U.S. Department of the Interior

Bureau of Reclamation

Estimates of Dissolved-Solids Load of the Dolores River in 

the Paradox Valley, Montrose County, Colorado, 1988 

through 2009

Administrative Report

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia 2010

 

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

endorsement by the U.S. Government.
iii

Contents

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

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

Data ........................................................................................................................................................................... 2

Estimating Concentration of Dissolved Solids from Specific Conductance.................................................................... 5

Estimates of Dissolved-Solids Load of the Dolores River in the Paradox Valley, 1988 through 2009 .......................... 8

Acknowledgments ........................................................................................................................................................10

References Cited..........................................................................................................................................................11

Supplemental Data .......................................................................................................................................................13

Figures

Figure 1. Locations of streamgaging stations 09169500 and 09171100 and the Paradox Valley Unit brineproduction wells, injection well, and water-quality monitors, Montrose County, Colorado, 2010. .................................. 2

Figure 2. Piper diagrams showing proportions of major cations and anions, as percentage of milliequivalents per 

liter, in the Dolores River at Bedrock, Colorado (station 09169500) and near Bedrock, Colorado (station 09171100), 

August 27, 1987, through December 1, 2009. ............................................................................................................... 6

Figure 3. Relation of concentration of dissolved solids and specific conductance of the Dolores River at Bedrock, 

Colorado (station 09169500) and near Bedrock, Colorado (station 09171100), August 27, 1987, through December 1, 

2009. [DS = concentration of dissolved solids; SC = specific conductance] .................................................................. 6

Figure 4. Estimated mean-daily concentration of dissolved solids of the Dolores River at Bedrock, Colorado 

(station 09169500) and near Bedrock, Colorado (09171100), 1988 through 2009. ....................................................... 8
iv

Figure 5. Estimated daily dissolved-solids load of the Dolores River at Bedrock, Colorado (station 09169500) and 

near Bedrock, Colorado (09171100), 1988 through 2009.............................................................................................. 8

Figure 6. Estimated difference in dissolved-solids load of the Dolores River between gaging stations 09169500 and 

09171100, Paradox Valley, Montrose County, Colorado, 1988 through 2009. [Notes: 442 missing values prior to 

January 1, 1993, and 437 values with difference in loads less than 1 ton per day not shown.] ..................................... 9

Tables

Table 1. Specific conductance, concentration of dissolved solids, and discharge of the Dolores River at Bedrock, 

Colorado (station 09169500) and near Bedrock, Colorado (station 09171100), August 27, 1987, through December 1, 

2009. ................................................................................................................................................................. 13

Table 2. SYSTAT output regression analysis of dissolved-solids concentration and specific-conductance values 

for the Dolores River at Bedrock, Colorado (station 09169500) and near Bedrock, Colorado (station 09171100), 1987 

through 2009. .............................................................................................................................................................. 26

Table 3. DoloresRiverLoad_1988-2009.xlsx.......................................................................................................... 32
v

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

mile (mi) 1.609 kilometer (km)

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

gallon (gal) 3.785 cubic decimeter (dm3) 

cubic foot (ft3) 28.32 cubic decimeter (dm3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

cubic foot (ft3) 28.32 liter (L) 

Flow rate

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

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

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

Mass

ton, short (2,000 lb) 9.0718474 x 108 milligram (mg) 

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

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

ton per year (ton/yr) 0.9072 metric ton per year
1

Estimates of Dissolved-Solids Load of the Dolores River 

in the Paradox Valley, Montrose County, Colorado, 1988 

through 2009

By Kenneth R. Watts

Introduction 

Saline groundwater discharge to the Dolores River substantially increases the dissolved-solids 

load of the Dolores River as it crosses the Paradox Valley (fig. 1). In July 1996, the Bureau of 

Reclamation (BOR) began production operation of a salinity control project, the Paradox Valley Unit 

(PVU), to reduce discharge of saline groundwater (brine) to the Dolores River in the Paradox Valley. 

The PVU pumps brine from an alluvial aquifer, which is hydraulically connected to the Dolores River, 

at a rate of about 230 gal/min (about 0.5 ft3/s). The brine-production wells are completed near the base 

of the alluvial aquifer and below the freshwater/brine interface. Pumping the brine-production wells 

lowers the freshwater/brine interface, which reduces or reverses the vertical hydraulic gradient between 

the freshwater/brine interface and the river. As a result of changes in position of the freshwater/brine 

interface and the magnitude and (or) direction of the vertical hydraulic gradient, discharge of brine and 

the dissolved-solids load of the Dolores River decreases. The BOR evaluates the performance of the 

PVU based on estimates of the dissolved-solids load contributed to the Dolores River in the Paradox 

Valley. Specific conductance and concentrations of dissolved solids of water samples collected from 
2

the Dolores River at U.S. Geological Survey (USGS) streamgaging stations 09169500 and 09171100 

(fig. 1) and continuous streamflow and specific-conductance data previously have been used to estimate 

the dissolved-solids load of the Dolores River in the Paradox Valley (Watts, 2000; and Chafin, 2003). 

An update of estimated dissolved-solids load of the Dolores River was done because much additional 

data have been collected at the gaging stations since the previous estimates.

Figure 1. Locations of streamgaging stations 09169500 and 09171100 and the Paradox Valley Unit brineproduction wells, injection well, and water-quality monitors, Montrose County, Colorado, 2010.

Purpose and Scope 

The purpose of this report is to describe the data and methods used to estimate the dissolvedsolids load of the Dolores River in the Paradox Valley, Montrose County, Colorado, and to present 

estimates of dissolved-solids loads of the Dolores River in the Paradox Valley for the period January 1, 

1988, through December 31, 2009. 

Data

Streamflow and water-quality data used in this analysis were collected at USGS stations 

09169500 (Dolores River at Bedrock, Colorado) and 09171100 (Dolores River near Bedrock, Colorado) 

(fig. 1) during August 27, 1987, through December 31, 2009. The data includes mean-daily discharge 

and specific conductance, during 1988 through 2009, and measurements of specific conductance and 

concentrations of dissolved solids in samples collected from the Dolores River at the stations during 

August 27, 1987, through December 1, 2009. Station 09169500, the Dolores River at Bedrock, 

Colorado, is located upstream from the PVU and near upstream side of the valley; and station 

09171100, the Dolores River near Bedrock, Colorado, is located downstream from the PVU and the 

Paradox Valley (fig. 1). 
3

Stream stage and specific conductance are monitored continuously (15-minute intervals) at the 

stations. Stream discharge is estimated from the stage measurements and the relation between discharge 

and stage, as determined by measurements of instantaneous discharge (Carter and Davidian, 1968). 

Water-quality samples have been collected approximately monthly since August 27, 1987, to determine 

concentrations of major ions (bicarbonate, calcium, carbonate, chloride, magnesium, potassium, sodium, 

and sulfate) and dissolved solids and to measure specific conductance. The concentrations of 

bicarbonate and carbonate are estimated from sample alkalinity and pH (Rounds, 2003).

Mean daily discharge (ft3/s) and mean-daily specific conductance ( S/cm) of the Dolores River 

at Bedrock (station 09169500) and near Bedrock (station 09171100) were retrieved from the Web 

interface of the National Water Information System (NWIS) (accessed at 

http://waterdata.usgs.gov/co/nwis/) for the period January 1, 1988, through December 31, 2009. 

Concentration of dissolved solids in and specific conductance of water samples collected from 

the Dolores River at stations 09169500 and 09171100 were retrieved from the NWIS Web interface for

the period August 27, 1987, through December 1, 2009 (table 1, Supplemental Data). Data for two 

samples collected in 1978 at both stations that were used by Chafin (2003) were not included in this 

analysis because about 9 years separated the date of their collection from the beginning of periodic 

sampling during August 1987 and because the flow of the Dolores River upstream from the Paradox 

Valley has been regulated by McPhee Reservoir (not shown in figure 1) since March 19, 1984 (U.S. 

Geological Survey, 2009). 

Concentration of dissolved solids in water-quality samples collected from the Dolores River at 

Bedrock (station 09169500) during August 27, 1987, through December 1, 2009, ranged from 158 to 

2,260 mg/L and specific-conductance values ranged from 283 to 2,490 S/cm (Appendix 1, table 1). 

Mean-daily specific conductance of the Dolores River at Bedrock ranged from 185 to 2,860 S/cm 
4

during 1988 through 2009 (data available from the National Water Information System Web interface at 

http://waterdata.usgs.gov/co/nwis/). Concentration of dissolved solids in water-quality samples collected 

from the Dolores River near Bedrock (station 09171100) during August 27, 1987, through December 1, 

2009, ranged from 174 to 14,900 mg/L and specific-conductance values ranged from 304 to 25,700 

S/cm (Appendix 1, table 1). Mean-daily specific conductance of the Dolores River near Bedrock 

ranged from 262 to 33,200 S/cm during 1988 through 2009 (data available from the National Water 

Information System Web interface at http://waterdata.usgs.gov/co/nwis/). 

The large increases in maximum concentration of dissolved solids and maximum specificconductance values of the Dolores River between stations 09169500 and 09171100 result from the 

inflow of a relatively small volume of sodium-chloride brine. Concentration of dissolved solids in brine 

from the alluvial aquifer near the PVU ranges from 220,200 to 296,000 mg/L and averages about 

258,000 mg/L; specific conductance of the brine ranges from about 197,000 to 229,000 S/cm (Bureau 

of Reclamation, 1978). Groundwater in the alluvial aquifer is density stratified, with fresh groundwater, 

which has a relative density of about 1 g/cm3, overlying brine with a relative density of about 1.164 

g/cm

3

. Brine discharge to the river varies seasonally and from year to year in response to changes in the 

position of the water table and freshwater/brine interface. 

During 1988 through 2009, there were 882 missing values for mean-daily specific conductance 

at station 09169500 and 527 missing values for mean-daily specific conductance at station 09171100. 

Missing values for mean-daily specific conductance during 1988 through 1992 were not estimated. 

Estimates of missing mean-daily specific-conductance values during 1993 through 2009 were provided 

by Andrew Nicholas (Bureau of Reclamation, Bedrock, Colorado, electronic commun., June 10, 2010). 
5

Estimating Concentration of Dissolved Solids from Specific Conductance

The relation between ionic concentration and specific conductance is fairly simple for dilute 

solutions of single salts. Natural waters generally are not simple solutions but contain a variety of both 

ionic and undissociated species, and the amounts and proportions of each may range widely. Specific 

conductance of water primarily is a result of the concentrations of dissolved solids, primarily the major 

anions and cations (bicarbonate, calcium, carbonate, chloride, magnesium, potassium, sodium, and 

sulfate) (Hem, 1985). Although specific conductance of water cannot be expected simply to be related 

to ion concentrations or to concentrations of dissolved solids, it can display relatively well defined 

relations (Hem, 1985). The ratio of the concentration of dissolved solids (mg/L) with specific 

conductance ( S/cm) in natural waters ranges from about 0.54 to 0.96 but mostly is between 0.55 to 

0.75, and larger values are associated with water having larger sulfate concentrations (Hem, 1985). 

Brine associated with halite may contain as much as 10 times the dissolved-solids content as seawater 

(about 350,000 mg/L), and at these high concentrations the correlation between dissolved solids and 

specific conductance is not well defined (not linear) (Hem, 1985). 

The relation of concentration of dissolved solids and specific conductance of the Dolores River 

over the range of concentrations of dissolved solids and specific-conductance values observed during 

August 27, 1987, through December 1, 2009, is approximately linear. Previously, Watts (2000) and 

Chafin (2003) used linear regression to estimate the concentration of dissolved solids from specificconductance values for the Dolores River at stations 09169500 and 09171100. Chafin (2003) combined 

the water-quality data from 315 discrete samples collected at the stations from January 4, 1978, through

February 27, 2002, to develop a regression equation (DS = 0.5653×SC – 13) to predict concentration of 

dissolved solids (DS, in milligrams per liter) from specific conductance (SC, in microsiemens per 

centimeter at 25 degrees Celsius ). 
6

Because of differences in ionic proportions between water from the Dolores River at stations 

09169500 and 09171100 (fig. 2), it was expected that the relation between specific conductance and 

concentration of dissolved solids in the Dolores River would be different at the two gages; therefore, for 

this analysis, a regression equation was developed to predict concentration of dissolved solids from 

specific conductance for each gaging station. 

Figure 2. Piper diagrams showing proportions of major cations and anions, as percentage of milliequivalents per 

liter, in the Dolores River at Bedrock, Colorado (station 09169500) and near Bedrock, Colorado (station 

09171100), August 27, 1987, through December 1, 2009.

Least-squares regression analysis, as implemented in SYSTAT® for Windows®, version 

11.00.01, © SYSTAT Software, Inc. (2004), was used to estimate concentration of dissolved solids 

from the approximately linear relation with specific conductance for 218 samples collected from the 

Dolores River at Bedrock (station 09169500) and for 218 samples collected from the Dolores River near

Bedrock (station 09171100) (fig. 3).

Figure 3. Relation of concentration of dissolved solids and specific conductance of the Dolores River at Bedrock, 

Colorado (station 09169500) and near Bedrock, Colorado (station 09171100), August 27, 1987, through 

December 1, 2009. [DS = concentration of dissolved solids; SC = specific conductance]

The coefficient of determination, R2, for the regression model of concentration of dissolved 

solids with specific conductance for the Dolores River at Bedrock (station 09169500) was 0.928 and for 

the Dolores River near Bedrock (station 091171100) was 0.995. The coefficient of determination is the 

proportion of variance of the dependent variable (concentration of dissolved solids) related with the 

variance of the independent variable (specific conductance) (Montgomery and Peck, 1982). The pvalues (probability values) for the regression coefficients for both regression models were less than 
7

0.001. The p-value is the probability of seeing a result as extreme in a collection of random data in 

which the independent variable has no effect on the dependent variable. The regression model 

(equation) for predicting concentration of dissolved solids from specific conductance for the Dolores 

River at Bedrock, Colorado (station 09169500), was

DS = 0.6945×SC – 81.4 (1)

and for the Dolores River near Bedrock, Colorado (station 09171100) was

DS = 0.5809×SC – 48.7 (2)

where DS is the concentration of dissolved solids (in milligrams per liter) and SC is the specific 

conductance (in microsiemens per centimeter at 25 degrees Celsius). 

The fit of the regression model also is judged on the basis of the distribution of model error (the 

difference between the observed and predicted value) plotted against the predicted value. The leastsquares regressions method is based on the assumption that the error is randomly distributed. If the 

points in a residual plot, a plot of error against either the predicted value (or the independent variable),

are randomly dispersed around the horizontal axis, a linear regression model is appropriate for the data; 

otherwise, a nonlinear model may be more appropriate. Residual plots for the regression models are 

included in the SYSTAT output (table 2, Supplemental data) and in table 3 (worksheet SampleData in 

spreadsheet DoloresRiverLoad_1988-2009.xlsx). The residuals (errors) appear to be proportional to the 

predicted values (independent variables) in the residual plots (shown on worksheet SampleData), 

indicating that nonlinear models might improve estimates of concentrations of dissolved solids. 
8

Estimates of Dissolved-Solids Load of the Dolores River in the Paradox Valley, 

1988 through 2009

Mean-daily concentration of dissolved solids of the Dolores River at station 09169500 and at 

station 09171100 (fig. 4) was estimated from the mean-daily specific-conductance value, using either 

equation 1 or 2, as appropriate, for the period January 1, 1988, through December 31, 2009. Mean-daily 

concentration of dissolved solids was not estimated for those days during 1988 through 1992 when the 

mean-daily specific-conductance value was not reported in the NWIS database (295 days for station 

09169500 and 235 days for station 09171100). Estimates of mean-daily specific conductance, which 

were provided by Andrew Nicholas (Bureau of Reclamation, Bedrock, Colorado, electronic commun., 

June 10, 2010), were used to estimate concentrations of dissolved solids for the 1993 through 2009 

period, when the mean-daily specific-conductance value was not reported in NWIS (587 days for station 

09169500 and 292 days for station 09171100). 

Figure 4. Estimated mean-daily concentration of dissolved solids of the Dolores River at Bedrock, Colorado 

(station 09169500) and near Bedrock, Colorado (09171100), 1988 through 2009.

Daily dissolved-solids loads of the Dolores River at Bedrock (station 09169500) and near 

Bedrock (station 09171100) (fig. 5) were estimated as the product of mean-daily discharge (ft3/s), 

estimated mean-daily concentration of dissolved solids (mg/L), and a factor to convert from load in 

(mg/L∙ft3/s) to load in tons per day (the conversion factor: 0.0026969 = 86,400 seconds/day × 28.3168 

L/ft3∕ 907,184,740 mg/ton). [Note: The horizontal dashed lines in figure 5 are equal to a dissolvedsolids load of 274 tons/day or about 100,000 tons/year.]

Figure 5. Estimated daily dissolved-solids load of the Dolores River at Bedrock, Colorado (station 09169500) and 

near Bedrock, Colorado (09171100), 1988 through 2009.
9

The increase in dissolved-solids load of the Dolores River between stations 09169500 and 

09171100 (fig. 6) primarily results from discharge of brine from the alluvial aquifer but also includes an 

unknown amount of load from ―fresh‖ groundwater, surface runoff, and irrigation return flow. The 

ultimate source of the brine is from the collapse-breccia aquifer that underlies the alluvial aquifer. The 

collapse-breccia aquifer was formed as salt (halite) and other evaporite minerals were dissolved and 

removed from the Paradox Member of the Hermosa Formation (Gutiérrez, 2004). Computed differences 

in dissolved-solids load ranged from about –920 to 1,885 tons/day. The average difference in dissolvedsolids load prior to production operation of the PVU (prior to July 1996) was about 336 tons/day or 

about 122,700 tons/year. The average difference in dissolved-solids load after production operation of 

the PVU began in July 1996 was about 128 tons/day or 46,750 tons/year. 

Figure 6. Estimated difference in dissolved-solids load of the Dolores River between gaging stations 09169500 

and 09171100, Paradox Valley, Montrose County, Colorado, 1988 through 2009. [Notes: 442 missing values 

prior to January 1, 1993, and 437 values with difference in loads less than 1 ton per day not shown.]

Decreases in dissolved-solids load (negative load differences) were computed for 419 days in the 

8,036 day period from January 1, 1988, through December 31, 2009, and positive load differences less 

than 1 ton/day were computed for 18 days. Differences in dissolved-solids load less than 1 ton/day are 

not shown in figure 6. Chafin (2003) also noted negative load differences and attributed them largely to

streamflow losses that recharge the alluvial aquifer of the Paradox Valley during the rise in river stage 

in early spring. Other causes of negative load differences include errors in measurement of streamflow 

and specific conductance and errors in the regression models. Errors in measurement of streamflow and 

specific conductance probably are randomly distributed and on average do not bias estimates of load 

differences. Because the relation between dissolved solids and specific conductance varies with the 

proportions of major cations and anions in the water, errors in the estimated concentrations of dissolved 
10

solids from the regression models likely result from variability of dissolved cations and anions 

contributed by various sources within the drainage. An additional source of error occurs when there are 

rapid changes in streamflow and the peak flow occurs on different days at the two gages, which could 

result in apparent gains or losses in streamflow when mean-daily discharge is used to estimate 

dissolved-solids load.

The annual increase in dissolved-solids load of the Dolores River as it crosses the Paradox 

Valley ranged from an estimated 16,790 ton in 2002 to 206,424 tons in 1988 (table 3, worksheet Annual 

Dissolved-Solids Load in spreadsheet DoloresRiverLoad_1988-2009.xlsx). The average increase in 

dissolved-solids load during 1988 through 1996 (production operation of the PVU began in July 1996) 

was about 120,000 tons per year and during 1997 through 2009 was about 46,000 tons per year. Some 

of the load reduction during 2001 and 2002 likely is related to effects of drought on groundwater levels 

within the Paradox Valley.

Applicability of the regression equations for estimating concentrations of dissolved solids and 

dissolved-solids loads should be reviewed periodically, particularly when (1) streamflow and waterquality conditions are much different than those that occurred during 1988–2009, (2) results from 

continued water-quality sampling at the stations indicate a substantial change in water chemistry at 

either site, or (3) operations of the Paradox Valley Unit are modified substantially.

Acknowledgments

Andrew Nicholas, BOR Facility Operations Specialist for the Paradox Valley Unit, provided 

estimates of mean-daily specific conductance for the Dolores River and brine injection rates for the 

Paradox Valley Unit for the period January 1, 1993, through December 31, 2009. Roderick Ortiz and 

Katie Walton-Day, USGS Colorado Water Science Center, provided technical reviews of the report.
11

References Cited

Bureau of Reclamation, 1978, Colorado River Basin salinity control project Paradox Valley Unit 

definite plan report, Appendix B—Hydrosalinity: Bureau of Reclamation, Upper Colorado Region, 

173 p.

Carter, R.W., and Davidian, Jacob, 1968, General procedures for gaging streams: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 3, chap. A6, 13 p.

Chafin, D.T., 2003, Effect of the Paradox Valley Unit on the dissolved-solids load of the Dolores River 

near Bedrock, Colorado, 1988–2001: U.S. Geological Survey Water-Resources Investigations Report 

2002–4275, 6 p.

Gutiérrez, F., 2004, Origin of the salt valleys in the Canyonlands section of the Colorado Plateau 

evaporite-dissolution collapse versus tectonic subsidence: Geomorphology, vol. 57, p. 423-435.

Hem, J.D., 1985, Study and interpretation of the chemical characteristics of natural water: U.S. 

Geological Survey Water-Supply Paper 2254, 264 p.

Montgomery, D.C., and Peck, E.A., 1982, Introduction to linear regression analysis: John Wiley, New

York, 504 p.

SYSTAT Software, Inc., 2004, SYSTAT® for Windows®, version 11.00.01: Systat Software, Inc., 

Chicago, Illinois.

Rounds, S.A., July 2003, Alkalinity and acid neutralizing capacity (version 3.0), in National field 

manual for the collection of water-quality data, Wilde, F.D., and Radtke, D.B., eds.: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 9, chap. A6, section 6.6, 53 p. 

U.S. Geological Survey, 2009, Water resources data for the United States, water year 2009: U.S. 

Geological Survey Water Data Report US–2009, no pagination, available online only at 

http://wdr.water.usgs.gov/wy2009/search.jsp.
12

Watts, K.R., 2000, Effects of the Paradox Valley Unit on dissolved solids, sodium, and chloride in the 

Dolores River near Bedrock, Colorado, water years 1988–98: U.S. Geological Survey WaterResources Investigations Report 2000–4011, 8 p.
13

Supplemental Data

Table 1. Specific conductance, concentration of dissolved solids, and discharge of the Dolores River at Bedrock, 

Colorado (station 09169500) and near Bedrock, Colorado (station 09171100), August 27, 1987, through 

December 1, 2009.

[Note: Dissolved-solids values in red are reported as estimated. Specific-conductance values in red are laboratory values of 

specific conductance, other values are from filed measurements. Discharge is instantaneous discharge at time of sample 

collection. --, instantaneous discharge not reported]

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

Dolores River at Bedrock, Colorado – Station 09169500

1987/08/27 10:30 1,460 1,050 252

1987/10/05 10:30 782 446 78

1987/11/17 11:00 800 500 109

1988/01/13 12:00 880 444 99

1988/03/01 11:30 808 502 253

1988/04/05 12:30 690 440 378

1988/05/11 12:05 380 238 618

1988/05/24 11:50 389 242 673

1988/06/09 14:25 361 211 625

1988/06/28 11:40 762 404 285

1988/08/02 13:15 425 251 151

1988/09/21 17:15 837 513 79

1988/09/22 8:45 841 500 78

1988/10/06 15:10 691 379 80

1988/11/22 11:40 842 486 84

1988/12/09 9:50 620 370 89

1989/01/04 15:00 627 368 85

1989/04/20 9:30 409 236 991

1989/05/17 12:40 460 258 242

1989/06/12 12:30 679 368 72

1989/07/06 14:00 650 328 60

1989/08/17 8:00 585 315 65

1989/09/05 16:30 594 310 59
14

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

1989/10/02 13:40 540 320 63

1989/11/14 12:30 556 294 80

1990/01/02 11:30 562 307 83

1990/03/06 14:40 660 369 66

1990/04/11 14:00 1,200 645 32

1990/05/16 12:10 1,560 964 26

1990/06/01 12:00 1,430 939 32

1990/06/06 20:00 1,590 950 8

1990/07/17 13:30 760 440 45

1990/08/08 10:00 618 327 31

1990/09/05 12:30 670 396 193

1990/09/06 9:15 842 552 400

1990/10/11 9:30 1,280 859 42

1990/11/19 12:30 998 583 34

1991/01/08 14:10 970 521 --

1991/03/05 14:00 1,540 1,020 64

1991/04/10 13:00 460 290 405

1991/05/07 12:00 1,140 737 65

1991/05/22 9:30 360 213 924

1991/06/11 9:00 897 564 72

1991/06/19 14:15 1,110 735 70

1991/07/26 11:50 790 456 68

1991/07/30 15:15 468 280 56

1991/08/20 16:50 600 334 71

1991/10/30 12:00 703 420 50

1991/11/18 15:20 1,720 1,440 73

1991/12/04 15:45 1,060 643 39

1992/01/13 12:30 1,060 624 41

1992/03/10 14:25 1,400 1,060 66

1992/03/23 12:30 1,110 733 76

1992/04/20 12:35 398 254 987

1992/05/05 13:15 355 198 1,250

1992/05/28 10:15 444 283 3,100

1992/06/17 13:45 420 247 392

1992/07/22 13:45 894 547 62

1992/08/26 10:00 544 319 76

1992/10/06 14:10 651 358 53
15

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

1992/11/12 12:00 810 426 49

1992/12/22 11:00 1,240 641 24

1993/01/26 12:00 1,140 739 66

1993/03/22 12:30 460 281 825

1993/05/19 14:00 360 229 4,410

1993/06/15 7:00 386 223 932

1993/07/07 16:00 500 284 215

1993/08/09 12:00 644 339 135

1993/09/07 14:05 738 433 105

1993/10/05 11:00 571 291 50

1993/11/16 13:00 758 417 55

1993/12/28 15:45 925 499 38

1994/01/27 9:50 935 490 52

1994/03/09 13:00 1,180 718 98

1994/04/26 14:30 752 454 167

1994/05/10 13:10 332 193 1,210

1994/05/22 12:35 283 162 2,060

1994/06/23 7:00 610 325 99

1994/07/27 7:30 623 338 56

1994/08/09 10:50 660 367 65

1994/08/18 10:00 547 300 80

1994/10/11 15:40 820 464 48

1994/11/15 15:45 600 326 71

1995/02/22 13:55 805 429 57

1995/04/06 10:20 603 363 425

1995/04/25 13:20 374 214 1,060

1995/05/22 15:15 307 172 2,940

1995/06/15 10:10 310 173 1,330

1995/06/28 8:20 301 167 1,370

1995/07/12 8:05 287 158 752

1995/07/25 12:45 547 301 160

1995/08/17 8:10 498 253 101

1995/08/29 9:25 629 365 101

1995/10/11 10:10 639 383 54

1995/12/13 12:10 970 577 51

1996/01/24 12:55 989 535 35

1996/02/28 10:30 894 506 46
16

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

1996/04/16 10:05 870 488 63

1996/05/07 12:00 907 549 96

1996/05/30 15:10 898 527 53

1996/06/19 14:05 578 303 55

1996/07/11 9:40 796 428 56

1996/08/07 10:40 471 250 56

1996/08/21 14:05 498 272 56

1996/08/28 14:50 471 247 108

1996/10/24 9:45 868 486 42

1996/12/10 12:50 1,010 621 72

1997/02/24 14:15 1,390 927 96

1997/04/07 13:10 566 359 652

1997/05/06 9:45 348 205 2,870

1997/06/05 6:20 321 178 2,050

1997/07/22 12:35 513 276 117

1997/07/28 14:50 450 234 129

1997/08/05 15:15 911 559 171

1997/08/20 8:45 564 316 130

1997/08/26 12:55 460 245 161

1997/09/03 13:15 525 296 135

1997/10/07 10:20 825 474 61

1997/11/18 12:25 858 510 53

1998/01/15 9:40 932 550 49

1998/03/03 12:25 1,010 615 52

1998/05/27 9:45 304 178 1,570

1998/07/08 14:00 533 283 127

1998/09/03 13:45 395 206 181

1998/10/15 9:00 855 502 47

1998/12/14 14:15 1,040 618 48

1999/03/10 15:05 1,140 718 61

1999/05/04 10:50 790 517 406

1999/05/26 11:45 302 176 3,000

1999/06/23 11:45 401 240 699

1999/08/04 11:45 993 644 343

1999/08/18 14:30 642 373 111

1999/08/31 13:00 1,340 974 124

1999/10/27 12:30 555 303 77
17

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

1999/12/17 10:30 806 445 45

2000/03/01 11:45 1,010 590 52

2000/04/06 13:45 1,100 691 163

2000/04/24 15:00 351 204 947

2000/05/15 13:45 342 199 716

2000/06/01 9:45 661 370 98

2000/07/06 7:15 645 339 55

2000/08/17 8:30 594 310 113

2000/11/02 12:00 685 396 87

2000/12/13 14:15 805 431 49

2001/02/15 15:00 791 431 44

2001/03/14 15:00 1,010 577 56

2001/04/26 9:15 657 398 154

2001/06/04 14:15 1,000 581 53

2001/07/03 8:15 641 326 45

2001/07/30 13:00 633 328 48

2001/08/30 8:00 755 446 53

2001/10/04 8:45 708 361 37

2001/11/20 9:30 858 463 32

2002/02/27 9:30 983 522 38

2002/04/23 9:30 1,060 571 29

2002/05/30 8:15 1,710 886 12

2002/06/19 7:45 1,350 724 2

2002/06/27 10:00 785 426 2

2002/08/05 12:15 545 296 3

2002/09/26 11:30 1,790 987 10

2002/11/19 9:45 1,340 751 22

2002/12/12 10:15 1,320 686 38

2003/02/13 9:30 1,280 699 31

2003/04/02 8:45 698 387 55

2003/04/23 9:45 776 452 59

2003/05/28 8:45 998 568 40

2003/06/19 8:45 1,980 1,120 12

2003/07/09 8:45 1,090 563 16

2003/08/21 11:45 2,490 2,260 30

2003/10/02 10:00 1,520 801 14

2003/12/02 9:00 1,180 635 22
18

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

2004/01/27 13:00 1,320 744 16

2004/03/30 9:15 637 386 117

2004/04/12 14:00 662 405 140

2004/05/20 8:00 930 571 74

2004/06/23 8:00 622 337 46

2004/07/23 8:30 655 369 57

2004/08/25 7:30 513 277 53

2004/10/27 9:15 770 416 42

2004/12/09 10:00 972 538 42

2005/02/03 9:00 954 574 62

2005/03/02 9:15 893 542 93

2005/04/19 13:30 347 205 834

2005/06/01 9:45 384 220 1,040

2005/06/29 11:20 413 234 458

2005/07/28 10:15 585 311 87

2005/08/17 10:00 531 313 282

2005/10/06 11:20 1,650 1,140 38

2006/02/09 8:30 1,190 616 20

2006/04/12 10:00 543 307 141

2006/05/31 9:20 963 539 49

2006/07/19 8:30 697 374 56

2006/08/17 10:00 357 185 186

2006/08/24 7:15 444 236 86

2006/09/20 9:15 2,070 1,640 47

2006/11/08 10:00 1,150 642 40

2006/12/06 10:00 1,550 910 28

2007/01/09 9:00 1,450 828 29

2007/03/07 9:45 1,480 880 43

2007/05/23 9:00 790 519 438

2007/06/12 13:45 490 273 205

2007/07/31 9:15 785 500 83

2007/09/18 11:00 318 174 272

2007/10/01 15:30 1,380 916 31

2007/12/04 12:30 1,780 1,340 66

2008/02/21 10:45 1,170 769 65

2008/03/04 10:45 1,300 844 92

2008/04/01 14:30 305 185 1,500
19

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

2008/05/06 10:15 359 199 1,010

2008/06/17 12:45 325 181 874

2008/08/20 9:30 596 321 78

2008/11/19 9:15 795 424 41

2009/01/13 11:15 827 466 33

2009/03/11 10:45 1,020 630 64

2009/06/16 10:30 785 448 81

2009/07/28 14:00 550 296 59

2009/09/15 11:10 688 381 33

2009/12/01 15:40 860 471 41

Dolores River near Bedrock, Colorado – Station 09171100

1987/08/27 12:30 2,380 1,620 285

1988/01/13 13:00 5,100 3,060 130

1988/03/01 14:30 2,330 1,350 282

1988/04/05 15:00 1,710 987 393

1988/05/11 16:30 442 328 630

1988/05/24 14:30 538 335 698

1988/06/09 11:20 648 358 658

1988/06/28 15:45 5,550 3,100 135

1988/08/03 8:00 1,880 992 123

1988/09/21 16:30 3,700 2,040 81

1988/09/22 11:30 3,770 2,040 79

1988/10/06 17:20 4,840 2,630 86

1988/11/22 16:30 5,080 2,960 112

1988/12/09 11:30 8,310 5,180 65

1989/01/04 12:20 4,720 2,620 94

1989/02/13 14:00 4,500 2,350 112

1989/04/19 14:45 485 274 985

1989/05/17 16:30 1,550 818 246

1989/06/12 14:30 5,100 2,640 74

1989/07/07 8:30 3,920 2,000 57

1989/08/17 10:30 2,250 1,220 62

1989/09/05 14:00 2,240 1,130 62

1989/10/02 15:00 2,300 1,180 62

1989/11/14 14:00 3,700 2,050 81
20

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

1990/01/02 13:00 4,030 2,140 104

1990/03/06 16:40 6,320 3,390 72

1990/04/11 16:00 9,850 5,590 30

1990/05/16 16:55 8,790 5,250 29

1990/06/01 10:45 6,480 3,990 31

1990/06/06 18:30 18,100 11,100 12

1990/07/17 16:30 2,550 1,370 46

1990/08/09 10:00 2,870 1,520 32

1990/09/05 15:00 1,130 627 82

1990/09/06 12:00 657 371 468

1990/10/12 8:30 4,890 2,900 37

1990/11/19 15:00 5,180 2,960 38

1991/01/08 16:00 6,310 3,290

1991/04/10 15:00 694 412 417

1991/05/07 14:00 5,660 3,250 68

1991/05/21 14:30 441 251 851

1991/06/11 10:50 3,460 2,230 74

1991/06/19 13:15 3,850 2,420 69

1991/07/26 10:30 1,300 759 87

1991/07/31 9:15 2,140 1,130 53

1991/08/20 17:55 1,890 1,000 64

1991/10/30 16:10 2,810 1,720 48

1991/11/18 13:45 2,580 1,940 86

1991/12/04 12:15 20,300 12,000 20

1992/01/13 14:00 12,600 7,410 38

1992/03/10 13:30 5,770 3,780 76

1992/03/23 14:00 5,160 3,160 77

1992/04/20 16:15 474 279 998

1992/05/05 16:45 387 219 1,260

1992/05/28 15:00 468 299 3,210

1992/06/18 8:30 830 467 379

1992/07/23 9:30 3,630 2,210 63

1992/08/26 14:25 1,830 984 80

1992/10/07 9:30 2,720 1,490 52

1992/11/12 14:00 4,500 2,330 51

1992/12/21 16:15 11,400 6,550 50

1993/01/26 15:00 17,900 9,910 59
21

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

1993/03/22 17:00 705 392 770

1993/04/20 15:15 334 192 3,300

1993/05/19 17:50 352 208 4,560

1993/06/15 13:15 480 270 1,220

1993/07/08 10:00 700 396 457

1993/08/09 13:50 1,940 996 114

1993/09/07 15:35 2,360 1,270 108

1993/10/05 13:00 3,380 1,720 55

1993/11/15 15:45 4,780 2,790 68

1993/12/28 13:30 7,500 3,890 46

1994/01/27 11:35 5,710 3,050 60

1994/03/09 15:30 3,670 1,760 101

1994/04/26 15:35 2,360 1,270 175

1994/05/10 16:00 378 215 1,220

1994/05/22 16:15 304 174 1,990

1994/06/23 10:00 2,800 1,500 98

1994/07/27 9:30 3,170 1,620 57

1994/08/09 12:30 2,560 1,400 63

1994/08/18 9:35 1,900 1,000 69

1994/10/12 9:15 3,310 1,760 51

1994/11/16 14:30 2,680 1,400 63

1995/02/22 10:15 4,810 2,540 60

1995/04/06 13:30 925 529 445

1995/04/24 16:30 448 251 992

1995/05/23 9:50 320 177 2,870

1995/06/14 13:45 352 195 1,300

1995/06/27 15:45 349 193 1,270

1995/07/12 14:15 449 238 827

1995/07/25 10:40 3,150 1,650 169

1995/08/16 17:35 2,950 1,500 108

1995/08/29 11:20 2,450 1,280 120

1995/10/11 11:45 6,670 3,610 56

1995/12/12 14:25 8,600 4,970 63

1996/01/24 8:55 8,530 4,720 25

1996/02/28 13:55 7,410 4,140 55

1996/04/16 13:20 5,070 2,790 70

1996/05/06 15:15 3,330 1,840 95
22

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

1996/05/30 8:45 5,200 2,940 51

1996/06/19 9:15 3,460 1,820 51

1996/07/11 14:45 2,670 1,410 62

1996/08/07 7:15 1,480 760 59

1996/08/21 9:45 1,820 944 54

1996/08/28 11:35 1,230 603 145

1996/10/24 15:05 3,350 1,750 42

1996/12/10 14:55 5,480 3,200 75

1997/02/25 9:20 4,100 2,450 82

1997/04/08 8:45 728 463 643

1997/05/06 14:15 353 209 2,830

1997/06/04 11:20 312 174 2,450

1997/07/22 8:20 1,900 988 125

1997/07/28 11:25 1,060 546 180

1997/08/05 12:20 1,530 816 145

1997/08/20 11:55 1,470 766 123

1997/08/26 15:15 938 476 165

1997/09/03 15:30 1,290 676 131

1997/10/07 12:30 3,770 2,010 69

1997/11/18 14:35 4,440 2,470 55

1998/01/15 11:15 7,300 4,120 41

1998/03/03 13:50 4,780 2,740 60

1998/05/27 14:00 317 186 1,600

1998/07/08 8:30 1,870 963 119

1998/08/05 7:45 2,210 1,230 95

1998/09/03 16:00 592 314 169

1998/10/15 12:45 2,680 1,490 43

1998/12/14 11:15 7,090 4,060 34

1999/03/11 11:30 4,880 2,750 74

1999/05/04 13:20 898 575 387

1999/05/26 8:30 318 182 3,140

1999/06/23 8:00 427 257 765

1999/08/04 9:00 2,230 1,370 94

1999/08/18 12:30 1,550 851 99

1999/08/31 15:30 1,780 1,230 123

1999/10/27 15:45 2,010 1,070 76

1999/12/16 16:45 2,010 1,090 78
23

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

2000/03/01 14:00 4,130 2,290 60

2000/04/06 10:15 2,110 1,200 119

2000/04/24 16:45 372 213 1,030

2000/05/15 15:45 376 217 740

2000/06/01 7:30 2,260 1,190 101

2000/07/06 10:00 2,640 1,390 57

2000/08/16 15:00 1,350 691 68

2000/11/02 8:45 1,530 840 92

2000/12/13 16:00 2,650 1,500 54

2001/02/15 17:15 5,780 3,280 70

2001/03/14 17:00 2,160 1,200 58

2001/04/26 12:45 857 502 162

2001/06/04 16:15 2,010 1,120 50

2001/07/03 10:30 1,400 730 47

2001/07/30 15:30 1,090 559 47

2001/08/30 10:30 1,570 860 51

2001/10/04 11:15 1,330 679 36

2001/11/20 12:00 1,520 798 32

2002/02/27 12:00 1,930 1,020 32

2002/04/23 13:00 2,650 1,420 29

2002/05/30 11:15 4,570 2,490 14

2002/06/19 11:30 25,700 14,900 2

2002/06/27 7:00 20,800 12,200 2

2002/08/05 14:15 9,960 5,540 2

2002/09/26 14:45 3,990 2,230 10

2002/11/19 12:15 2,470 1,350 22

2002/12/12 12:45 3,530 1,950 34

2003/02/13 12:00 2,850 1,560 38

2003/04/02 11:00 3,110 1,680 50

2003/04/23 12:45 2,720 1,500 65

2003/05/28 11:45 2,750 1,490 38

2003/06/19 10:45 9,430 5,280 12

2003/07/09 11:00 2,050 1,060 15

2003/08/22 11:30 2,610 2,170 23

2003/10/02 15:00 2,130 1,560 14

2003/12/02 11:15 3,930 2,150 28

2004/01/26 13:30 11,800 6,940 51
24

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

2004/03/30 12:15 953 571 124

2004/04/12 15:45 919 550 151

2004/05/20 10:45 1,360 795 78

2004/06/23 11:15 832 467 47

2004/07/23 10:45 889 534 54

2004/08/25 9:30 583 324 53

2004/10/27 12:30 1,060 565 40

2004/12/09 12:45 2,410 1,280 40

2005/02/03 11:45 2,630 1,490 68

2005/03/02 12:00 2,300 1,290 103

2005/04/19 16:00 377 221 1,050

2005/05/31 16:15 384 224 1,330

2005/06/29 8:15 599 336 443

2005/07/28 13:30 1,440 749 82

2005/08/17 12:45 698 410 282

2005/10/05 16:30 5,450 3,370 46

2006/02/09 12:15 6,490 3,410 36

2006/04/12 13:00 1,590 860 153

2006/05/31 14:45 2,660 1,420 52

2006/07/19 11:00 1,550 801 50

2006/08/17 14:15 496 260 159

2006/08/24 9:30 621 325 90

2006/09/20 12:45 2,870 2,080 48

2006/11/08 12:30 4,900 2,670 45

2006/12/06 12:30 5,210 3,040 57

2007/01/09 11:30 7,080 3,980 59

2007/03/07 12:30 2,810 1,540 48

2007/05/23 12:45 831 528 419

2007/06/12 18:10 561 313 194

2007/07/31 12:30 1,060 664 81

2007/09/18 13:30 328 177 353

2007/10/01 17:15 2,370 1,450 34

2007/12/04 15:00 2,020 1,280 70

2008/02/21 14:00 3,470 1,980 80

2008/03/04 13:30 3,540 2,090 97

2008/04/01 10:45 318 188 1,460

2008/05/06 14:45 355 205 1,110
25

Sample date

(yyyy/mm/dd)

Sample time 

(hh:mm)

Specific 

conductance 

(microsiemens per 

centimeter at 25 

degrees Celsius

Dissolved solids 

(milligrams per 

liter)

Discharge 

(cubic feet per 

second)

2008/06/17 9:30 344 190 840

2008/08/19 14:15 1,100 586 73

2008/11/18 15:15 2,010 1,090 41

2009/01/13 14:15 2,790 1,480 50

2009/03/11 15:15 3,770 2,140 68

2009/06/16 14:15 2,120 1,160 75

2009/07/28 15:30 1,540 801 59

2009/09/15 13:00 1,590 839 38

2009/12/01 11:45 3,550 1,910 46
26

Table 2. SYSTAT output regression analysis of dissolved-solids concentration and specific-conductance values for the Dolores River at Bedrock, 

Colorado (station 09169500) and near Bedrock, Colorado (station 09171100), 1987 through 2009.

The following results are for station 09169500, August 27, 1987 through December 1, 2009. This regression model predicts 

concentration of dissolved solids (DS) from specific-conductance values (SC) for water samples collected at the upstream gaging 

station, station 09169500, the Dolores River at Bedrock, Colorado. 

[N = number of samples, P(2 Tail) = the probability that an equivalent coefficient would be obtained if the variables were unrelated, 

Std = standard, df = degrees of freedom, F-ratio = , P = probability of a larger F-ratio if the variables were unrelated, df = degrees of 

freedom]

Eigenvalues of unit scaled X'X

1 2

1.90425 0.09575

Condition indices

1 2

1.00000 4.45958

Variance proportions

1 2

CONSTANT 0.04787 0.95213

SC 0.04787 0.95213

Dependent Variable: DS N: 218 Multiple R: 0.96312 Squared multiple R: 0.92759

Adjusted squared multiple R (R2): 0.92726 Standard error of estimate: 73.92915
27

Effect Coefficient Std Error Std Coefficient Tolerance t P(2 Tail)

CONSTANT -81.36411 11.72620 0.00000 . -6.93866 0.00000

SC 0.69447 0.01320 0.96312 1.00000 52.60348 0.00000

Effect Coefficient Lower 95% Upper 95%

CONSTANT -81.36411 -104.47654 -58.25168

SC 0.69447 0.66845 0.72049

Correlation matrix of regression coefficients

 CONSTANT SC 

CONSTANT 1.00000

SC -0.90425 1.00000

Analysis of Variance

Source Sum-of-Squares df Mean-Square F-ratio P

Regression 1.51238E+07 1 1.51238E+07 2767.12627 0.00000

Residual 1.18055E+06 216 5465.51885

*** WARNING ***

Case 49 is an outlier (Studentized Residual = 4.70748)

Case 169 has large leverage (Leverage = 0.09533)

Case 169 is an outlier (Studentized Residual = 10.77962)

Case 195 is an outlier (Studentized Residual = 4.09218)

Durbin-Watson D Statistic 1.83803

First Order Autocorrelation 0.07429
28

NOTE: The following residual (error) plot indicates a slight bias in the regression model for dissolved-solids concentrations less than about 200 

milligrams per liter.

Plot of residuals against predicted values

0 500 1000 1500 2000

ESTIMATE

-300

-200

-100

0

100

200

300

400

500

600

700

RESIDUAL
29

The following results are for station 09171100, August 27, 1987 through December 1, 2009. This regression model predicts 

concentration of dissolved solids (DS) from specific-conductance values for water samples collected at the downstream gaging station 

(09171100), the Dolores River near Bedrock, Colorado. 

[N = number of samples, P(2 Tail) = the probability that a an equivalent coefficient would be obtained if DS and SC were unrelated, 

df = degrees of freedom]

Eigenvalues of unit scaled X'X

1 2

1.67439 0.32561

Condition indices

1 2

1.00000 2.26767

Variance proportions

1 2

CONSTANT 0.16280 0.83720

SC 0.16280 0.83720

Dependent Variable: DS N: 218 Multiple R: 0.99756 Squared multiple R: 0.99512

Adjusted squared multiple R (R2): 0.99510 Standard error of estimate: 145.78972

Effect Coefficient Std Error Std Coefficient Tolerance t P(2 Tail)

CONSTANT -48.72852 13.37279 0.00000 . -3.64386 0.00034

SC 0.58089 0.00277 0.99756 1.00000 2.09E02 0.00000
30

Effect Coefficient Lower 95% Upper 95%

CONSTANT -48.72852 -75.08640 -22.37065

SC 0.58089 0.57544 0.58635

Correlation matrix of regression coefficients

 CONSTANT SC 

CONSTANT 1.00000

SC -0.67439 1.00000

Analysis of Variance

Source Sum-of-Squares df Mean-Square F-ratio P

Regression 9.37072E+08 1 9.37072E+08 44087.87788 0.00000

Residual 4.59100E+06 216 21254.64333

*** WARNING ***

Case 248 has large leverage (Leverage = 0.08389)

Case 248 is an outlier (Studentized Residual = 4.77102)

Case 266 has large leverage (Leverage = 0.10915)

Case 279 has large leverage (Leverage = 0.08177)

Case 375 has large leverage (Leverage = 0.18592)

Case 376 has large leverage (Leverage = 0.11537)

Case 387 is an outlier (Studentized Residual = 5.10304)

Durbin-Watson D Statistic 1.35156

First Order Autocorrelation 0.31413

NOTE: The following residual (error) plot indicates a slight bias in the regression model for dissolved-solids concentrations less than about 1,000 

milligrams per liter.
31

Plot of residuals against predicted values

0 5000 10000 15000

ESTIMATE

-500

0

500

1000

RESIDUAL
32

Table 3. DoloresRiverLoad_1988-2009.xlsx

Table 3 is an attached MicroSoft Excel 2007 ® spreadsheet.