Hydrologic, Water-Quality, and 

Meteorological Data for the Cambridge, 

Massachusetts, Drinking-Water Source 

Area, Water Year 2006

By Kirk P. Smith

Prepared in cooperation with the

City of Cambridge, Massachusetts, Water Department

Open-File Report 2008–1175

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Smith, K.P., 2008, Hydrologic, water-quality, and meteorological data for the Cambridge, Massachusetts, drinkingwater source area, water year 2006: U.S. Geological Survey Open-File Report 2008–1175, 164 p.
iii

Contents

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

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

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

Description of Monitoring Network...................................................................................................4

Continuous Data Collection and Computation ..........................................................................................5

Hydrologic Data.....................................................................................................................................5

Water-Quality Data...............................................................................................................................6

Meteorological Data.............................................................................................................................6

Sample Collection and Analysis..................................................................................................................7

Presentation of Data .....................................................................................................................................8

Station History.......................................................................................................................................8

Streamflow Data ...................................................................................................................................8

Daily Mean Values.......................................................................................................................8

Annual Summary Statistics........................................................................................................9

Reservoir Data.......................................................................................................................................9

Meteorological Data and Physical Parameters ..............................................................................9

Water-Quality Data...............................................................................................................................9

Data for the Cambridge Drinking-Water Source Area ............................................................................9

Surface-water data ..............................................................................................................................9

Specific Conductance........................................................................................................................11

Water-Quality Data.............................................................................................................................17

Quality-Control Samples....................................................................................................................18

Meteorological data...........................................................................................................................19

References Cited..........................................................................................................................................21

Tables 4–17....................................................................................................................................................25

Glossary.......................................................................................................................................................161

Figures

1. Map showing the monitoring network for Cambridge, Massachusetts, drinking-water 

source area for water year 2006, eastern Massachusetts....................................................3

2–8. Graphs showing:

2.. (A ) Discharge from the Hobbs Brook Reservoir as a percentage of water entering 

the Stony Brook Reservoir, and discharge from the Stony Brook Reservoir to the 

Charles River as a percentage of total inflow to the Stony Brook Reservoir for 

water year 2006; (B ) monthly precipitation totals at the Cambridge Reservoir,

Stony Brook Reservoir, and Fresh Pond Reservoir in the Cambridge drinkingwater source area, water year 2006...............................................................................10

3. Monthly mean reservoir storage as a percentage of capacity for water year 2006

shown as percent capacity for the Cambridge Reservoir, Stony Brook Reservoir,

and Fresh Pond Reservoir, near Cambridge, Massachusetts....................................12
iv

Tables

1. Names, locations, drainage areas, and period of records for U.S. Geological Survey 

monitoring stations in the drinking-water source area for Cambridge, Massachusetts, 

water year 2006.............................................................................................................................4

2. Hydrologic, water-quality, and meteorological parameters measured at each 

continuous-monitoring station during water year 2006, in the drinking-water source 

area for Cambridge, Massachusetts, water year 2006 ..........................................................5

3. Rating classifications for continuous records of hydrologic, water quality, and 

meterologic parameters. .............................................................................................................6

4. Daily, monthly, and annual statistics for discharge for U.S. Geological Survey stations 

in the drinking-water source area for Cambridge, Massachusetts, for water 

year 2006 ......................................................................................................................................26

5. Daily, monthly, and annual statistics for reservoir altitude for U.S. Geological Survey 

station numbers 01104430, Hobbs Brook below Cambridge Reservoir near Kendal 

Green, 01104480, Stony Brook Reservoir in Waltham, and 422302071083801, Fresh Pond 

Reservoir at Cambridge, for water year 2006.........................................................................39

6. Daily, monthly, and annual statistics for reservoir capacity for U.S. Geological Survey station 01104430, Hobbs Brook below Cambridge Reservoir near Kendal Green; 

01104480, Stony Brook Reservoir in Waltham; and 422302071083801, Fresh Pond Reservoir at Cambridge, Massachusetts, water year 2006 ...........................................................52

7. Daily, monthly, and annual statistics for precipitation for U.S. Geological Survey stations 01104430, Hobbs Brook below Cambridge Reservoir near Kendal Green; 01104480, 

Stony Brook Reservoir in Waltham; and 422302071083801, Fresh Pond Reservoir at 

Cambridge, Massachusetts, water year 2006........................................................................65

4. Monthly mean specific conductance for water year 2006 for U.S. Geological 

Survey station 01104415, Cambridge Reservoir, unnamed tributary 2, near 

Lexington, Massachusetts; period-of-record maximum and minimum monthly 

mean specific conductance; and median monthly specific conductance for water 

years 1997–98 and 2004–05 ..............................................................................................13

5. Monthly mean specific conductance for water year 2006 for U.S. Geological 

Survey station 01104430, Hobbs Brook below Cambridge Reservoir near Kendal 

Green, Massachusetts; period-of-record maximum and minimum monthly mean 

specific conductance; and the median, 25th percentile, and 75th percentile 

monthly specific conductance for water years 1998 through 2005...........................14

6. Monthly mean specific conductance for water year 2006 for U.S. Geological 

Survey station 01104460, Stony Brook at Route 20 at Waltham, Massachusetts;

period-of-record maximum and minimum monthly mean specific conductance; 

and the median, 25th percentile, and 75th percentile monthly specific 

conductance for water years 1997–98 and 2002–05....................................................15

7. Monthly mean specific conductance for water years 2005 and 2006 for U.S.

Geological Survey station 422302071083801, Fresh Pond Reservoir at Cambridge,

Massachusetts...................................................................................................................16

8. Monthly mean air temperatures for water year 2006 for the Cambridge Reservoir,

Massachusetts, period-of-record maximum and minimum monthly mean air

temperatures, and the median monthly air temperatures for water 

years 2002–05 .....................................................................................................................20
v

8. Daily, monthly, and annual statistics for air temperature for U.S. Geological Survey stations 01104430, Hobbs Brook below Cambridge Reservoir near Kendal Green; 01104480, 

Stony Brook Reservoir in Waltham; and 422302071083801, Fresh Pond Reservoir at 

Cambridge, Massachusetts, water year 2006........................................................................77

9. Daily, monthly, and annual statistics for water temperature for U.S. Geological Survey 

stations in the drinking-water source area for Cambridge, Massachusetts, for water 

year 2006 ......................................................................................................................................89

10. Daily, monthly, and annual statistics for specific conductance for U.S. Geological 

Survey stations in the drinking-water source area for Cambridge, Massachusetts, for 

water year 2006.........................................................................................................................102

11. Extreme measurements of physical parameters for U.S. Geological Survey stations in 

the drinking-water source area for Cambridge, Massachusetts .....................................116

12. Extreme and median constituent concentrations measured in water samples for each 

U.S. Geological Survey water-monitoring station in the drinking-water source area for 

Cambridge, Massachusetts, for the period of record ........................................................118

13. Physical properties and concentrations of calcium, sodium, chloride, sulfate, total 

nutrients, and polar pesticides and metobolites for base-flow and stormflow water 

samples collected in eleven subbasins and for water samples collected from the Fresh 

Pond intake structure in the Cambridge drinking-water source area in water 

year 2006 ....................................................................................................................................120

14. Physical properties of and concentrations of dissolved calcium, sodium, chloride, 

sulfate, total nutrients, and polar pesticides and metabolites in quality-control samples 

collected in water year 2006...................................................................................................141

15. Characteristics of selected pesticides detected in base-flow and stormflow water 

samples collected in the Hobbs Brook and Stony Brook Basins, water 

year 2006 ....................................................................................................................................155

16. Frequency of detection and maximum concentration of selected pesticides and caffeine 

in six samples of base-flow and seven samples of stormflow collected in the Hobbs Brook 

and Stony Brook Basins and collected in three samples of raw water collected from the 

intake of the water-treatment facility at Fresh Pond, Cambridge Massachusetts, water 

year 2006 .....................................................................................................................................157

17. Analyte recovery statistics for field matrix spikes in environmental samples and the 

frequency of detection for available analytes in about 70 environmental samples 

collected in the Hobbs Brook and Stony Brook Basins, Massachusetts, for water 

year 2006 ....................................................................................................................................158
vi

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

inch (in.) 25,400 micron (μ)

inch (in.) 25,400,000 nanometer (nm)

mile (mi) 1.609 kilometer (km)

Area

square inch (in2

) 6.452 square centimeter (cm2)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

million gallons (Mgal) 3,785.4 cubic meter (m3

)

Flow rate

million gallons per day 

(Mgal/d)

 0.04381 cubic meter per second (m3

/s)

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

°F=(1.8×°C)+32

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

(NGVD 29).

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

Water- and sediment-quality constituents are expressed in milligrams per liter (mg/L), 

micrograms per liter (μg/L), parts per million (ppm), and parts per billion (ppb). Milligrams per 

liter is a unit expressing the concentration of chemical constituents in solution as weight 

(milligrams) of solute per unit volume (liter) of water. One thousand milligrams per liter is 

equivalent to one gram per liter. One thousand micrograms per liter is equivalent to one 

milligram per liter. For concentrations less than 7,000 mg/L, the numerical value is the same as 

for concentrations in ppm. 

Specific conductance of water is expressed in microsiemens per centimeter at 25 degrees 

Celsius (μS/cm at 25°C). 

ABBREVATIONS USED IN REPORT

ASTM American Society for Testing and Materials

COV Coefficient of variation

CWD City of Cambridge, Massachusetts, Water Department

HPLC High-performance liquid chromatography

ISO International Organization for Standardization

NIST National Institute of Standards and Technology

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

Conversion Factors, Datums, and Abbreviations
Abstract

Records of water quantity, water quality, and 

meteorological parameters were continuously collected from 

three reservoirs, two primary streams, and four subbasin 

tributaries in the Cambridge, Massachusetts, drinking-water 

source area during water year 2006 (October 2005 through 

September 2006). Water samples were collected during baseflow conditions and storms in the subbasins of the Cambridge 

Reservoir and Stony Brook Reservoir drainage areas and 

analyzed for dissolved calcium, sodium, chloride, and sulfate; 

total nitrogen and phosphorus; and polar pesticides and 

metabolites. These data were collected to assist watershed 

administrators in managing the drinking-water source area 

and to identify potential sources of contaminants and trends in 

contaminant loading to the water supply. 

Monthly reservoir contents for the Cambridge Reservoir 

varied from about 59 to 98 percent of capacity during water 

year 2006, while monthly reservoir contents for the Stony 

Brook Reservoir and the Fresh Pond Reservoir was maintained 

at greater than 83 and 94 percent of capacity, respectively. If 

water demand is assumed to be 15 million gallons per day 

by the city of Cambridge, the volume of water released from 

the Stony Brook Reservoir to the Charles River during the 

2006 water year is equivalent to an annual water surplus of 

about 127 percent. Recorded precipitation in the source area 

was about 16 percent greater for the 2006 water year than for 

the previous water year and was between 12 and 73 percent 

greater than for any recorded amount since water year 2002. 

The monthly mean specific-conductance values for all 

continuously monitored stations within the drinking-water 

source area were generally within the range of historical data 

collected since water year 1997, and in many cases were 

less than the historical medians. The annual mean specific 

conductance of 738 μS/cm (microsiemens per centimeter) 

for water discharged from the Cambridge Reservoir was 

nearly identical to the annual mean specific conductance for 

water year 2005 which was 737 μS/cm. However, the annual 

mean specific conductance at Stony Brook near Route 20 in 

Waltham (U.S. Geological Survey (USGS) station 01104460), 

on the principal tributary to the Stony Brook Reservoir, 

and at USGS station 01104475 on a smaller tributary to 

the Stony Brook Reservoir were about 15 and 13 percent 

lower, respectively, than the previous annual mean specific 

conductances of 538 and 284 μS/cm, respectively, for water 

year 2005. The annual mean specific conductance for Fresh 

Pond Reservoir decreased from 553 μS/cm in the 2005 water 

year to 514 μS/cm in the 2006 water year.

Water samples were collected in nearly all of the subbasins in the Cambridge drinking-water source area and from 

Fresh Pond during water year 2006. Discrete water samples 

were collected during base-flow conditions with an antecedent 

dry period of at least 4 days. Composite samples, consisting 

of as many as 100 subsamples, were collected by automatic 

samplers during storms. Concentrations of most dissolved 

constituents were generally lower in samples of stormwater 

than in samples collected during base flow; however, the 

average concentration of total phosphorus in samples of 

stormwater were from 160 to 1,109 percent greater than 

the average concentration in water samples collected during base-flow conditions. Concentrations of total nitrogen 

in water samples collected during base-flow conditions and 

composite samples of stormwater at USGS stations 01104415, 

01104460, and 01104475 were similar, but mean concentrations of total nitrogen in samples of stormwater differed by 

about 0.5 mg/L (milligrams per liter) from those in water 

samples collected during base-flow conditions at U.S. Geological Survey stations 01104433 and 01104455. In six water 

samples, measurements of pH were lower than the U.S. 

Environmental Protection Agency (USEPA) national recommended freshwater quality criteria and the USEPA secondary 

drinking water-standard of 6.5 pH units. Concentrations of 

dissolved chloride in all water samples collected during baseflow conditions from USGS stations 01104405, 01104415, 

01104420, 01104433, and 01104455 exceeded the USEPA 

recommended freshwater quality criterion of 230 mg/L. With 

the exception of one sample collected during base-flow conditions at USGS station 01104455, chloride concentrations in all 

Hydrologic, Water-Quality, and Meteorological Data for 

the Cambridge, Massachusetts, Drinking-Water Source 

Area, Water Year 2006

By Kirk P. Smith
2 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

of the respective samples also exceeded the USEPA secondary drinking-water standard of 250 mg/L. Concentrations of 

dissolved chloride in several composites of water collected 

during storms at USGS stations 01104415 and 01104433 also 

exceeded the USEPA recommended freshwater quality criterion and secondary drinking-water standard. Concentrations of 

dissolved sulfate in all water samples were below the USEPA 

secondary drinking-water standard of 250 mg/L.

Twenty pesticides and caffeine were detected in water 

samples collected from the primary streams and tributaries 

to the Cambridge Reservoir and Stony Brook Reservoir, and 

in raw water collected from the Cambridge water-treatment 

facility intake from the Fresh Pond Reservoir in water year 

2006. Caffeine was detected in 77 percent of all water 

samples. Imidacloprid, siduron, and carbaryl were the most 

frequently detected pesticides. The compounds 2,4-D, MCPA, 

and triclopyr were detected only in samples of stormwater. 

Caffeine, metalaxyl, and siduron were detected more 

frequently in water samples collected during storms than in 

water samples collected during base-flow conditions. Caffeine, 

2-hydroxy-4-isopropylamino-6-ethylamino-s-triazine, 

carbaryl, imidacloprid, norflurazon, and siduron also were 

detected in raw water from the Fresh Pond Reservoir.

Introduction

Hydrologic and water-quality monitoring is important 

for the effective management and protection of drinkingwater supplies. Both the quantity and the quality of water 

are monitored because these factors determine the physical, 

chemical, and biological state of the water supply. Without 

accurate information on the past and current condition of the 

water supply, effective preservation and remediation programs 

cannot be implemented or evaluated.

The U.S. Geological Survey (USGS) works closely with 

municipal water suppliers throughout the nation to address 

specific water problems by conducting hydrologic- and 

water-quality-monitoring programs and detailed investigations (Patterson, 1997). One such program, conducted during 1997–98 by the USGS in cooperation with the city of 

Cambridge, Massachusetts, Water Department (CWD), was 

designed to identify sources of contaminants in the drinkingwater source area for the city (Waldron and Bent, 2001). Subsequently the USGS, in cooperation with the CWD, designed 

and implemented a water-monitoring network in the drinkingwater source area. Data from this network have been published 

annually in various USGS reports (Smith, 2005 and 2007; 

Socolow and others, 1999, 2000, 2001, 2002, 2003, and 2004).

The CWD supplies approximately 15 Mgal/d (millions 

of gallons per day1

) (Waldron and Bent, 2001) to more than 

100,000 customers. Most of this water is obtained from three 

1

 Terms listed in the glossary at the back of this report are in bold type 

where first used in the text.

primary storage reservoirs (Cambridge Reservoir (also known 

as the Hobbs Brook Reservoir), Stony Brook Reservoir, 

and Fresh Pond Reservoir), in parts of Lexington, Lincoln, 

Waltham, Weston, and Cambridge (fig. 1). The drainage 

basin for the Cambridge Reservoir includes Hobbs Brook 

and three unnamed tributaries that discharge directly into 

the reservoir. Water is discharged from the southern end of 

the Cambridge Reservoir into Hobbs Brook, which receives 

additional water from an unnamed tributary about 0.5 mi 

below the reservoir. Hobbs Brook joins with Stony Brook 

about 1.6 mi downstream from the reservoir and flows south 

to the Stony Brook Reservoir. Two unnamed tributaries flow 

into Stony Brook about a 0.25 mi north of the Stony Brook 

Reservoir. In addition to Stony Brook, an unnamed tributary 

flows directly into the Stony Brook Reservoir on the southwest 

side of the reservoir. Additional water enters both reservoirs 

from other minor tributaries and highway and parking-lot 

storm drains. Water from Stony Brook Reservoir is piped 

through an aqueduct by the CWD directly to Fresh Pond 

Reservoir, where it is stored prior to treatment. Overflow and 

controlled discharges from the Stony Brook Reservoir flow 

into the Charles River in Waltham.

The drainage basin contributing water to these reservoirs 

has undergone rapid development since the 1990s and 

encompasses major transportation corridors (Interstate 95, 

Routes 2, 2A, 20, and 117), as well as large areas of industrial, 

commercial, and high-density residential land use. Because 

the city of Cambridge owns less than 5 percent of the land 

in the basin contributing to its water supply, the CWD relies 

heavily on monitoring to provide information for optimizing 

the management of its reservoirs for water quality and 

quantity. The USGS monitoring network provides near-realtime information that assists the CWD in responding rapidly 

to water-quality changes caused by accidental or intentional 

contamination. This information also benefits the CWD, other 

municipalities, and state agencies involved with water-resource 

development and management in the Charles River Basin by 

enhancing their understanding of the relation between local 

drinking-water-management practices and regional issues of 

water supply and hydrologic-system response.

Purpose and Scope 

This report presents records of water quantity, water quality, and meteorological parameters collected in the Cambridge, 

Massachusetts, drinking-water source area during water year

2006 (October 2005 through September 2006). It describes the 

monitoring network, data-collection methods for all types of 

data, and computation methods. It also describes the chemical 

characteristics of water samples collected during base-flow

conditions and during storms from nearly all of the streams 

and tributaries to Hobbs Brook and Stony Brook in the Stony 

Brook Basin, and of water samples collected from the rawwater intake at the Cambridge water-treatment facility. 
Introduction 3

Figure 1. The monitoring network for Cambridge, Massachusetts, drinking-water source area for water year 2006, 

eastern Massachusetts.

Lincoln

LEXINGTON

LINCOLN

WALTHAM

WESTON

01104415

01104430

01104433

01104455

01104460

01104475

01104480

01104453

01104390

01104405

01104420

01104410

0

0

1

1

2 MILES

2 KILOMETERS

Base from U.S. Geological Survey, 

MassGIS, Cambridge Water Department, 

Harvard Design and Mapping, and Boston Edison. 

EXPLANATION

01104460

Basins

 Cambridge Reservoir Basin

 Stony Brook Reservoir Basin 

Forested and nonforested 

 wetlands

Town boundary

Basin boundary

Continuously monitored 

 stations and number

Primary sampling station

Secondary sampling station

71°15'

42°

22'

30"

71°19'

42°

27'

Hobbs Brook

Trapelo Road

128 Cherry Brook

Stony Brook

Hobbs Brook

2A

2

95

Stony Brook

Reservoir 20

Sandy

Pond

117 Cambridge

Reservoir

42°

73° 72° 

71°

70°

MASSACHUSETTS

41°30'

42°30'

0

0

50 KILOMETERS

50 MILES

MASSACHUSETTS

CAMBRIDGE

NEWTON

WALTHAM

LINCOLN

LEXINGTON WINCHESTER

WESTON

MEDFORD

ARLINGTON

BELMONT

128

2

2A

20

117

95

90

Aqueduct to Fresh Pond

Cambridge

Reservoir

Basin

Stony Brook

Reservoir

Basin

PAYSON PARK

RESERVOIR

Aqueduct to Fresh Pond

STONY BROOK

RESERVOIR

FRESH

POND

CAMBRIDGE

RESERVOIR

CHARLES RIVER

42o

26'

71o 71 08' o

19'

42o

20'

0

0

5 MILES

5 KILOMETERS

422302071083801 
4 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

Description of Monitoring Network

Stations installed and operated by the USGS in the 

drinking-water source area continuously monitored various 

hydrologic, water-quality, and meteorological parameters 

including stream stage, stream-water temperature, stream 

specific conductance, reservoir altitude, air temperature, 

and precipitation. Stations were selected for continuous 

monitoring on the basis of the necessity for water-supply 

regulation by the CWD and of information gained in a 

previous USGS investigation (Waldron and Bent, 2001) 

that identified specific areas as potentially important sources 

of contaminants. Attributes of the monitoring stations are 

listed in table 1; locations of stations selected for continuous 

monitoring are shown in figure 1. 

Stream-stage measurements were recorded at monitoring 

stations at the outlet of the Cambridge Reservoir, on an 

unnamed tributary to Stony Brook, on Stony Brook, and at the 

outlet of Stony Brook Reservoir (USGS stations 01104430, 

01104453, 01104460, and 01104480, respectively). Equipment 

for the measurement of stream stage was installed at USGS 

station 01104453 late in the water year. Water-quality 

measurements were recorded at the outlet of the Cambridge 

Reservoir and at Stony Brook (USGS stations 01104430 and 

01104460). Physical parameters monitored at these sites are 

listed in table 2. These data were recorded at a frequency of 

15 minutes and, with the exception of data from USGS station 

01104453, which was not equipped with telemetry, were 

uploaded to a USGS database hourly by phone modem. In 

addition to measurements made on these streams, stream-stage 

Table 1. Names, locations, drainage areas, and period of records for U.S. Geological Survey monitoring stations in the drinking-water 

source area for Cambridge, Massachusetts, water year 2006.

[USGS, U.S. Geological Survey; mi2, square miles; latitude and longitude: In degrees, minutes, and seconds]

Station name USGS station

 number Latitude Longitude

Draingage 

area

 (mi2

)

Period of record

Stony Brook at Kendal Green 01104390 42 22 36 71 16 55 10.4 03/07/97–09/17/98

Hobbs Brook at Mill Street near Lincoln 01104405 42 26 11 71 16 12 2.16 03/05/97–09/16/98

Cambridge Reservoir, unnamed tributary 1, 

near Lexington

01104410 42 26 15 71 15 53 2.10 03/05/97–09/16/98

Cambridge Reservoir, unnamed tributary 2, 

near Lexington

01104415 42 26 09 71 15 38 0.41 10/22/97–09/22/98; 

10/01/00–09/30/06

Cambridge Reservoir, unnamed tributary 3, 

near Lexington

01104420 42 25 11 71 15 29 0.73 04/09/97–09/16/98

Hobbs Brook below Cambridge Reservoir 

near Kendal Green

01104430 42 23 53 71 16 26 6.86 04/09/97–09/16/98

Hobbs Brook, unnamed tributary number 1 

near Kendal Green

01104433 42 23 28 71 16 18 0.36 10/23/97–09/15/05; 

06/28/04–09/30/06

Stony Brook, unnamed tributary number 2 

near Weston Station

01104453 42 22 17 71 16 31 2.23 06/01/2006–09/30/06

Stony Brook, unnamed tributary number 1 

near Waltham

01104455 42 22 21 71 16 15 0.48 10/22/97–09/22/98; 

10/01/00–09/30/06

Stony Brook at Route 20 at Waltham 01104460 42 21 08 71 16 16 22.0 03/07/97–10/28/98; 

05/14/02–09/30/06

Stony Brook Reservoir, unnamed tributary 1 

near Weston

01104475 42 21 16 71 16 07 0.85 12/17/97–09/17/98; 

08/26/04–09/30/06

Stony Brook Reservoir at dam 

near Waltham

01104480 42 21 20 71 15 56 23.7 03/1997–09/30/06

Fresh Pond in gate house at Cambridge 422302071083801 42 23 02 71 08 38 0.00 1998; 10/01/03–09/30/06
Continuous Data Collection and Computation 5

measurements and water-quality measurements were recorded 

at monitoring stations on four of the small tributaries (USGS 

stations 01104415, 01104433, 01104455, and 01104475). 

Because the drainage areas of these sites are small (less 

than 1 mi2

) and contain many roadways, parking lots, and 

other impervious surfaces (Waldron and Bent, 2001), the 

hydrologic responses, and often the water-quality responses, 

change rapidly. To document these responses effectively, the 

monitoring stations recorded stream-stage and water-quality 

measurements at variable frequencies, as often as every 

minute. These data were uploaded to a USGS database hourly 

by digital cellular modem. 

Measurements of reservoir altitude, precipitation, and 

air temperature were recorded at the Cambridge, Stony 

Brook, and Fresh Pond Reservoirs (USGS stations 01104430, 

01104480, and 422302071083801). Measurements of reservoir water quality also were recorded at the Fresh Pond Reservoir. Physical parameters monitored at these sites are listed in 

table 2. These data were recorded at a frequency of 15 minutes 

and were uploaded to a USGS database on an hourly basis by 

phone modem. 

Continuous Data Collection and 

Computation

The monitoring network provides near-real-time information used to manage the quantity and quality of water in the 

CWD drinking-water source area. Data from each station are 

available to watershed managers through the USGS Massachusetts-Rhode Island Water Science Center on the World Wide 

Web (http://ma.water.usgs.gov).

Hydrologic Data

Basic data collected at the monitoring stations include 

records of stream stage and measurements of discharge of 

streams, and water altitude and contents of reservoirs. In addition, observations of factors affecting the stage-discharge 

relation or the altitude-contents relation, weather records, 

and other information are used to supplement the basic data 

in determining the daily flow or water in storage. Measurements of discharge are made with a current meter or acoustic Doppler current profiler by standard USGS methods 

(Buchanan and Somers, 1968, 1969; Carter and Davidian, 

1968; Rantz and others, 1982; Kennedy, 1983 and 1984; 

Oberg and others, 2005). The methods are consistent with the 

American Society for Testing and Materials (ASTM) standards and generally follow the standards of the International 

Organization for Standards (ISO).

To determine streamflow at each USGS monitoring station in the CWD drinking-water source area, discharge-rating 

tables for any stage are prepared from stage-discharge curves 

(Rantz and others, 1982). The daily mean discharge is computed from these stage and rating tables, and then the monthly 

and yearly mean discharges are computed from these daily 

values. If the stage-discharge relation for a station is changed 

temporarily by aquatic growth, scour, or debris in the control

section, the daily mean discharge is computed by the shiftingcontrol method (Rantz and others, 1982). 

For the USGS monitoring stations on reservoirs in the 

CWD drinking-water source area, altitude-capacity tables 

giving the volume for any reservoir water altitude are prepared 

from water altitude-volume relation curves defined by surveys 

(Fugro East, Inc., 1996). From the altitude-capacity tables, the 

daily, monthly, or yearly changes in volume are computed. 

For some stations, recorder or sensor malfunctions can 

cause gaps in the water-stage record or inaccurate readings, 

which cannot be used to compute daily discharge. For periods 

Table 2. Hydrologic, water-quality, and meteorological parameters measured at each continuous-monitoring station during water 

year 2006, in the drinking-water source area for Cambridge, Massachusetts, water year 2006.

[USGS, U.S. Geological Survey; X, indicates parameter is measured]

Parameter

USGS station number

01104415 01104430 01104433 01104453 01104455 01104460 01104475 01104480 422302071083801

Stream stage X X X X X X X X

Reservoir altitude X X X

Precipitation X X X

Air temperature X X X

Water temperature X X X X X X X

Specific conductance X X X X X X X
6 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

of malfunction, the daily mean discharges are estimated on 

the basis of the recorded range in stage, prior and subsequent 

records, discharge measurements, weather records, and comparison with records from other stations in the same or nearby 

basins. Likewise, reservoir volumes may be estimated on the 

basis of operator’s log, prior and subsequent records, and 

other information. 

The accuracy of hydrologic data depends primarily on (1) 

the stability of the stage-discharge relation or, if the control is 

unstable, the frequency of discharge measurements, and (2) 

the accuracy of observations of stage, measurements of discharge, and interpretations of records. The degree of accuracy 

of the records is defined in table 3. Different accuracies may 

be attributed to different portions of a streamflow record.

Water-Quality Data

Water-temperature and specific-conductance data 

were collected from continuous water-quality monitors in 

each stream, tributary, or reservoir except at USGS station 

01104480. The accuracy of the water-quality records depends 

primarily on the rate of sensor drift, sensor fouling, and debris 

collection. Typically, sensors became fouled by aquatic growth 

more rapidly in the warmer months. In most cases, corrections for fouling and drift can be applied to the data to improve 

their accuracy (Wagner and others, 2006a). For parameters 

other than water temperature, such corrections were made on 

the basis of the performance of the sensor before and after 

sensor maintenance and by noting the response of the clean 

sensor after placing it in several standardized solutions. The 

accuracy of water-temperature data is determined by comparing measurements made by the monitoring system and by an 

independent probe calibrated against a National Institute of 

Standards and Technology (NIST) traceable thermometer. 

One of four accuracy classifications ranging from excellent to 

poor is applied to physical properties measured at each station. 

The accuracy rating is based on data values recorded before 

any shifts or corrections are made for fouling and drift. The 

basis for each rating classification is listed in table 3.

Meteorological Data

Precipitation data were collected with heated tippingbucket precipitation gages that measure the volume of rain or 

melted snow in 0.01-in. increments. The precipitation gages at 

the Cambridge Reservoir and Stony Brook Reservoir include 

wind screens that reduce bias generated by precipitation missing the instrument. Precipitation data are summed for each day 

and then for each month. In general, the accuracy of precipitation data is assured by proper maintenance and calibration of 

the device. Precipitation measurements, especially when the 

precipitation is in the form of snow, are affected by strong 

winds and are subject to errors. These errors generally result in 

underestimating the total precipitation at a station.

Air-temperature data were collected with thermistors 

housed in gill radiation shields. The probes are installed 

approximately 8 ft above ground surface. The maximum, 

minimum, and mean temperature values are computed for 

each day. Monthly statistics are then computed from daily 

values. The accuracy of air-temperature data is determined 

by comparing measurements made by the monitoring system 

and by an independent probe calibrated against a NIST traceable thermometer.

Under rare circumstances, when no records of precipitation or air temperature were available, daily values were 

estimated on the basis of records from nearby stations. These 

circumstances may include a recorder malfunction, the plugging of the precipitation gage, or a malfunction of the heating 

element in the precipitation gage.

Table 3. Rating classifications for continuous records of hydrologic, water quality, and meterologic parameters.

[Modified from Wagner and others, 2006a; and Socolow and others, 2003; ≤, less than or equal to; ±, plus or minus value shown; °C, degree Celsius; >, greater 

than; %, percent; ft, feet]

Parameter Rating

Excellent Good Fair Poor

Discharge ≤ ± 5% > ±5 to 10% > ±10 to 15% > ±15%

Reservoir altitude ≤ ± 0.1 ft > ±0.1 to 0.2 ft > ±0.2 to 0.3 ft > ±0.3 ft

Reservoir contents ≤ ± 1% > ±1 to 2% > ±2 to 4% > ±4%

Precipitation ≤ ± 2% > ±2 to 6% > ±6 to 10% > ±10%

Air temperature ≤ ± 0.4°C > ±0.4 to 0.8°C > ±0.8 to 2°C > ±2°C

Water temperature ≤ ± 0.2°C > ±0.2 to 0.5°C > ±0.5 to 0.8°C > ±0.8°C

Specific conductance ≤ ± 3% > ±3 to 10% > ±10 to 15% > ±15%
Sample Collection and Analysis 7

Sample Collection and Analysis

Water samples were collected during base-flow conditions and during rain and mixed-precipitation storms in 

selected streams in the Cambridge Reservoir and Stony Brook 

Reservoir basins throughout water year 2006. Samples of 

water from Fresh Pond also were collected from the raw-water 

intake at the Cambridge water-treatment plant. All water 

samples were analyzed for physical parameters; dissolved

calcium, sodium, chloride, and sulfate; total nitrogen and 

total phosphorus; dissolved caffeine; and 60 pesticides and 

metabolites. 

Water samples were collected during base-flow conditions and during storms at five continuously monitored stations in the Hobbs Brook and Stony Brook Basins—four on 

tributaries (USGS monitoring stations 01104415, 01104433, 

01104455, and 01104475) and one on Stony Brook (USGS 

monitoring station 01104460) (fig. 1 and table 1). Water 

samples were collected during base-flow conditions on July 

18 at several previously monitored USGS stations (Waldron 

and Bent, 2001) in the Cambridge Reservoir and Stony Brook 

Reservoir basins. These secondary sampling stations (fig. 1 

and table 1) include Stony Brook above the confluence of 

Hobbs Brook, Hobbs Brook above the Cambridge Reservoir, 

two unnamed tributaries to the Cambridge Reservoir, Hobbs 

Brook below the Cambridge Reservoir, and an unnamed tributary to Stony Brook (USGS stations 01104390, 01104405, 

01104410, 01104420, 01104430, and 01104453, respectively). 

Samples of stream water were collected manually (Wilde and 

others, 1999) under base-flow conditions with an antecedent 

dry period of at least 4 days. During storms, water samples for 

chemical analysis were collected with an automatic sampler 

controlled by a datalogger. The first sample was collected 

when flow exceeded a preset discharge threshold, and subsequent samples were collected at flow-proportional intervals. 

Each automatic sampler was configured to hold one 20-L 

glass bottle and fitted with a pre-cleaned 1/2-in. inner diameter 

Teflon intake and discharge tube, and a short piece of silicon 

pump-head tube. 

A multi-step process was used to clean all wetted parts 

associated with the automatic sampler and the processing 

equipment before each sample collection. The initial cleaning consisted of washing the interior and exterior with a 

phosphate-free laboratory-grade soap and tap water, scrubbing surfaces with a plastic brush, and rinsing with tap water. 

Circulating the solution through the tubing cleaned the interior 

of the sampler tubing. Lint-free wipes were forced hydraulically through the tubing to remove internal deposits or films 

that were difficult to remove by circulating solution alone. 

After the components dried, they were placed in a large stainless-steel pan in a fume hood and immersed in Optima-grade 

methanol. A Teflon diaphragm pump was used to circulate the 

solution through the sampler tubing. The components were 

allowed to soak, with occasional agitation, for a minimum 

period of about 4 hours. After appropriately dispensing the 

waste solution, all components except the tubing were rinsed 

with HPLC-grade methanol and air-dried in a fume hood over 

night. Because the rate of cleaning-solution volatilization was 

limited within the sampler tubing, the tubing was purged with 

purified air for approximately 20 minutes. All components 

were thoroughly rinsed with deionized water until the specific 

conductance of the waste rinse water was less than 1 μS/cm 

(microsiemen per centimeter). 

Water samples were processed in the Massachusetts 

Water Science Center laboratory in Northborough at the conclusion of each sampling round or storm. For water samples 

collected during base-flow conditions when the flow and depth 

of water in the streams were small, water samples generally 

were collected in separate bottles designated for whole water, 

dissolved constituents, and organic compounds; therefore, 

only limited splitting was necessary at the Water Science Center laboratory. For water samples collected during storms, subsamples to be analyzed for inorganic and organic constituents 

were split directly from the 20-L glass bottle by transferring 

the water with a Teflon-diaphragm pump while the contents 

of the sample bottle were homogenized with a stainless-steel 

laboratory mixer. Water to be analyzed for dissolved inorganic constituents was filtered through a 600-cm2

 capsule 

filter with a 0.45-micrometer pore size. Water to be analyzed 

for dissolved caffeine, pesticides, and pesticide metabolites 

was filtered through a 142-mm pre-combusted glass-fiber 

filter with a nominal 0.7-mm pore diameter to remove suspended particulate matter. After the samples were processed, 

they were packed in ice and shipped overnight to the USGS 

National Water Quality Laboratory (NWQL) in Denver, 

Colorado, where they were analyzed for concentrations of dissolved calcium, sodium, chloride, sulfate, total nutrients, and 

polar pesticides and metabolites (Garbarino and others, 2006; 

Patton and Kryskalla, 2003; Furlong and others, 2001; American Public Health Association, 1998; Garbarino and Struzeski, 

1998; Hoffman and others, 1996; Fishman, 1993; Fishman and 

Friedman, 1989). 

The reliability of the chemical data was ensured by the 

preparation and analysis of several types of quality-control 

samples. These quality-control samples include two sourcesolution blanks, three field blanks, six replicate samples, 

and six field-matrix spike samples and replicate field-matrix 

spike samples. These analyses provided the basis for the 

interpretation of chemical data collected in the drinking-water 

source area.

Source-solution blanks were prepared from deionized 

water produced by a laboratory-grade water-purification 

system that uses ion-exchange packs and reverse osmosis. The 

source-solution water was stored in pre-cleaned glass bottles 

until it was subsequently used as blank water for the collection 

of field blanks. 

A field blank is used to test for positive bias 

that can result from contamination at any stage of the 

sample-collection, -processing, or analysis process. One field 

blank was collected during sampling at base-flow conditions 
8 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

in February 2006, and two additional field blanks were 

collected in preparation for the sampling of stormwater in 

December 2005 and July 2006. During collection of baseflow samples, the field blank was collected by transferring 

blank water from the holding bottle to the sample-collection 

bottles. It was then processed in a manner consistent with the 

collection of other environmental samples. The remaining field 

blanks were collected by the automatic sampler in preparation 

for storm sampling. These samples were collected by pumping 

blank water through the automatic sampler tubing and into the 

collection bottle, and processing it in a manner consistent with 

the collection of environmental samples of stormwater. 

Replicate samples are samples that are thought to be 

identical in composition to the environmental samples. Replicate samples provide a measure of bias and variability for 

the method of sample collection, sample processing (splitting, filtering, and preservation), and laboratory analysis, and 

for effects such as analyte degradation that can occur prior 

to laboratory analysis. A total of six replicate samples were 

collected during base-flow conditions and during storms. 

Three replicate samples were collected to test for potential 

differences between samples collected manually and samples 

collected concurrently by automatic samplers. These samples 

were collected during base-flow conditions. The remaining 

three replicates were collected during storms. These samples 

were collected by two independent automatic samplers that 

were triggered simultaneously. These replicates were used to 

test for potential differences between samples collected with 

the same method during periods of rapidly changing flow and 

water quality.

Field-matrix spikes are quality-control samples in which 

known amounts of target compounds are added to environmental replicate-split samples and then measured. The degree 

of recovery for each target analyte added to the environmental 

sample is used to determine the bias and variability attributed 

to the amount of degradation of target analytes during holding and shipment to the laboratory, the analytical method, and 

interferences contained in the environmental sample that mask 

or enhance determinations of the target analytes, or matrix 

effects. Replicate field-matrix spikes also were submitted to 

the NWQL for analysis. Similarly, known amounts of target 

compounds are added to replicate field-matrix spike samples. 

These samples are processed in the same manner as the fieldmatrix spike such that the samples are expected to be essentially identical in composition. Comparing the recovery of a 

field-matrix spike replicate to the recovery of the paired fieldmatrix spike provides a measure of the variability attributed to 

the aforementioned processes that can affect the concentration 

of each analyte.

In addition to the quality-assurance samples collected 

during this project, the NWQL routinely analyzes various 

quality-control samples including laboratory reagent blanks, 

interference check solutions, laboratory control samples, 

standard reference materials, laboratory reagent spike samples, 

and laboratory duplicate samples to test and track method 

performance (Garbarino and others, 2006, and Furlong and 

others, 2001). The NWQL also adds surrogate compounds to 

all samples for determinations of pesticides and caffeine. Surrogate compounds, such as 2,4,5-T, caffeine-13C, and barban, 

are expected to perform similarly to the compounds being 

analyzed in the laboratory method. Because these compounds 

are not normally found in the environment, the recovery of the 

surrogate compounds can be used to qualify the performance 

of the analysis.

Presentation of Data 

Hydrologic, water-quality, and meteorological data 

collected at the USGS monitoring stations during water year 

2006 are presented in tables 4–10 (tables 4–17 are in back 

of the report). Where available, each table includes a summary of daily values, monthly statistics, annual statistics, 

gage datums, and an accuracy rating for each station. The 

period of record and the period-of-record extremes for each 

physical parameter are presented in table 11 by USGS station 

number. The maximum, median, and minimum statistics for 

selected analytical results for the period of record for each 

USGS monitoring station are presented in table 12. Analytical 

results for all base-flow, stormflow, and raw-water samples are 

presented in table 13.

Station History

The station history for each USGS monitoring station 

in the Cambridge drinking-water source area is presented 

in table 11. This table includes basic information about the 

period of record and the extremes for the period of record and 

for water year 2006 for each physical parameter for current 

USGS stations in the Cambridge drinking-water source area. 

The “period of record” is the time during which each type of 

data has been collected at the station. These data may have 

been collected manually on an intermittent basis or continuously with a monitoring system. The “extremes for the period 

of record” refer to the maximum and minimum values measured during the period of record. 

Streamflow Data

Streamflow data are presented in table 4. This table 

includes the daily mean values of discharge by USGS station 

number for the 2006 water year, monthly summary statistics, 

annual summary statistics, and data pertaining to annual 

runoff and flow duration.

Daily Mean Values

The daily table of streamflow records (table 4) gives the 

total discharge for each day of the water year. In the monthly 

summary (at the bottom of the table), the line labeled TOTAL 
Data for the Cambridge Drinking-Water Source Area 9

gives the sum of the daily streamflows for each month; the 

line labeled MEAN gives the arithmetic average of the daily 

streamflows for the month; the lines labeled MAX and MIN 

give the maximum (peak flow) and minimum daily streamflows respectively, for each month; and the line labeled MED 

gives the median daily streamflow for each month. Discharge 

per unit area of the drainage basin for the month is expressed 

in million gallons per day per square mile (line labeled 

MGDSM); runoff is given in inches (line labeled IN.) of water 

over the drainage basin. Values for discharge per unit area 

and runoff in inches are not calculated for stations affected by 

reservoir regulation. 

Annual Summary Statistics

Annual summary statistics are presented at the end of 

table 4 following the daily mean values and monthly summaries. These statistics include the annual total, annual 

mean, annual runoff, and selected streamflow duration-curve 

statistics. In the annual summary for the table, the line labeled 

ANNUAL TOTAL gives the sum of all the daily discharges 

for the water year; the line labeled ANNUAL MEAN gives the 

arithmetic average of the daily discharges for the water year. 

Million gallons per day per square mile (ANNUAL MGDSM) 

is the average number of millions of gallons of water flowing 

per day from each square mile of area drained; the runoff is 

assumed to be distributed uniformly in time and area. Inches 

(ANUUAL IN.) indicates the depth to which the drainage area 

would be covered if all of the runoff for a given time period 

were uniformly distributed on it. Runoff data are omitted for 

stations affected by reservoir regulation. The line labeled 10 

PERCENT EXCEEDS indicates that the discharge that was 

exceeded 10 percent of the time for the designated period 

(the 10-percent flow-duration discharge). The lines labeled 

50 PERCENT EXCEEDS and 90 PERCENT EXCEEDS are 

similarly defined. The line labeled RECORD QUALITY indicates the accuracy of the records (table 3). 

Reservoir Data

Continuous records of reservoir altitude and contents 

for the Cambridge Reservoir, Stony Brook Reservoir, and 

Fresh Pond Reservoir are presented in tables 5 and 6 (tables 

are in back of the report), respectively. Data tables for each 

parameter consist of daily mean values; monthly and annual 

mean, maximum, and minimum values; a gage description; 

and an accuracy rating description. The line labeled GAGE 

indicates the value and definition of the datum used to monitor 

reservoir altitudes. The line labeled RECORD QUALITY 

indicates the accuracy of the records (table 3). The accuracy of 

reservoir contents is determined on the basis of the difference 

in contents associated with the error in the measurements of 

the reservoir altitude. 

Meteorological Data and Physical Parameters

Continuous records of meteorological and physical 

parameters are presented in tables 7 through 10. Data tables 

for precipitation (table 7) consist of daily totals, monthly and 

annual total and maximum values, and an accuracy rating 

description. Data tables for all other parameters (tables 8–10) 

consist of daily maximum, minimum, and mean values; 

monthly and annual maximum, minimum, and mean values; 

and an accuracy rating description. Extreme measurements 

of meteorological and physical parameters recorded during 

water year 2006 and for the period of record are presented in 

table 11 for each USGS station.

Water-Quality Data

The maximum, median, and minimum statistics for concentrations of selected constituents in water samples collected 

during the period of record for each USGS station in the Cambridge drinking-water source area are presented in table 12. 

Detailed analytical results for water samples collected in water 

year 2006 are presented in table 13. Results for quality-control 

samples are presented in table 14.

Data for the Cambridge Drinking-Water 

Source Area

The data presented in this report can be used by the 

watershed managers in the city of Cambridge, Massachusetts, 

to optimize the management of the drinking-water-supply 

reservoirs for water quality and quantity. The data allow 

clarification of the relation of reservoir management practices 

and current conditions to trends in the quantity and quality of 

water in the subbasins of the hydrologic system. 

Surface-Water Data

From October 2005 through July 2006, mean monthly 

discharge from the Hobbs Brook Reservoir accounted for 

less than 30 percent (estimated by dividing the monthly 

discharges measured at USGS station 01104430 by the sum 

of monthly discharges measured at USGS stations 01104460 

and 01104475) of the water entering the downstream Stony 

Brook Reservoir (fig. 2A). During the remainder of the water 

year (August through September 2006), the amount of water 

released from the Cambridge Reservoir, increased to about 

43 percent of the total inflow to the Stony Brook Reservoir. 

This represents a substantial decrease in the amount of water 

released from the Cambridge Reservoir compared to the same 

period in water year 2005, when nearly 99 percent of the water 

entering the downstream Stony Brook Reservoir was released 

from the Cambridge Reservoir (Smith, 2007). This difference 

was the result of the local basins receiving nearly 19 in. of 
10 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006 PERCENT PRECIPITATION, IN INCHES

WATER YEAR 2006

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

B

A

100

90

80

70

60

50

40

30

20

10

0

14

12

10

8

6

4

2

0

Discharge from Hobbs Brook Basin

Water surplus from Stony Brook Reservoir

Station 01104430 Cambridge Reservoir

Station 01104480 Stony Brook Reservoir

Station 422302071083801 Fresh Pond Reservoir

Figure 2. (A ) Discharge from the Hobbs Brook Reservoir as a percentage of water entering the Stony Brook Reservoir, and 

discharge from the Stony Brook Reservoir to the Charles River as a percentage of total inflow to the Stony Brook Reservoir for 

water year 2006; (B ) monthly precipitation totals at the Cambridge Reservoir, Stony Brook Reservoir, and Fresh Pond Reservoir 

in the Cambridge drinking-water source area, Massachusetts, water year 2006.
Data for the Cambridge Drinking-Water Source Area 11

rain during the months of May and June and an additional 10 

in. of rain distributed during the remainder of the water year 

(fig. 2B). From October 2005 through February 2006, and 

during May and June, about 47 percent of all water entering 

the Stony Brook Reservoir (estimated by dividing the sum 

of monthly reservoir outflows measured at USGS station 

01104480 by the sum of monthly discharges measured at 

USGS stations 01104460 and 01104475) was diverted to the 

Charles River (fig. 2A). The volume of water released from 

the Stony Brook Reservoir to the Charles River during water 

year 2006 represents an annual surplus of about 127 percent of 

the total annual water demand by the city of Cambridge. During 1999–2005, this surplus has ranged from 29 to 155 percent 

if average demand is assumed to be 15 Mgal/d. 

The annual runoff for USGS stations 01104415, 

01104455, and 01104475 ranged from 1.38 to 1.70 MGDSM 

(table 4). However, the annual runoff for USGS station 

01104433 was 0.82 MGDSM or about half that of the other 

stations (table 4). The low yield at USGS station 01104433 

may be the result of high flows diverted to a neighboring 

intermittent stream caused by a back-water condition from a 

drainage pipe upstream of the monitoring station that limits 

the rate of flow.

Monthly reservoir contents for the Cambridge Reservoir 

varied from about 59 to 98 percent of capacity during water 

year 2006 (fig. 3). The reservoir storage was at its lowest 

during the month of October. The reservoir storage was near 

capacity in the spring but was subsequently drawn down to 

about 84 percent of its capacity as additional water was needed 

to supplement the city of Cambridge water supply when 

the yield from the Stony Brook Basin diminished. Monthly 

reservoir storage values for the Stony Brook and Fresh Pond 

Reservoirs were maintained at greater than 83 and 94 percent 

of capacity, respectively, during water year 2006 (fig. 3). 

Specific Conductance

Monthly mean specific-conductance values for USGS 

station 01104415 for water year 2006 generally were lower 

than the median of monthly specific-conductance values for 

available data for the period from water year 1997 to water 

year 2005 (Smith, 2005 and 2007; Socolow and others, 1999, 

2000, 2001, 2002, 2003, and 2004) (fig. 4) The monthly mean 

specific conductances for streamflow for Hobbs Brook below 

the Cambridge Reservoir (USGS station 01104430) were 

within the interquartile range of the monthly mean specific 

conductances for the same period (fig. 5). The annual mean 

specific conductance of 738 μS/cm (table 10) was nearly identical to the annual mean specific conductance for water 2005 

which was 737 μS/cm (Smith, 2007). Monthly mean specificconductance values for USGS station 01104433 for water year 

2006 were consistently lower than those for water year 2005 

(Smith, 2007), differing by -11 percent to -49 percent. 

Because of construction activities near USGS station 

01104455, the site was temporarily decommissioned from 

August 2005 through April 2006. As a result, no records of 

water quality are available for the period from October through 

April, except for values estimated from data collected during 

field visits. Monthly mean specific-conductance values during 

the remainder of water year 2006 were consistently lower than 

those for water year 2005 (Smith, 2007), differing by -8 percent 

to -44 percent. For the months of April, June, August, and 

September, the monthly mean conductance values were similar 

to monthly means values for the period from water year 1998 

to 2005 (Smith, 2005 and 2007; Socolow and others, 2000, 

2001, 2002, 2003, and 2004). The monthly mean conductance for May was less than the 25th-percentile value (964 μS/

cm), and the monthly mean conductance for July was greater 

than the 75th-percentile value (1,260 μS/cm) for the same 

period. The interquartile ranges for these months were 263 and 

120 μS/cm, respectively. 

New maximum values for monthly mean specific conductances for Stony Brook at USGS station 01104460 were calculated for the months of December and January. For all other 

months, the monthly mean specific conductances were within 

the established maximum and minimum values for the period 

1997 through 1998 and 2002 through 2005 (fig. 6). For USGS 

station 01104475, monthly mean conductance values for water 

year 2006 were consistently lower than those for the previous 2 

water years (Smith, 2005 and 2007), differing by -2 percent to 

-32 percent. The annual mean specific conductances for USGS 

stations 01104460 and 01104475 were about 15 and 13 percent 

lower, respectively, than the annual mean specific conductances 

for water year 2005, which were 538 and 284 μS/cm, respectively (Smith, 2007).

Many of the small tributaries to the reservoirs differ from 

the primary streams in that both the quantity and quality of 

water in the tributaries respond more rapidly to stormwater 

runoff. The daily mean specific-conductance values for USGS 

stations 01104415, 01104433, and 01104455 differed by as 

much as 826 percent from the annual mean values during 

water year 2006. Daily mean specific-conductance values for 

USGS station 01104475 differed by about 578 μS/cm, or about 

233 percent of the mean annual value during water year 2006. 

The coefficient of variation (COV) (the standard deviation 

divided by the mean) for monthly mean specific-conductance 

values ranged from about 5 percent to about 36 percent (01104

433>01104455>01104415>01104475).

The annual mean specific conductance for Fresh Pond 

Reservoir decreased from 553 μS/cm in the 2005 water year 

(Smith, 2007) to 514 μS/cm in the 2006 water year (table 10 

and fig. 7). The monthly mean specific conductance remained 

between 515 μS/cm and 450 μS/cm from December 2005 

through September 2006. In water year 2005, the specific 

conductance increased during the summer months as a result 

of the increasing influx of water from the Cambridge Reservoir 

(fig. 2A), which had a greater specific conductance than water 

from the primary stream in the Stony Brook Basin (table 10). 

As a result of large amounts of rainfall during the spring and 

throughout the summer of 2006, lower conductance water was 

available from the Stony Brook Basin to buffer the higher conductance water from the Cambridge Reservoir. 
12 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

100

90

80

70

60

50

40

30

20

10

0

MEAN RESERVOIR STORAGE, IN PERCENT

WATER YEAR 2006

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

Station 422302071083801 Fresh Pond Reservoir

Station 01104480 Stony Brook Reservoir

Station 01104430 Cambridge Reservoir

EXPLANATION

Figure 3. Monthly mean reservoir storage as a percentage of capacity for water year 2006 shown as percent capacity for the 

Cambridge Reservoir, Stony Brook Reservoir, and Fresh Pond Reservoir, near Cambridge, Massachusetts.
Data for the Cambridge Drinking-Water Source Area 13

OCT

800

1,000

1,200

1,400

1,600

1,800

2,000

2,200

2,400

2,600

2,800

3,000

3,200

3,400

3,600

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

WATER YEAR 2006

NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

EXPLANATION

Unshaded area shows range between the maximum and minimum monthly mean

value for period of record

Median monthly specific conductance for water years 1997–98 and 2004−05

Monthly mean specific conductance for 2006 water year

Figure 4. Monthly mean specific conductance for water year 2006 for U.S. Geological Survey station 01104415, Cambridge 

Reservoir, unnamed tributary 2, near Lexington, Massachusetts; period-of-record maximum and minimum monthly mean specific 

conductance; and median monthly specific conductance for water years 1997–98 and 2004–05.
14 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

1,500

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

WATER YEAR 2006

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

Unshaded areas show range between the 25th percentile and

the 75th percentile. The lightly shaded areas show the range

between the 75th percentile and the maximum monthly mean

value and the 25th percentile and the minimum monthly mean

value for the water years 1998–2005.

Median monthly specific conductance for water years 1998–2005

Monthly mean specific conductance for 2006 water year

EXPLANATION

Figure 5. Monthly mean specific conductance for water year 2006 for U.S. Geological Survey station 01104430, Hobbs Brook 

below Cambridge Reservoir near Kendal Green, Massachusetts; period-of-record maximum and minimum monthly mean 

specific conductance; and the median, 25th percentile, and 75th percentile monthly specific conductance for water years 

1998 through 2005. 
Data for the Cambridge Drinking-Water Source Area 15

Unshaded areas show range between the 25th percentile and the

75th percentile. The lightly shaded areas show the range between

the 75th percentile and the maximum monthly mean value and the

25th percentile and the minimum monthly mean value for the water

years 1997–98 and 2002–05.

Median monthly specific conductance for water years 1997−98 and 2002−05

Monthly mean specific conductance for 2006 water year

EXPLANATION

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

WATER YEAR 2006

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

300

400

500

600

700

800

200

Figure 6. Monthly mean specific conductance for water year 2006 for U.S. Geological Survey station 01104460, 

Stony Brook at Route 20 at Waltham, Massachusetts; period-of-record maximum and minimum monthly mean specific 

conductance; and the median, 25th percentile, and 75th percentile monthly specific conductance for water years 

1997–98 and 2002–05.
16 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

EXPLANATION

Water year 2005

Water year 2006

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

MONTH OF YEAR

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

500

550

600

650

700

750

400

450

Figure 7. Monthly mean specific conductance for water years 2005 and 2006 for U.S. Geological Survey station 422302071083801, 

Fresh Pond Reservoir at Cambridge, Massachusetts.
Data for the Cambridge Drinking-Water Source Area 17

Water-Quality Data

Water samples were collected in nearly all of the subbasins in the Cambridge drinking-water source area and 

from Fresh Pond during water year 2006. Six water samples 

were collected manually during base-flow conditions and 

seven composites of stormwater were collected with automatic samplers at the primary sampling sites (USGS stations 

01104415, 01104433, 01104455, 01104460, and 01104475). 

Three samples of water from Fresh Pond were collected from 

the raw-water intake at the Cambridge water treatment plant. 

A single water sample also was collected from secondary sampling sites (USGS stations 01104390, 01104405, 01104410, 

01104420, 01104430, and 01104453) during a synchronous 

sampling round on July 18 when samples of water were 

collected at most of the subbasins within the Hobbs Brook 

and Stony Brook basin during the same day. Various qualityassurance samples also were collected to determine bias and 

precision associated with the sample data. All samples were 

analyzed for physical properties and concentrations of dissolved calcium, sodium, chloride, sulfate, total nutrients, and 

polar pesticides and metobolites.

The physical properties and chemical concentrations 

for water samples were compared to the U.S. Environmental 

Protection Agency (USEPA) recommended freshwater-quality 

criterion and the USEPA secondary drinking-water standards, 

where available. Secondary drinking-water regulations are 

non-mandatory water-quality standards established by the 

USEPA. They are guidelines designed to assist public water 

suppliers in managing their drinking water for aesthetic 

considerations, such as taste, odor, color, foaming, corrosivity, 

staining, scaling, and sedimentation. These constituents do 

not present a risk to human health at the secondary maximum 

contaminant level (U.S. Environmental Protection Agency, 

2007). Although these standards typically are applied to 

finished water, the presence of these constituents in concentrations that exceed the respective standards can damage water 

equipment or reduce the effectiveness of treatment for other 

contaminants. Some constituents, such as chloride, sodium, 

and nitrogen, cannot be effectively removed or reduced during 

the water-treatment process (Smith, 2007).

 In 6 of 71 water samples, measurements of pH were 

less than the USEPA recommended freshwater-quality 

criterion and the USEPA secondary drinking-water standard 

of 6.5 pH units. Concentrations of dissolved chloride in all 

water samples collected during base-flow conditions from 

USGS stations 01104405, 01104415, 01104420, 01104433, 

and 01104455 exceeded the USEPA national recommended 

freshwater-quality criterion of 230 mg/L (milligrams per 

liter). With the exception of one of six samples collected during base-flow conditions at USGS station 01104455, chloride 

concentrations in all of the respective samples also exceeded 

the USEPA secondary drinking-water standard of 250 mg/L. 

Concentrations of dissolved chloride in three out of seven and 

three out of eight composites of water collected during storms 

at USGS stations 01104415 and 01104433, respectively, also 

exceeded the USEPA recommended freshwater-quality criterion and secondary drinking-water standard. Concentrations 

of dissolved sulfate in all 71 water samples were below the 

USEPA secondary drinking-water standard of 250 mg/L.

Concentrations of dissolved calcium, sodium, chloride, 

and sulfate in water samples collected in the drinking-water 

source area varied from 6.55 to 112, 19.6 to 449, 31.1 to 793, 

and 5.78 to 57.6 mg/L, respectively (table 13). The average concentrations of dissolved calcium and sulfate in water 

samples collected during storms were lower than the average 

concentrations observed in water samples collected during 

base-flow conditions at the primary sampling stations. With 

the exception of USGS station 01104475, the average concentrations of dissolved sodium and chloride in water samples 

collected during storms also were lower than the average concentrations observed in water samples collected during baseflow conditions at the primary sampling stations. The highest 

concentrations of dissolved sodium, chloride, and sulfate were 

found in a water sample collected on March 13, 2006, during a 

winter storm at USGS station 01104415. The highest concentration of dissolved calcium was found in a water sample 

collected on April 21, 2006, at USGS station 01104433. 

Concentrations of dissolved calcium in water samples collected at USGS stations 01104405, 01104430, 01104433, and 

01104460 in water year 2006 were the highest measured by 

the USGS for water years 1997 to 2006 (table 12). Similarly, 

concentrations of dissolved sodium and chloride in water 

samples collected at USGS stations 01104390, 01104430, 

01104433, 01104460, and 01104475 in water year 2006 were 

greater than the previous maximum concentration recorded by 

the USGS since water year 1997 (table 12).

The concentration of total nitrogen in water samples for 

all subbasins ranged from 0.55 to 3.12 mg/L. Average nitrogen concentrations in water samples for the tributaries at the 

primary sampling sites ranged from 1.41 to 1.77 mg/L. The 

average concentration of nitrogen in water samples collected 

during base-flow conditions was not substantially different from the average concentration of nitrogen in composite 

samples of stormwater at USGS stations 01104415, 01104460, 

and 01104475. The difference between average concentrations 

of total nitrogen in samples of base flow and stormwater was 

about 0.5 mg/L at USGS stations 01104433 and 01104455. 

The highest concentration of total nitrogen (3.12 mg/L) was 

observed in a sample of water collected on December 12, 

2005, during base-flow conditions at USGS station 01104433. 

Concentrations of total nitrogen in water samples collected 

in water year 2006 at USGS stations 01104410, 01104430, 

01104433, and 01104460 were greater than the previous maximum concentrations of total nitrogen recorded by the USGS 

since water year 1997 (table 12).

Concentrations of total phosphorus were similar in water 

samples collected during base-flow conditions for all subbasins; however, the average concentration of total phosphorus in 

samples of stormwater at the primary sampling stations were 

from 160 to 1,109 percent greater than the average concentration in water samples collected during base-flow conditions 
18 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

at the same stations. Concentrations of total phosphorus in 

water samples collected in water year 2006 were greater than 

the previous maximum concentrations of total phosphorus 

recorded by the USGS since water year 1997 for USGS stations 01104390 and 01104420 (table 12). 

Twenty pesticides and caffeine were detected in water 

samples collected in the primary streams and tributaries to 

the Cambridge Reservoir and Stony Brook Reservoir, and 

in raw water collected from the Cambridge water-treatment 

facility intake from the Fresh Pond Reservoir in water year 

2006. Most of these pesticides are found in over-the-counter 

products used for turf management and the treatment of ornamental shrubs (table 15). Caffeine was detected in 77 percent 

of 70 water samples at concentrations ranging from 0.003 to 

1.82 μg/L (micrograms per liter). Imidacloprid, siduron, 

and carbaryl were the most frequently detected pesticides 

(table 16). The compounds 2,4-D, MCPA, and triclopyr were 

detected only in samples of stormwater runoff. Caffeine, 

metalaxyl, and siduron were more frequently detected in water 

samples collected during storms than in water samples collected during base-flow conditions. Imazaquin, imidacloprid, 

and siduron were the only widespread pesticides detected 

in water samples collected at USGS stations 01104415, 

01104433, 01104455, 01104460, and 01104475. The herbicide norflurazon was detected in all water samples collected 

at USGS station 01104455. The insecticide imidacloprid and 

the fungicides benomyl, metalaxyl, and propiconazole were 

detected in water samples collected at USGS station 01104475 

at a frequency equal to or greater than about 85 percent. With 

the exception of USGS stations 01104405 (in the Hobbs 

Brook Basin) and 01104453 (in the Stony Brook Basin), neither caffeine nor any pesticides listed in table 13 were detected 

in water samples collected at any of the secondary sampling 

sites. Caffeine, 2-Hydroxy-4-isopropylamino-6-ethylamino-striazine, carbaryl, imidacloprid, norflurazon, and siduron also 

were detected in water from the Fresh Pond Reservoir.

Quality-Control Samples

Trace amounts of calcium, sodium, total nitrogen, phosphorus, and caffeine were detected in one or more field blanks 

(table 14). The maximum concentration of calcium, sodium, 

and total nitrogen measured in field blanks was one or more 

orders of magnitude less than the lowest concentration found 

in all environmental samples and was within the precision of 

the laboratory methods (Patton and Kryskalla, 2003; Fishman 

and Friedman, 1989). Although the concentrations of total 

phosphorus and caffeine measured in a single field blank were 

low, the results for several environmental samples (particularly those samples collected during base-flow conditions 

and analyzed for total phosphorus) also were low and should 

be viewed with caution. If it is assumed that the amount of 

phosphorus and caffeine measured in the field-blank water 

represents the maximum amount of contamination present in 

any given sample, the potential positive bias for concentrations of total phosphorus and caffeine compared to the average 

concentrations in all samples collected during the 2006 water 

year is 11 and 2 percent, respectively.

Field and laboratory concurrent replicate sets were 

analyzed by comparing the relative percent differences 

(RPDs) of the results for each pair of samples where the same 

analyte was detected in both samples. The maximum RPD 

for measurements of turbidity for replicate sets was less 

than about 14 percent, or 2 NTRUs. Measurements of pH 

for replicate sets were within 0.1 pH unit of each other. The 

maximum RPD for both field and laboratory measurements 

of specific conductance was less than about 5 percent. The 

RPDs for calcium, sodium, chloride, sulfate, total nitrogen, 

and total phosphorus were also precise and varied by no more 

than about 6 percent, except the RPD for total phosphorus in a 

single replicate set, which was about 10 percent, or 0.01 mg/L. 

Total phosphorus was inconsistently detected in replicate pairs 

collected during base-flow conditions, and as a result, fewer 

observations were available to determine the RPD for that constiuent. Similarly, norflurazon and triclopyr were detected only 

in the environmental samples and not in the replicate samples. 

The RPDs for 2,4-D, metalaxyl, propiconazole, and siduron 

were less than 8 percent. The RPDs for benomyl, caffeine, carbaryl, and imidacloprid ranged from 0 to 50 percent; however, 

the RPDs for replicate pairs in composites of stormwater were 

less than 8 percent. The concentrations of these compounds 

in replicate sets collected during base-flow conditions were 

generally low and were estimated by the NWQL. As a result, 

the uncertainty in these measurements is greater than the 

uncertainty in measurements made at higher concentrations 

and above the laboratory reporting level. Therefore, the difference in the variability associated with the replicate sets collected during different flow conditions is more likely attributed 

to the precision of the analytical method than to any potential 

bias associated with the sample-collection method. 

Polar pesticides and metabolites are detected, identified, and quantified under different ionization modes. Some 

compounds preferentially form positive ions during the 

analytical method, while other compounds form negative ions 

(Furlong and others, 2001). Because field-matrix spike and 

field-matrix spike replicate samples were fortified with either 

compounds determined under positive ionization conditions or 

with compounds determined under negative ionization conditions, the RPD for background concentrations of non-fortified 

compounds was determined for each pair of samples where 
Data for the Cambridge Drinking-Water Source Area 19

the same analyte was detected in both samples. The RPD for 

concentrations of benomyl, carbaryl, metalaxyl, imidacloprid, propiconazole, and siduron in environmental samples 

and paired field-matrix spike and field-matrix spike replicate 

samples that were not fortified was less than 9 percent. Caffeine and propoxur were not consistently detected in either 

the environmental sample or the non-fortified samples, and 

therefore, RPDs were not computed.

The average recovery for all compounds determined 

under positive ionization conditions in spiked deionized water 

was about 83 percent. Individual recoveries for these compounds ranged from about 10 percent to 140 percent. Spike 

recoveries for analytes detected in environmental samples and 

determined under positive ionization conditions ranged from 

43 to 140. The RPDs for all analyte recoveries in the pair of 

spike samples ranged from about -30 percent to 13 percent. 

The RPDs for all analyte recoveries for those compounds 

detected in environmental samples and in the pair of spike 

samples were less than 6 percent. These recoveries represent 

variability associated with sample processing, spiking technique, sample degradation, and laboratory method performance in the absence of any environmental matrix effect. 

Spike recoveries for compounds determined under negative 

ionization conditions in the sample of deionized water were 

not available.

The average of the mean recoveries for all compounds 

except 2-Hydroxy-4-isopropylamino-6-ethylamino-s-triazine 

and chlorodiamino-s-triazine, which were not included in the 

spike solutions, in spiked environmental samples was about 

87 percent with a relative standard deviation of about 37 

percent. Recoveries for these analytes ranged from about 20 

to 202 percent (table 17). The average of the mean recoveries for all compounds determined under positive ionization 

conditions was about 76 percent, and the average of the mean 

recoveries for all compounds determined under negative 

ionization conditions was about 124 percent. Spike recoveries 

for analytes detected in environmental samples ranged from 

about 80 to 107 percent, except for 2-Chloro-6-ethylamino4-amino-s-triazine, benomyl, caffeine, and imazaquin, which 

had mean recoveries of 35, 49, 61, and 66 percent, respectively. The RPD for all replicate spike recoveries ranged 

from about -35 percent to 13 percent. The RPDs for analyte 

recoveries between paired spike samples for compounds that 

were detected in environmental samples were within about 

30 percent. These recoveries represent variability associated with sample splitting and processing, spiking technique, 

sample degradation, laboratory method performance, and 

potential matrix effects.

The average recovery for the surrogate compounds 

2,4,5-T, barban, and caffeine-13C for all environmental 

samples was 119, 103, and 77 percent, respectively. The 

COV for these compounds was 62, 49, and 30 percent, 

respectively. Surrogate recoveries provide a measure of 

method performance for each individual sample. When the 

difference between surrogate recoveries is outside acceptable 

control limits (usually low) as a result of an identified process failure, the results for the associated analytes are usually 

flagged by the NWQL with the “E” code (estimated value), or 

even deleted, if the recovery is poor. Reporting levels may also 

be adjusted accordingly under some circumstances.

Meteorological Data

Monthly precipitation totals for the Cambridge drinkingwater source area varied from about 0.5 in. to more than 12 in. 

during water year 2006 (fig. 2B and table 7). The COVs for 

monthly precipitation totals for each site were similar, ranging 

from about 65 to 78 percent. Monthly precipitation totals for 

USGS stations 01104480 and 422302071083801 differed from 

those for USGS station 01104430 by -25 to 27 percent with 

average differences of about 5 and 11 percent, respectively. In 

general, variability between monthly precipitation totals for 

all stations is attributed to differences in storm tracks, stormintensity patterns, and storm wind intensity. Additionally, variability between monthly precipitation totals during the winter 

months is compounded by a change in precipitation type—that 

is, snow is less dense than rain and, therefore, is affected more 

strongly by wind. The precipitation gages at USGS stations 

01104480 and 422302071083801 are more susceptible to wind 

bias than the gage at USGS station 01104430, and therefore, 

the totals are generally lower (fig. 2B and table 7). The annual 

precipitation total recorded at station 01104430 during water 

year 2006 was about 16 percent greater than the total for water 

year 2005 and was from 12 and 73 percent greater than any 

amount recorded since water year 2002 (Smith, 2005 and 

2007; Socolow and others, 2003 and 2004).

Mean monthly air-temperature values were generally 

similar from site to site, differing by no more than about 

1.6 ̊C. Mean monthly air-temperature values varied most in 

January, February, and September. During water year 2006, 

mean monthly air-temperature values were within 2 ̊C of the 

median values for water years 2002 through 2005 (fig. 8), 

except for the months of January and September 2006 when 

they were about 6.5 and -8.1 ̊C from the median values for 

water years 2002 through 2005 (Smith, 2005 and 2007; 

Socolow and others, 2002 and 2003). 
20 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

-10

-5

0

5

10

15

20

25

WATER YEAR 2006

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

Unshaded area shows range between the maximum and

minimum monthly mean value for period of record

Median monthly air temperature for water years 2002–05

Monthly mean air temperature for 2006 water year

EXPLANATION

AIR TEMPERATURE, IN DEGREES CELSIUS

Figure 8. Monthly mean air temperatures for water year 2006 for the Cambridge Reservoir, Massachusetts, periodof-record maximum and minimum monthly mean air temperatures, and the median monthly air temperatures for 

water years 2002–05.
References Cited 21

References Cited

American Public Health Association, 1998, Standard methods 

for the examination of water and wastewater (20th ed.): 

Washington, D.C., American Public Health Association, 

American Water Works Association, and Water Environment Federation, p. 3–37, 3–43.

Anderson, C.W., 2004 (2d ed.), Turbidity, in Wilde, F.D., and 

Radtke, D.B., eds., Field measurements: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chap. A6.7, 64 p., accessed April 7, 2005, at http: //water.

usgs.gov/owq/FieldManual/Chapter6/6.7_contents.html

ASTM International, 2003, D1889–00 Standard test method 

for turbidity of water, in ASTM International, Annual Book 

of ASTM Standards, Water and Environmental Technology, 

v. 11.01: West Conshohocken, Pa., 6 p.

Buchanan, T.J., and Somers, W.P., 1968, Stage measurements 

at gaging stations: Techniques of Water-Resources Investigations of the U.S. Geological Survey, book 3, chap. A7, 

28 p.

Buchanan, T.J., and Somers, W.P., 1969, Discharge measurements at gaging stations: Techniques of Water-Resources 

Investigations of the U.S. Geological Survey, book 3, 

chap. A8, 65 p.

Carter, R.W., and Davidian, Jacob, 1968, General procedure 

for gaging streams: Techniques of Water-Resources Investigations of the U.S. Geological Survey, book 3, chap. A6, 

13 p.

Extension Toxicology Network, 1993a, Pesticide information 

profile for diuron, accessed on April 05, 2006, at http://

pmep.cce.cornell.edu/profiles/extoxnet/dienochlorglyphosate/diuron-ext.html

Extension Toxicology Network, 1993b, Pesticide information 

profile for MCPA, accessed on April 05, 2006, at 

http://pmep.cce.cornell.edu/profiles/extoxnet/haloxyfopmethylparathion/mcpa-ext.html

Extension Toxicology Network, 1993c, Pesticide information 

profile for metalaxyl, accessed on April 05, 2006, at 

http://pmep.cce.cornell.edu/profiles/extoxnet/haloxyfopmethylparathion/metalaxyl-ext.html 

Extension Toxicology Network, 1993d, Pesticide information 

profile for metsulfuron-methyl, accessed on April 05, 2006, 

at http://pmep.cce.cornell.edu/profiles/extoxnet/metirampropoxur/metsulfuron-methyl-ext.html

Extension Toxicology Network, 1993e, Pesticide information 

profile for propoxur, accessed on April 05, 2006, at 

http://pmep.cce.cornell.edu/profiles/extoxnet/metirampropoxur/propoxur-ext.html

Extension Toxicology Network, 1993f, Pesticide information 

profile for triclopyr, accessed on April 05, 2006, at 

http://pmep.cce.cornell.edu/profiles/extoxnet/pyrethrinsziram/triclopyr-ext.html

Extension Toxicology Network, 1996a, Pesticide information 

profile for fluometuron, accessed on August 28, 2007, at 

http://extoxnet.orst.edu/pips/fluometu.htm

Extension Toxicology Network, 1996b, Pesticide information profile for imazaquin, accessed on April 05, 

2006, at http://pmep.cce.cornell.edu/profiles/extoxnet/

haloxyfop-methylparathion/imazaquin-ext.html

Extension Toxicology Network, 1997, Pesticide information profile for propiconazole, accessed on April 05, 

2006, at http://pmep.cce.cornell.edu/profiles/extoxnet/

metiram-propoxur/propiconazole-ext.html

Extension Toxicology Network, 2005, Pesticide information profile for imidacloprid, accessed on April 05, 

2006, at http://pmep.cce.cornell.edu/profiles/extoxnet/

haloxyfop-methylparathion/imidacloprid-ext.html

Fishman, M.J., ed., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

Determination of inorganic and organic constituents in 

water and fluvial sediments: U.S. Geological Survey 

Open-File Report 93–125, 217 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

Fugro East, Inc., 1996, Limnological investigations of the 

Cambridge Reservoir system—Impacts of watershed inputs 

and alum sludge discharge: Cambridge, Mass., Cambridge 

Water Department, 77 p., plus appendixes.

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of pesticides in 

water by graphitized carbon-based solid-phase extraction 

and high-performance liquid chromatography/mass 

spectrometry: U.S. Geological Survey Water-Resources 

Investigations Report 01–4134, 73 p.

Garbarino, J.R., Kanagy, L.K., and Cree, M.E., 2006, 

Determination of elements in natural-water, biota, sediment 

and soil samples using collision/reaction cell inductively 

coupled plasma-mass spectrometry: U.S. Geological 

Survey Techniques and Methods, book 5, sec. B, chap. 1, 

88 p.
22 Hydrologic, Water-Quality, and Meteorological Data for the Cambridge, Mass., Drinking-Water Source Area, WY 2006

Garbarino, J.R., and Struzeski, T.M., 1998, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—Determination of elements in wholewater digests using inductively coupled plasma-optical 

emission spectrometry and inductively coupled plasmamass spectrometry: U.S. Geological Survey Open-File 

Report 98–165, 101 p.

Hoffman, G.L., Fishman, M.J., and Garbarino, J.R., 1996, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory-In-bottle acid digestion of wholewater samples: U.S. Geological Survey Open-File Report 

96–225, 28 p.

Hornsby, A.G., Wauchope, R.D., and Herner, A.E., 1996, 

Pesticide properties in the environment: New York, 

Springer-Verlag, 227 p.

Kennedy, E.J., 1983, Computation of continuous records of 

streamflow: Techniques of Water-Resources Investigations 

of the U.S. Geological Survey, book 3, chap. A13, 52 p.

Kennedy, E.J., 1984, Discharge ratings at gaging stations: 

Techniques of Water-Resources Investigations of the U.S. 

Geological Survey, book 3, chap. A10, 59 p.

Oberg, K.A., Morlock, S.E., and Caldwell, W.S., 2005, 

Quality-assurance plan for discharge measurements using 

acoustic Doppler current profilers: U.S. Geological Survey 

Scientific Investigations Report 2005–5183, 35 p.

Patterson, Glenn, 1997, The U.S. Geological Survey drinking 

water initiative: U.S. Geological Survey Fact Sheet 047–97, 

2 p.

Patton, C.J., and Kryskalla, J.R., 2003, Methods of analysis 

by the U.S. Geological Survey National Water Quality 

Laboratory—Evaluation of alkaline persulfate digestion 

as an alternative to kjeldahl digestion for determination 

of total and dissolved nitrogen and phosphorus in water: 

U.S. Geological Survey Water-Resources Investigations 

Report 03–4174, 33 p.

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow—Volume 1. Measurement of stage and 

discharge: U.S. Geological Survey Water-Supply Paper 

2175, 284 p.

Seiler, R.L., Zaugg, S.D., Thomas, J.M., and Howcroft 

D.L., 1999, Caffeine and pharmaceuticals as indicators of 

waste water contamination in wells: Ground Water, v. 37, 

no. 3, p. 405–410.

Smith, K.P., 2007, Hydrologic, water-quality, and meteorological data for the Cambridge, Massachusetts, drinking-water 

source area, water year 2005: U.S. Geological Survey 

Open-File Report 2007–1049, 119 p.

Smith, K.P., 2005, Hydrologic, water-quality, bed-sediment, 

soil-chemistry, and statistical summaries of data for the 

Cambridge, Massachusetts, drinking-water source area, 

water year 2004: U.S. Geological Survey Open-File Report 

2005–1383, 110 p.

Socolow, R.S., Comeau, L.Y., Zanca, J.L., and Ramsbey, L.R., 

1999, Water-resources data for Massachusetts and Rhode 

Island, water year 1998: U.S. Geological Survey WaterData Report MA-RI-98-1, 438 p. 

Socolow, R.S., Girouard, G.G., and Ramsbey, L.R., 2003, 

Water-resources data for Massachusetts and Rhode Island, 

water year 2002: U.S. Geological Survey Water-Data 

Report MA-RI-02-1, 339 p.

Socolow, R.S., Leighton, J.F., Whitley, J.F., and Ventetuolo, 

D.J., 2002, Water-resources data for Massachusetts and 

Rhode Island, water year 2001: U.S. Geological Survey 

Water-Data Report MA-RI-01-1, 307 p.

Socolow, R.S., Whitley, J.S., Murino, D., Jr., and Ramsbey, 

L.R., 2001, Water-resources data for Massachusetts and 

Rhode Island, water year 2000: U.S. Geological Survey 

Water-Data Report MA-RI-00-1, 459 p.

Socolow, R.S., Zanca, J.L., Driskell, T.R., and Ramsbey, L.R., 

2004, Water-resources data for Massachusetts and Rhode 

Island, water year 2003: U.S. Geological Survey WaterData Report MA-RI-03-1, 368 p.

Socolow, R.S., Zanca, J.L., Murino, D., Jr., and Ramsbey, 

L.R., 2000, Water-resources data for Massachusetts and 

Rhode Island, water year 1999: U.S. Geological Survey 

Water-Data Report MA-RI-99-1, 401 p.

U.S. Environmental Protection Agency, 2006a, Consumer factsheet on 2,4-D, accessed on April 05, 2006, at http: //www.

epa.gov/safewater/contaminants/dw_contamfs/24-d.html

U.S. Environmental Protection Agency, 2006b, Consumer 

factsheet on oxamyl (vydate), accessed on August 28, 2007, 

at http://www.epa.gov/safewater/contaminants/dw_contamfs/oxamyl.html

U.S. Environmental Protection Agency, 2004a, Carbaryl IRED 

facts, accessed on April 05, 2006, at http://www.epa.gov/

oppsrrd1/REDs/factsheets/carbaryl_factsheet.pdf

U.S. Environmental Protection Agency, 2004b, Drinking 

water assessment for flumetsulam for uses on field corn and 

soybeans, accessed on August 28, 2007, at http://www.fluorideaction.org/pesticides/flumetsulam.drink.h2o.may04.pdf

U.S. Environmental Protection Agency, 2004c, RED FACTS 

MCPA, accessed on April 05, 2006, at http://www.epa.gov/

oppsrrd1/REDs/factsheets/mcpa_red_fs.pdf
References Cited 23

U.S. Environmental Protection Agency, 2007, List of national 

secondary drinking water regulations, accessed September 

24, 2007, at http://www.epa.gov/safewater/contaminants/

index.html#sec 

U.S. Environmental Protection Agency, 2001, Benomyl RED 

Facts: Benomyl fact sheet, EPA-738-F-02-001.

U.S. Environmental Protection Agency, 1996, RED FACTS 

Norflurazon, accessed on April 05, 2006, at http://www.epa.

gov/oppsrrd1/REDs/factsheets/0229fact.pdf

U.S. Environmental Protection Agency, 1994, RED FACTS 

Metalaxyl, accessed on April 05, 2006, at http://www.epa.

gov/oppsrrd1/REDs/factsheets/0081fact.pdf

Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, 

B.A., 2006a, Guidelines and standard procedures for 

continuous water-quality monitors—Station operation, 

record computation, and data reporting: U.S. Geological 

Survey Techniques and Methods 1–D3, 51 p., + 8 attach-

ments, accessed April 10, 2006, at http://pubs.water.usgs.

gov/tm1d3

Wagner, R.J., Frans, L.M., and Huffman, R.L., 2006b, Occur-

rence, distribution, and transport of pesticides in agricul-

tural irrigation return flow from four drainage basins in 

the Columbia Basin Project, Washington, 2002–2004, and 

comparison with historical data: U.S. Geological Survey 

Scientific Investigations Report 2006–5005, 54 p.

Waldron, M.C., and Bent, G.C., 2001, Factors affecting 

reservoir and stream-water quality in the Cambridge, 

Massachusetts, drinking-water source area and implications 

for source-water protection: U.S. Geological Survey WaterResources Investigations Report 00–4262, 89 p.

Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., 

eds., September 1999, Collection of water samples: U.S. 

Geological Survey Techniques of Water-Resources Investi-

gations, book 9, chap. A4, accessed on November 2, 2006, 

at http://pubs.water.usgs.gov/twri9A4/