arsenic sulfide mineral (possibly gersdorffite) that occurs exclusively within the clay. 

Nickel is concentrated in the coarsely crystalline core, whereas 

arsenic is more evenly distributed. 

A sample from horizon 2A was examined with the SEM. 

The sample was composed mainly of carbonate rock fragments along with sedimentary and igneous rock fragments and 

liberated grains of quartz and feldspar (Appendix 4). Framboidal pyrite was abundant in the thin section, but arsenic was not 

detected at the limits of the SEM. Skeletal iron oxides were 

present in the dolomite fragments but not in association with 

remnants of arsenic-bearing pyrite, as in horizon 1A. 

A thin section from horizon 2B was examined with the 

SEM and EPMA. The sample was mainly composed of liberated grains of quartz and feldspar along with igneous, carbonate, and other sedimentary rock fragments (Appendix 4). 

Figure 8 shows a shale fragment in which framboidal pyrite 

appears to have replaced a shell or bone fragment. Arsenic was 

not detected in the framboidal pyrite, but it was detected in a 

second generation of coarse-grained pyrite that coats the framboidal pyrite. Arsenic concentrations in the coarse-grained 

pyrite were up to 1 weight percent. 

A sample from horizon 2C was examined with the 

SEM. The sample was very poorly sorted, with pebble-sized 

quartz, feldspar, and rounded carbonate clasts in a matrix of 

micritic calcite and silt-sized quartz grains (Appendix 4). The 

sample also had large fragments of cellular organic material that had been replaced by massive arsenic-bearing pyrite 

and iron oxides (fig. 9). The arsenic content of the pyrite was 

0.3 weight percent, and pyrite made up 4 percent of the total 

sample. An element-distribution map shows that arsenic is 

evenly distributed throughout the massive pyrite.

Figure 7. Micrograph of a sample from the unconsolidated bedrock zone at site 1. A, Etched dolomite rhombs in a clay matrix. 

B, Enlarged view of arsenic- and nickel-bearing sulfides in the clay matrix.

B

A

Dolomite

Nickel, arsenic,

iron sulfides

Clay

Clay

Clay

Nickel, arsenic sulfides

with alteration rinds

B

100 micrometers 25 micrometers
Solid-Phase Characteristics 17

A B

C D

Quartz Quartz

Quartz

Quartz

Clay

(1) Framboidal

pyrite

(2) Coarsegrained

pyrite

coating

framboids (1) Framboidal

pyrite

(2) Coarsegrained

pyrite

coating

framboids

Second stage of

pyrite precipitation

is arsenic-rich

Round, dark forms 

are an earlier generation 

of framboidal pyrite

Quartz

Quartz

Quartz

Pyrite

Pyrite

Figure 8. Micrograph of a sample from horizon 2B (small scale bars in lower left corners of images represent 

10 micrometers). A, Backscatter image of a shaly clast with quartz, clay, framboidal pyrite, and shell or bone 

material replaced by pyrite. An early generation of (1) framboidal pyrite is coated by (2) a coarse-grained pyrite. 

B, Element distribution map of sulfur showing different generations of pyrite. C, Element distribution map of 

aluminum showing clay distributions in shaly clast. D, Element distribution map of arsenic showing that framboidal 

pyrite does not contain arsenic, whereas the second generation of coarse-grained pyrite is arsenic-rich.

100 micrometers 20 micrometers

A B

Figure 9. Micrograph of a sample from horizon 2C. A, Element distribution map of arsenic showing organic 

material replaced by pyrite; arsenic is evenly distributed throughout the pyrite. Reds, yellows, and greens indicate 

relatively high concentration of arsenic, and blues indicate lower concentration. Black areas are dolomite rhombs. 

B, Enlarged area of organic material replaced by pyrite. Note that the cellular structure of the organic matter is 

retained.
18 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Ground-Water Quality 

Ground-water samples from six horizons were analyzed for pH, alkalinity, specific 

conductance, dissolved oxygen (DO), dissolved organic carbon (DOC), major ions, nutrients, and trace elements. Selected water-quality constituents and properties are presented in 

table 6, and the entire dataset is available in Shindel and others (2005). Redox conditions 

were assessed using threshold concentrations of DO, nitrate, manganese, iron, and sulfate 

(table 4) (Paschke, 2007; McMahon and Chapelle, 2008). In addition, for samples classified as “iron or sulfate reducing,” mass ratios of ferrous iron to sulfide (Fe/S) were used to 

assess which of the two redox processes is predominant (Chapelle and others, in press). 

Two of the six ground-water samples had arsenic concentrations greater than the 

USEPA MCL of 10 μg/L—horizon 1A had a dissolved arsenic concentration of 13 μg/L, 

and horizon 2C had a dissolved arsenic concentration of 51 μg/L. The other four samples 

had arsenic concentrations of 0.2 to 6 μg/L. Arsenite and arsenate species were present 

in all six water samples. Arsenite, the reduced form, is more mobile in ground water and 

considered to be more toxic to humans. Arsenite was the predominant species in the two 

horizons with dissolved arsenic concentrations above the MCL, 1A and 2C. For the other 

four horizons, concentrations of arsenite were less than, or similar to, concentrations of 

arsenate (table 6). 

Dissolved arsenic concentrations are not known for some of the stratigraphic intervals with the highest solid-phase arsenic concentrations. For glacial deposits, the highest 

solid-phase arsenic concentrations were in fine-grained deposits and therefore not representative of aquifers in the study area. The horizon with the maximum solid-phase arsenic 

concentration—the unconsolidated bedrock zone—could have been included as part of a 

water-producing zone, but the solid-phase arsenic concentration was not known to be high 

at the time of monitor-well installation. 

At each site, dissolved arsenic concentrations varied with depth, as did concentrations 

of constituents related to redox conditions: iron, sulfate, sulfide, and DOC (fig. 10).

A mobile-laboratory setup similar to the one pictured here was used for water-quality sampling 

and sample processing at sites 1 and 2. Interior photo shows extensive sealing of equipment to 

prevent sample contamination. (Photos by Mary Ann Thomas, U.S. Geological Survey.)
Ground-Water Quality 19

Table 6. Selected water-quality constituents and properties from six horizons. 

[BLS, below land surface; fltrd, filtered; unfltrd, unfiltered; mg/L, milligrams per liter; μg/L, micrograms per liter; NTU, nephelometric turbidity units]

Horizon Well 

identifier

Well

depth

(feet BLS)

Turbidity

(NTU)

Dissolved

oxygen

(mg/L)

pH

Alkalinity,

fltrd,

(mg/L as 

CaCO3

)

1A 395430084415400 35 150 0.7 7.2 403

1B 395429084415500 52 3.0 .1 7.2 398

1C 395429084415600 88 2.5 .1 7.4 359

2A 395236084403600 37 2.4 .1 7.4 373

2B 395236084403601 80 2.7 .1 7.2 375

2C 395237084403600 93 6.8 .1 7.4 338

Horizon Chloride

(mg/L)

Sulfate,

fltrd

(mg/L)

Sulfide,

unfltrd

(mg/L)

Ammonia,

fltrd

(mg/L as 

N)

Nitrate +

nitrite, 

fltrd (mg/L 

as N)

Orthophosphorus,

fltrd

(mg/L as P)

Organic 

carbon,

fltrd 

(mg/L)

1A 7.4 249 0.099 .52 <0.06 <0.006 1.5

1B 4.5 164 .015 .74 <.06 .006 1.4

1C 21 75 .007 .38 .11 <.006 1.1

2A 67 72 .002 .96 <.06 <.006 1.2

2B 9.1 34 .032 1.36 <.06 .014 2.6

2C 3.7 .1 .016 2.17 <.06 .032 3.6

Horizon

Arsenate,

fltrd 

(μg/L)

Arsenic,

fltrd 

(μg/L)

Arsenite,

fltrd

(μg/L)

Iron,

fltrd

(μg/L)

Manganese,

fltrd

(μg/L)

Redox 

designation

Mass ratio 

of iron to

sulfide

1A 5.9 12.9 8.1 1,560 92.1 Fe/SO4

 reducing or 

mixed

16

1B 2.4 4.6 1.7 2,810 61.6 Fe/SO4

 reducing 187

1C 1.3 1.8 <1.0 4,460 59.4 Fe/SO4

 reducing 637

2A 3.2 6.1 2.8 2,450 24.6 Fe/SO4

 reducing 1,225

2B <1.2 .2 <1.0 3,800 152 Fe/SO4

 reducing 119

2C 8.6 51.1 40.6 1,390 44.5 Methanogenic 87
20 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Site 1

At site 1, dissolved arsenic concentrations decreased progressively with depth (fig. 

10). In horizon 1A (glacial deposits at 30–35 ft), the arsenic concentration was 13 μg/L. In 

horizon 1B (glacial deposits at 47–52 ft), the arsenic concentration was 5 μg/L. In horizon 

1C (carbonate bedrock at 83–88 ft), the arsenic concentration was 2 μg/L. 

For the two deeper horizons—1B and 1C—the redox condition was estimated to be 

predominantly iron reducing, with sulfate reduction also indicated. For horizon 1A, the 

redox designation was similar, except that the DO concentration was just above the threshold indicative of oxygen reduction. Horizon 1A was 10 to 15 ft below the water table in a 

recharge area, so it is possible that (1) horizon 1A spans multiple redox zones, (2) pumping 

caused drawdown of oxygenated water through fractures in the overlying glacial till, or (3) 

a small amount of oxygen was introduced during the sampling process. 

Site 2

At site 2, dissolved arsenic concentrations and redox conditions were more varied 

than at site 1 (fig. 10). In horizon 2A (glacial deposits at 32–37 ft), the arsenic concentration was 6 μg/L, and in horizon 2B (glacial deposits at 75–80 ft), the arsenic concentration 

was 0.2 μg/L. In both horizons, the predominant redox process was iron reduction, with 

sulfate reduction also indicated. However, sulfate reduction appears to be more prevalent 

in the deeper horizon (2B) because the water had a strong rotten-egg odor and the concentration of sulfide was high relative to iron. In horizon 2C (organic-rich glacial deposits at 

90–93 ft), the dissolved arsenic concentration was 51 μg/L, 5 times the MCL. The redox 

condition was methanogenic because the sulfate concentration was less than 0.5 mg/L, the 

approximate threshold below which sulfate reduction is replaced by methanogenesis as the 

predominant redox process (McMahon and Chapelle, 2008). 

At site 2, redox conditions appeared to be progressively more reducing with depth, 

which is consistent with the increase in DOC concentrations with depth (fig. 10). However, 

the relation between depth and dissolved arsenic was more erratic: arsenic concentrations 

showed large shifts, especially between horizons 2B and 2C, where dissolved arsenic 

increased from 0.2 to 51 μg/L over a depth of 15 ft and a distance of 150 ft. 

Coauthors Bruce Pletsch and Tom Schumann at work: Bruce (at left) titrates a water-quality 

subsample for alkalinity, while Tom (right) gathers information on a sampled well. (Photographs 

by the two coauthors.)
Ground-Water Quality 21 Figure 10. Concentrations of dissolved arsenic, iron, sulfate and sulfide, and organic carbon at sites 1 and 2 in northern Preble County, Ohio.
22 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Relation Between Arsenic in Ground 

Water and the Solid Phase 

In the study area, arsenic concentrations in the ground 

water are not simply a function of arsenic concentrations 

of the aquifer materials (fig. 11). There appears to be some 

relation between the two phases because the horizon with 

the highest concentration of solid-phase arsenic also had the 

highest dissolved arsenic (2C), and the horizon with the lowest 

solid-phase arsenic concentration had one of the lowest concentrations of dissolved arsenic (1C). However, for two pairs 

of horizons (1A and 1B; 2A and 2B), arsenic concentrations in 

the ground water were inversely related to those of the solid 

phase. 

In this section of the report, ground water and solidphase characteristics of each horizon are examined in light of 

Figure 11. Relation between arsenic concentrations in the solid phase and ground water in northern 

Preble County, Ohio. (DOC, dissolved organic carbon.)

hypotheses for arsenic mobilization. Simplified geochemical modeling was used to further assess the hypotheses. Two 

types of geochemical models were run with PHREEQC 

(Parkhurst and Appelo, 1999). Speciation modeling calculates 

the saturation state of ground water with respect to a particular set of minerals. Inverse mass-balance modeling identifies 

solid-water reactions that can account for changes in the water 

composition between two or more samples along a flow path. 

The geochemical modeling approach was simplified in that the 

focus was not directly on arsenic but on the two most common 

arsenic-bearing minerals: sulfides and iron oxides. The results 

of chemical equilibrium modeling are hypothetical because 

(1) the assumption of chemical equilibrium may not be met, 

(2) one of more of the presumed solid-phase reactants may not 

be present, or (3) the kinetics of reactions may not be favorable. In addition, the mineral stoichiometry for arsenic, as well 

as other trace elements, is often not known. 
Relation Between Arsenic in Ground Water and the Solid Phase 23

For this study, inverse mass-balance models were run 

for pairs of samples from glacial deposits that appear to be 

hydraulically connected on the basis of water levels in monitor wells (table 3). The selection of the solid-phase reactants 

was guided by the mineralogical descriptions (Appendix 4). 

Solid-phase reactants were postulated to be dolomite, calcite, chalcedony (silica), potassium feldspar, pyrite, goethite 

(iron oxides), organic matter, and illite and kaolinite (clays). 

Although gypsum can be an important source of sulfate to 

ground water, it was not included as a solid-phase reactant 

because it was not identified in any of the thin sections or in 

the bedrock cores. Halite was not observed in the thin sections, but it was included as a reactant to account for dissolved 

chloride concentrations that were probably from anthropogenic sources at land surface. Exchange sites were added to 

allow cation exchange for calcium, magnesium, sodium, and 

potassium. Gas reactants were postulated to be oxygen and 

carbon dioxide.

Glacial Deposits 

Horizons 1A and 1B are lenses or layers of sand and 

gravel within glacial till. A large fraction of the sand and 

gravel is composed of carbonate bedrock clasts, along with 

clasts of igneous and sedimentary rocks and grains of quartz 

and feldspar. In horizon 1A, at 30 to 35 ft, the dissolved arsenic concentration was 13 μg/L, which exceeds the MCL. In 

horizon 1B, at 47 to 52 ft, the dissolved arsenic concentration 

decreased to 5 μg/L. Over the same interval, solid-phase arsenic concentrations increased slightly, from 3 μg/L in horizon 

1A to 5 μg/L in horizon 1B. The redox conditions in both horizons were predominantly iron reducing, with sulfate reduction 

also indicated. In horizon 1A, which is 10 ft below the water 

table, a small amount of dissolved oxygen was detected. 

In the study area, the hypothesis is that arsenic is released 

from iron oxides under reducing conditions. As a broad generalization, ground water becomes more reducing with depth, so 

dissolved arsenic concentrations might be expected to increase 

with depth. However, between horizons 1A and 1B, concentrations of dissolved arsenic decreased, and solid-phase concentrations increased slightly. 

Similar relations among depth and concentrations of dissolved and solid phase arsenic were observed at site 2. In horizon 2A, at 32 to 37 ft, the arsenic concentration was 6 μg/L in 

the ground water and 4 mg/kg the solid phase. In horizon 2B, 

at 75 to 80 ft, the arsenic concentration was 0.2 μg/L in the 

ground water and 5 mg/kg in the solid phase. In both horizons, 

the predominant redox process was iron reduction, with sulfate 

reduction also indicated. Sulfate reduction was more prevalent in horizon 2B than elsewhere. A similar relation between 

depth and dissolved arsenic concentrations was also noted for 

a larger area of southwestern Ohio (Thomas and others, 2005). 

Ten ground-water samples from similar glacial deposits—sand 

and gravel lenses within till—were analyzed for arsenic during 

2002–3, and the samples showed a trend of decreased arsenic 

concentrations with depth. 

One possible explanation for these observations is that 

a greater proportion of the arsenic in the shallower horizons 

is associated with iron oxides and is therefore mobile under 

reducing conditions, whereas in the deeper horizons, a greater 

proportion of the solid-phase arsenic is associated with pyrite 

and is therefore not mobile under reducing conditions (table 

2). This idea is generally consistent with micrographs from 

horizons 1A and 1B; arsenic-bearing pyrite was observed in 

both horizons, but in the shallower horizon, they were coated 

with arsenic-bearing iron oxides (fig. 5), and in the deeper 

horizon, the arsenic-bearing pyrite showed no evidence of 

weathering (fig. 6). 

A second possible explanation is that the arsenic in the 

deeper horizons was removed from the ground water and 

sequestered in the solid phase as a result of pyrite precipitation. This is consistent with the observation that horizon 2B 

had the strongest evidence of active sulfate reduction and 

the lowest concentration of dissolved arsenic. In addition, a 

micrograph from horizon 2B showed arsenic associated with 

a second generation of pyrite that coats the older framboidal 

pyrite (fig. 8). 

The results of geochemical modeling are generally 

consistent with these two ideas, although it is not possible to 

differentiate between them. Results of speciation modeling 

showed that horizons 1A, 1B, 2A, and 2B were oversaturated 

with respect to pyrite. This indicates that pyrite could precipitate, but it should not dissolve. So, in these horizons, pyrite is 

likely to be a sink for dissolved arsenic rather than a source. 

(The results of speciation modeling were similar for the other 

two water-producing horizons, 1C and 2C.)

 Inverse mass-balance modeling was used to identify possible solid-water reactions that could account for changes in 

water composition between horizons 1A and 1B. The groundwater sample from horizon 1A was used as the initial water 

composition and the sample from horizon 1B as the final 

water composition (Appendix 5A). Using the specified set 

of reactants, four models can account for the change in water 

composition, and each model includes the dissolution of iron 

oxides (and organic carbon) and the precipitation of pyrite. 

The same is true for mass-balance modeling between horizons 

2A and 2B (Appendix 5B) and horizons 2B and 2C (Appendix 

5C). 

Horizon 2C consists of organic-rich glacial deposits at a 

depth of 90 to 93 ft. The solid-phase arsenic concentration was 

8.5 mg/kg. Although this is the highest solid-phase concentration among the six water-producing horizons, it is within 

the range of typical values for unconsolidated deposits (table 

1). The dissolved arsenic concentration was 51 μg/L, which 

is 5 times the MCL. The thin section of the aquifer material 

showed large fragments of cellular organic matter, which 

could account for the relatively high DOC concentration and 

the methanogenic redox designation of horizon 2C.

The large increase in dissolved arsenic concentrations 

between horizons 2B and 2C is not unusual; similar extreme 

variations in arsenic concentrations over relatively short 

distances and (or) depths have been observed elsewhere. For 
24 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

example, the Mahomet Aquifer system of central Illinois is a 

glacial valley-fill deposit overlain by a thick layer of glacial till. The ground water is reducing, and elevated arsenic 

concentrations are common. Kirk and others (2004) observed 

that arsenic concentrations were low in sulfate-reducing 

conditions and were high in methanogenic conditions. The 

authors concluded that, under sulfate-reducing conditions, 

sulfide precipitation removed arsenic from the ground water 

and sequestered it in the solid phase. On the other hand, under 

methanogenic conditions, sulfate reduction was not active, and 

sulfide precipitation did not remove arsenic from the ground 

water; so, arsenic accumulated in the ground water to high 

concentrations (Kirk and others, 2004). 

There is also some evidence from the study area to support the idea that elevated arsenic concentrations in ground 

water can result from a shift from oxic to reducing conditions. Under oxic conditions, arsenic-bearing sulfide minerals dissolve and form arsenic-bearing iron oxides, which are 

stable under oxic conditions. However, if redox conditions 

become reducing—for example, in response to a rise in the 

water table—iron oxides can dissolve and release arsenic to 

the ground water. This idea is consistent with the observation 

that the highest arsenic concentrations in the solid phase were 

detected near the transition zone between the top of Silurian 

bedrock and the base of Wisconsinan glacial deposits. In 

addition, the micrograph from horizon 1A (fig. 5) shows a 

carbonate-rock fragment with arsenic-bearing pyrite that has 

been partially dissolved and coated with arsenic-bearing iron 

oxides. The iron oxides also show evidence of partial dissolution, which could be the result of the current redox state of that 

horizon. 

Inverse mass-balance modeling was done using hypothetical rainwater as the initial water and the ground-water sample 

from horizon 1A as the final water (Appendix 5D). Horizon 

1A is 10 to 15 ft below the water table, so this simulation 

relates to reactions in the unsaturated zone and (or) just below 

the water table. Two inverse models were found for the specified set of reactants. Both models indicated that the dissolution 

of pyrite and the precipitation of iron oxides could account for 

the composition of ground water in horizon 1A. These modeling results are consistent with the conceptual model shown in 

figure 2: dissolution of pyrite and precipitation of iron oxides 

can occur in oxic ground water (presumably from land surface 

to just below the water table). Conversely, dissolution of 

iron oxides and precipitation of pyrite can occur in reducing 

ground water (presumably at about the depth of horizon 1A 

and deeper).

Carbonate Bedrock 

Horizon 1C was at a depth of 83 to 88 ft in the Lockport 

Dolomite at site 1. The dissolved arsenic concentration was 

2 μg/L, and the predominant redox process was iron reduction, 

with sulfate reduction also indicated. The solid-phase arsenic 

concentration was less than 1 mg/kg, which is relatively low. 

The solid phase also had low concentrations of iron, sulfur, 

and organic carbon (fig. 4). A thin section from horizon 1C 

shows iron-bearing dolomite with framboidal pyrite, but no 

arsenic was detected at the limits of the SEM. For horizon 1C, 

the low concentration of dissolved arsenic might be related to 

the low concentration of arsenic in the solid phase. 

However, solid-phase arsenic concentrations in bedrock 

were not uniformly low; the unconsolidated bedrock zone at 

site 1 had a high outlier concentration of arsenic in addition to 

high concentrations of zinc, lead, nickel, and strontium. This 

was a 6-in. layer of dolomite clasts and clay at a depth of 77 ft, 

which is about 10 ft below the top of bedrock. The zone was 

sandwiched in between competent bedrock, so it was interpreted as cavity fill. Mineralogical evidence suggested that the 

sediments had been altered by geothermal fluids. It is possible 

that this was a porous zone that served as a conduit for the 

migration of mineralized fluids through bedrock. 

Goldhaber and others (2003) proposed that arsenicbearing sulfides were deposited in Paleozoic carbonates 

by large-scale migrations of hydrothermal fluids related to 

mountain-building events in the Ouachita and Appalachian 

Basins. The mineralized fluids were related to Mississippi 

Valley-type (MVT) ores. They migrated out of structural 

basins and towards arches through porous and laterally 

continuous bedrock formations, some of which now serve as 

important aquifers in the midcontinent (Goldhaber and others, 

2003). Further study might be warranted to investigate the link 

between this hypothesis and observations from the study area. 

Mineral assemblages in some of the thin sections appear to be 

related to MVT mineralization. In addition, the geology and 

structural setting of the study area are appropriate: the Lockport Dolomite is part of an extensive carbonate formation that 

underlies the Illinois Basin and subcrops along the Cincinnati 

Arch in southwestern Ohio. 

Further study might be warranted to determine whether 

similar mineralized zones are present elsewhere in the carbonate aquifer and whether ground water from these zones has 

elevated arsenic concentrations. If so, it might be possible to 

reduce the arsenic concentration of ground water produced 

from a well in carbonate bedrock by excluding discrete horizons from the open interval of the well. The concentration 

of arsenic in ground water from the unconsolidated bedrock 

zone is not known. However, a domestic well about 300 ft 

east of site 1 was sampled as part of the previous investigation 

(Thomas and others, 2005). The well produced water from a 

34-ft open interval in carbonate bedrock, and the arsenic concentration was 11 μg/L, which exceeds the MCL. It is possible 

that the domestic well produced water from a thick interval of 

low-arsenic bedrock and a thin interval of high-arsenic bedrock 

(fig. 4). In contrast, the monitor well in horizon 1C (83–88 ft) 

had a 5-ft well screen, so all of the water could have come from 

the interval of bedrock with low solid-phase arsenic concentrations. It is not known whether a higher rate of pumping, similar 

to that for a domestic well, would induce flow of water from 

the high-arsenic zone at 77 ft into the well screen at 83 to 88 ft.
Summary and Conclusions 25

A widespread permeable zone at or near the top of the 

Lockport Dolomite was identified as a possible important 

source of water in west-central Ohio (Strobel and Bugliosi, 

1991). It is not known whether that widespread permeable 

zone is related to the arsenic-rich unconsolidated sediment 

near the top of the Lockport Dolomite at site 1.

Summary and Conclusions 

In southwestern Ohio, elevated arsenic concentrations 

have been detected at a range of depths within the groundwater system. In 2002, the U.S. Geological Survey (USGS), 

in cooperation with the Miami Conservancy District, began an 

investigation to determine which parts of the aquifer system 

are most (and least) likely to produce water with elevated 

arsenic concentrations. During 2002 and 2003, the focus of 

the study was on water-quality data from domestic wells. 

A followup investigation began in 2004 to compare arsenic 

in ground water to characteristics of the solid-phase aquifer 

materials. Analysis of the solid phase was done by scientists 

from USGS Geologic Discipline and the Ohio Department of 

Natural Resources, Division of Geological Survey. 

The study was in northern Preble County, Ohio. In this 

area, Pleistocene glacial deposits overlie Silurian carbonate 

bedrock, both of which are used as a source of water to domestic and public-supply wells. Two sites were chosen for study 

and, at each site, ground-water and solid-phase data were 

collected from three horizons. The solid phase was described 

in terms of the stratigraphy, bulk elemental composition of 

70 samples, and microscopic analysis of thin sections. The 

ground water was characterized by analysis of samples from 

six water-producing horizons. Simplified geochemical modeling was used to investigate possible interactions between the 

ground water and the aquifer materials. Solid-phase arsenic 

concentrations were generally within normal ranges for similar 

geologic materials. At both study sites, the highest solid-phase 

arsenic concentrations were from a roughly similar stratigraphic position, a transition zone that extends from just above 

the Wisconsinan/Illinoian contact to just below the Pleistocene/Silurian contact. 

Arsenic concentrations greater than the USEPA Maximum Contaminant Level (MCL) of 10 μg/L were detected in 

two of the six water-producing horizons. One was the shallowest horizon in glacial deposits at site 1, which had an arsenic 

concentration of 13 μg/L. The second was the deepest horizon 

in glacial deposits at site 2, which had a dissolved arsenic 

concentration of 51 μg/L, which is 5 times the MCL. The 

concentrations of arsenic in the ground water were not directly 

related to concentrations in the solid phase. 

Observations from the study area are generally consistent 

with the concept that arsenic in the ground water was released 

from iron oxides under reducing conditions, either by dissolution or desorption. Iron oxides were observed in thin sections 

of all six water-producing horizons, and the redox conditions 

were predominantly iron reducing, which is conducive to 

reductive dissolution or desorption from iron oxides. Sulfide 

minerals were also detected in each horizon, but sulfides 

are not soluble under reducing conditions and so are not the 

likely source of the dissolved arsenic. Results of speciation 

modeling indicated that the ground water in all horizons was 

oversaturated with respect to pyrite, so pyrite could precipitate 

but should not dissolve. Results of simplified mass-balance 

modeling indicated that the observed changes in water chemistry between pairs of horizons in glacial deposits are consistent with dissolution of iron oxides and organic carbon, and 

precipitation of pyrite. 

Observations from the study area are also generally 

consistent with the concept that the release of arsenic can be 

related to a shift from oxic to reducing conditions. The highest 

concentrations of solid-phase arsenic were detected in a broad 

transition zone that extends from just above the Wisconsin/

Illinoian contact to just below the Pleistocene/Silurian contact. 

This is a zone where arsenic-bearing pyrite could have been 

transformed to arsenic-bearing iron oxides during a decline 

of sea level. A subsequent rise in sea level could presumably 

create reducing conditions conducive to release of arsenic 

from iron oxides. A thin section from horizon 1A showed 

evidence of pyrite dissolution and iron oxide formation, which 

would have required oxic conditions, and dissolution of the 

iron oxides, which would have required reducing conditions. 

Horizon 1A was about 10 ft below the water table, presumably 

near the boundary between oxic and reducing conditions. 

In addition, observations from the study area are generally consistent with the idea that dissolved arsenic can be 

removed from the ground water by precipitation of sulfide 

minerals under sulfate-reducing conditions; however, once sulfate is depleted, arsenic can accumulate in the ground water. 

At site 2, dissolved organic carbon concentrations increased 

and redox conditions became more reducing with depth, but 

arsenic concentrations showed erratic shifts with depth. The 

lowest arsenic concentration was in horizon 2B, where sulfate 

reduction was most prevalent, and the highest arsenic concentration was in horizon 2C—only about 15 ft deeper—where 

the redox was estimated to be methanogenic. Presumably, 

when sulfate reduction is not active, arsenic is not sequestered 

in the solid phase, so it can accumulate in the ground water. 

Solid-phase arsenic concentrations in carbonate bedrock 

were generally lower than in glacial deposits. However, there 

was one notable exception; a solid-phase arsenic concentration of 42 mg/kg was detected in a thin horizon that showed 

evidence of alteration by geothermal fluids. Further study 

might be warranted to determine (1) whether similar mineralized zones are the source of elevated arsenic in the carbonate 

aquifer, and (2) whether excluding such a zone from the open 

interval of a well could decrease the arsenic concentration of 

produced water. 
26 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

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Appendixes 29

Appendixes
30 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 1. Core log descriptions compiled by the Ohio Department of Natural 

Resources, Division of Geological Survey—A. Site 1, glacial deposits. 

STATE OF OHIO 

DEPARTMENT OF NATURAL RESOURCES 

DIVISION OF GEOLOGICAL SURVEY 

CORE LOG 

File Number: 3571

FILE NO.: 3571 

COUNTY: Preble 

TOWNSHIP: Monroe 

SECTION: T9N, R2E, Sec. 6 

QUADRANGLE: New Madison 7.5-min. 

FIELD NO.: MCD 3, Hole 2 

MEASURED BY: R. R. Pavey

DATE: July 29, 2004 

STATE PLANE SOUTH 1983 COORDINATES: X: 1,351,779 Y: 702,438 

REMARKS: Site located by GPS at 39° 54’ 28.7” N, 84° 41’ 55.0” W. 

4121 Eldorado-Whitewater Rd., Eldorado, OH 45321. Hole was drilled for the U.S. Geological Survey, 

Water Resources Division, Columbus, OH. Geology was supervised by Mary Ann Thomas of the USGS 

for arsenic in groundwater investigation. Drilled by USGS-WRD Wisconsin District with a CME-75, 4” 

diameter continuous sampler to 43 ft., switched to 3” diameter split-spoon sampler. 

Top of 

interval (in 

feet) 

Bottom of 

interval (in 

feet) 

Interval 

thickness 

(in feet) 

Cumulative 

thickness (in 

feet) 

Description 

0 .3 .3 .3 Mostly silt, some fine sand, dark brown, moist, turf 

roots, non-calcareous. 

.3 2.0 1.7 2.0 Silty sandy till, common pebbles, mottled medium to 

light brown, calcareous at 1.0 ft., secondary carbonate 

mottling. Very hard and dry. 1.3 ft. recovered. 

2.0 7.5 5.5 7.5 Silty sandy till, medium to light brown, mottling 

decreases with depth, very calcareous, common 

horizontal partings and vertical fractures lined with 

secondary carbonate, dry and hard. Very broken from 

5.0 to 6.3 ft. Total of 6.8 ft. recovered. 

7.5 11.3 3.8 11.3 Silty sandy till, medium brown, some orange-brown 

blobs, massive, calcareous, no obvious secondary 

carbonate, pebbles up to 2.5”. 

11.3 16.0 4.7 16.0 Silty sandy till, medium gray, some brownish-gray 

spots, massive, calcareous, slightly moist, hard. 4” 

cobble at base. 

16.0 27.2 11.2 27.2 Silty sandy till, medium gray, pebbly, massive, 

calcareous, slightly moist, hard. 

27.2 27.7 .5 27.7 Silty fine sand, medium to light gray, calcareous, 

moist. 

27.7 28.2 .5 28.2 Silt, brownish-gray, massive, calcareous, moist. 
Appendix 1 31

Appendix 1A. Site 1, glacial deposits.—Continued

28.2 28.8 .6 28.8 Silty sandy till, grayish-brown, pebbly, massive, 

calcareous, slightly moist, hard. 

28.8 29.1 .3 29.1 Sandy silty gravel, grayish-brown, calcareous, moist. 

29.1 31.7 1.6 31.7 Silty sandy till, grayish-brown, pebbly, massive, 

calcareous, slightly moist, hard. 

31.7 33.7 2.0 33.7 Medium sand to 1” pebbles, gray, very poorly sorted, 

subrounded to angular, calcareous. 

33.7 34.0 .3 34.0 Fragments of silty sandy till, dark grayish-brown, 

calcareous, with sandy wash from above interval. 

34.0 35.0 1.0 35.0 No core recovery. 

35.0 38.5 3.5 38.5 Silty sandy till, brownish-gray, massive, calcareous, 

hard. 

38.5 39.2 .7 39.2 Silt, brownish-gray, massive, calcareous, a few small 

pebbles, soft. 

39.2 39.5 .3 39.5 Silty sandy till, brownish-gray, massive, calcareous, 

hard. 

39.5 40.0 .5 40.0 Fragments of silty sandy till, brownish-gray, 

calcareous, hard, and loose pebbles, appears to be 

washed during drilling. 

40.0 42.0 2.0 42.0 Silty sandy till, brownish-gray, changing downward 

to grayish-brown, massive, calcareous, hard. 

42.0 43.0 1.0 43.0 Fragments of silty sandy till, light to medium brown, 

dry, hard. 

43.0 44.0 1.0 44.0 Begin split-spoon samples. Silty sandy till, brownishgray, massive, calcareous, hard. 

44.0 47.0 3.0 47.0 No core recovery. 

47.0 49.0 2.0 49.0 Medium to fine sand with some silt, coarsening 

downward to medium to coarse sand with some 

pebbles up to .25”, gray, calcareous, settled wet in 

box. 

49.0 52.0 3.0 52.0 No core recovery. 

52.0 52.5 .5 52.5 Silt to medium sand, brownish gray, poorly sorted, 

calcareous, settled wet in box. 

52.5 53.8 1.3 53.8 Silty sandy till, brownish-gray, massive, calcareous, 

hard. 

53.8 57.0 3.2 57.0 No core recovery. 

57.0 57.5 .5 57.5 Silty sandy till, brownish-gray, calcareous, very hard. 

57.5 59.0 1.5 59.0 Clayey silt till, yellowish brown to orange-brown, 

leached, not as hard as above. Some medium gray 

reduction mottles. Probable paleosol. 

59.0 62.0 3.0 62.0 No core recovery. 

62.0 63.3 1.3 63.3 Silty sandy till with some clay, mottled medium 

brown to medium gray, becomes grayer with depth, 

calcareous, hard. 

63.3 64.8 1.5 64.8 No core recovery. 

64.8 65.0 .2 65.0 Fragments of silty sandy till with some clay, medium 

gray, calcareous, very hard. 

65.0 End of hole. 
32 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 1B. Site 1, bedrock.

STATE OF OHIO 

DEPARTMENT OF NATURAL RESOURCES 

DIVISION OF GEOLOGICAL SURVEY 

CORE LOG 

File Number: 3570 

FILE NO.: 3570 

COUNTY: Preble 

TOWNSHIP: Monroe 

SECTION: T9N, R2E, Sec. 6 

QUADRANGLE: New Madison 7.5-min. 

FIELD NO.: MCD3, Hole 1 

MEASURED BY: E.M. Swinford 

DATE: July 26, 2004 

SURFACE ELEVATION: 1150 FEET S.L. 

TOTAL DEPTH: 177.0 FEET 

STATE PLANE SOUTH 1983 COORDINATES: X: 1,351,732 Y: 702,441 

REMARKS: Site located by GPS at 39° 54’ 28.7”N, 84° 41’ 55.6”W. 

4121 Whitewater-Eldorado Road, Eldorado, OH 45321. Hole was drilled for the U.S. Geological 

Survey, Water Resources Division, Columbus, OH. Geology was supervised by Mary Ann 

Thomas of the USGS for arsenic in groundwater investigation. Bedrock units are the Lockport 

Dolomite and the Laurel Dolomite. 

Top of 

interval (in 

feet) 

Bottom of 

interval (in 

feet) 

Interval 

thickness 

(in feet) 

Cumulative 

thickness (in 

feet) 

Description 

0 73.0 73 73 Glacial drift – not sampled 

73.0 73.3 0.3 0.3 Dolomite, light gray (5Y 7/1), medium to fine 

crystalline, slightly argillaceous to clean, welldeveloped moldic porosity and abundant 

petroliferous staining, black (5Y2 5/1) to live 

petroleum tar oozing for rock. 

73.3 76.7 3.4 3.7 Dolomite, light gray (5Y 7/1) to pale yellow (5Y 

8/2), fine to coarse crystalline, sucrosic, generally 

clean, highly dolomitized fossil remnants, friable in 

part, massive bedded with scattered layers of welldeveloped porosity and medium crystalline 

dolomite within by layers of lower porosity and 

finer crystalline dolomite. 

76.7 77.3 0.6 4.3 Clay and dolomite, soft, very friable, pebble-sized 

clasts of clay, dark olive gray (5Y 3/2), soft to 

poorly indurated and particles of sucrosic dolomite. 

Possible fracture fill or inwashed paleosol(?). 

77.3 94.7 17.4 21.7 Dolomite, pale yellow (5Y 8/2) to light gray (5Y 

7/1), fine to coarse crystalline, clean to slightly 

argillaceous, mottled, moldic porosity with some 

vuggy porosity, massive bedded. General color 

trend from top to bottom is pale-yellow changing to 

gray Some high-angle fractures from 83.0’ to 

86.4’: lower contact sharp. 
Appendix 1 33

Appendix 1B. Site 1, bedrock.—Continued

94.7 96.9 2.2 23.9 Dolomite, light gray (5Y 7/1) to pale yellow (5Y 

8/2), fine crystalline intervals 94.7’ to 95.1’ and 

form 97.0’ to 97.4’ with medium to coarse 

crystalline intervals between, clean to slightly 

argillaceous, sucrosic, moldic, to vuggy porosity, 

high angle fractures, massive bedded. Lower 

contact at base of lower fine crystalline zone. 

96.9 103.0 6.1 30.0 Dolomite, pale yellow (5Y 8/2) to light gray (5Y 

7/2), coarse to medium crystalline, slightly 

argillaceous to clean, with zones of fine crystalline 

dolomite pale yellow (5Y8/2) somewhat friable 

dominated by well-developed moldic and 

intercrystalline porosity. High angle fractures from 

99.4’ to 100.8’. 

103.0 108.7 5.7 35.7 Dolomite, pale yellow (5Y 8/2) to light gray (5Y 

7/1), fine to coarse crystaline, moldic, vuggy, and 

intercrystalline porosity containing thin to medium 

beds of light pale yellow (5Y8/4). High-angle 

fractures from 103.4’ to 103.7’, from 104.6’ to 

105.0’, 106.0 to 107.5’. Shale laminae, light 

greenish gray (Gley1 7/1), soft, present in the 

interval from 104.3 to 105.2’. 

108.7 118.2 9.5 45.2 Dolomite, light gray (5Y7/1), coarse crystalline 

with thin intervals of fine to medium crystalline, 

clean to slightly argillaceous, moldic and 

intercrystalline porosity, with some intervals of 

vuggy porosity, generally massive bedded. High 

angle fractures at 115.0’. 

118.2 124.6 6.4 51.6 Dolomite, pale yellow (5Y 8/2) to light gray (5Y 

7/1), generally fine to medium crystalline, minor 

intercrystalline to fine moldic porosity, massive 

bedded, , medium gray (2.5Y 5/1) argillaceous 

laminae from 121.2 to 121.6’. Distinct pale yellow 

zone from 122.8’ to 124.6’. Lower contact sharp at 

color change at base of pale yellow zone. 

124.6 146.7 22.1 73.7 Dolomite, light gray (5Y 7/1), coarse crystalline, 

well developed moldic, vuggy, and intercrystaline 

porosity throughout, massive bedded, clean to 

slightly argillaceous, with thin zones of sucrosic, 

fine crystalline dolomite; high angle fractures at 

129.6’. Some yellow (2.5Y 7/8) iron stain along 

bedding planes at 138.6’ to 137.3’, at 141.0’, and 

142.1’. 

146.7 149.8 3.1 76.8 Dolomite, light gray (5Y 7/1), fine to coarse 

crystalline, thin to massive bedded, thin zones of 

moldic and intercrystaline porosity, with 

moderately indurated, gray (5Y 6/1), dolomitic, 

shale laminae that are discontinuous, soft from 

146.7’ to 147.3’ and from 148.5’ to 148.7’. 

149.8 154.6 4.8 81.6 Dolomite, light gray (5Y7/1) to gray (5Y 6/1), 

mottled, coarse crystalline, massive bedded, 

abundant moldic and intercrystalline porosity, 

grades downward into pale yellow (5Y 8/2) 

dolomite in lowest 1.00’. Lower contact sharp at 

interface with chert nodule. Approximate base of 

the Lockport Dolomite. 
34 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 1B. Site 1, bedrock.—Continued

154.6 158.1 3.5 85.1 Dolomite, light gray (5Y 7/2) to pale yellow (5Y 

8/2), fine crystalline with minor thin intervals of 

coarse, sucrosic dolomite beds; intercrystalline and 

moldic porosity in upper 3 feet. Chert, light gray 

(5Y 7/1) to white (5Y 8/1), mottled, nodular 

bedded, fossil remnants and dark pyritic or 

manganese (?)-rich zones. Sparse greenish gray 

(Gley1 4/1), discontinuous, dolomitic shale 

laminae. Approximate top of the Laurel 

Dolomite. 

158.1 169.2 11.1 96.2 Limestone, mottled light gray (5Y 7/1) to pale 

yellow (5Y 8/2), dolomitic, fine to medium 

crystalline, nodular bedded; chert, light grey to 

white (Gley1 7/1) (Gley1 8/1) with pyrite and 

manganese in chert. Lower contact gradational. 

169.2 177.0 7.8 104.0 Limestone, greenish gray (Gley1 6/1) to dark 

greenish gray (Gley1 4/1), dolomitic, argillaceous, 

bioclastic, mottled, minor chert nodules that are 

light gray (Gley2 7/1); interval is mottled in the 

lowermost 2 feet, dolomitic, and argillaceous more 

thin above. 

177.0 0 T.D 
Appendix 2 35

Appendix 2. Core log descriptions compiled by the Ohio Department of Natural 

Resources, Division of Geological Survey—Site 2. 

STATE OF OHIO 

DEPARTMENT OF NATURAL RESOURCES 

DIVISION OF GEOLOGICAL SURVEY 

CORE LOG 

File Number: 3572 

FILE NO.: 3572 

COUNTY: Preble 

TOWNSHIP: Monroe 

SECTION: T9N, R2E, Sec. 17 

QUADRANGLE: New Madison 7.5-min. 

FIELD NO.: MCD 3, Hole 5 

MEASURED BY: R. R. Pavey, E. M. Swinford 

DATE: Aug. 19 & 26, 2004 

STATE PLANE SOUTH 1983 COORDINATES: X: 1,357,661 Y: 690,897 

REMARKS: Site located by GPS at 39° 52’ 36.0” N, 84° 40’ 35.9” W. 

7160 State Rt.726, Eldorado, OH 45321. Hole was drilled for the U.S. Geological Survey, Water 

Resources Division, Columbus, OH. Geology was supervised by Mary Ann Thomas of the USGS for an 

arsenic in groundwater investigation. Drilled by Bowser-Morner with a rotosonic rig producing 4” 

continuous core. 

Top of 

interval (in 

feet) 

Bottom of 

interval (in 

feet) 

Iinterval 

thickness 

(in feet) 

Cumulative 

thickness (in 

feet) 

Description 

0.0 .8 .8 .8 Silt, some sand, few pebbles, light to medium 

brown, many roots, friable, non-calcareous. 

.8 2.2 1.4 2.2 Clayey silty till, common pebbles, medium brown, 

mottled with orange-brown, common black organic 

pods, weakly calcareous at 1.8 ft. 

2.2 3.9 1.7 3.9 Silty sandy till, common pebbles, medium brown, 

1.5” pebble at 3.2 ft., calcareous, massive. 

3.9 10.0 6.1 10.0 No core recovery. 

10.0 10.5 .5 10.5 Muddy poorly sorted fine sand to fine gravel, light 

to medium brown, fluid, calcareous. 

10.5 12.5 2.0 12.5 Silty sandy till, common pebbles, mottled medium 

yellow-brown to medium brownish gray, irregular 

horizontal parting, calcareous. 

12.5 14.2 1.7 14.2 Silty sandy till, common pebbles, medium gray 

with medium yellow-brown oxidation on joint 

faces, calcareous. 

14.2 29.1 14.9 29.1 Silty sandy till, common pebbles, medium gray, 

calcareous, massive. 

29.1 30.0 .9 30.0 Silt, light to medium gray, wet, grading downward 

to silty very fine sand, light gray, moist, calcareous. 

30.0 32.8 2.8 32.8 No core recovery. 

32.8 33.9 1.1 33.9 Very fine sand to silt, grayish brown, wet, 

calcareous. 
36 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 2. Site 2.—Continued

33.9 35.7 1.8 35.7 Medium sand to small cobbles, brown, poorly 

sorted, wet, calcareous. 

35.7 36.2 .5 36.2 Silty sandy till, medium yellow-brown, calcareous. 

36.2 36.6 .4 36.6 Fine sand, light brown, wet, calcareous. 

36.6 37.2 .6 37.2 Medium sand to 1” pebbles, brown, poorly sorted, 

wet, calcareous. 

37.2 40.0 2.8 40.0 Silty sandy till, grayish brown, calcareous, massive. 

40.0 41.0 1.0 41.0 No core recovery. 

41.0 41.2 .2 41.2 Medium to coarse sand, brown, wet, calcareous. 

41.2 48.3 7.1 48.3 Silty sandy till, medium brownish gray, calcareous, 

massive. 

48.3 52.4 4.1 52.4 Medium sand to medium gravel, grayish brown, 

with fragments of silty fine sand to medium gravel, 

dark brownish gray, cohesive, friable, calcareous. 

52.4 53.0 .6 53.0 Silty fine sand to fine gravel, medium brown, 

cohesive, calcareous. 

53.0 56.0 3.0 56.0 Silt to fine sand, some grains of coarse sand to fine 

gravel, light to medium brown, calcareous, moist, 

grading downward to silt and fine sand with some 

clay, medium brown, calcareous, moist. 

56.0 60.0 4.0 60.0 Silty sandy till, common pebbles, light to medium 

brown grading downward to grayish brown, 

calcareous, some platy structure in upper 2.4 ft., 

dry. 

60.0 69.3 9.3 69.3 Silt and fine sand, medium brown, well sorted, 

calcareous, moist. 

69.3 71.7 2.4 71.7 Medium sand, medium brown, well sorted, 

calcareous, moist. 

71.7 78.8 7.1 78.8 Fine to medium sand, medium brown, calcareous, 

moist, with clasts of silty fine sand, dark brown, 

cohesive, calcareous, moist. 

78.8 80.0 1.2 80.0 Clayey silt, mottled dark gray to dark grayish 

brown, calcareous, moist. 

80.0 80.7 .7 80.7 Fine to medium sand, medium brown, calcareous, 

moist, with clasts of silty fine sand, dark brown, 

cohesive, calcareous, moist. 

80.7 90.0 9.3 90.0 Clayey silt, medium brown to grayish brown, 

calcareous, massive, moderately plastic, moist. 

90.0 90.5 .5 90.5 Silt, dark brownish gray, some pebbles in lower 

part, leached. Probable paleosol. 

90.5 91.7 1.2 91.7 Clayey silt till, many pebbles, medium to dark 

brown with common black organic streaks, weakly 

calcareous to leached, moist, HCl releases odor of 

sulfuric compound, organic odor on fresh break. 

Probable paleosol. 

91.7 102.7 11.0 102.7 Clayey silt till, medium to dark brown, moderately 

calcareous, moist, very broken, becoming 

fragmented and muddy with depth, organic odor on 

fresh break. 

102.7 104.7 2.0 104.7 Silt, medium brown, calcareous, broken. 

104.7 107.1 2.4 107.1 Clayey silt till, dark brown, very calcareous, hard, 

dry. 

107.1 108.3 1.2 108.3 Very fine sand and silt grading downward from 

light brown to nearly white, weakly calcareous, 

moist. Probable paleosol. 
Appendix 2 37

Appendix 2. Site 2.—Continued

108.3 110.0 1.7 110.0 Dolomite fragments, with very fine sand, silt, and 

clay, light tan, weakly calcareous. Probable 

paleosol. 

110.00 112.0 2.00 112.00 Dolomite, pale-yellow (5Y 8/2) to light gray (N7), 

fine to medium crystalline, intercrystalline and 

moldic porosity, massive bedded; yellowish-brown 

iron stain along select bedding planes; lower 

contact in missing interval. 

112.00 112.3 .30 112.3 Missing interval. 

112.3 114.0 1.70 114.0 Dolomite, light-gray (N7) to medium- light gray 

(N6), coarse to fine crystalline, slightly 

argillaceous, zones of moldic porosity and some 

intercrystalline porosity, stylolitic, medium to thin 

bedded with thinner bedded zone being more 

argillaceous; bedding planes appear water worn. 

Lower contact in missing interval. 

114.0 115.5 1.50 115.5` Missing interval. 

115.5 117.4 1.90 117.4 Dolomite, light-gray (N7) to medium-light gray 

(N6), coarse to fine crystalline, slightly 

argillaceous, zones of moldic porosity and some 

intercrystalline porosity, stylolitic, medium to thin 

bedded with thinner bedded zone being more 

argillaceous, bedding planes appear water worn. 

High angle fractures at 115.5 – 116.3. Lower 

contact sharp and undulatory where light gray (N7) 

dolomite in sharp contact with medium light gray 

(N6) dolomite with medium gray (N5) .03 layer at 

contact. 

117.4 119.6 2.20 119.6 Dolomite, light gray (N7), light medium gray (N6) 

to light olive gray (5Y 6/1), fine to medium 

crystalline, light gray chert, fossil brachiopods 

molds, intercrystalline porosity with moldic 

porosity along bedding planes, stylolitic in part, 

medium to thin bedded; core broken along bedding 

planes. Rock core is Silurian Lockport Dolomite. 

Total Depth. 
38 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 3A. Bulk elemental composition of solid-phase samples, site 1. 

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

 Depth

(feet)

Organic

carbon

(pct)

Total

carbon

(pct)

CO2

(pct)

Carbonate

carbon

(pct)

Total

sulfur

(pct)

Aluminum

(pct)

Calcium

(pct)

Iron

(pct)

30.3 -0.44 8.23 31.76 8.67 0.05 1.72 17.26 0.85

31.3 0.22 5.35 18.81 5.13 0.05 2.65 11.35 1.06

32 0.29 8.97 31.79 8.68 0.06 1.61 16.01 0.77

33 0.27 9.12 32.43 8.85 0.06 1.25 15.9 0.67

33.3 0.12 8.02 28.95 7.9 0.07 1.67 14.74 0.77

34 0.49 9.4 32.65 8.91 0.07 1.23 17.52 0.66

34.8 0.19 1.62 5.25 1.43 <0.05 5.54 4.72 1.96

42 0.42 5.73 19.44 5.31 0.1 2.92 11.44 1.69

48 0.39 5.84 19.97 5.45 0.16 2.4 12.77 1.21

49 0.7 6.89 22.68 6.19 0.21 1.96 13.72 1.12

52.5 0.3 6.34 22.12 6.04 0.22 2.22 13.78 1.26

57.8 0.23 0.5 0.98 0.27 <0.05 4.48 1.31 7.93

58 0.24 0.38 0.52 0.14 <0.05 5.78 1.04 4.6

58.5 0.42 0.58 0.58 0.16 <0.05 6.62 0.89 7.3

62.4 0.13 0.29 0.58 0.16 <0.05 5.82 0.94 5.38

67.1 0.71 3.16 8.99 2.45 0.34 5.14 6.12 2.69

73 1.75 13.9 44.51 12.15 <0.05 0.06 20.26 0.06

75.4 -1 11.7 46.52 12.7 <0.05 0.03 20.03 0.06

77 -0.07 6.15 22.8 6.22 0.09 6.55 11.11 3.08

80 -1.02 11.6 46.25 12.62 <0.05 0.05 19.95 0.14

82 -2.15 10.6 46.7 12.75 <0.05 0.03 19.93 0.16

83 -0.43 12.2 46.26 12.63 <0.05 0.02 19.71 0.11

84 -0.58 12.1 46.46 12.68 <0.05 0.03 19.87 0.12

85 -0.6 12.1 46.53 12.7 <0.05 0.04 19.82 0.1

86 0.09 12.4 45.09 12.31 <0.05 0.02 19.87 0.14

87 -0.25 12.5 46.73 12.75 <0.05 0.01 19.74 0.17

88 -0.33 11.9 44.81 12.23 <0.05 0.02 20.04 0.23

92 -0.24 12.4 46.33 12.64 <0.05 0.01 19.71 0.21

95.5 -0.36 12.2 46.01 12.56 <0.05 0.06 19.68 0.09

99.4 0.22 12.2 43.91 11.98 <0.05 0.09 19.65 0.11

104.5 -0.37 12 45.32 12.37 <0.05 0.24 19.86 0.09

116.5 0.38 12.7 45.13 12.32 <0.05 0.05 19.59 0.08

123.5 -0.36 11.3 42.74 11.66 <0.05 0.42 19.44 0.29

140.5 -0.41 12.5 47.3 12.91 <0.05 0.09 18.75 0.13

154.5 -0.17 12.1 44.94 12.27 <0.05 0.2 19.39 0.14

160.3 0.01 0.05 0.13 0.04 1.07 0.11 0.11 1.28
Appendix 3 39

Appendix 3A. Bulk elemental composition of solid-phase samples, 

site 1.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth 

(feet)

Potassium

(pct)

Magnesium

(pct)

Sodium

(pct)

Sulfur 

(pct)

Titanium

(pct)

Silver

(ppm)

Arsenic

(ppm)

Barium

(ppm)

30.3 0.71 8.38 0.44 0.1 0.06 <1 2 241

31.3 1.01 4.93 0.82 0.09 0.08 <1 2 322

32 0.74 7.42 0.34 0.12 0.04 <1 3 188

33 0.53 6.9 0.29 0.1 0.03 <1 3 172

33.3 0.71 6.69 0.43 0.1 0.04 <1 3 211

34 0.56 8.17 0.27 0.13 0.04 <1 3 152

34.8 1.85 1.82 1.95 0.05 0.14 <1 2 449

42 1.09 4.46 0.63 0.12 0.1 <1 6 270

48 0.95 4.67 0.64 0.24 0.07 <1 5 237

49 0.78 5.21 0.49 0.26 0.07 <1 5 204

52.5 0.84 5.06 0.6 0.28 0.08 <1 6 222

57.8 1.4 0.69 0.79 0.02 0.16 <1 14 371

58 1.87 0.84 0.86 0.01 0.19 <1 11 465

58.5 2.18 0.9 0.58 0.02 0.15 <1 20 503

62.4 1.63 0.72 0.71 0.02 0.16 <1 9 464

67.1 1.52 2.4 0.61 0.4 0.16 <1 11 398

73 0.03 11.68 0.02 0.04 <0.01 <1 4 8

75.4 0.01 11.58 0.02 0.01 <0.01 <1 <1 5

77 0.67 6.87 0.08 0.13 0.14 <1 42 188

80 0.01 11.61 0.02 0.01 <0.01 <1 <1 8

82 <0.01 11.63 0.02 0.01 <0.01 <1 <1 <5

83 <0.01 11.57 0.02 <0.01 <0.01 <1 <1 <5

84 0.01 11.7 0.02 0.01 <0.01 <1 <1 <5

85 <0.01 11.52 0.03 0.02 <0.01 <1 <1 5

86 <0.01 11.59 0.02 0.01 <0.01 <1 <1 <5

87 <0.01 11.41 0.02 0.01 <0.01 <1 <1 <5

88 <0.01 11.53 0.03 0.01 <0.01 <1 <1 <5

92 <0.01 11.44 0.02 0.02 <0.01 <1 <1 <5

95.5 <0.01 11.44 0.03 0.03 <0.01 <1 1 6

99.4 <0.01 11.49 0.03 0.03 <0.01 <1 <1 6

104.5 0.11 11.52 0.02 0.02 <0.01 <1 <1 12

116.5 0.02 11.46 0.04 0.05 <0.01 <1 <1 <5

123.5 0.24 11.32 0.02 0.02 0.02 <1 <1 22

140.5 0.04 10.91 0.03 0.03 <0.01 <1 1 8

154.5 0.1 11.13 0.03 0.05 <0.01 <1 <1 12

160.3 0.03 0.06 0.03 1.28 <0.01 <1 2 32
40 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 3A. Bulk elemental composition of solid-phase samples, 

site 1.—Continued 

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram. Organic carbon concentrations were 

computed by subtracting carbonate carbon from total carbon concentrations; negative values for organic carbon are due to small amounts of 

measurement error.]

Depth

(feet)

Beryllium

(ppm)

Bismuth

(ppm)

Cadmium

(ppm)

Cerium

(ppm)

Cobalt

(ppm)

Chromium 

(ppm)

Cesium 

(ppm)

Copper

(ppm)

30.3 0.6 <0.04 <0.1 16.1 2.5 11 0.6 8.7

31.3 0.8 <0.04 <0.1 20.9 3.1 15 0.7 7.8

32 0.6 0.05 0.1 16.6 2.9 10 0.88 10.2

33 0.5 <0.04 0.1 13.2 3.2 9 0.68 8.7

33.3 0.5 <0.04 <0.1 16.5 2.7 11 0.72 8.9

34 0.4 <0.04 0.1 12 2.8 9 0.58 11.5

34.8 1.3 0.07 <0.1 43.1 9.2 44 1.54 19.8

42 0.8 0.07 0.2 29.2 5.9 20 1.63 15.4

48 0.7 0.07 0.1 25.3 4.5 18 0.97 11.4

49 0.7 0.07 0.2 18.2 4.3 16 0.83 12.8

52.5 0.7 0.08 0.2 20.3 6.1 21 0.83 12.2

57.8 1.7 0.1 0.4 41.3 13.1 32 2.44 23.8

58 1.9 0.1 0.2 54.9 12.2 42 3.6 27.1

58.5 2.1 0.13 0.3 61.5 17.1 53 6.03 31.1

62.4 1.7 0.1 0.2 50.1 11.5 47 3.72 24.6

67.1 1.5 0.18 0.2 47.9 14.1 39 3.75 21.5

73 <0.1 <0.04 <0.1 1.76 5.8 3 0.05 5.7

75.4 <0.1 <0.04 <0.1 1.7 0.4 3 <0.05 4.5

77 2.1 0.11 0.3 17.1 18.3 45 5.85 28.6

80 <0.1 <0.04 <0.1 1.64 0.4 2 <0.05 5.2

82 <0.1 <0.04 <0.1 1.36 0.4 2 <0.05 4.7

83 <0.1 <0.04 <0.1 1.04 0.3 2 <0.05 5.2

84 <0.1 <0.04 <0.1 1.68 0.4 2 <0.05 5

85 <0.1 <0.04 <0.1 1.83 0.4 <1 <0.05 5.7

86 <0.1 <0.04 <0.1 1.02 0.4 1 <0.05 7.2

87 <0.1 <0.04 <0.1 1.48 0.4 <1 <0.05 4.7

88 <0.1 <0.04 <0.1 1.12 0.4 2 <0.05 6.4

92 <0.1 <0.04 0.2 0.84 0.4 1 <0.05 4.9

95.5 <0.1 <0.04 <0.1 1.25 0.6 2 <0.05 5.9

99.4 <0.1 <0.04 <0.1 1.46 0.6 2 <0.05 7.9

 104.5 <0.1 <0.04 <0.1 4.11 0.5 3 0.18 5.3

116.5 <0.1 <0.04 <0.1 4.8 0.5 1 <0.05 5.2

123.5 0.1 <0.04 <0.1 9.06 0.9 6 0.31 5.3

140.5 <0.1 <0.04 <0.1 5.88 0.6 2 <0.05 5

154.5 <0.1 <0.04 <0.1 6.76 0.5 5 0.23 4.4

160.3 <0.1 <0.04 0.1 0.26 0.6 2 <0.05 1.1
Appendix 3 41

Appendix 3A. Bulk elemental composition of solid-phase samples, 

site 1.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth

(feet)

Gallium

(ppm)

Indium

(ppm)

Lanthanum

(ppm)

Lithium

(ppm)

Manganese 

(ppm)

Molybdenum 

(ppm)

Niobium

(ppm)

Nickel 

(ppm)

30.3 3.56 <0.02 7.9 10 291 1.64 2 3.3

31.3 5.48 <0.02 9.9 8 286 1.9 2.8 4.8

32 3.78 <0.02 8.5 10 277 2.46 2 5.5

33 3.02 <0.02 6.8 8 273 2.4 1.5 3.8

33.3 3.8 <0.02 8.3 9 251 2.09 1.9 4.5

34 2.7 <0.02 6.3 9 261 1.64 1.2 2.7

34.8 12.7 0.02 22.1 13 369 0.66 4.7 25

42 6.61 0.03 14.2 14 447 3.18 3.7 11.7

48 5.3 <0.02 12.7 10 359 3.6 2.5 10.5

49 4.34 <0.02 8.9 10 371 3 2.2 8.5

52.5 4.85 <0.02 10.4 9 388 2.86 2.4 8.5

57.8 9.82 0.04 21.8 18 1130 7.14 4.8 27.9

58 13 0.06 27.9 27 456 4.62 6.3 32.7

58.5 15.5 0.06 31.3 30 614 7.5 5.3 42.4

62.4 12.9 0.05 25.8 25 526 3.95 5.6 35.1

67.1 10.9 0.05 24.2 29 549 8.69 5.8 21.8

73 0.16 <0.02 1.5 3 58 0.43 0.2 4.7

75.4 0.08 <0.02 1.6 2 108 <0.05 0.2 <0.5

77 15.8 0.06 10.9 66 160 9.53 6.7 64.4

80 0.15 <0.02 1.8 2 134 0.07 0.1 <0.5

82 0.1 <0.02 1.5 2 152 0.14 <0.1 <0.5

83 0.06 <0.02 1 2 106 0.23 <0.1 <0.5

84 0.08 <0.02 1.5 <1 135 0.08 0.2 <0.5

85 0.09 <0.02 1.7 1 120 0.08 <0.1 <0.5

86 0.07 <0.02 1 1 172 0.07 <0.1 <0.5

87 0.05 <0.02 1.3 <1 135 <0.05 <0.1 <0.5

88 0.08 <0.02 1.1 2 100 0.11 0.1 <0.5

92 0.06 <0.02 0.8 <1 129 0.06 <0.1 <0.5

95.5 0.16 <0.02 1.1 1 125 0.2 <0.1 <0.5

99.4 0.2 <0.02 1.3 2 120 0.06 0.1 1.2

104.5 0.52 <0.02 2.8 4 68 <0.05 0.6 <0.5

116.5 0.14 <0.02 4.5 1 99 0.07 0.2 <0.5

123.5 0.89 <0.02 6.6 5 151 0.42 0.7 <0.5

140.5 0.29 <0.02 4.7 2 173 0.16 0.4 1.2

154.5 0.48 <0.02 6.2 3 206 0.08 0.5 <0.5

160.3 0.21 <0.02 <0.5 5 30 0.41 0.2 8.3
42 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 3A. Bulk elemental composition of solid-phase samples, 

site 1.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth

(feet)

Phosphorus

(ppm)

Lead

(ppm)

Rubidium

(ppm)

Antimony

(ppm)

Scandium

(ppm)

Tin

(ppm)

Strontium

(ppm)

Tellurium

(ppm)

30.3 206 6.1 21.5 0.16 2.5 0.4 191 <0.1

31.3 306 7.9 30.3 0.18 3.5 0.5 219.4 <0.1

32 185 7.3 27.3 0.23 2.7 0.4 164.3 <0.1

33 148 4.8 20.8 0.2 2.2 0.3 152.3 <0.1

33.3 190 5.8 24.9 0.19 2.7 0.4 172.7 <0.1

34 167 4.7 19 0.18 2.2 0.4 156 <0.1

34.8 414 12.4 83.5 0.17 6.9 0.9 313 <0.1

42 332 9.6 43.9 0.37 5.1 0.7 219.8 <0.1

48 252 7.6 33 0.26 3.5 0.5 206.7 <0.1

49 215 7.1 27.6 0.28 3.6 0.5 193.2 <0.1

52.5 240 6.8 28.3 0.24 3.6 0.5 204.5 <0.1

57.8 697 17.6 61.6 1.39 8.4 1 407.6 <0.1

58 679 19.6 83.9 1.06 11 2 493.6 <0.1

58.5 651 21.3 117.3 1.5 12.6 1.9 562 <0.1

62.4 515 19.2 85.9 0.93 10 1.3 580.1 <0.1

67.1 331 16 75.2 0.59 8.3 1.4 437.5 <0.1

73 <50 1.3 1.3 0.07 0.2 <0.1 71.5 <0.1

75.4 <50 0.6 0.5 <0.05 0.3 0.1 54.7 <0.1

77 206 46.9 93.8 0.8 11.8 1.9 656.7 <0.1

80 <50 0.9 0.8 <0.05 0.3 0.2 58 <0.1

82 <50 0.7 0.6 <0.05 0.2 0.1 53 <0.1

83 <50 0.8 0.3 <0.05 0.1 <0.1 49.5 <0.1

84 <50 0.6 0.6 <0.05 0.2 <0.1 49.9 <0.1

85 <50 0.9 0.4 0.06 0.2 0.2 49.8 <0.1

86 <50 0.7 0.3 <0.05 <0.1 0.2 47.7 <0.1

87 <50 0.5 0.2 <0.05 0.2 <0.1 45.3 <0.1

88 <50 0.9 0.3 0.05 0.2 0.1 54.7 <0.1

92 <50 0.6 0.2 0.05 <0.1 <0.1 47.7 <0.1

95.5 <50 0.8 0.9 <0.05 <0.1 <0.1 53.7 <0.1

99.4 <50 0.9 1.1 0.08 <0.1 0.1 57.1 <0.1

104.5 51 1.2 4.7 0.05 0.5 0.1 62.6 <0.1

116.5 <50 1.7 1.1 0.06 0.3 0.2 64.8 <0.1

123.5 66 2.6 8.3 0.11 0.7 0.2 69 <0.1

140.5 <50 2.1 1.7 0.13 0.3 <0.1 51.6 <0.1

154.5 52 1.6 4.6 <0.05 0.5 0.1 61.9 <0.1

160.3 <50 5.3 0.8 0.08 <0.1 0.2 19.8 <0.1
Appendix 3 43

Appendix 3A. Bulk elemental composition of solid-phase samples, 

site 1.—Continued

[pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth

(feet)

Thorium

(ppm)

Thallium

(ppm)

Uranium

(ppm)

Vanadium

(ppm)

Tungsten

(ppm)

Ytterbium

(ppm)

Zinc

(ppm)

30.3 1.7 0.2 1.6 23 0.1 6.8 28

31.3 2.2 0.2 1.5 28 0.2 9.2 24

32 2.5 0.2 2.2 25 0.2 6.6 25

33 1.6 0.2 1.9 19 0.1 5.7 21

33.3 2.1 0.2 1.8 22 0.2 6.5 23

34 1.7 0.2 1.9 18 0.2 5.9 34

34.8 9.3 0.5 1.8 49 0.2 9.5 49

42 3.9 0.4 2.5 38 0.3 12.1 45

48 3.1 0.3 2.1 30 3.1 9.4 42

49 2 0.3 1.9 28 0.5 9.4 35

52.5 2.3 0.3 1.8 28 16.1 9.4 44

57.8 5.3 0.7 2.8 82 0.5 27.7 134

58 8 0.9 3.8 105 0.7 23.5 115

58.5 9.2 1.4 4.5 138 0.8 25 146

62.4 7 1 3 99 0.6 24.3 105

67.1 7.2 0.8 3.3 78 32.9 16.4 58

73 <0.2 0.2 0.4 8 0.1 3 96

75.4 <0.2 <0.1 <0.1 4 <0.1 4.1 9

77 7.7 1.7 2.9 142 8.1 10.3 571

80 <0.2 <0.1 <0.1 5 0.3 4.6 21

82 <0.2 <0.1 <0.1 4 <0.1 4 19

83 <0.2 <0.1 <0.1 3 <0.1 3.2 21

84 <0.2 <0.1 0.2 4 <0.1 3.8 11

85 <0.2 <0.1 <0.1 3 <0.1 4.6 9

86 <0.2 <0.1 <0.1 3 <0.1 3.3 18

87 <0.2 <0.1 0.2 4 <0.1 4.2 12

88 <0.2 <0.1 <0.1 4 <0.1 3.5 16

92 <0.2 <0.1 <0.1 3 <0.1 2.6 15

95.5 <0.2 <0.1 0.1 4 0.2 2.9 12

99.4 <0.2 <0.1 0.2 4 0.2 3.1 16

104.5 0.5 <0.1 0.4 6 0.1 3.8 10

116.5 0.3 <0.1 0.1 4 <0.1 6.4 8

123.5 1 <0.1 0.5 8 0.1 6.7 7

140.5 0.5 <0.1 0.2 5 <0.1 6 19

154.5 0.5 <0.1 0.7 8 <0.1 6.8 3

160.3 <0.2 0.2 0.2 <1 <0.1 0.1 47
44 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 3B. Bulk elemental composition of solid-phase samples, 

site 2.

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram. Organic carbon concentrations were 

computed by subtracting carbonate carbon from total carbon concentrations; negative values for organic carbon are due to small amounts of 

measurement error.]

Depth 

(feet) 

Organic

carbon

(pct)

Total

carbon

(pct)

CO2

(pct)

Carbonate

carbon

(pct)

Total

sulfur

(pct)

Aluminum

(pct)

Calcium

(pct)

Iron

(pct)

29 0.8 6.38 20.45 5.58 0.38 3.76 11.4 1.87

34 0.5 7.87 27.01 7.37 0.08 2.5 14.9 1.35

35 0.47 8.33 28.81 7.86 0.09 2.07 15.55 1.17

37 0.43 6.57 22.48 6.14 0.07 2.3 13.55 1.2

39 0.59 4.81 15.45 4.22 0.06 3.56 9.14 1.92

45 0.83 4.53 13.55 3.7 0.38 4.38 8.97 2.26

51 0.43 5.41 18.23 4.98 0.34 3.14 12.13 1.59

55 0.5 4.11 13.22 3.61 0.36 3.85 9.01 1.79

58 0.44 4.37 14.4 3.93 0.34 4.6 9.66 2.39

63 0.16 2.92 10.1 2.76 0.25 3.44 7.55 1.49

69 0.24 4.97 17.33 4.73 0.28 3.11 11.98 1.96

75 0.31 3.12 10.31 2.81 0.24 3.26 7.81 1.39

77 0.05 3.01 10.83 2.96 0.34 3.19 8.38 1.97

79 0.16 3 10.4 2.84 0.14 3.22 8.13 1.05

85 0.78 4.04 11.95 3.26 0.36 5.77 8.06 3.26

89 2.1 4.75 9.7 2.65 0.18 4.2 5.81 2.18

90 0.19 6.89 24.54 6.7 0.1 2.14 11.84 1.89

91 0.51 4.51 14.64 4 0.1 4.51 8.45 2.69

93 0.75 3.91 11.56 3.16 0.06 5.2 7.81 3

95 0.53 4.35 14.01 3.82 0.16 4.59 8.39 2.6

99 0.44 3.57 11.47 3.13 0.13 4.96 7.21 3.32

103 0.23 4.5 15.65 4.27 0.05 2.8 9.63 1.57

106 0.19 5.84 20.7 5.65 0.12 4.14 10.95 2.54

107 -0.65 9.75 38.11 10.4 <0.05 1.6 16.92 0.87

108 -1.52 10.7 44.78 12.22 <0.05 0.41 20.25 0.27

109 -1.88 10.6 45.72 12.48 <0.05 0.22 20.36 0.13

111 -0.38 11.2 42.44 11.58 <0.05 0.35 21.17 0.28

112 -1.32 10 41.48 11.32 <0.05 0.58 21.14 0.51

114 -0.38 10.7 40.6 11.08 0.07 0.18 31.14 0.18

119 0.06 1.46 5.12 1.4 <0.05 0.19 5.19 0.07
Appendix 3 45

Appendix 3B. Bulk elemental composition of solid-phase samples, 

site 2.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth

(feet)

Potassium

(pct)

Magnesium

(pct)

Sodium 

(pct)

Sulfur 

(pct)

Titanium

(pct)

Arsenic 

(ppm)

Barium 

(ppm)

Silver

(ppm)

29 1.5 4.63 0.52 0.42 0.11 9 290 <1

34 0.99 6.28 0.49 0.1 0.08 4 203 <1

35 0.87 6.6 0.45 0.12 0.08 4 181 <1

37 0.91 4.98 0.59 0.09 0.08 5 229 <1

39 1.35 3.77 0.69 0.07 0.12 9 306 <1

45 1.69 3.54 0.76 0.44 0.13 8 348 <1

51 1.19 3.74 0.82 0.4 0.1 6 275 <1

55 1.47 3.18 1.01 0.42 0.1 6 360 <1

58 1.74 3.49 0.84 0.43 0.14 8 376 <1

63 1.25 2.09 1.14 0.28 0.12 4 375 <1

69 1.03 3.63 0.86 0.37 0.12 6 276 <1

75 1.18 1.92 1 0.27 0.09 4 337 <1

77 1.01 2.25 1 0.4 0.15 6 322 <1

79 1.11 1.9 1.07 0.17 0.07 3 343 <1

85 2.17 3.32 0.66 0.42 0.19 14 415 <1

89 1.52 3.14 0.77 0.19 0.15 9 399 <1

90 0.71 6.13 0.38 0.12 0.18 7 185 <1

91 1.65 4.05 0.32 0.12 0.15 8 297 <1

93 1.94 3.41 0.3 0.07 0.15 10 337 <1

95 1.69 3.77 0.29 0.19 0.13 9 315 <1

99 2.21 3.39 0.47 0.16 0.21 8 422 <1

103 1.19 3.55 0.39 0.06 0.1 5 251 <1

106 1.46 5.51 0.18 0.16 0.11 8 242 <1

107 0.42 9.73 0.07 0.04 0.06 11 120 <1

108 0.13 11.5 0.04 0.04 0.02 4 36 <1

109 0.08 11.55 0.04 0.04 <0.01 2 11 <1

111 0.2 10.3 0.02 0.04 0.01 <1 19 <1

112 0.32 10.77 0.02 0.05 0.03 <1 26 <1

114 0.1 4.1 0.02 0.17 <0.01 <1 10 <1

119 0.06 0.12 0.04 0.02 <0.01 <1 40 <1
46 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 3B. Bulk elemental composition of solid-phase samples, 

site 2.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth 

(feet)

Beryllium

(ppm)

Bismuth

(ppm)

Cadmium 

(ppm)

Cerium

(ppm)

Cobalt 

(ppm)

Chromium 

(ppm)

Cesium 

(ppm)

Copper

(ppm)

29 1.4 0.11 0.4 37.4 8.3 28 3.45 19.4

34 0.9 0.06 0.2 26.8 5.3 17 1.66 16.5

35 0.6 0.09 0.2 24.2 5.2 17 1.16 16.4

37 0.7 0.05 0.1 19.7 3.4 16 1.04 11.5

39 1.2 0.08 0.2 35.6 7.4 24 2.38 16.3

45 1.3 0.08 0.1 39.4 9.3 32 3.13 19

51 1 0.06 0.1 26.2 6 21 1.54 15.7

55 1.2 0.07 0.1 28 6.6 25 1.76 17.2

58 1.6 0.1 0.1 38.5 9.5 37 3.1 19

63 0.9 0.06 0.1 25.5 5 19 0.89 10.3

69 0.8 0.06 0.1 26.7 7 29 1.03 11.3

75 0.9 0.06 0.1 22.1 4.7 17 0.99 11.8

77 0.9 0.07 0.2 26.5 5.6 25 0.7 11.5

79 0.8 <0.04 <0.1 18.2 3.8 13 0.73 7.7

85 1.8 0.11 0.1 56.5 12.9 45 5.03 26.7

89 1.2 0.11 0.3 47 8.1 30 2.62 16.7

90 0.7 0.08 0.2 28.4 6.7 17 1.22 12.4

91 1.8 0.1 0.3 47.3 11.3 37 4.36 24.7

93 1.9 0.1 0.4 55.2 11.4 43 5.1 23.1

95 1.7 0.09 0.3 49.1 10.7 36 4.48 19.2

99 1.5 0.33 0.3 52.7 13 46 3.97 21.8

103 1 0.08 0.3 36.5 6.1 22 1.96 14.7

106 1.4 0.13 0.3 50.3 10.1 33 3.95 17.8

107 0.6 0.12 <0.1 31.4 5.3 16 1.54 9.1

108 0.2 0.08 <0.1 12.4 2 8 0.36 6.1

109 0.2 <0.04 <0.1 8.96 0.8 6 0.17 6.3

111 0.2 <0.04 <0.1 10.5 0.8 7 0.34 6

112 0.3 <0.04 <0.1 10.7 0.8 18 0.61 6.8

114 0.1 <0.04 <0.1 12.6 1.8 8 0.26 9.5

119 <0.1 <0.04 <0.1 3.26 0.3 3 0.11 4.3
Appendix 3 47

Appendix 3B. Bulk elemental composition of solid-phase samples, 

site 2.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth 

(feet)

Gallium

(ppm)

Indium

(ppm)

Lanthanum

(ppm)

Lithium, 

(ppm)

Manganese 

(ppm)

Molybdenum 

(ppm)

Niobium

(ppm)

Nickel 

(ppm)

29 8.8 0.03 19 22 384 7.13 4.8 20.5

34 5.79 0.02 13.4 15 358 2.8 3.3 9.1

35 4.97 <0.02 12.1 11 326 3.2 2.3 12.4

37 4.73 <0.02 9.8 11 330 3.32 2.6 9

39 8.28 0.03 17.9 19 414 3.9 4.3 15.3

45 10.1 0.04 19.4 25 479 5.73 5.2 20.3

51 6.78 0.02 13.2 13 479 5.7 3.5 11.7

55 8.01 0.03 14.1 15 421 4.63 3.7 14.9

58 10.3 0.04 19.7 24 513 4.92 5.1 22

63 7.17 0.02 12.6 8 409 2.38 3.5 10

69 6.73 0.02 13.2 12 581 3.08 3.4 12.7

75 6.86 0.02 11.2 9 381 2.94 2.8 10.9

77 6.69 0.03 12.4 7 531 1.97 4.9 10.9

79 6.34 <0.02 9.5 7 332 1.62 2 8.7

85 13.2 0.05 27.9 35 579 4.45 7.3 32.5

89 8.82 0.04 22.9 20 490 3.71 5.4 19.7

90 5.48 0.03 12.9 12 635 1.97 3.7 10

91 11 0.05 22.9 33 720 2.21 5.7 23.4

93 12.2 0.05 27.1 39 648 2.9 6.3 26.6

95 10.5 0.05 23.8 36 590 2.82 5.5 21.7

99 11.7 0.06 26.2 41 630 2.63 7.1 26.6

103 6.13 0.03 18.2 17 559 1.42 3.7 13.7

106 9.65 0.04 23.3 35 842 2.15 4.6 19.3

107 3.85 <0.02 17 15 438 0.89 3.1 9.8

108 0.98 <0.02 9 4 356 0.27 1.2 1.3

109 0.54 <0.02 7.2 3 205 0.08 0.7 2.1

111 0.83 <0.02 7.9 4 238 0.27 0.8 1.6

112 1.38 <0.02 7.9 5 192 0.58 1.3 <0.5

114 0.52 <0.02 12.9 2 135 0.08 0.6 0.8

119 0.31 <0.02 2.3 7 22 0.16 0.2 <0.5
48 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 3B. Bulk elemental composition of solid-phase samples, 

site 2.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth, 

(feet)

Phosphorus

(ppm)

Lead

(ppm)

Rubidium

(ppm)

Antimon,

(ppm)

Scandium

(ppm)

Tin

(ppm)

Strontium

(ppm)

Tellurium

(ppm)

29 354 27.8 69.4 0.7 7 1.1 296.1 <0.1

34 277 9 40.5 0.34 4.5 0.7 267.7 <0.1

35 215 6.9 34.5 0.32 4.1 0.5 212.4 <0.1

37 240 7.2 32.1 0.32 3.5 1.3 243.6 <0.1

39 364 11.8 56.3 0.45 6.2 1 328.7 <0.1

45 427 12.6 72.1 0.41 8 1.2 364.3 0.1

51 302 9.6 44.5 0.34 5.3 0.7 270.4 <0.1

55 390 11.4 51.1 0.33 5.8 0.8 304.9 <0.1

58 454 12.5 72.3 0.39 8 1.2 364.3 <0.1

63 326 10 39.7 0.25 4.8 0.6 266.7 <0.1

69 351 8 36.8 0.26 6 0.7 244.9 <0.1

75 269 9.6 39.5 0.27 4.4 0.6 258.4 <0.1

77 350 8.8 31.4 0.24 6.2 0.8 257.7 <0.1

79 221 8.5 34.7 0.13 3.6 0.4 265.7 <0.1

85 563 16.1 98 0.51 10.9 1.8 318.8 <0.1

89 481 14.5 61.9 0.37 7.1 1.1 300.7 <0.1

90 345 10.6 31.4 0.4 5.6 0.7 136.6 <0.1

91 380 16.1 79.9 0.87 9.2 1.6 160.2 <0.1

93 418 16.8 92.8 0.65 9.6 1.7 167.7 <0.1

95 381 15.5 82.8 0.66 8.7 1.5 153.9 <0.1

99 387 16.2 89.2 0.59 10.4 1.8 145.9 <0.1

103 384 10.6 47 0.42 5.1 0.8 145.9 <0.1

106 317 15.8 71.6 0.51 7.7 1.3 152.8 <0.1

107 110 10.1 27.5 0.38 3.5 0.6 101.4 <0.1

108 58 5.6 7 0.17 1.3 0.2 64.2 <0.1

109 <50 2.7 3.7 0.11 0.9 0.1 56 <0.1

111 55 2.7 7.6 0.09 0.9 0.2 62.8 <0.1

112 59 4.1 12.4 0.15 1.5 0.2 76.4 <0.1

114 59 4.5 4.3 0.09 1.4 <0.1 121.7 <0.1

119 <50 1.1 2 0.07 0.2 0.1 58 <0.1
Appendix 3 49

Appendix 3B. Bulk elemental composition of solid-phase 

samples, site 2.—Continued

[<, less than; pct, percent; ppm, parts per million; ppm is equivalent to milligrams per kilogram]

Depth, 

(feet)

Thorium

(ppm)

Thallium

(ppm)

Uranium

(ppm)

Vanadium

(ppm)

Tungsten

(ppm)

Ytterbium

(ppm)

Zinc

(ppm)

29 5.6 0.8 4.4 71 0.5 13.3 54

34 3.6 0.4 2.4 35 0.4 9.8 34

35 3.6 0.3 2.6 55 0.2 8.3 29

37 2.4 0.2 2 31 0.2 8.7 37

39 5.1 0.6 2.7 51 0.4 13.3 48

45 6 0.6 3.3 61 0.5 14.4 54

51 3.6 0.4 3 41 0.3 12.4 39

55 4.2 0.5 2.6 44 0.5 11.6 42

58 6 0.6 3 64 0.5 14.4 50

63 3.1 0.3 1.7 34 0.3 11 42

69 3.5 0.3 2 46 0.3 12.6 40

75 2.8 0.3 1.8 33 0.3 9.3 40

77 2.7 0.3 1.4 43 0.2 14.6 83

79 2.1 0.3 1.2 26 0.2 7.6 32

85 9.3 0.8 3.7 89 0.7 17.8 67

89 7.2 0.6 2.8 59 0.5 16.6 61

90 3.5 0.3 1.8 49 0.5 13 35

91 7.6 0.8 3.1 86 0.7 15.2 73

93 8.8 0.8 3.3 95 0.7 15.8 77

95 7.8 0.7 2.8 82 0.6 14.6 70

99 8.2 0.7 2.6 88 2.1 13.8 73

103 5.5 0.4 2.3 46 0.3 12 43

106 7.2 0.6 2.8 72 0.5 17 59

107 3.9 0.2 1.1 33 0.4 13.4 44

108 1.4 <0.1 0.4 13 0.2 9.3 22

109 1 <0.1 0.2 10 0.1 8.2 11

111 1.1 <0.1 0.6 9 0.2 8.7 11

112 1.8 <0.1 1.2 17 0.2 8.4 10

114 1.1 <0.1 1.1 15 <0.1 12.1 23

119 0.2 <0.1 0.2 <1 <0.1 1.7 17
50 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 4. Mineralogical description of seven solid-phase samples.

[%, percent]

Composition Description

Horizon 1A

Site 1, glacial deposits at 33 feet 

64% Carbonate 

fragments 

Includes rounded micritic calcite, dolomitized micritic calcite, and dolomite clasts. In dolomite clasts, 

crystals are rhombic and range from fine- to coarse-grained. Carbonate clasts are commonly fossiliferous. 

Barite is commonly associated with dolomite. Carbonate grains host pyrite with arsenic concentration up 

to 2.56 weight percent. 

8% Feldspar grains Mainly plagioclase(?); some potassium feldspar. Some feldspar partially altered to sericitic clays. 

12% Quartz grains Many grains with sweeping extinction, possibly metamorphic origin. Many grains were intensely cracked, 

interfering with interference figures.

13% Igneous-rock 

fragments

Granite (quartz, feldspar, pyroxene, biotite altered to chlorite); rare fragments with myrmekitic texture. 

Several highly altered volcanic clasts with oriented plagioclase laths. 

2% Sedimentary-rock 

fragments

Shaly illitic clay-rich clasts with iron oxide stain. Framboidal pyrite common. 

1% Other Pyroxene as liberated large grains. Accessory ilmenite, rutile, chalcopyrite, zircon

Horizon 1B

Site 1, glacial deposits at 48 feet

57% Carbonate 

fragments

Includes rounded micritic calcite, dolomitized micritic calcite, and dolomite clasts. In dolomite fragments, 

crystals are rhombic and range from fine- to coarse-grained. Carbonate fragments host abundant fossils, 

some altered to silica. Barite is commonly associated with dolomite. 

2% Feldspar grains Mainly plagioclase(?). Partially alteration to sericitic clays. 

17% Quartz grains Many grains with sweeping extinction, possibly metamorphic origin. Many grains were intensely cracked, 

interfering with interference figures.

12% Igneous-rock 

fragments

Mainly granite (quartz, feldspar, pyroxene, biotite altered to chlorite). Rare fragments with myrmekitic 

texture. 

Other Accessory monazite, rutile, framboidal pyrite, chalcopyrite, zircon, magnetite(?) altered to hematite(?). 

Fine- to medium-grained carbonate matrix common around all grain types.

12% Sedimentary-rock 

fragments

6% Shaly illitic clay-rich fragments with iron-oxide stain. Framboidal pyrite common. 

6% Siltstone (?), chert grains. Iron-oxide-stained clay-rich layers are associated with the siltstone. One 

fragment showed a lithologic boundary between the two rock types. Arsenic-bearing pyrite and nickelarsenic sulfide hosted in siltstone. Arsenic detected at concentrations (in pyrite within siltstone?) up to 

0.44 weight percent. 

 
Appendix 4 51

Appendix 4. Mineralogical description of seven solid-phase samples.—

Continued

Site 1, unconsolidated bedrock zone at 77 feet

47% Carbonate 

fragments

Dolomite clasts with occasional fossil fragments. Minor rounded micritic calcite clasts. Dolomite rhombs are 

etched and corroded and float in the clay matrix.

46% Clay Iron-oxide-stained illitic (?) clay coats etched dolomite rhombs. Nickel-arsenic sulfide minerals abundant in 

clay matrix. Arsenic detected at concentrations up to 4.3 weight percent in nickel-arsenic sulfide minerals. 

7% Igneous-rock 

fragments

Granite (feldspar, quartz, mica). Metamorphic (?) clasts (hornblende, quartz, and sericitized feldspar). 

Horizon 1C

Site 1, carbonate bedrock at 86 feet

100% Carbonate 

fragments

Dolomite. 

Others: Iron oxide pseudomorphs after coarsely crystalline pyrite (?). Framboidal pyrite, barite, sylvite, 

occasional detrital quartz grains. 

Horizon 2A

Site 2, glacial deposits at 34 feet

75% Carbonate 

fragments 

Includes rounded micritic calcite, dolomitized micritic calcite, and dolomite clasts. Dolomite crystals are rhombic, 

fine- to coarse-grained. Micritic carbonate clasts host silt-size quartz and feldspar grains. Carbonate clasts host 

fossils, some altered to silica. Barite is commonly associated with dolomite. Framboidal pyrite. 

2% Feldspar grains Mainly plagioclase (?). Partial alteration to sericitic clays. 

4% Quartz grains Many grains with sweeping extinction, possibly metamorphic. Many grains were intensely cracked, 

interfering with interference figures.

6% Igneous-rock 

fragments

Granite (coarse-grained quartz, feldspar, ferromagnesium minerals, mica). Some fine-grained altered volcanic 

fragments with oriented plagioclase crystals. 

13% Sedimentary-rock 

fragments

2% Shaly illitic clay-rich fragments with iron-oxide stain. Framboidal pyrite common. 

11% Siltstone (?) and chert (?). Siltstone clasts have quartz, feldspar, mica, and carbonate and iron-oxide 

cement. Chert is partially replaced by dolomite. 

Horizon 2B

Site 2, glacial deposits at 77 feet

32% Carbonate 

fragments 

Includes rounded micritic calcite, dolomitized micritic calcite, and dolomite clasts. Dolomite crystals are 

rhombic, fine- to coarse-grained. Micritic carbonate clasts host silt-size quartz and feldspar grains. 

Carbonate fragments host fossils, some altered to silica. Barite is commonly associated with dolomite. 

14% Feldspar grains Plagioclase and potassium feldspar. Some feldspars partially altered to sericitic clays. 

27% Quartz grains Many grains with sweeping extinction, possibly metamorphic. Many grains were intensely cracked, 

interfering with interference figures.

21% Igneous-rock 

fragments

Granite (coarse-grained quartz, feldspar, ferromagnesium minerals, mica). Some fine-grained altered volcanic 

fragments with oriented plagioclase crystals. 

1% Sedimentary-rock 

fragments

Shaly illitic clay-rich fragments with iron-oxide stain. Chert fragments with abundant framboidal pyrite. Rare 

phosphatic (?) shell fragments. Framboidal pyrite has replaced shell fragment(s); framboids in turn are 

coated by second-generation coarsely crystalline pyrite that contains up to 1.3 weight percent arsenic.

5% Other Liberated grains of pyroxene, hornblende, and barite. 
52 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 4. Mineralogical description of seven solid-phase samples.—

Continued

Horizon 2C

Site 2, glacial deposits at 90 feet

95% Carbonate/

Sedimentary-rock 

fragments

Rounded clasts are composed of poorly sorted micritic carbonate and silt- to pebble-size feldspar, quartz 

grains, and ferromagnesium mineral fragments. The clasts also host abundant organic material, wherein 

cellular material is commonly replaced by iron sulfides (pyrite?). Some carbonate fragments host fossil 

fragments. Framboidal pyrite is common. 

1% Quartz Medium- to coarse-size grains in carbonate. 

4% Pyrite Massive pyrite replaces large fragments of cellular organic material. Arsenic detected at concentrations up to 

0.26 weight percent. 
Appendix 5 53

Appendix 5A. Results of inverse mass-balance modeling. Initial 

water is ground-water sample from horizon 1A; final water is sample 

from horizon 1B. 

 [All data are in moles; positive values indicate mineral dissolution, negative values indicate mineral precipitation; --, constituent not used 

in model calculations] 

Chemical constituent Model 1 Model 2 Model 3 Model 4

Dolomite -- -- -- --

Calcite -- -- -2.795 x 10-4 -2.793 x 10-4

Pyrite -3.145 x 10-4 -3.145 x 10-4 -3.145 x 10-4 -3.145 x 10-4

Goethite 3.369 x 10-4 3.369 x 10-4 3.369 x 10-4 3.369 x 10-4

CH2O 1.180 x 10-3 1.180 x 10-3 1.180 x 10-3 1.180 x 10-3

CO2 (gas) 3.558 x 10-4 3.558 x 10-4 -- --

O2

 (gas) -- -- -- --

Chalcedony -- -- -- --

K-feldpsar -- -- -- --

Illite -- -- -- --

Kaolinite -- -- -- --

CaX2 -- 3.584 x 10-5 -- 3.584 x 10-5

MgX2 -- -- -- --

NaX 6.307 x 10-5 -- 6.307 x 10-5 --

KX -6.307 x 10-5 -7.168 x 10-5 -6.307 x 10-5 -7.168 x 10-5

Halite -7.462 x 10-5 -5.648 x 10-5 -7.462 x 10-5 -5.648 x 10-5
54 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 5B. Results of inverse mass-balance 

modeling. Initial water is ground-water sample from 

horizon 2A; final water is sample from horizon 2B.

 [All data are in moles; positive values indicate mineral dissolution, negative values indicate mineral precipitation; --, constituent not used in model calculations] 

Chemical constituent Model 1 Model 2 Model 3

Dolomite -- -- --

Calcite -4.978 x 10-4 -4.546 x 10-4 -4.782 x 10-4

Pyrite -1.975 x 10-4 -1.975 x 10-4 -1.975 x 10-4

Goethite 2.217 x 10-4 2.217 x 10-4 2.217 x 10-4

CH2O 7.485 x 10-4 7.485 x 10-4 7.485 x 10-4

CO2 (gas) -- -- --

O2

 (gas) -- -- --

Chalcedony -5.120 x 10-5 -- -5.120 x 10-5

K-feldpsar -- -- 2.558 x 10-5

Illite 4.263 x 10-5 -- --

Kaolinite -4.903 x 10-5 -- 1.279 x 10-5

CaX2 5.113 x 10-4 4.681 x 10-4 4.917 x 10-4

MgX2 -8.727 x 10-4 -8.424 x 10-4 -8.531 x 10-4

NaX 7.229 x 10-4 7.229 x 10-4 7.229 x 10-4

KX -- 2.558 x 10-5 --

Halite -1.637 x 10-3 -- -1.637 x 10-3
Appendix 5 55

Appendix 5C. Results of inverse mass-balance 

modeling. Initial water is ground-water sample from 

horizon 2B; final water is sample from horizon 2C.

[All data are in moles; positive values indicate mineral dissolution, negative values indicate mineral precipitation; --, constituent not used in model calculations]

Chemical constituent Model 1 Model 2 Model 3

Dolomite -- -- --

Calcite -1.546 x 10-3 -1.546 x 10-3 -5.619 x 10-4

Pyrite -1.768 x 10-4 -1.768 x 10-4 -1.768 x 10-4

Goethite 1.336 x 10-4 1.336 x 10-4 1.336 x 10-4

CH2O 6.512 x 10-4 6.512 x 10-4 6.512 x 10-4

CO2 (gas) -- -- -9.838 x 10-4

O2 (gas) -- -- --

Chalcedony -2.263 x 10-3 -4.263 x 10-3 -1.166 x 10-4

K-feldpsar -- 1.968 x 10-3 --

Kaolinite -2.057 x 10-3 -9.838 x 10-4 --

Illite 1.789 x 10-3 -- --

CaX2 1.234 x 10-3 1.234 x 10-3 2.497 x 10-4

MgX2 -7.354 x 10-4 -- -2.882 x 10-4

NaX 1.410 x 10-4 1.410 x 10-4 1.410 x 10-4

KX -1.137 x 10-3 -2.032 x 10-3 -6.398 x 10-5

Halite -1.411 x 10-4 -1.411 x 10-4 -1.411 x 10-4
56 Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio

Appendix 5D. Results of inverse 

mass-balance modeling. Initial water is 

hypothetical rain water; final water is 

sample from horizon 1A.

[All data are in moles; positive values indicate mineral dissolution, negative values 

indicate mineral precipitation; --, constituent not used in model calculations] 

Chemical constituent Model 1 Model 2

Dolomite 3.256 x 10-3 3.256 x 10-3

Calcite -- --

Pyrite 1.292 x 10-3 1.292 x 10-3

Goethite -1.264 x 10-3 -1.264 x 10-3

CH2O 2.631 x 10-3 --

CO2

 (gas) -- 2.631 x 10-3

O2 (gas) 7.462 x 10-3 4.832 x 10-3

Chalcedony 7.140 x 10-5 7.140 x 10-5

K-feldpsar 1.475 x 10-4 1.475 x 10-4

Kaolinite -7.377 x 10-5 -7.377 x 10-5

CaX2 -4.674 x 10-4 -4.674 x 10-4

NaX 9.349 x 10-4 9.349 x 10-4

Halite 1.910 x 10-4 1.910 x 10-4
Thomas and others—Solid-Phase and Dissolved Arsenic in the Ground-Water System, Northern Preble County, Ohio—Scientific Investigations Report 2008–5205

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