78 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Appendix 1—Summary Information 

Relating to Quality-Control, WaterQuality, and Continuous Streamflow 

Data

Summary information is presented relating to qualitycontrol, water-quality, and continuous streamflow data. Results 

for quality-control equipment blank and replicate samples 

collected during water years 1993–2010 are summarized in 

table 1–1. Spike recoveries for laboratory-spiked deionizedwater blank samples collected during water years 1993–2010 

are presented in table 1–2. Spike recoveries for laboratoryspiked stream-water blank samples collected during water 

years 1993–2010 are presented in table 1–3. Statistical 

summaries of water-quality data collected during water years 

2001–10 are presented in table 1–4. For reference, aquatic life 

standards (based on median hardness for water years 2001–10, 

Montana Department of Environmental Quality, 2012a) are 

presented in table 1–5. Statistical summaries of continuous 

streamflow data collected during water years 2001–10 are 

presented in table 1–6.

Evaluation of long-term spike-recovery data is of particular relevance to the long-term trend analysis. Spike-recoveries 

during water years 1993–2010 for laboratory-spiked 

deionized-water blank samples (table 1–2 and fig. 1–1) and 

laboratory-spiked stream-water samples (table 1–3 and 

fig. 1–2) indicate generally consistent recoveries over time, 

typically varying within plus or minus 10 percent of 100 percent recovery. However, before about water year 2000, spike 

recoveries for unfiltered-recoverable copper in spiked streamwater samples generally were near 100 percent (mean annual 

spike recovery for water years 1993–1999 of 99.1 percent), 

whereas after about water year 2000, spike recoveries were 

consistently less than 100 percent (mean annual spike recovery 

for water years 2000–2010 of 93.9 percent). Changes in spike 

recoveries in about water year 2000 probably were related 

to a change in about water year 2000 by the U.S. Geological 

Survey National Water Quality Laboratory from analysis of 

most metallic elements by graphite furnace atomic absorption 

spectrophotometry (Fishman, 1993) to inductively coupled 

plasma-mass spectrometry (Garbarino and Struzeski, 1998; 

Garbarino and others, 2006). Potential effects on trend results 

of differences in spike recoveries between pre-2000 and post2000 data relate only to sites with long-term data that were 

analyzed by using the TSM. 

The potential effects of temporal differences in spike 

recoveries on trend results were evaluated by using two 

approaches: (1) exploratory TSM analysis with inclusion 

of a step trend in the trend model, and (2) exploratory TSM 

analysis on constituent concentrations adjusted based on 

annual mean spike recoveries. For the exploratory step-trend 

approach, for each site and constituent combination a step 

trend for the period water years 1996–1999 was included in 

the TSM model in addition to including applicable trends for 

periods 1 through 3 (depending on available data for the given 

site and constituent combination). Inclusion of a step trend 

allowed evaluation of whether there was a distinct change in 

data structure between pre-2000 and post-2000 data that might 

have affected trend results. Results of the exploratory steptrend analysis indicated that for all site and constituent combinations, the step trend was nonsignificant, and inclusion of 

the step trend had minor effects on trend results with respect to 

magnitude, direction, and significance on constituent concentration trends. For the exploratory spike-recovery adjustment 

approach, before TSM analysis constituent concentrations for 

each year were adjusted by multiplying the concentrations 

divided by the annual mean spike recovery for laboratoryspiked stream-water samples. Results of the exploratory 

spike-recovery adjustment analysis were more variable than 

results for the exploratory step-trend approach but resulted in 

the same general conclusion that temporal differences in spike 

recoveries had minor effects on trend results.
Table 1–1. Summary information relating to quality-control samples (equipment blank and replicate samples) collected at sites in the upper Clark Fon data collected during water years 1993–2010.[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. LRL, laboratory reporting level; SRL, study reporting deviation; μS/cm, microsiemens per centimeter at 25 degrees Celsius; NA, not applicable; μg/L, micrograms per liter; mg/L, milligrams per liter]

Constituent or property, units of 

measurement

Summary information relating to field blank samples

Number of field 

blank samples

Number of field 

blank samples with 

detected concen-

trations greater 

than the LRL at the 

time of analysis

Percent of field 

blank samples with 

detected concen-

trations greater 

than the LRL at the 

time of analysis

Maximum detected 

concentration for 

field blank samples

Median concentra-

tion in field blank 

samples with de-

tected concentra-

tions greater than 

the LRL at the time 

of analysis

SRL used in ap-

plication of the 

time-series model

Percent of detec-

tions in blank 

samples at con-

centrations greater 

than the SRL used 

in the application 

of the time-series 

model

Specific conductance, μS/cm NA NA NA NA NA 8 NA 

Cadmium, filtered, μg/L 158 3 1.9 0.34 0.07 0.05 3.2 Cadmium, unfiltered-recoverable, 

μg/L

154 0 0 no detections no detections 0.09 0 

Copper, filtered, μg/L 157 8 5.1 3.6 0.52 1 1.3 Copper, unfiltered-recoverable, 

μg/L

154 6 3.9 3.0 1.0 1 1.9 

Iron, filtered,μg/L 154 0 0 no detections no detections 6 0 Iron unfiltered-recoverable, μg/L 150 4 2.7 36 7 20 2.0 Lead, filtered, μg/L 158 4 2.5 0.60 0.23 0.5 0.6 Lead, unfiltered-recoverable, μg/L 154 3 1.9 0.16 0.06 0.5 0 Manganese, filtered, μg/L 153 0 0 no detections no detections 1 0 Manganese, unfiltered-recoverable, 

μg/L

150 2 1.3 0.30 0.15 1 0 

Zinc, filtered, μg/L 156 23 14.7 6.20 0.90 5 0.6 Zinc, unfiltered-recoverable, μg/L 152 10 6.6 3.40 1.40 2 3.3 Arsenic, filtered, μg/L 158 0 0 no detections no detections 1 0 Arsenic, unfiltered-recoverable, 

μg/L

154 0 0 no detections no detections 1 0 

Suspended sediment, mg/L NA NA NA NA NA 1 NA 

1The RSD is calculated according to the following equation (Taylor, 1987):

where

RSD is the relative standard deviation;

S is the standard deviation; and

x is the mean contentration for all replicates.

RSD = x 100, Sx
Table 1–2. Summary information relating to quality-control samples (laboratory-spiked deionized-water blank samples) collected at sites in the uppMontana, based on data collected during water years 1993–2010. [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. F, filtered; UFR, unfiltered-recoverable] Water year Mean spike recovery, percent (values in parentheses indicate 95-percent confidence intervals) Cadmium, F Cadmium, UFR Copper, F Copper, UFR Iron, F Iron, UFR Lead, F Lead, UFR Manganese, F Manganese, UFR Zinc, F Zinc

UFR 

1993 93.4 (85.9, 101) 97 (93.5, 101) 99.5 (95.9, 103) 101.7 (94.4, 109) 94 (90.0, 98.0) 103.3 (92.4, 114) 105.8 (99.5, 112) 100.5 (95.2, 106) 96.9 (96.3, 97.5) 95.6 (82.2, 109) 106.5 (99.7, 113) 96.3 (94

98.

1994 97.5 (89.1, 106) 98.8 (90.6, 107) 101.1 (98.4, 104) 99.7 (94.3, 105) 100 (93.0, 107) 94.6 (84.2, 105) 100.5 (98.5, 102) 99.1 (94.3, 104) 95.7 (90.8, 100) 101.5 (96.2, 107) 106.5 (95.8, 117) 102.6 (91

114

1995 100 (97.3, 103) 101.3 (97.5, 105) 102.7 (101, 105) 97.6 (92.3, 103) 102.2 (97.8, 107) 93.8 (87.9, 99.7) 1023 (97.7, 107) 100.8 (96.6, 105) 96.5 (92.0, 101) 98.5 (93.1, 104) 102.3 (97.1, 108) 101.5 (97

106

1996 95.3 (92.2, 98.4) 82.3 (79.7, 84.9) 99.2 (91.4, 107) 99.6 (93.5, 106) 89.8 (76.0, 104) 90.8 (70.9, 111) 100.5 (93.3, 108) 97.4 (80.2, 115) 89.2 (77.9, 100) 96.5 (91.6, 101) 96.1 (84.3, 108) 87.8 (82

92.

1997 98.5 (92.1, 105) 85.7 (77.7, 93.7) 101.1 (86.2, 116) 106.4 (82.0, 131) 94.7 (78.5, 111) 96.1 (80.2, 112) 101 (93.4, 109) 101.1 (88.9, 113) 90.3 (82.7, 97.9) 99.3 (95.8, 103) 97.9 (78.1, 118) 92.7 (86

99.

1998 104 (93.8, 114) 97.4 (87.0, 108) 100.4 (93.4, 107) 103.4 (98.8, 108) 101.8 (90.7, 113) 95.7 (89.9, 102) 100.2 (91.8, 109) 104.8 (88.8, 121) 102.8 (94.4, 111) 99 (92.1, 106) 95.2 (85.9, 104) 101.3 (86

116

1999 100.9 (92.6, 109) 103.4 (99.9, 107) 107.5 (99.5, 116) 105 (102, 108) 97.7 (94.3, 101) 96.5 (90.0, 103) 97.4 (87.9, 107) 96.2 (85.2, 107) 96 (91.8, 100) 95.9 (86.3, 106) 96.9 (92.9, 101) 93.3 (88

97.

2000 103.8 (97.3, 110) 105 (96.0, 114) 104 (96.0, 112) 100.3 (92.4, 108) 97.4 (92.3, 102) 100.6 (89.2, 112) 98.3 (88.9, 108) 102.6 (97.3, 108) 100.8 (93.3, 108) 103.2 (96.8, 110) 107.8 (95.8, 120) 102.6 (90

115

2001 102.9 (98.9, 107) 107.9 (101, 115) 105.2 (98.6, 112) 96.8 (93.7, 99.9) 101.3 (95.5, 107) 98.3 (86.7, 110) 97.3 (91.9, 103) 96.4 (93.7, 99.1) 101.9 (79.0, 125) 103.7 (89.9, 118) 102 (87.9, 116) 99.1 (82

116

2002 101.1 (98.8, 103) 97.6 (96.3, 98.9) 99.4 (95.0, 104) 98.8 (96.7, 101) 95.1 (89.3, 101) 102.3 (93.0, 112) 98.5 (89.9, 107) 96.9 (90.5, 103) 98.5 (95.4, 102) 96.5 (88.8, 104) 103.9 (94.4, 113) 98.3 (91

105

2003 98.6 (92.6, 105) 97.5 (94.1, 101) 100.4 (93.0, 108) 97.6 (93.2, 102) 101.6 (96.4, 107) 93.1 (87.4, 8.8) 97.2 (92.3, 102) 96 (93.9, 98.1) 95.8 (90.7, 101) 96.6 (79.7, 114) 101.4 (89.8, 113) 99.1 (93

105

2004 97.4 (95.6, 99.2) 100 (98.6, 101) 98.9 (92.7, 105) 99.6 (95.4, 104) 101 (96.3, 106) 96.1 (88.8, 103) 96 (91.9, 100) 98.9 (97.3, 100) 99.1 (92.3, 106) 98.6 (90.6, 107) 102 (91.7, 112) 100 (96

104

2005 102 (97.3, 106) 97.5 (88.1, 107) 102 (97.4, 107) 97.6 (88.4, 107) 97.6 (90.5, 105) 100 (95.2, 105) 101 (95.5, 106) 104 (99.4, 108) 93.8 (82.2, 105) 102 (86.4, 117) 102 (88.3, 116) 96.1 (83

109
2006 100 (92.6, 107) 98.9 (94.1, 104) 102 (97.7, 107) 98.7 (93.8, 104) 106 (101, 112) 103 (95.4, 111) 99 (89.3, 109) 98 (91.2, 105) 97 (90.7, 103) 105 (95.3, 115) 105 (95.4, 115) 94.9 (90

100

2007 107 (103, 112) 103 (94.4, 111) 105 (99.2, 111) 98.4 (86.9, 110) 99.9 (92.1, 108) 104 (98.5, 110) 99.6 (93.9, 105) 103 (100, 106) 107 (99.9, 114) 107 (97.0, 116) 107 (102, 113) 103 (96

110

2008 102 (88.2, 116) 101 (91.9, 110) 105 (88, 121) 97.9 (87.2, 109) 103 (95.9, 110) 101 (96.5, 106) 101 (89, 112) 101 (98, 105) 102 (92.9, 111) 102 (92.5, 112) 99.8 (87.9, 112) 103 (9

111

2009 102 (97.4, 107) 97.2 (93.6, 101) 102 (92.0, 113) 96 (94.0, 97.0) 102 (91.4, 112) 104 (78.8, 130) 102 (96.0, 107) 98.4 (96.1, 101) 105 (103, 106) 99.7 (94.6, 105) 111 (104, 118) 93.3 (88

98.

2010 106 (94.9, 117) 100 (88.4, 112) 97.2 (84.9, 109) 98.6 (84.0, 113) 108 (101, 115) 102 (95.8, 108) 102 (91.5, 113) 102 (91.0, 113) 103 (95.2, 111) 105 (97.2, 112) 113 (94.7, 132) 101 (89

113

Table 1–2. Summary information relating to quality-control samples (laboratory-spiked deionized-water blank samples) collected at sites in the uppMontana, based on data collected during water years 1993–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. F, filtered; UFR, unfiltered-recoverable]

Water 

year

Mean spike recovery, percent (values in parentheses indicate 95-percent confidence intervals)

Cadmium, 

F

Cadmium, 

UFR

Copper, 

F

Copper, 

UFR

Iron, 

F

Iron, 

UFR

Lead, 

F

Lead, 

UFR

Manganese, 

F

Manganese, 

UFR

Zinc, 

F

Zinc

UFR
Table 1–3. Summary information relating to quality-control samples (laboratory-spiked stream-water samples) collected at sites in the upper Cla

based on data collected during water years 1993–2010. [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. F, filtered; UFR, unfiltered-recoverable] Water year Mean spike recovery, percent (values in parentheses indicate 95-percent confidence intervals) Cadmium, F Cadmium, UFR Copper, F Copper, UFR Iron, F Iron, UFR Lead, F Lead, UFR Manganese, F Manganese, UFR Zinc, F Zin

UF

1993 97.1 (92.3, 102) 98.1 (95.2, 101) 97.4 (95.8, 99.0) 97.2 (92.3, 102) 94.6 (86.7, 103) 102.2 (94.4, 110) 104.7 (98.5, 111) 96 (93.0, 99.0) 95.7 (92.1, 99.3) 100.2 (96.4, 104) 105.7 (93.4, 118) 95.7 (92

99.

1994 101.3 (97.5, 105) 97.9 (94.4, 101) 96.6 (93.3, 99.8) 98.4 (91.1, 106) 98.2 (94.8, 102) 99.3 (90.6, 108) 103 (101, 105) 99.3 (95.6, 103) 98.1 (95.4, 101) 100.4 (95.4, 105) 97.5 (92.4, 102) 106 (95

117

1995 101.3 (96.7, 106) 102.9 (98.0, 108) 99.8 (96.2, 103) 98 (92.7, 103) 99.5 (96.1, 103) 101.4 (96.2, 107) 102.9 (98.6, 107) 100 (96.7, 103) 97.4 (92.9, 102) 103.8 (99.0, 109) 104.7 (101, 108) 101.1 (99

103

1996 100.2 (91.5, 109) 88.4 (57.8, 119) 101.1 (91.9, 110) 100.3 (92.3, 108) 93.8 (73.3, 114) 101.5 (88.5, 114) 105.1 (90.4, 120) 105.6 (98.4, 113) 90.3 (79.1, 102) 99.5 (92.9, 106) 103.2 (90.2, 116) 99.3 (74

124

1997 98.1 (83.5, 113) 84.3 (75.0, 93.6) 97.3 (88.3, 106) 100.5 (71.9, 129) 99.3 (81.0, 118) 97.5 (78.2, 117) 100.8 (91.6, 110) 102.1 (99.1, 105) 93 (84.0, 102) 99.8 (94.5, 105) 97 (89.9, 104) 92.7 (74

111

1998 104.4 (97.3, 112) 99.5 (92.7, 106) 97.2 (90.6, 104) 99.1 (88.4, 110) 97.5 (82.8, 112) 101.8 (90.2, 113) 102.2 (94.3, 110) 105 (92.9, 117) 99.5 (85.8, 113) 101.5 (98.0, 105) 99.5 (89.1, 110) 98.8 (85

112

1999 102.6 (92.4, 113) 103 (100, 106) 102.7 (89.1, 116) 100.5 (97.5, 104) 97.2 (93.5, 101) 99.9 (90.6, 109) 100.2 (94.0, 106) 101.1 (93.7, 108) 99.8 (92.8, 107) 98.8 (89.3, 108) 98.6 (95.7, 102) 96.2 (91

10

2000 104.2 (100, 108) 98.1 (88.9, 107) 101.6 (97.3, 106) 94.6 (87.7, 102) 96.5 (88.0, 105) 98 (88.3, 108) 101.4 (97.3, 106) 105.3 (103, 108) 97.3 (83.3, 111) 101.7 (91.4, 112) 101.5 (90.9, 112) 97.8 (91

104

2001 103.2 (100, 106) 105.8 (95.9, 116) 106.8 (104, 110) 91.8 (87.7, 95.9) 95.8 (91.4, 100) 101.6 (92.1, 111) 99.7 (95.2, 104) 97.3 (95.3, 99.3) 100 (84.4, 116) 100.9 (90.3, 112) 100.8 (85.7, 116) 96.9 (75

118

2002 106 (97.5, 114) 102 (98.6, 101) 97.3 (91.2, 103) 96.9 (92.9, 101) 92.6 (83.3, 102) 107.1 (103, 111) 101.4 (91.9, 111) 98.9 (92.2, 106) 98.3 (92.5, 104) 94.3 (88.4, 100) 101.3 (92.6, 110) 95.8 (89

102

2003 100.5 (91.4, 110) 99 (94.4, 104) 95.8 (88.9, 103) 91.6 (89.7, 93.5) 106.4 (100, 113) 96.7 (91.6, 102) 96 (90.2, 102) 96.8 (93.7, 99.9) 93.9 (78.8, 109) 99.3 (86.2, 112) 98.4 (93.6, 103) 93 (87

98.

2004 101 (94.2, 108) 101 (100, 103) 95.4 (93.8, 97) 93.8 (89.5, 98.1) 104 (99.5, 108) 111 (91.2, 130) 98.7 (93, 104) 100 (98.6, 102) 103 (89.8, 117) 96 (91.8, 100) 100 (95.3, 105) 94.4 (

97.

2005 97.8 (62.7, 133) 98.2 (88.5, 108) 93.6 (57.9, 129) 93 (84.8, 101) 102 (95.9, 108) 99.3 (95.6, 103) 102 (96.1, 109) 103 (99.7, 106) 88.3 (78.3, 98.3) 97.5 (87.3, 108) 94.3 (60.8, 128) 91.6 (80

102
2006 104 (99.0, 108) 99.6 (94.7, 104) 101 (96.7, 104) 94.8 (91.0, 98.6) 105 (102, 109) 102 (93.6, 110) 102 (94.2, 111) 100 (92.9, 106) 94.9 (88.2, 102) 106 (97.9, 113) 108 (93.3, 123) 91.2 (87

94.

2007 108 (102, 114) 98 (92.2, 104) 100 (89.8, 110) 96.3 (91.8, 101) 107 (103, 111) 103 (94.7, 112) 109 (103, 115) 104 (102, 107) 106 (100, 113) 101 (96.1, 106) 104 (95.7, 113) 98 (89

107

2008 101 (91, 112) 97 (93.6, 100) 98.9 (92, 106) 92.8 (86.4, 99.1) 105 (94.1, 117) 99.4 (92, 107) 100 (91.3, 109) 103 (99.5, 106) 98.9 (90.3, 108) 98.4 (92.5, 104) 106 (88.1, 124) 95.7 (93

98.

2009 106 (101, 112) 94.7 (89.5, 99.8) 96.2 (91.2, 101) 91.4 (87.8, 95.0) 107 (89.7, 124) 102 (86.9, 118) 100 (97.0, 103) 100 (98.8, 101) 97 (88.0, 106) 92.8 (81.7, 104) 114 (104, 124) 89.8 (80

99.

2010 110 (87.6, 132) 98.2 (87.1, 109) 93.8 (83.6, 104) 96.5 (84.4, 108) 105 (91.7, 119) 111 (103, 118) 101 (87.7, 115) 104 (91.5, 116) 104 (93.3, 114) 98.7 (86.4, 111) 109 (101, 118) 94 (81

107

Table 1–3. Summary information relating to quality-control samples (laboratory-spiked deionized-water blank samples) collected at sites in the uppMontana, based on data collected during water years 1993–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. F, filtered; UFR, unfiltered-recoverable]

Mean spike recovery, percent (values in parentheses indicate 95-percent confidence intervals) Water 

year Cadmium, F Cadmium, UFR Copper, F Copper, UFR Iron, F Iron, UFR Lead, F Lead, UFR Manganese, F Manganese, UFR Zinc, F Zinc

UFR 
84 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Figure 1–1. Spike recoveries for laboratory-spiked deionized-water blank samples, based on data collected during water 

years 1993–2010. A, Copper, filtered; B, Copper, unfiltered-recoverable; C, Arsenic, filtered; D, Arsenic, unfiltered-recoverable.

1990 1995 2000 2005 2010

75

150

125

100

50

75

150

125

100

50

75

150

125

100

50

75

150

125

100

50

95-percent confidence interval about the mean spike recovery

Mean spike recovery 

EXPLANATION

Water year (October–September)

B. Copper, unfiltered-recoverable

A. Copper, filtered

C. Arsenic, filtered

D. Arsenic, unfiltered-recoverable

Spike recovery, in percent
Appendix 1—Summary Information Relating to Quality-Control, Water-Quality, and Continuous Streamflow Data 85

Figure 1–2. Spike recoveries for laboratory-spiked stream-water samples, based on data collected during water years 

1993–2010. A, Copper, filtered; B, Copper, unfiltered-recoverable; C, Arsenic, filtered; D, Arsenic, unfiltered-recoverable.

A. Copper, filtered

B. Copper, unfiltered-recoverable

C. Arsenic, filtered

D. Arsenic, unfiltered-recoverable

Spike recovery, in percent

1990 1995 2000 2005 2010

75

150

125

100

50

75

150

125

100

50

75

150

125

100

50

75

150

125

100

50

95-percent confidence interval about the mean spike recovery

Mean spike recovery 

EXPLANATION

Water year (October–September)
Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010. [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max

Blacktail Creek (site 1, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 72 1.9 4.6 8.8 12 17 5

Specific conductance, μS/cm 72 161 226 265 267 316 36

pH, standard units 72 7.3 7.6 7.7 7.7 7.8 

Hardness, filtered, mg/L as CaCO3 72 65 87 106 105 122 14

Calcium, filtered, mg/L 72 19.2 25.0 30.5 30.1 35.0 4

Magnesium, filtered, mg/L 72 4.09 6.00 7.23 7.24 8.68 1

Cadmium, filtered, μg/L 70 (12) 0.02 0.03 0.04 0.04 0.05 

Cadmium, unfiltered-recoverable, μg/L 72 (18) 0.02 0.02 0.03 0.04 0.05 Copper, filtered, μg/L 71 (1) 0.80 1.6 3.0 3.6 5.2 

Copper, unfiltered-recoverable, μg/L 72 1.7 3.4 5.0 5.8 7.6 1

Iron, filtered, μg/L 72 15 68 163 180 277 64

Iron unfiltered-recoverable, μg/L 72 150 334 544 561 693 1,64

Lead, filtered, μg/L 72 (20) 0.04 0.06 0.11 0.17 0.21 

Lead, unfiltered-recoverable, μg/L 72 (9) 0.10 0.35 0.59 0.79 0.92 Manganese, filtered, μg/L 72 14 29 34 41 44 14

Manganese, unfiltered-recoverable, μg/L 72 24 42 48 55 60 17Zinc, filtered, μg/L 70 (2) 0.82 2.2 2.9 3.2 3.9 

Zinc, unfiltered-recoverable, μg/L 72 2.0 3.0 4.3 6.0 6.3 3

Arsenic, filtered, μg/L 71 1.1 2.2 3.1 3.9 5.1 

Arsenic, unfiltered-recoverable, μg/L 72 (1) 1.0 3.0 4.2 4.9 6.5 1Suspended sediment, mg/L 72 1 4 7 8 10 3

Suspended sediment, percent fines4 72 54 77 82 81 87 9
10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 13 17 22 27 33 7

Specific conductance, μS/cm 80 238 402 484 468 546 61pH, standard units 80 7.4 7.6 7.6 7.6 7.7 Hardness, filtered, mg/L as CaCO3 80 79 126 154 149 170 21

Calcium, filtered, mg/L 80 23.4 36.7 43.9 42.5 48.1 6Magnesium, filtered, mg/L 80 5.02 8.86 10.6 10.4 12.0 1Cadmium, filtered, μg/L 80 0.05 0.10 0.13 0.33 0.24 

Cadmium, unfiltered-recoverable, μg/L 80 0.09 0.15 0.22 0.46 0.57 Copper, filtered, μg/L 80 3.20 8.3 11 11 13 2

Copper, unfiltered-recoverable, μg/L 80 9.5 16 20 24 25 11Iron, filtered, μg/L 80 10.0 28 51 85 143 26

Iron unfiltered-recoverable, μg/L 80 85 278 414 480 571 2,97Lead, filtered, μg/L 79 (8) 0.12 0.20 0.25 0.27 0.33 

Lead, unfiltered-recoverable, μg/L 80 (1) 0.64 1.4 2.0 2.8 2.8 3Manganese, filtered, μg/L 80 21 71 109 150 177 50

Manganese, unfiltered-recoverable, μg/L 80 26 98 129 180 200 55Zinc, filtered, μg/L 80 16 34 47 100 104 47

Zinc, unfiltered-recoverable, μg/L 80 29 44 59 120 173 47Arsenic, filtered, μg/L 80 2.3 4.3 5.2 5.4 6.5 

Arsenic, unfiltered-recoverable, μg/L 80 3.0 5.0 6.3 7.0 8.9 1Suspended sediment, mg/L 80 2 6 8 11 11 9Suspended sediment, percent fines4 80 70 81 86 85 89 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max

Silver Bow Creek at Butte (site 2, fig. 1, table 1)
Silver Bow Creek at Opportunity (site 3, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 13 29 44 65 88 22

Specific conductance, μS/cm 80 248 348 441 437 527 63pH, standard units 80 7.8 8.2 8.4 8.4 8.8 Hardness, filtered, mg/L as CaCO3 80 81 129 159 157 184 24

Calcium, filtered, mg/L 80 24.2 38.9 47.3 46.5 54.3 7Magnesium, filtered, mg/L 80 4.96 7.30 9.89 9.87 12.0 1Cadmium, filtered, μg/L 79 0.17 0.26 0.40 0.55 0.70 

Cadmium, unfiltered-recoverable, μg/L 80 0.38 0.67 0.80 1.2 1.3 Copper, filtered, μg/L 78 12 20 25 31 36 14

Copper, unfiltered-recoverable, μg/L 80 31 61 79 120 110 86Iron, filtered, μg/L 80 (1) 7.0 14 23 42 67 24

Iron unfiltered-recoverable, μg/L 79 240 463 621 1,136 889 9,19Lead, filtered, μg/L 80 (8) 0.20 0.29 0.44 0.54 0.60 

Lead, unfiltered-recoverable, μg/L 80 5.0 10 13 25 20 26Manganese, filtered, μg/L 80 30 120 223 254 342 93

Manganese, unfiltered-recoverable, μg/L 80 85 200 290 361 437 1,52Zinc, filtered, μg/L 79 11 48 80 129 175 61

Zinc, unfiltered-recoverable, μg/L 80 70 139 197 273 284 1,23Arsenic, filtered, μg/L 80 6.4 9.5 11 12 13 2

Arsenic, unfiltered-recoverable, μg/L 80 9.1 14 16 20 20 9Suspended sediment, mg/L 80 5 13 18 33 30 28Suspended sediment, percent fines4 80 45 78 84 81 86 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Mill Creek near Anaconda (site 4, fig. 1, table 1) 12/2004– 8/2010 Streamflow, instantaneous, ft3/s 48 7.4 13 26 58 102 21

Specific conductance, μS/cm 48 56 87 133 132 177 21pH, standard units 48 7.6 7.9 8.1 8.1 8.2 Hardness, filtered, mg/L as CaCO3 48 24 36 60 57 79 9

Calcium, filtered, mg/L 48 7.00 10.5 16.9 15.8 21.7 2Magnesium, filtered, mg/L 48 1.45 2.39 4.22 4.28 5.96 Cadmium, filtered, μg/L 47 (2) 0.02 0.03 0.04 0.04 0.05 

Cadmium, unfiltered-recoverable, μg/L 48 0.03 0.05 0.07 0.08 0.09 Copper, filtered, μg/L 48 0.72 1.3 2.1 2.3 3.1 

Copper, unfiltered-recoverable, μg/L 48 (1) 1.3 2.1 3.5 3.9 5.4 1Iron, filtered, μg/L 48 21.0 30 41 47 63 12

Iron unfiltered-recoverable, μg/L 48 78 123 163 192 203 61Lead, filtered, μg/L 48 (3) 0.02 0.08 0.11 0.12 0.16 

Lead, unfiltered-recoverable, μg/L 48 0.15 0.42 0.59 0.76 0.88 Manganese, filtered, μg/L 48 3.2 4.2 5.9 5.9 6.9 1

Manganese, unfiltered-recoverable, μg/L 48 7.4 11 13 14 15 3Zinc, filtered, μg/L 48 (5) 0.73 1.1 1.4 1.5 1.9 

Zinc, unfiltered-recoverable, μg/L 48 1.0 1.8 2.6 3.0 3.9 Arsenic, filtered, μg/L 48 7.3 12 15 16 20 3

Arsenic, unfiltered-recoverable, μg/L 48 8.6 13 17 18 23 3Suspended sediment, mg/L 48 1 2 3 6 6 2Suspended sediment, percent fines4 48 28 57 67 64 75 8

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Mill Creek at Opportunity (site 5, fig. 1, table 1) 3/2003– 8/2010 Streamflow, instantaneous, ft3/s 64 0.43 3.6 9.7 35 48 26

Specific conductance, μS/cm 64 59 95 153 148 196 23pH, standard units 64 7.7 7.9 8.0 8.0 8.1 Hardness, filtered, mg/L as CaCO3 64 24 39 67 63 85 10

Calcium, filtered, mg/L 64 7.01 11.5 18.8 17.6 23.5 2Magnesium, filtered, mg/L 64 1.56 2.64 4.67 4.56 6.30 Cadmium, filtered, μg/L 64 0.02 0.05 0.06 0.06 0.07 

Cadmium, unfiltered-recoverable, μg/L 64 0.04 0.07 0.10 0.15 0.13 Copper, filtered, μg/L 64 1.0 1.9 2.7 3.0 3.9 

Copper, unfiltered-recoverable, μg/L 64 1.5 2.8 4.4 6.8 7.2 3Iron, filtered, μg/L 64 16 36 43 48 60 9

Iron unfiltered-recoverable, μg/L 64 44 113 145 299 264 1,96Lead, filtered, μg/L 64 (6) 0.02 0.09 0.13 0.14 0.17 

Lead, unfiltered-recoverable, μg/L 64 0.07 0.23 0.45 1.5 1.6 1Manganese, filtered, μg/L 64 2.2 4.5 5.6 7.7 9.2 3

Manganese, unfiltered-recoverable, μg/L 64 3.3 10 13 20 18 11

Zinc, filtered, μg/L 63 (1) 1.3 2.1 2.8 3.0 3.8 

Zinc, unfiltered-recoverable, μg/L 64 1.7 3.0 4.9 6.7 7.0 4Arsenic, filtered, μg/L 64 9.0 16 21 22 28 5

Arsenic, unfiltered-recoverable, μg/L 64 10 20 25 26 31 5Suspended sediment, mg/L 64 1 1 2 12 10 10Suspended sediment, percent fines4 64 26 57 74 69 82 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Willow Creek near Anaconda (site 6, fig. 1, table 1) 12/2004– 8/2010 Streamflow, instantaneous, ft3/s 44 1.0 2.5 7.6 14 16 7

Specific conductance, μS/cm 44 66 88 108 102 114 14pH, standard units 44 7.5 7.6 7.7 7.7 7.8 Hardness, filtered, mg/L as CaCO3 44 22 32 38 37 41 5

Calcium, filtered, mg/L 44 7.56 10.8 13.0 12.4 13.8 1Magnesium, filtered, mg/L 44 0.78 1.18 1.43 1.44 1.64 Cadmium, filtered, μg/L 42 (5) 0.02 0.02 0.03 0.03 0.04 

Cadmium, unfiltered-recoverable, μg/L 44 (3) 0.02 0.04 0.05 0.06 0.07 Copper, filtered, μg/L 44 0.90 1.3 1.9 2.0 2.4 

Copper, unfiltered-recoverable, μg/L 44 (1) 1.0 2.1 3.1 3.7 4.1 1Iron, filtered, μg/L 44 28 51 65 80 85 27

Iron unfiltered-recoverable, μg/L 44 86 134 216 342 405 2,38Lead, filtered, μg/L 44 0.03 0.07 0.13 0.14 0.16 

Lead, unfiltered-recoverable, μg/L 44 0.10 0.24 0.49 0.87 0.94 Manganese, filtered, μg/L 44 6.0 11 13 14 18 3

Manganese, unfiltered-recoverable, μg/L 44 14 19 23 26 28 10Zinc, filtered, μg/L 44 (4) 0.65 1.2 1.6 1.7 2.0 

Zinc, unfiltered-recoverable, μg/L 44 (4) 1.0 1.5 2.1 3.1 3.9 1Arsenic, filtered, μg/L 44 9.9 13 14 15 17 2

Arsenic, unfiltered-recoverable, μg/L 44 10 14 15 16 18 2Suspended sediment, mg/L 44 1 3 6 17 13 19Suspended sediment, percent fines4 44 25 62 78 73 88 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Willow Creek at Opportunity (site 7, fig. 1, table 1) 3/2003– 8/2010 Streamflow, instantaneous, ft3/s 64 4.5 6.2 9.1 17 20 7

Specific conductance, μS/cm 64 116 227 297 276 315 37pH, standard units 64 7.7 8.0 8.1 8.1 8.3 Hardness, filtered, mg/L as CaCO3 64 65 98 130 120 137 16

Calcium, filtered, mg/L 64 20.10 28.8 36.9 34.8 39.8 4Magnesium, filtered, mg/L 64 3.52 6.27 8.56 7.98 9.40 1Cadmium, filtered, μg/L 64 (5) 0.02 0.03 0.04 0.04 0.06 

Cadmium, unfiltered-recoverable, μg/L 64 (1) 0.02 0.05 0.07 0.10 0.14 Copper, filtered, μg/L 64 1.1 2.4 3.6 5.6 8.6 2

Copper, unfiltered-recoverable, μg/L 64 2.8 4.6 8.1 12 16 4Iron, filtered, μg/L 64 7.0 14 36 44 68 17

Iron unfiltered-recoverable, μg/L 64 27 108 205 272 332 1,42Lead, filtered, μg/L 64 (1) 0.04 0.10 0.19 0.22 0.30 

Lead, unfiltered-recoverable, μg/L 64 0.27 0.85 1.5 2.3 2.6 1Manganese, filtered, μg/L 64 3.3 15 24 32 45 20

Manganese, unfiltered-recoverable, μg/L 64 4.7 19 35 45 58 22Zinc, filtered, μg/L 64 (3) 0.84 2.3 3.9 5.3 7.0 2

Zinc, unfiltered-recoverable, μg/L 64 1.1 4.8 9.5 13 17 6Arsenic, filtered, μg/L 64 11 17 32 42 63 16

Arsenic, unfiltered-recoverable, μg/L 64 12 19 33 45 65 16Suspended sediment, mg/L 64 1 3 5 11 15 8Suspended sediment, percent fines4 64 55 80 88 85 92 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Silver Bow Creek at Warm Springs (site 8, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 21 41 65 112 146 48

Specific conductance, μS/cm 80 253 386 507 488 582 78pH, standard units 80 8.1 8.5 8.8 8.8 9.0 Hardness, filtered, mg/L as CaCO3 80 104 154 207 203 242 31

Calcium, filtered, mg/L 80 29.1 45.4 60.7 58.8 69.6 9Magnesium, filtered, mg/L 80 6.04 10.5 13.7 13.5 16.5 2Cadmium, filtered, μg/L 80 (14) 0.02 0.03 0.04 0.05 0.06 

Cadmium, unfiltered-recoverable, μg/L 80 (4) 0.03 0.07 0.10 0.12 0.14 Copper, filtered, μg/L 80 1.7 3.3 4.3 5.0 6.0 2

Copper, unfiltered-recoverable, μg/L 80 2.4 5.7 8.0 11 12 9Iron, filtered, μg/L 80 (7) 4.0 8.0 15 18 24 7

Iron unfiltered-recoverable, μg/L 80 36 143 218 258 272 1,42Lead, filtered, μg/L 80 (23) 0.03 0.05 0.08 0.10 0.13 

Lead, unfiltered-recoverable, μg/L 80 (7) 0.15 0.58 1.2 1.6 1.8 4Manganese, filtered, μg/L 80 13 50 78 122 167 87

Manganese, unfiltered-recoverable, μg/L 80 24 95 138 175 221 89Zinc, filtered, μg/L 80 (2) 0.59 2.1 3.5 4.5 5.2 3

Zinc, unfiltered-recoverable, μg/L 80 2.0 6.5 11 15 17 15Arsenic, filtered, μg/L 80 6.8 15 26 24 32 4

Arsenic, unfiltered-recoverable, μg/L 80 10.0 18 29 28 35 5Suspended sediment, mg/L 80 1 3 5 7 7 4Suspended sediment, percent fines4 80 47 79 84 82 88 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Warm Springs Creek near Anaconda (site 9, fig. 1, table 1) 10/2005– 8/2010 Streamflow, instantaneous, ft3/s 30 41 61 84 137 170 57

Specific conductance, μS/cm 30 125 184 235 217 253 27pH, standard units 30 8.0 8.4 8.5 8.5 8.6 Hardness, filtered, mg/L as CaCO3 30 58 89 112 105 124 13

Calcium, filtered, mg/L 30 18.5 27.5 33.8 31.6 36.5 3Magnesium, filtered, mg/L 30 2.96 4.90 6.90 6.36 7.85 Cadmium, filtered, μg/L 30 (9) 0.02 0.02 0.02 0.02 0.02 

Cadmium, unfiltered-recoverable, μg/L 30 (3) 0.01 0.02 0.03 0.04 0.04 Copper, filtered, μg/L 30 (2) 0.57 0.68 0.91 1.1 1.3 

Copper, unfiltered-recoverable, μg/L 30 (3) 1.1 1.5 2.1 3.2 3.3 2Iron, filtered, μg/L 30 (3) 2.0 5.0 6.0 7.1 10 1

Iron unfiltered-recoverable, μg/L 30 28 64 75 144 123 1,00Lead, filtered, μg/L 30 (21) 0.02 0.01 0.02 0.03 0.03 

Lead, unfiltered-recoverable, μg/L 30 0.08 0.20 0.26 0.52 0.43 Manganese, filtered, μg/L 30 (1) 0.50 0.70 0.95 1.2 1.5 

Manganese, unfiltered-recoverable, μg/L 30 1.20 2.8 4.3 6.9 6.9 4Zinc, filtered, μg/L 30 (14) 0.30 0.50 0.74 0.89 1.1 

Zinc, unfiltered-recoverable, μg/L 30 (4) 1.0 1.0 2.0 3.2 3.6 2Arsenic, filtered, μg/L 30 1.8 2 2 2 2 

Arsenic, unfiltered-recoverable, μg/L 30 2 2 3 3 3 Suspended sediment, mg/L 30 1 3 4 9 6 6Suspended sediment, percent fines4 30 32 61 66 64 70 8

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Warm Springs Creek at Warm Springs (site 10, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 63 14 37 48 83 102 38

Specific conductance, μS/cm 63 155 219 308 287 339 43pH, standard units 63 7.8 8.1 8.2 8.3 8.4 Hardness, filtered, mg/L as CaCO3 63 40 106 148 138 167 22

Calcium, filtered, mg/L 63 10.5 32.5 45.4 42.2 50.8 6Magnesium, filtered, mg/L 63 3.29 5.84 8.49 7.93 9.48 1Cadmium, filtered, μg/L 63 (14) 0.02 0.02 0.03 0.03 0.04 

Cadmium, unfiltered-recoverable, μg/L 63 (9) 0.03 0.04 0.05 0.08 0.08 Copper, filtered, μg/L 63 (1) 1.1 2.0 2.7 2.9 3.2 1Copper, unfiltered-recoverable, μg/L 63 3.9 6.4 8.1 18 14 14Iron, filtered, μg/L 63 (4) 5.0 8.0 10 11 14 2

Iron unfiltered-recoverable, μg/L 63 39 76 102 272 219 2,11Lead, filtered, μg/L 63 (31) 0.03 0.03 0.04 0.05 0.06 

Lead, unfiltered-recoverable, μg/L 63 (10) 0.21 0.34 0.60 1.3 1.2 1Manganese, filtered, μg/L 63 19 48 78 98 135 39

Manganese, unfiltered-recoverable, μg/L 63 37 95 142 180 203 1,27Zinc, filtered, μg/L 62 (7) 0.60 0.92 1.5 1.6 1.9 

Zinc, unfiltered-recoverable, μg/L 63 1.0 2.7 3.0 7.1 6.0 4Arsenic, filtered, μg/L 63 3.0 3.9 4.5 5.0 5.7 1

Arsenic, unfiltered-recoverable, μg/L 63 3.7 5.0 5.5 6.9 7.1 2Suspended sediment, mg/L 63 1 3 6 15 12 12Suspended sediment, percent fines4 63 43 65 68 68 73 8

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Clark Fork near Galen (site 11, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 33 79 127 203 258 90

Specific conductance, μS/cm 80 216 320 416 405 480 60pH, standard units 80 8.1 8.4 8.6 8.6 8.8 Hardness, filtered, mg/L as CaCO3 80 91 135 188 176 211 28

Calcium, filtered, mg/L 80 27.5 41.0 55.5 52.2 62.0 8Magnesium, filtered, mg/L 80 5.11 8.30 11.8 11.2 13.8 1Cadmium, filtered, μg/L 80 (13) 0.02 0.03 0.04 0.05 0.05 

Cadmium, unfiltered-recoverable, μg/L 80 (5) 0.04 0.07 0.10 0.12 0.15 Copper, filtered, μg/L 80 1.7 3.4 4.2 4.8 5.6 2

Copper, unfiltered-recoverable, μg/L 80 4.1 8.4 12 19 17 9Iron, filtered, μg/L 80 (5) 4.0 7.0 11 14 19 6

Iron unfiltered-recoverable, μg/L 80 56 135 224 332 324 2,03Lead, filtered, μg/L 80 (26) 0.04 0.04 0.06 0.08 0.10 

Lead, unfiltered-recoverable, μg/L 80 (8) 0.36 0.69 1.3 2.3 2.1 3Manganese, filtered, μg/L 80 24 42 67 94 120 46

Manganese, unfiltered-recoverable, μg/L 80 47 104 149 177 227 78Zinc, filtered, μg/L 80 (3) 0.90 1.7 2.7 3.5 4.7 3

Zinc, unfiltered-recoverable, μg/L 80 2.7 7.5 11 16 18 11

Arsenic, filtered, μg/L 80 5.7 10 16 16 20 3

Arsenic, unfiltered-recoverable, μg/L 80 7.5 12 18 19 23 5Suspended sediment, mg/L 80 1 4 7 13 12 9Suspended sediment, percent fines4 80 40 70 76 75 80 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Lost Creek near Anaconda (site 12, fig. 1, table 1) 12/2004– 8/2010 Streamflow, instantaneous, ft3/s 47 0.37 4.3 8.0 10 13 5

Specific conductance, μS/cm 47 121 173 211 198 221 25pH, standard units 47 7.4 8.2 8.2 8.2 8.3 Hardness, filtered, mg/L as CaCO3 47 50 85 99 94 106 12

Calcium, filtered, mg/L 47 15.7 26.3 30.0 28.5 32.2 3Magnesium, filtered, mg/L 47 2.71 4.54 5.78 5.50 6.45 Cadmium, filtered, μg/L 46 (5) 0.01 0.02 0.03 0.03 0.03 

Cadmium, unfiltered-recoverable, μg/L 47 (5) 0.01 0.03 0.04 0.12 0.07 14Copper, filtered, μg/L 47 0.86 1.3 1.8 3.9 2.9 9

Copper, unfiltered-recoverable, μg/L 47 (1) 1.7 2.8 4.4 16.3 8.3 29,10Iron, filtered, μg/L 47 (4) 4.0 6.0 9.0 10 12 2

Iron unfiltered-recoverable, μg/L 47 22 61 98 2,300 217 99,70Lead, filtered, μg/L 47 (26) 0.02 0.02 0.03 0.04 0.05 

Lead, unfiltered-recoverable, μg/L 47 0.10 0.28 0.42 28 1.0 1,29Manganese, filtered, μg/L 47 (1) 0.40 0.80 1.1 1.6 1.5 4

Manganese, unfiltered-recoverable, μg/L 47 1.2 2.8 4.6 194 7.6 8,83Zinc, filtered, μg/L 47 (14) 0.62 0.71 1.1 1.3 1.5 3

Zinc, unfiltered-recoverable, μg/L 47 (2) 1.0 2.0 2.4 7.7 4.0 7,78Arsenic, filtered, μg/L 47 1.8 2.7 3.4 7.8 5.8 15

Arsenic, unfiltered-recoverable, μg/L 47 2.0 3.2 3.7 87 7.7 3,86Suspended sediment, mg/L 47 1 3 5 1,270 15 58,90Suspended sediment, percent fines4 47 22 49 61 58 67 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Lost Creek near Galen (site 13, fig. 1, table 1) 3/2003– 8/2010 Streamflow, instantaneous, ft3/s 64 1.3 3.5 13 21 41 7

Specific conductance, μS/cm 64 540 611 631 648 672 93pH, standard units 64 8.0 8.2 8.3 8.3 8.5 Hardness, filtered, mg/L as CaCO3 64 203 281 298 301 316 45

Calcium, filtered, mg/L 64 48.5 78.5 85.2 84.7 92.2 12Magnesium, filtered, mg/L 64 17.3 19.9 21.0 21.7 23.2 3Cadmium, filtered, μg/L 63 (10) 0.01 0.02 0.02 0.03 0.03 

Cadmium, unfiltered-recoverable, μg/L 64 (5) 0.01 0.03 0.04 0.04 0.05 Copper, filtered, μg/L 64 0.99 1.6 2.4 2.4 2.9 

Copper, unfiltered-recoverable, μg/L 64 1.6 3.7 4.4 5.5 6.3 2Iron, filtered, μg/L 64 (3) 4.0 7.0 10 13 16 6

Iron unfiltered-recoverable, μg/L 64 14 47 77 99 128 29Lead, filtered, μg/L 63 (35) 0.02 0.02 0.03 0.04 0.05 

Lead, unfiltered-recoverable, μg/L 64 0.04 0.14 0.24 0.35 0.44 Manganese, filtered, μg/L 64 1.9 6.9 14 15 20 5

Manganese, unfiltered-recoverable, μg/L 64 2.2 9.6 18 20 29 5Zinc, filtered, μg/L 63 (9) 0.40 0.87 1.3 1.5 1.8 

Zinc, unfiltered-recoverable, μg/L 64 (6) 1.0 1.3 2.0 2.8 3.9 Arsenic, filtered, μg/L 64 6.0 10 13 14 16 4

Arsenic, unfiltered-recoverable, μg/L 64 6.0 11 14 15 16 4Suspended sediment, mg/L 64 2 8 15 16 22 7Suspended sediment, percent fines4 64 18 46 60 57 68 8

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Clark Fork at Deer Lodge (site 14, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 38 151 215 282 343 1,13

Specific conductance, μS/cm 80 245 360 489 452 524 60pH, standard units 80 8.0 8.2 8.3 8.3 8.5 Hardness, filtered, mg/L as CaCO3 80 102 152 210 196 230 28

Calcium, filtered, mg/L 80 31.8 45.3 62.3 58.1 67.5 8Magnesium, filtered, mg/L 80 5.53 10.1 13.2 12.5 14.7 1Cadmium, filtered, μg/L 79 (9) 0.02 0.04 0.06 0.06 0.07 

Cadmium, unfiltered-recoverable, μg/L 79 (1) 0.02 0.10 0.15 0.22 0.24 Copper, filtered, μg/L 80 3.2 5.6 7.1 7.9 9.5 1

Copper, unfiltered-recoverable, μg/L 79 8.2 18 27 49 57 46Iron, filtered, μg/L 80 (9) 3.0 6.0 8.0 12 17 4

Iron unfiltered-recoverable, μg/L 80 27 218 393 711 823 6,96

Lead, filtered, μg/L 79 (19) 0.04 0.05 0.08 0.10 0.13 

Lead, unfiltered-recoverable, μg/L 80 (2) 0.33 1.8 3.0 6.7 7.0 6Manganese, filtered, μg/L 80 4.0 24 34 38 49 9

Manganese, unfiltered-recoverable, μg/L 80 12 76 112 143 164 1,01

Zinc, filtered, μg/L 80 0.90 4.5 5.9 6.5 8.1 1

Zinc, unfiltered-recoverable, μg/L 78 4.0 16 26 40 44 35Arsenic, filtered, μg/L 80 6.0 11 15 15 17 2

Arsenic, unfiltered-recoverable, μg/L 79 4.8 13 17 20 24 7Suspended sediment, mg/L 80 1 11 18 37 40 38Suspended sediment, percent fines4 80 31 67 73 71 79 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Little Blackfoot River (site 15, fig. 1, table 1) 11/2000– 8/2004 Streamflow, instantaneous, ft3/s 20 19.0 56.3 135 176 297 45

Specific conductance, μS/cm 20 174 211 259 255 287 34pH, standard units 20 8.0 8.1 8.2 8.3 8.4 Hardness, filtered, mg/L as CaCO3 20 79 94 116 117 136 17

Calcium, filtered, mg/L 20 22.9 27.6 34.0 34.1 39.9 4Magnesium, filtered, mg/L 20 5.33 6.03 7.56 7.69 8.83 1Cadmium, filtered, μg/L 20 (18) 0.02 ND ND ND ND 

Cadmium, unfiltered-recoverable, μg/L 20 (14) 0.02 0.01 0.02 0.02 0.03 Copper, filtered, μg/L 20 (3) 0.60 0.75 1.1 1.3 1.5 

Copper, unfiltered-recoverable, μg/L 20 0.80 1.2 1.7 1.9 2.4 Iron, filtered, μg/L 20 (3) 5.0 5.5 16 27 33 11Iron unfiltered-recoverable, μg/L 20 38 63 178 236 305 70Lead, filtered, μg/L 19 (13) 0.05 0.03 0.04 0.05 0.06 

Lead, unfiltered-recoverable, μg/L 20 (8) 0.06 0.11 0.24 0.45 0.51 Manganese, filtered, μg/L 20 2.5 7.9 8.5 11 11 4

Manganese, unfiltered-recoverable, μg/L 20 6.8 18 23 28 32 9Zinc, filtered, μg/L 20 (4) 0.50 0.50 1.2 1.1 1.4 

Zinc, unfiltered-recoverable, μg/L 20 (5) 1.0 0.89 2.0 2.8 3.5 Arsenic, filtered, μg/L 20 3.9 4.6 5.1 5.2 5.8 

Arsenic, unfiltered-recoverable, μg/L 20 4.0 5.0 6.0 5.7 6.0 Suspended sediment, mg/L 20 2 3 8 13 14 4Suspended sediment, percent fines4 20 54 73 83 80 85 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Clark Fork at Goldcreek (site 16, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 100 310 495 690 876 2,30

Specific conductance, μS/cm 80 206 304 384 370 435 49pH, standard units 80 8.0 8.3 8.4 8.4 8.6 Hardness, filtered, mg/L as CaCO3 80 90 132 169 163 196 22

Calcium, filtered, mg/L 80 27.0 39.4 50.3 48.2 57.9 6Magnesium, filtered, mg/L 80 5.40 8.17 10.6 10.3 12.8 1Cadmium, filtered, μg/L 80 (18) 0.02 0.03 0.04 0.04 0.05 

Cadmium, unfiltered-recoverable, μg/L 80 (3) 0.03 0.08 0.12 0.17 0.21 Copper, filtered, μg/L 80 2.1 4.1 4.9 5.6 6.6 1

Copper, unfiltered-recoverable, μg/L 80 5.2 12 20 31 43 12Iron, filtered, μg/L 80 (10) 3.0 5.1 11 18 25 7

Iron unfiltered-recoverable, μg/L 80 27 198 371 640 870 3,02Lead, filtered, μg/L 79 (30) 0.04 0.04 0.07 0.10 0.12 

Lead, unfiltered-recoverable, μg/L 80 (2) 0.14 1.3 2.4 4.8 5.8 2Manganese, filtered, μg/L 80 4.0 11 15 17 21 5

Manganese, unfiltered-recoverable, μg/L 80 11 56 76 99 117 34Zinc, filtered, μg/L 80 (1) 0.70 2.2 3.1 4.0 5.2 1

Zinc, unfiltered-recoverable, μg/L 80 2.0 12 20 30 42 12Arsenic, filtered, μg/L 80 5.8 7.8 10 10 12 1

Arsenic, unfiltered-recoverable, μg/L 80 7.0 10 12 13 15 2Suspended sediment, mg/L 80 1 10 17 35 44 19Suspended sediment, percent fines4 80 44 66 77 74 82 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Flint Creek (site 17, fig. 1, table 1) 11/2000– 8/2004 Streamflow, instantaneous, ft3/s 23 5.4 29 76 84 113 33

Specific conductance, μS/cm 23 276 305 350 373 430 52pH, standard units 23 8.1 8.3 8.4 8.4 8.5 Hardness, filtered, mg/L as CaCO3 23 115 140 161 172 204 25

Calcium, filtered, mg/L 23 30.5 38.5 43.8 46.8 56.6 7Magnesium, filtered, mg/L 23 9.51 10.9 12.5 13.3 15.4 1Cadmium, filtered, μg/L 23 (20) 0.02 ND ND ND ND 

Cadmium, unfiltered-recoverable, μg/L 23 (9) 0.02 0.02 0.04 0.06 0.07 Copper, filtered, μg/L 23 (2) 0.70 1.0 1.2 1.4 1.4 

Copper, unfiltered-recoverable, μg/L 23 1.4 1.8 2.3 3.3 3.3 1Iron, filtered, μg/L 23 (2) 5.0 8.0 15 23 21 11Iron unfiltered-recoverable, μg/L 23 56 127 245 374 432 2,05Lead, filtered, μg/L 21 (6) 0.05 0.08 0.13 0.16 0.19 

Lead, unfiltered-recoverable, μg/L 23 (2) 0.65 1.5 3.1 5.3 5.6 3Manganese, filtered, μg/L 23 22 38 51 56 59 13

Manganese, unfiltered-recoverable, μg/L 23 53 78 101 143 142 59Zinc, filtered, μg/L 23 (1) 1.1 1.2 1.6 2.0 1.9 

Zinc, unfiltered-recoverable, μg/L 23 2.0 5.0 10 15 15 8Arsenic, filtered, μg/L 23 6.1 7.8 10 9.5 11 1

Arsenic, unfiltered-recoverable, μg/L 23 7.0 11 12 13 14 3Suspended sediment, mg/L 23 3 8 15 30 26 19Suspended sediment, percent fines4 23 30 84 88 83 90 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Clark Fork near Drummond (site 18, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 157 464 709 964 1,158 3,35

Specific conductance, μS/cm 80 236 346 415 414 480 60pH, standard units 80 7.9 8.2 8.3 8.3 8.4 Hardness, filtered, mg/L as CaCO3 80 102 154 184 186 221 28

Calcium, filtered, mg/L 80 30.6 44.5 53.4 53.4 63.4 8Magnesium, filtered, mg/L 80 6.07 10.1 12.6 12.8 15.3 2Cadmium, filtered, μg/L 79 (14) 0.02 0.03 0.04 0.05 0.05 

Cadmium, unfiltered-recoverable, μg/L 80 (2) 0.02 0.08 0.14 0.22 0.27 Copper, filtered, μg/L 79 2.0 3.8 4.7 5.9 7.0 2

Copper, unfiltered-recoverable, μg/L 80 4.6 10 20 37 43 21Iron, filtered, μg/L 80 (18) 3.0 4.0 8.0 16 23 8

Iron unfiltered-recoverable, μg/L 79 20 179 379 822 1,140 5,77Lead, filtered, μg/L 79 (23) 0.04 0.04 0.09 0.14 0.17 

Lead, unfiltered-recoverable, μg/L 80 (2) 0.18 1.3 3.2 7.4 8.3 4Manganese, filtered, μg/L 79 3.3 10 12 16 18 6

Manganese, unfiltered-recoverable, μg/L 80 8.0 53 84 129 157 69Zinc, filtered, μg/L 80 (1) 0.95 2.9 4.1 4.7 5.8 1

Zinc, unfiltered-recoverable, μg/L 80 2.9 12 25 46 57 27Arsenic, filtered, μg/L 80 3.2 8.4 10 10 12 1

Arsenic, unfiltered-recoverable, μg/L 80 8.0 10 13 15 17 4Suspended sediment, mg/L 80 2 11 23 52 63 31Suspended sediment, percent fines4 80 50 66 74 74 81 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Rock Creek (site 19, fig. 1, table 1) 11/2000– 8/2004 Streamflow, instantaneous, ft3/s 20 149 209 356 608 915 2,08

Specific conductance, μS/cm 20 68 88 129 118 145 16pH, standard units 20 7.7 8.0 8.2 8.1 8.3 Hardness, filtered, mg/L as CaCO3 20 28 38 57 53 67 7

Calcium, filtered, mg/L 20 7.23 9.90 14.5 13.7 17.2 1Magnesium, filtered, mg/L 20 2.46 3.32 4.78 4.51 5.77 Cadmium, filtered, μg/L 20 (17) 0.02 ND ND ND ND 

Cadmium, unfiltered-recoverable, μg/L 20 (18) 0.02 ND ND ND ND Copper, filtered, μg/L 20 (6) 0.20 0.34 0.46 0.52 0.70 

Copper, unfiltered-recoverable, μg/L 20 (3) 0.30 0.45 0.60 0.80 1.2 Iron, filtered, μg/L 20 (1) 6.0 8.0 15 19 25 5

Iron unfiltered-recoverable, μg/L 20 23 41 72 88 114 26Lead, filtered, μg/L 20 (19) 0.05 ND ND ND ND 

Lead, unfiltered-recoverable, μg/L 20 (15) 0.03 0.02 0.04 0.05 0.06 Manganese, filtered, μg/L 20 0.60 1.0 1.6 1.5 1.8 

Manganese, unfiltered-recoverable, μg/L 20 1.5 3.5 5.2 5.6 7.2 1Zinc, filtered, μg/L 20 (15) 0.40 0.15 0.25 0.32 0.41 

Zinc, unfiltered-recoverable, μg/L 20 (15) 1.0 0.11 0.27 0.66 0.80 Arsenic, filtered, μg/L 20 0.50 0.50 0.60 0.61 0.63 

Arsenic, unfiltered-recoverable, μg/L 18 (15) 1.0 ND ND ND ND Suspended sediment, mg/L 20 1 3 4 5 6 1Suspended sediment, percent fines4 20 57 73 76 75 80 8

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Clark Fork at Turah Bridge (site 20, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 331 744 1,200 1,940 2,550 7,56

Specific conductance, μS/cm 80 139 226 303 290 359 41pH, standard units 80 7.9 8.1 8.3 8.3 8.5 Hardness, filtered, mg/L as CaCO3 80 54 98 130 128 159 19

Calcium, filtered, mg/L 80 14.9 28.1 36.9 36.1 44.0 5Magnesium, filtered, mg/L 80 3.97 6.82 9.19 9.29 11.9 1Cadmium, filtered, μg/L 79 (29) 0.02 0.02 0.03 0.03 0.04 

Cadmium, unfiltered-recoverable, μg/L 80 (7) 0.03 0.05 0.10 0.14 0.16 Copper, filtered, μg/L 80 1.1 2.4 3.0 3.8 4.4 1

Copper, unfiltered-recoverable, μg/L 80 2.7 5.8 12 21 25 11Iron, filtered, μg/L 80 (16) 3.0 4.3 11.0 22 30 9

Iron unfiltered-recoverable, μg/L 80 33 117 289 590 711 4,25Lead, filtered, μg/L 80 (30) 0.03 0.04 0.07 0.10 0.13 

Lead, unfiltered-recoverable, μg/L 80 (6) 0.17 0.58 2.0 4.2 4.3 3Manganese, filtered, μg/L 80 2.9 4.8 7.3 8.1 10 3

Manganese, unfiltered-recoverable, μg/L 80 8.9 24 53 80 92 62Zinc, filtered, μg/L 78 0.94 2.1 3.1 3.6 4.6 1

Zinc, unfiltered-recoverable, μg/L 80 2.9 9.0 18 31 35 23Arsenic, filtered, μg/L 80 3.1 4.9 5.6 5.9 6.7 1

Arsenic, unfiltered-recoverable, μg/L 80 3.0 6.0 7.0 8.3 9.3 2Suspended sediment, mg/L 80 2 7 17 39 43 30Suspended sediment, percent fines4 80 54 69 77 76 83 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Blackfoot River (site 21, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 57 450 634 1,310 2,430 3,980 9,32

Specific conductance, μS/cm 57 140 174 205 215 260 28pH, standard units 57 8.0 8.2 8.4 8.4 8.5 Hardness, filtered, mg/L as CaCO3 56 68 86 108 107 130 14

Calcium, filtered, mg/L 56 18.6 22.5 27.9 27.3 32.0 3Magnesium, filtered, mg/L 56 5.37 7.14 9.46 9.48 11.9 1Cadmium, filtered, μg/L 55 (48) 0.01 ND ND ND ND 

Cadmium, unfiltered-recoverable, μg/L 57 (44) 0.01 <0.01 <0.01 0.01 0.01 Copper, filtered, μg/L 55 (10) 0.23 0.44 0.63 0.72 0.93 

Copper, unfiltered-recoverable, μg/L 57 (8) 0.30 0.72 1.3 1.8 2.2 Iron, filtered, μg/L 56 (13) 3.0 3.6 7.0 13 17 10

Iron unfiltered-recoverable, μg/L 57 14 30 86 232 387 2,20Lead, filtered, μg/L 55 (45) 0.02 ND ND ND ND 

Lead, unfiltered-recoverable, μg/L 57 (18) 0.04 0.05 0.12 0.33 0.31 Manganese, filtered, μg/L 56 0.50 1.2 1.7 2.0 2.5 

Manganese, unfiltered-recoverable, μg/L 57 2.0 5.0 8.6 19 28 15Zinc, filtered, μg/L 55 (24) 0.30 0.36 0.57 0.70 0.88 

Zinc, unfiltered-recoverable, μg/L 57 (26) 1.0 0.49 1.0 2.0 2.7 1Arsenic, filtered, μg/L 56 0.41 0.80 0.97 1.0 1.2 

Arsenic, unfiltered-recoverable, μg/L 54 (10) 0.93 1.0 1.1 1.2 1.3 Suspended sediment, mg/L 57 1 2 5 19 28 22Suspended sediment, percent fines4 57 69 79 82 82 85 9

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than] Period of water- quality sampling during water years 2001–10 Constituent or property, unadjusted (not flow adjusted) units of measurement Statistical summaries of water-quality data1 

Number of samples (values in parentheses indicate number of censored values) Minimum uncensored value2 25th percentile Median Mean 75th percentile Max
Clark Fork above Missoula (site 22, fig. 1, table 1) 10/2000– 8/2010 Streamflow, instantaneous, ft3/s 80 772 1,320 3,300 4,280 6,510 15,4

Specific conductance, μS/cm 80 148 196 256 252 311 35pH, standard units 80 7.9 8.2 8.3 8.3 8.4 

Hardness, filtered, mg/L as CaCO3 80 70 91 118 117 142 16

Calcium, filtered, mg/L 80 19.3 24.7 31.5 31.5 38.3 4

Magnesium, filtered, mg/L 80 5.34 7.08 9.08 9.22 11.6 1

Cadmium, filtered, μg/L 79 (40) 0.01 0.01 0.02 0.02 0.03 

Cadmium, unfiltered-recoverable, μg/L 80 (8) 0.02 0.05 0.08 0.14 0.15 Copper, filtered, mg/L 80 0.90 1.7 2.3 2.7 3.3 1

Copper, unfiltered-recoverable, μg/L 80 2.5 6.0 10 23 20 38Iron, filtered, μg/L 80 (9) 3.0 7.0 13.5 20 25 10

Iron unfiltered-recoverable, μg/L 80 43 141 246 603 724 5,98Lead, filtered, μg/L 78 (20) 0.04 0.05 0.07 0.10 0.12 

Lead, unfiltered-recoverable, μg/L 80 (7) 0.18 0.77 1.7 3.4 3.8 5Manganese, filtered, μg/L 80 5.9 9.5 13 14 17 3

Manganese, unfiltered-recoverable, μg/L 80 11.7 28 45 64 72 31Zinc, filtered, μg/L 79 (2) 0.80 1.5 2.4 2.7 3.4 

Zinc, unfiltered-recoverable, μg/L 80 3.3 8.5 15 35 33 49Arsenic, filtered, μg/L 80 1.6 3.0 3.6 3.7 4.4 

Arsenic, unfiltered-recoverable, μg/L 80 2.0 3.8 4.3 5.6 6.0 2Suspended sediment, mg/L 80 2 9 15 52 56 95

Suspended sediment, percent fines4 80 14 69 83 77 90 9

1Distributional parameters affected by censored observations (that is, concentrations reported as less than the laboratory reporting level) were estimated by using adjusted ma

(Cohn, 1988). 2Minimum uncensored value refers to the smallest concentration reported as detected above any of the various laboratory reporting levels applicable for a given constituent. 3Ratio of median filtered to unfiltered-recoverable concentration greater than 100 percent affected by low median concentrations near minimum laboratory reporting levels (t

concentrations. 4Percent fines refers to the percentage of suspended sediment smaller than 0.062-millimeter diameter.

Table 1–4. Summary information relating to water-quality constituents and properties in samples collected at sites in the upper Clark Fork Basin, Mcollected during water years 2001–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ft3/s, cubic feet per second; NA, not applicable; μS/cm

at 25 degrees Celsius; CaCO3, calcium carbonate; μg/L, micrograms per liter; mg/L, milligrams per liter; ND, distributional parameter not determined because of excessive num

than]

Period of 

waterquality 

sampling 

during 

water years 

2001–10

Constituent or property, 

unadjusted (not flow adjusted) 

units of measurement

Statistical summaries of water-quality data1 

Number of 

samples (values 

in parentheses 

indicate number 

of censored 

values)

Minimum 

uncensored 

value2

25th 

percentile Median Mean 75th percentile Max
Table 1–5. Aquatic life standards (based on median hardness for water years 2001–10) for selected sites in the upper Clark Fork Basin, Montana. [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. CaCO3, calcium carbonate] Site number (fig. 1, table 1) Site name (fig. 1, table 1) Median hard- ness for water years 2001–10, in milligrams per liter as CaCO3 Aquatic life standards (Montana Department of Environmental Quality, 2012a), in mic

(adjusted for hardness) Cadmium Copper Lead 

Acute Chronic Acute Chronic Acute Chronic 

1 Blacktail Creek 106 2.26 0.283 14.8 9.81 87.9 3.43 

2 Silver Bow Creek at Butte 154 3.31 0.373 21.0 13.5 141 5.51 

3 Silver Bow Creek at Op- portunity 159 3.42 0.382 21.7 13.9 147 5.74 

4 Mill Creek near Anaconda 59.8 1.26 0.185 8.62 6.01 42.4 1.65 

5 Mill Creek at Opportunity 67.0 1.42 0.201 9.60 6.63 49.0 1.91 

6 Willow Creek near Ana- conda 38.4 0.806 0.133 5.68 4.12 24.1 0.941 

7 Willow Creek at Oppor- tunity 130 2.79 0.329 17.9 11.7 114 4.44 

8 Silver Bow Creek at Warm Springs 207 4.47 0.464 27.8 17.4 206 8.03 

9 Warm Springs Creek near Anaconda 112 2.39 0.294 15.6 10.3 94.3 3.68 

10 Warm Springs Creek at Warm Springs 148 3.18 0.362 20.3 13.0 134 5.24 

11 Clark Fork near Galen 188 4.05 0.432 25.4 16.0 182 7.11 

12 Lost Creek near Anaconda 98.8 2.11 0.268 13.8 9.23 80.4 3.13 

13 Lost Creek near Galen 298 6.47 0.608 39.2 23.7 328 12.8 14 Clark Fork at Deer Lodge 210 4.54 0.469 28.2 17.6 210 8.18 

15 Little Blackfoot River 116 2.48 0.302 16.1 10.6 98.6 3.84 16 Clark Fork at Goldcreek 169 3.64 0.399 23.0 14.6 159 6.21 

17 Flint Creek near Drum- mond 161 3.46 0.385 21.9 14.0 150 5.83 

18 Clark Fork near Drum- mond 184 3.96 0.425 24.9 15.7 177 6.91 

19 Rock Creek 56.9 1.20 0.178 8.23 5.76 39.8 1.55 

20 Clark Fork at Turah Bridge 130 2.79 0.329 17.9 11.7 114 4.44 

21 Blackfoot River 108 2.31 0.287 15.1 9.96 90.0 3.51 

22 Clark Fork above Missoula 118 2.52 0.306 16.4 10.7 101 3.93 
Table 1–6. Summary information relating to continuous streamflow data for sites in the upper Clark Fork Basin, Montana , based on data collected d2001–2010.[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site 

number 

(fig. 1, 

table 1)

Site name 

(fig. 1, table 1)

Drainage 

area, 

square 

miles

Water years 

summarized 

based on available data during 

water years 

2001–10

Daily mean streamflow, cubic feet per secon

Minimum 25th percentile Median Mean 

p

1 Blacktail Creek at Harrison Avenue, at 

Butte, Mont.

85 2001–10 4.4 7.2 8.9 13 

2 Silver Bow Creek below Blacktail 

Creek, at Butte, Mont.

103 2001–10 11 15 17 21 

3 Silver Bow Creek at Opportunity, Mont. 363 2001–10 11 24 30 44 4 Mill Creek near Anaconda, Mont. 34 2005–10 5.5 10 14 33 

5 Mill Creek at Opportunity, Mont. 43 2004–10 0.20 1.7 4.3 15 

6 Willow Creek near Anaconda, Mont. 14 2005–10 0.50 1.5 2.2 7.0 7 Willow Creek at Opportunity, Mont. 31 2004–10 2.5 5.1 6.6 10 

8 Silver Bow Creek at Warm Springs, 

Mont.

473 2001–10 15 35 47 70 

9 Warm Springs Creek near Anaconda, 

Mont.

157 2001–10 13 46 61 84 

10 Warm Springs Creek at Warm Springs, 

Mont.

163 2001–10 5.0 30 40 58 

11 Clark Fork near Galen, Mont. 651 2001–10 26 68 89 130 

12 Lost Creek near Anaconda, Mont. 26 2005–10 0.00 3.1 4.7 6.5 

13 Lost Creek near Galen, Mont. 61 2004–10 1.4 8.5 36 29 14 Clark Fork at Deer Lodge, Mont. 995 2001–10 27 147 187 216 

15 Little Blackfoot River near Garrison, 

Mont.

407 2001–10 16 52 72 145 

16 Clark Fork at Goldcreek, Mont. 1,704 2001–10 73 271 332 460 

17 Flint Creek near Drummond, Mont. 490 2001–10 2.1 66 98 123 18 Clark Fork near Drummond, Mont. 2,501 2001–10 100 401 503 648 

19 Rock Creek near Clinton, Mont. 885 2001–10 40 180 240 471 

20 Clark Fork at Turah Bridge, near Bonner, Mont. 3,641 2001–10 177 654 816 1,200 

21 Blackfoot River near Bonner, Mont. 2,290 2001–10 180 490 624 1,330 22 Clark Fork above Missoula, Mont. 5,999 2001–10 450 1,130 1,420 2,500 
110 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Appendix 2—Summary of the TimeSeries Model (TSM) as Applied in this 

Study

The theory and parameter estimation for the model are 

described in detail in Vecchia (2005). In the time-series model, 

log-transformed concentration data were partitioned into several components according to equation 2:

log(C) = MC+ANNC+SEASC+TREND+HFVC (2)

where

log is the base-10 logarithm;

C is the concentration, in milligrams per liter;

MC is the long-term mean of the log-transformed 

concentration, as the base-10 logarithm of 

milligrams per liter;

ANNC is the annual concentration anomaly 

(dimensionless);

SEASC is the seasonal concentration anomaly 

(dimensionless);

TREND is the concentration trend (dimensionless); 

and

HFVC is the high-frequency variability of the 

concentration (dimensionless).

In equation 2, the annual concentration anomaly (ANNC), 

seasonal concentration anomaly (SEASC), and high-frequency 

variability (HFVC) terms represent natural variability in concentration for different time scales. ANNC is an estimate of the 

interannual variability in concentration that can be attributed 

to long-term variability in streamflow. ANNC is quantified by 

relating annual means (for the 365-day period immediately 

before a given sample) of log concentration and log streamflow to long-term means (for the entire period of record). 

Extended droughts and wet periods can change the chemical and suspended-material composition of streamflow by 

changing the degree of contact between surface runoff and soil 

particles, availability of particulate material in stream channels 

and near-stream areas, and changing the relative composition 

of runoff among groundwater, overland flow, and subsurface 

flow (Vecchia, 2005).

SEASC is an estimate of the seasonal variability in 

concentration that can be attributed to seasonal variability in 

streamflow or to factors other than variability in streamflow. 

SEASC is quantified by relating seasonal means (for the 90-day 

period immediately before a given sample was collected) of 

log concentration and log streamflow to annual means (for 

the 365-day period immediately before a given sample was 

collected). For example, the seasonal snow-accumulation and 

snowmelt cycle causes seasonal fluctuations in streamflow 

and water quality. Seasonal differences in the relative amount 

of streamflow that comes from natural sources compared to 

anthropogenic contributions (such as wastewater inputs) also 

might cause seasonal fluctuations in concentration that are 

more complicated than a simple relation between concentration and streamflow could produce. 

HFVC is an estimate of the variability in concentration for 

time scales that are smaller than the seasonal time scale (time 

scales of several days to several weeks). Thus, high-frequency 

variability is the variability that remains after the removal of 

seasonal and annual anomalies and trends. HFVC is quantified by relating log concentration and log streamflow for the 

day of sampling to log concentration and log streamflow for 

each of the two 10-day periods immediately before a given 

sample. Short-term changes in meteorological conditions 

might cause high-frequency variability in concentration and 

streamflow. The high-frequency variability depends on a timeseries model, called a periodic autoregressive moving average model, that accounts for the presence of serial correlation 

among concentrations (for example, the tendency for high or 

low values to persist for several days to several weeks before 

returning to normal levels; Vecchia, 2005).

TREND is an estimate of the long-term systematic 

changes in concentration during the study period that are unrelated to long-term variability in streamflow. For this report, a 

significant trend might indicate changes in the extent to which 

mining wastes affect chemical composition of surface water 

or changes in other activities, such as agricultural practices, 

that can change the amount of suspended sediment or trace 

elements that reach the stream. TREND consists of piecewise 

monotonic trends during specified trend-analysis periods. The 

overall significance of TREND (determined by using 

the generalized likelihood ratio principle; Vecchia, 2005, 

appendix 1) specifies whether there were any significant 

changes during any of the specified trend-analysis periods. 

For a given site and constituent combination, if TREND was 

determined to be nonsignificant, the trends for all of the specified trend-analysis periods were considered nonsignificant 

and p-values were not reported. Infrequently, overall significance of TREND could not be determined (and thus TREND

was assumed to be nonsignificant), but the individual trend 

coefficient for a specified trend-analysis period was highly significant and of large magnitude. In those cases, with TREND

included in the model, the numerical procedure for minimizing 

the likelihood function apparently converged to a local, rather 

than global, minimum and produced unrealistic results relative to the model without TREND included. However, trend 

directions and magnitudes for those infrequent cases generally 

were consistent with trends for other constituents that would 

be expected to behave in a similar manner, and with trends 

for upstream or downstream sites. Therefore, the TSM was 

presumed to provide reasonably accurate trend magnitudes for 

the specified trend-analysis period and overall trend patterns 

were not strongly affected. For a given site and constituent 

combination, if TREND was determined to be significant, the 

slope coefficient (γ; Vecchia, 2005, appendix 1) for the trend 

for each specified trend-analysis period was used to determine 

the significance and magnitude of the trend for the specified 

trend-analysis period. The null hypothesis in the test for trend 

significance in a given trend analysis period is that there is 
Appendix 2—Summary of the Time-Series Model (TSM) as Applied in this Study 111

no trend (that is, γ = 0). If the two-tailed p-value for γ was 

less than the selected alpha level (0.01 in this report), the null 

hypothesis was rejected and the trend was determined to be 

significant. Determination of a nonsignificant trend (that is, a 

p-value greater than 0.01) does not imply that the null hypothesis is accepted (that is, that there is no trend). It indicates that 

within the statistical framework of the analysis, a significant 

trend was not detected. The magnitude of the trend for a specified trend-analysis period is expressed as the percent difference between the geometric mean concentration at the end of 

the period and the geometric mean concentration at the start of 

the period and is determined by the equation:

%∆FAC=100(10γ-1), (3)

where

%∆FAC is the percent change in the geometric mean 

of the flow-adjusted concentration, and 

γ is the slope coefficient of the trend for the 

specified trend-analysis period in logtransformed units.

Log-transformed concentrations that have ANNC and 

SEASC removed are referred to in this report as flow-adjusted 

concentrations. Using equation 2, the flow-adjusted concentration is defined as:

 FAC =log(C)–ANNC–SEASC=MC+TREND+HFVC (4)

where

FAC is the flow-adjusted value, as the base10 logarithm of the original units of 

measurement. 

The FACs defined by equation 4 are analogous to FACs 

defined in previous publications as the residuals from a 

regression model that relates concentration to concurrent daily 

streamflow (Helsel and Hirsch, 2002); however, the TSM 

approach generally is more effective than a regression-based 

approach for removing streamflow-related variability (Vecchia, 2005). Time-series plots showing the FACs along with 

the fitted trend (MC+TREND) illustrate long-term changes in 

geometric mean concentration that might indicate changes 

in effects of mining wastes on water-quality in the selected 

watersheds. 

The key to making TSM a powerful trend analysis tool is 

that the entire time series of daily streamflow data are used in 

the model, not just streamflow for the days when concentration samples are available. The model uses a three-per-month, 

or approximately 10-day, sampling frequency. Each month 

is divided into three intervals—days 1 through 10, days 11 

through 20, and day 21 through the end of the month. If a 

water-quality sample is available for a particular interval, it is 

paired with daily streamflow for the same day of the waterquality sample. If no water-quality sample is available, the 

concentration value for the interval is missing and streamflow 

for the middle of the interval (day 5, 15, or 25) is used. If more 

than one concentration sample is available for the interval, 

the value nearest to the midpoint of the interval is used. The 

log-transformed streamflow time series (consisting of three 

values per month) is divided into an annual anomaly, seasonal 

anomaly, and high-frequency variability according to the following equation,

log(Q) = MQ+ANNQ+SEASQ+HFVQ (5)

where

Q is daily mean streamflow, in cubic feet per 

second;

MQ is the mean of the log-transformed streamflow 

for the entire trend analysis period, as the 

base-10 logarithm of cubic feet per second;

ANNQ is the annual streamflow anomaly, computed 

as the 1-year lagged moving average of 

log(Q)-MQ (dimensionless);

SEASQ is the seasonal streamflow anomaly, computed 

as the 3-month lagged moving average of 

log(Q)-MQ-ANNQ (dimensionless); and

HFVQ is log(Q)-MQ-ANNQ-SEASQ is the highfrequency streamflow variability 

(dimensionless). 

The water-quality time-series model (equation 2) is 

directly tied to the streamflow time-series model because the 

streamflow anomalies (ANNQ and SEASQ from equation 5) 

are used as predictor variables for concentration (equation 2). 

For example, ANNC is assumed to equal a constant coefficient 

(estimated from the time-series model) times ANNQ. The different scales of streamflow variability often affect concentration in different ways. The relation between HFVC and HFVQ

can be particularly complicated, changing depending on the 

time-of-year and the degree of serial correlation in the concentration data and cross-correlation between concentration and 

streamflow. 

The TSM residuals for each site and constituent combination were examined graphically to verify the model assumptions that the residuals had constant variance, were serially 

uncorrelated, and were approximately normally distributed. 

Because of the application of the TSM to the large number 

of site and constituent combinations, and practical considerations to keep the trend periods comparable among sites and 

constituents, some minor deviations of the residuals from 

model assumptions were tolerated. Such deviations included 

small changes in residual variance through time and shortterm (about 1 to 2 years) unresolved trending in the residuals. 

In cases where unresolved residual trends were considered to 

be large enough to possibly affect the magnitudes and significance levels of reported fitted trends, more complicated trend 

models were tested and in nearly all cases the more complicated models did not change the general findings and conclusions of this report. Therefore, the reported TSM results were 

judged to provide acceptable fits representative of linearity 

through nearly all of the range in FACs for a given site and 

constituent combination. Standard errors of estimates (SEEs) 

for the TSM analyses are presented in table 2–1. In this report, 
112 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

SEEs are expressed in percent and were converted from log 

units by using procedures described by Tasker (1978). For all 

trace elements, mean SEEs range from 20.9 to 64.5 percent. 

Mean SEEs for unfiltered-recoverable copper and arsenic 

concentrations are 47.0 and 28.8 percent, respectively. Mean 

SEE for suspended-sediment concentration (62.8) is substantially higher than for mean SEEs for trace elements. The 

SEEs indicate reasonably accurate definition of concentration 

and streamflow relations for the purpose of trend analysis. 

However, higher mean SEE for suspended sediment than mean 

SEEs for trace elements indicates lower confidence in results. 

For each site and constituent combination, the fit of the TSM 

can be assessed by examination of the fitted trends in relation 

to the FACs that are shown in figures 4–1 through 4–3, 4–8 

through 4–11, and 4–14 through 4–22. The distribution of the 

FACs about the fitted trend lines shows the extent to which the 

residuals might exhibit nonconstant variance or unresolved 

trends.

Table 2–1. Statistical summaries of standard errors of estimates (SEEs) for the time-series 

model (TSM) analyses1.

[NA, not applicable]

Constituent or property

Number of sites for 

which trend results 

are reported

SEE, percent

Minimum Mean Maximum

Specific conductance 15 6.1 10.5 15.5

Cadmium, filtered 2 54.0 64.5 74.9

Cadmium, unfiltered-recoverable 2 52.1 56.5 61.0

Copper, filtered 11 22.0 32.0 40.2

Copper, unfiltered-recoverable 13 33.9 47.0 63.4

Iron, filtered 7 29.9 44.4 54.0

Iron unfiltered-recoverable 15 30.1 48.5 65.5

Lead, filtered 0 NA NA NA

Lead, unfiltered-recoverable 6 51.9 58.8 65.9

Manganese, filtered 14 29.0 38.9 60.7

Manganese, unfiltered-recoverable 14 33.7 42.8 51.2

Zinc, filtered 2 56.4 62.0 67.6

Zinc, unfiltered-recoverable 11 42.4 52.1 77.1

Arsenic, filtered 13 12.8 20.9 28.2

Arsenic, unfiltered-recoverable 13 18.0 28.8 45.1

Suspended sediment 15 48.6 62.8 73.8

1

The TSM was applied to the following 15 sites (fig. 1, table 1): Blacktail Creek (site 1), Silver Bow Creek 

at Butte (site 2), Silver Bow Creek at Opportunity (site 3), Silver Bow Creek at Warm Springs (site 8), Warm 

Springs Creek at Warm Springs (site 10), Clark Fork near Galen (site 11), Clark Fork at Deer Lodge (site 14), 

Little Blackfoot River (site 15), Clark Fork at Goldcreek (site 16), Flint Creek (site 17), Clark Fork near Drummond (site 18), Rock Creek (site 19), Clark Fork at Turah Bridge (site 20), Blackfoot River (site 21), and Clark 

Fork above Missoula (site 22). For some of the site and constituent combinations, trend results are not reported 

because greater than 6 percent of values were affected by recensoring at study reporting level, as discussed in 

the section of this report “Time-Series Model.” The statistical summaries present the mean and ranges of SEE 

for the TSM analyses for each constituent or property for which trend results are reported.
Appendix 3—Summary of Multiple Linear Regression of Water-Quality Constituents on Time, Streamflow, and Season 113

Appendix 3—Summary of Multiple 

Linear Regression of Water-Quality 

Constituents on Time, Streamflow, and 

Season, as Applied in this Study

Multiple linear regression of water-quality constituents 

on time, streamflow, and season (MLR) was applied in this 

study following guidelines presented in Helsel and Hirsch 

(2002). The basic multiple linear regression model used is 

represented by the equation:

log(Ct

) = b0 + b1 Tt + b2logQt+ b3 sin(2πTt) + 

 b4

 cos(2πTt) + b5 sin(4πTt) + b6 cos(4πTt) + Et (6)

where

log denotes the base-10 logarithm;

Ct is the value of the water-quality constituent 

or property, in indicated units of 

measurement, at time t;

b0 is the intercept;

b1 through b6 are the estimated slope coefficients associated 

with the various explanatory variables;

Tt is decimal time (day of year expressed in 

decimal form; for example, June 30, 2010, 

is expressed as 2010.5) at time t;

Qt is instantaneous streamflow at the time of 

sampling, in cubic feet per second;

sin(2πTt), cos(2πTt), sin(4πTt), and cos(4πTt)

are periodic functions that describe 

seasonal variability; and

Et is an approximately normally distributed 

random error.

The MLR used ordinary least squares if the concentration 

data contained no censored observations. If censored observations were present, the MLR used adjusted maximum-likelihood estimation (Cohn, 1988, 2005) with the same formulation of dependent and explanatory variables.

Use of MLR for trend analysis involves regression of 

constituent concentration [log(Ct

), equation 6] on streamflow 

(Qt

, equation 6), which inherently provides for flow adjustment and quantifies concentration and streamflow relations. 

The residuals from the regression of concentration on streamflow represent flow-adjusted concentrations (FACs; Helsel and 

Hirsch, 2002). Including periodic functions that describe seasonal variability [sin(2πTt

), cos(2πTt), sin(4πTt), and cos(4πTt), 

equation 6] accounts for the effect of repetitive seasonal 

variability on concentration and streamflow relations. The 

residuals from the regression of concentration on streamflow 

and the periodic functions represent changes in concentration 

and streamflow relations through the trend-analysis period. 

Including decimal time (Tt

, equation 6) in the model provides 

quantification of the change in concentration and streamflow 

relations through time and describes the temporal trend in 

FACs for the specified trend-analysis period. The slope coefficient for decimal time (b1

, equation 6) is used to determine the 

significance and magnitude of the trend. The null hypothesis in 

the test for trend significance is that there is no trend (that is, 

b1

 = 0). If the two-tailed p-value for b1 is less than the selected 

alpha level (0.01 in this report), the null hypothesis is rejected 

and the trend is determined to be significant. Determination 

of a nonsignificant trend (that is, a p-value greater than 0.01) 

does not imply that the null hypothesis is accepted (that is, that 

there is no trend). It indicates that within the statistical framework of the analysis, a significant trend was not detected. The 

magnitude of the trend is expressed as the percent difference 

between the geometric mean concentration at the end of the 

period and the geometric mean concentration at the start of the 

period and is determined by the equation:

%∆FAC = 100(10(Nb1) – 1) (7)

where

%∆FAC is the percent change in the geometric mean 

of the flow-adjusted concentration; and

N is the number of years in the trend-analysis 

period.

Application of linear regression for flow-adjusted trend 

analysis assumes that the data are normally distributed and 

that relations between the response variable (a given waterquality constituent) and the combined explanatory variables 

(time, streamflow, and periodic functions that describe seasonal variability) can be represented appropriately by a linear 

fit. Further, the relation between the water-quality constituent 

and streamflow must be statistically significant to accurately 

determine significance level. Data for many water-quality 

constituents typically do not conform to a normal distribution 

because of positive skew (Helsel and Hirsch, 2002). To approximate normality, constituent concentrations and streamflow were transformed to logarithm (base 10) units. 

In accounting for seasonal variability, 2π and 4π sine and 

cosine terms were included in the regression model for all site 

and constituent combinations. During exploratory analysis, 

different multiples of π were added to the model and evaluated 

for significant effect. The 2π and 4π terms frequently, but not 

always, were significant. Inclusion of the periodic functions 

when they were not significant in the regression model for 

some site and constituent combinations probably had small 

effect on the trend analysis results.

Effects of serial correlation on MLR results were evaluated for each site and constituent combination. Significant 

serial correlation was determined if Spearman’s correlation coefficient on the lag-one residuals produced a p-value less than 

0.05 (Helsel and Hirsch, 2002). Significant serial correlation 

was infrequent, but for site and constituent combinations with 

significant serial correlation the significance level of the trend 

results was not reported. It is notable that the simple measure 

of serial correlation used in this report can be affected by 

many factors and also might not completely represent all serial 

correlation effects in a given MLR model. Serial correlation 

does not affect the unbiased estimate of the trend line, but can 
114 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

result in unrepresentatively deflated SEEs and p-values.

The regression model results for each site and constituent combination were evaluated by examining the SEEs, the 

significance of the concentration and streamflow relation, 

influence and leverage statistics, and homoscedasticity and 

normality of residuals. Statistical summaries of SEE for the 

regression models are presented in table 3–1. In this report, 

SEEs are expressed in percent and were converted from log 

units by using procedures described by Tasker (1978). For 

all trace elements, mean SEEs range from 29.7–58.6 percent. 

Mean SEEs for unfiltered-recoverable copper and arsenic concentrations are 41.2 and 29.7 percent, respectively. SEEs for 

trace-element MLR models are similar to SEEs for regressions 

of constituents on streamflow previously used to estimate 

trace-element loads in the Clark Fork Basin (Lambing, 1991; 

Hornberger and others, 1997; Lambing, 1998; Lambing and 

Sando, 2008, 2009; Sando and Lambing, 2011). Mean SEE 

for suspended-sediment concentration (70.9) is substantially 

higher than for mean SEEs for trace elements, but also generally is less than or similar to SEEs for regressions previously 

used to estimate suspended-sediment loads in the Clark Fork 

Basin (Lambing, 1991; Hornberger and others, 1997; Lambing, 1998; Lambing and Sando, 2008, 2009; Sando and Lambing, 2011). The SEEs indicate reasonably accurate definition 

of concentration and streamflow relations for the purpose of 

trend analysis. However, higher mean SEE for suspended sediment than mean SEEs for trace elements indicates lower confidence in results. For a given site and constituent combination, 

the significance level of the trend results was not reported if 

the concentration and streamflow relation was nonsignificant 

(p-value greater than 0.05). No data values were determined 

to have significant high influence for any of the MLR models. 

Because of the application of a consistent regression model 

to the large number of site and constituent combinations, and 

practical considerations to keep the trend periods comparable 

among sites and constituents, some minor deviations of the 

residuals from model assumptions was tolerated. However, 

the reported regression model results were judged to provide 

acceptable fits representative of linearity through nearly all of 

the range in FACs for a given site and constituent combination. For each site and constituent combination, the fit of the 

regression model can be assessed by examination of the fitted 

trends in relation to the FACs that are shown in figures 4–4 

through 4–7, 4–9, and 4–12 through 4–13. For plotting purposes, the FACs were determined by adding the residuals from 

the regression of concentration on streamflow to the geometric 

mean concentration based on data collected during water years 

2001–2010. The distribution of the FACs about the fitted trend 

lines shows the extent to which the regression model results 

were affected by factors such as residual heteroscedasticity 

and curvature.

Table 3–1. Statistical summaries of standard errors of 

estimates (SEEs) for multiple linear regression models of waterquality constituents on time, streamflow, and season (MLR)1

.

Constituent or property SEE, percent

Minimum Mean Maximum

Specific conductance 4.7 9.4 17.5

Cadmium, filtered 21.4 34.9 43.9

Cadmium, unfiltered-recoverable34.0 42.4 50.1

Copper, filtered 23.9 30.5 35.6

Copper, unfiltered-recoverable 27.1 41.2 57.3

Iron, filtered 36.3 50.2 63.9

Iron unfiltered-recoverable 34.0 43.1 64.9

Lead, filtered 43.8 48.2 57.6

Lead, unfiltered-recoverable 42.3 58.6 68.8

Manganese, filtered 19.5 43.1 63.6

Manganese, unfiltered-recoverable35.4 51.8 69.1

Zinc, filtered 24.2 35.9 51.9

Zinc, unfiltered-recoverable 35.9 46.4 61.5

Arsenic, filtered 17.4 30.1 38.4

Arsenic, unfiltered-recoverable 20.3 29.7 36.3

Suspended sediment 48.1 70.9 81.6

1

MLR was applied to the following seven sites (fig. 1, table 1): Mill 

Creek near Anaconda (site 4); Mill Creek at Opportunity (site 5); Willow 

Creek near Anaconda (site 6); Willow Creek at Opportunity (site 7); Warm 

Springs Creek near Anaconda (site 9); Lost Creek near Anaconda (site 12); 

and Lost Creek near Galen (site 13). The statistical summaries present the 

mean and ranges of SEE for the seven regression models for each constituent or property.
Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010. [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than] Constituent or property Number of samples Total percent change for water years 1996–2000 (period 1) Total percent change for water years 2001–05 (period 2) Total percent change for water years 2006–2010 (period 3) p-value for overall trend analysis1 SEASC ANNC SEE 

Blacktail Creek (site 1, fig. 1, table 1) Specific conductance 131 7 (NR3) -1 (NR3) -2 (NR3) 1.000 -0.32 (<0.001) -0.17 (<0.001) 8.7 

Cadmium, filtered 129 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 131 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 130 -11 (NR3) -2 (NR3) -5 (NR3) 0.038 1.43 (<0.001) -0.13 (0.136) 40.2 

Copper, unfiltered-recoverable 131 -17 (0.060) 0 (0.974) -12 (0.327) 0.005 1.31 (<0.001) -0.11 (0.416) 33.9 

Iron, filtered 131 -38 (0.001) 56 (0.004) 27 (0.215) <0.001 1.89 (<0.001) 1.61 (<0.001) 43.4 

Iron unfiltered-recoverable 131 -22 (NR3) -14 (NR3) 48 (NR3) 0.030 1.17 (<0.001) 0.38 (0.007) 37.4 

Lead, filtered 129 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Lead, unfiltered-recoverable 131 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Manganese, filtered 131 1 (NR3) -19 (NR3) 31 (NR3) 0.579 -0.40 (0.006) -0.03 (0.705) 33.3 

Manganese, unfiltered-recoverable 131 -16 (0.007) -17 (0.010) 45 (<0.001) 0.001 -0.42 (0.004) -0.20 (0.010) 34.1 

Zinc, filtered 129 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 131 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Arsenic, filtered 130 -27 (<0.001) 18 (0.003) 7 (0.371) <0.001 0.88 (<0.001) 0.31 (<0.001) 22.0 Arsenic, unfiltered-recoverable 130 -26 (<0.001) 9 (0.246) 7 (0.499) 0.001 0.98 (<0.001) 0.51 (<0.001) 22.3 Suspended sediment 131 7 (0.648) -21 (0.150) -10 (0.599) 0.089 1.09 (<0.001) 0.20 (0.335) 61.8 

Silver Bow Creek at Butte (site 2, fig. 1, table 1)

Specific conductance 139 -5 (NR3) 0 (NR3) -3 (NR3) 0.010 -0.36 (<0.001) -0.19 (<0.001) 9.7 

Cadmium, filtered 138 -69 (<0.001) -66 (<0.001) -68 (<0.001) <0.001 1.07 (0.043) 0.97 (0.009) 74.9 

Cadmium, unfiltered-recoverable 137 -58 (<0.001) -64 (<0.001) -73 (<0.001) <0.001 1.65 (<0.001) 0.47 (0.103) 61.0 

Copper, filtered 139 -79 (<0.001) 6 (0.717) -56 (<0.001) <0.001 1.96 (<0.001) 0.96 (<0.001) 36.5 

Copper, unfiltered-recoverable 139 -76 (<0.001) -29 (<0.001) -55 (<0.001) <0.001 1.71 (<0.001) 0.89 (<0.001) 34.1 

Iron, filtered 139 -68 (<0.001) 67 (<0.001) 73 (0.003) <0.001 1.54 (<0.001) 0.74 (0.005) 46.2 

Iron unfiltered-recoverable 139 -55 (<0.001) -17 (0.080) 28 (0.072) <0.001 2.07 (<0.001) 0.73 (<0.001) 47.6 

Lead, filtered 134 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Lead, unfiltered-recoverable 138 -66 (<0.001) -50 (<0.001) -9 (0.535) <0.001 2.20 (<0.001) 0.73 (0.004) 65.5 
Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEAS , seasonal concentration anomaly coefficient; ANN , annual 

C C ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than] Constituent or property Number of samples Total percent change for water years 1996–2000 (period 1) Total percent change for water years 2001–05 (period 2) Total percent change for water years 2006–2010 (period 3) p-value for overall trend analysis1 SEAS C ANN C SEE 

Silver Bow Creek at Butte (site 2, fig. 1, table 1)—Continued Manganese, filtered Manganese, unfiltered-recoverable Zinc, filtered Zinc, unfiltered-recoverable Arsenic, filtered Arsenic, unfiltered-recoverable Suspended sediment 139 139 139 139 139 139 138 -56 (<0.001) -49 (<0.001) -69 (<0.001) -66 (<0.001) 4 (0.525) -26 (<0.001) -9 (0.530) -7 (0.234) -35 (<0.001) -73 (<0.001) -72 (<0.001) -41 (<0.001) -44 (<0.001) -46 (<0.001) -75 (<0.001) -54 (<0.001) -59 (<0.001) -57 (<0.001) 7 (0.420) 8 (0.381) -2 (0.939) <0.001 0.003 <0.001 <0.001 <0.001 <0.001 <0.001 1.32 (<0.001) 1.24 (<0.001) 1.16 (0.004) 1.40 (<0.001) 0.21 (0.150) 0.73 (<0.001) 1.19 (0.001) 0.00 (0.988) 0.07 (0.576) 0.42 (0.134) 0.13 (0.580) -0.28 (0.021) -0.19 (0.136) 0.00 (0.990) 39.1 42.3 56.4 49.7 19.9 25.9 68.5 

Silver Bow Creek at Opportunity (site 3, fig. 1, table 1) Specific conductance Cadmium, filtered Cadmium, unfiltered-recoverable Copper, filtered Copper, unfiltered-recoverable Iron, filtered Iron unfiltered-recoverable Lead, filtered Lead, unfiltered-recoverable Manganese, filtered Manganese, unfiltered-recoverable Zinc, filtered Zinc, unfiltered-recoverable Arsenic, filtered Arsenic, unfiltered-recoverable Suspended sediment 141 139 138 139 141 139 140 137 141 141 141 140 141 141 141 122 9 (<0.001) -25 (0.018) -6 (0.581) -11 (0.197) -8 (0.197) -4 (NR3) -4 (NR3) NR4 35 (0.080) -20 (<0.001) -10 (0.276) -25 (0.038) -13 (0.250) 19 (0.005) 7 (0.121) -26 (NR3) 1 (0.187) -36 (<0.001) -28 (<0.001) -33 (<0.001) -23 (<0.001) -8 (NR3) 6 (NR3) NR4 2 (0.877) -36 (<0.001) -36 (<0.001) -39 (<0.001) -42 (<0.001) 14 (0.005) 6 (0.036) 20 (NR3) -7 (0.008) -45 (<0.001) -60 (<0.001) -40 (<0.001) -53 (<0.001) 19 (NR3) -22 (NR3) NR4 -65 (<0.001) -49 (<0.001) -45 (<0.001) -60 (<0.001) -52 (<0.001) -40 (<0.001) -51 (<0.001) -10 (NR3) <0.001 <0.001 <0.001 <0.001 <0.001 0.267 0.885 NR4 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.671 -0.31 (<0.001) 0.44 (0.017) 0.51 (<0.001) 0.47 (<0.001) 0.35 (<0.001) 0.88 (<0.001) 0.71 (<0.001) NR4 0.86 (<0.001) 0.01 (0.916) 0.14 (0.303) 0.32 (0.139) 0.46 (0.006) -0.17 (0.016) 0.02 (0.730) 0.62 (0.004) -0.25 (<0.001) 0.36 (0.016) 0.38 (0.001) 0.22 (0.034) 0.40 (<0.001) 0.86 (<0.001) 0.73 (<0.001) NR4 0.81 (<0.001) -0.19 (0.051) 0.00 (0.977) 0.17 (0.357) 0.23 (0.110) -0.16 (0.014) 0.15 (0.008) 0.76 (0.001) 7.8 54.0 52.1 34.6 63.4 54.0 58.7 NR4 65.9 55.2 48.4 67.6 54.3 28.2 45.1 54.3 
Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEAS , seasonal concentration anomaly coefficient; ANN , annual 

C C

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent 

change for 

water years 

1996–2000 

(period 1)

Total percent 

change for 

water years 

2001–05 

(period 2)

Total percent 

change for 

water years 

2006–2010 

(period 3)

p-value 

for overall 

trend 

analysis1

SEAS C ANN C SEE

Silver Bow Creek at Warm Springs (site 8, fig. 1, table 1)

Specific conductanceCadmium, filteredCadmium, unfiltered-recoverableCopper, filtered

Copper, unfiltered-recoverable

Iron, filtered

Iron unfiltered-recoverable

Lead, filtered

Lead, unfiltered-recoverableManganese, filteredManganese, unfiltered-recoverable

Zinc, filtered

Zinc, unfiltered-recoverableArsenic, filtered

Arsenic, unfiltered-recoverableSuspended sediment

146146146146

146

146

146

145

146146146

146

139146

146148

0 (0.918)

NR4

NR4

-54 (<0.001)

-51 (<0.001)

NR4

-27 (0.009)

NR4

NR4

-8 (NR3)

-16 (NR3)

NR4

-64 (<0.001)

11 (NR3)

12 (NR3)

9 (0.679)

-4 (0.063)

NR4

NR4

-12 (0.201)

-9 (0.328)

NR4

-10 (0.336)

NR4

NR4

10 (NR3)

2 (NR3)

NR4

-47 (<0.001)

0 (NR3)

-3 (NR3)

-30 (0.026)

5 (0.114)

NR4

NR4

-5 (0.683)

-13 (0.234)

NR4

-18 (0.147)

NR4NR4

-38 (NR3)

-35 (NR3)

NR4

1 (0.963)

4 (NR3)

7 (NR3)

-55 (<0.001)

0.002

NR4

NR4

<0.001

<0.001

NR4

<0.001

NR4

NR4

1.0000.039

NR4

<0.001

0.5620.630

<0.001

-0.24 (<0.001)

NR4

NR4

0.31 (0.020)

0.49 (<0.001)

NR4

0.46 (0.002)

NR4NR4

0.38 (0.099)

-0.01 (0.955)

NR4

0.42 (0.008)

0.26 (0.001)

0.28 (<0.001)

0.29 (0.147)

-0.28 (<0.001)

NR4

NR4

0.24 (0.034)

0.27 (0.014)

NR4

0.03 (0.780)

NR4

NR4

0.10 (0.647)

-0.17 (0.322)

NR4

0.17 (0.180)

0.00 (0.996)0.01 (0.930)

0.16 (0.403)

10.4

NR4

NR4

31.9

38.1

NR4

39.7

NR4

NR4

60.7

43.0

NR4

43.5

25.926.3

64.7

Warm Springs Creek at Warm Springs (site 10, fig. 1, table 1)

Specific conductance

Cadmium, filtered

Cadmium, unfiltered-recoverableCopper, filteredCopper, unfiltered-recoverableIron, filteredIron unfiltered-recoverable

Lead, filtered

Lead, unfiltered-recoverable

108

108

108107108108108

108

108

-12 (<0.001)

NR4

NR4

-2 (0.837)

-26 (<0.001)

NR4

-32 (NR3)

NR4

NR4

0 (0.853)

NR4

NR4

-6 (0.451)

5 (0.589)

NR4

11 (NR3)

NR4

NR4

-7 (0.040)

NR4

NR4

-34 (<0.001)

27 (0.070)

NR4

58 (NR3)

NR4

NR4

<0.001

NR4

NR4

<0.001

<0.001

NR4

0.044

NR4

NR4

-0.26 (<0.001)

NR4

NR4

-0.15 (0.029)

0.08 (0.336)

NR4

0.34 (<0.001)

NR4

NR4

-0.17 (<0.001)

NR4

NR4

-0.03 (0.576)

0.15 (<0.001)

NR4

0.30 (0.010)

NR4

NR4

15.5

NR4

NR4

32.360.9

NR4

60.8

NR4

NR4
Manganese, filtered 108 -40 (<0.001) 21 (0.150) -52 (<0.001) <0.001 -0.30 (0.047) -0.23 (0.010) 44.8 

Manganese, unfiltered-recoverable 108 -37 (NR3) 24 (NR3) -34 (NR3) 0.081 -0.33 (0.010) -0.29 (0.001) 46.9 

Zinc, filtered 108 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 108 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Arsenic, filtered 108 13 (<0.001) -1 (0.685) -24 (<0.001) <0.001 -0.13 (<0.001) -0.24 (<0.001) 24.4 Arsenic, unfiltered-recoverable 108 -10 (NR3) 5 (NR3) -12 (NR3) 0.353 -0.09 (0.171) -0.17 (<0.001) 35.8 

Suspended sediment 109 -46 (0.004) -33 (0.051) 144 (<0.001) <0.001 -0.19 (0.226) 0.26 (0.072) 68.3 

Clark Fork near Galen (site 11, fig. 1, table 1) Specific conductance 147 -2 (NR3) -2 (NR3) -2 (NR3) 0.016 -0.23 (<0.001) -0.27 (<0.001) 11.8 

Cadmium, filtered 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 147 -49 (<0.001) -6 (0.409) -12 (0.194) <0.001 -0.17 (0.015) -0.19 (0.026) 27.1 

Copper, unfiltered-recoverable 147 -38 (<0.001) 9 (0.409) -10 (0.437) <0.001 0.12 (0.211) 0.13 (0.226) 46.5 

Iron, filtered 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Iron unfiltered-recoverable 147 -36 (<0.001) 17 (0.194) 0 (0.986) 0.023 0.45 (<0.001) 0.32 (0.003) 44.9 Lead, filtered 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Lead, unfiltered-recoverable 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Manganese, filtered 147 -16 (0.114) 20 (0.114) -42 (<0.001) <0.001 -0.07 (0.575) -0.09 (0.391) 34.3 

Manganese, unfiltered-recoverable 147 -23 (0.007) 7 (0.491) -29 (0.011) <0.001 0.09 (0.468) -0.24 (0.008) 33.7 

Zinc, filtered 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 140 -59 (<0.001) -32 (<0.001) 9 (0.576) <0.001 0.32 (0.029) 0.23 (0.043) 42.4 

Arsenic, filtered 147 -4 (0.667) 9 (0.276) -17 (0.078) 1.000 -0.13 (0.091) 0.17 (0.032) 25.6 

Arsenic, unfiltered-recoverable 147 -10 (0.187) 14 (0.009) -25 (<0.001) <0.001 -0.07 (0.180) 0.10 (0.174) 26.4 

Suspended sediment 148 -3 (0.859) -18 (0.208) 1 (0.966) 1.000 0.53 (0.002) 0.55 (<0.001) 57.5 

Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than] Constituent or property Number of samples Total percent change for water years 1996–2000 (period 1) Total percent change for water years 2001–05 (period 2) Total percent change for water years 2006–2010 (period 3) p-value for overall trend analysis1 SEASC ANNC SEE 

Warm Springs Creek at Warm Springs (site 10, fig. 1, table 1)—Continued
Clark Fork at Deer Lodge (site 14, fig. 1, table 1)

Specific conductance 146 -2 (0.355) -1 (0.394) -7 (0.002) <0.001 -0.04 (0.001) -0.20 (<0.001) 11.2 

Cadmium, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 146 -18 (0.002) 3 (0.691) -17 (0.030) 0.002 0.18 (<0.001) 0.16 (0.023) 22.0 Copper, unfiltered-recoverable 145 -14 (NR3) -2 (NR3) 2 (NR3) 0.753 0.23 (0.034) 0.28 (0.030) 45.0 

Iron, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Iron unfiltered-recoverable 146 -25 (NR3) 9 (NR3) 18 (NR3) 0.059 0.30 (0.042) 0.43 (0.002) 51.8 

Lead, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Lead, unfiltered-recoverable 143 -3 (NR3) -11 (NR3) 33 (NR3) 0.666 0.26 (0.101) 0.35 (0.039) 59.5 

Manganese, filtered 146 -15 (NR3) 45 (NR3) -31 (NR3) 0.013 -0.08 (0.464) -0.08 (0.443) 42.8 

Manganese, unfiltered-recoverable 146 -29 (NR3) 13 (NR3) -7 (NR3) 0.090 -0.16 (0.258) -0.09 (0.465) 46.9 Zinc, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 142 -36 (<0.001) -8 (0.490) -5 (0.775) <0.001 0.27 (0.054) 0.25 (0.049) 46.6 

Arsenic, filtered 146 -2 (0.575) 19 (<0.001) -14 (0.001) 0.004 0.17 (<0.001) 0.21 (<0.001) 14.7 

Arsenic, unfiltered-recoverable 146 -3 (NR3) 5 (NR3) -7 (NR3) 0.554 0.24 (<0.001) 0.24 (<0.001) 26.5 

Suspended sediment 147 -15 (0.144) -11 (0.380) 3 (0.870) <0.001 -0.11 (0.565) 0.31 (0.033) 64.4 

Little Blackfoot River (site 15, fig. 1, table 1)

Specific conductance 65 3 (NR3) 1 (NR3) NR5 0.357 -0.10 (<0.001) -0.06 (<0.001) 10.7 

Cadmium, filtered 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Copper, filtered 63 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Copper, unfiltered-recoverable 65 -15 (NR3) 11 (NR3) NR5 0.705 -0.29 (0.144) -0.09 (0.643) 47.4 

Iron, filtered 60 18 (NR3) -49 (NR3) NR5 0.019 0.30 (<0.001) 0.50 (<0.001) 51.9 

Iron unfiltered-recoverable 65 -48 (<0.001) 33 (0.027) NR5 <0.001 0.36 (<0.001) -0.33 (0.019) 51.4 

Lead, filtered 65 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Lead, unfiltered-recoverable 65 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent 

change for 

water years 

1996–2000 

(period 1)

Total percent 

change for 

water years 

2001–05 

(period 2)

Total percent 

change for 

water years 

2006–2010 

(period 3)

p-value 

for overall 

trend 

analysis1

SEASC ANNC SEE
Manganese, filtered 65 -12 (NR3) -13 (NR3) NR5 1.000 -0.55 (<0.001) -0.10 (0.406) 35.4 

Manganese, unfiltered-recoverable 62 -39 (0.003) 32 (0.201) NR5 0.002 0.03 (0.860) -0.30 (0.136) 44.5 

Zinc, filtered 65 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 65 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Arsenic, filtered 65 -4 (NR3) 12 (NR3) NR5 0.077 0.00 (0.976) 0.03 (0.501) 12.8 

Arsenic, unfiltered-recoverable 65 -23 (<0.001) -5 (0.051) NR5 <0.001 0.15 (<0.001) -0.21 (<0.001) 18.0 Suspended sediment 66 -26 (NR3) -25 (NR3) NR5 0.146 0.03 (0.865) 0.24 (0.267) 67.9 

Clark Fork at Goldcreek (site 16, fig. 1, table 1) Specific conductance 146 0 (NR3) -2 (NR3) -5 (NR3) 0.197 -0.09 (<0.001) -0.14 (<0.001) 10.0 

Cadmium, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 145 -21 (NR3) 12 (NR3) -6 (NR3) 0.019 0.01 (0.856) 0.35 (<0.001) 23.8 

Copper, unfiltered-recoverable 145 -14 (0.168) -18 (0.047) 3 (0.796) 0.005 0.37 (<0.001) 0.62 (<0.001) 43.1 Iron, filtered 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Iron unfiltered-recoverable 146 -16 (0.121) -28 (0.005) 45 (0.028) <0.001 0.49 (0.001) 0.68 (<0.001) 49.3 Lead, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Lead, unfiltered-recoverable 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Manganese, filtered 146 -6 (NR3) -8 (NR3) 3 (NR3) 0.341 0.05 (0.648) -0.02 (0.833) 32.3 

Manganese, unfiltered-recoverable 146 -18 (0.017) -20 (0.016) 22 (0.139) <0.001 0.06 (0.631) 0.13 (0.208) 38.8 

Zinc, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 144 -33 (<0.001) -34 (<0.001) 36 (0.046) <0.001 0.34 (0.010) 0.46 (<0.001) 42.7 Arsenic, filtered 146 -9 (NR3) 10 (NR3) -2 (NR3) 0.811 -0.06 (0.089) 0.15 (0.001) 15.7 

Arsenic, unfiltered-recoverable 146 -13 (0.003) 6 (0.056) 5 (0.162) 0.003 0.06 (0.066) 0.23 (<0.001) 23.1 

Suspended sediment 147 18 (0.263) -53 (<0.001) 69 (0.011) <0.001 0.48 (0.006) 0.50 (0.003) 58.9 

Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than] Constituent or property Number of samples Total percent change for water years 1996–2000 (period 1) Total percent change for water years 2001–05 (period 2) Total percent change for water years 2006–2010 (period 3) p-value for overall trend analysis1 SEASC ANNC SEE 

Little Blackfoot River (site 15, fig. 1, table 1)—Continued
Flint Creek (site 17, fig. 1, table 1)

Specific conductance 89 7 (NR3) 10 (NR3) NR5 0.024 -0.12 (<0.001) -0.12 (<0.001) 15.2 

Cadmium, filtered 85 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 85 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Copper, filtered 88 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Copper, unfiltered-recoverable 89 -21 (NR3) -16 (NR3) NR5 0.055 0.32 (<0.001) 0.23 (0.011) 37.9 

Iron, filtered 84 -2 (NR3) 0 (NR3) NR5 1.000 0.37 (<0.001) 0.35 (<0.001) 47.8 

Iron unfiltered-recoverable 89 -41 (NR3) 38 (NR3) NR5 1.000 0.65 (<0.001) 0.36 (<0.001) 37.0 Lead, filtered 85 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Lead, unfiltered-recoverable 84 -31 (0.002) -9 (0.481) NR5 <0.001 0.88 (<0.001) 0.52 (<0.001) 52.6 

Manganese, filtered 89 -4 (NR3) 32 (NR3) NR5 0.072 0.00 (0.974) -0.45 (<0.001) 33.0 

Manganese, unfiltered-recoverable 89 -23 (0.003) 0 (0.977) NR5 0.003 0.09 (0.095) -0.14 (0.002) 39.6 

Zinc, filtered 85 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 81 -33 (0.017) -38 (0.047) NR5 <0.001 0.60 (<0.001) 0.30 (0.016) 44.7 

Arsenic, filtered 89 -7 (NR3) -4 (NR3) NR5 0.106 -0.08 (0.009) -0.15 (<0.001) 20.1 

Arsenic, unfiltered-recoverable 89 -19 (0.005) -3 (0.687) NR5 0.040 0.12 (0.017) -0.05 (0.327) 29.6 

Suspended sediment 90 -9 (NR3) -43 (NR3) NR5 1.000 0.62 (<0.001) 0.43 (0.002) 59.7 

Clark Fork near Drummond (site 18, fig. 1, table 1)

Specific conductance 146 -3 (0.103) -3 (0.026) -3 (0.084) 0.009 -0.19 (<0.001) -0.22 (<0.001) 9.5 Cadmium, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 143 2 (0.547) 15 (<0.001) -23 (<0.001) 0.002 0.15 (0.029) 0.68 (<0.001) 36.2 

Copper, unfiltered-recoverable 144 -23 (0.014) -15 (0.107) 5 (0.755) <0.001 0.68 (<0.001) 0.47 (<0.001) 52.9 

Iron, filtered 143 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Iron unfiltered-recoverable 145 -61 (<0.001) 7 (0.194) 44 (0.013) <0.001 0.95 (<0.001) 0.33 (<0.001) 65.5 Lead, filtered 146 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Lead, unfiltered-recoverable 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent 

change for 

water years 

1996–2000 

(period 1)

Total percent 

change for 

water years 

2001–05 

(period 2)

Total percent 

change for 

water years 

2006–2010 

(period 3)

p-value 

for overall 

trend 

analysis1

SEASC ANNC SEE
Manganese, filtered 145 -8 (NR3) 1 (NR3) -3 (NR3) 0.736 0.38 (<0.001) 0.15 (0.162) 34.6 

Manganese, unfiltered-recoverable 146 -35 (<0.001) 1 (0.901) 17 (0.353) 0.005 0.54 (<0.001) 0.32 (0.038) 46.6 

Zinc, filtered 145 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 143 -55 (<0.001) -16 (<0.001) 10 (0.448) <0.001 0.78 (<0.001) 0.30 (<0.001) 56.2 Arsenic, filtered 146 -8 (NR3) 8 (NR3) -10 (NR3) 0.030 0.11 (<0.001) 0.06 (0.153) 15.8 

Arsenic, unfiltered-recoverable 146 -15 (NR3) 1 (NR3) 1 (NR3) 0.163 0.21 (<0.001) 0.10 (0.121) 24.7 

Suspended sediment 147 -39 (<0.001) -11 (0.084) 8 (0.686) <0.001 0.40 (0.009) 0.52 (<0.001) 65.0 

Rock Creek (site 19, fig. 1, table 1) Specific conductance 65 2 (NR3) -8 (NR3) NR5 1.000 -0.27 (<0.001) -0.23 (<0.001) 9.7 

Cadmium, filtered 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 63 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Copper, filtered 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Copper, unfiltered-recoverable 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Iron, filtered 64 -15 (NR3) -29 (NR3) NR5 0.013 0.77 (0.001) 0.69 (<0.001) 29.9 

Iron unfiltered-recoverable 64 -26 (<0.001) -27 (0.044) NR5 <0.001 1.20 (<0.001) 0.60 (<0.001) 30.1 

Lead, filtered 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 

Lead, unfiltered-recoverable 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Manganese, filtered 63 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Manganese, unfiltered-recoverable 63 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Zinc, filtered 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Zinc, unfiltered-recoverable 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Arsenic, filtered 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Arsenic, unfiltered-recoverable 64 NR4 NR4 NR5 NR4 NR4 NR4 NR4 Suspended sediment 66 52 (<0.001) -56 (<0.001) NR5 <0.001 3.04 (<0.001) 0.86 (<0.001) 54.5 

Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than] Constituent or property Number of samples Total percent change for water years 1996–2000 (period 1) Total percent change for water years 2001–05 (period 2) Total percent change for water years 2006–2010 (period 3) p-value for overall trend analysis1 SEASC ANNC SEE 

Clark Fork near Drummond (site 18, fig. 1, table 1)—Continued
Clark Fork at Turah Bridge (site 20, fig. 1, table 1)

Specific conductance 193 -5 (NR3) -1 (NR3) 0 (NR3) 0.016 -0.12 (<0.001) -0.20 (<0.001) 12.8 

Cadmium, filtered 170 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 170 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 169 -20 (NR3) 8 (NR3) -12 (NR3) 0.012 0.57 (<0.001) 0.51 (<0.001) 30.0 Copper, unfiltered-recoverable 168 -6 (NR3) -16 (NR3) 27 (NR3) 0.110 0.65 (<0.001) 0.58 (<0.001) 47.2 

Iron, filtered 150 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Iron unfiltered-recoverable 170 -28 (<0.001) -15 (0.222) 58 (0.082) <0.001 0.84 (<0.001) 0.44 (<0.001) 57.1 Lead, filtered 170 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Lead, unfiltered-recoverable 170 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Manganese, filtered 170 1 (NR3) -10 (NR3) 18 (NR3) 1.000 0.41 (<0.001) 0.27 (<0.001) 29.0 

Manganese, unfiltered-recoverable 170 -20 (0.131) -16 (0.147) 45 (0.025) <0.001 0.67 (<0.001) 0.19 (0.035) 51.2 Zinc, filtered 170 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Zinc, unfiltered-recoverable 161 -33 (0.317) -39 (0.001) 82 (0.007) <0.001 0.49 (0.001) -0.10 (0.483) 56.3 

Arsenic, filtered 170 -4 (NR3) 7 (NR3) 2 (NR3) 0.022 0.23 (<0.001) 0.28 (<0.001) 19.7 

Arsenic, unfiltered-recoverable 170 -7 (NR3) -6 (NR3) 21(NR3) 0.173 0.35 (<0.001) 0.21 (<0.001) 31.2 

Suspended sediment 209 -7 (0.895) -32 (0.197) 60 (0.531) 0.002 0.65 (<0.001) 0.18 (<0.001) 58.1 

Blackfoot River (site 21, fig. 1, table 1)

Specific conductance 102 0 (0.796) -4 (<0.001) 6 (<0.001) <0.001 -0.14 (<0.001) -0.05 (0.009) 6.1 

Cadmium, filtered 101 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfiltered-recoverable 100 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 102 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, unfiltered-recoverable 102 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Iron, filtered 102 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Iron unfiltered-recoverable 102 -37 (<0.001) 29 (0.032) -28 (0.021) <0.001 1.13 (<0.001) 0.95 (<0.001) 43.6 Lead, filtered 101 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Lead, unfiltered-recoverable 102 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent 

change for 

water years 

1996–2000 

(period 1)

Total percent 

change for 

water years 

2001–05 

(period 2)

Total percent 

change for 

water years 

2006–2010 

(period 3)

p-value 

for overall 

trend 

analysis1

SEASC ANNC SEE
Manganese, filtered 99 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Manganese, unfiltered-recoverable 100 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Zinc, filtered 101 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Zinc, unfiltered-recoverable 102 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Arsenic, filtered 101 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Arsenic, unfiltered-recoverable 101 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Suspended sediment 103 -12 (NR3) 4 (NR3) -24 (NR3) 0.403 1.21 (<0.001) 1.31 (<0.001) 48.6 

1Determination of and distinction between p-value for individual trend period and p-value for overall trend analysis are discussed in “Supplement 2: Summary of the Time-S

in this Study.” 2Procedures for determining and applying the study reporting level used in the application of the time-series model are discussed in the section of this report “Time-Series M

3Results not reported because of nonsignificant overall trend analysis (p-value greater than 0.01). 4Results not reported because greater than 6 percent of values were affected by recensoring at study reporting level, as discussed in the section of this report “Time-Series Mo5Results not reported because of no or insufficient data for application of the TSM during indicated trend-analysis period. Table 4–1. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for 

the upper Clark Fork Basin, Montana, water years 1996–2010.—Continued [Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than] Constituent or property Number of samples Total percent change for water years 1996–2000 (period 1) Total percent change for water years 2001–05 (period 2) Total percent change for water years 2006–2010 (period 3) p-value for overall trend analysis1 SEASC ANNC SEE 

Blackfoot River (site 21, fig. 1, table 1)—Continued
Table 4–2. Flow-adjusted trend results determined by using the time-series model (TSM) for selected water-quality constituents and properties for (site 22, fig. 1, table 1), water years 1996–2010.[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate p-values for associated Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEASC, seasonal concentration anomaly coefficient; ANNC, annual 

ficient; SEE, standard error of estimate in percent; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent 

change for 

water years 

1996–2000 

(period 1)

Total percent 

change for 

water years 

2001–05 

(period 2)

Total percent 

change for 

October 1, 

2005–March 27, 

2008 (period 3A)

Total percent 

change for 

March 28, 2008–

September 30, 

2010 (period 3B)

p-value 

for overall 

trend 

analysis1

SEASC ANNC S

Clark Fork above Missoula (site 22, fig. 1, table 1)

Specific conductance 186 0 (NR3) -2 (NR3) 0 (NR3) 5 (NR3) 0.031 -0.18 (<0.001) -0.19 (<0.001) 

Cadmium, filtered 166 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Cadmium, unfilteredrecoverable 167 NR4 NR4 NR4 NR4 NR4 NR4 NR4 Copper, filtered 166 -21 (NR3) 21 (NR3) 7 (NR3) 11 (NR3) 0.027 0.53 (<0.001) 0.37 (0.007) 3

Copper, unfilteredrecoverable 165 -18 (0.026) 52 (<0.001) 104 (<0.001) -59 (0.002) <0.001 0.55 (<0.001) 0.62 (<0.001) 6

Iron, filtered 167 NR4 NR4 NR4 NR4 NR4 NR4 NR4 

Iron unfiltered-recoverable 167 -30 (<0.001) 61 (<0.001) 79 (<0.001) -58 (0.001) <0.001 0.77 (<0.001) 0.76 (<0.001) 

Lead, filtered 160 NR4 NR4 NR4 NR4 NR4 NR4 NR4 N

Lead, unfiltered-recoverable 162 NR4 NR4 NR4 NR4 NR4 NR4 NR4 NManganese, filtered 167 -8 (0.312) 1 (0.938) 2 (0.854) -44 (0.001) <0.001 -0.17 (0.303) 0.01 (0.930) 3

Manganese, unfilteredrecoverable 167 -20 (0.023) 17 (0.242) 71 (<0.001) -45 (0.005) <0.001 0.13 (0.461) 0.17 (0.267) 4

Zinc, filtered 166 NR4 NR4 NR4 NR4 NR4 NR4 NR4 N

Zinc, unfiltered-recoverable 150 NR4 NR4 NR4 NR4 NR4 NR4 NR4 NArsenic, filtered 167 -2 (0.636) 12 (0.078) 7 (0.365) 12 (0.276) 0.005 0.19 (0.015) -0.02 (0.765) 2

Arsenic, unfilteredrecoverable 167 -6 (0.410) 14 (0.184) 24 (0.070) -2 (0.921) 0.008 0.49 (<0.001) 0.08 (0.540) 3

Suspended sediment 209 -15 (0.211) 32 (0.150) 147 (<0.001) -60 (0.004) <0.001 1.28 (<0.001) 0.72 (<0.001) 7

1Determination of and distinction between p-value for individual trend period and p-value for overall trend analysis are discussed in “Supplement 2: Summary of the Time-S

in this Study.”

2Procedures for determining and applying the study reporting level used in the application of the time-series model are discussed in the section of this report “Time-Series M3Results not reported because of nonsignificant overall trend analysis (p-value greater than 0.01).4Results not reported because greater than 6 percent of values were affected by recensoring at study reporting level, as discussed in the section of this report “Time-Series M
126 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 4–3. Flow-adjusted trend results determined by using multiple linear regression on time, streamflow, and season (MLR) 

for selected water-quality constituents and properties for selected sampling sites in the upper Clark Fork Basin, Montana, water 

years 2006–2010.

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate 

95-percent confidence intervals. Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEE, standard 

error of estimate; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent change 

for water years 

2006–2010 (period 5)

Percent 

censored 

values

p-value for 

streamflow 

coefficient

SEE p-value for 

regression

Mill Creek near Anaconda (site 4, fig. 1, table 1)

Specific conductance 48 7 (0.031) 0 <0.001 7.0 <0.001

Cadmium, filtered 47 0 (NR1

) 4 0.989 41.7 0.081

Cadmium, unfiltered-recoverable48 -11 (0.433) 0 0.024 35.6 <0.001

Copper, filtered 48 -15 (0.253) 0 <0.001 33.8 <0.001

Copper, unfiltered-recoverable 48 -21 (0.091) 2 0.003 32.6 <0.001

Iron, filtered 48 -33 (NR1

) 0 0.507 34.9 <0.001

Iron unfiltered-recoverable 48 -25 (0.055) 0 0.022 36.3 <0.001

Lead, filtered 48 -36 (NR1

) 6 0.280 57.6 <0.001

Lead, unfiltered-recoverable 48 -29 (0.046) 0 0.010 19.5 <0.001

Manganese, filtered 48 -4 (NR1

) 0 0.210 19.5 <0.001

Manganese, unfiltered-recoverable48 -15 (NR1

) 0 0.260 35.4 <0.001

Zinc, filtered 48 16 (0.258) 10 <0.001 29.6 <0.001

Zinc, unfiltered-recoverable 48 0 (0.982) 0 <0.001 35.9 <0.001

Arsenic, filtered 48 -9 (NR1

) 0 0.758 38.4 0.002

Arsenic, unfiltered-recoverable 48 -13 (NR1

) 0 0.960 34.7 <0.001

Suspended sediment 48 -20 (0.252) 0 <0.001 48.1 <0.001

Mill Creek at Opportunity (site 5, fig. 1, table 1)

Specific conductance 64 11 (0.010) 0 <0.001 10.4 <0.001

Cadmium, filtered 64 -21 (NR1

) 0 0.343 27.5 <0.001

Cadmium, unfiltered-recoverable64 -33 (0.007) 0 <0.001 41.1 <0.001

Copper, filtered 64 -36 (<0.001) 0 <0.001 26.2 <0.001

Copper, unfiltered-recoverable 64 -35 (0.003) 0 <0.001 38.0 <0.001

Iron, filtered 64 -27 (NR1

) 0 0.733 34.0 <0.001

Iron unfiltered-recoverable 64 -26 (0.116) 0 <0.001 54.0 <0.001

Lead, filtered 64 -40 (0.003) 9 <0.001 47.0 <0.001

Lead, unfiltered-recoverable 64 -23 (0.214) 0 <0.001 47.9 <0.001

Manganese, filtered 64 -32 (0.027) 0 <0.001 47.9 <0.001

Manganese, unfiltered-recoverable64 -23 (NR1

) 0 0.222 69.1 <0.001

Zinc, filtered 63 -42 (NR1

) 2 0.534 24.2 <0.001

Zinc, unfiltered-recoverable 64 -33 (0.013) 0 <0.001 45.4 <0.001

Arsenic, filtered 64 -33 (NR1

) 0 0.071 33.0 <0.001

Arsenic, unfiltered-recoverable 64 -34 (<0.001) 0 0.009 30.7 <0.001

Suspended sediment 64 -15 (0.504) 0 <0.001 72.4 <0.001
Appendix 4—Trend Analysis Results 127

Table 4–3. Flow-adjusted trend results determined by using multiple linear regression on time, streamflow, and season (MLR) 

for selected water-quality constituents and properties for selected sampling sites in the upper Clark Fork Basin, Montana, water 

years 2006–2010.—Continued

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate 

95-percent confidence intervals. Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEE, standard 

error of estimate; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent change 

for water years 

2006–2010 (period 5)

Percent 

censored 

values

p-value for 

streamflow 

coefficient

SEE p-value for 

regression

Willow Creek near Anaconda (site 6, fig. 1, table 1)

Specific conductance 44 24 (<0.001) 0 <0.001 8.5 <0.001

Cadmium, filtered 42 -14 (0.314) 12 0.040 33.1 0.005

Cadmium, unfiltered-recoverable44 -33 (0.054) 7 0.001 47.9 <0.001

Copper, filtered 44 -23 (0.016) 0 <0.001 23.9 <0.001

Copper, unfiltered-recoverable 44 -32 (0.064) 2 0.009 48.3 <0.001

Iron, filtered 44 -16 (0.388) 0 0.017 47.0 <0.001

Iron unfiltered-recoverable 44 -29 (0.096) 0 <0.001 49.0 <0.001

Lead, filtered 44 -38 (0.014) 0 <0.001 44.2 <0.001

Lead, unfiltered-recoverable 44 -44 (0.022) 0 <0.001 30.2 <0.001

Manganese, filtered 44 -24 (NR1

) 0 0.086 30.2 <0.001

Manganese, unfiltered-recoverable44 -26 (NR1

) 0 0.114 39.8 0.006

Zinc, filtered 44 -26 (0.055) 9 0.003 34.6 <0.001

Zinc, unfiltered-recoverable 44 -18 (0.317) 9 <0.001 44.7 <0.001

Arsenic, filtered 44 -16 (0.038) 0 0.042 18.3 <0.001

Arsenic, unfiltered-recoverable 44 -18 (0.026) 0 0.020 20.3 <0.001

Suspended sediment 44 -54 (0.015) 0 <0.001 80.8 <0.001

Willow Creek at Opportunity (site 7, fig. 1, table 1)

Specific conductance 64 -13 (0.027) 0 0.020 17.5 <0.001

Cadmium, filtered 64 -25 (0.064) 8 <0.001 43.9 <0.001

Cadmium, unfiltered-recoverable64 7 (0.611) 2 <0.001 39.7 <0.001

Copper, filtered 64 -26 (0.008) 0 <0.001 31.8 <0.001

Copper, unfiltered-recoverable 64 -15 (0.199) 0 <0.001 35.4 <0.001

Iron, filtered 64 54 (0.008) 0 <0.001 46.6 <0.001

Iron unfiltered-recoverable 64 61 (0.004) 0 <0.001 47.3 <0.001

Lead, filtered 64 32 (0.066) 2 <0.001 43.8 <0.001

Lead, unfiltered-recoverable 64 19 (0.358) 0 <0.001 57.4 <0.001

Manganese, filtered 64 41 (NR1

) 0 0.886 57.4 <0.001

Manganese, unfiltered-recoverable

64 70 (NR1

) 0 0.239 54.1 <0.001

Zinc, filtered 64 -21 (0.142) 5 <0.001 47.3 <0.001

Zinc, unfiltered-recoverable 64 6 (0.734) 0 <0.001 50.0 <0.001

Arsenic, filtered 64 -23 (0.041) 0 <0.001 37.1 <0.001

Arsenic, unfiltered-recoverable 64 -19 (0.090) 0 <0.001 36.3 <0.001

Suspended sediment 64 10 (0.657) 0 <0.001 66.4 <0.001
128 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 4–3. Flow-adjusted trend results determined by using multiple linear regression on time, streamflow, and season (MLR) 

for selected water-quality constituents and properties for selected sampling sites in the upper Clark Fork Basin, Montana, water 

years 2006–2010.—Continued

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate 

95-percent confidence intervals. Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEE, standard 

error of estimate; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent change 

for water years 

2006–2010 (period 5)

Percent 

censored 

values

p-value for 

streamflow 

coefficient

SEE p-value for 

regression

Warm Springs Creek near Anaconda (site 9, fig. 1, table 1)

Specific conductance 30 16 (<0.001) 0 <0.001 4.7 <0.001

Cadmium, filtered 30 24 (NR1

) 30 0.224 21.4 <0.001

Cadmium, unfiltered-recoverable30 1 (NR1

) 10 0.246 50.1 <0.001

Copper, filtered 30 -15 (NR1

) 7 0.060 32.1 <0.001

Copper, unfiltered-recoverable 30 24 (NR1

) 10 0.193 57.3 <0.001

Iron, filtered 30 -38 (NR1

) 10 0.768 39.1 <0.001

Iron unfiltered-recoverable 30 -1 (0.969) 0 0.038 57.2 <0.001

Lead, filtered 30 NR2 70 NR2 NR2 NR2

Lead, unfiltered-recoverable 30 4 (0.923) 0 0.016 67.6 <0.001

Manganese, filtered 30 91 (NR1

) 3 0.326 38.8 <0.001

Manganese, unfiltered-recoverable30 18 (0.592) 0 0.029 53.2 <0.001

Zinc, filtered 30 NR2 47 NR2 NR2 NR2

Zinc, unfiltered-recoverable 30 22 (0.564) 13 0.005 61.5 <0.001

Arsenic, filtered 30 -9 (NR1

) 0 0.130 17.4 0.010

Arsenic, unfiltered-recoverable 30 18 (NR1

) 0 0.058 20.3 <0.001

Suspended sediment 30 -24 (0.498) 0 <0.001 72.3 <0.001

Lost Creek near Anaconda (site 12, fig. 1, table 1)

Specific conductance 47 -4 (0.315) 0 <0.001 8.7 <0.001

Cadmium, filtered 46 -44 (NR1

) 11 0.504 41.9 <0.001

Cadmium, unfiltered-recoverable47 -50 (NR1

) 11 0.526 48.4 <0.001

Copper, filtered 47 -46 (NR1

) 0 0.879 30.2 <0.001

Copper, unfiltered-recoverable 47 -42 (NR1

) 2 0.160 49.9 <0.001

Iron, filtered 47 25 (0.193) 9 0.034 35.3 <0.001

Iron unfiltered-recoverable 47 -20 (0.426) 0 0.002 63.9 <0.001

Lead, filtered 47 NR2 57 NR2 NR2 NR2

Lead, unfiltered-recoverable 47 -28 (0.286) 0 0.022 44.3 <0.001

Manganese, filtered 47 -16 (NR1

) 2 0.429 44.3 <0.001

Manganese, unfiltered-recoverable

47 -3 (NR1

) 0 0.067 52.6 <0.001

Zinc, filtered 47 -32 (NR1

) 30 0.245 28.1 <0.001

Zinc, unfiltered-recoverable 47 -43 (NR1

) 4 0.081 47.4 <0.001

Arsenic, filtered 47 -51 (NR1

) 0 0.161 32.3 <0.001

Arsenic, unfiltered-recoverable 47 -44 (NR1

) 0 0.375 31.3 <0.001

Suspended sediment 47 -56 (0.013) 0 <0.001 74.8 <0.001
Appendix 4—Trend Analysis Results 129

Table 4–3. Flow-adjusted trend results determined by using multiple linear regression on time, streamflow, and season (MLR) 

for selected water-quality constituents and properties for selected sampling sites in the upper Clark Fork Basin, Montana, water 

years 2006–2010.—Continued

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. Values in parentheses indicate 

95-percent confidence intervals. Gray shading indicates statistical significance at p-value less than 0.01. p-value, statistical probability level; SEE, standard 

error of estimate; NR, not reported; <, less than]

Constituent or property

Number 

of 

samples

Total percent change 

for water years 

2006–2010 (period 5)

Percent 

censored 

values

p-value for 

streamflow 

coefficient

SEE p-value for 

regression

Lost Creek near Galen (site 13, fig. 1, table 1)

Specific conductance 62 4 (NR1

) 0 0.230 7.4 <0.001

Cadmium, filtered 61 8 (NR1

) 16 0.375 35.3 0.026

Cadmium, unfiltered-recoverable62 -51 (<0.001) 8 0.026 34.3 <0.001

Copper, filtered 61 -52 (NR1

) 0 0.360 27.6 <0.001

Copper, unfiltered-recoverable 62 -49 (<0.001) 0 0.003 23.8 <0.001

Iron, filtered 62 129 (NR1

) 5 0.110 58.1 <0.001

Iron unfiltered-recoverable 62 31 (NR1

) 0 0.378 44.1 <0.001

Lead, filtered 61 4 (NR1) 57 0.760 81.2 0.011

Lead, unfiltered-recoverable 62 -10 (0.601) 0 0.002 61.7 <0.001

Manganese, filtered 62 141 (NR1

) 0 0.075 61.7 <0.001

Manganese, unfiltered-recoverable62 140 (NR1

) 0 0.317 57.1 <0.001

Zinc, filtered 61 13 (NR1

) 15 0.911 50.5 <0.001

Zinc, unfiltered-recoverable 62 -24 (0.055) 10 0.004 37.6 <0.001

Arsenic, filtered 62 -3 (0.774) 0 0.030 32.6 <0.001

Arsenic, unfiltered-recoverable 62 6 (0.616) 0 0.038 32.8 <0.001

Suspended sediment 62 16 (0.588) 0 0.526 81.3 <0.001

1

Results not reported because of nonsignificant relation between streamflow and consituent concentration as indicated by p-value greater than 0.05.

2

Results not reported because greater than 45 percent of values were censored (that is, concentrations reported as less than the laboratory reporting level).
130 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

100

1,000 1,000

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

100

10

1

279 297 295 289

2.3 2.0 2.0 1.9

2.9 2.1 2.5 2.6

6.7 7.2 5.6 5.1

5.2 4.3 4.3 3.8

3.8

3.8 2.8 3.1 3.3

Flow-adjusted values, in indicated units of measrement

Filtered zinc (micrograms per liter) Unfiltered-recoverable

zinc (micrograms per liter)

Water year (October–September)

1 2 3 1 2 3

Period Period

1990199520002005201019901995200020052010

Filtered arsenic (micrograms per liter) Unfiltered-recoverable

arsenic (micrograms per liter)

Unfiltered-recoverable

copper (micrograms per liter) Filtered copper (micrograms per liter)

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

2.8

Figure 4–1. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Blacktail Creek (site 1, fig. 1, table 1), water years 1996–2010.
Appendix 4—Trend Analysis Results 131

522 493 493 476

60 13 13 6.0

6.5 6.8 4.0 4.3

15 14 7.5 7.3

7.3

180 44 31 14

14

13 10 5.6 6.0

890 280 77 32 1,100 350 98 43

Filtered copper (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered arsenic (micrograms per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1,000

10,000

10

100

1

1,000

10

100

1,000

1,000

10,000

10

100

1,000

1

10

100

1

1,000

10

1

100

1,000

10

1

100

100

1,000

Figure 4–2. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Silver Bow Creek at Butte (site 2, fig. 1, table 1), water years 1996–2010.
132 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Figure 4.3. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected constituents and properties for Silver Bow Creek at

Opportunity (site 3, fig. 1, table 1), water years 1996–2010.

424 463 470 440

48 42 29 17

9.0 11 12 7.4

24 18 21 19

19

130 120 94 44

44

16 17 18 8.8

290 220 130 53 540 470 270 130

21

1 2 3 1 2 3

Period Period

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1,000

10,000

10

100

1

1,000

10

100

1,000

1,000

10,000

10

100

1,000

1

10

100

1

1,000

10

1

100

1,000

10

1

100

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic (micrograms per liter) Unfiltered-recoverable

arsenic (micrograms per liter)

Figure 4–3. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Silver Bow Creek at Opportunity (site 3, fig. 1, table 1), water years 1996–2010.
Appendix 4—Trend Analysis Results 133

120 128

4.1 3.3

3.3

3.6 2.8

2.5 2.5

18 16

2.1 1.8

1.3 1.6

17 15

1 2 3 1 2 3

Period Period

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

10

100

1

1,000

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

50

100

500

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter) Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic (micrograms per liter) Unfiltered-recoverable

arsenic (micrograms per liter)

Flow-adjusted concentration (FAC) determined by 

using multiple linear 

regression

Flow-adjusted fitted trend 

determined by using 

multiple linear regression

Fitted trend value at start or 

end of period

Figure 4–4. Flow-adjusted fitted trends determined by using multiple linear regression on time, discharge, and season (MLR) for 

selected water-quality constituents and properties for Mill Creek near Anaconda (site 4, fig. 1, table 1), water years 2006–2010.
134 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

134 148

4.0

4.0

3.4

5.1 3.4

3.4

5.0 3.3

27 18

2.9 1.9

2.9 1.7

24 16

1 2 3 1 2 3

Period Period

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using multiple linear 

regression

Flow-adjusted fitted trend 

determined by using 

multiple linear regression

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

50

100

500

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic (micrograms per liter) Unfiltered-recoverable

arsenic (micrograms per liter)

Figure 4–5. Flow-adjusted fitted trends determined by using multiple linear regression on time, discharge, and season (MLR) for 

selected water-quality constituents and properties for Mill Creek at Opportunity (site 5, fig. 1, table 1), water years 2006–10.
Appendix 4—Trend Analysis Results 135

Figure 4.6. Flow-adjusted fitted trends determined by using multiple linear regression on time, streamflow, and season (MLR) for selected

constituents and properties for Willow Creek near Anaconda (site 6, fig. 1, table 1), water years 2006–10.

90 111 8.0

8.0

3.6

3.6

3.5 2.4

2.7 2.2

17 14

2.0 1.6

1.7 1.3

16 14

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using multiple linear 

regression

Flow-adjusted fitted trend 

determined by using 

multiple linear regression

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

50

100

500

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic (micrograms per liter) Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–6. Flow-adjusted fitted trends determined by using multiple linear regression on time, discharge, and season (MLR) for 

selected water-quality constituents and properties for Willow Creek near Anaconda (site 6, fig. 1, table 1), water years 2006–10.
136 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

274 238

6.3 6.9

6.9

9.3 7.9

8.4 8.9

38 31

4.7 3.5 3.5

3.9 3.1

36 27

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using multiple linear 

regression

Flow-adjusted fitted trend 

determined by using 

multiple linear regression

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

50

100

500

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–7. Flow-adjusted fitted trends determined by using multiple linear regression on time, discharge, and season (MLR) for 

selected water-quality constituents and properties for Mill Creek at Opportunity (site 7, fig. 1, table 1), water years 2006–10.
Appendix 4—Trend Analysis Results 137

527 526 506 530

11 4.8 4.2 4.0

17 19 19 20

5.4 5.8 4.1 1.9

18 8.8

8.8

8.0 7.0

7.0

20 22 21 23

48 17 9.1 9.2

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Figure 4–8. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Silver Bow Creek at Warm Springs (site 8, fig. 1, table 1), water years 1996–2010.
138 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

194 225

225

5.6 4.3

4.3

2.4 3.0

2.1 2.6

2.4 2.8

1.0 0.88

2.3 2.1

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using multiple linear 

regression

Flow-adjusted fitted trend 

determined by using 

multiple linear regression

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Results not presented because greater than

45 percent of values were censored.

[Graph included as a place holder to assist in

comparison with other stations.]

Figure 4–9. Flow-adjusted fitted trends determined by using multiple linear regression on time, discharge, and season (MLR) for 

selected water-quality constituents and properties for Warm Springs Creek near Anaconda (site 9, fig. 1, table 1), water years 2006–10.
Appendix 4—Trend Analysis Results 139

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

1

426 376 377 351

2.4 2.4 2.2 1.5

4.7 5.3 5.2 4.0

8.7 4.7 3.1

3.1

7.7

7.7

9.9 7.4 7.7 9.8

6.2 5.6 5.9 5.2

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Results not reported because greater than

6 percent of values were affected by recensoring

at study reporting level, as discussed in the

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Figure 4–10. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Warm Springs Creek at Warm Springs (site 10, fig. 1, table 1), water years 1996–10.
140 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

459 450 440 431

8.0 4.1 3.8 3.3

12 12 13 10

6.0 5.8 4.8 4.8

4.8

16 10

10

11 10

16 14 16 12

32 13 8.8 10

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000 1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–11. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Clark Fork near Galen (site 11, fig. 1, table 1), water years 1996–2010.
Appendix 4—Trend Analysis Results 141

200 192

7.4 3.3

3.3

6.0 3.5

3.3 1.9

5.4 3.1

2.2 1.2

1.5 1.0

4.9 2.4

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using multiple linear 

regression

Flow-adjusted fitted trend 

determined by using 

multiple linear regression

Fitted trend value at start or 

end of period

10

100

1

1,000

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

1

10

0.1

100

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

1

10

0.1

100

Filtered zinc (micrograms per liter)

Figure 4–12. Flow-adjusted fitted trends determined by using multiple linear regression on time, discharge, and season (MLR) for 

selected water-quality constituents and properties for Lost Creek near Anaconda (site 12, fig. 1, table 1), water years 2006–10.
142 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

632 659 11 13

13

5.1 2.6 2.6

2.4 1.8

14 15

2.3 1.1

1.3 1.5

13 13

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using multiple linear 

regression

Flow-adjusted fitted trend 

determined by using the 

multiple linear regression

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

10

100

0.1

1

200

1,000

2,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1

1 2 3 1 2 3

Period Period

Filtered zinc (micrograms per liter)

Figure 4–13. Flow-adjusted fitted trends determined by using multiple linear regression on time, discharge, and season (MLR) for 

selected water-quality constituents and properties for Lost Creek near Galen (site 13, fig. 1, table 1), water years 2006–10.
Appendix 4—Trend Analysis Results 143

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

495 488 481 449

7.1 5.8 6.0 5.0

11 10 12 11

17 14 13 13

13

26 23 22 23

14 14 15 14

36 23

23

21 20

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–14. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Clark Fork at Deer Lodge (site 14, fig. 1, table 1), water years 1996–2010.
144 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Figure 4.15. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected constituents and properties for Little Blackfoot

River (site 15, fig. 1, table 1), water years 1996–2005.

253 261 264

4.9 4.7 5.3

5.4 4.0 3.0

6.5 5.0

5.0

4.7

1.1 0.94 1.0

1.0

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

1

10

0.1

100

100 100

1

10

0.1

1

10

0.1

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Filtered zinc (micrograms per liter)

Figure 4–15. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Little Blackfoot River (site 15, fig. 1, table 1), water years 1996–2005.
Appendix 4—Trend Analysis Results 145

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

422 422 411 391

4.9 3.9 4.3 4.0

9.0 8.2 9.1 8.9

15 17 8.1

8.1

14

22 19 15 16

16

11 9.8 10 11

28 19 12 17

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–16. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Clark Fork at Goldcreek (site 16, fig. 1, table 1), water years 1996–2010.
146 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

324 346 376

8.7 8.1 7.8 13 11

11

10

18 17 10

3.4 2.6 2.4

2.4

18 13 8.0

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–17. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Flint Creek (site 17, fig. 1, table 1), water years 1996–2005.
Appendix 4—Trend Analysis Results 147

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

486 472 458 445

3.7 3.7 4.3 3.3

9.3 8.6 9.3 8.3

21 13 11 12

19 15 13 13

13

12 10 10 10

40 18 15

15

17

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–18. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Clark Fork near Drummond (site 18, fig. 1, table 1), water years 1996–2010.
148 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Unfiltered-recoverable

zinc (micrograms per liter)

121 123 113 4.7

4.7

7.1

7.1

3.2

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

1

100

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–19. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Rock Creek (site19, fig. 1, table 1), water years 1996–2005.
Appendix 4—Trend Analysis Results 149

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

344 327 324 325

3.3 2.7 2.9 2.6

5.3 5.1 5.4 5.5

13 12 8.4 13

9.4 8.9 7.4 9.5

9.5

6.8 6.3 5.9 7.2

22 15 9.0 16

16

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–20. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Clark For at Turah Bridge (site 20, fig. 1, table 1), water years 1996–2010.
150 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

Unfiltered-recoverable

arsenic (micrograms per liter)

237 238 229 243

243

4.4 3.9 4.0 3.1

3.1

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

1

100

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter) Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–21. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Blackfoot River (site 21, fig. 1, table 1) water years 1996–2010.
Appendix 4—Trend Analysis Results 151

Results not reported because greater than 

6 percent of values were affected by recensoring 

at study reporting level, as discussed in the 

section of this report "Time-Series Model."

[Graph included as a place holder to assist in

comparison with other stations.]

BA BA

274 274 270 286

2.2 1.7 2.1 2.5

2.9 2.9 3.2 3.9

8.5 7.2 9.4 9.3

5.6 4.6

4.6

7.0 5.9

5.9

3.8 3.6 4.1 5.0

272

2.2

3.4

23

14

15 8.6 12 31 13

5.1

Flow-adjusted values, in indicated units of measrement

Water year (October–September)

1990199520002005201019901995200020052010

EXPLANATION

[Water year is defined as the 12-month 

period from October 1 through September 

30 and is designated by the year in which 

it ends. μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; p-value, 

statistical probability level]

Flow-adjusted concentration (FAC) determined by 

using the time-series 

model

Flow-adjusted fitted trend 

determined by using the 

time-series model

Fitted trend value at start or 

end of period

Bold values indicate 

statistical significance 

(p-value less than 0.01) for 

period before value 

presented in bold

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

10

100

1

1,000

100

1,000

Specific conductance (μS/cm) Suspended sediment (milligrams per liter)

Unfiltered-recoverable

copper (micrograms per liter)

Unfiltered-recoverable

zinc (micrograms per liter)

Filtered zinc (micrograms per liter)

Filtered copper (micrograms per liter)

Filtered arsenic 

(micrograms per liter)

Unfiltered-recoverable

arsenic (micrograms per liter)

1 2 3 1 2 3

Period Period

Figure 4–22. Flow-adjusted fitted trends determined by using the time-series model (TSM) for selected water-quality constituents and 

properties for Clark Fork above Missoula (site 22, fig. 1, table 1), water years 1996–2010.
152 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 5–1. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 1, extending 

from Blacktail Creek (site 1, fig. 1, table 1) to Silver Bow Creek at Butte (site 2, fig. 1, table 1) for selected periods, water years 

1996–2010.

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Blacktail Creek (site 1) 0.13 0.093 200

Outflow Silver Bow Creek at Butte (site 2) 5.0 0.59 740

Total within-reach change in load—outflow (site 2) minus 

inflow (site 1) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

4.9 0.50 540

Water years 2001–05 (period 2)

Inflow Blacktail Creek (site 1) 0.12 0.083 180

Outflow Silver Bow Creek at Butte (site 2) 1.9 0.39 530

Total within-reach change in load—outflow (site 2) minus 

inflow (site 1) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

1.7 0.30 350

Water years 2006–10 (period 3)

Inflow Blacktail Creek (site 1) 0.11 0.090 150

Outflow Silver Bow Creek at Butte (site 2) 1.1 0.30 380

Total within-reach change in load—outflow (site 2) minus 

inflow (site 1) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

1.0 0.21 220

1

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report “Estimation of Normalized Constituent Loads.” Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.
Appendix 5—Transport-Analysis Balance Calculations for Data-Summary Reaches 153

Table 5–2. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 2, extending 

from Silver Bow Creek at Butte (site 2, fig. 1, table 1) to Silver Bow Creek at Opportunity (site 3, fig. 1, table 1) for selected periods, 

water years 1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Silver Bow Creek at Butte (site 2) 5.0 0.59 740

Outflow Silver Bow Creek at Opportunity (site 3) 12 1.6 2,000

Total within-reach change in load—outflow (site 3) minus 

inflow (site 2) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

7.3 1.0 1,300

Water years 2001–05 (period 2)

Inflow Silver Bow Creek at Butte (site 2) 1.9 0.39 530

Outflow Silver Bow Creek at Opportunity (site 3) 10 1.7 1,900

Total within-reach change in load—outflow (site 3) minus 

inflow (site 2) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

8.6 1.3 1,400

Water years 2006–10 (period 3)

Inflow Silver Bow Creek at Butte (site 2) 1.1 0.29 380

Outflow Silver Bow Creek at Opportunity (site 3) 6.5 1.3 2,000

Total within-reach change in load—outflow (site 3) minus 

inflow (site 2) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

5.4 1.0 1,600

1

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report “Estimation of Normalized Constituent Loads.” Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.
154 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 5–3. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 31, extending 

from Silver Bow Creek at Opportunity (site 3, fig. 1, table 1) to Silver Bow Creek at Warm Springs (site 8, fig. 1, table 1) for selected 

periods, water years 1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load2

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Silver Bow Creek at Opportunity (site 3) 12 1.6 2,000

Outflow Silver Bow Creek at Warm Springs (site 8) 2.0 3.1 850

Total within-reach change in load—outflow (site 8) minus 

inflow (site 3) (negative values indicate net accumulation in 

Warm Springs Ponds; positive values indicate net mobilization 

from within-reach sources including groundwater inflow, the 

Mill-Willow bypass, the outflow from Warm Springs Ponds, 

and the main-stem channel and floodplain downstream from 

Warm Springs Ponds)

-10 1.6 -1,200

Water years 2001–05 (period 2)

Inflow Silver Bow Creek at Opportunity (site 3) 10 1.7 1,900

Outflow Silver Bow Creek at Warm Springs (site 8) 1.3 3.3 740

Total within-reach change in load—outflow (site 8) minus 

inflow (site 3) (negative values indicate net accumulation in 

Warm Springs Ponds; positive values indicate net mobilization 

from within-reach sources including groundwater inflow, the 

Mill-Willow bypass, the outflow from Warm Springs Ponds, 

and the main-stem channel and floodplain downstream from 

Warm Springs Ponds)

-9.2 1.6 -1,200

Water years 2006–10 (period 3)

Inflow Silver Bow Creek at Opportunity (site 3) 6.5 1.3 2,000

Outflow Silver Bow Creek at Warm Springs (site 8) 1.1 3.4 430

Total within-reach change in load—outflow (site 8) minus 

inflow (site 3) (negative values indicate net accumulation in 

Warm Springs Ponds; positive values indicate net mobilization 

from within-reach sources including groundwater inflow, the 

Mill-Willow bypass, the outflow from Warm Springs Ponds, 

and the main-stem channel and floodplain downstream from 

Warm Springs Ponds)

-5.4 2.1 -1,600

1

Data for Mill Creek at Opportunity (site 5) and Willow Creek at Opportunity (site 7) were not included as monitored tributary inflows because of factors 

that complicate directly combining the TSM results and multiple linear regression on time, streamflow, and season (MLR) results within a single analysis. The 

inability to distinguish the relative magnitudes of the within-reach contributions from the Mill-Willow bypass and Warm Springs Ponds to the reach outflow 

required simplifying assumptions. As a result, when net accumulation in the reach 3 channel is indicated for unfiltered-recoverable copper and suspended 

sediment, it is presumed that all of the reach inflow at site 3 is stored in Warm Springs Ponds.

2

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report "Estimation of Normalized Constituent Loads." Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.
Appendix 5—Transport-Analysis Balance Calculations for Data-Summary Reaches 155

Table 5–4. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 4, extending 

from Silver Bow Creek at Warm Springs (site 8, fig. 1, table 1) to Clark Fork near Galen (site 11, fig. 1, table 1) for selected periods, 

water years 1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Silver Bow Creek at Warm Springs (site 8) 2.0 3.1 850

 Monitored tributary inflow within reach Warm Springs 

Creek at Warm Springs (site 10)

1.0 0.70 780

Combined inflow (sum of sites 8 and 10) 3.0 3.9 1,600

Outflow Clark Fork near Galen (site 11) 3.6 4.1 1,600

Total within-reach change in load—outflow (site 11) minus 

inflow (site 8) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

1.7 1.0 790

Within-reach change in load after accounting for the monitored tributary—outflow (site 11) minus combined inflow 

(sum of sites 8 and 10) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries and the main-stem channel and 

floodplain; negative values indicate net accumulation in reach 

channel)

0.67 0.29 19

Water years 2001–05 (period 2)

Inflow Silver Bow Creek at Warm Springs (site 8) 1.3 3.3 740

 Monitored tributary inflow within reach

Warm Springs Creek at Warm Springs (site 10)

0.89 0.68 460

Combined inflow (sum of sites 8 and 10) 2.2 4.0 1,200

Outflow Clark Fork near Galen (site 11) 2.9 4.2 1,500

Total within-reach change in load—outflow (site 11) minus 

inflow (site 8) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

1.7 0.91 720

Within-reach change in load after accounting for the monitored tributary—outflow (site 11) minus combined inflow 

(sum of sites 8 and 10) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries and the main-stem channel and 

floodplain)

0.78 0.23 260

Water years 2006–10 (period 3)

Inflow Silver Bow Creek at Warm Springs (site 8) 1.1 3.4 430

 Monitored tributary inflow within reach

Warm Springs Creek at Warm Springs (site 10)

1.0 0.66 610

Combined inflow (sum of sites 8 and 10) 2.1 4.0 1,040

Outflow Clark Fork near Galen (site 11) 2.9 3.9 1,300
156 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 5–4. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 4, extending 

from Silver Bow Creek at Warm Springs (site 8, fig. 1, table 1) to Clark Fork near Galen (site 11, fig. 1, table 1) for selected periods, 

water years 1996–2010.—Continued 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 2006–10 (period 3)—Continued

Total within-reach change in load—outflow (site 11) minus 

inflow (site 8) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

1.8 0.53 900

Within-reach change in load after accounting for the monitored tributary—outflow (site 11) minus combined inflow 

(sum of sites 8 and 10) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries and the main-stem channel and 

floodplain; negative values indicate net accumulation in reach 

channel)

0.74 -0.12 290

1

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report “Estimation of Normalized Constituent Loads.” Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.
Appendix 5—Transport-Analysis Balance Calculations for Data-Summary Reaches 157

Table 5–5. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 51, extending 

from Clark Fork near Galen (site 11, fig. 1, table 1) to Clark Fork at Deer Lodge (site 14, fig. 1, table 1) for selected periods, water years 

1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load2

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Clark Fork near Galen (site 11) 3.6 4.1 1,600

Outflow Clark Fork at Deer Lodge (site 14) 12 6.9 7,500

Total within-reach change in load—outflow (site 14) minus 

inflow (site 11) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

8.4 2.8 5,900

Water years 2001–05 (period 2)

Inflow Clark Fork near Galen (site 11) 2.9 4.2 1,500

Outflow Clark Fork at Deer Lodge (site 14) 11 7.0 6,600

Total within-reach change in load—outflow (site 14) minus 

inflow (site 11) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

8.1 2.8 5,100

Water years 2006–10 (period 3)

Inflow Clark Fork near Galen (site 11) 2.9 3.9 1,300

Outflow Clark Fork at Deer Lodge (site 14) 11 7.0 6,300

Total within-reach change in load—outflow (site 14) minus 

inflow (site 11) (positive values indicate net mobilization from 

within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

8.1 3.1 5,000

1

Data for Lost Creek near Galen (site 13) were not included as monitored tributary inflows because of factors that complicate directly combining the TSM 

results and multiple linear regression on time, streamflow, and season (MLR) results within a single analysis. 

2

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report "Estimation of Normalized Constituent Loads." Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.
158 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 5–6. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 6, extending 

from Clark Fork at Deer Lodge (site 14, fig. 1, table 1) to Clark Fork at Goldcreek (site 16, fig. 1, table 1) for selected periods, water years 

1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Clark Fork at Deer Lodge (site 14) 12 6.9 7,500

 Monitored tributary inflow within reach

Little Blackfoot River (site 15)

0.24 1.3 1,100

Combined inflow (sum of sites 14 and 15) 12 8.3 8,600

Outflow Clark Fork at Goldcreek (site 16) 19 10 16,000

Total within-reach change in load—outflow (site 16) minus 

inflow (site 14) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

7.3 3.2 8,000

Within-reach change in load after accounting for the monitored tributary—outflow (site 16) minus combined inflow 

(sum of sites 14 and 15) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries, and the mainstem channel and 

floodplain)

7.1 1.9 6,900

Water years 2001–05 (period 2)

Inflow Clark Fork at Deer Lodge (site 14) 11 7.0 6,600

 Monitored tributary inflow within reach

Little Blackfoot River (site 15)

0.23 1.1 800

Combined inflow (sum of sites 14 and 15) 11 8.1 7,400

Outflow Clark Fork at Goldcreek (site 16) 16 9.7 12,000

Total within-reach change in load—outflow (site 16) minus 

inflow (site 14) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

5.3 2.7 5,300

Within-reach change in load after accounting for the monitored tributary—outflow (site 16) minus combined inflow 

(sum of sites 14 and 15) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries, and the mainstem channel and 

floodplain)

5.1 1.6 4,500

Water years 2006–10 (period 32

)

Inflow Clark Fork at Deer Lodge (site 14) 11 7.0 6,300

Outflow Clark Fork at Goldcreek (site 16) 15 10 10,000

Total within-reach change in load—outflow (site 16) minus 

inflow (site 14) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

4.0 3.3 4,000

1

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report "Estimation of Normalized Constituent Loads." Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.

2

No data available for site 15 for water years 2006–10 (period 3); thus loads from site 15 are not accounted for and contribute to the within-reach change in 

load for period 3. Further, for period 3, loads from site 15 are included in net mobilization from within-reach sources.
Appendix 5—Transport-Analysis Balance Calculations for Data-Summary Reaches 159

Table 5–7. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 7, extending 

from Clark Fork at Goldcreek (site 16, fig. 1, table 1) to Clark Fork near Drummond (site 18, fig. 1, table 1) for selected periods, water 

years 1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Clark Fork at Goldcreek (site 16) 19 10 16,000

 Monitored tributary inflow within reach 

 Flint Creek (site 17)

0.69 2.7 4,100

Combined inflow (sum of sites 16 and 17) 20 13 20,000

Outflow Clark Fork near Drummond (site 18) 24 16 24,000

Total within-reach change in load—outflow (site 18) minus 

inflow (site 16) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

4.8 5.5 8,000

Within-reach change in load after accounting for the monitored tributary—outflow (site 18) minus combined inflow 

(sum of sites 16 and 17) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries and the main-stem channel and 

floodplain)

4.1 2.8 3,900

Water years 2001–05 (period 2)

Inflow Clark Fork at Goldcreek (site 16) 16 9.7 12,000

 Monitored tributary inflow within reach

Flint Creek (site 17)

0.57 2.4 3,000

Combined inflow (sum of sites 16 and 17) 17 12 15,000

Outflow Clark Fork near Drummond (site 18) 19 15 17,000

Total within-reach change in load—outflow (site 18) minus 

inflow (site 16) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

3.1 4.8 5,100

Within-reach change in load after accounting for the monitored tributary—outflow (site 18) minus combined inflow 

(sum of sites 16 and 17) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries and the main-stem channel and 

floodplain)

2.5 2.3 2,100

Water years 2006–10 (period 32

)

Inflow Clark Fork at Goldcreek (site 16) 15 10 10,000

Outflow Clark Fork near Drummond (site 18) 18 15 17,000

Total within-reach change in load—outflow (site 18) minus 

inflow (site 16) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

3.3 4.5 6,300

1

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report "Estimation of Normalized Constituent Loads." Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.

2

No data available for site 17 for water years 2006–10 (period 3); thus loads from site 17 are not accounted for and contribute to the total within-reach 

change in load for period 3. Further, for period 3, loads from site 17 are included in net mobilization from within-reach sources.
160 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 5–8. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 8, extending 

from Clark Fork near Drummond (site 18, fig. 1, table 1) to Clark Fork at Turah Bridge (site 20, fig. 1, table 1) for selected periods, water 

years 1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

InflowClark Fork near Drummond (site 18) 24 16 24,000

 Monitored tributary inflow within reach2

Rock Creek (site 19)

ND ND 4,900

Combined inflow (sum of sites 18 and 19) ND ND 28,000

Outflow Clark Fork at Turah Bridge (site 20) 23 17 32,000

Total within-reach change in load—outflow (site 20) minus 

inflow (site 18) (negative values indicate net accumulation in 

reach channel; positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

-1.0 0.89 8,900

Within-reach change in load after accounting for the monitored tributary—outflow (site 20) minus combined inflow 

(sum of sites 18 and 19) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries, and the main-stem channel and 

floodplain)

ND ND 4,000

Water years 2001–05 (period 2)

Inflow Clark Fork near Drummond (site 18) 19 15 17,000

 Monitored tributary inflow within reach2

Rock Creek (site 19)

ND ND 3,900

Combined inflow (sum of sites 18 and 19) ND ND 21,000

Outflow Clark Fork at Turah Bridge (site 20) 21 15 26,000

Total within-reach change in load—outflow (site 20) minus 

inflow (site 18) (negative values indicate net accumulation in 

reach channel; positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

1.1 0.92 9,000

Within-reach change in load after accounting for the monitored tributary—outflow (site 20) minus combined inflow 

(sum of sites 18 and 19) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries, and the main-stem channel and 

floodplain)

ND ND 5,100

Water years 2006–10 (period 32

)

Inflow Clark Fork near Drummond (site 18) 18 15 17,000

Outflow Clark Fork at Turah Bridge (site 20) 21 16 27,000

Total within-reach change in load—outflow (site 20) minus 

inflow (site 18) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, unmonitored tributaries, and the main-stem channel and floodplain)

3.0 1.8 10,000

1

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report "Estimation of Normalized Constituent Loads." Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.

2

Load results for Rock Creek near Clinton (site 19) for copper and arsenic not reported because greater than 6 percent of data values were affected by 

recensoring at study reporting level, as discussed in the section of this report "Time-Series Model." No suspended-sediment data available for site 19 for 

period 3; thus loads from site 19 of copper and arsenic for all periods and suspended sediment for period 3 are not accounted for and contribute to the withinreach change in load.
Appendix 5—Transport-Analysis Balance Calculations for Data-Summary Reaches 161

Table 5–9. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 9, extending 

from Clark Fork at Turah Bridge (site 20, fig. 1, table 1) to Clark Fork above Missoula (site 22, fig. 1, table 1) for selected periods, water 

years 1996–2010. 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends. ND, not determined because of 

greater than 6 percent of values affected by recensoring at study reporting level, as discussed in the section of this report “Time-Series Model.”]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 1996–2000 (period 1)

Inflow Clark Fork at Turah Bridge (site 20) 23 17 32,000

 Monitored tributary inflow within reach2

Blackfoot River (site 21)

ND ND 9,900

Combined inflow (sum of sites 20 and 21) ND ND 42,000

Outflow Clark Fork above Missoula (site 22) 25 18 39,000

Total within-reach change in load—outflow (site 22) minus 

inflow (site 20) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

2.4 1.9 6,500

Within-reach change in load after accounting for the monitored tributary—outflow (site 22) minus combined inflow 

(sum of sites 20 and 21) (negative values indicate net accumulation in reach channel)

ND ND -3,300

Water years 2001–05 (period 2)

Inflow Clark Fork at Turah Bridge (site 20) 21 15 26,000

 Monitored tributary inflow within reach2

Blackfoot River (site 21)

ND ND 9,400

Combined inflow (sum of sites 20 and 21) 21 15 35,000

OutflowClark Fork above Missoula (site 22)" 29 19 41,000

Total within-reach change in load—outflow (site 22) minus 

inflow (site 20) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

8.0 3.6 15,000

Within-reach change in load after accounting for the monitored tributary—outflow (site 22) minus combined inflow 

(sum of sites 20 and 21) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries, and the main-stem channel and 

floodplain)

ND ND 5,600

Water years 2006–10 (period 3)

Inflow Clark Fork at Turah Bridge (site 20) 21 16 27,000

 Monitored tributary inflow within reach2

Blackfoot River (site 21)

ND ND 8,400

Combined inflow (sum of sites 20 and 21 21 16 36,000

Outflow Clark Fork above Missoula (site 22) 50 24 77,000
162 Water-Quality Trends for Selected Sampling Sites in the Upper Clark Fork Basin, Montana, Water Years 1996–2010

Table 5–9. Transport-analysis balance calculations for sites analyzed by using the time series model (TSM) in reach 9, extending 

from Clark Fork at Turah Bridge (site 20, fig. 1, table 1) to Clark Fork above Missoula (site 22, fig. 1, table 1) for selected periods, water 

years 1996–2010.—Continued 

[Water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends]

Site name and number or summation category

Estimated normalized load1

(kilograms per day)

Unfiltered-recoverable copperUnfiltered-recoverable arsenic Suspended sediment

Water years 2006–10 (period 3)—Continued

Total within-reach change in load—outflow (site 22) minus 

inflow (site 20) (positive values indicate net mobilization from 

all within-reach sources including groundwater inflow, the 

monitored tributary, unmonitored tributaries, and the main-stem 

channel and floodplain)

28 7.4 50,000

Within-reach change in load after accounting for the monitored tributary—outflow (site 22) minus combined inflow 

(sum of sites 20 and 21) (positive values indicate net mobilization from other within-reach sources including groundwater 

inflow, unmonitored tributaries, and the main-stem channel and 

floodplain)

ND ND 42,000

1

The estimated normalized load was computed by multiplying the mean annual fitted trend concentration (determined by using the time-series model) for 

the indicated period times the geometric mean streamflow for water years 1996–2010 and a units conversion factor according to equation 1 in the section of 

this report “Estimation of Normalized Constituent Loads.” Loads are reported to two significant figures; however, before final rounding, calculations used 

three significant figures when necessary. As a result, some of the load values have minor rounding artifacts.

2

Loads results for Blackfoot River near Bonner (site 21) for copper and arsenic not reported because greater than 6 percent of data values were affected 

by recensoring at study reporting level, as discussed in the section of this report “Time-Series Model.” Thus loads from site 21 of copper and arsenic for all 

periods are not accounted for and contribute to the within-reach change in load.