U.S. Department of the Interior 

U.S. Geological Survey 

Prepared in cooperation with the U.S. Environmental Protection Agency and the 

New Hampshire Department of Environmental Services 

Geophysical and Flow-Weighted NaturalContaminant Characterization of Three 

Water-Supply Wells in New Hampshire 

Fractured

crystalline

bedrock

Sediment

Open-File Report 2011–1019 
Cover. Photograph shows a tripod and cable, used to log a water-supply well, along with a depiction of fractured bedrock, a 

geophysical probe, and processed data. 
 

 

 

 

 

 

 

 

 

Geophysical and Flow-Weighted NaturalContaminant Characterization of Three 

Water-Supply Wells in New Hampshire 

By Thomas J. Mack, Marcel Belaval, James R. Degnan, Stephen J. Roy, and 

Joseph D. Ayotte 

Prepared in cooperation with the U.S. Environmental Protection Agency and the 

New Hampshire Department of Environmental Services 

Open-File Report 2011–1019 

U.S. Department of the Interior 

U.S. Geological Survey 
 

U.S. Department of the Interior 

KEN SALAZAR, Secretary 

U.S. Geological Survey 

Marcia K. McNutt, Director 

U.S. Geological Survey, Reston, Virginia: 2011 

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U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual copyright owners to 


reproduce any copyrighted materials contained within this report.
 

Suggested citation:
 

Mack, T.J., Belaval, Marcel, Degnan, J.R., Roy, S.J., and Ayotte, J.D., 2011, Geophysical and flow-weighted natural-


contaminant characterization of three water-supply wells in New Hampshire: U.S. Geological Survey Open-File 


Report 2011–1019, 20 p., at http://pubs.usgs.gov/of/2011/1019/.
 
iii 

Acknowledgments 

The authors thank the residents and operators of the water systems investigated for their 

cooperation and assistance with this study. Special appreciation goes to Denise M. Argue 

and Jeffrey R. Deacon, of the U.S. Geological Survey, for assistance with water sampling. 

This project was funded in part by the New Hampshire Department of Environmental Services 

(NHDES) and the U.S. Environmental Protection Agency (USEPA), Office of Research and 

Development (ORD), Regional Applied Research Effort (RARE) program in collaboration with 

USEPA Region 1. Special thanks go to Randall Ross, USEPA ORD, for technical review of project 

work plans, and to Brandon Kernen, NHDES, for conceptual planning. 
THIS PAGE INTENTIONALLY LEFT BLANK
 
v 

Contents 

Acknowledgments........................................................................................................................................iii
 

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

Introduction.....................................................................................................................................................1
 

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

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

Previous Investigations........................................................................................................................2
 

Methods and Approach.......................................................................................................................3
 

Borehole Geophysics..................................................................................................................4
 

Groundwater Sampling and Water-Quality Analysis.............................................................4
 

Borehole Flow and Water Quality Characterization ................................................................................7
 

Francestown..........................................................................................................................................7
 

Borehole Geophysical Logs .......................................................................................................7
 

Water Quality and Flow-Weighted Chemical Constituents ..................................................8
 

Londonderry...........................................................................................................................................9
 

Borehole Geophysical Log Analysis.........................................................................................9
 

Water Quality and Flow-Weighted Chemical Constituents ................................................11
 

Salem....... .............................................................................................................................................12
 

Borehole Geophysical Log Analysis.......................................................................................13
 

Water Quality and Flow-Weighted Chemical Constituents ................................................13
 

Limitations and Alternatives to the Methods Used................................................................................16
 

Summary and Conclusions.........................................................................................................................17
 

References Cited..........................................................................................................................................18
 

Appendix 1. Sampling Time, Depth, Contaminant Concentration, and Field Parameters for 


Water Sampled from Wells in Francestown, Londonderry, and Salem, New Hampshire .20
 

Figures 

1.	 Map showing locations of the water-supply systems investigated in Francestown, 


Londonderry, and Salem, New Hampshire...............................................................................3
 

2.	 Borehole geophysical logs for well FBRW-1, Francestown, New Hampshire, 2008.........5
 

3.	 Borehole geophysical logs for well LBRW-1, Londonderry, New Hampshire, 2009........10
 

4.	 Borehole geophysical logs for well SBRW-2, Salem, New Hampshire, 2009...................14
 
 

 

 

vi 

Tables 

1.	 Depth of fractures, sampling depth, flow fraction, arsenic concentration, and flowweighted arsenic concentration for water sampled from well FBRW-1, Francestown, 

New Hampshire, 2008 ..................................................................................................................8 

2.	 Depth of fractures, sampling depth, flow fraction, uranium concentration, and flowweighted uranium concentration for water sampled from well LBRW-2 for two 

pumping scenarios, Londonderry, New Hampshire..............................................................12 

3.	 Depth of fractures, sampling depth, flow fractures, uranium concentrations, and 

flow-weighted uranium concentrations in well SBRW-2 for two pumping scenarios, 

Salem, New Hampshire, 2009 ...................................................................................................15 

Conversion Factors and Datum 

Inch/Pound to SI 

Multiply By To obtain 

Length 

inch (in.) 2.54 centimeter (cm) 

inch (in.) 25.4 millimeter (mm) 

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km) 

gallon (gal) 0.003785 cubic meter (m3

) 

Flow rate 

gallon per minute (gal/min) 0.06309 liter per second (L/s) 

gallon per day (gal/d) 0.003785 cubic meter per day (m3

/d) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: 

°F=(1.8×°C)+32 

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: 

°C=(°F–32)/1.8 

Vertical coordinate information is referenced to North American Vertical Datum of 1988 


(NAVD 88).
 

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

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).
 
Geophysical and Flow-Weighted Natural-Contaminant 

Characterization of Three Water-Supply Wells in 

New Hampshire 

By Thomas J. Mack1, Marcel Belaval2, James R. Degnan1, Stephen J. Roy3, and Joseph D. Ayotte1 

Abstract 

Three bedrock water-supply systems in New Hampshire were studied, using borehole geophysics and flowweighted sampling techniques, to determine the sources and distribution of natural contaminants in water entering 

the boreholes and to assess whether borehole modifications might be used to reduce contaminant levels. Well water 

in more than 100 community water-supply systems in New Hampshire have natural contaminants, such as arsenic 

and uranium, above the U.S. Environmental Protection Agency maximum contaminant levels of 10 and 30 micrograms per liter, respectively. The water-system wells were studied to identify fractional contributions of natural contaminants from specific fracture zones. The yields and flow-weighted contaminant levels of such fracture zones were 

assessed to determine if a modification of the borehole might lead to a reduction in the system’s contaminant levels. 

The water-supply systems investigated were typical of small community water systems in New Hampshire 

where a water system may serve 100 connections or less. Each water system consisted of two wells, approximately 

300 to 400 feet deep, in generally low-yielding (about 10 gallons per minute or less) crystalline bedrock. The wells 

were typically operated a few hours per day to fill a storage tank and had tens of feet of drawdown caused by the low 

well yields. The systems selected had contaminant concentrations slightly above MCL, or a low-level contamination. One of the water systems investigated had low-level (10 to 24 micrograms per liter) arsenic contamination, and 

two of the water systems had low-level uranium (30 to 40 micrograms per liter) contamination. The contaminant 

values were blended-water concentrations from the two wells in a system. Each water system had differences in 

contaminant concentrations between the two wells. In each case, the well with the greater concentration of the two 

was selected for investigation. In two of the three systems investigated, there was either not enough variation in the 

borehole contaminant concentration or not enough water-yielding fractures for borehole modifications to be a viable 

potential remedy to elevated contamination. However, borehole and contaminant conditions in one of the bedrock 

supply-well systems may be favorable to potential improvement of supplied water by borehole modification where 

selected fracture zones are sealed off from supplying water to the well. 

Introduction 

Arsenic and uranium are common naturally occurring contaminants in groundwater in bedrock aquifers in New 

England (Ayotte and others, 1999, 2003, 2007; Moore, 2004; Montgomery and others, 2003; Peters and Blum, 2003; 

Welch and Stollenwerk, 2003; Robinson and others, 2006). Many bedrock water-supply wells in New England have 

U.S. Environmental Protection Agency (USEPA) maximum contaminant level (MCL) exceedances of these naturally 

occurring contaminants. In the case of arsenic, many community water systems in New England have a problem 

complying with the 10 μg/L (micrograms per liter) arsenic drinking-water standard, and many of such systems have 

concentrations in the range of 10 to 20 μg/L. In New Hampshire, about 100 community groundwater systems have 

arsenic in source water in this concentration range. For public water systems with low-level exceedances of naturally 

occurring contaminants, defined as contaminant concentrations slightly above MCL, a treatment system generally is 

1

 U.S. Geological Survey. 

2

 U.S. Environmental Protection Agency. 

3

 New Hampshire Department of Environmental Services. 

1 
 

 

installed to comply with drinking-water regulations. In addition to the costs associated with treatment installation, 

operation, and maintenance, there also is an added future burden of ongoing disposal of treatment residuals that may 

contain hazardous levels of arsenic or radionuclides. 

In 2008 and 2009, the USEPA, New Hampshire Department of Environmental Services (NHDES), and U.S. 

Geological Survey (USGS) initiated this study to evaluate borehole characterization methods for identifying natural 

contaminant flow into bedrock water-supply wells from individual fractures or fracture zones. If natural contaminants in a bedrock water-supply well are found to originate from specific fractures in a borehole, it may be possible 

to block or modify a section of the borehole to reduce the inflow of the contaminant. This investigation allows for 

(1) testing of methods at a variety of bedrock supply-well systems, and (2) testing characterization techniques to 

assess if borehole modifications may provide a cost effective treatment option. 

Purpose and Scope 

This report presents the results of borehole geophysical well logging and flow-weighted water-quality sampling 

to determine concentrations of selected natural contaminants in water supplied by three bedrock water systems in 

New Hampshire. This report presents the methods used to (1) characterize boreholes using standard geophysical 

tools and sampling techniques; (2) identify the predominant bedrock fractures and the flow-weighted concentration 

of contaminants contributing to a well; and (3) help identify borehole and contaminant conditions where borehole 

modifications may help to achieve MCL compliance for naturally occurring arsenic and uranium in bedrock supply 

wells. This report also describes two alternative approaches for borehole characterization that may warrant application in wells with attributes that differ from the three wells investigated. 

Description of Study Area 

Many communities in New Hampshire rely on wells completed in fractured crystalline bedrock for their water 

supply. The quality of groundwater in the bedrock aquifer is generally good; however, occurrences of arsenic and 

other metals have been found to be associated with lithochemical bedrock groups in areas of the state (Montgomery 

and others, 2003; Moore, 2004). Bedrock public water-supply well sites with exceedances of naturally occurring 

regulated contaminants that were slightly greater than (within about 20 percent) the MCL were selected for study. 

Sites with greater exceedances were not investigated because such sites are less likely to be remediated to levels less 

than the MCL using borehole modifications. The study area is characterized as a fractured-crystalline bedrock setting 

where overburden sediments are generally less than 30 ft thick. Water-supply wells in this setting are typically 300 to 

500 ft deep with low yields, 10 gal/min or less. The water-supply systems investigated were typically well systems 

serving small housing developments in rural areas with about 100 service connections. The water systems generally 

consisted of two water-supply wells installed in fractured-crystalline bedrock, a storage tank, and sometimes chlorination and pH adjustment. 

Previous Investigations 

In 2006, the NHDES and the USEPA Region 1 evaluated three small drinking-water systems in southern New 

Hampshire as candidates for borehole modification (Marcel Belaval, U.S. Environmental Protection Agency, written commun., 2007; Stephen Roy, New Hampshire Department of Environmental Services, written commun., 2007). 

The results of that evaluation indicated that arsenic levels varied by fracture and that borehole modification may 

be successful at reducing overall arsenic concentrations in well water. On the basis of these preliminary findings, 

borehole characterization and modifications were believed to provide a potential means for a rapid and inexpensive 

remediation of low-level naturally occurring contaminants. 

Borehole modifications have been used in non-crystalline bedrock settings to remediate naturally occurring arsenic contamination in well water. Smith (2005) found elevated arsenic concentrations in specific sandstone units in 

Oklahoma that could be selectively removed from the screened zones of public-supply wells to reduce natural arsenic contamination. Halford and others (2010) found selected aquifers composed of lacustrine sediments that could be 

removed from the screened zones of public-supply wells in California to reduce natural arsenic contamination. 

2 
Methods and Approach 

The USEPA and USGS worked with the NHDES to identify groundwater-supply systems that had exceedances 

of selected contaminants slightly (less than about 20 percent) greater than their respective MCLs. Water-supply systems with exceedances greater than 20 percent for the whole well would likely have multiple fractures with elevated 

concentrations or a few elevated-concentration fractures that constitute a large fraction of the borehole’s total yield. 

Such systems would be less likely to be ameliorated to levels below the MCL by borehole modification and groundwater mixing. Additionally, the study avoided the selection of supply systems that had multiple natural contaminants 

because modifications of a borehole to reduce one contaminant might result in an increase in another contaminant. 

The borehole being considered needed to have sufficient yield (greater than 10 gal/min), such that it was likely to 

have multiple yielding fractures. If fractures are removed from a low-yielding well, by borehole modification, the 

resultant borehole may not have enough yield to be a reliable water-supply well. Finally, candidate systems needed 

an owner/operator willing to be part of the study and to be able to remove one well from service during the evaluation for up to 1 week. 

In summary, the criteria for investigation included (1) systems that have concentrations of arsenic or uranium 

that slightly exceeded their respective MCLs (10 and 30 μg/L), (2) systems that have sufficient storage or redundant 

capacity to allow for a multi-day borehole testing program and owners/operators willing to participate in this 

study, and (3) the system had individual well yields of at least 10 gal/min. Although tens of supply systems in New 

Hampshire and Vermont were evaluated for possible investigation, relatively few systems met the necessary study 

criteria. The three groundwater-supply systems selected for investigation (fig. 1) and the field investigation periods 

were Francestown, October 2008; Londonderry, June 2009; and Salem, October 2009. 

CANADA 

New 

Hampshire 

71o 

44o 

43o 

45o 

Concord 

Lake 

Winnipesaukee 

Salem 

Atlantic Ocean 

Maine 

Massachusetts 

Vermont 

72o 

Francestown Londonderry

Merrimack 

River 

40 MILES 0	 

0 40 KILOMETERS 

Figure 1. Locations of the water-supply systems 

investigated in Francestown, Londonderry, and 

Salem, New Hampshire.

3 
 

Borehole Geophysics 

Standard borehole geophysical logs, including caliper, natural-gamma radiation, electromagnetic induction, and 

fluid temperature and specific conductance, were collected and are presented for the borehole investigated at each 

water-supply system. A multiparameter fluid log, which included pH, dissolved oxygen, and oxidation-reduction 

potential (redox), also was collected at each site. Fluid temperature and conductance logs were collected under ambient (non-pumping) and low-flow (approximately 1 gal/min) pumping conditions. All results are referenced in feet 

below top of casing (TOC). A description of standard borehole geophysical logging methods and interpretation is 

given by Keys (1990). 

Optical televiewer logs were collected to further identify fractures and to confirm areas of competent borehole 

wall for heat-pulse flowmeter measurements. Where a hydraulic connection with another borehole in the water 

system was apparent, or suspected, the orientations of selected features were described. Standard and televiewer logs 

were used to identify zones for flowmeter logging. A description of optical televiewer logging methods is given by 

Johnson (1996). 

Heat-pulse flowmeter measurements were made under ambient flow and under low-flow pumped conditions. 

Where it was difficult to obtain stable (steady state) conditions in the borehole, due to interferences of a second well 

or unknown influences, heat-pulse flowmeter data were difficult to interpret quantitatively. If the water levels in 

the borehole investigated were affected by unavoidable withdrawals in the systems second supply well, additional 

heat-pulse flowmeter measurements were made to qualitatively investigate fracture connections. Negative values (for 

example, see fig. 2) indicate downflow, and positive values indicate upflow. Flow directions, upflow or downflow in 

the borehole, and relative amounts were compared to determine flow in and out of the borehole (Keys, 1990). Flow 

measurements were repeated at individual measurement points in the borehole to assess the variability of flow in the 

borehole and potential magnitude of measurement error or the occurrence of transient flow disturbances. Repeated 

measurements indicated that measurement error in some cases was potentially as low as 0.001 gal/min (gallons per 

minute). However, repeated measurements also indicated variations between measurements at a point that were 

caused by undetermined factors such as changes in flowmeter pumping rates; pumping at the second well in the 

water system; or other transient flow disturbances from an unknown source, such as another withdrawal well close 

enough to affect the measured borehole. The standard deviations of variations in flow were usually between 5 and 

10 percent of the flow measurement. Measurements that were greater than 10 percent of other flows at a point and 

were not repeatable were ignored; the remaining measurements were used to provide an average flow measurement. 

Groundwater Sampling and Water-Quality Analysis 

Untreated whole-well water reconnaissance samples were analyzed for arsenic and uranium by the USEPA 

New England Region; discrete interval samples were analyzed by the NHDES Water Laboratory. Reconnaissance 

water samples were collected with the production pump from the open borehole (whole well) and represent a flowweighted average of all the water-producing fractures in the borehole on the basis of their transmissivity (Shapiro, 

2002). After reconnaissance samples were evaluated, the existing submersible pump was removed so that geophysical logs could be collected in the open borehole (see discussion on geophysical logs in the previous section) and 

analyzed to select discrete intervals for flowmeter and sampling analysis. 

While the pump for the supply well was shut off and removed from service, some groundwater flow in the 

borehole may have moved water from one part of the aquifer system to another. Prior to water-quality sampling, an 

assessment of the potential volume of water distributed in the borehole through ambient (non-pumping) flow while 

the supply pumps were off, termed intraborehole flow, was made to quantify that volume of water before sampling. 

An amount of water at least equal to the intraborehole flow was removed from each borehole. Because of stagnant 

intervals in the borehole and differential removal of water during low-flow pumping, that amount of water may not 

necessarily represent all the water that flowed from one zone of the borehole to another during ambient conditions. 

For example, the water at the base of a borehole with few or no transmissive fractures may have very little intraborehole inflow water, but any stagnant water in that zone of the borehole will also not be removed during low-flow 

pumping from the top of a well. 

4 
Depth 

Feet 

Optical Televiewer Image 

0° 90° 180° 270° 0°

Total Gamma 

0 Counts per Second 200

Caliper 

5 Diameter in Inches 7

Formation Resisitivity 

-70 Ohm Meters 70

Flowmeter, ambient 

-0.5 Gallons per minute1.5

Flowmeter, pumping 

-0.5 Gallons per minute 1.5

Fluid Temperature 

10 Degrees Celsius 12

50 

60 

70 

80 

90 

100 

110 

120 

130 

140 

150 

160 

170 

180 

190 

200 

210 

220 

230 

240 

250 

260 

270 

280 

290 

300 

310 

320 

330 

340 

350 

360 

370 

380 

390 

400 

0.00 

-0.27 

-0.31 

-0.29 

-0.41 

-0.33 

-0.38 

-0.33 

-0.01 

-0.01 

-0.01 

0.00 

0.00 

-0.00 

-0.00 

0.00 

-0.00 

0.02 

0.02 

0.02 

0.03 

0.00 

0.00 

1.1 1.2 

0.84 

0.84 

0.84 

0.62 

0.57 

0.44 

0.69 

0.04 

0.05 

0.08 

0.06 

0.03 

0.11 

0.02 

0.02 

0.03 

0.00 

0.00 

0.00 

0.00 

-0.02 

0.00 

In 

In 

In 

In 

Out 

EXPLANATION

All measurements are in feet below the top of the casing. 

Blue—Ambient flow in the logged well Circle shows measurement point; flowmeter line shows general trend. 

Red—Pumping in the logged well Negative numbers indicate downflow; positive numbers upflow. 

Arrows show points of inflow or outflow to the borehole. 

Figure 2. Borehole geophysical logs for well FBRW-1, Francestown, New Hampshire, 2008. 

5 
 

 

 

 

 

During the study, borehole groundwater was sampled at depths above and below selected transmissive fractures, 

identified by changes in borehole fluid properties or flow using borehole geophysical logs. Depth-integrated samples 

were collected using a fluid sample chamber that was activated by compressed nitrogen to capture and seal the water 

sample at a specific depth for retrieval. Each sample represented a composite of the arsenic or uranium concentrations from all contributing fractures or zones below the sampling device. Samples were collected from top to bottom 

of the borehole to minimize disturbance of the borehole walls and to reduce the effects of turbidity in the borehole. 

The contaminant concentrations in each flow zone were subsequently calculated from borehole-flowmeter data and 

the laboratory results. 

The NHDES Water Quality Laboratory analyzed water samples for uranium and arsenic using inductively 

coupled plasma mass spectrometry, according to USEPA method 200.8. The laboratory reporting level (LRL) for 

the study was 1 μg/L using USEPA method 200.8. The USEPA New England Regional Laboratory analyzed arsenic 

samples from the Francestown system by the graphite furnace method with a LRL of 10 μg/L. This higher LRL was 

acceptable for the range of concentrations at this system. Replicate, equipment blank (from arsenic- and uraniumfree water), and discharge time-variant samples were collected throughout the investigation (approximately every 10, 

3, and 3 samples, respectively). One of the three sequential replication samples had a 5.3 relative percent difference; 

this test is meant to analyze sample collection reproducibility. None of the 11 equipment blank samples had a 

measurable concentration of arsenic or uranium. Split replicate performance-evaluation samples (designed to test 

lab result reproducibility) prepared using environmental samples had a 0 percent relative percent difference. Timevariant samples, collected throughout each test and borehole site, showed the contaminant level varied up to 

14.3 percent (a range in whole well arsenic concentrations of 21 to 24 μg/L at Francestown) over the period of 

sampling (appendix 1). Time-variant sample results were considered on a site-by-site basis because they are 

influenced by transient-flow conditions in the borehole and in the bedrock aquifer, which may be caused by 

fluctuations of the pump rate, previous ambient intraborehole flows, or unknown conditions such as other nearby 

withdrawals. The quality-assurance data indicated the environmental data were acceptable, and there was little 

potential bias due to sampling. However, time-variant relative percent difference values of up to 14.3 percent 

indicated that pumping during sampling either did not overcome ambient intraborehole flow displacement or nearby 

pumping influences, or that the water quality in the aquifer is not uniform, or a combination of these factors. 

Flow-weighted contaminant contributions were calculated using an equation described by Izbicki and others 

(1999): 

C a

 = (CiQi – Ci+1 Qi+1)/Qa , (1) 

where 

C is the contaminant concentration, 

Q is the flow of water within the well, 

i is the first sample collection and flow measurement depth, 

i+1 is the second or subsequent sample collection and flow measurement depth, and 

a is the interval between i and i+1. 

Equation 1 provides a means to differentiate variations in sample concentrations that can be attributed to zones 

of inflow with depth. By this method, inflows must be quantified and the water quality must be sampled at multiple 

points along the borehole. The more points along the borehole that are logged for flow and sampled, the finer the 

flow-weighted contaminant zones in the borehole can be delineated. However, because a flow term is in the denominator of equation 1, small variations in flow result in unrealistically high flow-weighted concentrations. Where flow 

in the well stayed the same between sample depths or decreased, which occasionally occurs with low-flow sampling 

because of external factors, flow-weighted concentrations could not be calculated. Therefore, flow variations of less 

than 5 percent were considered to be negligible and were not evaluated in flow-weighted concentrations. 

6 
 

 

Borehole Flow and Water Quality Characterization 

Three bedrock groundwater-supply systems were selected for investigation between October 2008 and 

November 2009 on the basis of the criteria described previously. Each supply system had unique water-use, borehole, and water-quality characteristics. 

Francestown 

The water system investigated in Francestown consists of 2 wells, located about 300 ft apart, that serve a community of 145 people. Francestown bedrock well FBRW-1 was installed prior to 1984 and, therefore, is not listed 

in the NHDES database of well-completion reports. This well was reported as being drilled to 370 ft, with a 0.5-ft 

diameter steel casing installed and a yield of 3 gal/min. During the investigation, well FBRW-1 was determined to be 

392 ft deep, from TOC, with 126 ft of casing. Well FBRW-1 was hydrofractured in 2005 and was reported to obtain a 

yield of 10 gal/min. 

Francestown well FBRW-2 was installed to 400 ft, using 0.5-ft diameter 126 ft-long steel casing, with a yield of 

approximately 3 gal/min. Well FBRW-2 was hydrofractured in 2002 and was reported to obtain a yield of 8 gal/min. 

Between August 2006 and April 2008, the arsenic concentration for blended water samples (water from both wells 

blended together) ranged from 10.0 to 11.1 μg/L. In 2008, the water system delivered water at a rate of approximately 6,000 gal/d (gallons per day), and well FBRW-1 accounted for about 60 percent of the total water supply. 

Water samples collected from the individual wells on October 8, 2008, by this project and analyzed by NHDES had 

arsenic concentrations of 14.6 μg/L for well FBRW-1 and 2.7 μg/L for well FBRW-2. On the basis of these results, 

well FBRW-1 was selected for investigation. The well pump at FBRW-1 was turned off on Saturday, October 17, and 

removed from the borehole Monday morning, October 19, 2008. 

The area of the well field is on a mapped northeast-southwest trending approximate contact between metasedimentary rocks—the Perry Mountain Formation to the northwest and the Smalls Falls Formation to the southeast, 

both of Silurian age; a similar trending contact with the Kinsman Granodiorite, of Devonian age, is mapped about 

500 ft southeast of the wells (Lyons and others, 1997). Greene (1970) shows the Kinsman Granodiorite near the 

location of the wells with a northwest dipping contact that trends toward the supply wells. The Perry Mountain 

Formation consists of sharply interbedded quartzite, metapelite, and metaturbidites with common coticule (finegrained quartz garnet) layers. The Small Falls Formation is a rusty weathering thin-bedded sulfidic-graphitic schist 

and pyrrhotitic calc-silicate granofels. The Kinsman Granodiorite is commonly identified by large crystals of potassium feldspar in a finer matrix of foliated granite, granodiorite, tonalite, and minor quartz diorite. At well FBRW-1, 

the surficial sediments consist of approximately 115 to 125 ft of glacial till (based on indications from the gamma 

log). Well FBRW-2 also penetrates through the till; however, kame terrace deposits are within a few hundred feet 

west of the well (Hildreth, 1990). 

Borehole Geophysical Logs 

Geophysical logs collected at well FBRW-1 indicated the depths and characteristics of fractures in the borehole 

(fig. 2). The optical televiewer log was expanded (not shown) to examine the borehole wall in detail to help locate 

fracture zones and provide measurement points for the heat-pulse flowmeter. All depths given are from TOC. The 

two water-supply wells were determined to be hydrologically independent on the basis of the water-level responses. 

The water level in well FBRW-1 recovered prior to collection of the borehole logging data, and well FBRW-2 

remained in use for water supply. Therefore, ambient (non-pumped) and low-flow pumped borehole flow measurements were made under stable conditions. 

During ambient conditions, water enters the well at 0.3 gal/min at about 128 ft, flows down the borehole with 

minor inflows and outflows (of about 0.1 gal/min), and flows out of the well at 222 ft. Borehole flows, ambient and 

low-flow pumping, below 222 ft (fig. 2) were not significant (much less than 0.1 gal/min). Flow was measured at the 

fracture at 128 ft but flowmeter measurements above and below the bottom of the casing (126 ft) did not indicate 

flow (leaking) at the bottom of the casing. 

7 
 

Stressed flowmeter measurements were made while pumping at approximately 1 gal/min at the water surface 

(70 ft) under steady-state (stable water-level) conditions. On the basis of variations between measured flows, flows 

less than 5 percent of the total inflow were not considered meaningful. Inflows below 334 ft were minor, and inflows 

below 280 ft were about 5 percent of the total flow. Approximately 50 percent of the total inflow was at 222 ft, 

21 percent at 128 ft, and minor inflows (less than 10 percent) were measured at about 172 and 205 ft. 

Water Quality and Flow-Weighted Chemical Constituents 

Ambient flow in the borehole during the period that well FBRW-1 was not pumping (between Saturday morning and Monday morning) was estimated to result in approximately 1,150 gal of water flowing down the borehole 

from the upper bedrock unit to the lower bedrock unit. Prior to depth-discrete sampling on October 23, 2008, 

approximately 1,560 gal of water was pumped out of the well. On the basis of these calculations and the estimates of 

fracture contributions determined above, it is likely that water from the primary fracture (222 ft), not recent inflow 

from upper zones, was sampled. If casing storage and stagnant areas at the base of the borehole are factored in, more 

water may have been withdrawn from the primary fracture prior to sampling. Time-variant sampling indicated that 

contaminant concentrations varied by as much as 15 percent during sampling (appendix 1). It is unclear whether 

these variations were due to intraborehole flow that occurred while the borehole was not pumped or if such variations naturally occur in the bedrock aquifer. 

Analysis of the borehole logs (fig. 2) indicated that, under low-flow pumping conditions, water enters well 

FBRW-1 primarily from fractures located at 128 and 222 ft; relatively less water enters at 172 and 205 ft. Water 

samples were collected above and below each fracture while pumping the well and at other selected points in the 

borehole (table 1). The flow-weighted arsenic concentration from each fracture was calculated on the basis of an 

integration of flowmeter and water-quality analyses. Analysis of whole-well water samples collected on October 23, 

2008, indicated a 3 μg/L time-variation in arsenic concentration at the borehole. 

Table 1. Depth of fractures, sampling depth, flow fraction, arsenic concentration, and flow-weighted arsenic concentration for 


water sampled from well FBRW-1, Francestown, New Hampshire, 2008.
 

[Samples were analyzed at the New Hampshire Department of Environmental Services Water Quality Laboratory; ft, feet below top of casing; 

μg/L, micrograms per liter; --, not calculated]
	

Dominant 

fractures 

(ft) 

Zone 

investigated 

(ft) 

Water 

sample depth 

(ft) 

Borehole 

zone flow 

(cumulative 

fraction) 

Sample 

arsenic 

concentration 

(μg/L) 

Flow-weighted 

borehole 

zone arsenic 

concentration 

(μg/L) 

Comment and primary flow zones 

100 1 21 In casing, whole well 

126, 128 100–135 23 At base of casing 

135 0.7 20 

142, 152 135–160 --

160 0.7 19 

172 160–180 19 Flow 

180 0.62 19 

192 180–196 --

196 0.62 18 

205 196–210 10 

210 0.55 19 

213, 222, 227, 232 210–240 19 Flow 

240 0.05 23 

240–320 

320 0 22 --

254 320–380 

380 0 13 --

8 
 

The fractures at 172 and 222 ft had calculated arsenic concentrations of about 19 μg/L, and the fracture at 128 ft 

had a calculated arsenic concentration of 25 μg/L. The results are summarized in table 1 showing depth, percentage 

of water inflow in the borehole, sample arsenic concentration, field parameters, and calculated flow-weighted arsenic 

concentrations. 

Whole-well arsenic concentrations in groundwater at well FBRW-1 were between 21 and 24 μg/L 

(appendix 1). The fracture zone between 196 and 210 ft had the lowest flow-weighted arsenic concentration 

(10 μg/L, table 1). However, this zone contributed only a little more than 10 percent of the total flow in the borehole 

and would not sustain the flow rates needed for supply purposes. Because of the small difference in arsenic concentration detected (19 to 23 μg/L) between the other water-bearing fracture zones, it was determined that borehole 

modification would not reduce arsenic concentrations enough to reduce the arsenic level below the MCL of 10 μg/L. 

Although the fracture at 128 ft is producing slightly higher levels of arsenic, it is only contributing a small portion 

of the total flow into the borehole (about 21 percent); therefore, the total contribution of arsenic to the well water by 

removing the water from this fracture is very small, approximately 1 μg/L. 

Londonderry 

The water system investigated in Londonderry consisted of 2 bedrock wells, located about 50 ft apart, that 

serve approximately 130 people. The wells LBRW-1 (USGS NH-LRW-937) and LBRW-2 (USGS NH-LRW-938) 

were reported to be 355 and 400 ft deep with yields of about 10 gal/min. Each borehole has a 6-in. steel casing 

set into bedrock (about 20 ft below land surface) and a PVC well seal extending to 68 ft below land surface 

(determined by induction and caliper logs). The well seals were installed in 1990 to address a reported bacterial 

contamination problem. 

Wells LBRW-1 and LBRW-2 are located within the approximate boundary of a muscovite granite pluton of the 

New Hampshire Plutonic Suite of Devonian age (Walsh and Clark, 1999). This portion of the pluton is elongated in 

the northeast-southwest direction and is in contact with the Berwick Formation of Silurian-Ordovician age on each 

side. Walsh and Clark (1999) map the Berwick Formation in this area as a biotite-plagioclase-quartz granofels and 

schist and calc-silicate rock. Surficial geology at the site determined from the natural-gamma log consists of 20 ft 

of glacial till. About 500 ft southeast of the wells is a contact with lake-bottom deposits consisting of sand and silt 

(Larsen, 1984), in a northeasterly trending swale containing a brook. The wells are in a low-lying area, and the water 

table was noted to be at the land surface at the time of the study. 

When investigated, the water system had been withdrawing water from both wells with a blended uranium concentration of 30 to 40 μg/L in 2008. Samples collected during a site visit on May 5, 2009, had uranium concentrations in the wells of 26 (LBRW-1) and 54 μg/L (LBRW-2). On the basis of these results, well LBRW-2 was selected 

for characterization. 

Borehole Geophysical Log Analysis 

Analysis of the geophysical logs showed that well LBRW-2 had few large fracture zones (caliper log, fig. 3). 

Prominent fractures were measured at 129, 255, and 382 ft (bottom of the borehole). The fracture at 255 ft spans 

nearly 1 ft of borehole length and is essentially horizontal. The fracture at 129 ft is also nearly horizontal. The 

gamma log indicated some distinct zones of rock that appear darker and nearly horizontal in the optical log, at 260 

to 270 ft and 345 to 362 ft. Trends in the temperature log (fig. 3) did not indicate any prominent flow zones but did 

indicate likely stagnant water below about 320 ft. Oxygen and redox in the fluid multiparameter log (not shown) 

indicated fluid contrasts at 265 ft (non-pumped) and at 290 ft (pumped) that are likely due to stagnant water in the 

base of the borehole. Fluid conductance (fig. 3) and oxygen, from the multiparameter log, indicated a fluid chemistry 

contrast at about 50 ft that together with caliper deflections (45 ft) indicated a possible leak in the PVC casing and 

groundwater inflow between 45 and 50 ft. 

Heat-pulse flowmeter measurements (fig. 3) made while pumping approximately 1.2 gal/min from the top of 

the water column indicated little flow (near zero) below 140 ft, total inflow to the borehole of 22 percent at 128 ft, 

53 percent at 95 ft, and 25 percent at about 69 ft or just below the casing. The ambient flowmeter log (not shown) 

indicated that without pumping and with stable heads in the well field, there was essentially no flow in well 

9 
Depth Optical Televiewer Image 

0° 90° 180° 270° 0°

Caliper 

4 Diameter in Inches 

Fluid Conductivity 

Fluid Temperature 

10 Degrees Celsius 

Formation Resisitivity 

2 Ohm Meters 6

Total Gamma 

100 Counts per second 

Flowmeter, ambient 

-0.15 Gallons per minute 

Flowmeter, pump nearby well 

-0.15 Gallons per minute 

Flowmeter, pumping 

-0.5 Gallons per minute 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

110 

120 

130 

140 

150 

160 

170 

180 

190 

200 

210 

220 

230 

240 

250 

260 

270 

280 

290 

300 

310 

320 

330 

340 

350 

360 

370 

380 

-0.04 

0.0 

0 

0.01 

0.01 

0.01 

0.00 

0.00 

0.00 

0.00 

-0.06 

-0.04 

-0.05 

-0.04 

0.00 

-0.14 

0.0 

1.2 

1 

1 0.85 

0.90 

0.26 

0.26 

0.00 

0.00 

0.00 

0.00 

-0.00 

0.01 

0.01 

0.01 

0.00 

500 1.5 9 

12 0.05 

Feet 0.05

Out 

In 

In 

In 

microsiemens 

per centimeter 500 650 

EXPLANATION

All measurements are in feet below the top of the casing. 

Blue—Ambient flow in the logged well Circle shows measurement point; flowmeter line shows general trend. 

Red—Pumping in the logged well Negative numbers indicate downflow; positive numbers upflow. 

Green—Pumping in adjacent well Arrows show points of inflow or outflow to the borehole. 

Figure 3. Borehole geophysical logs for well LBRW-1, Londonderry, New Hampshire, 2009. 

10 
 

LBRW-2. Flowmeter measurements made while well LBRW-1 was operating indicated that water flows down the 

LBRW-2 borehole, from just below the casing, and leaves well LBRW-2 at 129 ft. During this test, water is also 

flowing up the borehole from zones above about 280 ft and leaves the borehole at 129 ft. With well LBRW-1 

pumping, about 83 percent of the water leaving well LBRW-2, at 129 ft, comes from above this point and 17 percent 

from below this point. The possible casing leak between 45 and 50 ft could not be definitively confirmed with flowmeter measurements. 

During collection of borehole logs, it was observed that wells LBRW-1 and LBRW-2 were highly interconnected, pumping in LBRW-1 would cause rapid drawdowns in LBRW-2, and both wells recovered rapidly from 

drawdowns. For example, after withdrawals at well LBRW-1 ceased, drawdowns at LBRW-1 and LBRW-2 recovered from 35 and 18 ft, respectively, to about 4 ft in less than an hour. The geophysical logs, water-level response, 

and the proximity of the wells to each other indicated a likely direct and nearly horizontal connection at 129 ft. 

Water Quality and Flow-Weighted Chemical Constituents 

On the basis of the borehole logs, groundwater samples were collected on June 17, 2009, at 60, 100, 145, 200, 

300, and 380 ft to bracket fractures, fracture zones, or fluid-property changes measured in the borehole. Depthintegrated samples were collected while water was withdrawn from the top of the water column in the borehole 

under stable head conditions. 

Flow-weighted uranium concentrations in well LBRW-2 were calculated for two conditions—with the well 

pumped at the water table and with well LBRW-1 not pumping, and with well LBRW-1 pumping, assuming all water 

leaves well LBRW-2 at the fracture at 129 ft (table 2). Flow-weighted concentrations of 52, 59, and 54 μg/L represent water from below 145 ft, from the fracture at 129 ft, and from between 100 ft and the bottom of casing (69 ft), 

respectively. The small variation of uranium concentrations in the borehole (range of 7 μg/L) indicated that borehole 

modifications would not be useful in altering the uranium concentration of the water pumped from well LBRW-2 to 

levels less than the drinking-water standard. However, on the basis of water-level observations in wells LBRW-1 and 

LBRW-2, it was determined that LBRW-1 has a sufficient yield to serve as the sole community water supply, allowing LBRW-2 and its higher uranium concentration to serve only as an emergency backup. 

Using the borehole uranium concentrations determined above, and assuming a direct hydraulic connection 

at 129 ft to well LBRW-1 and similar uranium concentrations as measured during low-flow sampling, it was estimated that well LBRW-2 contributes an inflow of 50 μg/L to well LBRW-1 from the fracture at 129 ft. If the zone of 

elevated uranium concentration above 60 ft (54 μg/L) were sealed, the estimated concentration leaving the borehole 

at 129 ft would be slightly reduced to 45 μg/L. Given that the whole-water uranium concentrations measured at 

wells LBRW-1 and LBRW-2 were markedly different (26 and 54 μg/L, respectively), it is possible that the fractures 

contributing water to LBRW-1 have very different uranium concentrations than those contributing to LBRW-2. The 

fracture zone at 129 ft (fig. 3) in well LBRW-2 is a relatively horizontal fracture (determined by optical televiewer 

log), and because well LBRW-1 is very close to well LBRW-2 (50 ft), this fracture likely dominates the hydraulic 

characteristics of LBRW-1 in the same manner as LBRW-2. Water-level monitoring during the investigation indicated that the two wells were highly connected hydraulically (each well responded rapidly to pumping in the other 

well). If the fracture at 129 ft contributes 40 percent of the flow into well LBRW-1 with a uranium concentration of 

50 to 59 μg/L, flow from this fracture might contribute a large fraction of the total uranium concentration measured 

in LBRW-1. Without inflow from this fracture, the uranium concentration in well LBRW-1 may possibly be less than 

20 μg/L. If this zone has hydraulic characteristics similar to the hydraulic characteristics of this same zone in well 

LBRW-2, it would account for about 22 percent of the well yield. 

11 
Table 2. Depth of fractures, sampling depth, flow fraction, uranium concentration, and flow-weighted uranium concentration for 

water sampled from well LBRW-2 for two pumping scenarios, Londonderry, New Hampshire. 

[Samples were analyzed at the New Hampshire Department of Environmental Services Water Quality Laboratory; ft, feet below top of casing; 

μg/L, micrograms per liter; gal/min, gallon per minute; --, not calculated] 

Dominant 

fractures 

(ft) 

Zone 

investigated 

(ft) 

Water 

sample depth 

(ft) 

Borehole

zone flow 

(cumulative 

fraction) 

Sample uranium 

concentration 

(μg/L) 

Flow-weighted

borehole

zone uranium

concentration

(μg/L) 

Comment and primary

flow zones

Scenario A. Sampling of LBRW-2 while pumping 1.2 gal/min at the water surface in LBRW-2. 

45–50 

69, 95 

45–60 

60–100 

45 

60 

1 

1 

54 

54 

--

50 

In casing, whole well 

Possible casing leak 

Above casing bottom 

Flow 

100 59 

129 100–145 0.42 59 Flow 

145 52 

158, 213, 255, 314 145–bottom 0.01 52 

Dominant 

fractures 

(ft) 

Zone 

investigated 

(ft) 

Water 

sample depth 

(ft) 

Borehole 

zone flow 

(relative 

fraction) 

Flow-weighted

borehole

zone uranium

concentration

(μg/L) 

Estimated

fracture uranium 

concentration 

(μg/L)

Comment and primary

flow zones

Scenario B. Estimated flow-weighted concentrations of uranium in water leaving LBRW-2, at 129 ft, while LBRW-1 operating 

(assuming all flow leaves borehole LBRW-2 at 129 ft). 

45–50 45–60 0 

60 

69, 95 60–100 0.83 50 Inflow 

100 

129 100–145 -- 50 Outflow 

145 

158, 213, 255, 314 145–bottom 0.17 52 Inflow 

Salem 

The water system investigated in Salem consisted of 2 bedrock wells, about 45 ft apart, that serve approximately 

213 people (fig. 1). Well SBRW-1 is operated as a primary or lead well, and well SBRW-2 supplies additional water 

to the system as needed. The reported yields of the wells were 55 and 15 gal/min for wells SBRW-1 and SBRW-2, 

respectively, and combined water uranium concentrations of approximately 10 to 88 μg/L, with a median of 40 μg/L. 

Samples collected during a site visit (September 19, 2009) had uranium concentrations of 30 μg/L for well SBRW-1 

and 32 μg/L for well SBRW-2. Well SBRW-2 was selected for characterization for analysis because it had a slightly 

higher uranium concentration. 

Wells SBRW-1 and SBRW-2 are located on a northeast-southwest trending approximate contact between two 

units of the Berwick Formation of Silurian-Ordovician age. A southwest strike, northwest dipping approximate 

contact with a binary granite of the New Hampshire Plutonic Suite of Devonian age is located about 500 ft to the 

southeast, and a syncline axis with a similar strike is adjacent to the wells to the northwest (Walsh and Clark, 1999). 

The Berwick Formation is a biotite-plagioclase-quartz granofels and calc-silicate rock; one unit contains schist, and 

the other quartzite. Surficial deposits at the well field consist of glacial till, and swamp deposits were about 1,000 ft 

west of the well field (Larson, 1984). 

12 
 

 

Borehole Geophysical Log Analysis 

Analysis of the borehole logs of well SBRW-2 indicated relatively few geologic contrasts in the borehole 

(fig. 4). The rock at the bottom and top of the hole is felsic and fine- to medium-grained binary granite, the darker 

rock observed in the rest of the hole is likely the schist unit of the Berwick Formation. The gamma log indicated 

somewhat uniform lithology with the exception of zones at 207 to 220 ft and 245 to 250 ft. The caliper log indicated 

numerous small fractures, with less than a 7-in. caliper span, from the bottom of the casing (38 ft) to about 85 ft. 

Minor fractures were noted at 150 and 160 ft that coincide with changes in fluid conductance. Other minor fractures 

(less than 7 in.) were measured at 265, 304, and 309 ft. A large fairly horizontal fracture, spanning at least 11 in. in 

diameter (out from the center of the borehole) was measured from 283 to 284 ft. The fluid-conductance log indicated 

a slight fluid contrast at about 150 to 160 ft and a constant fluid thermal gradient increase below that depth indicative 

of relatively little water movement. 

The pump in well SBRW-2 was removed 3 days before borehole logging; however, withdrawals at well 

SBRW-1 caused a delayed response in SBRW-2. The delayed response led to constantly changing (unstable) heads 

in SBRW-2 that made quantitative flowmeter analysis difficult (fig. 4). For example, small (less than 0.03 gal/min) 

upward flows measured while well SBRW-2 was not pumped were attributed to recovering (rising) water levels and 

not ambient borehole flows. Although transient (non-repeatable) flows were noted at 283 ft, the non-pumped (ambient) flowmeter log (fig. 4) indicated relatively no flow changes with depth. On the basis of flowmeter measurements 

with a withdrawal of 0.6 gal/min at the water surface in well SBRW-2, inflows greater than 5 percent of the withdrawal rate were measured and attributed to fractures at the bottom of the well (6 percent), 309 ft (13 percent), 

280 ft (12 percent), 160 ft (8 percent), 78 ft (6 percent), 49 ft (11 percent), and at the bottom of the casing (50 percent). The inflow percentages do not add up to 100 percent because there were flow changes that were attributed to 

lesser inflows and outflows (less than plus or minus 5 percent) along the borehole. However, moderate outflows were 

attributed to fractures at 226 to 240 ft (-14 percent) and at 126 ft (-8 percent). Considerable inflow (50 percent) was 

measured at the base of the casing and may represent inflow of water stored in the overlying till sediments. It is also 

notable that essentially no flow was detected at the large fracture at 283 ft at the pumping rate used in these tests. A 

qualitative borehole flowmeter test was conducted with no pumping in well SBRW-2 at the initiation of pumping in 

well SBRW-1. Although flow conditions in the well were transient, it appeared that flow leaves well SBRW-2 at a 

number of points along the borehole; however, the fracture at 160 ft may have a greater hydraulic connection to 

well SBRW-1 than other fractures in SBRW-2. 

Water Quality and Flow-Weighted Chemical Constituents 

Groundwater samples were collected on November 4, 2009, at depths selected on the basis of geophysical logs 

while water was withdrawn from the top of the water column at a rate of approximately 0.6 gal/min with stable head 

conditions. Field constituents and laboratory uranium results are listed in appendix 1. 

Flow-weighted uranium concentrations presented in table 3 are based on the sampling results and borehole log 

analysis. At sections of the borehole, such as sections from 252 to 220 ft and 150 to 120 ft (fig. 4), decreases in flow 

were measured from one interval to shallower intervals, which present complications for calculating flow-weighted 

concentrations. The change in flow may be caused by transient flow conditions during borehole logging due to 

unsteady pumping in well SBRW-2, interference from pumping at SBRW-1, or other unknown causes. However, 

the magnitudes of such flow changes likely represent negligible flow-weighted inflows or outflows of uranium. The 

flow-weighted concentrations from the fracture zone at about 274 ft yielded a fracture concentration of 59 μg/L 

(table 3); however, this inflow may not be meaningful on the basis of the variations in sample concentrations that 

were close to the whole-water sampling variations. The inflows throughout the borehole above 270 ft were likely not 

substantially different from each other and indicated that uranium inflow concentrations were low. If the fractures 

below 270 ft were removed from the borehole flow system, the uranium concentration of the whole well was estimated to be 28 μg/L, or essentially unchanged. 

13 
Depth Optical Televiewer Image 

0° 90° 180° 270° 0°

Total Gamma 

50 Counts per 400

Second 

Fluid Conductivity 

270 310 

Fluid Temperature 

11 Degrees Celsius 12

Formation Resisitivity 

0 Ohm Meters 200

Caliper 

5 Diameter in Inches 8

Flowmeter, pump nearby well 

-0.6 Gallons per minute0.6

Flowmeter, pumping 0.6 

-0.6 Gallons per minute0.6

Flowmeter, ambient 2 

-0.1 Gallons per minute0.2

Flowmeter, ambient 

-0.1 Gallons per minute0.2

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

110 

120 

130 

140 

150 

160 

170 

180 

190 

200 

210 

220 

230 

240 

250 

260 

270 

280 

290 

300 

310 

-0.15 

-0.20 

-0.15 

-0.18 

-0.18 

-0.19 

-0.20 

-0.30 

-0.20 

-0.16 

-0.13 

-0.10 

-0.08 

-0.04 

0.03 

0.05 

0.02 

0.27 

0.20 

0.22 

0.22 

0.19 

0.19 

0.23 

0.21 

0.17 

0.16 

0.24 

0.24 

0.21 

0.18 

0.19 

0.12 

0.14 

0.06 0.06 

0.01 

0.01 

0.02 

0.02 

0.01 

0.00 

0.02 

0.02 

0.03 

0.03 

0.01 

0.02 

0.01 

0.02 

0.03 

0.02 

0.03 

0.03 

0.02 

0.02 

0.03 0.01 

0.10 -0.04 

-0.06 

0.05 

0.01 

0.00 

microsiemens 

per centimeter Feet 

Out 

In 

In 

In 

EXPLANATION

All measurements are in feet below the top of the casing. 

Blue—Ambient flow in the logged well Circle shows measurement point; flowmeter line shows general trend. 

Red—Pumping in the logged well Negative numbers indicate downflow; positive numbers upflow. 

Green—Pumping in adjacent well Arrows show points of inflow or outflow to the borehole. 

Figure 4. Borehole geophysical logs for well SBRW-2, Salem, New Hampshire, 2009. 

14 
Table 3. Depth of fractures, sampling depth, flow fractures, uranium concentrations, and flow-weighted uranium concentrations in 

well SBRW-2 for two pumping scenarios, Salem, New Hampshire, 2009. 

[Samples were analyzed at the New Hampshire Department of Environmental Services Water Quality Laboratory; ft, feet below top of casing; μg/L, micrograms 

per liter; gal/min, gallon per minute; --, not calculated] 

Dominant 

fractures 

(ft) 

Zone 

investigated 

(ft) 

Water sample 

depth 

(ft) 

Borehole 

zone flow 

(cumulative 

fraction) 

Sample

uranium 

concentration 

(μg/L) 

Flow-weighted

borehole

zone uranium

concentration

(μg/L) 

Comment and primary

flow zones

Scenario A. Sampling SBRW-2 while pumping 0.6 gal/min at the water surface in SBRW-2. 

39 

38 1.00 31 In casing, whole well 

41 0.45 28 

33 Inflow, base of casing 

49, 78 41–120 31 Flow 

-- 0.40 --

126, 150, 160 120–170 Flow 

-- 0.40 --

220 170–252 

252 0.40 31 

254 252–260 --

260 0.40 31 

265 260–270 3 

270 0.35 35 

274 270–280 59 

280 0.30 31 

283–284 280–307 19 Large fracture (283–284), 

flow below fracture 

307 0.24 34 

304, 309 307–312 Flow 

312 0.11 --

Well bottom 

Dominant 

fractures 

(ft) 

Zone 

investigated 

(ft) 

Water sample 

depth 

(ft) 

Borehole 

zone flow 

(relative 

fraction) 

Fracture

uranium 

concentration 

(μg/L) 

Uranium

(μg/L) Comment

Scenario B. Estimated flow-weighted borehole zone concentration and total uranium for well SBRW-2 assuming borehole sealed below 270 ft. 

39 Base of casing to 41 

41 

0.84 31 28 Whole well 

41–252 0.05 31 

252 

252–270 0.05 3 

270 Assuming a seal at 270 ft 

15 
Limitations and Alternatives to the Methods Used 

The efficacy of a borehole-modification solution to naturally occurring contaminants in a borehole depends on 

the specific hydraulic characteristics of the borehole, which, for water-supply wells installed in fractured-crystalline 

bedrock, is highly variable and unique from well to well. Because of the high cost of installing and maintaining treatment (including the disposal costs of potential treatment residuals), a modest investment in characterization to assess 

the potential for a borehole-modification solution may be justified. Although the wells investigated in this study 

showed either little variability in contaminant concentrations between fracture zones or had an insufficient number 

of transmissive fractures (within the same borehole) to allow for sealing one or more contaminated fractures, the 

approach for borehole characterization used in this study shows promise for application at other public-water systems with exceedances of naturally occurring contaminants. Even if a modification in a given borehole is not capable 

of reducing contaminant concentrations to below the MCL, a reduction in contaminant load would reduce the treatment costs by extending treatment media life, reducing the mass of residuals for disposal, and possibly reducing 

the design size of the treatment system. Decreased treatment costs could justify, therefore, the initial investment in 

borehole characterization. 

A goal of the study was to establish an approach for borehole investigation that could be replicated at other 

fractured, crystalline-rock water-supply wells. The methodology used in this study was optimized to provide reliable 

data on fracture-specific flow and contaminant concentrations while being technologically and financially feasible 

for most water systems and (or) water-industry consultants. As the study progressed through the three water systems, 

it was determined that it was important to ensure (by adequate pre-sampling water removal) that ambient flows, 

while the pump was offline, had minimal impact on the subsequent sampling effort. 

The borehole geophysical logs that were most useful to this study were caliper, fluid specific conductance and 

temperature, and optical televiewer. Other logs, such as natural-gamma radiation and electromagnetic conductance, 

may have been less useful but provided additional information and were worthwhile to collect while working at a 

site when the pump was removed from the well. Multi-parameter fluid logs required more effort than was worthwhile for this study, particularly if similar information could be gained from fluid temperature and conductance logs 

during ambient and low-flow pumping. 

The approach for this study used borehole geophysics and sampling techniques analogous to low-flow sampling. 

Another characterization approach uses a tracer introduced at the surface with depth-dependant samples collected 

with the production well pump in place and withdrawing water near the bottom of the borehole (Izbicki and others, 1999). The tracer approach may also enable resolution of fracture-specific flow and contaminant concentrations 

and has the advantage of sampling actual withdrawal-well operating conditions without the effort and expenses of 

pump removal and borehole geophysical logging. However, the operating conditions common to withdrawal wells in 

fractured-crystalline bedrock in New Hampshire typically involve large drawdowns of tens to over one hundred feet, 

and several point (fracture-controlled) inflows above and below the resulting water level in the well. An additional 

complication with such low-yield wells is the unsteady flow conditions—heads continue to decline during pumping, and the pumping ceases when head declines reach a point close to the pump level in the borehole. Under large 

drawdowns and with inflows near the base of a borehole, the tracer approach would be unable to resolve differences 

between inflows above the water level and below the pump. Additionally, advancing a sampling device down a 6- or 

8-in. borehole past pipe, pump cables, and other obstructions can be problematic. An ideal borehole setup for conducting a tracer-type characterization would consist of a fully screened rigid PVC stilling tube (with at least a 1-in. 

diameter) installed in the borehole to allow a sampler to be easily advanced down the borehole. 

Time-dependent sampling and analysis is another, very simple, technique that warrants additional investigation, 

either as a screening method for future investigation sites or possibly as a non-treatment option for reducing 

contaminant inflows. Bedrock withdrawal wells in New Hampshire are typically cycled on, to fill a system’s storage 

tank, and cycled off when storage is met or drawdown in the well is near the depth of the pump. In a low-yield, 

two-well system typical of the study area, one well may be operated at a time allowing the second well to recover. 

Of the sites investigated in this study, individual wells were generally operated for less than 12 hours a day. Using 

a time-dependant sampling approach, samples are collected over the course of a withdrawal-well pump cycle, with 

frequent samples collected during the initial pump-on period. This technique may require considerable sampling 

over the course of a pumping cycle but if successful could result in a considerable reduction of investigative efforts. 

16 
 

This technique may indicate contaminant variations that may occur in a unique hydrogeologic setting; for example, 

as a primary fracture zone with low-contaminant concentration is depleted, a secondary fracture zone with highcontaminant concentration may contribute a larger percentage of the water supply. Use of an optimized pumping 

cycle may provide a means to either limit inflows from certain fractured zones or to enhance contributions from 

other zones, such as allowing adequate recovery time for recharge from overburden sediments. Used as a screening 

approach, by monitoring water quality with time during a typical withdrawal cycle, this method may make it 

possible to detect variations in contaminant concentration that would indicate variable source concentrations with 

time, in the bedrock or bedrock and overburden aquifer, which could be exploited. If aquifer contaminant variability 

exists either between fractures or spatially within the same fracture zone, it is possible that optimized pumping could 

be used to maximize the volume of lower contaminant concentration water produced by the well and minimize 

water with elevated contaminant concentrations. This approach was tested at the Francestown site; however, arsenic 

concentrations showed little variability during the pumping cycle investigated. Every fractured-rock well system 

is unique, however, and this approach warrants further testing at additional systems because of its low cost and 

potential benefits if successful. 

Summary and Conclusions 

Bedrock borehole fracture, flow, and water-quality characteristics were investigated at three small public-supply 

wells in southern New Hampshire in 2008 and 2009 in cooperation with the U.S. Environmental Protection Agency 

and the New Hampshire Department of Environmental Services. The public-supply systems each served approximately 50 to 200 individuals and were under regulatory constraints for exceedances of the Federal and State drinking-water standards for arsenic or uranium. Arsenic and uranium are naturally occurring contaminants that affect 

bedrock water-supply wells in New Hampshire and parts of New England. The investigation was conducted to quantify the flow-weighted concentrations of arsenic or uranium in the supply wells and assess whether specific fracture 

zones, if sealed, would result in acceptable concentrations of these contaminants. The investigation used borehole 

geophysical logging and zone-specific water-quality sampling to characterize boreholes and provide estimates of 

flow-weighted contaminant concentrations within each borehole. The public-supply wells were selected from systems in New Hampshire that had contaminant concentrations that were slightly greater than regulatory limits (within 

about 20 percent), had accessible wells, had sufficient secondary well capacity and water storage to allow for periods where a well could be taken offline and the pump removed for borehole characterization, and the water-system 

owners or operators were willing to participate in this investigation. Investigation of groundwater flow and quality in 

fractured-bedrock wells is challenging because fracture characteristics at each site are unique and the particular flow 

characteristics and water quality vary considerably from borehole to borehole. 

The bedrock supply well investigated in Francestown, New Hampshire, was 392 ft deep, and the arsenic concentration of the well water was 14 μg/L. The water from this well accounted for about 60 percent of the total water 

supply in the Francestown water system. The borehole had few water yielding fractures; 30 percent of the well yield 

originated from a fracture at a depth of 128 ft and 50 percent from a fracture at a depth of 222 ft below top of casing. 

Because the range (3–4 μg/L) in flow-weighted arsenic concentrations between fracture zones was small, the possibility of reducing whole-water arsenic concentrations by borehole modification was not feasible. 

The bedrock supply well investigated in Londonderry, New Hampshire, was 400 ft deep and yielded water 

with a uranium concentration of 54 μg/L (well LBRW-2). Water from a second supply well (LBRW-1), located 

50 ft away, had a uranium concentration of 26 μg/L. Well LBRW-2 contained numerous fractures, including one 

very large, near-horizontal fracture, spanning 1 ft, at 255 ft below top of casing. Analysis of flow in the borehole 

indicated that nearly all flow into this well was from fractures located at 129 ft (22 percent), 95 ft (53 percent), and 

69 ft (25 percent) below top of casing. However, with the other well in the system operating (well LBRW-1), nearly 

all flow leaves well LBRW-2 at the fracture at 129 ft. Flow-weighted uranium concentrations ranged between 52 and 

59 μg/L. With the large contrast in uranium concentrations between the wells and a distinct hydraulic connection 

between the wells detected at 129 ft, it was estimated that this fracture may contribute a considerable amount of the 

uranium measured in well LBRW-1. 

17 
The bedrock supply well investigated in Salem, New Hampshire (well SBRW-2), was 315 ft deep and yielded 

water with a uranium concentration of 32 μg/L in 2009. Water from a second supply well, located 45 ft away 

(well SBRW-1), had a uranium concentration of 30 μg/L. The supply well investigated had about 10 fracture zones 

along the borehole length, including a large fracture spanning 1 ft at 283 ft below the top of casing. However, more 

than 50 percent of the inflow to the well was at the base of the well casing, presumably from overlying unconsolidated sediments, and the individual fractures identified each contributed less than 10 percent of the total flow to the 

well. The two boreholes appeared to have a poor hydraulic connection. The flow-weighted uranium concentrations 

varied from 3 to 59 μg/L; however, given the low yield of some of the fractures, borehole modifications were not 

estimated to help alleviate contaminant concerns. 

Characterization of groundwater flow and quality in the fractured-bedrock wells that are typical of New 

Hampshire, and much of New England, is complex. Bedrock water-supply wells generally have unique fracture 

and hydraulic characteristics that control the water quality and the prevalence of naturally occurring contaminants 

therein. This report presents the results of three different fractured-bedrock supply wells. At two of the systems, 

there was either not enough variation in contaminant concentration or not enough yielding fractures for borehole 

modifications to be a viable potential remedy to elevated contaminant contaminations. The conditions at one of 

the bedrock supply-well systems investigated, however, showed promise for improvement of supplied water by 

borehole modification. 

References Cited 

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Report 2007–5037, 84 p. 

Ayotte, J.D., Montgomery, D.L., Flanagan, S.M., and Robinson, K.W., 2003, Arsenic in groundwater in eastern 

New England—Occurrence, controls, and human health implications: Environmental Science & Technology, 

v. 37, no. 10, p. 2075–2083. 

Ayotte, J.D., Nielsen, M.G., Robinson, G.R., Jr., and Moore, R.B., 1999, Relation of arsenic, iron, and manganese in 

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depth-dependent water sampler: U.S. Geological Survey Fact Sheet 196–99, 2 p., accessed February 3, 2010, at 

http://ca.water.usgs.gov/archive/reports/fs19699.pdf. 

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18 
Larson, G.J., 1984, Surficial geologic map of the Windham quadrangle, Rockingham and Hillsborough Counties, 

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in southeastern New Hampshire: U.S. Geological Survey Fact Sheet FS–051–03, 8 p. 

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19 
Appendix 1. Sampling time, depth, contaminant concentration, and field parameters for water sampled from wells in Francestown, 

Londonderry, and Salem, New Hampshire. 

[Samples were analyzed at the New Hampshire Department of Environmental Services Water Quality Laboratory; ft, feet below top of casing; μg/L, micrograms 

per liter; °C, degrees Celsius; μS/cm, microsiemen per centimeter; mg/L, milligram per liter; --, not calculated]

Site Date 

MM/DD/YYY

Time 

hhmm

Depth 

(ft)

Sample 

concentration 

(μg/L)

Temperature 

(°C)

pH

Specific 

conductance 

(μS/cm)

Dissolved 

oxygen 

(mg/L)

Sample comment

Francestown Arsenic

FBRW-1

FBRW-2

FBRW-1

FBRW-1

FBRW-1

FBRW-1

FBRW-1

FBRW-1

FBRW-1

10/8/2008

10/8/2008

10/23/2008

10/23/2008

10/23/2008

10/23/2008

10/23/2008

10/23/2008

10/23/2008

--

--

0915

1345

1545

1000

1001

1130

1131

--

--

84

84

84

135

135

180

180

14.6

2.7

22

21

24

20

20

19

18

--

--

6.8

9.1

9.2

6.5

6.5

7.7

7.8

--

--

8.1

8.4

8.4

8.4

8.4

8.4

8.4

--

--

121

123

124

128

128

126

127

--

--

1

1

0.9

--

--

--

1

Supply pump and discharge line (whole well)

Supply pump and discharge line (whole well)

Pump discharge line (whole well)

Pump discharge line (whole well)

Pump discharge line (whole well)

Downhole sampler

Split replicate (of sample above)

Downhole sampler

Sequential replicate (of sample above)

Londonderry Uranium

LBRW-1

LBRW-2

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

LBRW-1

5/5/2009

5/5/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

6/17/2009

--

--

1630

1730

1830

1830

1800

1801

1730

1600

1601

1545

1445

1930

--

--

30

30

30

60

100

100

145

200

200

300

320

380

26

54

53

54

54

54

58

59

52

54

54

54

53

50

--

--

12.6

12.3

12.5

15.1

15.5

--

15.2

14.6

--

14.4

19.2

--

--

--

6.7

6.8

6.8

6.78

6.8

--

6.8

6.9

--

6.9

6.9

--

--

--

652

644

649

634

613

--

656

610

--

633

627

--

--

--

1

1

1

--

--

--

--

--

--

--

--

--

Supply pump and discharge line (whole well)

Supply pump and discharge line (whole well)

Pump discharge line (whole well)

Pump discharge line (whole well)

Pump discharge line (whole well)

Downhole sampler, in casing

Downhole sampler

Sequential replicate (of sample above)

Downhole sampler

Downhole sampler

Sequential replicate (of sample above)

Downhole sampler

Downhole sampler

Downhole sampler

Salem Uranium

SBRW-1

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

SBRW-2

9/19/2009

9/19/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

11/4/2009

--

--

1145

1430

1520

1115

1140

1200

1230

1300

1330

1400

1415

1445

1515

--

--

30

30

30

38

41

76

157

190

252

260

270

280

307

30

32

28

27

27

31

28

25

29

30

31

31

35

31

34

--

--

10.9

--

--

10.9

10.6

10.6

10.4

10.2

10.1

--

9.5

9.3

9.9

--

--

6.7

--

--

6.8

6.7

6.6

6.69

6.69

6.68

--

6.69

6.72

6.71

--

--

335

--

--

331

332

315

351

333

340

--

347

353

354

--

--

1

--

--

4

1.3

1.5

5

1.5

3

--

1

2

1

Supply pump and discharge line (whole well)

Supply pump and discharge line (whole well)

Pump discharge line (whole well)

Pump discharge line (whole well)

Pump discharge line (whole well)

Downhole sampler

Downhole sampler

Downhole sampler

Downhole sampler

Downhole sampler

Downhole sampler

Downhole sampler

Downhole sampler

Downhole sampler

Downhole sampler

20
Prepared by the Pembroke and West Trenton Publishing 

Service Centers. 

For more information concerning this report, contact: 

Director 

U.S. Geological Survey 

New Hampshire-Vermont Water Science Center 

331 Commerce Way, Suite 2 

Pembroke, NH 03275 

dc_nh@usgs.gov 

or visit our Web site at: 

http://nh.water.usgs.gov 
Printed on recycled paper 

Mack and others—Geophysical and Flow-Weighted Natural-Contaminant Characterization of Three Water-Supply Wells in New Hampshire—OFR 2011–1019