U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5236

Prepared in cooperation with the Vermont Agency of Transportation

Effects of Highway Road Salting on the Water Quality 

of Selected Streams in Chittenden County, Vermont, 

November 2005–2007
Cover. Photograph shows Allen Brook, at the Route 2A crossing, Chittenden County, Vermont (view is upstream).
Effects of Highway Road Salting on the 

Water Quality of Selected Streams in 

Chittenden County, Vermont, 

November 2005–2007

By Jon C. Denner, Stewart F. Clark, Jr., Thor E. Smith, and Laura Medalie

Prepared in cooperation with the Vermont Agency of Transportation

Scientific Investigations Report 2009–5236

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: 2010

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Suggested citation:

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, November 2005–2007: U.S. Geological Survey Scientific 

Investigations Report 2009–5236, 43 p. (Also available at http://pubs.usgs.gov/sir/2009/5236.)
iii

Acknowledgments

The authors appreciate the support of John Narowski, David Blackmore, and Kevin Viani and 

other members of the Vermont Agency of Transportation. The authors also thank John Mullaney 

and Kevin Richards, U.S. Geological Survey (USGS), for providing valuable review comments on 

the manuscript. Thanks are also extended to the following USGS employees: Craig Johnston 

and Christine Mendelsohn for assistance with graphics, Dale Simmons for the editorial report 

review, and Ann Marie Squillacci for manuscript preparation and layout.
THIS PAGE INTENTIONALLY LEFT BLANK
v

Contents

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

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

Purpose and Scope ..............................................................................................................................3

Road Deicing Practices in Vermont...................................................................................................3

Description of the Study Area ............................................................................................................6

Methods of Data Collection and Analysis .................................................................................................7

Site Selection.........................................................................................................................................7

Hydrologic and Water-Quality Data Collection................................................................................7

Data Analysis.........................................................................................................................................8

Quality-Control Procedures ................................................................................................................8

Stream Hydrology and Water Quality.........................................................................................................9

Mill Brook at VT 117 near Essex Junction, VT, Stations 04289880 and 04289881 .......................9

Alder Brook at VT 289, near Essex Junction, VT, Stations 04290160 and 04290161 .................19

Alder Brook Tributary at Mouth near Essex Junction, VT, Station 042901608 ..........................25

Allen Brook at VT 2A near Essex Junction, VT, Stations 042903349 and 04290335 ..................30

Effects of Highway Road Salting on Water Quality................................................................................36

Summary and Conclusions.........................................................................................................................40

References Cited..........................................................................................................................................41

Figures

1. Map showing location of stream basins and general land-cover classes for the three 

stream-sampling stations in Chittenden County, VT...............................................................4

2. Map showing location of upstream- and downstream-sampling stations, basin 

delineations, state road network, and photograph of the downstream-sampling station 

for Mill Brook at VT 117 near Essex Junction, VT, stations 04289880 and 04289881........13

3. Graph showing (A) daily mean streamflow and time distribution of water-quality 

samples and (B) daily mean specific conductance and concentrations of chloride for 

Mill Brook at VT 117 near Essex Junction, VT, stations 04289880 and 04289881..............14

4. Graph showing (A) relation between specific conductance and chloride 

concentration in routine water-quality samples and (B) estimated daily mean chloride 

concentrations and chloride concentration in routine water-quality samples for the 

study period at Mill Brook at VT 117 near Essex Junction, VT, station 04289881.............16

5. Graph showing relation of estimated chloride concentration to (A) stream stage 

during a rain-on-snow event (January 18, 2006) and (B) streamflow during a snowmelt 

event (March 2007) at Mill Brook at VT 117 near Essex Junction, VT, stations 04289880 

and 04289881................................................................................................................................17

6. Graph showing estimated applied road deicing and measured chloride load for 

Mill Brook at VT 117 near Essex Junction, VT, station 04289881.........................................18

7. Map showing location of upstream- and downstream-sampling stations, basin 

delineations, state road network, and photograph of the downstream- and tributarysampling stations for Alder Brook at VT 289 near Essex Junction, VT, stations 

04290160, 042901608, and 04290161..........................................................................................20
vi

8. Graph showing (A) daily mean streamflow and time distribution of water-quality 

samples and (B) daily mean specific conductance and concentrations of chloride for 

Alder Brook at VT 289 near Essex Junction, VT, stations 04290160 and 04290161...........21

9. Graph showing (A) relation between specific conductance and chloride 

concentration in routine water-quality samples and (B) estimated daily mean chloride 

concentrations and chloride concentration in routine water-quality samples for the 

study period at Alder Brook at VT 289 near Essex Junction, VT, station 04290161..........23

10. Graph showing relation of estimated chloride concentration to (A) stream stage 

during a rain-on-snow event (January 18, 2006) and (B) streamflow during a 

snowmelt event (March 2007) at Alder Brook at VT 289 near Essex Junction, VT, 

stations 04290160 and 04290161 ...............................................................................................24

11. Graph showing estimated applied road deicing and measured chloride load for 

Alder Brook at VT 289 near Essex Junction, VT, station 04290161......................................25

12. Graph showing (A) daily mean streamflow and time distribution of water-quality 

samples and (B) daily mean specific conductance and concentrations of chloride for 

Alder Brook tributary at mouth near Essex Junction, VT, station 042901608....................26

13. Graph showing (A) relation between specific conductance and chloride 

concentration in the routine water-quality samples and (B) estimated daily mean 

chloride concentrations and chloride concentration in routine water-quality samples 

for the study period at Alder Brook tributary at mouth near Essex Junction, VT, 

station 042901608 ........................................................................................................................28

14. Graph showing relation of estimated chloride concentration to streamflow during a 

snowmelt event (March 2007) at Alder Brook tributary at mouth near Essex Junction, 

VT, station 042901608..................................................................................................................29

15. Map showing location of upstream- and downstream-sampling stations, basin 

delineations, state road network, and photograph of the downstream-sampling station 

for Allen Brook at VT 2A near Essex Junction, VT, stations 042903349 and 04290335.....31

16. Graph showing (A) daily mean streamflow and time distribution of water-quality 

samples and (B) daily mean specific conductance and concentrations of chloride for 

Allen Brook at VT 2A near Essex Junction, VT, stations 042903349 and 04290335...........32

17. Graph showing (A) relation between specific conductance values and chloride 

concentration in routine water-quality samples and (B) estimated daily mean chloride 

concentrations and chloride concentration in routine water-quality samples for the 

study period at Allen Brook at VT 2A near Essex Junction, VT, station 04290335............34

18. Graph showing relation of estimated chloride concentration to (A) stream stage 

during a rain-on-snow event (January 18, 2006) and (B) streamflow during a snowmelt event (March 2007) at Allen Brook at VT 2A near Essex Junction, VT, stations 

042903349 and 04290335.............................................................................................................35

19. Graph showing estimated applied road deicing and measured chloride load for 

Allen Brook at VT 2A near Essex Junction, VT, station 042903349 .....................................36

20. Ternary diagram showing general cation composition (in percent) for Mill Brook at 

VT 117, Alder Brook at VT 289, and Allen Brook at VT 2A near Essex Junction, VT........37

21. Graph showing the range in chloride concentrations in the routine water-quality 

samples for the paired sampling stations at Mill Brook at VT 117, Allen Brook at 

VT 2A, Alder Brook at VT 289, and Alder Brook tributary at mouth near Essex 

Junction, VT.................................................................................................................................38

22. Graph showing estimated monthly chloride loads and measured runoff for 

(A) Mill Brook at VT 117 near Essex Junction, VT, station 04289881, (B) Alder Brook at 

VT 289 near Essex Junction, VT, station 04290161 and (C) Allen Brook at VT 2A near 

Essex Junction, VT, station 04290335.......................................................................................39
vii

Tables

1. Selected characteristics of the three paired stream-sampling stations and the 

tributary sampling station in Chittenden County, VT...............................................................5

2. Estimated mean annual loads, yields, confidence intervals, standard error of 

prediction, and the ratio of the standard error of prediction to the mean annual 

load for chloride at sampling stations for the 2-year sampling period in 

Chittenden County, VT................................................................................................................10

3. Estimated annual loads, yields, and confidence intervals for chloride by year at 

sampling stations in Chittenden County, VT...........................................................................11

4. Summary statistics for values of specific conductance and pH and concentrations 

of chloride, sodium, calcium, potassium, magnesium, sulfate, and nitrite plus 

nitrate for routine water-quality samples collected at Mill Brook at VT 117, near 

Essex Junction, VT .....................................................................................................................15

5. Daily mean summary statistics for continuous specific conductance and 

estimated continuous chloride concentrations at Mill Brook at VT 117, near 

Essex Junction, VT .....................................................................................................................15

6. Difference in the estimated annual stream chloride load at upstream and 

downstream sampling stations and estimated Vermont Agency of Transportation 

(VTrans) applied chloride load at sampling sites in Chittenden County, VT......................18

7. Summary statistics for values of specific conductance and pH and concentrations 

of chloride, sodium, calcium, potassium, magnesium, sulfate, and nitrite plus 

nitrate for routine water-quality samples collected at Alder Brook at VT 289, near 

Essex Junction, VT .....................................................................................................................22

8. Daily mean summary statistics for continuous specific conductance and 

estimated continuous chloride concentrations at Alder Brook at VT 289, near 

Essex Junction, VT .....................................................................................................................22

9. Summary statistics for values of specific conductance and pH and concentrations 

of chloride, sodium, calcium, potassium, magnesium, sulfate, and nitrite plus nitrate 

for routine water-quality samples collected at Alder Brook tributary at mouth near 

Essex Junction, VT .....................................................................................................................27

10. Daily mean summary statistics for continuous specific conductance and estimated 

continuous chloride concentrations at Alder Brook tributary at mouth near 

Essex Junction, VT .....................................................................................................................27

11. Summary statistics for values of specific conductance and pH and concentrations 

of chloride, sodium, calcium, potassium, magnesium, sulfate, and nitrite plus nitrate 

for routine water-quality samples collected at Allen Brook at VT 2A, near Essex 

Junction, VT.................................................................................................................................33

12. Daily mean summary statistics for continuous specific conductance and 

estimated continuous chloride concentrations at Allen Brook at VT 2A, near 

Essex Junction, VT .....................................................................................................................33
viii

Conversion Factors, Abbreviated Water-Quality Units, 

and Datums

Multiply By To obtain

Length

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

inch (in.) 2.54 centimeter

Area

square foot (ft2) 0.09290 square meter

square mile (mi2) 2.590 square kilometer

Flow rate

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

Mass

pound (lb) 0.4536 kilogram

pound per day (lb/d) 0.4536 kilogram per day

pound per year (lb/yr) 0.4536 kilogram per year

pound per year (lb/yr) 0.0005 ton per year

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

 °F=(1.8 x °C)+32

Abbreviated water-quality units used in this report: Concentrations of chemical constituents 

in water are reported in milligrams per liter (mg/L).

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

(μS/cm at 25°C).

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).
Abstract

A study of road-deicing chloride (Cl) concentrations and 

loads was conducted at three streams in Chittenden County, 

VT, from November 2005 to 2007. This study was done by 

the U.S. Geological Survey, in cooperation with the Vermont 

Agency of Transportation. The streams, Alder Brook, Allen 

Brook, and Mill Brook, were selected to represent different 

land uses in the upstream watershed, different road types and 

densities, and different geometric patterns of the roadway 

draining to the receiving stream to assess the relative contribution of and differences in state road-salt applications to stream 

Cl concentrations and loads. Water-quality samples were collected and specific conductance was measured continuously at 

paired stations upstream and downstream from State highways 

and related to Cl concentrations to assist in determining the 

effects of road-salting operations during winter maintenance 

on the levels of Cl in the streams. 

Mean concentrations of Cl ranged from 8.2 to 72 mg/L 

(milligrams per liter) in the water-quality samples collected 

at sampling stations upstream from State highway bridges 

and from 7.9 to 80 mg/L in those collected at sampling 

stations downstream of highway bridges. Mean Cl loads 

ranged from 1,100 to 4,090 lb/d (pounds per day) at upstream 

stations and from 1,110 to 4,200 lb/d at downstream stations. 

Estimated mean annual Cl loads ranged from 402,000 to 

1,490,000 lb/yr (pounds per year) at upstream stations and 

from 405,000 to 1,530,000 lb/yr at downstream stations. 

Mean Cl concentrations in samples collected at the three 

paired stations were lowest at Mill Brook at VT 117 near 

Essex Junction, VT (7.9 mg/L) and highest at Allen Brook 

at VT 2A near Essex Junction, VT (80.7 mg/L). None of the 

monitored Cl concentrations in the water-quality samples 

collected at the three paired sampling stations exceeded either 

of the U.S. Environmental Protection Agency’s (USEPA) 

recommended chronic and acute Cl toxicity criteria of 230 

and 860 mg/L, respectively. 

A fourth stream site, a small tributary draining to Alder 

Brook between the upstream and downstream stations, was 

monitored from December 2006 to November 2007. This tributary collected runoff from a state highway and an interchange 

before flowing through a wetlands retention basin. The mean 

Cl concentration in water-quality samples collected at the 

tributary was 449 mg/L. The USEPA recommended chronic 

toxicity criterion of 230 mg/L was exceeded about 

65 percent of the monitoring period. The USEPA recommended acute toxicity criterion of 860 mg/L was not exceeded.

Estimated Cl loads below the State highway bridges 

exceeded loads above the bridges at all three paired stations 

during both years of the study. The differences in the annual 

loads between the upstream and downstream stations were 

0.7, 3.0 and 14 percent at Mill, Allen, and Alder Brooks, 

respectively. Almost all of the difference (92 percent) at Alder 

Brook was due to the tributary. Cl applied by the State of 

Vermont for deicing purposes represented less than 20 percent 

of the annual estimated Cl load in all 3 streams below the 

state highways. 

The highest monthly Cl loads during the first year of the 

study were observed in January 2006 at all three stream stations because of an early snowmelt event. The highest monthly 

Cl loads during the second year of the study were observed 

in April 2007 at all three streams during spring snowmelt 

and were followed by decrease in Cl loading through the 

summer. Generally, the relation of Cl loads to runoff was 

similar at all three streams. In July and October 2007, loads 

increased slightly with an increase in runoff, indicating that 

Cl in the soils and groundwater may be contributing to the Cl 

levels during the summer and fall, well after the road-salting 

season. Cl loads in all three streams appear to be due primarily to sources in the watersheds upstream of the state highway 

bridge where road salt was applied and (or) Cl retained in soils 

and streambed sediments. 

Effects of Highway Road Salting on the Water Quality 

of Selected Streams in Chittenden County, Vermont, 

November 2005–2007

By Jon C. Denner, Stewart F. Clark, Jr., Thor E. Smith, and Laura Medalie
2 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Introduction

In 2002, an estimated $2 billion was spent nationally on 

chemicals, materials, labor, and equipment for winter maintenance of roads (U.S. Environmental Protection Agency, 

2002). Road-salt (sodium chloride (NaCl)) use for deicing and 

anti-icing of roads has increased steadily since its initial use in 

the late 1930s and early 1940s. From 1940 to 2004, national 

sales of salt for deicing purposes increased from 164,000 to 

16,014,000 tons annually (Salt Institute, 2004). During this 

period, salt use was greatest (20,117,000 tons) in 1996. The 

use of NaCl and other chemicals for road deicing is designed 

to improve the safety of drivers during winter driving conditions; but there has been an environmental concern in many 

parts of the United States and other regions of the world 

because of the use of these deicing materials. Many investigations have been conducted since the 1960s to study the effects 

of road-deicing materials (Granato, 2000). These investigations have shown that road-deicing activities can have an 

effect on the receiving environment, including waters, soils, 

and vegetation. Most of these studies have focused on NaCl, 

although fewer studies also have assessed the effects of other 

deicing and anti-icing compounds. These other compounds 

include calcium chloride (CaCl2), magnesium chloride, potassium acetate, calcium magnesium acetate, and biobased deicers (Kievit-Kylar, 2004; Staples and others, 2004).

The sources of chloride (Cl) and sodium (Na) to 

the environment are varied and include rock weathering, 

precipitation and winds, agriculture, human sewage (on-site 

disposal systems, municipal wastewater treatment facilities), 

and road deicing. All surface waters contain a natural 

amount of Cl and Na. Hanes and others (1970) report that 

concentrations of Cl in uncontaminated rivers typically range 

from 0 to 15 mg/L and numerous studies have reported natural 

Cl levels in rivers to be higher adjacent to coastal waters. 

Kelly and others (2007), in a study of a rural watershed in 

New York, found that road salt contributed 91 percent of the 

total inputs of NaCl to the watershed, and rock weathering 

and atmospheric deposition combined accounted for less 

than 2 percent.

NaCl and other deicing chemicals are transported with 

melting ice and snow onto impervious surfaces, onto adjacent 

soils and vegetation, and eventually to rivers, streams, and 

other bodies of water (Environmental Literacy Council, 

2005). The actual amount of runoff containing deicing salts 

that reaches the surface and groundwaters is a function 

of site-specific characteristics such as soil permeability, 

vegetative cover, gradients, and highway-drainage techniques 

(D’Itri, 1992). During and after storms and spring snowmelt, 

streamflow may contain high concentrations of Na and Cl. 

These high concentrations are diluted once they enter larger 

water systems. 

Applied deicing salts can follow various pathways 

from the roadway to receiving waters. Saline wash from the 

roadbed may flow directly to streams through surface runoff 

over impervious surfaces, which may at times include frozen 

ground. In addition, Cl-enriched water can infiltrate soils near 

the pavement and subsequently percolate through the unsaturated zone to groundwater. Road salt also can accumulate in 

snowbanks within the road right-of-way. 

Studies of the environmental effects of deicing show that 

its influence is greatest near the roadway that is salted. From 

a water-quality standpoint, small drainages from the roadway 

itself (such as swales) and small streams, lakes, wetlands, 

and groundwater directly receiving the roadway runoff are 

most affected. Trowbridge (2007) reported that the effects of 

road-salting on a number of small streams draining sections 

of an interstate highway in New Hampshire caused exceedances of the U.S. Environmental Protection Agency (USEPA) 

recommended chronic Cl toxicity criterion of 230 mg/L for the 

protection of aquatic life. 

Soils and shallow groundwaters also can be affected 

(Jones and Sroka, 1997), although these environments are less 

commonly monitored and studied than surface water. The constituents in deicing chemicals affect water quality by increasing total dissolved solids and mobilizing metals by promoting 

processes such as ion exchange, desorption, complexing, 

acidification, and mineral dissolution (Shanley, 1994; Granato 

and others, 1995; Bricker, 1999).

Road salt can accumulate in soil and affect trees and 

other vegetation. Elevated salt levels in soils inhibit the ability 

of plants to absorb nutrients and water, impeding long-term 

growth. Degradation of roadside vegetation also can reduce 

the ability of roadside areas to act as a buffer to slow the 

runoff of contaminants into the watershed (Environmental 

Literacy Council, 2005). 

Buttle and Labadia (1999) showed that less than 

50 percent of the applied salt was retained in the snowpack 

during the latter stages of snow-cover development. This 

finding indicated that 50 percent of the salt was released 

from the snowpack during mid-winter thaws and rains. The 

remaining portion was released to surface runoff and soil 

infiltration during the diminishing snow cover. Blomqvist 

and Johansson (1999) indicated that the occurrence of 

salt decreased rapidly with distance from the roadway. 

Spray transport beyond about 70 ft was determined to be 

insignificant. Jebb (1988) documented that 98 percent of salt 

dispersed from the road surface was recovered within about 

150 ft of the road edge.

Howard and Haynes (1993) estimated that 45 percent of 

Cl was removed by overland flow, and the remaining portion 

entered soil water and groundwater. In a Massachusetts 

highway study, 55 percent of Cl in deicers was transported in 

surface runoff and the remaining 45 percent infiltrated through 

soils into groundwater (Church and Friez, 1993). Toler and 

Pollock (1974), in another study conducted in Massachusetts, 

determined that 15 to 55 percent of the annual amount of 

Cl applied to the highway was initially retained in soil water 

above the water table. Most of the Cl, however, was leached 

downward to groundwater with infiltrating rainwater by 

late fall.
Introduction 3

In Vermont, increasing Cl levels have been identified in 

the Lake Champlain Basin (Shambaugh, 2008). In addition, 

concerns about road salting were identified in the Vermont 

Agency of Transportation (VTrans) and the Federal Highway 

Administration (FHWA) National Environmental Policy Act 

reevaluation in 2004 for the proposed Chittenden County 

Circumferential Highway. This proposed highway would 

pass over a number of streams east of Burlington, VT. In 

response to this concern, the U.S. Geological Survey (USGS) 

in cooperation with VTrans, conducted a study of the effects 

of state roadway-deicing practices on the water quality of 

selected streams in Chittenden County, VT, from November 

2005 to 2007. 

Purpose and Scope

This report describes the results of a study to assess the 

effects of road salting of state highway bridges and connecting roadways on the water quality of three stream sites 

in Chittenden County, VT (fig. 1; table 1). This report 

(1) describes the relation between specific conductance values 

and Cl concentrations, (2) determines the frequency with 

which Cl concentrations exceeded USEPA recommended 

chronic and acute toxicity criteria for protection of aquatic 

life, (3) assesses the relative contribution of state road-salt 

applications to Cl concentrations and loads in three streams, 

and (4) compares general water chemistry and chloride 

concentrations and loads among the three streams. A fourth 

stream, a tributary to one of the streams studied, was sampled 

to assess the effects of the tributary on the receiving stream.

The data presented in this report were collected from 

November 2005 to 2007 and include streamflow; specific 

conductance; pH; and concentrations of Cl, Na, Ca, potassium 

(K), magnesium (Mg), sulfate (S), and nitrite plus nitrate 

(NO2+NO3). Streamflow and water-quality data collected for 

the study are stored in the USGS National Water Information 

System (U.S. Geological Survey, 2003) at http://nwis.

waterdata.usgs.gov/nwis.

Road Deicing Practices in Vermont

NaCl and sand are primarily used in Vermont for deicing 

and anti-icing (Gil Newbury and Michael Morissette, Vermont 

Agency of Transportation, written commun., 2005). During 

very cold events, CaCl2 is used with NaCl. The amount of 

CaCl2 and other substitutes for NaCl is not quantified by 

VTrans (Gil Newbury and Michael Morissette, Vermont 

Agency of Transportation, written commun., 2005). VTrans 

also uses ferric ferrocyanide, “Prussian Blue,” as an anticaking agent in the deicing salt.

VTrans has operated a Safe Roads Policy since 1981 

that promotes the efficient use of deicing materials on state 

roads. Under this policy, roads are to be returned to bare 

pavement after a storm is over on a priority schedule based 

on the amount of traffic. There is no “bare road” designation 

for any State highway during a storm. Vermont is the only 

state in the Nation that requires an environmental permit for 

deicing. VTrans obtains an annual permit (10 VSA section 

1272) from the Vermont Agency of Natural Resources 

(VTANR), Department of Environmental Conservation 

(VTDEC) for deicing roadways and state-owned airport 

runways. This permit typically defines procedures to follow 

for the deicing of state roads as described in annually updated 

VTrans Operations Snow and Ice Control Plans. These plans 

are structured as a guide to relate winter conditions to levels 

of deicing service provided by state maintenance crews. The 

Snow and Ice Control Plans contain standards for correlating 

recommended salt-application rates to pavement temperatures. 

The Snow and Ice Control Plans also identify an economic 

salting range, which extends from 30 to 20°F. 

VTrans conducted a study during the winter of 

1993–94 of deicing-salt effectiveness at different pavement 

temperatures called: “Smart Salting: A Winter Maintenance 

Strategy” (Vermont Agency of Transportation, 1995; Smith 

and Zogg, 1998). The results of the Smart Salting study 

indicated that at temperatures greater than 25°F, potential 

savings in materials exist when a material-application rate 

curve is used. At lower temperatures, the savings were 

smaller; therefore, the investigators recommended higher 

application rates with decreasing temperature. 

The Smart Salting study also recommended that 

winter highway maintenance crews (1) determine pavement 

temperature through the use of infrared thermometers mounted 

on supervisors’ vehicles, and (2) determine salt-application 

rates on the basis of pavement temperature, melting 

capacity of the salt, and the thickness of the ice or snow on 

the pavement (Smith and Zogg, 1998). The Smart Salting 

study created anti-icing and deicing strategies that included 

application curves relating salt-application rates to snowpack 

and ice. As the pavement temperature decreases, more salt is 

needed to melt the ice; therefore, pavement temperature is the 

controlling factor in the treatment of highways during winter 

storms (Smith and Zogg, 1998). 

The Smart Salting winter maintenance strategy was 

adopted throughout Vermont during the winter of 1994–95. 

For anti-icing, action is taken to prevent formation of a 

strong bond between the ice or snowpack and the pavement. 

The weight of the expected snowfall prior to plowing is 

approximated, and then the amount of deicer required to 

melt from 4 to 6 percent of that weight already bonded to the 

pavement is calculated. 

The VTrans Maintenance Division is responsible for 

salting, sanding, and plowing more than 6,500 single-lane 

miles of state-owned roadway. During October 1, 2003– 

September 31, 2004, VTrans used 89,865 tons of road salt and 

76,675 cubic yards of sand statewide (Michael Morrisette, 

Vermont Agency of Transportation, written commun., 2005). 

From 1981 to 2005, an average annual load of 16.6 tons of 

road salt per lane-mile was used throughout Vermont. The 

amount of road-deicing chemicals applied by VTrans from 

1981 to 2005 increased from about 12.5 tons per lane-mile in 
4 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 1. Location of stream basins and general land-cover classes for the three stream-sampling stations in Chittenden County, VT.

EXPLANATION

Land-cover class

Stream-sampling  station and number (Refer to table 1)

Barren

Developed

AgricultureForest

Wetland

1

County boundary Water

Stream

Road

73° 72°

45°

44° Vermont

Area ofdetail

0 30 60 MILES

0 30 60 KILOMETERS

43°

2A

2A

2

2

15

15

15

128

289

116

7

117

89

89

4

7 6

5

3

2 1

CHITTENDEN

LAMOILLE

WASHINGTON

Underhill

Jericho

Colchester

Essex Junction

Winooski

South

 Burlington

Williston

Richmond

Burlington

International

Airport

Mill Brook

l A

or B red

ko

Allen Brook

Lake

Champlain

Browns

River

Lee River

W ni oosk i River

72°52'30" 73° 73°07'30"

44°35'

44°30'

44°25'

0 2 4 MILES

0 2 4 KILOMETERS

Shaded relief from U.S. Geological Survey, National Elevation Dataset, 1999. Hydrography from U.S. Geological Survey, 1:100,000-scale National Hydrography Dataset Plus, 2006. Land cover from the University of Vermont, 2002 Land Cover/Land Use Dataset for Vermont, 2005. Roads from Vermont Agency of Transportation, 1:24,000-scale Functional Classification of Vermont Roads, 2001. 

LakeChamplain
Introduction 5

Table 1. Selected characteristics of the three paired stream-sampling stations and the tributary sampling station in Chittenden 

County, VT.

[Latitude and longitude are given in degrees (°), minutes (′), and seconds (′′); USGS, U.S. Geological Survey; mi2, square miles; ft3/s, cubic feet per second; 

Min, minimum; Max, maximum; na, not applicable; mi/mi2, miles per square mile; --, not calculated]

Site 

number

(fig. 1)

Site name

USGS 

station 

number

Latitude Longitude

Drainage 

area

(mi2)

Streamflow

(ft3/s)1

Min Mean Max

1 Mill Brook above VT 117, near Essex Junction, VT 04289880 44°27′19′′ 73°01′06′′ 16.3 na na na

2 Mill Brook below VT 117, near Essex Junction, VT 04289881 44°27′19′′ 73°01′06′′ 16.4 2.98 37.3 645

3 Alder Brook above VT 289, near Essex Junction, VT 04290160 44°27′19′′ 73°01′06′′ 8.87 na na na

4 Alder Brook tributary at mouth, near Essex Junction, VT 042901608 44°27′19′′ 73°01′06′′ 0.05 0.04 0.17 1.25

5 Alder Brook below VT 289, near Essex Junction, VT 04290161 44°33′01′′ 73°04′19′′ 8.93 0.49 16.0 331

6 Allen Brook above VT 2A, near Essex Junction, VT 042903349 44°27′19′′ 73°01′06′′ 9.85 na na na

7 Allen Brook below VT 2A, near Essex Junction, VT 04290335 44°27′42′′ 73°06′46′′ 9.88 0.12 16.2 247

Site number

(fig. 1)

Impervious surface2

(percent)

Road density

(mi/mi2)

Septic system density

(percent)

Land use, in percent

Forest Developed Agriculture Other3

1 0.48 1.6 -- -- -- -- --

2 0.52 1.7 24 72 4 15 9

3 3.4 3.7 -- -- -- -- --

4 20 40 -- -- -- -- --

5 3.6 3.8 28 34 9 47 10

6 4.7 4.1 -- -- -- -- --

7 4.8 4.2 26 50 13 35 4

1

Streamflow statistics are calculated from the daily mean streamflow for the 2-year study period at the downstream sampling station for Mill Brook, 

Alder Brook, and Allen Brook, and for the 1-year study period at the Alder Brook tributary-sampling station.

2

U.S. Geological Survey, 2003.

3

Other consists of wetlands, water, and barren land-use categories.
6 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

1981 to about 16.5 tons per lane-mile in 2005. The maximum 

annual load of road salt used per lane-mile throughout 

Vermont was 23.9 tons in 1999 and the minimum annual load 

of road salt used per single-lane mile was 9.2 tons in 1983. 

Application rates per lane-mile have decreased or remained 

similar in most areas of the State since implementation of the 

VTrans Smart Salting Program. Road-salt application rates in 

Chittenden County (District 5) averaged approximately 

15 tons per lane mile per year (average District salt application 

1981–2005) (Michael Morrisette, Vermont Agency of 

Transportation, written commun., 2005). 

Weather conditions, road-surface conditions, and the type 

of road, and changing deicing practices affect the application rate and total amount of road salt used. Recent studies 

by VTrans have shown increased efficiencies in road deicing 

with the use of brines (Vermont Agency of Transportation, 

2009); such practices may be adopted in the future and would 

affect the amount of road salts applied. Therefore, the amount 

of road salt applied to roads in Vermont varies from year to 

year and from region to region on different stretches of road. 

In addition to VTrans, many local highway departments and 

independent private contractors apply deicing compounds 

to highways in the State. No current (2009) estimates of the 

amount of deicing material used by these agencies and organizations are available. 

Description of the Study Area

Chittenden County was selected for the study because it 

is the location of the proposed circumferential highway and 

contains a mix of state road types and land uses representative 

of the State of Vermont. Chittenden County, VT, encompasses 

620 mi2 of which about 540 mi2 is land and 80 mi2 is water 

(Lake Champlain). It is the most populous county in the 

state and includes the metropolitan area of Burlington-South 

Burlington. Topography is characterized by broad lowlands in 

the western portion of the county and by rolling hills and the 

Green Mountain range in the eastern portion of the county. 

Elevations range from about 90 ft near the shore of Lake 

Champlain to more than 4,000 ft at the summit of Mount 

Mansfield in the Green Mountains. The county is about 

45 percent forest, 26 percent agriculture, 18 percent water, 

8 percent developed, and 3 percent wetlands and barren 

(U.S. Geological Survey, 2001).

The Winooski River, a tributary of Lake Champlain, is 

approximately 90 mi long and, although it is not Vermont's 

longest river, it is one of the State’s most important, forming a 

major valley from Lake Champlain to the Green Mountains in 

Chittenden County. The river’s headwaters are in Washington

County, north and east of Montpelier. From Montpelier, 

it flows northwest into Chittenden County, passing north 

of the city of Burlington. It enters the eastern side of Lake 

Champlain approximately 5 mi northwest of Burlington. The 

river was historically used for the transportation of timber for 

logging purposes during the 19th century and is now used for a 

variety of recreational purposes including canoeing, kayaking, 

fishing, and swimming. Additionally, several hydroelectric 

dams in the watershed are used for generating electricity. The 

river valley downstream from Montpelier is used as a corridor 

for U.S. Highway 2 and Interstate Highway 89. 

Bedrock beneath Chittenden County is composed of 

sandstones, limestones, dolomites, and shales. To the east, 

shales and sandstones are metamorphosed to phyllites and 

granofels composed primarily of quartz and mica (Doll and 

others, 1961; Kim and others, 2007). Easily weathered limestone, dolomite, and calcareous shale contribute dissolved 

constituents to streamwater in the Allen Brook Basin. The 

metamorphic rocks underlying the upper Allen Brook, as well 

as the Alder and Mill Brook Basins, are relatively resistant to 

chemical weathering and, therefore, contribute fewer constituents to streams than the calcareous shale. 

Glacial till and water-transported sediments related to 

deglaciation cover much of the bedrock throughout the region 

(Springston and DeSimone, 2007; Wright, 2003). Calcareous rocks in the region have been dragged southeastward by 

glaciation. Calcareous till and calcareous stratified deposits 

are found along Alder Brook and calcareous till is found along 

Allen Brook. The calcareous rocks (Allen Brook) and calcareous glacial till deposits (Allen and Alder Brooks) locally 

contribute to streamwater chemistry. The headwaters of Mill 

Brook are in non-calcareous bedrock and flow primarily 

through fine sands and non-calcareous till (Clark and others, 

2005; Ladue, 1982).

Average temperatures in Burlington, VT, range from 

less than 20°F in the winter to about 70°F in summer. Annual 

precipitation during the first year of the study (2006) was 

47.4 in. (130 percent of normal), and annual precipitation 

during the second year of the study (2007) was 36.8 in. 

(104 percent of normal). Snowfall totals for early winter 2006 

were near normal through mid-January. Record rainfall in 

January 2006 completely depleted the snowpack. The snow 

cover did not recover to any substantial degree during late 

winter because snowfall was below normal, monthly average 

temperatures were above normal, and rainfall was frequent. 

Snowfall totals were below normal for the beginning of the 

2007 winter season. No snowfall was recorded in November, 

and snowfall in December was 65 percent of normal. 

The snow accumulated in January 2007 and continued to 

accumulate through early spring because of above-normal 

snowfall and below-normal monthly average temperatures. 

Total snowfall in February 2007 was 229 percent of normal. 

A record monthly total snowstorm accumulation was recorded 

on February 14–15, 2007. This storm resulted in the second 

greatest snowfall for the period of record at Burlington (1884–

present). Total snowfall during the winter of 2007 was 94.6 in. 

(130 percent of normal). All climate data were obtained from 

the National Weather Service in Burlington, VT (http://www.

weather.gov/climate/index.php?wfo=btv).
Methods of Data Collection and Analysis 7

Methods of Data Collection and 

Analysis

The sampling program for this study was designed 

to determine the frequency with which Cl concentrations 

exceeded USEPA recommended chronic and acute toxicity 

criteria and to assess differences in Cl loads upstream and 

downstream from State highway bridges to determine whether 

road-salt application affected streamwater Cl levels in the 

three streams in Chittenden County, VT. Streamflow and 

specific conductance were continuously monitored at three 

paired sampling stations to characterize the variations in these 

parameters during two annual cycles (November 2005–2007) 

and to establish relations between Cl and specific conductance. 

Specific conductance is a measure of the capacity of water to 

conduct an electrical current and is a function of the types and 

quantities of dissolved substances in water (Wilde and Radtke, 

1998b). As concentrations of dissolved ions increase, conductivity of water increases. 

Water samples representing the different climatic and 

hydrologic conditions that can affect constituent concentrations in samples were collected manually approximately 

monthly, and by using automated sample-collection techniques 

during thaw and precipitation periods in the winter. These 

water samples were analyzed for dissolved chloride, dissolved 

sodium, and dissolved calcium. A reduced number of samples 

were analyzed for a group of major cations for characterizing 

basic water chemistry of the streams.

Site Selection

Approximately 10 streams were initially considered as 

a location for potential sampling stations. The streams were 

categorized by drainage-basin size, percentage of various land 

uses, and road density in the watershed. A geographic information system was used to determine watershed characteristics 

(percent imperviousness, percent land-use types, road density, 

and septic-system density) (U.S. Geological Survey, 2001). 

Three streams were selected for this study based on representation of different land uses, road types, the drainage pattern 

of the roadway to the receiving stream, and the suitability for 

streamflow and water-quality monitoring (fig. 1). Sampling 

stations were established upstream and downstream (paired 

stations) (table 1) from a highway bridge at each of these 

locations. An additional monitoring station (the Alder Brook 

tributary) was established in December 2006 at the outlet of a 

roadway runoff retention basin adjacent to VT 289 and Alder 

Brook to determine the effects of this tributary on the Cl load 

in Alder Brook (table 1). The tributary flows into Alder Brook 

between the upstream and downstream stations.

Hydrologic and Water-Quality Data Collection

Continuously recording streamflow-gaging stations 

were established at Alder Brook at VT 289 and Mill Brook 

at VT 117 near Essex Junction, VT, (table 1) using protocols 

described in Rantz and others (1982). The existing streamflowgaging station at Allen Brook at VT 2A near Essex Junction, 

VT, was used (table 1). All discharge measurements in the 

three streams were made downstream of the highway bridges. 

Records of stage were obtained using electronic dataloggers 

and stage sensors. Stage values were recorded every 15 minutes during the study period. Stage readings were related to 

measurements of streamflow to obtain a stage-streamflow relation used in computing continuous streamflow. An additional 

streamflow-gaging station was added in December 2006 at the 

Alder Brook tributary. Streamflow at the Alder Brook tributary 

station was measured using a 120-degree thin-plate v-notch 

weir. A theoretical equation was used to rate the streamflow 

through the weir (Rantz and others, 1982).

Specific-conductance and water-temperature data also 

were collected continuously at all three paired stations and at 

the tributary to Alder Brook using published USGS protocols 

(Wagner and others, 2006). Water temperature and specific 

conductance were measured at 15-minute intervals during the 

study period using digital dataloggers.

Water samples were collected approximately monthly 

at the three paired stream-sampling stations using standardsurface-water sampling protocols (U.S. Geological Survey, 

variously dated; Wilde and Radtke, 1998a and b). Approximately 25 samples were collected at each of the upstream 

stations and approximately 40 samples were collected at each 

of the downstream stations. Automated sampling for Cl was 

used at the downstream stations to better define the changes 

in Cl concentrations from daily thaws, freezing precipitation, 

and snowmelt events. These samples assisted in characterizing the range in Cl concentrations and specific-conductance 

values in relation to hydrologic and weather conditions at each 

station. The monthly and automated water-quality sample 

collection is referred to as “routine” sampling from this point 

forward in this report. Samples were collected during base 

flow, rain-on-snow, and snowmelt conditions. Water samples 

also were collected from December 2006 to October 2007 at 

the Alder Brook tributary. During each stream-station visit, onsite measurements were made for specific conductance, pH, 

and water temperature, and water samples were collected for 

subsequent determination of the concentrations of Cl, Na, and 

Ca. In addition to the routine sample analysis, samples also 

were collected four times per year (seasonally) for determination of potassium (K), magnesium (Mg), sulfate (S), and nitrite 

plus nitrate (NO2+NO3) concentrations. Water samples were 

analyzed at the USGS water-quality laboratory in Lakewood, 

CO, according to methods in Fishman and Friedman (1985) 

and Fishman (1993). 
8 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Data Analysis

For each stream site described in the section “Stream 

Hydrology and Water Quality,” water-quality conditions are 

described, and a map and graphs of selected data are presented. Ranges of constituent values not plotted in the graphs 

are statistically summarized in the text. Mean pH values 

for samples collected during this study were determined by 

converting instantaneous pH values to hydrogen-ion (H+) 

concentrations, calculating the mean of the instantaneous H+ 

concentrations, and converting the mean H+ concentrations 

back to pH units (Radtke and others, 2003). 

For each stream site, the illustration begin with a 

map of the stream showing the major stream network, 

monitoring stations, the State road network, and a photograph. 

Information about land cover and the road network assists in 

the understanding of natural and anthropogenic factors that 

affect water quality. 

On the second page of illustrations, two graphs 

describe the distribution of water-quality samples in relation 

to streamflow for both the upstream and downstream 

stations and specific-conductance values in relation to Cl 

concentrations for each year (2006 and 2007). In the first 

graph, daily mean streamflow for the data-collection period 

as well as dates and instantaneous streamflow values for 

the associated water-quality samples are presented. The 

distribution of water-quality samples with respect to time 

also is represented. Because the water-quality samples are 

displayed with the corresponding instantaneous-streamflow 

values, these points do not always fall on the line representing 

the daily mean discharge. In the second graph, daily mean 

specific conductance for the data-collection period and Cl 

concentrations for the water-quality samples are presented for 

the paired stations.

On the third page of illustrations, the first graph 

shows the linear relation between specific-conductance 

values and Cl concentrations. These relations were used to 

develop regression equations for estimating daily mean Cl 

concentrations at the downstream-sampling stations. The 

concentrations of constituents in surface water commonly are 

related to other constituent concentrations and factors such as 

hydrologic conditions, season, and location. One constituent 

concentration can be expressed in terms of another constituent 

concentration using simple regression equations (Helsel and 

Hirsch, 1992). Regression analysis is commonly used to define 

the mathematical relation between specific conductance and 

dissolved constituents, such as Cl (Hem, 1992). The second 

graph on the third page of illustrations for each stream shows 

the estimated daily mean Cl concentrations for the study 

period relative to individual measured Cl concentrations and 

the USEPA recommended chronic toxicity criterion for Cl 

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

The first graph on the fourth page of illustrations shows 

the effects of rain-on-snow on Cl concentrations and stream 

stage during January 2006. The second graph shows the effects 

of snowmelt on Cl concentrations and streamflow during 

March 2007. These two graphs represent important runoff and 

snowmelt periods during the two years of study. The fifth page 

of illustrations for each stream contains a graph comparing 

estimated stream loads of Cl to estimated loads of Cl applied 

as road deicing material by VTrans during each winter season.

The LOAD ESTimator (LOADEST) computer program 

(Runkel and others, 2004) was used to estimate Cl loads at 

the sampling stations. LOADEST is based on a regression 

equation in which time series of streamflow and concurrent 

Cl concentrations from the upstream and downstream stations 

are used as calibration data for the estimation of constituent 

loads. For this study, a user-defined model that included two 

explanatory variables (streamflow and specific conductance) 

was used. Two explanatory variables in the calibration and 

estimation files are useful in the formulation of the regression 

for load estimation. 

The number of pounds of Cl applied to State highways 

in the study area was estimated from data provided by VTrans 

(Michael Morissette, Vermont Agency of Transportation, 

written commun., 2007). Snowplow drivers were required to 

record dates and application rates for each trip during which 

NaCl was applied. Markers were set on the roadway at the 

basin boundaries to define the road-surface lengths traversed 

by snowplows within the watershed of the stream stations. 

From these data, pounds of Cl applied to state highways per 

lane-mile were calculated. Conversion of NaCl loads applied 

to roadways to Cl loads was necessary for comparison to data 

in this study and is a function of atomic weight of Cl relative 

to salt. Sodium and Cl ions are monovalent, thus the conversion is obtained by dividing the NaCl load by 1.648. The result 

is the load of Cl. All descriptive statistics were calculated 

using Excel and SAS statistical software (Microsoft, 2003; 

SAS Institute, Inc., 1998, 2000).

A ternary plot (Helsel and Hirsch, 1992) was used to 

describe the general water chemistry (with respect to cation 

composition) at the three sampling stations. The ternary plot is 

trilinear and shows the difference in cation distribution among 

the stations. Concentrations were converted to milliequivalents 

and used to determine the percentage of cation composition. 

Boxplots were used to compare the range in chloride concentrations and instantaneous yields among the three paired 

sampling stations. 

Quality-Control Procedures

Field quality-control procedures included the collection 

of replicate and blank samples. Field-blank samples provided 

information on bias or the potential for contamination as a 

result of sample collection, processing, and analysis. Analytical results from the field-blank samples showed that concentrations of constituents discussed in this report were less than 

the laboratory reporting level. Replicate samples provided 

information on the variability of analytical results caused by 

sample collection, processing, and analysis. Relative differences in concentrations in environmental and replicate 
Stream Hydrology and Water Quality 9

samples were less than 3 percent for constituents discussed 

in this report. These results indicate that sample collection, 

processing, and analysis did not introduce any variation in the 

environmental data to affect the interpretation of results. 

Quality-control procedures for the collection of 

continuous specific-conductance data followed procedures in 

Wagner and others (2006). The sensors were cleaned during 

each field visit for measuring streamflow or the collection of 

water-quality samples. Field calibration was performed if the 

cleaned sensor readings obtained during the calibration check 

differed by more than the calibration criteria (Wagner and 

others, 2006). 

Stream Hydrology and Water Quality

Local streamflow conditions during the study were above 

normal based on 78 years of streamflow record (1929–2007) 

at the USGS streamflow-gaging station Lamoille River at 

East Georgia, VT (station 04292500). Normal streamflow is 

defined as annual mean streamflow that falls within the 25thto 75th-percentile streamflow duration. The normal range of 

streamflow statistics for the period of record for the Lamoille 

River at East Georgia, VT, is 1,082 ft3/s at the 25th percentile 

and 1,408 ft3/s at the 75th percentile. Mean streamflows 

for water years 2006 and 2007 were 1,910 and 1,540 ft3/s, 

respectively (http://wdr.water.usgs.gov/). Annual mean 

discharge for 2007 was less than the annual mean discharge 

for 2006, reflecting a decrease in annual precipitation in 2007.

Total annual runoff (based on the annual average volume 

of water in each stream normalized for drainage area) for 

2006 at the three paired stations was 28.6 in. for Alder Brook, 

24.3 in. for Allen Brook, and 37.5 in. for Mill Brook. Total 

annual runoff for 2007 was 17.9 in. for Alder Brook, 17.2 in. 

for Allen Brook, and 24.7 in. for Mill Brook. Total runoff for 

the Alder Brook tributary station was 39.9 in. (partial year) 

and was greater than expected possibly due to unaccounted 

for drainage to the station. These comparisons show that total 

annual runoff in the watersheds of Alder and Allen Brooks was 

similar and total annual runoff in the Mill Brook watershed 

was greater than runoff in the other two watersheds. The 

difference was likely the result of lower topographic relief in 

the Alder and Allen Brook watersheds than in the Mill Brook 

watershed. The headwaters of Mill Brook originate on the 

western slopes of the Green Mountains. Precipitation also 

tends to be greater in the higher altitude mountainous terrain 

than in the lower altitude areas. 

Mean concentrations of Cl in the routine water-quality 

samples collected at upstream-sampling stations ranged from 

8.2 to 72 mg/L and those in samples collected at downstream 

stations ranged from 7.9 to 80.7 mg/L. Mean Cl loads in 

samples collected at upstream stations ranged from 1,100 

to 4,090 lb/d and those in samples collected at downstream 

stations ranged from 1,110 to 4,200 lb/d. Estimated mean 

annual Cl loads at upstream stations ranged from 402,000 to 

1,490,000 lb/yr and those at downstream stations ranged from 

405,000 to 1,530,000 lb/yr (table 2). 

In the following sections describing hydrology and water 

quality for each stream, concentrations of selected constituents 

and loads of Cl are summarized. Relations of streamflow to 

specific conductance and Cl concentrations are also summarized. Comparisons are made between (1) measured and 

estimated Cl concentrations to USEPA recommended chronic 

toxicity criteria to determine the frequency and duration of 

exceedances, and (2) the VTrans Cl application rates for winter maintenance to the estimated Cl load measured at each of 

the downstream stations. 

Estimated loads and yields of Cl at the sampling stations for the 2-year study period are presented in table 2 along 

with the 95-percent confidence intervals of the mean load, the 

standard error of prediction, and the ratio of the standard error 

of prediction to the mean load. The ratio of the standard error 

of prediction to the mean load standardizes the model error 

and provides a comparison among stations having large differences in load estimates. The prediction error ranged from 2.0 

to 6.1 percent of the mean loads. This indicates that the model 

error for the estimates of Cl loads was low. Mean streamflow, 

estimated loads and yields, and the 95-percent confidence 

intervals for Cl loads for individual years (2006 and 2007) for 

each station are presented in table 3.

Mill Brook at VT 117 near Essex Junction, VT, 

Stations 04289880 and 04289881

The Mill Brook stations above and below VT 117 near 

Essex Junction, VT, represent drainage from a two-lane 

highway in a rural setting. The Mill Brook watershed is 

predominantly a forested and agricultural area. The two-lane 

rural State highway VT 117 crosses Mill Brook between the 

upstream and downstream stations and serves traffic from 

interstate I-89 going to the rural communities of Jericho, 

Underhill, and parts of Essex, VT (fig. 2). The contributing 

drainage basins for the upstream and downstream stations 

are 16.3 and 16.4 mi2, respectively (fig. 2). The downstream 

station on Mill Brook has the lowest road density (1.7 mi/mi2) 

and percent impervious surface (0.52 percent) of the three 

downstream stations (table 1). Land use in the Mill Brook 

watershed is about 72 percent forest, 15 percent agriculture, 

9 percent wetlands, water, and barren, and 4 percent developed 

(table 1; fig. 1). 

Annual mean discharge for the years 2006 and 2007 

was 45 and 30 ft3/s, respectively. Daily mean streamflow and 

time distribution for water-quality samples are shown in 

figure 3A. The minimum and maximum streamflow at which 

water-quality samples were collected was 3.7 ft3/s and 

217 ft3/s, respectively. 

Continuous specific-conductance values and concentrations of Cl in the routine water-quality samples are shown in 

figure 3B and summary statistics are presented in tables 4 and 

5. The minimum and maximum specific-conductance value at 
10 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont Table 2. Estimated mean annual loads, yields, confidence intervals, standard error of prediction, and the ratio of the standard error of prediction to the mean annual load for chloride at sampling stations for the 2-year sampling period in Chittenden County, VT. [Numbers have been independently rounded; USGS, U.S. Geological Survey; lb/d, pounds per day; lb/yr, pounds per year; (lb/mi2)/yr, pounds per square mile per year] Site number (table 1; fig. 1) USGS station number Station name Mean load (lb/d) Mean load (lb/yr) Yield (lb/mi2)/yr 95-percent confidence interval Standard error of prediction (lb/yr) Ratio of standard error of prediction to mean load (percent) Lower (lb/yr) Upper (lb/yr)

1 04289880 Mill Brook above VT 117, near Essex Junction, VT 1,100 402,000 24,600 387,000 420,000 8,400 2.12 04289881 Mill Brook below VT 117, near Essex Junction, VT 1,110 405,000 24,700 391,000 423,000 8,030 2.03 04290160 Alder Brook above VT 289, near Essex Junction, VT 1,940 708,000 79,800 628,000 799,000 43,400 6.1

1

4 042901608 Alder Brook tributary at mouth, near Essex Junction, VT 280 93,800 1,900,000 92,100 98,800 1,710 1.85 04290161 Alder Brook below VT 289, near Essex Junction, VT 2,220 810,000 90,700 767,000 854,000 22,600 2.86 042903349 Allen Brook above VT 2A, near Essex Junction, VT 4,090 1,490,000 152,000 1,400,000 1,590,000 50,000 3.47 04290335 Allen Brook below VT 2A, near Essex Junction, VT 4,200 1,530,000 155,000 1,470,000 1,600,000 34,300 2.2

1Time period is from December 15, 2006, to November 15, 2007.
Stream Hydrology and Water Quality 11

Table 3. Estimated annual loads, yields, and confidence intervals for chloride by year at sampling stations in Chittenden County, VT.[Numbers have been independently rounded; USGS, U.S. Geological Survey; lb/d, pounds per day; lb/yr, pounds per year; (lb/mi2)/yr, pounds per square mile per year]

Site 

number

(table 1; 

fig. 1)

USGS 

station 

number

Station name Year

Mean 

streamflow

(in thousands 

of acre-feet)

Chloride

Load

(lb/d)

Load

(lb/yr)

Yield

(lb/mi2)/yr

95-percent 

confidence interval

Lower

(lb/yr)

Upper

(lb/yr)

1 04289880 Mill Brook above VT 117, near Essex Junction, VT 2006 32,600 1,290 471,000 28,900 449,000 489,000

2007 21,400 920 336,000 20,600 321,000 347,000

2 04289881 Mill Brook below VT 117, near Essex Junction, VT 2006 32,600 1,300 475,000 28,900 453,000 493,000

2007 21,400 930 339,000 20,700 329,000 354,000

3 04290160 Alder Brook above VT 289, near Essex Junction, VT 2006 13,600 2,420 883,000 99,600 767,000 1,010,000

2007 8,540 1,470 537,000 60,500 482,000 599,000

14 042901608 Alder Brook tributary at mouth, near Essex Junction, VT 2007 116 280 93,800 1,900,000 92,100 98,800

5 04290161 Alder Brook below VT 289, near Essex Junction, VT 2006 13,600 2,670 975,000 109,000 913,000 1,040,000

2007 8,540 1,770 646,000 72,300 613,000 675,000

6 042903349 Allen Brook above VT 2A, near Essex Junction, VT 2006 12,800 4,830 1,760,000 179,000 1,640,000 1,890,000

2007 9,050 3,350 1,220,000 124,000 1,150,000 1,300,000

7 04290335 Allen Brook below VT 2A, near Essex Junction, VT 2006 12,800 4,960 1,810,000 203,000 1,730,000 1,900,000

2007 9,050 3,450 1,260,000 141,000 1,200,000 1,310,000

1Time period is from December 15, 2006, to November 15, 2007.
12 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

which water-quality samples were collected was 58 and 

184 μS/cm, respectively. Mean specific conductance of the 

routine water-quality samples was 118 μS/cm at the upstream 

station and 110 μS/cm at the downstream station. Continuous 

specific conductance measurements found little difference 

between the upstream and downstream stations over the 2-year 

monitoring period (table 5). 

Mean Cl concentrations in the routine samples were 

8.2 mg/L at the upstream station and 7.9 mg/L at the 

downstream station (table 4). The relation between specificconductance values and Cl concentrations (fig. 4A) was used 

to estimate daily mean Cl concentrations on the basis of the 

continuous specific-conductance data collected at the station 

(fig. 4B); this regression relation had an R2 of .91. The 

estimated mean Cl concentrations based on this relation 

were 8.2 mg/L at the upstream station and 8.3 mg/L at the 

downstream station for the 2-year study period (table 5). 

The highest estimated daily mean Cl concentrations in 

2006 (12.6 mg/L upstream and 12.8 mg/L downstream) 

(table 5) occurred during periods of summer low flow in 

August following an intense summer rainstorm of 1.61 in. 

Possible explanations of higher Cl concentrations in the 

summer and fall is that road salt may be retained in soils and 

leached during precipitation events, and or other Cl sources 

are present in the stream watershed. 

The highest estimated daily mean Cl concentrations in 

2007 also occurred during a period of summer low flow and 

following a period of below-normal rainfall in September 

(16.0 mg/L at both stations) (table 5). In contrast, the lowest 

estimated daily-mean Cl concentrations occurred following 

rainstorms in October 2006 (2.4 mg/L downstream and 

2.1 mg/L upstream) and in April 2007 (2.3 mg/L downstream 

and 2.2 mg/L upstream), likely as a result of dilution. None 

of the Cl concentrations in the routine water-quality samples 

or the estimated daily mean Cl concentrations in samples 

from either the upstream or downstream stations exceeded the 

USEPA recommended chronic toxicity criterion of 230 mg/L 

or the acute toxicity criterion of 860 mg/L (U.S. Environmental Protection Agency, 1988) (fig. 4B; tables 4 and 5).

The January 2006 rain-on-snow event and its effects 

on concentrations of Cl in relation to stage are shown in 

figure 5A. Stage was used as a surrogate for discharge because 

ice in the stream affected the instantaneous-streamflow values 

and precluded the use of streamflow in the analysis. This event 

resulted in only a very slight rise in Cl concentrations 

(fig. 5A). Estimated maximum instantaneous Cl concentrations during this event were 8.9 mg/L upstream and 8.6 mg/L 

downstream (fig. 5A). The stage rise (apparent discharge 

increase) at the end of the day was attributed to ice jams 

(fig. 5A). 

The March 2007 snowmelt event and its effects on 

concentrations of Cl in relation to streamflow from March 2 

to March 5 are shown in figure 5B. The estimated maximum 

instantaneous Cl concentrations during this event were 

12.9 mg/L on March 3 at the downstream station and 

13.0 mg/L on March 2 at the upstream station (fig. 5B). 

Streamflow was stable during the melt period, decreasing slightly as Cl concentrations increased. The decrease in 

streamflow was likely the result of minor ice jams upstream 

from the Mill Brook stations. The reduced discharge may 

have contributed to slightly higher concentrations because of 

reduced dilution. 

The difference in the estimated Cl loads upstream and 

downstream of the state highway were calculated by subtracting the estimated upstream Cl load from the estimated 

downstream Cl load. This difference was 4,000 lbs in 2006 

and 3,000 lbs in 2007 (table 6; fig. 6). The portion of Rte 117 

draining to Mill Brook had an estimated 11,600 lbs of applied 

Cl from VTrans snowplow operations in the winter of 2006 

and 7,560 lbs in the winter of 2007 (table 6; fig. 6). VTrans 

maintained 0.47 lane-miles in the Mill Brook Basin, but an 

additional 0.17 lane-miles of other non-state roads in the 

watershed also are maintained and are not accounted for in the 

road-salt application estimate. The applied Cl amount from 

State deicing operations represents about 2 percent of the total 

annual Cl load downstream of the highway crossing. State 

applications were greater than the gain in Cl loads between the 

upstream and downstream stations in both years. Because the 

amount of applied Cl by VTrans is greater than the difference 

in Cl loads between the upstream and downstream stations, the 

applied Cl is likely being sequestered in the surrounding soils 

and vegetation.

Overall, since only about 2 percent of the total Cl load 

in Mill Brook may be attributed to VTrans road salt applications, inputs derived from other sources in the watershed 

account for nearly all of the Cl measured in samples collected 

at the Mill Brook stations. Low Cl concentrations in Mill 

Brook may result from two important basin characteristics, 

that is, the watershed is minimally urbanized and the highway 

density is relatively low. Moreover, the watershed area and 

discharge are twice those of the other study streams 

(table 1). Therefore, salt runoff from road-stream crossings 

can be diluted rapidly by relatively high streamflow and or 

assimilated into adjacent soils. 
Stream Hydrology and Water Quality 13 Figure 2. Location of upstream- and downstream-sampling stations, basin delineations, state road network, and photograph of the downstream-sampling station for Mill Brook at VT 117 near Essex Junction, VT, stations 04289880 and 04289881 (Refer to table 1 and figure 1 for additional station information).

Aerial photography acquired in 2003 by the U.S. Department of Agriculture, National Agriculture Imagery Program.Hydrography from the U.S. Geological Survey, 1:5,000-scale National Hydrography Dataset, 2008. Roads from the Vermont Agency of Transportation, 1:5,000-scale Road Centerlines, 2008.

72°54'

73°

44°28'

44°26'

EXPLANATION

Sampling-station  drainage basin

Upstream basinDownstream basin

Downstream station

04289881

Upstream station

04289880

Stream

Winooski

River

Mill Brook

Mill Brook

0 1 2 MILES

0 1 2 KILOMETERS

Stream-sampling station and number

Route 117

Barber Farm Road

Jericho

Aerial photography acquired in 2003 by the U.S. Department of Agriculture, National Agriculture Imagery Program.Hydrography from the U.S. Geological Survey, 1:5,000-scale National Hydrography Dataset, 2008. Roads from the Vermont Agency of Transportation, 1:5,000-scale Road Centerlines, 2008.

04289881
14 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 3. (A) Daily mean streamflow and time distribution of water-quality samples and (B) daily mean specific conductance 

and concentrations of chloride for Mill Brook at VT 117 near Essex Junction, VT, stations 04289880 and 04289881. 

0

100

200

300

400

500

600

700

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Daily mean streamflow

Water-quality sample

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

WATER YEAR

2006 2007

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

0

50

100

150

200

250

0

5

10

15

20

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Downstream station

WATER YEAR

2006 2007

0

50

100

150

200

250

0

5

10

15

20

Upstream station

Daily mean specific conductance

Chloride concentration

A

B
Stream Hydrology and Water Quality 15

Table 4. Summary statistics for values of specific conductance and pH and concentrations of chloride, sodium, calcium, potassium, 

magnesium, sulfate, and nitrite plus nitrate for routine water-quality samples collected at Mill Brook at VT 117, near Essex Junction, VT.

[Min, minimum; Med, median; Max, maximum]

Water-quality 

constituent1

Upstream site, station 04289880 Downstream site, station 04289881

Number of 

samples Min Mean Med Max Number of samples Min Mean Med Max

Specific conductance 24 58 118 118 183 35 58 110 114 184

pH 20 6.6 7.4 7.5 8.1 32 6.6 7.4 7.6 8.2

Chloride 24 3.0 8.2 7.9 17 35 3.0 7.9 7.5 17

Sodium 24 2.46 5.64 5.55 10.9 35 2.44 5.25 5.21 11.1

Calcium 24 6.32 12.8 12.6 20.1 35 6.27 11.6 11.5 20.5

Potassium 7 0.45 0.73 0.79 0.96 7 0.44 0.74 0.76 1.01

Magnesium 7 1.21 2.19 2.36 3.32 7 1.20 2.26 2.42 3.58

Sulfate 7 4.4 5.7 5.9 6.9 7 4.4 5.6 5.8 6.9

Nitrite plus nitrate 5 0.09 0.29 0.29 0.50 5 0.10 0.28 0.28 0.50

1

All constituents are dissolved and reported as milligrams per liter except specific conductance, which is reported as microsiemens per centimeter at 

25 degrees Celsius, and pH, which is reported as standard units.

Table 5. Daily mean summary statistics for continuous specific conductance and estimated continuous chloride concentrations at 

Mill Brook at VT 117, near Essex Junction, VT.

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; Min, minimum; Med, median; Max, maximum]

Water-quality constituent Upstream site, station 04289880 Downstream site, station 04289881

Min Mean Med Max Min Mean Med Max

Specific conductance (μS/cm) 45 113 109 201 45 114 110 202

Chloride (mg/L) 2.2 8.2 7.8 16 2.3 8.3 8.0 16
16 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 4. (A) Relation between specific conductance and chloride concentration in routine water-quality samples 

and (B) estimated daily mean chloride concentrations and chloride concentration in routine water-quality samples for 

the study period at Mill Brook at VT 117 near Essex Junction, VT, station 04289881. 

SPECIFIC CONDUCTANCE, 

IN MICROSIEMENS PER CENTIMETER

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

CHLORIDE CO

NCEN

TRA

TIO

N, IN

MILLIGRA

MS PER LITER

A

0

5

10

15

20

0 50 100 150 200 250

R2 = 0.91

0

5

10

15

20

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Estimated daily mean chloride concentration

Measured chloride concentration

WATER YEAR

2006 2007

U.S. Environmental Protection Agency recommended 

 chronic toxicity criterion = 230 milligrams per liter

B

y = 0.087x – 1.732
Stream Hydrology and Water Quality 17

Figure 5. Relation of estimated chloride concentration to (A) stream stage during a rain-on-snow event 

(January 18, 2006) and (B) streamflow during a snowmelt event (March 2007) at Mill Brook at VT 117 near 

Essex Junction, VT, stations 04289880 and 04289881. CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

TIME OF DAY, JANUARY 18, 2006

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

DATE AND TIME

A

B

0

2

4

6

8

10

12

0

1

2

3

4

5

6

7

8

00:00 06:00 12:00 18:00 24:00

Estimated chloride concentration, at upstream site

Estimated chloride concentration, at downstream site

Stream stage

Cumulative precipitation

0

5

10

15

20

0

5

10

15

20

00:00 24:00 48:00 72:00 96:00

Estimated chloride concentration, at upstream site

Estimated chloride concentration, at downstream site

Streamflow

Air temperature

STREAMFLOW, IN CUBIC FEET PER SECOND

TEMPERATURE, IN DEGREES CELSIUS

2007

March 2 March 3 March 4 March 5

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter

STAGE, IN FEET

PRECIPITATION, IN INCHES
18 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Table 6. Difference in the estimated annual stream chloride load at upstream and downstream sampling stations and estimated 

Vermont Agency of Transportation (VTrans) applied chloride load at sampling sites in Chittenden County, VT. 

[Numbers have been independently rounded; USGS, U.S. Geological Survey; lb/yr, pounds per year]

Site number

(table 1; fig. 1)

USGS station numbers

(upstream, downstream) Station name Year

Difference in 

chloride load1

(lb/yr)

Estimated 

VTrans load2

(lb/yr)

1 04289880, 04289881 Mill Brook at VT 117, near Essex Junction, VT 2006 4,000 11,600

2007 3,000 7,560

3 04290160, 04290161 Alder Brook at VT 289, near Essex Junction, VT 2006 92,000 55,700

2007 109,000 67,800

6 042903349, 04290335 Allen Brook at VT 2A, near Essex Junction, VT 2006 50,000 12,000

2007 40,000 8,660

1

Downstream load minus upstream load. 

2

Estimated chloride load applied by Vermont Agency of Transportation (source of data). 

Figure 6. Estimated applied road deicing and measured 

chloride load for Mill Brook at VT 117 near Essex Junction, VT, 

station 04289881.

0

2,000

4,000

6,000

8,000

10,000

12,000

2006 2007

Applied (estimated)

Measured

CHLORIDE LOAD, IN POUNDS PER YEAR

YEAR
Stream Hydrology and Water Quality 19

Alder Brook at VT 289, near Essex Junction, VT, 

Stations 04290160 and 04290161

Alder Brook above and below VT 289 near Essex 

Junction, VT, are stations that represent drainage from a twolane State highway, constructed on a four-lane right-of-way. 

The highway was opened in October 1993 and is a segment 

of the proposed Chittenden County Circumferential Highway. 

The completed segment links VT 117 to VT 2A in Essex. 

The upstream station has a drainage area of 8.87 mi2 and is 

upstream from both a highway culvert and the confluence of 

a small tributary, and the downstream station has a drainage 

area of 8.93 mi2 (table 1; fig. 7). The drainage area of the 

downstream station on Alder Brook has a greater road density 

(3.8 mi/mi2) and percent impervious surface area (3.6 percent) 

than the downstream station on Mill Brook and a similar road 

density and percent impervious surface to the downstream 

station on Allen Brook (table 1). The Alder Brook watershed 

is predominantly an agricultural and forested area. Land use in 

the Alder Brook watershed is about 47 percent agricultural, 

34 percent forested, 10 percent wetlands and water, and 

9 percent developed (table 1; fig. 1). 

Annual mean discharge for the years 2006 and 2007 was 

18.8 and 11.8 ft3/s, respectively. Daily mean streamflow and 

time distribution for water-quality samples are shown 

in figure 8A. The minimum and maximum streamflow at 

which water-quality samples were collected was 0.70 and 

121 ft3/s, respectively. 

Continuous specific-conductance values and 

concentrations of Cl in the routine water-quality samples 

are shown in figure 8B and summary statistics are presented 

in tables 7 and 8. The minimum and maximum specificconductance value at which water-quality samples were 

collected was 148 and 727 μS/cm, respectively. Mean specific 

conductance of the routine water-quality samples was 

349 μS/cm at the upstream station and 380 μS/cm at the 

downstream station. Mean continuous specific conductance 

measurements (table 8) were similar to the mean specific 

conductance values of the routine water-quality samples 

at both the upstream and downstream stations. The mean 

continuous specific conductance value over the 2-year 

monitoring period was 12 percent greater downstream than 

the upstream mean value (table 8).

Mean Cl concentrations in the routine samples were 

39.3 mg/L at the upstream station and 52.3 mg/L at the 

downstream station (table 7). The relation between specificconductance values and Cl concentrations at the downstream 

sampling (fig. 9A) was used to estimate daily mean Cl 

concentrations on the basis of the continuous specificconductance data collected at the station (fig. 9B); the 

regression relation had an R2 of 0.86. Estimated mean Cl 

concentrations during 2006–2007 generated from this relation 

were 46.9 mg/L at the upstream station and 54.3 mg/L at the 

downstream station (table 8). The highest estimated daily 

mean Cl concentration in 2006 for the downstream station 

(112 mg/L) occurred during a period of summer low flow in 

August (fig. 9B) following an intense summer rainstorm. This 

indicates that Cl may be stored in streambed sediments and 

nearby soils, or that there are other sources of Cl in the Alder 

Brook Basin.

The greatest estimated daily mean Cl concentration 

at the downstream station in 2007 (128 mg/L) occurred 

during a period of snowmelt in March (fig. 9B). Estimated 

Cl concentrations greater than 100 mg/L were observed at 

Alder Brook in August 2006 and October 2007 following 

intense rainstorms. In contrast, the lowest estimated daily 

mean Cl concentration at the downstream station (7.7 mg/L) 

also occurred following a rainstorm in October 2006. The 

low concentration was likely a result of dilution. None of the 

Cl concentrations in the routine water-quality samples or the 

estimated daily mean Cl concentrations in samples from either 

the upstream- or downstream-sampling stations exceeded the 

USEPA recommended chronic toxicity criterion of 230 mg/L 

or the acute toxicity criterion of 860 mg/L (figs. 8B and 9B; 

tables 7 and 8).

The January 2006 rain-on-snow event and its effects on 

concentrations of Cl in relation to stream stage are shown in 

figure 10A. Stream stage was used as a surrogate for discharge, in this case, because of the effects of ice. The stage 

measurement reading did not change substantially during the 

beginning of the event, indicating that runoff was small. Cl 

concentrations increased at the downstream station prior to 

an increase at the upstream station, possibly indicating that 

runoff containing a higher Cl concentration was discharging to 

the stream between the two stations. The estimated maximum 

instantaneous Cl concentration during this event was 

219 mg/L at the downstream station (fig. 10A). The highest 

Cl concentration was observed just prior to the large rise in 

stream stage. The Cl concentration decreased as streamflow 

increased as a result of dilution (fig. 10A). 

The March 2007 snowmelt event and its effects on 

concentrations of Cl in relation to streamflow from March 2 

to March 5 are shown in figure 10B. The small increase in 

Cl concentration at the downstream station only (fig. 10B) 

indicates that Cl inputs from melting snow along the highway 

were discharging to Alder Brook below the upstream station. 

An increase in Cl concentration was observed concurrently 

at both stations on the evening of March 2. Chloride 

concentrations decreased (fig. 10B), and snowmelt did not 

occur again until mid-day on March 3, as air temperature 

increased (fig. 10B). A slight increase in Cl concentration was 

again observed at the downstream station, prior to the large 

increase in Cl concentrations at both stations (fig. 10B). The 

estimated maximum instantaneous Cl concentration during 

this event was 232 mg/L at both stations (fig. 10B). These 

similar concentrations indicate that the dominant source(s) 

of Cl was further upstream from the stations. The USEPA 

recommended chronic toxicity criterion of 230 mg/L was 

slightly exceeded during the event, but the associated USEPA 

4-day average criterion was not exceeded (U.S. Environmental 

Protection Agency, 1988) (fig. 10B). 
20 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 7. Location of upstream- and downstream-sampling stations, basin delineations, state road network, and photograph of the downstream- and tributary-sampling stations for Alder Brook at VT 289 near Essex Junction, VT, stations 04290160, 042901608, and 04290161 (Refer to table 1 and figure 1 for additional site information).

73°03'

73°05'15"

44°

35'

15"

44°

33'

44°

30'

45" 0 1 2 MILES

0 1 2 KILOMETERS

EXPLANATION

Sampling-station  drainage basin

Upstream basinDownstream basin

Stream

Tributary sampling station

Downstream sampling station Road

Stream-sampling station and number

Detention pond basin

Route 289

Route 15

Route 15

Essex

Way

Lang

Drive

Essex 

Center

Lake Champlain

Upstream station

04290160

Downstream station

04290161

Pond station

042901608 Upstream station

04290160

Downstream station

04290161

Pond station

042901608

Detention pond Pond-sampling station and number

Alder

Brook

redl A or B ok

Tributary sampling station

Downstream sampling station

Aerial photography acquired in 2003 by the U.S. Department of Agriculture, National Agriculture Imagery Program. Hydrography from the U.S. Geological Survey, 1:5,000-scale, National Hydrography Dataset, 2008. Roads from the Vermont Agency of Transportation, 1:5,000-scale Road Centerlines, 2008.

04290160

042901608
Stream Hydrology and Water Quality 21

Figure 8. (A) Daily mean streamflow and time distribution of water-quality samples and (B) daily mean specific 

conductance and concentrations of chloride for Alder Brook at VT 289 near Essex Junction, VT, stations 04290160 

and 04290161. 

0

50

100

150

200

250

300

350

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Daily mean streamflow

Water-quality sample

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

WATER YEAR

2006 2007

0

200

400

600

800

1,000

0

50

100

150

200

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Downstream station

WATER YEAR

2006 2007

0

200

400

600

800

1,000

0

20

40

60

80

100

Upstream station

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

A

B

Daily mean specific conductance

Chloride concentration
22 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

The difference in the estimated Cl loads upstream and 

downstream of the State highway were 92,000 lbs in 2006 

and 109,000 lbs in 2007 (table 6; fig. 11). The state highway 

draining to Alder Brook received an estimated 55,700 lbs of 

applied Cl from VTrans snowplow operations in the winter of 

2006 and 67,800 lbs in 2007 (table 6; fig. 11). VTrans maintained 1.32 lane-miles but an additional 0.76 lane-miles of 

other non-state roads in the watershed are maintained and are 

not accounted for in this estimate. The applied Cl amount from 

State snowplow operations represents about 9 and 17 percent 

of the total annual Cl load downstream of Rte 289 in 2006 and 

2007, respectively, and about 60 percent of the difference in 

the loads at the upstream and downstream stations. Comparison of the estimated Cl loads in Alder Brook to Cl applications by VTrans indicate that most of the Cl loads in the Alder 

Brook watershed likely originates from other sources. Some 

of the Cl in the stream may also be originating from shallow 

groundwaters and nearby soils that have retained Cl applied in 

previous years. Another possible source of salt to Alder Brook 

between the upstream and downstream stations is the Alder 

Brook tributary. Streamflow and Cl concentrations and loads 

from this tributary are described in the following section.

Table 7. Summary statistics for values of specific conductance and pH and concentrations of chloride, sodium, calcium, potassium, 

magnesium, sulfate, and nitrite plus nitrate for routine water-quality samples collected at Alder Brook at VT 289, near Essex Junction, VT.

[Min, minimum; Med, median; Max, maximum]

Water-quality 

constituent1

Upstream site, station 04290160 Downstream site, station 04290161

Number of 

samples Min Mean Med Max Number of samples Min Mean Med Max

Specific conductance 28 148 349 338 620 38 155 380 349 727

pH 24 7.3 7.7 7.8 8.9 33 6.7 7.5 7.7 8.7

Chloride 28 11.1 39.3 36.1 78.2 38 12.2 52.3 41.0 147

Sodium 28 8.1 24.4 22.8 45.3 38 9.0 29.8 24.7 80.9

Calcium 28 13.2 32.1 31.7 59.5 38 14.0 30.5 29.4 61.8

Potassium 8 0.99 1.61 1.72 1.97 7 1.00 1.57 1.61 1.94

Magnesium 8 3.12 8.10 7.15 15.4 7 3.26 7.89 7.06 16.9

Sulfate 8 5.3 12.0 11.5 21.4 7 5.74 13.2 11.9 25.5

Nitrite plus nitrate 6 0.18 0.35 0.30 0.68 5 0.19 0.36 0.31 0.68

1

All constituents are dissolved and reported as milligrams per liter except specific conductance, which is reported as microsiemens per centimeter at 

25 degrees Celsius, and pH, which is reported as standard units.

Table 8. Daily mean summary statistics for continuous specific conductance and estimated continuous chloride concentrations at 

Alder Brook at VT 289, near Essex Junction, VT.

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; Min, minimum; Med, median; Max, maximum]

Water-quality constituent Upstream site, station 04290160 Downstream site, station 04290161

Min Mean Med Max Min Mean Med Max

Specific conductance (μS/cm) 109 349 320 777 131 390 357 805

Chloride (mg/L) 3.8 46.9 41.6 124 7.7 54.3 48.3 128
Stream Hydrology and Water Quality 23

Figure 9. (A) Relation between specific conductance and chloride concentration in routine water-quality samples and 

(B) estimated daily mean chloride concentrations and chloride concentration in routine water-quality samples for the study 

period at Alder Brook at VT 289 near Essex Junction, VT, station 04290161.

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

y = 0.18x − 16.169

CHLORIDE CO

NCEN

TRA

TIO

N, IN

MILLIGRA

MS PER LITER

WATER YEAR

A

B

R2 = 0.86

0

20

40

60

80

100

120

140

160

180

100 200 300 400 500 600 700 800 900

0

50

100

150

200

250

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Estimated daily mean chloride concentration

Measured chloride concentration

2006 2007

U.S. Environmental Protection Agency 

 recommended chronic toxicity criterion
24 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 10. Relation of estimated chloride concentration to (A) stream stage during a rain-on-snow event 

(January 18, 2006) and (B) streamflow during a snowmelt event (March 2007) at Alder Brook at VT 289 near Essex 

Junction, VT, stations 04290160 and 04290161.

0

50

100

150

200

250

300

0

1

2

3

4

5

00:00 06:00 12:00 18:00 24:00

Stream stage

0

50

100

150

200

250

300

0

2

4

6

8

10

00:00 24:00 48:00 72:00 96:00

2007

March 2 March 3 March 4 March 5

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

TIME OF DAY, JANUARY 18, 2006

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

A

B

Estimated chloride concentration, at downstream site

Estimated chloride concentration, at upstream site

Cumulative precipitation

STAGE, IN FEET

PRECIPITATION, IN INCHES

STREAMFLOW, IN CUBIC FEET PER SECOND

TEMPERATURE, IN DEGREES CELSIUS

DATE AND TIME

Estimated chloride concentration, at upstream site

Estimated chloride concentration, at downstream site

Streamflow

Air temperature

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter
Stream Hydrology and Water Quality 25

Alder Brook Tributary at Mouth near 

Essex Junction, VT, Station 042901608

The Alder Brook tributary station was established in 

December 2006 to expand and supplement data collected at 

the paired Alder Brook stations. The Alder Brook tributary is a 

constructed culverted drainage system and retention basin with 

a topographically defined drainage area of 0.05 mi2. The area 

draining to the Alder Brook tributary has the highest 

road density (40 mi/mi2) and percent impervious surface 

(20 percent) of all the stations monitored (table 1). Direct 

overland flow from the highway can enter the culverted 

system. This water then discharges to a ditch about 250 ft 

upstream from a retention basin (also known as a sedimentation pool); the surface area of the retention basin is about 

two-thirds aquatic vegetation. The retention basin collects 

drainage from a highway interchange area. Water flowing from 

the outlet of the retention basin discharges into Alder Brook 

upstream of VT 289, just downstream from the upstream Alder 

Brook station (fig. 7). 

Mean discharge from December 2006 to November 2007 

was 0.17 ft3/s. Daily mean streamflow and time distribution for 

water-quality samples are shown in figure 12A. The minimum 

and maximum streamflow at which water quality samples 

were collected was 0.08 and 0.98 ft3/s, respectively. 

Continuous specific-conductance values and concentrations of Cl for the routine water-quality samples are shown in 

figure 12B and summary statistics presented in tables 9 and 

10. The minimum, mean and maximum specific-conductance 

value at which water-quality samples were collected was 

1,095, 1,810 and 2,330 μS/cm, respectively. 

The mean Cl concentration in the routine water-quality 

samples was 449 mg/L (table 9). The relation between 

specific-conductance values and Cl concentrations (fig. 13A) 

was used to estimate daily mean Cl concentrations on the basis 

of the continuous specific-conductance data collected at the 

station (fig. 13B); this regression relation had an R2 of 0.93. 

The estimated mean Cl concentration was 292 mg/L during 

the 1-year monitoring period (table 10). The highest estimated 

daily mean Cl concentration was 721 mg/L in March 2007 

(fig. 13B), during a snowmelt period and 3 days after a peak 

in streamflow. The minimum estimated daily mean Cl concentration (31.0 mg/L) occurred in October 2007, following an 

intense fall rainstorm indicating that Cl concentrations were 

diluted at this time. The USEPA recommended chronic toxicity criterion of 230 mg/L was exceeded about 65 percent of the 

monitoring period (fig. 13B). The recommended acute toxicity 

criterion of 860 mg/L was not exceeded (fig. 13B).

Samples collected in March 2007 were used to describe 

the effects of snowmelt on Cl concentrations in the tributary 

(fig. 14). An increase in the estimated Cl concentration at 

Alder Brook tributary was observed on March 4. The estimated maximum instantaneous Cl concentration during this 

event was 460 mg/L (fig. 14). During the period of 

March 15–22 instantaneous Cl concentrations were greater 

than 600 mg/L with a maximum instantaneous concentration 

of nearly 800 mg/L. The dominant source of Cl was most 

likely from highway runoff and other sources in the drainage 

area. The USEPA recommended chronic toxicity criterion of 

230 mg/L was exceeded during the event and for the remainder of the month of March and the snowmelt period (fig. 14). 

There are no VTrans estimates of the road-salt applied in 

the drainage area of the tributary. The estimated Cl load from 

the Alder Brook tributary from December 2006 to November 

2007 is 93,800 lbs (table 2), this load amount is 86 percent of 

the difference in the upstream and downstream loads at the 

paired monitoring stations in 2007. As such, the Alder Brook 

tributary appears to be a major contributor to the increase in Cl 

loads in Alder Brook.

Streamflow and runoff data indicate that the actual 

contributing drainage area to the Alder Brook tributary may 

be at least two times the topographically defined drainage 

area. Watershed boundaries were redefined by high-resolution 

light-detection and ranging (LiDAR) data. The use of LiDAR 

data, with its increased terrain detail, did not result in any 

substantial change in the watershed area. This indicates 

that some unaccounted-for sources of flow and Cl, such 

as additional parking lots and roads may be present in the 

tributary watershed or some runoff entering swales (possibly 

originating outside of the defined drainage area) may infiltrate 

soils and percolate to groundwater. 

Figure 11. Estimated applied road deicing and measured 

chloride load for Alder Brook at VT 289 near Essex Junction, VT, 

station 04290161.

0

20,000

40,000

60,000

80,000

100,000

120,000

2006 2007

Applied (estimated)

Measured

CHLORIDE LOAD, IN POUNDS PER YEAR

YEAR
26 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 12. (A) Daily mean streamflow and time distribution of water-quality samples and (B) daily mean specific 

conductance and concentrations of chloride for Alder Brook tributary at mouth near Essex Junction, VT, station 042901608. 

0

500

1,000

1,500

2,000

2,500

3,000

0

100

200

300

400

500

600

700

Jan. 1 Apr. 1 Jul. 1 Oct. 1

SPECIFIC CO

NDUCT

A

NCE, IN

MICROSIEMENS PER CEN

TIMETER

CHLORIDE CO

NCEN

TRA

TIO

N, IN

MILLIGRA

MS PER LITER

WATER YEAR

2007 2008

0

0.5

1

1.5

2

Jan. 1 Apr. 1 Jul. 1 Oct. 1

Daily mean streamflow

Water-quality sample

STREA

MFLO

W, IN CUBIC FEET PER SECO

ND

WATER YEAR

2007 2008

A

B

Daily mean specific conductance

Chloride concentration
Stream Hydrology and Water Quality 27

Table 9. Summary statistics for values of specific conductance and pH and concentrations of chloride, sodium, 

calcium, potassium, magnesium, sulfate, and nitrite plus nitrate for routine water-quality samples collected at 

Alder Brook tributary at mouth near Essex Junction, VT.

[Min, minimum; Med, median; Max, maximum]

Water-quality constituent1 Number of 

samples Min Mean Med Max

Specific conductance 24 1,095 1,810 1,980 2,330

pH 24 7.5 7.9 7.9 8.4

Chloride 24 191 449 506 634

Sodium 24 99 232 260 321

Calcium 24 34.8 82.6 85.8 103

Potassium 3 1.44 1.76 1.59 2.25

Magnesium 3 18.8 20.7 21.2 22.0

Sulfate 3 50.2 56.6 56.6 63.2

Nitrite plus nitrate 2 0.15 0.39 0.39 0.64

1

All constituents are dissolved and reported as milligrams per liter except specific conductance, which is reported as microsiemens 

per centimeter at 25 degrees Celsius, and pH, which is reported as standard units.

Table 10. Daily mean summary statistics for continuous specific conductance and 

estimated continuous chloride concentrations at Alder Brook tributary at mouth near 

Essex Junction, VT.

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; Min, minimum; 

Med, median; Max, maximum]

Water-quality constituent Min Mean Med Max

Specific conductance (μS/cm) 578 1,350 1,240 2,620

Chloride (mg/L) 31.0 292 255 721
28 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 13. (A) Relation between specific conductance and chloride concentration in the routine water-quality samples 

and (B) estimated daily mean chloride concentrations and chloride concentration in routine water-quality samples for the 

study period at Alder Brook tributary at mouth near Essex Junction, VT, station 042901608.

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

100

200

300

400

500

600

700

1,000 1,500 2,000 2,500

y = 0.337x − 164.31

R2 = 0.93

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

WATER YEAR

A

B

0

100

200

300

400

500

600

700

800

Jan. 1 Apr. 1 Jul. 1 Oct. 1

2007

Acute criteria = 860 milligrams per liter Estimated mean daily chloride concentration

Measured chloride concentration

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter
Stream Hydrology and Water Quality 29

Figure 14. Relation of estimated chloride concentration to streamflow during a snowmelt event (March 2007) at Alder Brook 

tributary at mouth near Essex Junction, VT, station 042901608. 

CHLORIDE CO

NCEN

TRA

TIO

N, IN

MILLIGRA

MS PER LITER

0

100

200

300

400

500

600

700

800

0

0.5

1

1.5

2

2.5

2 6 10 14 18 22 26 30

Estimated chloride concentration

Streamflow

Air temperature

MARCH 2007

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter

TEMPERATURE, IN DEGREES CELSIUS X 10

STREAMFLOW, IN CUBIC FEET PER SECOND
30 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Allen Brook at VT 2A near Essex Junction, VT, 

Stations 042903349 and 04290335

Allen Brook sampling stations above and below VT 2A 

near Essex Junction, VT, represent drainage from a twolane State highway that is the major road corridor between 

Interstate I-89 and the village of Essex Junction. The Allen 

Brook drainage basin is predominantly agricultural and 

forested, but the lower part of the watershed along VT 2A 

near Tafts Corner, VT, has experienced extensive growth and 

development in the last 2 decades. The contributing drainage 

basins for the upstream and downstream stations are 9.85 

and 9.88 mi2, respectively (fig. 15). The area draining to the 

downstream station on Allen Brook has a higher road density 

(4.2 mi/mi2) and percent impervious surface (4.8 percent) than 

the drainage to the downstream station on Mill Brook and a 

similar road density compared to the downstream station on 

Alder Brook (table 1). Land use in the Allen Brook watershed 

is about 50 percent forest, 33 percent agriculture, 13 percent 

developed, and 4 percent wetlands and barren (fig. 1). 

Annual mean discharge for the years 2006 and 2007 was 

17.7 and 12.5 ft3/s, respectively. Daily mean streamflow and 

time distribution for water-quality samples are shown in 

figure 16A. The minimum and maximum streamflow at 

which water-quality samples were collected was 0.22 and 

268 ft3/s, respectively. 

Continuous specific-conductance values and concentrations of Cl in the routine water-quality samples are shown in 

figure 16B and summary statistics are presented in tables 11 

and 12. The minimum and maximum specific-conductance 

values at which water-quality samples were collected was 

268 and 800 μS/cm, respectively. Mean specific conductance 

of the routine water-quality samples was 503 μS/cm and 

500 μS/cm at the upstream and downstream stations, respectively. There was a minor increase (less than 1 percent) in the 

mean of the continuous specific conductance values between 

the upstream and downstream stations.

Mean Cl concentrations in the routine samples were 

72.7 mg/L at the upstream station and 80.7 mg/L at the 

downstream station (table 11). The relation between specificconductance values and Cl concentrations (fig. 17A) was used 

to estimate daily mean Cl concentrations on the basis of the 

continuous specific-conductance data collected at the station 

(fig. 17B); this regression relation had an R2 of 0.87. Estimated 

mean daily Cl concentrations based on this relation were 

82.1 mg/L at the upstream station and 83.1 mg/L at the downstream station for the 2-year study period (table 12). Allen 

Brook had the highest estimated mean Cl concentrations and 

was the most urbanized of the three streams studied. Urbanization or road density and Cl concentrations can be positively 

correlated (Nimiroski and Waldren, 2002), which may explain 

the elevated Cl levels in Allen Brook. The highest estimated 

daily mean Cl concentrations in 2006 (122 mg/L upstream and 

124 mg/L downstream) were measured during August 

(fig. 17B) indicating that a continuous upstream source and 

(or) reduced dilution influences the maximum concentrations 

in Allen Brook. 

The highest estimated daily mean Cl concentration in 

2007 at the downstream station was 161 mg/L during a period 

of summer low flow (fig. 17B). Summer base flow was lower 

in 2007 than in 2006 because rainfall was lower. In contrast, 

the lowest daily mean Cl concentrations at the downstream 

station (25.0 and 23.3 mg/L) occurred following rainstorms in 

May 2006 and December 2007, respectively. None of the Cl 

concentrations in the routine water-quality samples or the estimated daily mean Cl concentrations at the downstream station 

exceeded the USEPA recommended chronic toxicity criterion 

of 230 mg/L or the acute toxicity criterion of 860 mg/L 

(fig. 17B; tables 11 and 12).

The January 2006 rain-on-snow event and its effects 

on instantaneous concentrations of Cl in relation to stream 

stage are shown in figure 18A. Stream stage was used as a 

surrogate for discharge, in this case, because the stream was 

ice-affected. Estimated Cl concentrations at the downstream 

station increased prior to an increase in the Cl concentration at 

the upstream station. This initial increase in Cl concentration 

at the downstream station is likely the result of direct runoff 

of salt from the bridge and roadway. However, Cl concentrations at both monitoring stations eventually increased with a 

gradual increase in stage (fig. 18A) indicating other watershed 

sources of Cl were contributing to the observed Cl concentrations. Estimated maximum instantaneous Cl concentrations 

during this event were 149 mg/L at the upstream station and 

156 mg/L at the downstream station (fig. 18A). Cl concentrations decreased sharply as streamflow increased. Maximum 

streamflow occurred about 8 hours after the maximum Cl concentration was observed. Instantaneous Cl concentrations did 

not exceed the USEPA recommended chronic toxicity criterion 

of 230 mg/L during this event. 

The March 2007 snowmelt event and its effects on 

instantaneous concentrations of Cl in relation to streamflow 

from March 2 to 5 are shown in figure 18B. A slight increase 

in Cl concentration was observed on March 2. Because this 

increase occurred long after the daily maximum air temperature was reached, it is likely that the Cl concentration 

increased in response to Cl sources upstream. The estimated 

maximum instantaneous Cl concentrations were 195 mg/L at 

the upstream station and 184 mg/L at the downstream station 

on March 3 (fig. 18B). Instantaneous Cl concentrations did not 

exceed the USEPA recommended chronic toxicity criterion of 

230 mg/L during this event. 
Stream Hydrology and Water Quality 31 Figure 15. Location of upstream- and downstream-sampling stations, basin delineations, state road network, and photograph of the downstream- sampling station for Allen Brook at VT 2A near Essex Junction, VT, stations 042903349 and 04290335 (Refer to table 1 and figure 1 for additional site information). 0 1 2 MILES 0 1 2 KILOMETERS

EXPLANATION

Sampling-station  drainage basin

Upstream basinDownstream basin

StreamRoadStream-sampling station and number

73°03'

73°06'

44°

27'

30"

44°

25'

04290335

Aerial photography acquired in 2003 by the 

U.S. Department of Agriculture, National Agriculture Imagery Program.Hydrography from the U.S. Geological Survey, 1:5,000-scale National Hydrography Dataset, 2008. Roads from the Vermont Agency of Transportation, 1:5,000-scale Road Centerlines, 2008.

Route 2

Interstate 89

Richmond

Camels Hump Bolton Mountain

Williston

Moun

at ni

V ei w

o R ad Allen Brook

Route 2A 

Route 2

Interstate 89

Richmond

Camels Hump Bolton Mountain

Williston

Moun

at ni

V ei w

o R ad

Upstream station

042903349

Downstream station

04290335

Allen Brook

Route 2A 

nell A

or B ok

Aerial photography acquired in 2003 by the U.S. Department of Agriculture, National Agriculture Imagery Program.Hydrography from the U.S. Geological Survey, 1:5,000-scale National Hydrography Dataset, 2008. Roads from the Vermont Agency of Transportation, 1:5,000-scale Road Centerlines, 2008.
32 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 16. (A) Daily mean streamflow and time distribution of water-quality samples and (B) daily mean specific conductance 

and concentrations of chloride for Allen Brook at VT 2A near Essex Junction, VT, stations 042903349 and 04290335. 

0

200

400

600

800

1,000

0

50

100

150

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Downstream station

WATER YEAR

2006 2007

0

200

400

600

800

1,000

0

50

100

150

Daily mean specific conductance Upstream station

Chloride concentration

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

0

50

100

150

200

250

300

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Daily mean streamflow

Water-quality sample

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

WATER YEAR

2006 2007

A

B
Stream Hydrology and Water Quality 33

The difference in the estimated Cl load upstream and 

downstream of the State highway was 50,000 lbs in 2006 and 

40,000 lbs in 2007 (table 6; fig. 19). The Allen Brook study 

area received an estimated 12,000 lbs of applied Cl from 

VTrans snowplow operations in the winter of 2006 and 

8,660 lbs in the winter of 2007 (table 6; fig. 19). VTrans maintained 0.87 lane-miles but an additional 0.73 lane-miles of 

other non-state roads in the watershed are maintained and are 

not accounted for in the VTrans application rates. The applied 

Cl amount from State snowplow operations represented 

(1) less than 1 and about 3 percent of the total annual Cl load 

downtream of Rte 2A in 2006 and 2007, respectively, and 

(2) about 20 percent of the difference between the upstream 

and downstream Cl loads. All of the Cl being applied by 

VTrans does not appear to be transported to Allen Brook during snowmelt events and may be stored in soils adjacent to the 

roadway. This stored Cl is likely released throughout the year 

and may be partially responsible for greater concentrations 

of Cl in the brook during low-flow periods. The dominant 

sources of Cl in Allen Brook at the monitoring stations are not 

known, but may include other roads and areas deiced in winter 

months and septic systems that are upstream of the stations. 

Table 12. Daily mean summary statistics for continuous specific conductance and estimated continuous chloride concentrations at 

Allen Brook at VT 2A, near Essex Junction, VT.

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; Min, minimum; Med, median; Max, maximum]

Water-quality constituent Upstream site, station 042903349 Downstream site, station 04290335 

Min Mean Med Max Min Mean Med Max

Specific conductance (μS/cm) 212 506 480 942 204 511 486 930

Chloride (mg/L) 24.6 82.1 76.8 163 23.3 83.1 77.8 161

Table 11. Summary statistics for values of specific conductance and pH and concentrations of chloride, sodium, calcium, potassium, 

magnesium, sulfate, and nitrite plus nitrate for routine water-quality samples collected at Allen Brook at VT 2A, near Essex Junction, VT. 

[Min, minimum; Med, median; Max, maximum]

Water-quality constituent1

Upstream site, station 042903349 Downstream site, station 04290335 

Number of 

samples Min Mean Med Max Number of samples Min Mean Med Max

Specific conductance 28 268 503 500 798 46 269 500 491 800

pH 25 7.4 7.8 7.9 8.5 42 7.1 7.6 7.7 8.5

Chloride 28 29.4 72.7 72.1 142 46 29.3 80.6 77.9 146

Sodium 28 19.0 43.6 42.4 79.4 46 7.7 45.5 43.2 83.7

Calcium 28 21.7 39.2 39.1 60.6 46 15.9 35.0 37.1 60.3

Potassium 8 1.29 1.95 1.92 3.01 7 1.34 1.94 1.81 3.11

Magnesium 8 5.14 9.62 8.98 16.8 7 5.15 9.12 8.96 17.3

Sulfate 8 8.1 12.9 13.5 16.9 7 8.2 12.7 13.4 16.5

Nitrite plus nitrate 6 0.06 0.26 0.26 0.56 5 0.04 0.30 0.31 0.57

1

All constituents are dissolved and reported as milligrams per liter except specific conductance, which is reported as microsiemens per centimeter at 

25 degrees Celsius, and pH, which is reported as standard units.
34 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Figure 17. (A) Relation between specific conductance values and chloride concentration in routine water-quality 

samples and (B) estimated daily mean chloride concentrations and chloride concentration in routine water-quality 

samples for the study period at Allen Brook at VT 2A near Essex Junction, VT, station 04290335.

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

y = 0.191x − 14.877

R2 = 0.87

CHLORIDE CO

NCEN

TRA

TIO

N, IN

MILLIGRA

MS PER LITER

WATER YEAR

A

B

20

40

60

80

100

120

140

160

200 300 400 500 600 700 800 900

0

50

100

150

200

250

Oct. 1 Apr. 1 Oct. 1 Apr. 1 Oct. 1

Estimated daily mean chloride concentration,

 at downstream site

Measured chloride concentration,

 at downstream site

2006 2007

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter
Stream Hydrology and Water Quality 35

Figure 18. Relation of estimated chloride concentration to (A) stream stage during a rain-on-snow event 

(January 18, 2006) and (B) streamflow during a snowmelt event (March 2007) at Allen Brook at VT 2A near Essex 

Junction, VT, stations 042903349 and 04290335. CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

TIME OF DAY, JANUARY 18, 2006

CHLORIDE CONCENTRATION, IN MILLIGRAMS PER LITER

DATE AND TIME

A

B

0

50

100

150

200

0

1

2

3

4

5

6

7

8

00:00 06:00 12:00 18:00 24:00

0

50

100

150

200

250

0

2

4

6

8

10

12

14

00:00 24:00 48:00 72:00 96:00

Estimated chloride concentration, at upstream site

Estimated chloride concentration,

 at downstream site

Streamflow

Air temperature

March 2 March 3 March 4 March 5

2007

STREAMFLOW, IN CUBIC FEET PER SECOND

TEMPERATURE, IN DEGREES CELSIUS

STAGE, IN FEET

PRECIPITATION, IN INCHES

Estimated chloride concentration, at upstream site

Estimated chloride concentration, at downstream site

Stream stage

Cumulative precipitation

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter

U.S. Environmental Protection Agency

 recommended chronic toxicity 

 criterion = 230 milligrams per liter
36 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Effects of Highway Road Salting on 

Water Quality

The median cationic composition of water samples 

collected at the downstream stations in this study is shown 

in figure 20. All of the samples clustered around the median 

value for each of the stream stations; therefore, the median 

value is plotted to represent the cationic composition of water 

at the three streams. The trilinear plot represents 100 percent 

of the cation composition (Ca, Mg, Na plus K), and the coordinates of a point plotted on the diagram add to 100 percent. 

The water type, as represented by cations, at all three stations 

was similar with respect to magnesium (about 20 percent). 

However, variations in composition with respect to Ca and Na 

plus K were observed. Samples collected at Mill Brook were 

dominated by Ca (about 60 percent) and contained a smaller 

percentage of Na plus K (about 20 percent) than samples collected at Alder and Allen Brooks. In samples from the Alder 

and Allen Brook watersheds, where highway density is greater 

than in the Mill Brook watershed, the percentage of Ca was 

smaller and Na plus K was greater than in the Mill Brook 

samples. Samples collected at Allen Brook, the most urbanized of the three basins, contained a higher percentage of Na 

plus K (about 40 percent) than samples collected at Mill Brook 

and Alder Brook (about 32 percent). A decrease in the ratio 

of Ca to Na plus K may be indicative of anthropogenic inputs 

to the stream. The difference in the ratio of Ca to Na plus K 

indicates that the difference in water composition among the 

three stations is likely a result of anthropogenic inputs. Collectively, these data suggest that the Mill Brook watershed is less 

affected by anthropogenic activities than the Alder and Allen 

Brook watersheds. 

Cl concentrations tended to vary inversely with streamflow—that is, as streamflow increased, Cl concentrations 

decreased. For example, nonpoint sources of Cl, such as 

widely dispersed road salt, are diluted by snowmelt and 

rainwater. However, Cl concentrations can increase with 

increasing flows during the initial part of storm or snowmelt 

runoff, and then generally decrease through dilution. The 

range in Cl concentrations among the three paired stations and 

the tributary station is shown in figure 21. At Mill Brook, Cl 

concentrations in samples collected at the upstream and downstream stations were similar, but at Alder and Allen Brooks, 

Cl concentrations were slightly higher in samples collected at 

the downstream station than in those samples collected at the 

upstream station (fig. 21). Cl concentrations were highest in 

samples collected at the Alder Brook tributary station 

(fig. 21). None of the Cl concentrations in the routine waterquality samples from the three paired stations exceeded either 

of the USEPA recommended chronic and acute toxicity criteria 

of 230 and 860 mg/L, respectively (U.S. Environmental 

Protection Agency, 1988) (fig. 21). Cl concentrations in 

samples collected at the Alder Brook tributary station generally fell between the USEPA recommended chronic and acute 

toxicity criteria (fig. 21), but the Cl concentrations from the 

tributary are diluted upon entering Alder Brook.

Elevated Cl concentrations were observed each winter as 

a result of two different hydrologic events at all three paired 

sampling stations. Intense rainfall occurred in January 2006 

and a rapid late-winter snowmelt event occurred in March 

2007. Intense rainfall can quickly wash off deicing salts previously deposited on roadways. Cl-rich meltwater can be transported from the road surfaces and pavement-edge snowbanks, 

by way of ditches and swales, to receiving waters. Streamflow 

was low at the beginning of March; therefore, dilution of Cl 

inputs from roadway drainage pathways was small. 

Cl concentrations were elevated during periods of base 

flow at all three paired stations. The persistence of elevated Cl 

concentrations during low flows in late summer and early fall 

indicates input from groundwater discharge or other continuous sources. Stream samples collected in a small basin during 

base flow periods can provide a composite sample of shallow 

groundwater discharge. The quality of groundwater discharge 

may indicate the presence of nonpoint-source contamination, 

such as road salt (Heisig, 2004). Elevated concentrations during base flows may also be indicative of a continuous source 

to the stream, such as a permitted wastewater discharge. 

However, no known wastewater discharges are present in the 

watersheds of the three streams.

Monthly Cl loads and runoff at the downstream-sampling 

stations are shown in figure 22. The highest monthly chloride 

loads during the first year of the study were observed in 

January 2006 at all three streams (figs. 22A, B and C). 

Figure 19. Estimated applied road deicing and measured 

chloride load for Allen Brook at VT 2A near Essex Junction, VT, 

station 042903349.

0

10,000

20,000

30,000

40,000

50,000

60,000

2006 2007

Applied (estimated)

Measured

CHLORIDE LOAD, IN POUNDS PER YEAR

YEAR
Effects of Highway Road Salting on Water Quality 37

The highest monthly chloride loads during the second 

year of the study were observed during spring snowmelt in 

March and April 2007 at all three streams and were followed 

by decreases in Cl loads through the summer. Generally, the 

relation of Cl load to runoff followed a similar pattern at 

all three streams in 2007. In July and October 2007, loads 

increased slightly with an increase in runoff, again indicating 

that salt in the soils and groundwater may be contributing to 

the Cl levels during the summer and fall, well after the roadsalting season.

Monitoring and assessment of Cl concentrations and 

loads in the three streams indicate that VTrans road-deicing 

practices do not appear to have a large influence on Cl concentrations and loads in the streams studied. Cl loads downstream 

of the state highways were greater than the loads upstream of 

the highways, but Cl applications for road deicing by VTrans 

were a small component (from less than 1 to 17 percent) of 

the total downstream Cl loads. The increase in Cl downstream 

of the state roadways is likely due to Cl usage on the state 

highways. The one exception would be the Alder Brook tributary where highway and interchange drainage appears to be 

an important component of the tributary’s flows and Cl loads. 

Sequestering of Cl by adjacent soils and streambed sediments 

appeared to be occurring in the drainages studied because the 

largest observed in-stream concentrations occurred generally 

during low-flow conditions and at times of the year when Cl 

applications were not occurring.

Results of the study also imply that most of the Cl loads 

in the three streams studied are originating farther upstream 

in the watersheds and possibly from Cl stored in the soils and 

shallow groundwater near the State highways. Other sources 

of Cl in these watersheds could include deicing of local roads, 

private roads and parking areas, household use of deicing 

salts, septic systems, fertilizers, and pet wastes.

Figure 20. General cation composition (in percent) for Mill Brook at VT 117, Alder Brook at VT 289, 

and Allen Brook at VT 2A near Essex Junction, VT.

SODIUM PLUS POTASSIUM

MAGNESIUM

CALCIUM

80 60 40 20

20

40

60

80

20

40

60

80

Mill Brook

Allen Brook

Alder Brook

EXPLANATION
38 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

MILL 

BROOK

ALLEN 

BROOK

ALDER 

BROOK

ALDER BROOK

TRIBUTARY

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

EXPLANATION

Downstream sampling site

Upstream sampling site

Tributary sampling site

1

10

100

1,000

Chronic criterion

Acute criterion

Maximum

75th percentile

50th percentile (median)

25th percentile

Minimum

Outlier

Outlier

Figure 21. The range in chloride concentrations in the routine water-quality samples for the paired sampling 

stations at Mill Brook at VT 117, Allen Brook at VT 2A, Alder Brook at VT 289, and Alder Brook tributary at 

mouth near Essex Junction, VT.
Effects of Highway Road Salting on Water Quality 39

Figure 22. Estimated monthly chloride 

loads and measured runoff for (A) Mill 

Brook at VT 117 near Essex Junction, 

VT, station 04289881, (B) Alder Brook at 

VT 289 near Essex Junction, VT, station 

04290161 and (C) Allen Brook at VT 2A 

near Essex Junction, VT, station 04290335.

RUNOFF, IN INCHES

2006 2007

WATER YEAR

A

B

C

0

500

1,000

1,500

2,000

2,500

0

1

2

3

4

5

6

7

8

Chloride load

Runoff

MONTHLY CHLORIDE LOAD, IN POUNDS PER DAY

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

0

1

2

3

4

5

6

Chloride load, Alder Brook

Chloride load, Alder Brook tributary

Runoff

0

2,000

4,000

6,000

8,000

10,000

12,000

0

1

2

3

4

5

Jan. Apr. Jul. Oct. Jan. Apr. Jul. Oct.

Chloride load

Runoff
40 Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont

Summary and Conclusions

The use of road salt (sodium chloride (NaCl)) for deicing 

of roads has increased steadily since its initial use in the late 

1930s and early 1940s. NaCl and sand are primarily used in 

Vermont for deicing and anti-icing, respectively, and Vermont 

is the only state in the Nation that requires an environmental 

permit for deicing. The sources of chloride (Cl) and sodium 

(Na) to the environment are varied and include rock weathering, precipitation and winds, agriculture, human sewage (onsite disposal systems, municipal wastewater-treatment facilities), and road deicing. Excess NaCl in streams can be harmful 

to aquatic life. This report describes the results of a study by 

the U.S. Geological Survey, in cooperation with the Vermont 

Agency of Transportation (VTrans), designed to determine the 

degree to which road-deicing practices affected Cl concentrations and loads in selected streams in Chittenden County, VT. 

The sampling program was designed to assess differences in 

Cl concentrations and loads above and below State highways 

to determine whether road-salt application affects Cl concentrations and loads in streams. 

A combination of continuous monitors and water-quality 

sampling was used to assess the surface-water hydrology and 

water quality of three paired stream-sampling stations over 

2 years. Streamflow and specific conductance were measured 

continuously at locations upstream and downstream on Mill 

Brook at VT 117, Alder Brook at VT 289, and Allen Brook 

at VT 2A, all near Essex Junction, Chittenden County, VT, 

from November 2005 to 2007. Water samples were collected 

routinely for determination of chloride (Cl), calcium (Ca), and 

sodium (Na) concentrations and seasonally for determination 

of Cl, Ca, Na, potassium, magnesium, sulfate, magnesium, 

and nitrite plus nitrate concentrations from November 2005 

to October 2007. Water quality and streamflow data were collected at a tributary to Alder Brook from December 2006 to 

November 2007.

Local streamflow conditions during the study were above 

normal and mean annual discharge for 2007 was less than 

mean annual discharge for 2006 as result of lower annual 

precipitation in 2007. Most of the snowfall in 2006 occurred 

early in the winter followed by warm temperatures and a large 

snowmelt in January 2006. In 2007 snowfall was greatest 

during February and March, with melt occurring in March 

and April. 

Mean concentrations of Cl in the water-quality samples 

collected at upstream and downstream stations ranged from 

8.2 to 72 mg/L and 7.9 to 80.7 mg/L, respectively. Mean Cl 

loads ranged from 1,100 to 4,090 lb/d (pounds per day) at 

upstream stations and from 1,110 to 4,200 lb/d at downstream 

stations. Estimated mean annual Cl loads ranged from 

402,000 to 1,490,000 lb/yr (pounds per year) at upstream 

stations and from 405,000 to 1,530,000 lb/yr at downstream 

stations, respectively. 

Chloride concentrations were similar between samples 

collected at the paired upstream and downstream stations for 

each stream. Mean Cl concentrations in samples collected 

at the three paired stations were lowest at Mill Brook at VT 

117 near Essex Junction and highest at Allen Brook at VT 

2A near Essex Junction, VT. Mean Cl concentrations were 

highest in samples collected at the Alder Brook tributary; 

however, concentrations were diluted as the tributary entered 

Alder Brook. None of the Cl concentrations in the waterquality samples collected at the three paired stations exceeded 

the U.S. Environmental Protection Agency’s (USEPA) 

recommended chronic or acute toxicity criteria of 230 and 

860 mg/L, respectively. 

The mean Cl concentration in water-quality samples collected at the Alder Brook tributary was 449 mg/L. The highest 

estimated daily mean Cl concentration was 721 mg/L in 

March 2007, 3 days after a peak in streamflow. The minimum 

estimated daily mean Cl concentration (31.0 mg/L) occurred 

in October 2007, following an intense fall rainstorm. The 

USEPA recommended chronic toxicity criterion of 230 mg/L 

was exceeded about 65 percent of the period monitored. The 

USEPA recommended acute toxicity criterion of 860 mg/L 

was not exceeded. 

Samples collected in January 2006 and March 2007 

were used to describe the effects of rain and snowmelt on Cl 

concentrations during the deicing season. Cl concentrations 

in samples collected at Mill Brook during rain and snowmelt 

events were lower than those in samples collected at Alder and 

Allen Brooks. In only one instance did an estimated Cl concentration (232 mg/L) during a snowmelt event in March 2007 

at Alder Brook reach the USEPA recommended chronic toxicity criterion at both the upstream and downstream stations; 

however, the period of exceedance was short and the concentration did not exceed the USEPA 4-day average criterion.

The highest monthly Cl loads during the first year of 

the study were observed in January 2006 at all three streams. 

The highest monthly Cl loads during the second year of the 

study were observed in April 2007 at all three streams during 

spring snowmelt and were followed by decreases in salt loads 

through the summer. Generally, the relation of salt loads 

relative to runoff in 2007 was similar at all three streams. 

In July and October 2007, Cl loads increased slightly with 

an increase in runoff, indicating that salt in the soils and 

groundwater may have been contributing to the Cl levels 

during the summer and fall. 

Estimated Cl loads below the State highway bridges 

exceeded loads above the bridges at all three paired stations 

during both years of the study. The differences in the annual 

loads between the upstream and downstream stations were 

0.7, 3.0 and 14 percent at Mill, Allen and Alder Brooks, 

respectively. Almost all of the difference (92 percent) at 

Alder Brook was due to the tributary. Cl applied by the State 

of Vermont for deicing purposes represented less than 

20 percent of the annual Cl load in the streams below the state 

highways; however, the Cl applications comprised from 20 to 

100 percent of difference in Cl loads between the upstream 

and downstream stations. 
References Cited 41

The differences in water composition, Cl concentrations, 

and Cl loads among the three paired stations indicated that the 

land use in each of the watersheds affected the water-quality 

data collected at each station. The Mill Brook watershed was 

selected to represent a rural two-lane-highway segment and a 

predominantly forested watershed. Samples collected at Mill 

Brook had the lowest concentrations and loads of Cl and an 

ionic water type representative of more natural conditions 

compared to the other two streams. The Alder and Allen Brook 

watersheds contained two-lane State highways and had high 

Cl concentrations and loads and higher ratios of Ca to Na plus 

K, indicating a difference in general water composition. The 

higher concentrations of Cl and the difference in general water 

chemistry at these streams indicate that anthropogenic inputs 

to these watersheds may be affecting water quality. 

State highway salt applications for snow and ice removal 

did not represent a major source of the Cl loads in the three 

streams monitored. Other sources of Cl must be present in 

the three watersheds, and may include Cl in soils and streambed sediments, other non-state deicing activities, and 

septic systems.

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Prepared by the Pembroke and West Trenton Publishing Service Centers.

For more information concerning this report, contact:

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Denner and others—Effects of Highway Road Salting on the Water Quality of Selected Streams in Chittenden County, Vermont, November 2005–2007—Scientific Investigations Report 2009–5236

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