Prepared in cooperation with the Federal Highway Administration and the Connecticut 

Department of Transportation

Preliminary Assessment of Chloride Concentrations, 

Loads, and Yields in Selected Watersheds along the 

Interstate 95 Corridor, Southeastern Connecticut, 2008–09

Open-File Report 2011–1018

U.S. Department of the Interior

U.S. Geological Survey
Cover. Photograph of the Oil Mill Brook downstream site in Waterford, Connecticut.
Preliminary Assessment of Chloride 

Concentrations, Loads, and Yields in 

Selected Watersheds along the Interstate 95 

Corridor, Southeastern Connecticut, 2008–09

By Craig J. Brown, John R. Mullaney, Jonathan Morrison, and Remo Mondazzi

Prepared in cooperation with the Federal Highway Administration 

and the Connecticut Department of Transportation

Open-File Report 2011–1018

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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reproduce any copyrighted materials contained within this report.

Suggested citation:

Brown, C.J., Mullaney, J. R., Morrison, Jonathan, and Mondazzi, Remo, 2011, Preliminary assessment of chloride 

concentrations, loads, and yields in selected watersheds along the Interstate 95 corridor, southeastern Connecticut, 

2008–09: U.S. Geological Survey Open-File Report 2011–1018, 41 p. at http://pubs.usgs.gov/ofr/2011–1018/.
iii

Contents

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

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

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

Description of Study Area ...................................................................................................................3

Sources of Dissolved Constituents to Streams and Groundwater...............................................3

Road Deicing Chemicals and their Application in the Study Areas .............................................6

Methods of Data Collection and Analysis ...............................................................................................10

Site Selection.......................................................................................................................................10

Weather Data ......................................................................................................................................10

Streamflow...........................................................................................................................................10

Water Quality.......................................................................................................................................10

Continuous Monitoring .............................................................................................................15

Water-Quality Sampling and Laboratory Analysis ...............................................................15

Quality Assurance......................................................................................................................15

Data Analysis.......................................................................................................................................15

Estimation of Chloride Concentrations...................................................................................15

Estimation of Cl Loads and Yields............................................................................................15

Preliminary Assessment of the Effects of Road Deicers on Water Quality .......................................17

Weather Data and Storm Events......................................................................................................17

Water Quality.......................................................................................................................................17

Base-Flow Chemistry ................................................................................................................17

Stormflow Chemistry.................................................................................................................18

Four Mile River..................................................................................................................19

Oil Mill Brook .....................................................................................................................23

Stony Brook .......................................................................................................................23

Jordan Brook.....................................................................................................................23

Chloride Loads............................................................................................................................27

Summary and Conclusions.........................................................................................................................35

Acknowledgments.......................................................................................................................................35

References Cited..........................................................................................................................................35

Appendix 1. Specific conductance and chloride concentrations in water samples from upstream 

and downstream monitoring sites at Four Mile River, Oil Mill Brook, Stony Brook, and Jordan 

Brook, southeastern Connecticut, November 2008 to January 2010.............................................38

Figures

1. Map showing location of water-quality monitoring sites for this study, and sites on

other rivers in Connecticut, and several weather stations, including the

Groton-New London airport weather station, a Snow Observation weather station,

and three National Atmospheric Deposition Program sites..................................................4

 2. Map showing upstream and downstream water-quality monitoring sites and

downstream streamgages on the four selected streams and their watersheds

along the Interstate 95 corridor study area, southeastern Connecticut.............................5
iv

3. Map showing water-quality monitoring sites and downstream streamgages,

watershed boundaries, and deicing salt storage and landfill locations in the study

areas, southeastern Connecticut...............................................................................................6

4. Graph showing estimated monthly median chloride loads in atmospheric

deposition based on three National Atmospheric Deposition Program stations,

November 2008 - September 2009. Data are from National Atmospheric Deposition

Program, 2009................................................................................................................................9

5. Graph showing A, Maximum and minimum daily air temperature and continuous

precipitation at the Groton-New London airport weather station, and B, estimated

hourly snow thickness and snow melt at a snow observation station in

southeastern Connecticut, November 2008–September 2009 ............................................18

6. Graph showing continuous streamflow at the downstream monitoring sites at Four

Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook, and precipitation at

Groton-New London airport weather station, southeastern Connecticut, November

2008–September 2009 ................................................................................................................19

7. Diagrams depicting the concentrations of major ions in water at upstream and

downstream monitoring sites at Four Mile River, Oil Mill Brook, Stony Brook, and

Jordan Brook, southeastern Connecticut, and shallow groundwater samples from

wells in forested land-use settings in Connecticut...............................................................21

8. Graphs showing A, Specific conductance in grab samples, continuous specific

conductance at Four Mile River upstream and downstream sites, continuous

streamflow at the downstream site, and precipitation at Groton-New London

airport weather station, and B, chloride concentrations measured in grab samples

and estimated continuous chloride concentrations at Four Mile River upstream and

downstream sites, southeastern Connecticut, November 2008–September 2009 ..........22

9. Graphs showing A, Specific conductance in grab samples and continuous specific

conductance at Oil Mill Brook upstream and downstream sites, continuous

streamflow at the downstream site, and precipitation at Groton-New London

airport weather station, and B, chloride concentrations measured in grab samples

and estimated continuous chloride concentrations at Oil Mill Brook upstream and

downstream sites, southeastern Connecticut, November 2008–September 2009 ..........24

10. Graphs showing A, Specific conductance in grab samples and continuous specific

conductance at Stony Brook upstream and downstream sites, continuous

streamflow at the downstream site, and precipitation at Groton-New London

airport weather station, and B, chloride concentrations measured in grab samples

and estimated continuous chloride concentrations at Stony Brook upstream and

downstream sites, southeastern Connecticut, November 2008–September 2009 ..........25

11. Graphs showing A, specific conductance in grab samples and continuous specific

conductance at Jordan Brook upstream and downstream sites, continuous

streamflow at the downstream site, and precipitation at Groton-New London

airport weather station, and B, chloride concentrations measured in grab samples

and estimated continuous chloride concentrations at Jordan Brook upstream and

downstream sites, southeastern Connecticut, November 2008–September 2009 ..........26

12. Graphs showing A, estimated daily mean chloride concentrations at Four Mile

River upstream and downstream sites, and B, estimated daily mean chloride load

and streamflow for the Four Mile River downstream site, southeastern

Connecticut, November 2008–September 2009....................................................................28

13. Graphs showing A, estimated daily mean chloride concentrations at Oil Mill Brook

upstream and downstream sites, and B, estimated daily mean chloride load and

streamflow for the Oil Mill Brook downstream site, southeastern Connecticut, 

November 2008–September 2009.............................................................................................29
v

14. Graphs showing A, estimated daily mean chloride concentrations at Stony Brook

upstream and downstream sites, and B, estimated daily mean chloride load and

streamflow for the Stony Brook downstream site, southeastern Connecticut,

November 2008–September 2009.............................................................................................30

15. Graphs showing A, estimated daily mean chloride concentrations at Jordan Brook

upstream and downstream sites, and B, estimated daily mean chloride load and

streamflow for the Jordan Brook downstream site, southeastern Connecticut,

November 2008–September 2009.............................................................................................31

16. Diagram showing distribution of annual chloride yields estimated using LOADEST

for selected rivers in Connecticut for water years 1998–2007, and estimated annual

chloride yields for the downstream sites at Four Mile River, Oil Mill Brook, Stony

Brook, and Jordan Brook for their periods of record...........................................................33

17. Graph showing percentage of impervious cover as a function of (1) the chloride

yields for the downstream monitoring stations at Four Mile River, Oil Mill Brook,

Stony Brook, and Jordan Brook during the periods of record for this study, and (2)

the median of the mean chloride yields at other selected rivers in Connecticut

during water years 1998–2007 ..................................................................................................34

Tables

1. Land use, numbers of salt-storage facilities and landfills, and percentage of

impervious area for four selected watersheds, southeastern Connecticut. .....................7

2. Classification of surficial materials for watersheds above each monitoring site in

the study area, southeastern Connecticut...............................................................................8

3. Estimated atmospheric deposition yields and loads of chloride for the four selected

watersheds in southeastern Connecticut. Loads were computed from National

Atmospheric Deposition Program station ..............................................................................10

4. Description of two areas of Interstate 95 in which the deicing chemicals were

applied to state-operated roads within areas of (1) the Four Mile River watershed,

and (2) the combined Oil Mill Brook, Stony Brook, and Jordan Brook watersheds, 

southeastern Connecticut.........................................................................................................11

5. Description of the applications of deicing materials to state-operated roads

during winter storms and deicing activities within the areas of (1) the Four Mile

River watershed, and (2) the Oil Mill Brook, Stony Brook, and Jordan Brook area

watersheds, southeastern Connecticut, for the 2008–09 winter seasons, and

summaries for the 2006–07 and 2007–08 winter seasons ....................................................12

6. Deicing materials applied to town roads during the 2008–09 winter season,

southeastern Connecticut.........................................................................................................14

7. Multiple linear regression estimates of model coefficients and standard 

errors, t-statistics, and p-values for the dependent variable chloride 

concentration at monitoring sites upstream and downstream from Interstate 95, 

southeastern Connecticut.........................................................................................................16

8. Summary statistics for A, specific conductance and B, estimated chloride

concentrations for continuous data, and grab samples at the eight

monitoring sites, southeastern Connecticut, November 2008–September 2009 .............20

9A. Estimated mean chloride loads for streams at the four monitoring sites

downstream from Interstate 95, southeastern Connecticut, November 2008 to

January 2010................................................................................................................................32

9B. Estimated mean chloride loads for streams, atmospheric deposition, and deicers

applied to town and state roads in the study areas of the Four Mile River

watershed and the Oil Mill Brook-Stony Brook-Jordan Brook watersheds,

November 2008 to January 2010 ..............................................................................................32
vi

Conversion Factors, Abbreviations, and Datums

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)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

ton, short (2,000 lb) 0.9072 megagram (Mg) 

ton per day (ton/d) 0.9072 metric ton per day

ton per day (ton/d) 0.9072 megagram per day (Mg/d)

ton per day per square mile 

[(ton/d)/mi2]

 0.3503 megagram per day per square kilometer [(Mg/d)/km2

]

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 the North American Vertical Datum of 1988 

(NAVD 88).

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

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

* Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

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

List of Abbreviations

ConnDOT Connecticut Department of Transportation

EIS Environmental Impact Statement

FHWA Federal Highway Administration

USGS U.S. Geological Survey

USEPA U.S. Environmental Protection Agency
Preliminary Assessment of Chloride Concentrations, 

Loads, and Yields in Selected Watersheds along the 

Interstate 95 Corridor, Southeastern Connecticut, 2008–09

By Craig J. Brown, John R. Mullaney, Jonathan Morrison, and Remo Mondazzi

Abstract 

Water-quality conditions were assessed to evaluate 

potential effects of road-deicer applications on stream-water 

quality in four watersheds along Interstate 95 (I-95) in 

southeastern Connecticut from November 1, 2008, through 

September 30, 2009. This preliminary study is part of a 

four-year cooperative study by the U.S. Geological Survey 

(USGS), the Federal Highway Administration (FHWA), and 

the Connecticut Department of Transportation (ConnDOT). 

Streamflow and water quality were studied at four 

watersheds—Four Mile River, Oil Mill Brook, Stony Brook, 

and Jordan Brook. Water-quality samples were collected and 

specific conductance was measured continuously at paired 

water-quality monitoring sites upstream and downstream from 

I-95. Specific conductance values were related to chloride 

(Cl) concentrations to assist in determining the effects of 

road-deicing operations on the levels of Cl in the streams. 

Streamflow and water-quality data were compared with 

weather data and with the timing, amount, and composition 

of deicers applied to state highways. Grab samples were 

collected during winter stormwater-runoff events, such as 

winter storms or periods of rain or warm temperatures in 

which melting takes place, and periodically during the spring 

and summer.

Cl concentrations at the eight water-quality monitoring 

sites were well below the U.S. Environmental Protection 

Agency (USEPA) recommended chronic and acute Cl 

toxicity criteria of 230 and 860 milligrams per liter (mg/L), 

respectively. Specific conductance and estimated Cl 

concentrations in streams, particularly at sites downstream 

from I-95, peaked during discharge events in the winter 

and early spring as a result of deicers applied to roads and 

washed off by stormwater or meltwater. During winter storms, 

deicing activities, or subsequent periods of melting, specific 

conductance and estimated Cl concentrations peaked as high 

as 703 microsiemens per centimeter (μS/cm) and 160 mg/L at 

the downstream sites. 

During most of the spring and summer, specific 

conductance and estimated Cl concentrations decreased 

during discharge events because the low-ionic strength of 

stormwater had a diluting effect on stream-water quality. 

However, peaks in specific conductance and estimated Cl 

concentrations at Jordan Brook and Stony Brook corresponded 

to peaks in streamflow well after winter snow or ice events; 

these delayed peaks in Cl concentration likely resulted from 

deicing salts that remained in melting snow piles and (or) 

that were flushed from soils and shallow groundwater, then 

discharged downstream.

Cl loads in streams generally were highest in the winter 

and early spring. The estimated load for the period of record 

at the four monitoring sites downstream from I-95 ranged 

from 0.33 ton per day (ton/d) at the Stony Brook watershed 

to 0.59 ton/d at the Jordan Brook watershed. The Cl yields 

ranged from 0.07 ton per day per square mile (ton/d/)mi2

) 

at Oil Mill Brook, one of the least developed watersheds, 

to 0.21 (ton/d)/mi2

) at Jordan Brook, the watershed with the 

highest percentage of urban development and impervious 

surfaces. The median estimates of Cl load from atmospheric 

deposition ranged from 11 to 19 tons, and contributed 4.3 to 

7.1 percent of the Cl load in streamflow from the watershed 

areas. A comparison of the Cl load input and output estimates 

indicates that less Cl is leaving the watersheds than is entering 

through atmospheric deposition and application of deicers. 

The lag time between introduction of Cl to the watershed and 

transport to the stream, and uncertainty in the load estimates 

may be the reasons for this discrepancy. In addition, estimates 

of direct infiltration of Cl to groundwater from atmospheric 

deposition, deicer applications, and septic-tank drainfields 

to groundwater were outside the scope of the November 

2008 to September 2009 assessment. However, increased 

concentrations of ions were observed between upstream and 

downstream sites and could result from deicer applications.

Cl yields per square mile at the downstream monitoring 

sites at each of the four streams were compared with Cl 

yield estimates for 10 selected rivers in Connecticut. Four 
2 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

Mile River and Oil Mill Brook had low estimated Cl yields, 

similar to yields at Bunnell (Burlington) Brook and Shetucket 

River, that reflect the low percentages of developed land and 

impervious area. Estimated Cl yields at Jordan Brook and 

Stony Brook were relatively high but were not as high as those 

in more urbanized watersheds such as those that drain the Still 

River at Brookfield Center and the Hockanum River. Cl yields 

for these sites were positively correlated with the percentage 

of impervious cover and probably reflect the application 

of deicers to roadways, as well as sources and practices 

associated with greater impervious cover, such as wastewater 

and septic-system discharges, and leachate from landfills and 

salt-storage areas.

Introduction

The Federal Highway Administration (FHWA) and 

the Connecticut Department of Transportation (ConnDOT) 

are developing an Environmental Impact Statement (EIS) 

for the expansion of Interstate 95 (I-95) between Old Lyme 

and New London, Conn. Concerns have been raised by the 

U.S. Environmental Protection Agency (USEPA) about 

the effects of highway expansion on the water quality and 

biological resources associated with streams crossed by I-95. 

Of particular concern are the water-quality changes that could 

result from expansion of impervious areas that require deicing 

and the subsequent changes in concentrations of chloride (Cl) 

and other ions and loads of Cl to streams.

A primary concern regarding road-deicing practices 

is the degradation of surface water and groundwater that 

may be used for aquatic habitat or for drinking-water 

supply. The USEPA-recommended chronic criterion for 

aquatic life is a 4-day average Cl concentration of 230 mg/L 

with an occurrence interval of once every 3 years, and 

the recommended acute criterion concentration for Cl is 

860 mg/L (U.S. Environmental Protection Agency, 1988). 

The latter criterion relates to a 1-hour average concentration 

with a recurrence interval of less than once every 3 years. 

The Connecticut Department of Environmental Protection 

(CTDEP) has recently proposed revisions to the standards 

for aquatic-life criteria for Cl that are identical to the USEPA 

standards (Connecticut Department of Environmental 

Protection, 2009). The USEPA has set a Secondary Maximum 

Contaminant Level (SMCL) of 250 mg/L for Cl in drinking 

water (U.S. Environmental Protection Agency, 1992). The 

SMCL for Cl is an unenforceable guideline that relates to the 

aesthetics of the water and the perceived salty taste of water 

at concentrations above 250 mg/L. Another concern regarding 

salt inputs is the effects of cation-exchange reactions, which 

result in the release of other constituents from soils that can be 

detrimental to the quality of water (Granato and others, 1995).

Widespread upward trends in Cl concentrations in 

streams have been reported nationwide and may be related 

to a variety of factors, including increased road area and 

consequent deicing, increased wastewater and septic-system 

discharges, livestock waste and fertilizers, and leachate from 

landfills and salt-storage areas (Smith and others, 1987; 

Mullaney and others, 2009). Similar trends have been reported 

in Connecticut from the 1970s to 1990s (Trench, 1996; 

Colombo and Trench, 2002). Elevated concentrations of Cl 

and sodium (Na) in glacial aquifers in Connecticut have been 

related to urban land use (Grady, 1993; Grady and Mullaney, 

1998). A dramatic increase in the use of salt in the United 

States since 1950 (Kostick, 1993; Kostick and others, 2007) 

primarily results from the use of salt for deicing of roads, 

parking lots, and other impervious surfaces during the winter 

months. The use of salt for deicing has raised awareness of 

potential adverse effects of its use and application on water 

resources (Ramakrishna and Viraraghavan, 2005; Kaushal and 

others, 2005; Kelly and others, 2010).

ConnDOT has recently adopted (2007–08) new roaddeicing practices to reduce the use of sand for traction control 

and to increase the use of pretreatment sodium chloride 

(NaCl) brine before storms (Connecticut Department of 

Transportation, 2009). ConnDOT also began using halite, 

amended with liquid calcium chloride (CaCl2), for ice or snow 

events during 2007–08.

Effects of road deicers on water quality can be 

monitored effectively through continuous records of specific 

conductance, together with periodic solute analysis, and 

continuous estimates of streamflow (Gurnell and others, 1994; 

Granato and Smith, 1999). Additional knowledge of the use 

of salt, including the timing, amount, and composition of 

deicers applied to roadways, as well as the weather details, is 

beneficial in understanding the effects of road-salt wash off 

on concentrations and loads of Cl in streamflow. Collection 

of data to determine the Cl concentrations and streamflow, 

and how they affect specific conductance, is important 

to the development of a regression model to estimate 

Cl concentrations.

A study is being conducted by the U.S. Geological 

Survey (USGS), in cooperation with the FHWA and 

ConnDOT, to assess the water quality of streams and the 

effects of deicing of roads on stream-water quality. This is 

an interim report on that study and covers November 2008 

through September 2009. The data collected for this study will 

be useful in understanding the water-quality implications of 

an I-95 expansion and can be used to assist in development of 

low-impact design alternatives. 

Purpose and Scope

This interim report, which covers part of the 2008–09 

winter season as well as the spring and summer of 2009, 

describes the collection and analysis of geologic, hydrologic, 

and water-quality data to assess baseline water-quality 

conditions along the I-95 corridor; the data can be used to 

develop an EIS on water quality. Specific conductance and 

Cl concentration data cover a longer period, 2008 to January 
Introduction 3

2010, at some sites and were used to improve the regression 

models. This report describes the effects of upstream land 

use on stream-water quality, the variations in concentrations 

and loads of Cl during winter storms or deicing activities, and 

concentrations and loads of Cl during base-flow conditions. 

Other major ions also are discussed. Baseline water-quality 

data were collected to evaluate the water-quality conditions 

in streams crossed by I-95 and to evaluate sources of Cl 

delivered from I-95 and upstream areas. Specific conductance, 

which was measured continuously, was used as a surrogate to 

estimate Cl concentrations. These data were used to determine 

whether Cl concentrations frequently exceeded recommended 

water-quality criteria for protection of aquatic life in 

watersheds that are typical of many parts of Connecticut. This 

report also describes the sampling sites in detail, as well as 

the collection of water stage and streamflow data, continuous 

water-quality monitoring, and water-quality sampling.

Description of Study Area

The study area encompasses four watersheds in 

southeastern Connecticut crossed by I-95—Four Mile 

River, Oil Mill Brook, Stony Brook, and Jordan Brook 

(figs. 1 and 2). The watersheds encompass parts of the towns 

of Lyme, Old Lyme, East Lyme, Montville, and Waterford 

(fig. 2). Two locations in each watershed were selected for 

sample collection and water-quality monitoring, including one 

upstream and one downstream from I-95 (fig. 3). Streamgages 

are located at the downstream sites. The watersheds vary in 

size from 1.86 to 5.98 mi2

 and include both commercial and 

undeveloped areas; developed land ranges from 9.4 percent 

at the Four Mile River watershed to 30.5 percent at the 

Jordan Brook watershed (table 1). Data on highway drainage, 

which were acquired from ConnDOT, were considered in 

the delineation of the watershed boundaries. Data on 2002 

land-use and land-cover characteristics were determined 

from LANDSAT Thematic Mapper (TM) data, retrieved from 

the Center for Land use Education And Research (CLEAR) 

website (University of Connecticut, 2009). Data on land-use 

and land-cover characteristics also were determined from TM 

images created for the National Land Cover Dataset (NLCD; 

U.S. Environmental Protection Agency, 2001). 

The study area is underlain by surficial deposits, 

including Pleistocene glacial stratified deposits, glacial till, 

and Holocene alluvial deposits, which occur primarily in 

stream channels (table 2). These deposits are underlain by 

crystalline bedrock. Effective recharge to the glacial stratified 

deposits (Melvin and Bingham, 1991) and groundwater 

storage and flow within these deposits is much larger than in 

till deposits. There is a 10-percent increase in coarse-grained 

surficial deposits (8.0 to 18.3 percent of watershed area) 

between the Stony Brook upstream and downstream sites; 

therefore, base flow is likely an important contribution to 

streamflow downstream from I-95 in this watershed.

Sources of Dissolved Constituents to Streams 

and Groundwater

The primary water-quality constituents of interest in 

this study are dissolved Cl, Na, and calcium (Ca) because 

these are the major dissolved ions in meltwater from road 

deicers applied to highways. These ions are derived from ionic 

compounds or “salts” such as NaCl, CaCl2

, and magnesium 

chloride (MgCl2

) that dissolve easily in water. Other 

anthropogenic sources of Cl include discharge from drinkingwater and wastewater-treatment facilities or septic systems, 

leachate from landfills, fertilizers, and petroleum or chemical 

spills. Natural sources of salts to freshwater resources include 

(1) atmospheric deposition; (2) the natural weathering of 

bedrock, surficial materials, and soils; (3) seawater; and 

(4) geologic deposits containing halite or saline groundwater 

(brines). Halite and brines are not present in geologic deposits 

in this area and, therefore, are not likely to affect stream 

chemistry in this study.

Atmospheric deposition generally transmits salts from 

both anthropogenic and natural sources to watersheds and 

groundwater. Atmospheric deposition of major ions is more 

concentrated in coastal areas than in inland areas (Gay and 

Melching, 1995). Cl load in precipitation can be a substantial 

part of the total Cl load in relatively undeveloped areas, 

particularly in coastal areas (Mullaney and others, 2009; 

National Atmospheric Deposition Program, 2009) (fig. 4). The 

Cl load from atmospheric deposition was estimated by using 

the monthly median concentrations and the amount of rainfall 

at three National Atmospheric Deposition Program (NADP) 

stations (fig. 1), then calculating the Cl mass per unit area. 

Estimated Cl loads ranged from 0.0012 (ton/d)/mi2

 at an inland 

site in Abington, Conn., to 0.11 (ton/d)/mi2

 at a coastal site 

in Cedar Beach, N.Y., during November 2008 to September 

2009. The Cedar Beach, N.Y., station is located on an island 

peninsula within 200 ft of saltwater and is strongly affected by 

sea spray; therefore, the value for Cedar Beach probably is an 

overestimate of atmospheric deposition for watersheds in this 

study (table 3). Chloride estimates for the station at Lexington, 

Mass., is probably most representative of the study area. The 

estimates of Cl load from the atmospheric deposition, based 

on the range of monthly concentrations at the NADP stations 

(fig. 1), vary from 0.1 ton per day (ton/d) for the Stony Brook 

downstream site watershed to 3.1 ton/d for the Four Mile 

River downstream site watershed (table 3). 

The primary road deicers used by the ConnDOT include 

NaCl (both in the brine and halite form) and CaCl2

; those 

used by the towns include NaCl (halite) and a product that 

contains MgCl2

 together with distillers condensed solubles, as 

described in the section “Road Deicing Chemicals and their 

Application in the Study Areas.” Stormwater runoff from 

I-95 is the primary focus of this study, but there are other 

contributions to streamflow in each watershed, including 

stormwater runoff from other roadways and impervious 

surfaces, interflow, and the groundwater component (base 

flow). Sources of major ions in base flow include groundwater 
4 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

KGON

LEXINGTON (MA13)

73 °

42 °

41 °

0 10 20 MILES

0 10 20 KILOMETERS

EXPLANATION

MASSACHUSETTS

NEW YORK

NEW

YORK

RHODE

ISLAND

Watershed and water-quality site (this study)

National Atmospheric Deposition Program site

Weather station

71 °

 CONNECTICUT

Water-quality site for chloride load comparison

LONG ISLAND SOUND

ATLANTIC OCEAN

Base from Connecticut Department of Environmental Protection, 1994, 1:24,000

Projection: Connecticut State Plane Feet

01201487

01208990

01209710

01208500

01196500

01188000

01184490

C

01192500 onnecticut River

01193500

011277695

MADIS AP750

Snow observation

Thames River

011277916 01127821

01122610

ABINGTON (CT15)

01127819

01208500

 CEDAR BEACH (NY96)

Housatonic Rive r

01127819

011277914

011277696

011277915

0112779135

Figure 1. Location of water-quality monitoring sites for this study, and sites on other rivers in Connecticut, and several weather 

stations, including the Groton-New London airport weather station, a Snow Observation weather station, and three National 

Atmospheric Deposition Program sites.
Introduction 5

72°20' 72°15' 72°10' 72°05'

41°25'

41°20'

I-395 I-95

I-95

Downstream water-quality site 

and streamgage

Upstream water-quality site and 

streamgage

Road type

Upstream watershed

Primary highway

Secondary highway

Local road

Minor road

Downstream watershed

Base from Connecticut Department of Environmental Protection, 1994, 1:24,000

Projection: Connecticut State Plane Feet 0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

EXPLANATION

Lyme

Waterford

New London

Montville

Groton

Old Lyme

East Lyme

Long Island Sound

Thames River

Niantic River

Connecticut 

River

Figure 2. Upstream and downstream water-quality monitoring sites and downstream 

streamgages on the four selected streams and their watersheds along the Interstate 95 

corridor study area, southeastern Connecticut.
6 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

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*

#*

#*

#*

#*

$+

$+

XY

X X

X

East Lyme Waterford

Lyme

Old Lyme

Montville

New London

Salem

72°15'

41°25'

41°20'

Niantic

River

EXPLANATION

Upstream watershed

X Land ll

$+ Deicing salt storage

#* Upstream sites

#* Downstream sites

Four Mile

River

Oil Mill

Brook

Stony Brook

Jordan

Brook

Salt storage and land lls from Connecticut Department of

Environmental Protection, Bureau of Water Management, 1995

0 1 2 MILES

0 21 KILOMETERS

Downstream watershed

and streamgages

Orthophoto imagery from U.S. Department of Agriculture,

National Agriculture Imagery Program, 2008, 1 m.

Base from Connecticut Department of Environmental

Protection, 1994, 1:24,000

Projection: Connecticut State Plane Feet

72°10'

Figure 3. Water-quality monitoring sites and downstream streamgages, watershed boundaries, and deicing 

salt storage and landfill locations in the study areas, southeastern Connecticut.

recharge, road deicers and deicer storage locations, septic-tank 

drainfields, landfills, fertilizers, and petroleum or chemical 

spills, as well as aquifer weathering. Potential point sources of 

Cl in each watershed were determined from a 1:50,000-scale 

data layer that includes point locations digitized from 

“Leachate and Wastewater Discharge Source” maps compiled 

by the CTDEP and point locations digitized on-screen from 

CTDEP sources (Connecticut Department of Environmental 

Protection, 1995).

Road Deicing Chemicals and their Application 

in the Study Areas

Road deicing chemicals are a primary source of Cl and 

other constituents to water resources near highways or other 

impervious surfaces in the northern United States (Bubeck 

and others, 1971; Mullaney and others, 2009; Wulkowicz and 

Saleem, 1974). Road deicers include NaCl, CaCl2

, MgCl2, and 

other mixtures that can include distillers condensed solubles1

. 

The use of NaCl in the United States has increased from 

42.9 million tons in 1975 to nearly 58.5 million tons in 2005 

(Kostick and others, 2007). The application of NaCl to roads 

is now the largest use of salt and represents 39.5 percent of the 

end use of salt in the United States (Kostick and others, 2007). 

During the past decade, deicing of state roads throughout 

New England and other northern states has changed (2000–09) 

from simply plowing and salting and sanding to include 

pretreating by spraying liquids that prevent snow and ice 

from bonding with the road (anti-icing) and using less sand. 

Under field conditions, NaCl lowers the freezing point of 

1

 Fermentation by-products, which include spent yeast cells and other 

nutrients, that remain after corn grain has been fermented to produce ethanol, 

known in the food industry as “corn syrup.”
Introduction 

7

Table 1. Land use, numbers of salt-storage facilities and landfills, and percentage of impervious area for four selected watersheds, southeastern Connecticut. [USGS, U.S. Geological Survey; USEPA, U.S. Environmental Protection Agency]

Watershed name

USGS 

site 

identification 

number

Watershed 

area, 

in 

square 

miles

Distance 

between 

upstream 

and 

downstream 

sites, 

in miles

Land use (percent of watershed area) Number 

of 

salt 

storage 

facilities1

Number 

of 

landfills1

Impervious area 

(percent of watershed 

area)

Developed 

land

Turf 

and 

grass

Agriculture 

and 

other 

grasses

Forest 

and 

wetland

University 

of 

Connecticut2, 

2009

USEPA, 

2001 

Four Mile River 

upstream

01127819 5.75

0.2

9.4 2.5 7.7 80.4 0 1 2.92 0.95

Four Mile River 

downstream

01127821 5.98 11.0 2.7 7.5 78.8 0 0 3.3 1.58

Difference between sites: 0.38 0.63

Oil Mill Brook 

upstream

0112779135 5.37

0.23

12.9 2.2 3.4 81.5 0 0 3.63 1.69

Oil Mill Brook 

downstream

011277914 5.67 13.5 2.2 3.5 80.9 0 0 3.75 1.91

Difference between sites: 0.12 0.22

Stony Brook 

upstream

0112779155 1.02

0.82

18.2 1.4 4.0 76.4 0 1 4.72 5.53

Stony Brook 

downstream

011277916 1.86 18.1 2.3 8.1 71.5 0 0 5.77 6.3

Difference between sites: 1.05 0.77

Jordan Brook 

upstream

011277695 2.67

0.32

30.5 4.9 4.1 60.5 2 2 6.02 7.84

Jordan Brook 

downstream

011277696 2.80 30.5 4.9 4.5 60.1 0 0 6.29 8.01

Difference between sites: 0.27 0.17

1Data on salt storage and landfill locations from Leachate and Wastewater Discharge Source maps at 1:50,000 scale compiled by the Connecticut Department of Environmental Protection (1995).2Center for Land use Education And Research, University of Connecticut, 2009, based on methods described by Chabaeva and others (2004) and Prisloe and others (2003).
8 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

Table 2. Classification of surficial materials for watersheds above each monitoring site in the study area, southeastern Connecticut.

[Data from Stone and others, 1992. USGS, U.S. Geological Survey; us, upstream; ds, downstream]

Watershed name

USGS 

site identification 

number

Surficial material, in percent of watershed area

Coarse grained Swamp or fines Till Thick till Water

Four Mile River us 01127819 16.3 1.6 73.7 7.5 0.9

Four Mile River ds 01127821 16.2 1.5 73.3 8.1 0.9

Oil Mill Brook us 0112779135 13.3 1.6 71.5 4.8 8.8

Oil Mill Brook ds 011277914 18.7 1.5 71.7 4.5 8.4

Stony Brook us

Stony Brook ds

0112779155

011277916

8.0

18.3

14.8

7.5

77.2

74.2

0.0

0.0

0.0

0.0

Jordan Brook us 011277695 17.9 3.1 74.7 4.3 0.0

Jordan Brook ds 011277696 18.7 3.0 74.2 4.1 0.0

water to -9°C; other salts, such as CaCl2, depress the freezing 

point even lower (to -29°C), but these are more expensive 

(Connecticut Department of Transportation, 2009). NaCl 

brine, therefore, is generally applied to state bridges, ramps, 

overpasses, and some roads before snow or ice events.

 ConnDOT initiated a new snow and ice removal 

program beginning in the 2006–07 winter season (Connecticut 

Department of Transportation, 2009). ConnDOT crews 

generally avoid using sand on roadways because it provides 

only temporary traction, fouls waterways and the air, clogs 

drains, and is costly to clean up. The primary purpose of the 

new program is to reduce the use of sand and improve winter 

driving conditions by (1) pretreating pavements with NaCl 

brine, thus preventing bonding of snow or ice, and (2) using 

liquid CaCl2

 as a wetting agent for rock salt (halite), which 

is applied during snow or ice events, to lower the freezing 

point, to reduce bounce and scatter, and to accelerate the 

melting time.

ConnDOT uses a 23-percent NaCl brine solution for 

anti-icing at a rate of about 30 gal per lane mile. Larger rates 

(40 gal per lane mile) of the NaCl brine solution are applied 

at pavement temperatures below -1°C, but none is applied 

below -5.5°C because it is ineffective at colder temperatures. 

The brine solution is applied by a tanker truck using spray 

bars with nozzles that are spaced about 10 in. apart. After 

application of the brine solution, the water evaporates as 

2-in. strips that melt frozen precipitation on contact. The 

program also calls for the pretreating of bridges and selected 

roadways with salt brine up to 5 days prior to an anticipated 

precipitation event.

 CaCl2

 in liquid form (about 32 percent by weight) has 

been used on Connecticut state roads since the 2006–07 

winter. It is sprayed onto halite rock salt in the spreader chute 

on plows and other snow-removal equipment. The CaCl2 brinehalite combination melts snow or ice faster during application 

than using only halite and sand. The typical mixing rate is 

10 gal of liquid CaCl2

 per ton of rock salt, but the rates are 

varied depending on such factors as temperature, humidity, the 

type and timing of storms, and traffic conditions (Connecticut 

Department of Transportation, 2009). In some situations where 

ice has already formed, liquid ice-control chemicals (CaCl2

 or 

NaCl brine) are applied directly to the pavement.

During this study, ConnDOT maintained records of 

deicers applied to I-95 along specific lengths of roads. 

These records include the length and type of state-operated 

roads within (1) the Four Mile River watershed and (2) the 

combined watersheds of Oil Mill Brook, Stony Brook, and 

Jordan Brook (table 4); the dates and times of application; 

and the quantity of deicers and sand applied over a given 

spreader route (table 5). All road salt applied to I-95 meets 

standards that specify chemical purity. NaCl conforms to the 

standard ASTM D632-84, which specifies that all samples 

tested must be at a minimum of 95-percent pure NaCl, and 

all CaCl2

 must be a minimum of 90-percent pure as specified 

by the standard ASTM D98-93. Typical spreading rates from 

trucks with calibrated spreaders are about 300 lb per lane-mile, 

+/- 20 percent (Connecticut Department of Transportation, 

2009). The total amount of deicers applied to the highway 

varied from storm to storm and year to year (table 5). The 

deicers applied to I-95 and other state roads for the 2008–09 

winter season were categorized by (1) storms, which refers
Introduction 9

0.04

0

0.08

0.12

11/2008

12/2008

1/2009

2/2009

3/2009

4/2009

5/2009

6/2009

7/2009

8/2009

9/2009

MONTH AND YEAR

CHLORIDE IN ATMOSPHERIC DEPOSITION,

 IN TONS PER DAY PER SQUARE MILE 

CT15

MA13

EXPLANATION

Abington, CT

Lexington, MA

NY96 Cedar Beach, NY

Figure 4. Estimated monthly median chloride loads in atmospheric deposition based on three National Atmospheric Deposition 

Program stations, November 2008 - September 2009. Data are from National Atmospheric Deposition Program, 2009. (Locations of 

sites are shown in fig. 1.)

to snow or ice storm events, and (2) activities, such as icy 

conditions or drifting snow, which generally require shorter 

periods of deicing (table 5; Connecticut Department of 

Transportation, 2009). The deicers and sand applied to these 

areas during the 2006–07 and 2007–08 winter seasons are 

summarized in table 5.

The town of Old Lyme used NaCl (halite) and sand to 

treat snow and ice on town roads during the 2008–09 winter 

season and applied 1.6 tons of Cl per road mile to roads 

within the Four Mile River watershed (E. Adanti, Town of 

Old Lyme, oral commun., 2009). The other towns in the 

study—East Lyme, Waterford, and Montville—used a deicing 

product called Ice B’ Gone® that contains MgCl2

 together 

with distillers condensed solubles (table 6). The mixture is 

described as having a synergistic melting effect that results in 

a melting temperature of -31°C (Sears Ecological Applications 

Co., LLC, 2009). The town of East Lyme applied an estimated 

5.6 tons of Cl per road mile to roads within the Four Mile 

River watershed during the 2008–09 winter season in the form 

of NaCl (halite) and Ice B’ Gone® (M. Giamattasio, Town 

of East Lyme, oral commun., 2009). The town of Montville 

also used a combination of NaCl (halite) and Ice B’ Gone® 

and applied about 21.1 tons per road mile to roads within the 

Oil Mill Brook watershed during the 2008–09 winter season 

(D. Bordeau, Town of Montville, oral commun., 2009). The 

town of Waterford, which used only Ice B’ Gone® during the 

2008–09 winter season, applied about 8.4 tons of Cl per road 

mile to roads within the Oil Mill Brook, Stony Brook, and 

Jordan Brook watersheds (R. Cusano, Town of Waterford, oral 

commun., 2009).
10 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

Table 3. Estimated atmospheric deposition yields and loads of chloride for the four selected watersheds in southeastern 

Connecticut. Loads were computed from National Atmospheric Deposition Program stations in Abington, Conn., Lexington, Mass., 

and Cedar Beach, N.Y., November 2008–September 2009. 

[Data from National Atmospheric Deposition Program (NADP), 2009. Location of stations shown in fig. 1.]

NADP 

station

NADP 

station location

Atmospheric deposition yields, 

in tons per day per square mile

Atmospheric deposition loads, 

in tons per day 

(November 2008 to September 2009)

Lower 

range

Upper 

range

Median1 Four Mile 

River

Oil Mill 

Brook

Stony 

Brook

Jordan 

Brook

CT15 Abington, CT 0.001 0.012 0.005 0.36 0.34 0.11 0.17

MA13 Lexington, MA 0.002 0.009 0.005 0.31 0.30 0.10 0.15

NY96 Cedar Beach, NY 0.013 0.11 0.040 3.1 2.9 0.96 1.4

1

Median values were used to compute atmospheric deposition for study watersheds.

Methods of Data Collection 

and Analysis

Data were collected during the interim study period (as 

early as November 1, 2008, to September 30, 2009) using 

methods described below to assess weather information, water 

quality, stream stage, and streamflow for the four selected 

streams. All water-quality, stream-stage, and streamflow data 

are stored in the USGS National Water Information System 

(NWIS) database.

Site Selection

Approximately 17 streams between the Connecticut 

River and the Thames River that are crossed by I-95 were 

initially considered as locations for potential monitoring sites. 

Site selection involved assessment of available geographic 

information system (GIS) data and streamflow characteristics 

of all the watersheds upstream from and encompassing parts 

of I-95. Four streams between the Connecticut River and the 

Thames River (fig. 1)—Four Mile River, Oil Mill Brook, 

Stony Brook, and Jordan Brook—were selected for study 

on the basis of the percentage of land-use types, percentage 

of impervious surfaces, road types and density, presence of 

coarse glacial stratified deposits, suitability for streamflow and 

water-quality monitoring, site accessibility, representativeness 

and transferability, and the absence of estuarine or 

brackish waters.

Weather Data

Hourly measurements of air temperature and precipitation 

for the study period were obtained from continuous 

temperature and precipitation data collected by the National 

Weather Service at the Groton-New London airport weather 

station (KGON; fig. 1) as part of the Meteorological 

Assimilation Data Ingest System (MADIS). The data were 

accessed through Weather Underground (http://www.

wunderground.com).

Another branch of the National Weather Service, the 

National Operational Hydrologic Remote Sensing Center, 

assembles daily ground-based, airborne, and satellite snow 

observations for the conterminous United States (National 

Operational Hydrologic Remote Sensing Center, 2005). 

These data are used together with estimates of snowpack 

characteristics generated by a snow model to generate the 

operational, daily NOAA National Snow Analysis for the 

United States, for which estimates are made for snow depth, 

snow-water equivalent, and snow melt. The snow observation 

station (MADIS AP750) nearest the study area is located at 

N41.36733°, W72.216°, at an altitude of 72 ft above NAVD 88 

(fig. 1).

Streamflow

Stream stage and streamflow were measured at four 

sites downstream from I-95 on Four Mile River, Oil Mill 

Brook, Stony Brook, and Jordan Brook (fig. 3) and used for 

computations of Cl loads in highway stormwater runoff. 

Stream stage was recorded at 5-minute intervals with pressure 

transducers and data loggers, and streamflow measurements 

were made periodically at these sites. These data were used 

to develop a rating curve to convert stage measurements 

into streamflow. All streamflow records were computed in 

accordance with standard USGS protocols for computation of 

streamflow records as described by Rantz and others (1982).

Water Quality

Water-quality data were collected at sites upstream and 

downstream from I-95 on the Four Mile River, Oil Mill Brook, 

Stony Brook, and Jordan Brook to monitor Cl concentrations 

and to evaluate the loads at downstream sites. Water quality 

was assessed using continuous monitors and periodic grab 

samples collected during base flow and winter storms.
Methods of Data Collection and Analysis 11

Table 4. Description of two areas of Interstate 95 in which the deicing chemicals were applied to state-operated roads within 

areas of (1) the Four Mile River watershed and (2) the combined Oil Mill Brook, Stony Brook, and Jordan Brook watersheds, 

southeastern Connecticut.

[Data from K. Carifa, Connecticut Department of Transportation, written commun., 2009; mi, mile; ft, feet; N/B, northbound; S/B, southbound]

(1) Four Mile River watershed study area Distance, 

in miles

(2) Oil Mill-Stony Brook-Jordan Brook watersheds 

study area:

Distance, 

in miles

I-95 N/B (Old Lyme/East Lym) Mile Marker 83 to 84 I-95 N/B (Waterford) Mile Marker 88 to 92

Two 12-ft lanes w/shoulder 1 Two 12-inch lanes with shoulder 4

N/B Exit 71 off ramp 0.24 On ramp from Oil Mill 0.11

N/B Exit 71 on ramp 0.30 Exit 81 Cross Roads off 0.09

N/B Exit 72 to Rocky Neck Connector 0.20 Exit 81 Cross Roads on 0.15

Scale House exit ramp 0.18

I-95 N/B (East Lyme/Old Lyme) Mile Marker 84 to 83 Scale House on ramp 0.18

Two 12-ft lanes with shoulder 1 Exit 82 off ramp to 85 0.19

S/B Exit 72 to Rocky Neck Connector 0 Exit 82 on ramp from 85 0.06

S/B on ramp from Rocky Neck Connector 0

S/B Exit 71 off ramp 0 I-95 S/B (Waterford) -Mile marker 92 to 88

S/B Exit 71 on ramp 0 Two 12-ft lanes with shoulder lane 4

Exit 82 off ramp to 85 0.13

Route 1 N & S (Old Lyme/East Lyme) Mile marker 87 to 90 Exit 82 on ramp to 85 0.14

Two 12-ft lanes with approximately 4 ft shoulder 3 Scale House exit ramp 0.18

Scale House on ramp 0.18

Service Road 432 East Lyme Exit 81 Cross Roads off 0.07

Two 12-ft lanes, no shoulder 0.54 Exit 81 Cross Roads on 0.16

Total 2 lane mi: 5.5 Off ramp to Oil Mill 0.12

Total ramp mileage: 1.7

I-395 N/B (Waterford) Mile Marker 1 to 3

Two 12-ft lanes with shoulder 3

Exit 77 N/B off ramp (Route 85) 0.22

Exit 77 N/B on ramp (Route 85) 0.18

I-395 S/B (Waterford) Mile Marker 3 to 1

Two 12 ft lanes with shoulder 3

exit 77S/B off ramp (Route 85) 0.18

exit 77S/B on ramp (Route 85) 0.19

Route 85 N/B (Waterford/Montville) Marker 1 to 7

Two 12-ft lanes with shoulder 6

Route 1 N & S

Route 1 N/B (Waterford) Marker 93 to 94 0.97

Total 2 lane mi 21

Total ramp mileage: 2.7
12 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09 Table 5. Description of the applications of deicing materials to state-operated roads during winter storms and deicing activities within the areas of (1) the Four Mile River watershed, and (2) the Oil Mill Brook, Stony Brook, and Jordan Brook area watersheds, southeastern Connecticut, for the 2008–09 winter seasons, and summaries for the 2006–07 and 2007–08 winter seasons. [Data from K. Carifa, Connecticut Department of Transportation (ConnDOT), written commun., 2009. Lengths of state roads that undergo deicing are shown in table 4. Cl, chloride; NaCl, sodium chloride; CaCl2, calcium chloride] Type Start End Duration, in hours Number of applications, 3-hour intervals (1) Four Mile River watershed study area NaCl (tons) CaCl2 (gallons) Total sand, in cubic yards Total Cl, in tons 2 lanes Multi lanes Ramps Total Two lanes Multi lanes Ramps Total Activity No. 1 11/30/08 16:30 11/30/08 18:00 11.5 3.83 2.53 1.41 1.19 5.13 27.2 15.3 12.7 55.2 Storm No. 1 12/6/08 19:00 12/7/08 10:00 16 5.33 3.52 1.97 1.65 7.14 37.8 21.3 17.7 76.8 Storm No. 2 12/16/08 16:00 12/17/08 8:00 17 5.66 3.74 2.09 1.75 7.58 40.1 22.6 18.8 81.6 Storm No. 3 12/19/08 8:00 12/20/08 16:00 32 10.66 7.04 3.94 3.3 14.3 75.6 42.6 35.4 153.6 Storm No. 4 12/21/08 3:00 12/21/08 21:00 18 6 3.96 2.22 1.86 8.04 42.5 24 19.9 86.5 Storm No. 5 12/24/08 1:00 12/24/08 10:00 9 3 1.98 1.11 0.93 4.02 21.3 12 10.0 43.2 Activity No. 2 12/26/08 22:00 12/27/08 9:00 12 4 2.64 1.48 1.24 5.36 28.4 16 13.3 57.6 Storm No. 6 12/31/08 4:00 1/1/09 9:00 29 9.66 6.38 3.57 3 13.0 68.5 38.6 32.1 139.2 Activity No. 3 1/4/09 0:00 1/5/09 8:00 9 3 1.98 1.11 0.93 4.02 21.3 12 10.0 43.2 Storm No. 7 1/6/09 16:00 1/7/09 15:59 24 8 5.28 2.96 2.48 10.7 56.7 32 26.6 115.3 Storm No. 8 1/10/09 11:00 1/11/09 14:00 28 9.33 6.16 3.45 2.89 12.5 66.2 37.3 31.0 134.5 Activity No. 4 1/15/09 0:30 1/15/09 16:00 14.5 4.83 3.19 1.78 1.5 6.47 34.2 19.3 16.0 69.6 Storm No. 9 1/18/09 0:30 1/19/09 12:00 23.5 7.83 5.17 2.9 2.43 10.5 55.4 31.3 26 112.7 Activity No. 5 1/19/09 15:00 1/20/09 1:45 11.75 3.91 2.58 1.45 1.21 5.24 27.7 15.6 13.0 56.3 Storm No. 10 1/27/09 22:00 1/29/09 8:00 35 11.66 7.7 4.31 3.61 15.6 82.7 46.6 38.7 168.0 Storm No. 11 2/2/09 21:30 2/4/09 8:00 35.5 11.83 7.8 4.38 3.67 15.9 83.9 47.3 39.3 170.5 Activity No. 6 2/18/09 16:00 2/19/09 8:00 17 5.66 3.74 2.09 1.75 7.58 40.1 22.6 18.8 81.6 Activity No. 7 2/19/09 15:59 2/20/09 8:00 17 5.66 3.74 2.09 1.75 7.58 40.1 22.6 18.8 81.6 Storm No. 12 2/22/09 11:00 2/23/09 8:00 22 7.33 4.84 2.71 2.27 9.82 52.0 29.3 24.3 105.6 Activity No. 8 3/1/09 2:00 3/1/09 14:00 12 4 2.64 1.48 1.24 5.36 28.4 16 13.3 57.6 Storm No. 13 3/1/09 20:00 3/2/09 21:00 25 8.33 5.5 3.08 2.58 11.2 59.1 33.3 27.7 120.0

Winter 2008-09 Summary total: 140 92.1 51.6 43.2 187 989 558 463 2,010 0 121Winter 2007-08 Summary total: 160 106 59.2 49.5 214 1,135 619 532 2,286 0 138

Winter 2006-07 Summary total: 77.9 51.5 28.8 24.1 104 553 312 259 1,123 46 67.4
Methods of Data Collection and Analysis 13

Table 5. Description of the applications of deicing materials to state-operated roads during winter storms and deicing activities within the areas of (1) the Four Mile River watershed, and (2) the Oil Mill Brook, Stony Brook, and Jordan Brook area watersheds, southeastern Connecticut, for the 2008–09 winter seasons, and summaries for the 2006–07 and 2007–08 winter seasons. —Continued[Data from K. Carifa, Connecticut Department of Transportation (ConnDOT), written commun., 2009. Lengths of state roads that undergo deicing are shown in table 4. Cl, chloride; NaCl, sodium chloride; CaCl2, calcium chloride]

Type Start End

Duration, 

in 

hours

Number 

of 

applications, 

3-hour 

intervals

(2) Oil Mill/Stony Brook/Jordan Brook watersheds study area

NaCl (tons) CaCl2 (gallons) Total 

sand, 

in 

cubic 

yards

Total 

Cl, 

in 

tons

2 lanes Multi lanes Ramps Total Two lanes Multi lanes Ramps Total

Activity No. 1 11/30/08 16:30 11/30/08 18:00 11.5 3.83 6.5 10.4 1.92 18.8 64.6 112.5 20.8 198Storm No. 1 12/6/08 19:00 12/7/08 10:00 16 5.33 9.0 14.5 2.67 26.2 89.9 156.5 28.9 275Storm No. 2 12/16/08 16:00 12/17/08 8:00 17 5.66 9.6 15.3 2.83 27.7 95.4 166.2 30.7 292Storm No. 3 12/19/08 8:00 12/20/08 16:00 32 10.66 18.0 29 5.33 52.4 180 313 57.8 550Storm No. 4 12/21/08 3:00 12/21/08 21:00 18 6 10.1 16.3 3.0 29.5 101 176 32.5 310Storm No. 5 12/24/08 1:00 12/24/08 10:00 9 3 5.1 8.2 1.5 14.7 50.6 88.1 16.3 155

Activity No. 2 12/26/08 22:00 12/27/08 9:00 12 4 6.8 10.9 2.0 19.6 67.4 117 21.7 207Storm No. 6 12/31/08 4:00 1/1/09 9:00 29 9.66 16.3 26.3 4.83 47.4 163 284 52.4 499

Activity No. 3 1/4/09 0:00 1/5/09 8:00 9 3 5.1 8.2 1.5 14.7 50.6 88.1 16.3 155Storm No. 7 1/6/09 16:00 1/7/09 15:59 24 8 13.5 21.8 4.0 39.3 135 235 43.4 413

Storm No. 8 1/10/09 11:00 1/11/09 14:00 28 9.33 15.8 25.4 4.67 45.8 157 274 50.6 482Activity No. 4 1/15/09 0:30 1/15/09 16:00 14.5 4.83 8.2 13.1 2.42 23.7 81.4 142 26.2 249Storm No. 9 1/18/09 0:30 1/19/09 12:00 23.5 7.83 4.6 21.3 3.92 29.9 132 230 42.4 404

Activity No. 5 1/19/09 15:00 1/20/09 1:45 11.75 3.91 6.6 14.7 1.96 23.3 65.9 115 21.2 202

Storm No. 10 1/27/09 22:00 1/29/09 8:00 35 11.66 19.7 43.8 5.83 69.3 197 342 63.2 602Storm No. 11 2/2/09 21:30 2/4/09 8:00 35.5 11.83 20.0 44.4 5.92 70.3 199 347 64.1 611Activity No. 6 2/18/09 16:00 2/19/09 8:00 17 5.66 9.6 5.4 2.83 17.8 95.4 166 30.7 292

Activity No. 7 2/19/09 15:59 2/20/09 8:00 17 5.66 9.6 5.4 2.83 17.8 95.4 166 30.7 292Storm No. 12 2/22/09 11:00 2/23/09 8:00 22 7.33 12.4 19.9 3.67 36.0 124 215 39.7 379

Activity No. 8 3/1/09 2:00 3/1/09 14:00 12 4 6.8 10.9 2 19.6 67.4 117 21.7 207Storm No. 13 3/1/09 20:00 3/2/09 21:00 25 8.33 14.1 22.7 4.17 40.9 140 245 45.2 430

Winter 2008-09 Summary total: 140 227 388 69.8 685 2,352 4,096 756.2 7,204 0 442Winter 2007-08 Summary total: 160 221 433 80.1 733.8 2,389 4,700 795 7,884 0 474Winter 2006-07 Summary total: 77.9 108 212 39.0 358.5 1,163 2,288 422 3,873 210 232
14 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09 Table 6. Deicing materials applied to town roads during the 2008–09 winter season, southeastern Connecticut. [--, none reported; Cl, chloride; NaCl, sodium chloride] Town Contact Total deicing product applied, in tons Total Cl amount applied, in tons Total length of town roads, in miles Cl amount applied per town road mile, in tons Length of town roads in basins, in miles Length of town roads in grouped areas, in miles Cl load in grouped study areas, in tons Sand and salt mixture NaCl from salt and sand mixture NaCl (halite) ICE B’ Gone1 blend Sand and salt mixture NaCl (halite) ICE B’ GONE blend Total Total Sand and salt mixture NaCl (halite) ICE B’ GONE blend Four Mile River watershed East Lyme M. Giannattasio -- -- 700 300 -- 425 201 626 112 5.6 -- 3.8 1.8 12.5 14.4 72.8 Old Lyme E. Adanti 220 55 99 -- 33.4 60.1 -- 93 60 1.6 0.56 1.0 -- 1.9 Oil Mill Brook, Stony Brook, and Jordan Brook watersheds Waterford R. Cusano -- -- -- 1,500 -- -- 1,005 1,005 120 8.4 -- -- 8.4 24.2 28 283 Montville D. Bordeau -- -- 2,623 1,379 -- 1,591 924 2,515 119 21.1 -- 13.4 7.8 3.8

1Ice B’ Gone blend consists of 14 percent magnesium chloride (MgCl2), 4.2 percent calcium chloride (CaCl2), 0.3 percent sodium chloride (NaCl), 0.1 percent potassium chloride (KCl), and 50 percent 

distillers condensed solubles (by weight) in 8 gallons of solution per ton of NaCl.
Methods of Data Collection and Analysis 15

Continuous Monitoring

Continuous monitoring of water quality at each sampling 

site was accomplished using a water-quality monitoring 

instrument for measurement of temperature, specific 

conductance, and pH at 10-minute intervals. All procedures 

relating to water-quality monitors (calibration, maintenance, 

record computation, storage, and archiving) are described by 

Wagner and others (2006).

Water-Quality Sampling and Laboratory Analysis

Water-quality grab samples were collected 

(1) approximately monthly during routine conditions, 

(2) during base-flow conditions, and (3) during winter 

runoff events, such as winter storms or warm periods 

in which snow or ice melts. Field characteristics, which 

include water temperature, pH, and specific conductance, 

were measured during sample collection in accordance with 

USGS procedures described by Wilde (2004; 2005). Grab 

samples generally were analyzed for Cl concentrations only, 

and samples collected on August 19, 2009, during base-flow 

conditions were analyzed for major ions. All water samples 

collected were analyzed by the USGS National Water-Quality 

Laboratory (NWQL) in Denver, Colo., using the methodology 

described in Fishman and Friedman (1989).

Quality Assurance

Field sensors were regularly cleaned and calibrated with 

standard solutions and checked periodically with independent 

field and laboratory sensors. Continuous stage data and 

water-quality data were checked and corrected or censored 

for interruptions or shifts caused by debris, ice, or low-flow 

conditions. Quality-control procedures for the collection of 

continuous specific-conductance data followed procedures 

described in Wagner and others (2006). 

Field quality-control procedures included the collection 

and analysis of replicate and blank samples. Fieldblank samples provided information on bias or possible 

contamination during sample collection, processing, or 

analysis. Analytical results from the field-blank samples 

showed that concentrations of constituents were less than 

the reporting level. Analysis of replicate samples provided 

information on the variability of analytical results caused 

by sample collection, processing, and analysis. Analytical 

methods used in the laboratory for analysis of constituent 

concentrations were reported to be accurate within 3 

to 12 percent for major ions, depending on the ionic 

concentration and the analytical method used (Fishman and 

Friedman, 1989). The charge balances for major ion analyses 

were all within +/- 3 percent.

Data Analysis

Data analysis included graphical plotting of 

concentrations of water-quality constituents, multiplecomparison tests, and statistical analyses of the relations 

between ancillary variables and Cl concentrations and yields 

in surface water. 

Estimation of Chloride Concentrations

Cl concentrations were estimated using regression models 

that described the relation among measured Cl concentrations, 

specific conductance, and instantaneous streamflow. Grab 

samples collected manually at each of the sites upstream and 

downstream from I-95 from November 2008 to January 2010 

and analyzed for Cl concentrations provided the “measured” 

Cl concentrations used in the regression models specific to 

each site (appendix 1). 

The resulting multiple linear regression models were 

then used to predict daily mean Cl concentrations on the 

basis of daily mean values of specific conductance and 

flow. Instantaneous Cl concentrations, based on specific 

conductance and flow data collected every 10 minutes, were 

calculated for the period of available record at each station 

from November 2008 to September 2009.

The variables specific conductance and natural log 

of estimated instantaneous streamflow were found to be 

significant in relating ancillary variables to the dependent 

variable Cl concentration at seven of the eight sites (table 7). 

The instantaneous streamflow estimates were made at each 

of the four downstream sites but were significant when 

applied to the corresponding upstream site as well. At Oil 

Mill Brook downstream from I-95, the variable instantaneous 

flow was significant at p less than 0.05, but natural log of 

instantaneous flow was not. The use of the instantaneous 

flow variable improved the fit of each regression model and 

helped to explain additional variability, in comparison with 

the traditional method of using only specific conductance in a 

simple linear regression.

Estimation of Cl Loads and Yields

Cl loads in streams were estimated for each of the 

four sites downstream from I-95. Loads were estimated 

by multiplying the daily mean estimated Cl concentration 

by the daily mean streamflow for each day with available 

record. Total Cl loads in streams for the period of record 

were summarized along with daily loads and daily yields per 

square mile of watershed area. Lower and upper bounds of a 

95-percent confidence interval were calculated for estimated 

Cl concentrations, and subsequently for daily Cl load and 

yield, to provide a range of plausible values.

Mean chloride yields per square mile at the downstream 

monitoring sites at Four Mile River, Oil Mill Brook, Stony 

Brook, and Jordan Brook were compared with annual Cl yield 
16 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09 Table 7. Multiple linear regression estimates of model coefficients and standard errors, t-statistics, and p-values for the dependent variable chloride concentration at monitoring sites upstream and downstream from Interstate 95, southeastern Connecticut. [μS/cm; microsiemens per centimeter; °C; degrees Celsius; ft3/s, cubic feet per second; <, less than] Adjusted r2 Variable Units Parameter estimate Standard error t-statistic

p-value

Four Mile River downstream 0.997 Intercept Dimensionless -8.541 0.969 -8.811 <0.0001

Specific conductance μS/cm at 25°C 0.198 0.007 29.115 <0.0001Natural log instantaneous flow ft3/s 1.336 0.196 6.808 <0.0001

Four Mile River upstream 0.798 Intercept Dimensionless -10.935 2.919 -3.746 0.002

Specific conductance μS/cm at 25°C 0.214 0.027 7.819 <0.0001Natural log instantaneous flow at downstream site ft3/s 1.659 0.341 4.872 0.000

Oil Mill Brook downstream 0.946 Intercept Dimensionless -6.134 1.379 -4.449 0.000

Specific conductance μS/cm at 25°C 0.240 0.016 15.232 <0.0001Instantaneous flow ft3/s 0.147 0.070 2.107 0.049

Oil Mill Brook upstream 0.958 Intercept Dimensionless -10.423 1.552 -6.715 <0.0001

Specific conductance μS/cm at 25°C 0.258 0.017 15.449 <0.0001Natural log instantaneous flow at downstream site ft3/s 1.803 0.455 3.959 0.002

Stony Brook downstream 0.917 Intercept Dimensionless -10.194 2.730 -3.735 0.002

Specific conductance μS/cm at 25°C 0.248 0.019 13.367 <0.0001Natural log instantaneous flow ft3/s 1.829 0.519 3.526 0.003

Stony Brook upstream 0.955 Intercept Dimensionless -16.420 3.140 -5.229 0.000

Specific conductance μS/cm at 25°C 0.297 0.018 16.250 <0.0001Natural log instantaneous flow at downstream site ft3/s 2.412 0.631 3.825 0.002

Jordan Brook downstream 0.918 Intercept Dimensionless -16.625 5.063 -3.284 0.008

Specific conductance μS/cm at 25°C 0.288 0.025 11.596 <0.0001Natural log instantaneous flow ft3/s 2.348 0.631 3.723 0.004

Jordan Brook upstream 0.966 Intercept Dimensionless -22.693 3.489 -6.505 <0.0001

Specific conductance μS/cm at 25°C 0.312 0.016 19.085 <0.0001Natural log instantaneous flow at downstream site ft3/s 3.295 0.505 6.526 <0.0001
Preliminary Assessment of the Effects of Road Deicers on Water Quality 17

estimates for 10 selected rivers in Connecticut for 1998 to 

2007 that were determined using the LOAD ESTimator 

(LOADEST) computer program (Runkel and others, 2004). 

LOADEST was used to estimate Cl yields for the 10 selected 

rivers in Connecticut by multiplying the daily mean estimated 

Cl concentration by the daily mean streamflow for each day 

with available record. Given a time series of streamflow, 

additional data variables, and constituent concentration, 

LOADEST assists the user in developing a regression model 

for the estimation of constituent load. Explanatory variables in 

the regression model include various functions of streamflow, 

decimal time, and additional user-specified data. The 

formulated regression model then is used to estimate loads 

over a user-specified time interval.

Preliminary Assessment of the Effects 

of Road Deicers on Water Quality

Specific conductance and Cl concentrations varied 

temporally with streamflow and season, and spatially between 

upstream and downstream sites on each of the four streams as 

described below. 

Weather Data and Storm Events

The spatially averaged annual total precipitation in 

Connecticut over the last 100 years shows a generally upward 

trend in precipitation with high year-to-year variability. 

The long-term mean annual precipitation is 44.8 in/yr and 

is distributed fairly evenly throughout the year (Miller and 

others, 2002). The average annual precipitation near the 

coast at Groton-New London airport weather station (fig. 2) 

is 48.7 in. for a 39-year period of record. Snowfall is a 

minor component of the total precipitation in Connecticut, 

particularly along the coastal regions where it is moderated 

by the ocean. The average snowfall in Connecticut is 

approximately 30 in. along the coast, 40 in. inland, and 60 in. 

in the northwest corner of the state (Miller and others, 2002). 

The average annual snowfall at Groton is 36.9 in. with an 

average winter temperature of -1.8°C.

Weather data, including maximum and minimum daily 

air temperature, precipitation amount (fig. 5A), measured 

and estimated thickness of snow, and estimated snow melt 

(fig. 5B), were compared to streamflow, specific conductance, 

and Cl concentration. Precipitation and (or) stormwater-runoff 

events generally coincide with an increased response of stream 

stage and streamflow. These responses also can be related to 

the type and amount of road deicers applied by ConnDOT to 

I-95 and associated roads in the Four Mile River watershed 

and in the Oil Mill Brook-Stony Brook-Jordan Brook 

watershed area in response to (or preceding) ice or snow 

events (table 5).

Streamflow varied among sites from a mean of 4.8 ft3

/s at 

Stony Brook to a mean of 14 ft3

/s at Four Mile River (fig. 6). 

Streamflow data were compared to precipitation events and 

stream chemistry to help determine sources and timing of Cl 

concentrations and loads.

Water Quality

Estimated Cl concentrations at the four stream sites 

were well below the chronic aquatic-habitat criteria for 

Cl of 230 mg/L over a 4-day average. Generally, the 

specific conductance and Cl concentrations in grab samples 

and continuous specific conductance and estimated Cl 

concentrations at downstream monitoring sites were higher 

during winter months than at other times of the year; increases 

corresponded to precipitation or melting events and increased 

streamflow, as discussed in “Stormflow Chemistry” below. 

During the spring and summer months, specific conductance 

and Cl concentration generally decreased in response to 

precipitation events and peaks in streamflow that cause 

dilution. Median continuous specific conductance and 

estimated Cl concentrations were lowest at the Four Mile 

River upstream site (82 μS/cm and 11 mg/L, respectively) 

and highest at the Jordan Brook upstream site (200 μS/cm 

and 45 mg/L, respectively) from November 1, 2008, through 

September 30, 2009 (table 8A).

Base-Flow Chemistry

Stream sites were sampled on August 19, 2009, during 

base-flow conditions to determine the background major-ion 

chemistry of groundwater. Concentrations of major ions in 

samples collected at all eight sites during base flow, and in 

other samples collected at the Oil Mill Brook and Stony Brook 

upstream sites during higher flows in February and March 

2009, are depicted on Stiff diagrams in figure 7. Cl and Na 

were the dominant ions in samples collected during base flow 

at most sites and during higher flows at the Oil Mill Brook 

upstream site and the Stony Brook downstream site (fig. 7).

Concentrations of Cl and Na in samples collected at Four 

Mile River and Stony Brook during base flow were higher at 

the downstream sites than at the upstream sites and probably 

reflect the greater contributions of shallow groundwater that 

was affected by deicing chemicals downstream from I-95. The 

concentrations of bicarbonate (HCO3

-

), Ca, and magnesium 

(Mg) at Four Mile River were comparable to concentrations of 

Cl and Na and may indicate a leachate source from a landfill 

that is upstream from I-95 (fig. 1). The concentrations of 

major ions at Oil Mill Brook and Jordan Brook during base 

flow were very similar for the upstream and downstream 

sites. At the Oil Mill Brook upstream site, concentrations 

of HCO3

-

, Mg, and Ca increased, and concentrations of Na, 

Cl, and sulfate (SO4

2-) decreased, from February to August 

2009, apparently as contributions from road-deicing sources 
18 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09 P RECIPITATION, IN INCHES

T EMPERATURE, IN DEGREES CELSIUS

ESTIMATED HOURLY SNOW 

THICKNESS, IN INCHES

ESTIMATED HOURLY SNOW 

 MELT, IN INCHES

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 3 4 5 6 7 8

0

5

10

15

20

0.06

0.08

0.04

0.02

0

Estimated snow thickness

Estimated snow melt

1

1 Storm (number dened in table 5)

PERIODS OF DEICER APPLICATION

EXPLANATION

Activity (number dened in table 5)

A

B

0

0.2

0.4

0.6

0.8

1.0

-10

0

10

20

30

-20

P re cipitation

EXPLANATION

Maximum daily air temperature

Minimum daily air temperature

Nov D ec Jan F eb M ar A pr M ay Jun Jul A ug S ep

2008

DATE

2009

Figure 5. A, Maximum and minimum daily air temperature and continuous precipitation at the Groton-New London airport weather 

station, and B, estimated hourly snow thickness and snow melt at a snow observation station in southeastern Connecticut, November 

2008–September 2009. (Details on application of deicers are shown in tables 4 and 5.)

decreased and contributions from base flow increased 

throughout the spring and summer. Major ion concentrations 

in base flow at the Four Mile River sites are comparable to 

concentrations in shallow groundwater from undeveloped 

areas. Concentrations of major ions in groundwater samples 

from three shallow wells in forested areas in Connecticut 

(Grady and Mullaney, 1998) indicate patterns of ions that are 

less dominated by Na and Cl than in stream-water samples 

that have relatively high concentrations of Ca, Mg, and HCO3 

(fig. 7).

Stormflow Chemistry

During winter months, specific conductance and 

Cl concentrations in streams generally increased with 

precipitation or melting events and subsequent increases 

in streamflow as a result of road deicers washed from road 

surfaces by stormwater. Periods of increased continuous 

specific conductance and estimated Cl concentrations were 

observed at downstream monitoring sites (1) in direct response 

to a storm or deicing activity (figs. 8–11; table 5) or (2) during 

a period of rain or melting that occurred after a storm or 

activity. Most of the increase in Cl concentrations between 

upstream and downstream sites probably resulted from deicing 

salts carried in stormwater washed from I-95 highway lanes, 

ramps, access roads (table 4), other state or town roads, 

parking lots, sidewalks, and driveways. Specific conductance 

and Cl concentrations at upstream monitoring sites generally 

decreased during precipitation and melting events as a result of 

dilution. Some upstream monitoring sites, however, including 

the Stony Brook upstream site (011277916), showed increased 

specific conductance and Cl concentrations during these 

events because some runoff from the highway is discharged 

to the upstream watershed. During the spring and summer 

months, specific conductance in continuous measurements and 

Cl concentrations in samples generally decreased in response 
Preliminary Assessment of the Effects of Road Deicers on Water Quality 19

1.0

0.8

0.6

0.4

0.2

0

PRECIPITATION, IN INCHES

Nov D ec Jan F eb

DATE

M ar A pr M ay Jun Jul A ug S ep

 2008 2009

0

40

80

120

150

F our Mile River streamow

EXPLANATION

O il Mill Brook streamow

S tony Brook streamow

Jordan Brook streamow

P recipitation

STREAMFLOW, IN CUBIC FEET PER SECOND

Figure 6. Continuous streamflow at the downstream monitoring sites at Four Mile River, Oil Mill Brook, Stony Brook, and 

Jordan Brook, and precipitation at Groton-New London airport weather station, southeastern Connecticut, November 

2008–September 2009.

to precipitation events and subsequent increases in streamflow. 

According to ConnDOT records, no road deicers were applied 

to state roads after March 2, 2009, during the 2008–09 winter 

season (table 5 and fig. 5). The continued increase in specific 

conductance and estimated Cl concentrations with increased 

stormflow at some sites after about April 21, 2009, when daily 

mean temperatures exceeded 0°C and all snow had melted 

indicates that high concentrations of Cl and other deicing 

constituents were retained in soils and or shallow groundwater 

and continued to affect stream chemistry through the early part 

of the spring.

Four Mile River

Water-quality data at the Four Mile River upstream and 

downstream sites were recorded continuously from January 

12, 2009, and December 19, 2008, respectively, through 

the interim study period. Median specific conductance and 

estimated Cl concentrations were slightly higher at the 

downstream site than at the upstream site through the study 

period (table 8A and fig. 8). During winter months, specific 

conductance and Cl concentrations at the downstream site 

increased in response to several deicing events—winter 

storms 4, 5, 7, 10, and 12 and activity 6, and rain or snow 

melting events on February 12 and February 27, 2009 (fig. 8 

and table 5). The estimated amount of salt applied to I-95 and 

associated roads in the Four Mile River area indicate that, 

although the date and amount of deicers applied to state roads 

correspond to increases in specific conductance in some cases 

(table 5 and fig. 8A), the response in stream chemistry better 

relates to both the cumulative amount and period of deicer 

application in addition to the occurrence of rain and (or) warm 

temperatures and subsequent melting that washes deicers 

into the stream. For example, storms 4 and 5 (fig. 5B), which 

represent the first winter storms during the recording of data 

at the Four Mile River downstream site, resulted in increased 

levels of specific conductance and estimated Cl concentrations 

in the stream (fig. 8). However, deicers applied during storm 
20 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09 Table 8. Summary statistics for specific conductance and estimated chloride concentrations for A, continuous data and B, grab samples at the eight monitoring sites, southeastern Connecticut, November 2008–September 2009. [Specific conductance is in microsiemens per centimeter at 25 degrees Celsius; concentration is in milligrams per liter] Stream Water-quality parameter Upstream site Downstream site Number of samples Minimum Mean Median Maximum Number of samples Minimum Mean Median Maximum A. Continuous data Four Mile River Specific conductance 37,652 51 82.7 82 126 41,258 55.0 89.6 89 527 Chloride concentration 37,652 6.5 11 11 21 51,258 7.7 12 12 100 Oil Mill Brook Specific conductance 30,713 34 89.3 91.0 231 30,720 34.0 90.2 92 703 Chloride concentration 30,713 6.7 16 16 54 30,720 8.8 17 17 160 Stony Brook Specific conductance 31,197 39 138 135 235 38,517 45.0 144 144 431 Chloride concentration 31,197 1 28 26 57 38,517 9.3 28 28 100 Jordan Brook Specific conductance 10,865 116 198 200 352 34,195 54 186 188 341 Estimated chloride concentration 10,865 26 45 45 95 34,195 8.9 40 40 87 B. Grab samples Four Mile River Specific conductance 12 64.0 80.5 83.5 98.0 12 66 84.7 89 100 Chloride concentration 14 7 10 11 14 14 8.6 12 12 14 Oil Mill Brook Specific conductance 13 77 88.9 89 98 13 71 88.9 89.0 100.0 Chloride concentration 17 14 16 15 19 16 14 16 17 19 Stony Brook Specific conductance 12 110 148 144 214 16 91.0 144 144 181 Chloride concentration 12 21 30 27 47 16 15 28 28 36 Jordan Brook Specific conductance 12 169 194 197 213 12 169 196 197 219 Chloride concentration 13 35 42 42 51 12 52 41 41 42
Preliminary Assessment of the Effects of Road Deicers on Water Quality 21

 1.5 1 0.5 0 0.5 1 1.5 Milliequivalents per liter

Na Cl

Ca SO4

2-

Mg

Na, sodium

Ca, calcium

Mg, magnesium

HCO3

-

Cl, chloride

SO4

2-, sulfate

HCO3

-

, bicarbonate

Site Identier

Date of sample

BASE FLOW

BASE FLOW

BASE FLOW

BASE FLOW

BASE FLOW

BASE FLOW

BASE FLOW

BASE FLOW

Jordan Brook

Four Mile River

Oil Mill Brook

Stony Brook

EXPLANATION

08/19/2009

08/05/1993

07/29/1994

09/03/1992

08/19/2009

08/19/2009

02/24/2009

03/12/2009

08/19/2009

08/19/2009

02/24/2009

03/12/2009

08/19/2009

08/19/2009

08/19/2008

08/19/2008

Shallow groundwater samples from wells in forested 

land-use settings in Connecticut

Upstream

Upstream

Upstream

Upstream

Downstream

Upstream

Upstream

Downstream

Downstream

Downstream

Downstream

Downstream

01127819

01127821

0112779135

011277914

0112779155

01127821

011277916

011277695

011277696

413427072355501

(CT- P 117)

415856072263101

(CT- SO 110)

415545073000601

(CT- BA 104)

Dissolved

anions

Dissolved

cations Dissolved ions

Figure 7. Diagrams depicting the concentrations of major ions in water at upstream 

and downstream monitoring sites at Four Mile River, Oil Mill Brook, Stony Brook, and 

Jordan Brook, southeastern Connecticut, and shallow groundwater samples from wells 

in forested land-use settings in Connecticut.
22 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

-100

0

100

200

300

400

500

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

0

100

200

STREAMFLOW AT THE DOWNSTREAM 

SITE, IN CUBIC FEET PER SECOND

Chloride concentration, downstream (estimated)

Chloride concentration, upstream (estimated)

Chloride concentration, downstream (grab sample)

Chloride concentration, upstream (grab sample)

EXPLANATION

C H LO R ID E CONCENTRATION,

 IN M ILLIG R A M S P E R LIT E R

0

20

40

60

80

100

1.0

0.8

0.6

0.4

0.2

0

NOV D EC JAN F EB M AR A PR M AY JUN JUL A UG S EP

PRECIPITATION, IN INCHES

DATE

 2008 2009

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 3 4 5 6 7 8

2/12/09

A

B

Four Mile River

Specic conductance, downstream (continuous)

Specic conductance, upstream (continuous)

Specic conductance, downstream (grab sample)

Specic conductance, upstream (grab sample)

Streamow

Precipitation

PERIODS OF DEICER APPLICATION

EXPLANATION

1

1 Storm (number dened in table 5)

Activity (number dened in table 5)

Figure 8. A, Specific conductance in grab samples, continuous specific conductance at Four Mile River upstream and downstream 

sites, continuous streamflow at the downstream site, and precipitation at Groton-New London airport weather station, and B, chloride 

concentrations measured in grab samples and estimated continuous chloride concentrations at Four Mile River upstream and 

downstream sites, southeastern Connecticut, November 2008–September 2009.
Preliminary Assessment of the Effects of Road Deicers on Water Quality 23

6, which consisted of several inches of snow with cold 

temperatures and no rain, and activities 2 and 3 (fig. 5B) did 

not lead to any observed response in specific conductance 

at the Four Mile River downstream site (fig. 8), most likely 

because of the subfreezing temperatures and absence of 

rain or melting and subsequent runoff. Storm 7 consisted of 

snow followed by rain and resulted in the highest specific 

conductance (527 μS/cm) and estimated Cl concentration 

(100 mg/L) during winter for this site (fig. 8 and table 8). An 

estimated 28.6 tons of NaCl and 307 gal of CaCl2 were applied 

to I-95 and associated state roadways (table 5) in the “frozen” 

period between the end of storm 5 on December 24 and the 

beginning of the increased levels of specific conductance on 

January 7 at 6 a.m., 14 hours into the deicer application. A 

similar cold period between storm 7 and storm 10 (during 

January 27–29) showed no increases in specific conductance 

or estimated Cl concentrations in response to applications 

for storms 8 and 9. Finally, the period between storm 10 and 

storm 12, and the deicer applications in between, had no major 

increases in specific conductance, except during a rain event 

on February 12, 2009, when specific conductance reached 

289 μS/cm.

Oil Mill Brook

Water-quality data at the Oil Mill Brook upstream and 

downstream sites were recorded continuously beginning 

January 7, 2009, through the interim study period; however, 

data are missing for the period from February 4 to March 13, 

2009, because of equipment failure. Specific conductance 

and estimated Cl concentrations were slightly higher at the 

downstream site than at the upstream site until the middle 

of August 2009 when values at the downstream site became 

slightly higher (fig. 9). 

Specific conductance and estimated Cl concentrations 

increased at Oil Mill Brook upstream and downstream sites 

in response to winter storms 7, 8, and 10 and increased 

streamflow (fig. 9). Larger increases in specific conductance 

and estimated Cl concentrations at the downstream site than at 

the upstream site in response to storms 7, 8, and 10 likely were 

caused by deicers washed from I-95. At the downstream site, 

stormwater runoff from a local road and bridge was observed 

to flow into the stream near the monitor and may have affected 

specific conductance and estimated Cl concentrations during 

snow melt. In March 2010 (after the interim period of study), 

an additional monitor was added upstream from the existing 

monitor to measure conditions that are not affected by runoff 

from the town road.

Stony Brook

 Water-quality data for Stony Brook were recorded 

continuously from January 6, 2009, at the downstream site 

and from February 2, 2009, at the upstream site through the 

interim study period (fig. 10); however, specific conductance 

and estimated Cl concentration data for the upstream site 

are missing for the period from May 20–29, 2009, because 

of equipment failure. Median specific conductance and 

estimated Cl concentrations were slightly higher at the 

downstream site than at the upstream site through the study 

period (table 8A). Specific conductance was elevated at the 

Stony Brook downstream site during discharge events on 

January 7 (storm 7), January 28 (storm 10), and February 

2–4, 2009 (storm 11), and during other deicing activities on 

February 18–19 and 19–20 (activities 6 and 7), presumably 

by increased concentrations of Cl, Na, and other ions in 

deicing chemicals washed off roads. Specific conductance 

and estimated Cl concentrations in February and early March, 

however, generally decreased during discharge events because 

of dilution (fig. 10). Specific conductance and estimated Cl 

concentrations were slightly higher at the downstream site 

than at the upstream site throughout the period of record 

with two exceptions. During February 15–18, 2009, elevated 

levels of specific conductance might have resulted from some 

melting of remaining snow near I-95 or other upstream roads; 

as discussed previously, some drainage from I-95 flows to 

the north and likely affects the upstream site water-quality 

monitor. Upstream and downstream sites are 0.82 mi apart; 

therefore, another possible cause for this discrepancy could be 

dilution from groundwater and (or) stormwater runoff between 

the upstream and downstream sites that acts to dampen the 

increase at the downstream site. Specific conductance also was 

higher at the upstream site than at the downstream site during 

August and September 2009. The reason for the increase at 

the upstream site is not known, but the absence of an increase 

in specific conductance at the downstream site could result 

from dilution. Elevated levels of specific conductance at the 

downstream site on March 9 and 12–13 were associated with 

rain events or warm air temperatures and likely resulted from 

salts in melting snow piles and (or) deicing salts that were 

flushed from soils and shallow groundwater, then discharged 

downstream. Studies have reported a substantial portion (45 

to 85 percent) of Cl in deicers is not removed by overland 

flow but infiltrates into soils and (or) groundwater (Howard 

and Haynes, 1993; Church and Friez, 1993; Toler and 

Pollock, 1974).

Jordan Brook

Water-quality data for the Jordan Brook upstream and 

downstream sites were recorded continuously beginning 

February 5, 2009 (fig. 11). Median specific conductance 

and estimated Cl concentrations were slightly lower at 

the downstream site than at the upstream site throughout 

the study period (table 8A). Runoff from a parking lot 

adjacent to the upstream site likely contributed deicing salts 

in winter and early spring; base flow, which can include 

anthropogenic sources such as septic-tank drainfields, is also 

a possible contributor of salts throughout the year. Specific 

conductance and estimated Cl concentrations generally 

increased concurrently at the Jordan Brook upstream and 

downstream sites during winter and early spring discharge 

events. Increased levels of specific conductance and estimated 
24 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

0

50

100

150

200

CHLORIDE CONCENTRATION,

 IN MILLIGRAMS PER LITER

1.0

0.8

0.6

0.4

0.2

0

-100

0

100

200

300

400

Oil M ill Brook

0

500

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

Missing record

Missing record

Missing record

STREAMFLOW, IN CUBIC

 FEET PER SECOND

PRECIPITATION, IN INCHES

Peak is o scale

(703 microsiemens per centimeter)

A

B

Nov Dec Jan Feb M ar Apr M ay Jun Jul Aug Sep

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 3 4 5 6 7 8

100

200

DATE

Chloride concentration, downstream (estimated)

Chloride concentration, upstream (estimated)

Chloride concentration, downstream (grab sample)

Chloride concentration, upstream (grab sample)

EXPLANATION

2008 2009

Specic conductance, downstream (continuous)

Specic conductance, upstream (continuous)

Specic conductance, downstream (grab sample)

Specic conductance, upstream (grab sample)

Streamow

Precipitation

PERIODS OF DEICER APPLICATION

EXPLANATION

1

1 Storm (number dened in table 5)

Activity (number dened in table 5)

Figure 9. A, Specific conductance in grab samples and continuous specific conductance at Oil Mill Brook upstream and 

downstream sites, continuous streamflow at the downstream site, and precipitation at Groton-New London airport weather 

station, and B, chloride concentrations measured in grab samples and estimated continuous chloride concentrations at Oil Mill 

Brook upstream and downstream sites, southeastern Connecticut, November 2008–September 2009.
Preliminary Assessment of the Effects of Road Deicers on Water Quality 25

0

50

100

150

200

C H LO R ID E CONCENTRATION,

 IN M ILLIG R A M S P E R LIT E R

Chloride concentration, downstream (estimated)

Chloride concentration, upstream (estimated)

Chloride concentration, downstream (grab sample)

Chloride concentration, upstream (grab sample)

EXPLANATION

Missing record

-100

0

100

200

300

400

500

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

S tony B rook

0

100

200

STRAMFLOW, IN CUBIC

 FEET PER SECOND

PRECIPITATION,

Melting

IN INCHES

events

Deicing salts from snow piles

or shallow groundwater

Missing record

2/15- 2/17

3/12- 3/13

3/9

A

B

NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 3 4 5 6 7 8

1.0

0.8

0.6

0.4

0.2

0

DATE

 2008 2009

Specic conductance, downstream (continuous)

Specic conductance, upstream (continuous)

Specic conductance, downstream (grab sample)

Specic conductance, upstream (grab sample)

Streamow

Precipitation

PERIODS OF DEICER APPLICATION

1

1 Storm (number dened in table 5)

Activity (number dened in table 5)

EXPLANATION

Figure 10. A, Specific conductance in grab samples and continuous specific conductance at Stony Brook upstream and downstream 

sites, continuous streamflow at the downstream site, and precipitation at Groton-New London airport weather station, and B, chloride 

concentrations measured in grab samples and estimated continuous chloride concentrations at Stony Brook upstream and downstream

sites, southeastern Connecticut, November 2008–September 2009.
26 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

Chloride concentration, downstream (estimated)

Chloride concentration, upstream (estimated)

Chloride concentration, downstream (grab sample)

Chloride concentration, upstream (grab sample)

EXPLANATION

STREAMFLOW, IN CUBIC

 FEET PER SECOND

-100

0

100

200

300

400

500

Jordan B rook

0

100

200

0

50

100

150

200

CHLORIDE CONCENTRATION,

 IN MILLIGRAMS PER LITER

2/8

3/9

3/19 3/6 2/28

2/12

PRECIPITATION, IN INCHES

}

A

B

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

Melting

events

Deicing salts from snow piles

or shallow groundwater

Specic conductance, downstream (continuous)

Specic conductance, upstream (continuous)

Specic conductance, downstream (grab sample)

Specic conductance, upstream (grab sample)

Streamow

Precipitation

PERIODS OF DEICER APPLICATION

EXPLANATION

1

1 Storm (number dened in table 5)

Activity (number dened in table 5)

Nov D ec Jan F eb M ar A pr M ay Jun Jul A ug S ep

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 3 4 5 6 7 8

1.0

0.8

0.6

0.4

0.2

0

DATE

 2008 2009

Figure 11. A, Specific conductance in grab samples and continuous specific conductance at Jordan Brook upstream and 

downstream sites, continuous streamflow at the downstream site, and precipitation at Groton-New London airport weather station, 

and B, chloride concentrations measured in grab samples and estimated continuous chloride concentrations at Jordan Brook 

upstream and downstream sites, southeastern Connecticut, November 2008–September 2009.
Preliminary Assessment of the Effects of Road Deicers on Water Quality 27

Cl concentrations coincided with several winter storms or 

deicing activities, presumably as a result of Cl and other ions 

washed from road surfaces. Increases in specific conductance 

and Cl concentration on January 28 coincided with storm 10, 

and the multiple peaks during February 19 and March 2 

coincided with deicing activities 6, 7, and 8 and storms 12 

and 13 (table 5 and fig. 11). The highest specific conductance 

measured and Cl concentration estimated were 352 μS/cm 

and 95 mg/L, respectively, on February 8; these values are 

associated with warm temperatures and melting of snow 

(figs. 5 and 11). 

Specific conductance and estimated Cl concentrations 

commonly were highest at the upstream site and probably 

relate to the large percentage of adjacent impervious surfaces, 

relative to the downstream site, that were subjected to deicing 

chemicals. The application of deicing chemicals to several 

large parking lots to the west of the upstream site during 

snow or ice events resulted in high concentrations of Cl, Na, 

and other ions that were washed into Jordan Brook. Large 

mounds of snow that are plowed from impervious surfaces 

contain deicers that are released through melting, which 

occurs well after winter storm events. Increases in specific 

conductance and estimated Cl concentrations at upstream and 

downstream sites on February 28 and March 3, 6, 9, and 19, 

2009, probably resulted from delayed snow melt. Increases 

in specific conductance at the downstream site on March 26, 

28, 29, and April 3, 2009, were associated with rain events 

and likely resulted from salts in melting snow piles and (or) 

Cl and other ions in deicers that were flushed from soils and 

shallow groundwater, then discharged downstream. A similar 

effect was observed at the Stony Brook downstream site 

(fig. 10). After April 3, specific conductance and estimated Cl 

concentrations in Jordan Brook decreased during precipitation 

and discharge events as a result of dilution (fig. 11).

Chloride Loads

Daily mean Cl concentrations were estimated for the 

periods of the study at each of the upstream and downstream 

sites, and daily loads were estimated for each of the 

downstream sites (figs. 12, 13, 14, and 15). The estimated 

daily mean Cl concentration at downstream sites, like 

instantaneous Cl concentrations, increased with streamflow 

(and stormwater runoff of road deicers) during most winter 

storms but decreased through dilution during the warmer 

months (figs. 12A, 13A, 14A, and 15A). Estimated daily loads, 

however, generally increased with streamflow and reflect 

the greater overall Cl amounts that were transported despite 

the dilution that occurred (figs. 12B, 13B, 14B, and 15B). 

Cl loads in streams generally were highest in the winter and 

early spring. Estimated Cl yields for the four monitoring sites 

downstream from Interstate 95 during the interim study period 

ranged from 17.3 tons per square mile (ton/mi2

 ) (98 tons total) 

at the Oil Mill Brook downstream site to 50 tons/mi2

 (140 

tons total) at the Jordan Brook downstream site (table 9A). 

The estimated daily yield in the downstream sites ranged from 

0.07 (ton/d)/mi2

 for Oil Mill Brook, which had the highest 

percentage of forest and wetland area, to 0.21 (ton/d)/mi2

 for 

Jordan Brook, which had the lowest percentage of forest and 

wetland area and the highest percentage of urban development. 

The lower and upper bounds of a 95-percent confidence 

interval for estimated Cl loads and yields show a narrow 

range of values and indicate reasonably low uncertainty in the 

predicted values (table 9A).

Based on data from the three NADP stations, the 

estimated percent contribution of Cl load from atmospheric 

deposition ranged from 9.5 to 94 tons for the Four Mile 

River watershed area and from 16 to 160 tons for the Oil Mill 

Brook-Stony Brook-Jordan Brook watershed area (table 9B). 

The contribution of Cl from atmospheric deposition to the 

watershed areas during the study period was 6.1, 7.1, and 

60 percent for the Four Mile River watershed and 3.9, 4.3, 

and 36 percent at the Oil Mill Brook-Stony Brook-Jordan 

Brook watersheds area, based on the concentrations at the 

Abington, Conn., Lexington, Mass., and Cedar Beach, N.Y., 

NADP stations, respectively. The highest value is based on the 

concentration at the Cedar Beach, N.Y., NADP station, which 

is strongly affected by sea spray. Atmospheric deposition 

in the watersheds in this study, in general, should not be as 

affected by seawater as is the Cedar Beach station, so the 

values based on the NADP station in Lexington, Mass., are 

considered to be most representative of the contribution from 

atmospheric deposition. 

The Cl loads in streams (outputs) were compared with 

Cl load inputs, including atmospheric deposition and deicer 

applications by ConnDOT and by towns (table 9B). Using 

data from the Lexington, Mass., NADP station, the Cl 

load inputs for the Four Mile River watershed represented 

about 32 percent of the Cl load leaving the watershed by 

the stream, and the Cl load inputs for the Oil Mill BrookStony Brook-Jordan Brook watersheds area represented 

about 69 percent of the Cl load leaving by the streams 

(table 9B). The percent contribution of chloride input that is 

unaccounted for in the mass balance for the watershed areas 

could be related to the lag period between the application 

of deicers and concentrations observed in streams, which is 

difficult to account for. Furthermore, this assessment of load 

balance is only qualitative and does not include the Cl load 

in groundwater leaving the study areas. Estimates of direct 

infiltration of Cl that originates from atmospheric deposition, 

deicer applications, septic-tank drainfields, and others sources 

of groundwater were not within the scope of this project. 

Cl yields at the downstream monitoring stations at Four 

Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook 

(table 9A) were compared with annual Cl yield estimates for 

10 selected rivers in Connecticut during 1998–2007 that were 

estimated using LOADEST (fig. 16). Four Mile River and Oil 

Mill Brook had low estimated Cl yields, similar to yields at 

Bunnell (Burlington) Brook and Shetucket River, and reflect 

the low percentages of developed land and impervious area 

(table 1). Estimated Cl yields at Jordan Brook and Stony 

Brook were relatively high but were not as high as those for 
28 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09 E S T IM A T E D MEAN C H LO R ID E CONCENTRATION, IN M ILLIG R A M S P E R LIT E R

STREAMFLOW, IN 

CUBIC FEET PER SECOND

Load

Streamow

EXPLANATION

Estimated load =133 tons 

Estimated daily mean load = 0.46 tons

0

1

2

3

4

5

ESTIMATED MEAN CHLORIDE LOAD,

 IN TONS PER DAY

11/1/2008 1/23/2009 4/16/2009

DATE

7/8/2009 9/30/2009

0

20

40

60

Downstream

Upstream

0

50

100

150

EXPLANATION

B

A

Figure 12. A, Estimated daily mean chloride concentrations at Four Mile River upstream and downstream sites, and 

B, estimated daily mean chloride load and streamflow for the Four Mile River downstream site, southeastern Connecticut, 

November 2008–September 2009.
Preliminary Assessment of the Effects of Road Deicers on Water Quality 29

11/1/2008 1/23/2009 4/16/2009 7/8/2009 9/30/2009

0

1

2

3

4

5

Estimated load = 98 tons (note missing record)

Estimated daily mean load = 0.40 tons

0

50

100

150

E S T IM A T E D MEAN C H LO R ID E LO A D ,

 IN T O N S P E R D A Y

Load

Streamf low

EXPLANATION

DATE

STREAMFLOW, IN 

CUBIC FEET PER SECOND

B

A

0

20

40

60

E S T IM A T E D MEAN C H LO R ID E 

CONCENTRATION, IN M ILLIG R A M S P E R LIT E R

Downstream

Upstream

EXPLANATION

Missing record

Missing record

Missing record

Figure 13. A, Estimated daily mean chloride concentrations at Oil Mill Brook upstream and downstream sites, and 

B, estimated daily mean chloride load and streamflow for the Oil Mill Brook downstream site, southeastern Connecticut, 

November 2008–September 2009.
30 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

11/1/2008 1/23/2009 4/16/2009 7/8/2009 9/30/2009

0

1

2

3

4

5 Estimated load = 88 tons

Estimated daily mean load = 0.32 tons

0

50

100

150

E S T IM A T E D MEAN C H LO R ID E LO A D ,

 IN T O N S P E R D A Y

Load

Streamow

EXPLANATION

DATE

fit

fit

0

STREAMFLOW, IN 

CUBIC FEET PER SECOND

Missing record

20

40

60

E S T IM A T E D MEAN C H LO R ID E 

CONCENTRATION, IN M ILLIG R A M S P E R LIT E R

Downstream

Upstream

EXPLANATION

Missing record

B

A

Figure 14. A, Estimated daily mean chloride concentrations at Stony Brook upstream and downstream sites, and B, estimated 

daily mean chloride load and streamflow for the Stony Brook downstream site, southeastern Connecticut, November 2008–

September 2009.
Preliminary Assessment of the Effects of Road Deicers on Water Quality 31

11/1/2008 1/23/2009 4/16/2009 7/8/2009 9/30/2009

0

1

2

3

4

5 Estimated load = 140 tons

Estimated daily mean load = 0.59 tons

0

50

100

150

E S T IM A T E D MEAN C H LO R ID E LO A D ,

 IN T O N S P E R D A Y

Load

Streamow

EXPLANATION

DATE

fit

fit

0

20

40

60

ESTIMATED MEAN CHLORIDE 

CONCENTRATION, IN MILLIGRAMS PER LITER

Downstream

Upstream

EXPLANATION

Missing record

STREAMFLOW, IN 

CUBIC FEET PER SECOND

B

A

Figure 15. A, Estimated daily mean chloride concentrations at Jordan Brook upstream and downstream sites, and B, estimated 

daily mean chloride load and streamflow for the Jordan Brook downstream site, southeastern Connecticut, November 2008–

September 2009.
32 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09 Table 9A. Estimated mean chloride loads for streams at the four monitoring sites downstream from Interstate 95, southeastern Connecticut, November 2008 to January 2010. [Cl, chloride; ds, downstream site; ton/d, tons per day; ton/mi2, tons per square mile; (ton/d)/mi2, tons per day per square mile; %, percent] Stream Period Total Cl load for period, in tons Number of days of record Cl yield, in ton/mi2 Mean Cl load, in ton/d Mean Cl load, in ton/d Mean Cl yield, in ton/mi2 Mean Cl yield, in (ton/d)/mi2 Cl load extrapolated for period November 1, 2008– September 30, 2009, in tons Equivalent annual Cl yield, in ton/mi2 Bounds of 95-percent confidence interval Bounds of 95-percent confidence interval Value Lower Upper Value Lower Upper Four Mile River ds 12/19/09– 9/30/09 133 287 22.2 0.46 0.45 0.48 0.077 0.075 0.080 155 28.3 Oil Mill Brook ds a12/18/08– 9/30/09 98 248 17.3 0.39 0.35 0.44 0.070 0.066 0.077 132 25.4 Stony Brook ds 1/7/09– 9/16/09 88 267 47.3 0.33 0.31 0.35 0.18 0.17 0.19 110 64.7 Jordan Brook ds 2/6/09– 9/30/09 140 237 50 0.59 0.56 0.62 0.21 0.20 0.22 198 77.0

aMissing record for this site.

Table 9B. Estimated mean chloride loads for streams, atmospheric deposition, and deicers applied to town and state roads in the study areas of the Four Mile River watershed and the Oil Mill Brook-Stony Brook-Jordan Brook watersheds, November 2008 to January 2010.[Cl, chloride; ton/d, tons per day; ton/mi2, tons per square mile; (ton/d)/mi2, tons per day per square mile; %, percent]

Study 

areas

Cl load for November 1, 2008–

September 30, 2009, 

in tons

Contribution of chloride 

in atmospheric deposition, 

in percent

Contribution of chloride in 

atmospheric deposition and deicers, 

in tons

Contribution of chloride inputs 

(atmospheric deposition and deicers) 

Streams Atmospheric deposition State roads Town roads Abington, Connecticut Cedar Beach, New York Lexington, Massachusetts Abington, Connecticut Cedar Beach, New York Lexington, Massachusetts Abington, Connecticut Cedar Beach, New York Lexington, Massachusetts

Four Mile River 155 a9.5, b11, c94 121 72.8 6.1 60 7.1 203 288 205 48 tons

(31%)

132 tons(85%)

49 tons(32%)

Oil Mill Brook-Stony 

Brook-Jordan Brook

441 a16, b19, c160 442 283 3.9 36 4.3 741 885 744 278 tons

(68%)

444 tons(101%)

281 tons(69%)

aEstimate determined from monthly chloride concentrations at National Atmospheric Deposition Program stations in Abington, Connecticut.bEstimate determined from monthly chloride concentrations at National Atmospheric Deposition Program stations in Lexington, Massachusetts.cEstimate determined from monthly chloride concentrations at National Atmospheric Deposition Program stations in Cedar Beach, New York.
Preliminary Assessment of the Effects of Road Deicers on Water Quality 33

x

Shetucket R.

(01122610)

Broad Br.

(01184490)

Bunnell (Burlington) Br.

(01188000)

Hockanum R.

(01192500)

Salmon R.

(01193500)

Quinnipiac R.

(01196500)

Still R.

(01201487)

Naugatuck R.

(01208500)

Saugatuck R.

(01208990)

Norwalk R.

(01209710)

Number of 

 values

EXPLANATION 

x

x

o

o

Upper adjacent

75th percentile

Median

Oil Mill Brook mean

Stony Brook mean

Jordan Brook mean

Four Mile River mean

25th percentile

Lower adjacent

Lower outside

Lower detached

Upper detached

Upper outside

U.S. GEOLOGICAL SURVEY MONITORING STATIONS

0

20

40

60

80

100

120

140

160

8 10 10 10 10 10 105 10 10

10

ESTIMATED CHLORIDE YIELD, IN TONS PER SQUARE MILE

Figure 16. Distribution of annual chloride yields estimated using LOADEST for selected rivers in Connecticut for water years 

1998–2007, and estimated annual chloride yields for the downstream sites at Four Mile River, Oil Mill Brook, Stony Brook, and 

Jordan Brook for their periods of record. Estimated annual chloride yields are based on daily loads. (See table 9 for periods of 

record. R, River; Br, Brook)
34 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

the more urbanized watersheds, such as those that drain the 

Still River at Brookfield Center and the Hockanum River 

(fig. 16). Cl yields for these sites were positively correlated 

with the percentage of impervious cover (U.S. Environmental 

Protection Agency, 2001; fig. 17) and probably reflect the 

application of deicers to roadways, as well as sources and 

practices associated with greater impervious cover such as 

wastewater and septic-system discharges, recycling of Cl 

from drinking water, and leachate from landfills and saltstorage areas.

0 5 10 15 20

IMPERVIOUS COVER, IN PERCENT OF WATERSHED AREA

0

0.1

0.2

0.3

0.4

MEDIAN OF MEAN CHLORIDE YIELD,

IN TONS PER DAY PER SQUARE MILE

Downstream sites for this study

Sites at other rivers in Connecticut

EXPLANATION

0.0713 + 0.0122*x

Adjusted R-squared: 0.7889

Shetucuck R. nr

South Windham

(01122610)

Broad Br. at Broad Brook

(01184490)

Bunnell Br. near Burlington (01188000)

Hockanum R. near East Hartford

(01192500)

Salmon R. at East Hampton (01193500)

Quinnipiac R. at Wallingford

(01196500)

Still R. at Brookeld Center (01201487)

Saugatuck R.

near Redding

(01208990)

Norwalk R. at Winnipauk

(01209710)

Norwalk R. at Beacon Falls

(01208500)

Jordan Br. ds

(011277696)

Oil Mill Br. ds (011277914)

Stony Br. ds

(011277916)

Four Mile R. ds

(01127821)

Figure 17. Percentage of impervious cover as a function of (1) the chloride yields for the downstream monitoring stations at 

Four Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook during the periods of record for this study, and (2) the median 

of the mean chloride yields at other selected rivers in Connecticut during water years 1998–2007. (Impervious cover data from 

National Land Cover Database, (U.S. Environmental Protection Agency, 2001; R., River; Br., Brook; ds, downstream)
References Cited 35

Summary and Conclusions

The U.S. Geological Survey, the Connecticut Department 

of Transportation, and the Federal Highway Administration 

conducted a cooperative study to evaluate potential effects 

of road-salt application on the quality of stream water in four 

watersheds crossed by Interstate 95 (I-95) in southeastern 

Connecticut. The results of the study will be considered in an 

Environmental Impact Statement (EIS) for the expansion of 

I-95 between Old Lyme and New London, Conn.

Streamflow and water quality were studied at four 

selected watersheds—Four Mile River, Oil Mill Brook, Stony 

Brook, and Jordan Brook. Streamgages were instrumented and 

maintained at downstream sites, and continuous water-quality 

monitors were installed and maintained at upstream and 

downstream sites. Water quality was assessed by analyzing the 

dissolved ions in grab samples and by continuous recording 

of data from water temperature, specific conductance, and 

pH sensors. Grab samples were collected (1) during winter 

stormwater-runoff events, such as winter storms or subsequent 

periods of rain or warm temperatures in which melting 

takes place, (2) approximately monthly during routine 

conditions and analyzed for chloride concentrations and 

specific conductance, and (3) during base-flow conditions and 

analyzed for major ions and concentrations of dissolved Fe, 

Mn, and Br.

Chloride (Cl) concentrations at the eight water-quality 

monitoring sites were well below the U.S. Environmental 

Protection Agency (USEPA) recommended chronic and acute 

Cl toxicity criteria for aquatic life. Specific conductance 

and estimated Cl concentrations in streams, particularly 

at sites downstream from I-95, increased during discharge 

events in the winter and early spring as a result of deicers 

applied to roads and washed off by stormwater or meltwater. 

During winter storms, deicing activities, or subsequent 

periods of melting, specific conductance peaked as high 

as 703 microsiemens per centimeter (160 milligrams per 

liter estimated Cl concentration) at the Oil Mill Brook 

downstream site.

Cl loads in streams generally were highest in the winter 

and early spring. The estimated daily yield for the four 

monitoring sites downstream from Interstate 95 ranged from 

0.07 ton per day per square mile ((ton/d)/mi2) for the least 

developed watershed to 0.21 (ton/d)/mi2 for the watershed with 

the highest percentage of urban development and impervious 

surfaces. The Cl load from atmospheric deposition was 

estimated on the basis of ranges of concentrations measured 

at National Atmospheric Deposition Program stations in 

Lexington, Mass.; Abington, Conn.; and Cedar Beach, N.Y. 

The estimated median contribution of Cl from atmospheric 

deposition ranged from 4.3 percent of Cl load at the Oil Mill 

Brook-Stony Brook-Jordan Brook study area to 7.1 percent at 

the Four Mile River watershed. A comparison of the Cl load 

estimated inputs and outputs indicates that more Cl is entering 

the watersheds through atmospheric deposition and application 

of deicers than is leaving in streams. The lag time between 

introduction of Cl to the watershed and transport to the stream, 

and uncertainty in the load estimates may be the cause of this 

discrepancy. In addition, estimates of direct infiltration of Cl 

to groundwater that originates from atmospheric deposition, 

deicer applications, septic-tank drainfields, and other sources 

to groundwater were not within the scope of this project.

Cl yields at the downstream monitoring stations at Four 

Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook 

were compared with annual Cl yield estimates for 10 selected 

rivers in Connecticut, which were generated using LOADEST. 

Four Mile River and Oil Mill Brook had low estimated Cl 

yields similar to yields at Bunnell (Burlington) Brook and 

Shetucket River, reflecting the low percentages of developed 

land and impervious area. Jordan Brook and Stony Brook 

had relatively high estimated Cl yields, but not as high as 

more urbanized watersheds such as those of the Still River 

at Brookfield Center and the Hockanum River. Cl yields for 

these sites were positively correlated with the percentage 

of impervious cover, probably reflecting the application 

of deicers to roadways, as well as sources and practices 

associated with greater impervious cover, such as wastewater 

and septic-system discharges, and leachate from landfills and 

salt-storage areas. 

Acknowledgments

The authors would like to thank Robert Turner, Eloise 

Powell, and Patricia Cazenas of FHWA, Paul Corrente and 

Kevin Carifa of Connecticut Department of Transportation, 

and the Connecticut Academy of Science and Engineering 

team for technical input and guidance and for providing data 

or information. In addition, the authors would like to thank 

U.S. Geological Survey employees Joseph Martin, Dan 

Lolos, Timothy Sargent, and Timothy Frick for maintenance 

of streamgages and water-quality monitors, and collection of 

water-quality samples.

References Cited

Bubeck, R.C., Diment, W.H., Deck, B.L., Baldwin, A.L., 

and Lipton, S.D., 1971, Runoff of deicing salt—Effect on 

Irondequoit Bay, Rochester, New York: Science, v. 172, p. 

1128–1132. 

Chabaeva, A.A., Civco, D.L., and Prisloe, S., 2004, 

Development of a population and land use based regression 

model to calculate the amount of imperviousness, in

Proceedings, 2004 ASPRS conference, Denver, Colorado, 

24–28 May: 9 p., accessed September 10, 2009, at http://

nemo.uconn.edu/tools/impervious_surfaces/pdfs/Chabaeva_

etal_2004.pdf.
36 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

Church, P.E., and Friesz, P.J., 1993, Effectiveness of highwaydrainage systems in preventing road-salt contamination 

of groundwater—Preliminary findings: Transportation 

Research Record, v. 1420, p. 56–64.

Colombo, M.J., and Trench, E.C.T., 2002, Trends in surfacewater quality in Connecticut: U.S. Geological Survey 

Water-Resources Investigations Report 02–4012, 39 p.

Connecticut Department of Transportation, 2009, Interim 

snow & ice guidelines—2008–09: Connecticut Department 

of Transportation, Bureau of Engineering & Highway 

Operations, 53 p.

Connecticut Department of Environmental Protection, 

1995, Leachate and wastewater discharge inventory: 

Hartford, Connecticut, Connecticut Department of 

Environmental Protection, Environmental and Geographic 

Information Center, Digital Shapefile, 1:50,000, accessed 

September 10, 2009, at http://www.ct.gov/dep/cwp/view.

asp?A=2698&Q=322898.

Connecticut Department of Environmental Protection, 

2009, CTDEP Proposed Revisions to Connecticut 

Water Quality Standards, December 22, accessed 

November 1, 2009, at http://www.ct.gov/dep/lib/dep/ 

water/water_quality_standards/water_quality_standards_

proposed_12_22_09.pdf.

Denner, J.C., Clark, S.F., Jr., Smith, T.E., and Medalie, 

Laura, 2010, Effects of highway road salting on the water 

quality of selected streams in Chittenden County, Vermont, 

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38 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

Appendix 1. Specific conductance and chloride concentrations in water samples from upstream and downstream monitoring 

sites at Four Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook, southeastern Connecticut, November 2008 to January 2010.

[ID, identifier; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter]

Site name Station ID Dates* Times

Specific 

conductance, 

in μS/cm

Chloride 

concentration, 

in mg/L

Jordan Brook above Waterford 011277695 11/23/2008 1145 177 35

Jordan Brook above Waterford 011277695 2/2/2009 1345 207 47

Jordan Brook above Waterford 011277695 2/23/2009 1320 209 51

Jordan Brook above Waterford 011277695 3/20/2009 1020 213 50

Jordan Brook above Waterford 011277695 4/9/2009 950 186 41

Jordan Brook above Waterford 011277695 5/5/2009 1120 170 36

Jordan Brook above Waterford 011277695 6/2/2009 1020 199 41

Jordan Brook above Waterford 011277695 6/30/2009 930 198 42

Jordan Brook above Waterford 011277695 7/22/2009 1020 169 37

Jordan Brook above Waterford 011277695 8/19/2009 1115 193 42

Jordan Brook above Waterford 011277695 9/2/2009 930 196 41

Jordan Brook above Waterford 011277695 9/30/2009 1220 211 44

Jordan Brook above Waterford 011277695 10/30/2009 1030 171 35

Jordan Brook above Waterford 011277695 11/30/2009 1050 179 39

Jordan Brook above Waterford 011277695 12/9/2009 801 144 30

Jordan Brook above Waterford 011277696 12/26/2009 1120 182 40

Jordan Brook below Waterford 011277696 11/23/2008 1205 178 35

Jordan Brook below Waterford 011277696 2/2/2009 1445 208 48

Jordan Brook below Waterford 011277696 2/5/2009 1220 219 48

Jordan Brook below Waterford 011277696 2/23/2009 1310 214 52

Jordan Brook below Waterford 011277696 4/9/2009 1250 187 41

Jordan Brook below Waterford 011277696 5/5/2009 1310 169 36

Jordan Brook below Waterford 011277696 6/2/2009 1220 199 41

Jordan Brook below Waterford 011277696 6/30/2009 1140 197 42

Jordan Brook below Waterford 011277696 7/22/2009 1220 171 37

Jordan Brook below Waterford 011277696 8/19/2009 1225 186 41

Jordan Brook below Waterford 011277696 9/2/2009 9300 192 41

Jordan Brook below Waterford 011277696 9/30/2009 1040 208 43

Jordan Brook beloow Waterford 011277696 10/30/2009 1200 173 35

Jordan Brook below Waterford 011277696 11/30/2009 1050 178 39

Jordan Brook below Waterford 011277696 12/9/2009 801 154 33

Jordan Brook below Waterford 011277696 12/26/2009 1135 187 41

Oil Mill Brook near Oil Mill 0112779135 11/23/2008 1110 89 15

Oil Mill Brook near Oil Mill 0112779135 12/17/2008 1130 77 14

Oil Mill Brook near Oil Mill 0112779135 2/2/2009 1515 98 18

Oil Mill Brook near Oil Mill 0112779135 2/4/2009 1250 95 17

Oil Mill Brook near Oil Mill 0112779135 3/13/2009 1110 98 19

Oil Mill Brook near Oil Mill 0112779135 4/8/2009 1120 86 17

Oil Mill Brook near Oil Mill 0112779135 5/6/2009 950 84 15

Oil Mill Brook near Oil Mill 0112779135 5/27/2009 1110 96 16
Appendix 1 39

Appendix 1. Specific conductance and chloride concentrations in water samples from upstream and downstream monitoring 

sites at Four Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook, southeastern Connecticut, November 2008 to January 2010.

[ID, identifier; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter]

Site name Station ID Dates* Times

Specific 

conductance, 

in μS/cm

Chloride 

concentration, 

in mg/L

Oil Mill Brook near Oil Mill 0112779135 6/22/2009 1100 77 14

Oil Mill Brook near Oil Mill 0112779135 7/14/2009 1050 89 15

Oil Mill Brook near Oil Mill 0112779135 8/19/2009 840 93 16

Oil Mill Brook near Oil Mill 0112779135 8/31/2009 1000 82.3 14

Oil Mill Brook near Oil Mill 0112779135 9/29/2009 945 92 15

Oil Mill Brook near Oil Mill 0112779135 10/28/2009 1100 83.7 15

Oil Mill Brook near Oil Mill 0112779135 12/7/2009 1350 70.6 13

Oil Mill Brook near Oil Mill 0112779135 12/9/2009 733 75.3 14

Oil Mill Brook near Oil Mill 0112779135 12/9/2009 1125 141 33

Oil Mill Brook near Oil Mill 0112779135 12/26/2009 1035 92.1 16

Oil Mill Brook at Gurley River 011277914 11/23/2008 1125 89 15

Oil Mill Brook at Gurley River 011277914 12/17/2008 1150 78 14

Oil Mill Brook at Gurley River 011277914 2/2/2009 1525 99 18

Oil Mill Brook at Gurley River 011277914 2/4/2009 1510 96 18

Oil Mill Brook at Gurley River 011277914 2/24/2009 1250 88 17

Oil Mill Brook at Gurley River 011277914 3/12/2009 1215 94 19

Oil Mill Brook at Gurley R 011277914 4/7/2009 825 81 15

Oil Mill Brook at Gurley River 011277914 4/8/2009 1300 87 17

Oil Mill Brook at Gurley River 011277914 5/6/2009 1150 88 16

Oil Mill Brook at Gurley River 011277914 5/27/2009 1220 97 17

Oil Mill Brook at Gurley River 011277914 6/22/2009 1220 79 14

Oil Mill Brook at Gurley River 011277914 7/14/2009 1320 90.8 17

Oil Mill Brook at Gurley River 011277914 8/19/2009 840 71 16

Oil Mill Brook at Gurley River 011277914 8/31/2009 1230 83.6 14

Oil Mill Brook at Gurley River 011277914 9/29/2009 810 92.3 15

Oil Mill Brook at Gurley River 011277914 10/28/2009 1215 84.4 15

Oil Mill Brook at Gurley River 011277914 12/7/2009 1430 71.1 13

Oil Mill Brook at Gurley River 011277914 12/9/2009 7110 74.7 14

Oil Mill Brook at Gurley River 011277914 12/9/2009 1100 186 46

Oil Mill Brook at Gurley River 011277914 12/26/2009 1025 95.3 17

Oil Mill Brook at Gurley River 011277914 1/17/2010 2200 150 30

Oil Mill Brook at Gurley River 011277914 1/17/2010 2330 144 28

Oil Mill Brook at Gurley River 011277914 1/18/2010 1140 90 18

Stony Brook above Waterford 0112779155 11/23/2008 1320 127 24

Stony Brook above Waterford 0112779155 2/2/2009 1215 188 44

Stony Brook above Waterford 0112779155 3/6/2009 1420 148 33

Stony Brook above Waterford 0112779155 4/1/2009 1030 142 31

Stony Brook above Waterford 0112779155 4/29/2009 1010 110 21

Stony Brook above Waterford 0112779155 5/20/2009 1030 120 23
40 Preliminary Assessment of Chloride Concentrations, Loads, and Yields, Southeastern Connecticut, 2008–09

Appendix 1. Specific conductance and chloride concentrations in water samples from upstream and downstream monitoring 

sites at Four Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook, southeastern Connecticut, November 2008 to January 2010.

[ID, identifier; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter]

Site name Station ID Dates* Times

Specific 

conductance, 

in μS/cm

Chloride 

concentration, 

in mg/L

Stony Brook above Waterford 0112779155 6/8/2009 1030 148 28

Stony Brook above Waterford 0112779155 7/1/2009 1050 135 24

Stony Brook above Waterford 0112779155 7/20/2009 1140 145 26

Stony Brook above Waterford 0112779155 8/19/2009 1302 131 24

Stony Brook above Waterford 0112779155 9/1/2009 1020 172 32

Stony Brook above Waterford 0112779155 9/28/2009 900 214 47

Stony Brook above Waterford 0112779155 10/26/2009 1115 121 23

Stony Brook above Waterford 0112779155 11/30/2009 1220 110 22

Stony Brook above Waterford 0112779155 12/9/2009 902 121 27

Stony Brook above Waterford 0112779155 12/9/2009 1010 81 13

Stony Brook above Waterford 0112779155 12/26/2009 1100 112 21

Stony Brook at Route 1 011277916 11/23/2008 1340 134 24

Stony Brook at Route 1 011277916 2/2/2009 1500 165 35

Stony Brook at Route 1 011277916 2/6/2009 1220 157 31

Stony Brook at Route 1 011277916 2/24/2009 1455 141 31

Stony Brook at Route 1 011277916 3/6/2009 1235 142 30

Stony Brook at Route 1 011277916 3/12/2009 1310 138 30

Stony Brook at Route 1 011277916 4/1/2009 1210 144 30

Stony Brook at Route 1 011277916 4/7/2009 750 144 28

Stony Brook at Route 1 011277916 4/29/2009 1250 128 24

Stony Brook at Route 1 011277916 5/20/2009 1130 131 25

Stony Brook at Route 1 011277916 6/8/2009 1150 152 28

Stony Brook at Route 1 011277916 7/1/2009 1320 91 15

Stony Brook at Route 1 011277916 7/20/2009 1400 149 27

Stony Brook at Route 1 011277916 8/19/2009 1330 145 27

Stony Brook at Route 1 011277916 9/1/2009 1330 162 29

Stony Brook at Route 1 011277916 9/28/2009 1130 181 36

Stony Brook at Route 1 011277916 10/26/2009 1230 128 24

Stony Brook at Route 1 011277916 11/30/2009 1330 125 24

Stony Brook at Route 1 011277916 12/9/2009 933 179 42

Stony Brook at Route 1 011277916 12/9/2009 1030 215 48

Stony Brook at Route 1 011277916 12/26/2009 1155 124 23

Four Mile River above I-95 01127819 11/23/2008 910 84 11

Four Mile River above I-95 01127819 1/23/2009 1040 85 10

Four Mile River above I-95 01127819 2/2/2009 1545 83 11

Four Mile River above I-95 01127819 2/25/2009 1220 78 11

Four Mile River above I-95 01127819 3/31/2009 1200 92 14

Four Mile River above I-95 01127819 5/1/2009 1050 79 10

Four Mile River above I-95 01127819 5/21/2009 1045 88 12
Appendix 1 41

Appendix 1. Specific conductance and chloride concentrations in water samples from upstream and downstream monitoring 

sites at Four Mile River, Oil Mill Brook, Stony Brook, and Jordan Brook, southeastern Connecticut, November 2008 to January 2010.

[ID, identifier; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter]

Site name Station ID Dates* Times

Specific 

conductance, 

in μS/cm

Chloride 

concentration, 

in mg/L

Four Mile River above I-95 01127819 6/19/2009 1120 67 9

Four Mile River above I-95 01127819 7/8/2009 1020 64 8

Four Mile River above I-95 01127819 7/29/2009 1040 64 7

Four Mile River above I-95 01127819 8/19/2008 1000 98 11

Four Mile River above I-95 01127819 9/3/2009 940 84.3 9.7

Four Mile River above I-95 01127819 10/6/2009 920 90.1 11

Four Mile River above I-95 01127819 11/2/2009 1030 79.6 9.9

Four Mile River above I-95 01127819 12/7/2009 1115 63.6 8.6

Four Mile River above I-95 01127819 12/9/2009 1011 72.2 11

Four Mile River above I-95 01127819 12/9/2009 1310 69 11

Four Mile River below I-95 01127821 11/23/2008 940 90 12

Four Mile River below I-95 01127821 12/18/2008 1145 67 8.7

Four Mile River below I-95 01127821 1/23/2009 1215 90 12

Four Mile River below I-95 01127821 2/2/2009 1550 91 13

Four Mile River below I-95 01127821 2/11/2009 1150 89 13

Four Mile River below I-95 01127821 2/25/2009 1545 86 13

Four Mile River below I-95 01127821 3/31/2009 1400 92 13

Four Mile River below I-95 01127821 5/1/2009 1200 89 12

Four Mile River below I-95 01127821 5/21/2009 1140 88 12

Four Mile River below I-95 01127821 6/19/2009 1330 73 10

Four Mile River below I-95 01127821 7/8/2009 1150 66 8.8

Four Mile River below I-95 01127821 7/27/2009 1210 70.3 8.6

Four Mile River below I-95 01127821 8/19/2008 1020 103 14

Four Mile River below I-95 01127821 9/3/2009 1240 91.7 11

Four Mile River below I-95 01127821 10/6/2009 1320 97.3 13

Four Mile River below I-95 01127821 11/2/2009 1100 82.5 11

Four Mile River below I-95 01127821 12/7/2010 1230 68 9.7

Four Mile River below I-95 01127821 12/9/2009 1029 86.8 15

Four Mile River below I-95 01127821 12/9/2009 1250 78 13

Four Mile River below I-95 01127821 1/17/2010 2130 157 26

Four Mile River below I-95 01127821 1/17/2010 2200 147 23

*

The actual study period is November 2008 to September 2009; a longer period of record was included to improve the regression model.

Prepared by the Pembroke and West Trenton Publishing 

Service Centers.

For more information concerning this report, contact:

Director

U.S. Geological Survey

Connecticut Water Science Center

101 Pitkin Street

East Hartford, CT 06108

dc_ct@usgs.gov

or visit our Web site at:

http://ct.water.usgs.gov
Brown and others—Preliminary Assessment of Chloride Concentrations, Loads, and Yields in Southeastern Connecticut, 2008–09—Open-File Report 2011-1018