Survey of Groundwater Composition in Northern Addison County, VT With

A SURVEY OF GROUNDWATER COMPOSITION IN NORTHERN ADDISON COUNTY, VERMONT: GEOLOGIC SOURCES OF CONTAMINATION

Environmental Studies 360 Spring 2002

Program in Environmental Studies Middlebury College Middlebury, VT 05753

Dr. Peter Ryan, Dr. Stephen Trombulak, and the members of ES 360 (listed in alphabetical order):

Lauren Aldrich Ian Ausprey Ben Brower Benjamin Calvi Sarah Groff Caitlin Hicks Katherine Johnston Morley McBride Lee Perlow Molly Yazwinski

ii This report was written as part of a research project conducted under the supervision of Dr. Peter Ryan and Dr. Stephen Trombulak for the Middlebury College course entitled "Environmental Science Practicum" (Environmental Studies 360). Copyright of this report and its contents is retained by the Trustees of Middlebury College. Please cite this report as follows:

Ryan, P., S. Trombulak, L. Aldrich, I. Ausprey, B. Brower, B. Calvi, S. Groff, C. Hicks, K. Johnston, M. McBride, L. Perlow, and M. Yazwinski. 2002. A survey of groundwater composition in northern Addison County, Vermont: geologic sources of contamination. Environmental Science Practicum research report: Environmental Studies Program, Middlebury College, Middlebury, Vermont.

Additional copies of this report can be obtained from the Program in Environmental Studies, Middlebury College, Middlebury, VT 05753 (802-443-5710) or by contacting either Dr. Peter Ryan (Department of Geology and Program in Environmental Studies, 802-443-2557, [email protected]) or Dr. Stephen C. Trombulak (Department of Biology and Program in Environmental Studies, 802-443-5439, [email protected]).

iii Table of Contents

Introduction ...... 1

Figure 1. Uranium decay series...... 2

Materials and Methods ...... 4

Study areas ...... 4 Sampling...... 4 Figure 2A-F. Study locations ...... 5-10 Analysis...... 11 Table 1. Concentrations of standards ...... 12 Table 2. Emission wavelengths and ICP detection levels...... 12

Results ...... 13

Within-site variation...... 13 Chemical signatures of locations...... 13 Table 3. Bedrock signatures...... 13 EPA Primary Standards...... 14 Uranium (Table 4 and Figure 3) ...... 14-15 Lead (Table 5 and Figure 4)...... 16-17 Copper (Table 6 and Figure 5)...... 18 Arsenic (Table 7 and Figure 6)...... 19 Chromium (Table 8 and Figure 7)...... 20 Selenium (Table 9 and Figure 8) ...... 21 EPA Secondary Standards...... 22 Aluminum (Table 10 and Figure 9) ...... 22-23 Iron (Table 11 and Figure 10)...... 24 Zinc (Table 12 and Figure 11)...... 25 Elements without EPA limits ...... 26 Calcium (Table 13 and Figure 12) ...... 26 Cadmium (Table 14 and Figure 13) ...... 27 Cobalt (Table 15 and Figure 14)...... 28 Potassium (Table 16 and Figure 15) ...... 29 Magnesium (Table 17 and Figure 16) ...... 30 Sodium (Table 18 and Figure 17)...... 31 Nickel (Table 19 and Figure 18)...... 32 Phosphorus (Table 20 and Figure 19)...... 33 Silicon (Table 21 and Figure 20)...... 34 Titanium (Table 222 and Figure 21) ...... 35 Table 23. Summary table ...... 36

Discussion...... 37

Implications for human health...... 37 Uranium and other radionuclides ...... 37

iv Lead...... 38 Copper, iron, and aluminum...... 39 Geologic interpretations of results ...... 39 Clarendon Springs Formation ...... 39 Cheshire Quartzite Formation ...... 40 Discussion of results for other elements ...... 40 Implications for a predictive model ...... 41 Recommendations for future studies...... 41 Sources of error and uncertainty ...... 42

Conclusion...... 43

Acknowledgements...... 43

Literature Cited...... 44

1 Introduction

Sources of health risks in water supplies are not always related to human activities. Metals such as arsenic (As), iron (Fe), copper (Cu), lead (Pb), and uranium (U) can originate from natural sources that include the weathering and dissolution of metal- bearing minerals in rocks and the proximity of groundwater to geologic features such as fractures and faults. For instance, surveys of drinking water in New Hampshire found high arsenic levels in the water of bedrock wells situated in Late-Devonian Concord-type granite. Based on a maximum contaminant level (MCL) of 5 parts per billion (ppb), water from 20% of domestic bedrock wells in New Hampshire would be considered to be unsafe for drinking (Peters et al. 1999). Approximately 50% of Vermont homeowners drink water produced from wells drilled into bedrock (Kim, personal communication) and only rarely do homeowners test their water for metals and radioactive elements. Considering that chronic, long-term exposure to some trace metals can cause cancer and organ damage, chemical analysis of water is important, especially in areas with bedrock types known to contain elevated concentrations of trace metals.

In this study, we measured the concentration of 19 elements in well water in northern Addison County, Vermont. Of the 19 elements, six are regulated by EPA primary drinking water standards and three are regulated by secondary standards. The health risks from exposure to contaminants was of particular concern in our research because, unlike municipal water supplies, which must pass federal Safe Drinking Water Standards, management and monitoring of private water supplies is voluntary (Swistock et al. 1993). Although it is difficult to prevent natural contamination of groundwater, there are options available to treat contaminated water once elevated levels have been detected.

In Vermont’s Champlain Valley, natural contaminants of particular concern are uranium and its radioactive decay products radon and radium. A study in 2001 by the Vermont Department of Health and the Vermont Geological Survey (VGS) detected elevated concentrations of uranium in groundwater in the towns of Milton, Colchester, and St. George (Kim and Becker 2001; Kim and Thompson 2002). Uranium isotopes (U238, U235 and rare quantities of U234) are naturally present in soil, air, water, rocks, and plants. The most common isotope, U238, is relatively stable with a half-life of 4.5 billion years. Uranium’s daughter elements, however, have shorter half-lives. For example, radon-222 (Rn222), a colorless, odorless radioactive gas, emits alpha particles when it decays and poses the greatest risk to human health.

Long-term exposure to alpha emitters such as radon leads to increased cancer risks (Hopke et al. 2000). The Surgeon General listed radon as the second leading cause of lung cancer (Swistock et al. 1993), and it is estimated that 168 people die every year in the United States as a result of exposure to radon in drinking water (EPA 1999). Most radon in houses is thought to enter through the soil or rock below foundations but groundwater can also be a source of indoor radon. When water is heated, aerated, or agitated, as in cooking or showering, the radon comes out of solution and enters the air (Gall et al. 1995).

Figure 1. Diagram illustrating the radioactive isotopes that result from the radioactive decay of uranium. These elements form sequentially from upper right to lower left by emitting alpha particles. Note the presence of radon (Rn) and radium (Ra) in this decay series. Other elements represented on this diagram include lead (Pb), bismuth (Bi), polonium (Po), astatine (At), francium (Fr), actinium (Ac), thorium (Th) and protactinium (Pa). (Adapted from http://www.dpi.state.nc.us/curriculum/science/Chemistry/uranium.htm.)

High concentrations of radionuclides (e.g., U, Ra, Rn) in groundwater have been associated with specific rock formations in Vermont (Kim and Becker 2001; Kim and Thompson 2002). While elevated uranium concentrations are commonly associated with acidic igneous rocks such as granites, other rock types such as carbonates and quartzites are also known to host elevated U concentrations (Banks et al. 1995, Sloto 2000). Potentially radiogenic lithologies in Vermont include pre-Cambrian metamorphic rocks (which comprise parts of the Green Mountains) along with some quartzites, dolomites, shales, and slates (Kim and Becker 2001). In the Milton-Colchester area, groundwater containing elevated radionuclide concentrations has been linked to the Clarendon Springs Formation, a dolomite-containing breccia (i.e., fractured, broken rock) zones rich in carbonaceous organic material (Kim and Thompson 2002).

The VGS study suggested that the source of elevated radionuclides in St. George (northeast of Hinesburg) is the Cheshire Quartzite Formation. There, high radionuclide levels in well water are associated with the St. George Fault, suggesting that faults may play an important role in radionuclide source and migration. Residents of a trailer park adjacent to the St. George Fault have been advised to drink bottled water until further research can be conducted.

Most wells in Vermont penetrate at least 100 feet through solid rock and may frequently intersect fracture systems created by faults (Kim, personal communication). The presence of extensive joint systems may provide pathways for the release of bedrock- derived contaminants into wells (Eyles and Scheidegger 1995). Faults and fractures offer ideal pathways for groundwater in bedrock flow given that fluids follow the course that poses the least resistance (Eyles and Scheidegger 1995). In addition, mechanical and chemical breakdown of radiogenic mineral-bearing lithologies along fault planes caused by stress and movement increase the likelihood that radionuclides and other trace elements will become dissolved in groundwater.

The focus of this study is the chemical composition of groundwater at five distinct locations in northern Addison County, Vermont. Given recent findings at Milton, Colchester and St. George (Kim and Becker 2001; Kim and Robinson 2002), we focused on well water drawn from the Clarendon Springs and Cheshire Quartzite Formations. Also, considering that the St. George area is located adjacent to the St. George Fault, and the Milton-Colchester area is not located near any known faults, we selected our five sampling locations based on lithology (rock type) as well as the presence or absence of bedrock faults. Of the five locations, two contain wells that produce from the Clarendon Springs Formation (one adjacent to faults and one not), two contain wells that produce from the Cheshire Quartzite Formation (one adjacent to faults and one not), and the fifth location is in a part of Addison County with no major faults and no outcrops of either Cheshire Quartzite or Clarendon Springs Formations. The Stony Point Shale is the main lithology in this location, and of the five locations, it likely represents a control site.

Materials and Methods

Study areas

This study was conducted in the northern Addison County towns of Weybridge, Bristol, Monkton and Ferrisburgh, all located in the Champlain Valley of western Vermont (Figure 2A). Bedrock in the Champlain Valley is comprised of folded and faulted meta- sedimentary rocks, including limestone, quartzite (metamorphosed sandstone) and shale. Included in this are the Clarendon Springs Formation and Cheshire Quartzite Formation (Figure 2B).

Field locations are as follows:

• Non-faulted carbonates and shales (mainly Stony Point Shale) in North Ferrisburgh, Vermont (Location 000, Figure 2C). • Non-faulted Clarendon Springs Formation in the Twin Bridges region of Weybridge, Vermont (Location 100, Figure 2D). • Faulted Clarendon Springs Formation in the vicinity of Weybridge Hill on Rte. 23, Quaker Village Road and James Rd. in Weybridge, Vermont (Location 200, Figure 2D). • Non-faulted Cheshire Quartzite Formation on Lower Notch Rd. in Bristol, Vermont (Location 300, Figure 2E). • Faulted Cheshire Quartzite Formation in Monkton, Vermont (Location 400, Figure 2F).

Sampling

Water samples were collected between 8 March and 9 April 2002 from 20 sites at four locations and 19 sites at one location, with two well-water samples collected at each site. We also initially collected an air sample at each site to verify that no contamination was being introduced from sources such as the sample bottles and dust at the sites. Analysis of 17 such samples showed no detectable levels of the elements of interest; therefore, this procedure was discontinued.

Prior to the collection of samples, we decontaminated polystyrene collection bottles in a 5% nitric acid bath. Water samples were taken upstream of water softeners, preferably from the holding tank of the house, but also occasionally from the kitchen tap or outdoor spigot. Care was taken to avoid sampling water that had been altered by water softeners. In order to simulate normal household water usage, we did not purge the wells before collecting samples. Water temperature and pH were recorded and each sample was acidified to a pH of 2 by adding 0.2 to 0.4 mL of 35% HNO3 , following protocols recommended by the EPA (http://www.epa.gov/region01/measure/well/lowflow8.pdf). Prior to chemical analysis, samples were stored in a cool, dark cabinet. The latitude and longitude of each wellhead was determined using a GPS unit. If an identification tag was present on the wellhead, we attempted to determine the well number and date of installation.

Figure 2A. The region in northern Addison County where well water was sampled. Shown here are some of the town centers (stars), roads (black lines), and lithologies (shaded polygons). Boxes surround the five general sampling locations, shown in more detail in Figs. 2C-F.

Figure 2B. Target lithologies for this study. The Clarendon Springs Formation is shown in black and the Cheshire Quartzite Formation is shown in crosshatch gray.

Figure 2C. Location 000 in Ferrisburgh, Vermont, associated with the Stony Point Shale. The black points indicate the locations of the wells from which we sampled in this location.

Figure 2D. Locations 100 (to the north) and 200 (to the south) in Weybridge, Vermont, associated with the Clarendon Springs Formation. The black points indicate the locations of the wells from which we sampled in this location.

Figure 2E. Location 300 in Bristol, Vermont, associated with the Cheshire Quartzite Formation. The black points indicate the locations of the wells from which we sampled in this location.

Figure 2F. Location 400 in Monkton, Vermont, associated with the Cheshire Quartzite Formation. The black points indicate the locations of the wells from which we sampled in this location.

Analysis

We analyzed the metals content of samples within one week of water sampling using a Thermo Jarrell Ash IRIS 2000 inductively coupled plasma-atomic emission spectrometer (ICP-AES) operating in axial mode. We used a 2% HNO3 blank and two multi-element standards to calibrate the spectrometer. Given that all water samples contained roughly 2% HNO3, standards were prepared in the same way. One standard was prepared to contain metal concentrations comparable to the groundwater of limestone bedrock aquifers (Drever 1997) (Table 1). Only iron and aluminum concentrations in this standard were significantly higher than in natural groundwater levels. The other standard contained 100 ppb Th and U in 2% HNO3. The standards were automatically reanalyzed after each set of 10 samples for quality control purposes. Emission wavelengths were chosen to provide the most distinct emission spectra with the least interference. Table 2 lists the emission wavelengths and ICP-AES detection limits for each element measured.

The element concentration data obtained using the ICP-AES were edited for statistical analysis. Trace element concentrations were reported as the minimum threshold value of the ICP-AES (Table 2). All calcium values are noted to be extrapolations by the ICP due to the high concentrations of this element.

In order to obtain more accurate uranium and lead data, we analyzed subsets of 65 (uranium) and 35 (lead) samples on ICP-mass spectrometers (ICM-MS), one at Union College (Schenectady, NY) and one at Dartmouth College (Hanover, NH). At Union College, U238 concentrations in 30 samples was analyzed using a Perkin Elemer ELAN 6100 DRC ICP-MS. Samples were spiked with bismuth (Bi) to account for instrumental drift. The standard contained 10 ppb of U in 2% HNO3. Following every 10 samples, the blank and the 10 ppb U standard were reanalyzed. At Dartmouth, 35 samples were analyzed for uranium and lead using a Finnegan I ICP-MS using multiple uranium and lead standards that ranged in concentration from 0.01 ppb to 10 ppb.

The locations of the wellheads were downloaded from GPS units and transformed into a file readable by ArcView. Data were then transferred to a Microsoft Excel® spreadsheet and statistical analysis of the data was performed using SPSS 10.0. The main reason for the statistical analyses was to examine variation between samples at a given site (i.e., well), variation between sites within the same location, and variation from location-to- location (i.e. to test geological controls).

Table 1. Concentration of elements in standards used for ICP-AES.

Element Concentration (ppm) Aluminum 50.5 Arsenic 0.1 Beryllium 0.1 Cadmium 0.025 Calcium 50.0 Chromium 0.1 Cobalt 0.1 Copper 0.1 Iron 50.1 Lead 0.1 Manganese 10.1 Nickel 0.1 Phosphorus 10.0 Potassium 10.0 Selenium 0.025 Sodium 10.0 Titanium 10.1 Vanadium 0.25 Zinc 0.1

Table 2. ICP-AES detection levels and emission wavelengths for the 19 elements assessed.

Element Concentration Wavelength (ppm) (Å) Aluminum 0.002 317.9 Arsenic 0.00009 396.1 Cadmium 0.0005 189.0 Calcium 0.001 226.5 Chromium 0.001 267.7 Cobalt 0.0006 228.6 Copper 0.002 324.7 Iron 0.001 259.9 Lead 0.00009 220.3 Magnesium 0.0002 285.2 Nickel 0.002 231.6 Phosphorus 0.01 178.2 Potassium 0.01 766.4 Selenium 0.00009 196.0 Silicon 0.001 251.6 Sodium 0.004 589.5 Titanium 0.001 337.2 Uranium 0.00009 385.9 Zinc 0.0003 213.8

13 Results Within-site variation

As a quality control and assurance measure, we determined the coefficient of variance for each element concentration between samples within a site. The coefficient of variation indicated that variation between samples was not significant, with the exception of selenium. Therefore data for each site is reported as the average of two samples.

Chemical signatures of locations: ratios of primary elements from the bedrock

Table 3 shows that Location 000 (Ferrisburgh) and Location 200 (southern Weybridge) have chemical signatures most representative of limestone as indicated by high ratios of calcium:silicon (Ca:Si) and calcium:magnesium (Ca:Mg). High Ca values are expected for wells producing from limestone given that calcium carbonate (CaCO3) is the dominant mineral in limestone. Based on low Ca:Mg and high Mg:Si ratios, Location 100 appears to produce groundwater from the most dolomitic of the rock formations studied, the Clarendon Springs Formation. Dolomite is a carbonate rock comprised predominantly of calcium (Ca), magnesium (Mg) and carbonate (CO3). Location 300 (Bristol) has the most quartzite-like signature based on low ratios of Ca:Si and Mg:Si, reflecting elevated Si concentrations produced by weathering and dissolution of quartz (SiO2) and other silicate minerals. This is consistent with groundwater production originating from the Cheshire Quartzite Formation. Differences in signatures indicate that wells in location 400 produce groundwater from a source that is more enriched in Mg and Ca than location 300. This suggests wells in location 400 are producing from rock that is more dolomitic than location 300. Perhaps many of those wells in location 400 produce from the Dunham Dolomite, which is possible given the structural complexity of the region.

Table 3. Summary of the ratios of primary bedrock elements--calcium (Ca), magnesium (Mg), and silicon (Si)--at each of five locations in Addison County.

Location Ca : Mg Ca : Si Mg : Si

000 2.22 12.01 4.79 100 1.43 9.73 7.91 200 2.46 15.47 6.61 300 2.52 3.46 1.61 400 2.19 9.42 4.40

14 Elements with maximum limits required by the EPA (primary standards)

EPA primary standards are legally enforceable thresholds used to regulate public water systems and protect public health by limiting the levels of contaminants in drinking water. Although all of the sites evaluated in this study draw their water from private wells, and thus are not regulated by EPA, these standards are useful in assessing health risk from contamination in private wells.

Uranium With the exception of a single site, none of the homes sampled in Addison County contain uranium in excess of the current state EPA MCL of 20 ppb. However, a single site in Location 100 (northern Weybridge) represents an extreme value, with measured uranium concentrations 10 times greater that of the next highest measurement in the region and approximately double the current EPA MCL. The concentration of uranium in groundwater at the five locations exhibited relatively little site-to-site variation within each location (Figure 3) and no significant variation among locations (ANOVA; F = 1.659; P = 0.173; Table 4). Note that the current EPA MCL for uranium is 20 ppb but will be elevated to 30 ppb in December 2003.

Table 4. Concentrations of Mean Sample Standard uranium at five locations Location concentration size Error Range (ppb) in Addison County, (ppb) (ppb) measured in parts per billion (ppb). Sample 000 0.800 12 0.226 0.013 - 2.390 size refers to the number 100 5.109 12 3.318 0.956 - 41.473 of homes sampled in that location. Range reports 200 1.807 12 0.428 0.281 - 5.276 the smallest and largest 300 0.147 12 0.078 0.012 - 0.974 value at that location. 400 1.222 12 0.262 0.117 - 3.213 All 1.817 60 0.688 0.012 - 41.473

30 EPA MCL

-10 URANIUM -100 0 100 200 300 400 500

SITELOCATION

Figure 3. A scatter plot of uranium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per billion (ppb).

16 Lead Based on ICP-AES (20 of 99) and ICP-MS analysis (6 of 35), approximately 20% of sites had lead concentrations that exceed the EPA MCL of 0.015 ppm. Three of the locations— Location 100 (Twin Bridges area of Weybridge), Location 200 (Weybridge Hill), and Location 300 (Bristol)--had average values that exceeded this limit, and all locations had some sites that exceeded the limit (although barely so for sites in Location 000 [Ferrisburgh]). Thus, there is a strong indication that a number of homes in several different areas of Addison County face health risks due to high levels of lead.

The concentration of lead in groundwater at the five locations showed considerable site- to-site variation within each location (Figure 4) but no significant variation among locations (ANOVA; F = 1.379; P = 0.247; Table 5). To determine whether measurements of lead made using the ICP-AES were accurate, we measured lead concentrations in a subset of 35 samples using the ICP-MS at Dartmouth College. Values measured with these two methods were highly correlated (Pearson's correlation = 0.808, P < 0.0001), and measurements made with the ICP-AES were, on average, 73.8% (± 37.3 S.E.) greater than those measured by the ICP-MS. These results indicate that the absolute values measured by the ICP-AES vary from those measured by the ICP-MS by less than an order of magnitude. The ICP-AES tends to produce slight overestimates but provides good relative measures of lead concentrations.

Table 5. Concentrations of lead at five locations in Addison County, measured in parts per million (ppm). Sample size refers to the number of homes sampled in that location. Range reports the smallest and largest value at that location.

Mean Sample Standard Location concentration size Error Range (ppm) (ppm) (ppm)

000 0.002 20 0.001 0.000 - 0.017

100 0.099 20 0.053 0.000 - 0.842 200 0.047 19 0.034 0.000 - 0.641 300 0.049 20 0.040 0.000 - 0.801 400 0.007 20 0.003 0.000 - 0.037

All 0.041 99 0.015 0.000 - 0.842

1.0

EPA MCL 0.0

-.2 LEAD -100 0 100 200 300 400 500

LOCATION

Figure 4. A scatter plot of lead concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

18 Copper Although none of the locations had average values that approached the EPA MCL of 1.3 ppm, each location except Location 400 (Monkton) had some sites where this threshold was exceeded. Therefore, at least some of the homes in a number of locations in Addison County contain elevated levels of copper in their well water. The concentration of copper in groundwater at the five locations showed considerable variation from site-to-site within a location (Figure 5) but no significant variation among locations (ANOVA; F = 1.114; P = 0.355; Table 6).

Table 6. Concentrations of copper at five Mean Sample Standard locations in Addison County, size Range (ppm) Location concentration Error measured in parts per million (ppm) (ppm) (ppm). Sample size refers to the number of homes sampled in 000 0.171 20 0.105 0.002 - 1.912 that location. Range reports 100 0.352 20 0.173 0.002 - 2.597 the smallest and largest value 200 0.359 19 0.139 0.010 - 2.419 at that location.

300 0.618 20 0.293 0.014 - 5.937 400 0.175 20 0.060 0.002 - 0.999 All 0.335 99 0.078 0.002 - 5.937

EPA MCL 1

-1 COPPER -100 0 100 200 300 400 500

LOCATION

Figure 5. A scatter plot of copper concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

19 Arsenic Measurements of the concentration of arsenic in groundwater at the five locations varied from 0.001 ppm to 0.009 ppm (Table 7), all well below the EPA MCL for arsenic of 0.01 ppm. Statistical analysis indicates a significant difference in the measured arsenic concentration among locations (ANOVA; F = 2.646; P = 0.038), caused by the difference between Location 0 (Ferrisburgh) and Location 200 (southern Weybridge) (Figure 6). However, this difference is slight and has no apparent implications for human health.

Table 7. Concentrations of arsenic Mean Sample Standard at five locations in Addison Location concentration size Error Range (ppm) (ppm) (ppm) County, measured in parts per million (ppm). Sample 000 0.001 20 0.000 0.000 - 0.004 size refers to the number of 100 0.001 20 0.000 0.000 - 0.009 homes sampled in that location. Range reports 200 0.000 19 0.000 0.000 - 0.001 the smallest and largest 300 0.001 20 0.000 0.000 - 0.004 value at that location. 400 0.001 20 0.000 0.000 - 0.004 All 0.001 99 0.000 0.000 - 0.009

.012

.010 EPA MCL

.008

.006

.004

.002

0.000

-.002 ARSENIC -100 0 100 200 300 400 500

LOCATION

Figure 6. A scatter plot of arsenic concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

20 Chromium The concentration of chromium in groundwater at the five locations ranged from 0.001 ppm to 0.008 ppm (Table 8, Figure 7), all well below the EPA MCL of 0.1 ppm. There was significant variation among locations with respect to this element (ANOVA; F = 3.057; P = 0.020), caused largely by the higher levels of chromium found at Location 200 (southern Weybridge) (Tamhane's T2 posthoc test; all P values < 0.05) compared to either Location 000 (Ferrisburgh) or Location 300 (Bristol).

Table 8. Concentrations of chromium Mean Sample Standard at five locations in Addison Location concentration size Error Range (ppm) County, measured in parts (ppm) (ppm) per million (ppm). Sample size refers to the number of 000 0.001 20 0.000 0.001 - 0.002 homes sampled in that 100 0.002 20 0.000 0.001 - 0.006 location. Range reports the 200 0.002 19 0.000 0.001 - 0.003 smallest and largest value at that location. 300 0.001 20 0.000 0.001 - 0.001 400 0.002 20 0.000 0.001 - 0.008 All 0.001 99 0.000 0.001 - 0.008

.010

.008

.006

.004

.002

0.000 CHROMIUM -100 0 100 200 300 400 500

LOCATION

Figure 7. Scatter plot of chromium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm). The EPA MCL of 0.1 ppm is too high to depict on this figure.

21 Selenium None of the locations have average concentrations of selenium anywhere close to the EPA MCL of 0.05 ppm, and only a few sites have concentrations that were greater than 50% of this threshold value. Therefore, there is no evidence that homes in Addison County face health risks due to high levels of selenium. The concentration of selenium in groundwater at the five locations showed considerable site-to-site variation within each location (Figure 8) as well as significant variation among locations (ANOVA; F = 8.620; P < 0.001; Table 9). The among-location differences are caused largely by the low levels of selenium at Location 300 (Bristol) relative to higher levels at Location 100 (Twin Bridges area of Weybridge) and Location 200 (Weybridge Hill).

Table 9. Concentrations of Mean Sample Standard selenium at five locations Location concentration size Error Range (ppm) in Addison County, (ppm) (ppm) measured in parts per million (ppm). Sample 000 0.003 20 0.001 0.000 - 0.009 size refers to the number 100 0.008 20 0.002 0.000 - 0.028 of homes sampled in that location. Range reports 200 0.007 19 0.001 0.000 - 0.028 the smallest and largest 300 0.001 20 0.000 0.000 - 0.003 value at that location. 400 0.002 20 0.001 0.000 - 0.007 All 0.005 99 0.001 0.000 - 0.028

.03

.02

.01

0.00

-.01 SELENIUM -100 0 100 200 300 400 500

LOCATION

Figure 8. A scatter plot of selenium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

22 Elements with maximum limits recommended by the EPA (secondary standards)

Secondary standards are non-enforceable guidelines assigned by the EPA to regulate contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water. The EPA recommends secondary standards to water systems but does not require systems to comply.

Aluminum The concentration of aluminum in groundwater at the five locations varied from 0.01 ppm to 0.477 ppm, a 50-fold difference (Table 10). The recommended EPA threshold for aluminum ranges between 0.05 and 0.2 ppm. Only one location, Location 100 (Twin Bridges, Weybridge), had average values that exceeded this recommended level; however, this was due to very high levels measured at a single home (Figure 9). Location 300 also contained a single site with aluminum concentration exceeding the EPA MCL. There was no significant difference in the measured aluminum concentrations among locations (ANOVA; F = 0.965; P = 0.430).

Table 10. Concentrations of Mean Sample Standard aluminum at five locations Location concentration size Error Range (ppm) in Addison County, (ppm) (ppm) measured in parts per million (ppm). Sample size 000 0.015 20 0.002 0.003 - 0.042 refers to the number of 100 0.434 20 0.411 0.002 - 8.241 homes sampled in that location. Range reports 200 0.035 19 0.009 0.002 - 0.129 the smallest and largest 300 0.029 20 0.013 0.002 - 0.278 value at that location. 400 0.031 20 0.007 0.002 - 0.109 All 0.109 99 0.083 0.002 - 8.241

EPA MCL 0

-2 ALUMINUM -100 0 100 200 300 400 500

LOCATION

Figure 9. A scatter plot of aluminum concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm). EPA thresholds are given as a range from least to greatest MCL.

24 Iron Three locations--Location 100 (northern Weybridge), Location 300 (Bristol), and Location 400 (Monkton)--had average values that exceeded the EPA recommended threshold for iron of 0.3 ppm, and each location contained a number of sites where this threshold was exceeded, in some cases by more than 15 times. Therefore, at least some of the homes in a number of locations in Addison County may face aesthetic issues due to high levels of iron. The concentration of iron in groundwater at the five locations showed considerable variation from site-to-site within a location (Figure 10) but no significant variation among locations (ANOVA; F = 1.576; P = 0.187; Table 11).

Table 11. Concentrations of iron at Mean Sample Standard five locations in Addison Location concentration size Error Range (ppm) County, measured in parts (ppm) (ppm) per million (ppm). Sample size refers to the number of 000 0.208 20 0.058 0.001 - 0.984 homes sampled in that 100 0.718 20 0.285 0.007 - 5.215 location. Range reports the smallest and largest 200 0.116 19 0.061 0.001 - 1.065 value at that location. 300 0.386 20 0.236 0.001 - 3.862 400 0.323 20 0.143 0.001 - 2.799 All 0.353 99 0.083 0.001 - 5.215

EPA MCL 0

-1 IRON -100 0 100 200 300 400 500

LOCATION

Figure 10. A scatter plot of iron concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

25 Zinc The concentration of zinc in groundwater at the five locations showed considerable site- to-site variation within each location (Figure 11) but no significant variation among locations (ANOVA; F = 1.623; P = 0.175; Table 12). The EPA has a recommended threshold for zinc of 5 ppm. No site tested in Addison County had levels of zinc approaching this level; therefore, there is no indication that any of the homes in Addison County face health risks due to high levels of this element.

Table 12. Concentrations of zinc at Mean Sample Standard five locations in Addison Location concentration size Error Range (ppm) County, measured in (ppm) (ppm) parts per million (ppm). Sample size refers to the 000 0.040 20 0.020 0.001 - 0.408 number of homes 100 0.128 20 0.063 0.004 - 1.252 sampled in that location. Range reports the 200 0.210 19 0.088 0.000 - 1.693 smallest and largest 300 0.073 20 0.031 0.003 - 0.562 value at that location. 400 0.086 20 0.018 0.001 - 0.328 All 0.106 99 0.023 0.000 - 1.693

2.0

1.5

1.0

0.0

-.5 ZINC -100 0 100 200 300 400 500

LOCATION

Figure 11. A scatter plot of zinc concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

26 Elements without EPA limits Calcium The concentration of calcium in groundwater at the five locations varied from 0.21 ppm to almost 182 ppm (Table 13), resulting in a highly significant difference in the measured calcium concentration among locations (ANOVA; F = 14.470; P < 0.001). Calcium concentrations varied widely within each location (Figure 12). Each location differed from at least one other location (Tamhane's T2 posthoc test; P < 0.05), suggesting widespread variation among locations as well. However, the EPA has no required or recommended thresholds for calcium; therefore, these levels and differences have no apparent implications for human health.

Table 13. Concentrations of Mean Sample Standard calcium at five locations size Range (ppm) Location concentration Error in Addison County, (ppm) (ppm) measured in parts per million (ppm). Sample 000 39.29 20 8.58 3.11 - 130.40 size refers to the number 100 51.44 20 4.43 6.08 - 89.39 of homes sampled in that 200 84.84 19 9.11 34.39 - 181.90 location. Range reports the smallest and largest 300 14.38 20 2.21 0.21 - 42.86 value at that location. 400 48.22 20 6.43 17.59 - 139.85 All 47.26 99 3.68 0.21 - 181.90

200

100

-100 CALCIUM -100 0 100 200 300 400 500

LOCATION

Figure 12. A scatter plot of calcium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

27 Cadmium The concentration of cadmium in groundwater at the five locations showed virtually no variation and, in fact, few sites had concentrations of cadmium above the minimum detectable level (Table 14, Figure 13). As a result, no location differed from any other with respect to this element (ANOVA; F = 0.986; P = 0.419).

Table 14. Concentrations of cadmium Mean Sample Standard at five locations in Addison size Range (ppm) Location concentration Error County, measured in parts

(ppm) (ppm) per million (ppm). Sample 000 0.001 20 0.000 0.001 - 0.001 size refers to the number of homes sampled in that 100 0.001 20 0.000 0.001 - 0.001 location. Range reports 200 0.001 19 0.000 0.001 - 0.006 the smallest and largest value at that location. 300 0.001 20 0.000 0.001 - 0.001 400 0.001 20 0.000 0.001 - 0.001 All 0.001 99 0.000 0.001 - 0.006

.007

.006

.005

.004

.003

.002

.001

0.000 CADMIUM -100 0 100 200 300 400 500

LOCATION

Figure 13. A scatter plot of cadmium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

28 Cobalt The concentration of cobalt in groundwater at the five locations showed little overall variation and only a few sites had concentrations of cobalt above the minimum detectable level (Table 15, Figure 14). No location differed from any other with respect to this element (ANOVA; F = 0.493; P = 0.741).

Table 15. Concentrations of cobalt at Mean Sample Standard five locations in Addison Location concentration size Error Range (ppm) County, measured in parts (ppm) (ppm) per million (ppm). Sample size refers to the number of 000 0.001 20 0.000 0.001 - 0.001 homes sampled in that 100 0.001 20 0.000 0.001 - 0.001 location. Range reports the smallest and largest 200 0.001 19 0.000 0.001 - 0.001 value at that location. 300 0.001 20 0.000 0.001 - 0.001 400 0.001 20 0.000 0.001 - 0.001 All 0.001 99 0.000 0.001 - 0.001

.0013

.0012

.0011

.0010

.0009

.0008

.0007

.0006

.0005 COBALT -100 0 100 200 300 400 500

LOCATION

Figure 14. A scatter plot of cobalt concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

29 Potassium The concentration of potassium in groundwater at the five locations showed considerable variation from site-to-site within a location (Figure 15), with the greatest variation seen at Location 000 (Ferrisburgh). There was no significant variation among locations (ANOVA; F = 2.243; P = 0.070; Table 16). The EPA has neither required nor recommended thresholds for potassium; therefore, there is no indication that, despite the high levels seen at some sites, any the homes in Addison County face health risks due to high levels of potassium.

Table 16. Concentrations of Mean Sample Standard potassium at five locations size Range (ppm) Location concentration Error in Addison County,

(ppm) (ppm) measured in parts per 000 3.395 20 1.129 0.913 - 22.280 million (ppm). Sample size refers to the number of 100 2.391 20 0.231 0.853 - 4.516 homes sampled in that 200 1.677 19 0.213 0.481 - 3.726 location. Range reports the smallest and largest 300 1.289 20 0.229 0.132 - 5.007 value at that location. 400 1.783 20 0.245 0.605 - 5.312 All 2.112 99 0.252 0.132 - 22.280

-10 Potassium -100 0 100 200 300 400 500

LOCATION

Figure 15. A scatter plot of potassium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

30 Magnesium The concentration of magnesium in groundwater at the five locations showed considerable site-to-site variation within each location (Figure 16) as well as significant variation among locations (ANOVA; F = 27.834; P < 0.001; Table 17). Each location differed significantly from at least three of the four other locations (Tamhane's T2 posthoc test, all P values < 0.007), indicating a great deal of regional identity in the concentrations of magnesium. The EPA has neither required nor recommended thresholds for magnesium; therefore, there is no indication that, despite the high levels seen at some sites, any the homes in Addison County face health risks due to high levels of magnesium.

Table 17. Concentrations of Mean Sample Standard magnesium at five size Range (ppm) Location concentration Error locations in Addison

(ppm) (ppm) County, measured in parts 000 17.279 20 2.465 1.798 - 37.310 per million (ppm). Sample size refers to the number of 100 39.343 20 3.394 13.523 - 79.340 homes sampled in that 200 36.461 19 2.841 16.255 - 68.610 location. Range reports the smallest and largest 300 6.487 20 1.089 0.029 - 22.455 value at that location. 400 22.094 20 2.598 5.733 - 50.795 All 24.210 99 1.675 0.029 - 79.340

100

-20 Magnesium -100 0 100 200 300 400 500

LOCATION

Figure 16. A scatter plot of magnesium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

31 Sodium The concentration of sodium in groundwater at the five locations showed considerable site-to-site variation within each location (Figure 17) as well as significant variation among locations (ANOVA; F = 4.561; P = 0.002; Table 18). This difference is caused by the very low concentrations of sodium at Location 300 (Bristol), which was significantly lower than all other locations except Location 000 (Ferrisburgh) (Tamhane's T2 posthoc test, all P values < 0.006). The EPA has neither required nor recommended thresholds for sodium; therefore, there is no indication that, despite the high levels seen at some sites, any the homes in Addison County face health risks due to high levels of sodium.

Table 18. Concentrations of sodium Mean Sample Standard at five locations in Addison Location concentration size Error Range (ppm) County, measured in parts (ppm) (ppm) per million (ppm). Sample size refers to the number of 000 15.344 20 4.355 0.004 - 50.585 homes sampled in that 100 20.943 20 2.907 0.004 - 48.060 location. Range reports the smallest and largest 200 18.374 19 3.144 0.004 - 57.415 value at that location. 300 4.107 20 1.367 0.934 - 29.410 400 15.582 20 2.566 0.004 - 36.545 All 14.835 99 1.447 0.004 - 57.415

-10 SODIUM -100 0 100 200 300 400 500

LOCATION

Figure 17. A scatter plot of sodium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

32 Nickel The concentration of nickel in groundwater at the five locations showed considerable site-to-site variation within each location (Figure 18); however, there was no significant variation among locations (ANOVA; F = 1.455; P = 0.222; Table 19). Concentrations are very low, and are very close to the detection limit of the ICP-AES.

Table 19. Concentrations of nickel at Mean Sample Standard five locations in Addison Location concentration size Error Range (ppm) County, measured in parts (ppm) (ppm) per million (ppm). Sample size refers to the number of 000 0.003 20 0.001 0.002 - 0.013 homes sampled in that 100 0.003 20 0.001 0.002 - 0.017 location. Range reports the smallest and largest value at 200 0.006 19 0.002 0.002 - 0.035 that location. 300 0.004 20 0.001 0.002 - 0.012 400 0.003 20 0.001 0.002 - 0.014 All 0.004 99 0.000 0.002 - 0.035

.04

.03

.02

.01

0.00 NICKLE -100 0 100 200 300 400 500

LOCATION

Figure 18. A scatter plot of nickel concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

33 Phosphorus The concentration of phosphorus in groundwater at the five locations showed considerable site-to-site variation within each location (Figure 19) as well as significant variation among locations (ANOVA; F = 3.558; P = 0.01; Table 20). The among- location variation is caused exclusively by the large number of sites in Location 000 (Ferrisburgh) where levels of phosphorus were above the minimum detectable level of 0.010 ppm.

Table 20. Concentrations of Mean Sample Standard phosphorus at five locations Location concentration size Error Range (ppm) in Addison County, measured (ppm) (ppm) in parts per million (ppm). Sample size refers to the 000 0.044 20 0.006 0.010 - 0.122 number of homes sampled in 100 0.021 20 0.005 0.010 - 0.117 that location. Range reports the smallest and largest value 200 0.021 19 0.006 0.010 - 0.115 at that location. 300 0.021 20 0.004 0.010 - 0.091 400 0.022 20 0.004 0.010 - 0.074 All 0.026 99 0.003 0.010 - 0.122

.14

.12

.10

.08

.06

.04

.02

0.00 Phosphorus -100 0 100 200 300 400 500

LOCATION

Figure 19. A scatter plot of phosphorus concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

34 Silicon The concentration of silicon in groundwater at the five locations showed considerable site-to-site variation within each location (Figure 20) as well as significant variation among locations (ANOVA; F = 7.534; P < 0.001; Table 21). The among-location differences are caused largely by the low levels of selenium at Location 000 (Ferrisburgh) relative to higher levels elsewhere (Tamhane's T2 posthoc test, all P values < 0.007). The EPA has neither required nor recommended thresholds for silicon; therefore, there is no indication that, despite the high levels seen at some sites, any the homes in Addison County face health risks due to high levels of this element.

Table 21. Concentrations of silicon Mean Sample Standard at five locations in Location concentration size Error Range (ppm) Addison County, (ppm) (ppm) measured in parts per million (ppm). Sample 000 3.735 20 0.197 2.538 - 6.063 size refers to the number 100 5.067 20 0.288 3.941 - 9.958 of homes sampled in that location. Range reports 200 5.626 19 0.398 2.787 - 9.037 the smallest and largest 300 4.141 20 0.297 2.389 - 6.843 value at that location. 400 5.116 20 0.188 3.733 - 7.031 All 4.728 99 0.141 2.389 - 9.958

2 SILICON -100 0 100 200 300 400 500

LOCATION

Figure 20. A scatter plot of silicon concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

35 Titanium The concentration of titanium in groundwater at the five locations showed considerable site-to-site variation within each location (Figure 21) as well as significant variation among locations (ANOVA; F = 5.611; P < 0.001; Table 22). The among-location differences are caused largely by the low levels of titanium at Location 300 (Bristol) relative to higher levels elsewhere (Tamhane's T2 posthoc test, all P values < 0.05). The EPA has neither required nor recommended thresholds for titanium, and there is no indication that any the homes in Addison County face health risks due to high levels of this element.

Table 22. Concentrations of Mean Sample Standard titanium at five locations Location concentration size Error Range (ppm) in Addison County, (ppm) (ppm) measured in parts per million (ppm). Sample 000 0.002 20 0.000 0.001 - 0.006 size refers to the number 100 0.003 20 0.000 0.001 - 0.006 of homes sampled in that location. Range reports 200 0.002 19 0.000 0.001 - 0.005 the smallest and largest 300 0.001 20 0.000 0.001 - 0.002 value at that location. 400 0.002 20 0.000 0.001 - 0.007 All 0.002 99 0.000 0.001 - 0.007

.008

.007

.006

.005

.004

.003

.002

.001

0.000 TITANIUM -100 0 100 200 300 400 500

LOCATION

Figure 21. A scatter plot of titanium concentration values at each site, grouped into the five locations examined in Addison County. Concentrations are given in parts per million (ppm).

36 Table 23. Locations with sites that exceed maximum contaminant levels for at least one element with an EPA MCL. Black boxes indicate locations where the average element concentration across all sites exceeds the EPA MCL. Grey boxes indicate locations where the element concentration exceeds the EPA MCL at one or more sites. Asterisks indicate those elements for which the EPA only has secondary standards.

ELEMENT 000 100 200 300 400 Aluminum* ********** ======Arsenic Chromium Copper* ********** ********** ********** ********** Iron* ********** +++++++++ ********** +++++++++ +++++++++ Lead +++++++++ +++++++++ +++++++++ +++++++++ +++++++++ Selenium Uranium ********** Zinc

37 Discussion Implications for human health

Of the nineteen elements we measured, nine have maximum contaminant levels (MCL) assigned by the EPA. Of these, only five elements exceeded the MCL for primary or secondary drinking water standards in one or more locations in our study area. These elements are uranium, lead, copper, iron, and aluminum. The following elements are either unregulated or did not exceed EPA standards: arsenic, chromium, selenium, zinc, calcium, cadmium, cobalt, potassium, magnesium, sodium, nickel, phosphorus, silicon, and titanium.

Uranium and other radionuclides

In our study, the only radionuclide for which we tested was U238, a substance regulated by the EPA under authority of the Safe Drinking Water Act. In 2000, the EPA proposed new national drinking water standards to be effective December 8, 2003. In their proposal, the Maximum Contaminant Level Goal (MCLG) is 0 ppb and the MCL is 30 ppb. The EPA set its MCLG (defined as a non-enforceable health-based goal) at a level of zero because of the inherent danger posed by uranium in drinking water due to its radioactive qualities (EPA 2000a).

Nearly all of the U238 levels detected at our study sites were well below the EPA’s MCL (Table 4, Figure 3). Therefore, with the exception of one site in location 100 (northern Weybridge above the Clarendon Springs Formation), none of the homes sampled in Addison County face health risks due to high levels of uranium. Further studies need to address whether or not elevated uranium levels occur in other sites in location 100 or in wells drilled through the Clarendon Springs Formation elsewhere across the state.

While uranium itself is not dangerous in terms of radioactive decay (because of its half- life of 4.5 billion years), uranium minerals in bedrock can serve as parent materials for other more radioactive elements such as radium, thorium, and radon. We did not have the equipment necessary to test for the presence of these other radionuclides. However, since uranium can be used as an indicator of their presence in water (Sloto 2000), there is a chance these radionuclides occur at some of the sites in our study area.

Radionuclides in drinking water pose three general health risks. First, they can be ingested and concentrated to toxic levels in digestive organs. Second, when ingested, they can release radiation in the body. And third, they can be released from drinking water and inhaled with indoor air, in turn releasing radiation from within the pulmonary tract.

Toxic concentrations of uranium can accumulate in the kidneys where normal functioning of the organs is disrupted by chemical action on processes associated with protein reabsorption. Furthermore, ionizing radiation released from radionuclides that have either been ingested or inhaled damages cells in the body and leads to cancerous growth (EPA 2000a). However, the more pressing human health concern is that Rn222, a daughter element of U238 (Figure 1), which can be released from drinking water during common household activities (e.g., dishwashing, showers). In turn, the progeny of Rn222

38 (Po218, Po214 and Pb214) emit alpha radiation that damages cells in the pulmonary tract, which may cause genetic mutation, tumor growth, or cancer formation.

While concerns regarding the effects of radon gas are great, they are mostly associated with situations in which the radon gas enters the house via soil under the foundation of a house. In the United States, as many as 22,000 deaths annually are due to lung cancer attributed to radon gas that has entered houses from soil below the foundations. Radon in groundwater is less of a concern. Radon in drinking water is responsible for 168 annual deaths, about 1-2 % of all deaths associated with radon exposure (EPA 1999). Although our study did not include any analysis of radon, future studies should address the issue of radon in both drinking water and indoor air.

Although all locations except Location 100 had uranium levels well below the EPA MCL, the potential for elevated concentrations of other radionuclides such as radium, radon, polonium and lead exists, especially for households with uranium concentrations above background levels of 1 ppb (0.001 ppm). The USGS has shown that radionuclides can be present at unsafe levels even when uranium is present in concentrations below the EPA MCL (Sloto 2000). Homeowners who have uranium concentrations greater than 1 ppb may want to contact the Vermont Department of Health to have their water tested for gross alpha uranium emissions, an approximation of total concentrations of radioactive elements in water. For more information regarding uranium and other radionuclides, contact the EPA or the Vermont Department of Health.

Lead

Mean concentrations of lead were elevated beyond the EPA MCL at locations 100, 200, and 300 (Table 5, Figure 4). Potential sources of lead in drinking water may be the erosion of natural deposits into the aquifer, atmospheric sources, or lead plumbing in households. The variation of lead concentrations from site-to-site within locations may indicate that elevated lead concentrations are affected by unique properties of individual houses and not the dominant bedrock. However, the lack of elevated lead at locations 000 and 400 suggests that geologic factors contribute to the spatial variability of lead in ground water in northern Addison County.

Potential health effects of prolonged lead exposure include delayed physical and mental development in children and kidney problems and elevated blood pressure in adults. Lead is known as a chronic contaminant because it is stored in the bloodstream, soft tissues, and the skeleton, which allows for the continual release of toxins after ingestion. Children are especially susceptible to lead poisoning because their gastrointestinal tracts more easily absorb the element (EPA 2000b).

Individual homeowners who have lead concentrations above the EPA MCL (0.015 ppm or 15 ppb) are encouraged to investigate the source of lead contamination and make adjustments accordingly. More information about the health risks of lead in drinking water is available from the EPA and the Vermont Department of Health.

39 Copper, iron, and aluminum

Copper concentrations exceeded the EPA MCL at some sites in each location except location 400 (Table 6, Figure 5). Severe copper concentrations in the human body can cause gastrointestinal disturbances and chronic indigestion due to irritation of the stomach by copper ions. People suffering from Wilson’s Disease are more likely to suffer from increased toxicity of the liver and brain. However, effects vary in accordance with diet and age (EPA 2000b).

Elevated levels of iron were detected at locations 100 (Twin Bridges area of Weybridge), 200 (Weybridge Hill), and 400 (Monkton), although these levels are not a major health concern (Table 11, Figure 10). The EPA categorizes iron as a secondary element, meaning elevated levels may have cosmetic effects on appliances or on the human body, such as discoloration of the teeth. However, no human health dangers are believed to exist.

Aluminum exceeded EPA secondary limits as well, but only in one site within location 100 (Table 10, Figure 9). For the same reasons that iron is not listed as a concern for human health, aluminum is not a dangerous element even at elevated levels.

More information about the implications of copper, iron, and aluminum in water can be obtained from the EPA.

Geologic interpretations of results

Clarendon Springs Formation

The unique chemical signature of location 100 (northern Weybridge), with relatively low Ca:Mg ratios and high Mg:Si ratios, is strong indication that wells at this location are producing groundwater from the dolomitic Clarendon Springs Formation. Dolomites, or dolostones, are carbonate rocks with high concentrations of Mg. The more Ca-rich values from Location 200 (southern Weybridge) suggest that wells in this region are producing from rocks that are less dolomitic than at Location 100. This finding is significant because the Vermont Geological Survey (VGS) has identified the Clarendon Springs Formation as a significant source of radionuclides in Milton and Colchester (Kim and Becker, 2001; Kim and Robinson 2002). The fact that it outcrops extensively in Addison County, and that our results document one well with uranium concentrations above the EPA MCL, indicates that the Clarendon Springs Formation is also a cause for concern in Addison County. Given that the Clarendon Springs Formation extends further south into Rutland and Bennington Counties, the potential for elevated radionuclides in groundwater exists throughout the Champlain Valley where this formation is present.

Recent field work (Kim and Robinson 2002) indicates that the Clarendon Springs Formation contains brecciated zones that are enriched in organic matter and produce readings on the gamma ray spectrometer that are orders of magnitude greater than surrounding unbrecciated dolostone. This suggests that the Clarendon Springs Formation contains small (on the order of meters to tens of meters), localized zones of radionuclide- rich rock. The chance that a well will penetrate one of these zones is unknown, but if it does, the well water is likely to contain elevated levels of radionuclides. As evidenced by

40 the analysis of the unique site in Weybridge (Location 100), these zones may also produce elevated concentrations of aluminum and other elements. The geological origin of these zones may be analogous to uranium roll-front deposits (Kim, personal communication). Metal-enriched, oxidized groundwater flowing through the Clarendon Springs Formation soon after deposition but before it had been cemented into rock deposited uranium and possibly other metals in chemically-reduced, organic rich zones. Such deposits are described by Drever (1997).

Thus, in spite of a sample size that is too small to provide statistically significant differences among locations in our study area, it appears that the Clarendon Springs Formation is capable of enriching groundwater with uranium. It also appears that the Clarendon Springs Formation is a source of elevated lead levels in groundwater, with five of the six highest lead concentrations occurring in wells that penetrate the Clarendon Springs Formation.

Cheshire Quartzite Formation

Studies by Kim and Becker (2001) and Corr (2002) indicate that the Cheshire Quartzite is also a potential source of radionuclides in groundwater. Elevated gross alpha readings in St. George have been attributed to the Cheshire Quartzite, and Corr (2002) suggests that the phyllitic part of the lower Cheshire Quartzite is the most likely source of radionuclides within this formation. Phyllitic beds are cleaved and foliated, providing a migration pathway and containing radiogenic minerals such as apatite, zircon, and sphene (Kim and Becker 2001, Corr 2002).

Interestingly, Location 300 (Bristol), which is situated directly atop the upper Cheshire Quartzite Formation, contained the lowest average uranium concentration of all the locations besides the control. This appears to confirm Corr’s (2002) assertion that the lower Cheshire is the more significant source of radionuclides. Both of our Cheshire- dominated sites (Locations 300 [Bristol] and 400 [Monkton]) are located predominantly in the upper Cheshire and likely contain little phyllite (Doll et al. 1961). Furthermore, Ca-Si-Mg signatures of Location 400 (Monkton) suggest that we analyzed water exposed to a combination of Cheshire Quartzite and Dunham Dolomite, which is not surprising considering the structural complexity and faulting in this part of the Champlain Valley.

It is interesting to note that location 000, above the Stony Point Shale, exhibited the lowest lead and uranium concentrations. Despite our small sample size, which failed to produce any statistically significant results, the Stony Point Shale appears to contain lower concentrations of both of these elements than the Clarendon Springs Formation, and less lead than the Cheshire Quartzite.

Discussion of Results for Other Elements

There were some elements that did not exceed EPA standards or vary significantly among locations. They include zinc, cadmium, cobalt, potassium, and nickel. All of these elements vary from site to site and are common in trace amounts in all three types of bedrock studied (Faure 1991). Because they were distributed uniformly across the study area and pose no human health risks, they are not of major concern to homeowners in Addison County.

We found that a number of elements varied significantly among locations: arsenic, chromium, selenium, calcium, magnesium, sodium, phosphorus, silicon, and titanium. Although none of these elements raise issues for human health, some of them are interesting in regards to this study in a number of ways. Of these elements, the most interesting are calcium, magnesium, and silicon. One of our primary goals was to investigate how different bedrock types and structures influence the chemical composition of well water in Addison County. As stated above, the different ratios of calcium, magnesium, and silicon can be thought of as chemical signatures of the different types of bedrock we studied (Table 3).

Implications for a Predictive Model

One of the goals of this study was to test whether or not a predictive model could be generated to approximate where elevated levels of uranium, lead, or other trace metals are likely to occur in Addison County based on geologic information. Our results indicate that the Clarendon Springs Formation is a potential source of elevated levels of uranium and lead— the one anomalously high uranium concentration and five of the six highest lead concentrations are from locations where the Clarendon Springs Formation outcrops at the surface or is inferred to be present at shallow depths (and thus would be providing water to wells). While our limited data set does not provide information pertaining to source minerals or migration pathways that would be required to form a comprehensive predictive model, it does indicate the need for further analysis of the spatial distribution and sources of uranium and lead in the Clarendon Springs Formation. Also, given the lack of statistically significant differences between locations, it would be worthwhile to (1) carry out more detailed analyses of groundwater from the Cheshire Quartzite Formation and other formations in the Champlain Valley, and (2) examine other lithologies such as the Precambrian metamorphic rocks associated with the Green Mountains and granite plutons found in central and northeastern Vermont. Further analysis of the Cheshire Quartzite Formation, for example, should clarify which zones within the Cheshire Quartzite are the most significant sources of radionuclides. Our results and those of Kim and Becker (2001) and Corr (2002) indicate that elevated uranium levels in the Cheshire Quartzite occur in foliated structures common to lower Cheshire Quartzite, but not in the unfoliated upper portion of this formation. Further analysis of well water from the Cheshire Quartzite will help refine this model.

Recommendations for Future Work

Additional considerations for future studies include:

(1) Sample well water directly from the well. We chose to sample from holding tanks (and occasionally taps) to facilitate mid-winter sampling, and also to obtain water as it enters the plumbing system of the house. However, it is also common to sample directly from wells to avoid potential effects from pipes and tanks between the well and the tap.

(2) Obtain more samples at each site to better understand the variation within and among sites. For example, if we had taken 10 samples at each site instead of 2, we could see how much real variation exists and reduce the probability that the variation is influenced by our methodology. Furthermore, if samples were collected on different days, in different

42 seasons, and in different years, we could get a better sense as to how the composition of groundwater varies with respect to time and season.

(3) Use of an ICP mass spectrometer to improve the accuracy of results, especially in the analysis of heavy elements such as uranium (and, to a lesser extent, lead). Our results indicate that ICP-AES is virtually useless in analyzing trace amounts (e.g. <50 ppb) of uranium. On the other hand, it is useful for other trace elements in well water, including lead, copper, nickel, chromium, aluminum, and iron.

(4) Increase sample size to better assess variation among locations, especially in regards to the elements that exceeded the EPA standards but did not differ significantly among locations.

Sources of Error and Uncertainty

In choosing the five locations in our study area, we made assumptions regarding the locations of contacts between geologic formations on the state Geologic Map, published in 1961 (Doll et al. 1961). We are confident that major lithologies and faults are mapped correctly. However, the extensive deposits of clay in the Champlain Valley cover much bedrock, and contacts are sometimes interpolated, and faults may be covered to the point they are unrecognizable. Consequently, towards the edge of formations and in regards to the minor fault lines mapped, the degree to which our map corresponds to the natural world becomes less known. Furthermore, we used only two-dimensional geologic maps of the study area. This is relevant to our study because well water samples were taken from sites where only the surface lithology is known. There is a good chance that deep bedrock wells cross a number of different lithologies, thereby making correlations between element composition and specific rock types difficult. Nonetheless, compositional differences in Ca-Si-Mg indicate that we generally sampled the lithologic units we initially targeted.

There is potential for error in some aspects of our methodology: (1) water samples came from a variety of locations: wellhead, water tank, and tap. Each of these locations may slightly influence the sample. We minimized this error by obtaining samples directly from a holding tank when ever possible. However, there were circumstances in which we were allowed samples from the tap only; (2) we did not purge the tank before taking samples. Letting the tank purge may draw water samples directly from the well. However, we reasoned that by taking an un-purged sample we would more closely simulate conditions to which people are actually exposed; (3) the accuracy of the ICP- AES and ICP-MS units varied from run to run. It is well known that these instruments have errors that range from <3% for elements in high concentrations (e.g., Ca, Mg) to >10% for trace elements; and (4) in studies such as these, sample size is always an issue. We took 19-20 samples in each of the 5 locations for a total of 99 samples. Increasing sample size would strengthen our results.

43 Conclusion

Our study of groundwater composition in northern Addison County found that water in approximately 20% of the wells sampled exceeded the EPA MCL for lead and that one site exceeded the EPA MCL for uranium. While the distribution of these elements was heterogeneous, some trends do emerge. Of particular concern is the Clarendon Springs Formation, a dolomitic rock formation that is the apparent source of elevated uranium at one site in Weybridge. This finding is consistent with the work of the Vermont Geological Survey (Kim and Becker 2001; Kim and Robinson 2002), who showed that the Clarendon Springs Formation is a source of radionuclides in the towns of Milton and Colchester. Preliminary fieldwork by Jon Kim of the VGS indicates that the occurrence of elevated uranium in groundwater may be related to organic-rich brecciated bedrock zones in the Clarendon Springs Formation. Our data show no indication of elevated uranium levels in the Cheshire Quartzite Formation; however, the wells we sampled probably did not penetrate foliated zones in the lower Cheshire Quartzite Formation, now suspected to be the main source of uranium and other radionuclides in the Cheshire Quartzite (Corr 2002).

The Clarendon Springs Formation is also the source of five of the six highest lead concentrations measured in this study. Of the 20 wells located where the Clarendon Springs Formation is at shallow depth (and thus most likely to influence well water), 45% (9/20) exceeded the EPA MCL for lead of 0.015 ppm. In all, 30% of wells (13/40) in the Clarendon Springs Formation contained lead at concentrations greater than the EPA MCL. Approximately 20% of wells (8/39) in the Cheshire Quartzite exceeded the EPA MCL, and only 5% (1/20) of wells in the Stony Point Shale exceeded the EPA MCL for lead.

These findings (1) suggest that certain bedrock formations are more likely to produce elevated levels of natural contaminants than others and (2) illustrate the need for more thorough analyses of groundwater composition to better understand geological controls.

Acknowledgements

We are particularly grateful to Jon Kim of the Vermont Geological Survey for advice and information throughout the development of this project. We also thank Brad Corr and Ray Coish of Middlebury College for access to information from their field work in this area and assistance with the ICP-AES at Middlebury College. We are grateful to Kurt Hollacher (Union College) and Stefan Sturup (Dartmouth College) for advice and access to the ICP-MS machines at their institutions. Finally, we thank all of the homeowners in Addison County who kindly allowed us to collect water samples from their wells.

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