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Figure 6. Year-by-year changes in regional percentiles for dissolved iron (Fe) in groundwater.

Total Fe concentrations (blue) used where dissolved Fe data were not available. All Y axis scales in mg/L. Numbers above X axes show the number of sites at which median values could be calculated for the region and calendar year of interest. Horizontal line on each graph represents the aesthetic Guideline Value (0.2 mg/L) specified in the DWSNZ.

Figure 6. Year-by-year changes in regional percentiles for dissolved iron (Fe) in groundwater

Figure 6. Year-by-year changes in regional percentiles for dissolved iron (Fe) in groundwater

Figure 6. Year-by-year changes in regional percentiles for dissolved iron (Fe) in groundwater

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 2 0.1115 0.118 0.13 0.13 0.14 0.14
1997 4 0.0465 0.113 0.62 2.38 5.44 6.20
1998 20 0.0077 0.011 0.02 0.13 5.14 7.00
1999 22 0.0005 0.005 0.02 0.10 3.26 6.60
2000 22 0.0012 0.010 0.02 0.11 3.23 6.50
2001 22 0.0005 0.007 0.02 0.12 3.64 7.15
2002 22 0.0009 0.005 0.02 0.11 3.44 6.90
2003 22 0.0008 0.006 0.02 0.06 4.08 6.60
2004 22 0.0004 0.002 0.02 0.08 3.60 5.85
2005 22 0.0017 0.010 0.05 0.90 4.70 6.40
2006 21 0.0018 0.011 0.04 1.04 5.22 6.60
2007 22 0.0013 0.011 0.05 1.01 5.94 6.30
2008 23 0.0017 0.019 0.04 1.11 5.63 6.40
Change in Percentile Value Over Time2   - - - - 0.282 -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6b) Bay of Plenty Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 2 0.0450 0.105 0.18 0.26 0.3 0.3
1996 48 0.0001 0.001 0.03 0.71 10.5 24.4
1997 53 0.0004 0.001 0.01 0.66 9.5 23.9
1998 52 0.0005 0.001 0.02 0.50 6.4 22.4
1999 12 0.0042 0.029 0.06 0.56 3.4 3.4
2000 12 0.0022 0.027 0.05 0.58 3.4 3.5
2001 6 0.0092 0.034 0.10 0.50 2.9 3.7
2002 25 0.0002 0.002 0.05 0.55 5.1 56.5
2003 15 0.0027 0.024 0.35 0.87 4.3 9.4
2004 49 0.0024 0.018 0.28 4.39 9.0 29.5
2005 37 0.0013 0.008 0.08 0.61 6.0 19.7
2006 47 0.0018 0.012 0.19 0.83 10.4 12.3
2007 38 0.0005 0.004 0.05 0.71 9.7 10.7
2008 41 0.0015 0.010 0.11 1.40 7.5 12.0
Change in Percentile Value Over Time2   - - - 0.038 - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6c) Canterbury Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 16 0.005 0.014 0.054 0.25 1.23 1.3
1996 4 0.002 0.011 0.027 0.07 0.15 0.2
1997 9 0.001 0.002 0.009 0.10 0.14 0.1
1998 9 0.000 0.001 0.030 0.17 1.82 2.9
1999 3 0.055 0.055 0.055 0.06 0.06 0.1
2000 3 0.032 0.032 0.032 0.03 0.03 0.0
2001 3 0.145 0.145 0.145 0.15 0.15 0.1
2002 3 0.070 0.070 0.070 0.07 0.07 0.1
2003 256 0.012 0.040 0.050 0.09 0.25 2.5
2004 255 0.009 0.040 0.061 0.14 0.43 12.0
2005 273 0.004 0.030 0.059 0.15 0.46 8.8
2006 277 0.000 0.004 0.040 0.16 0.63 9.1
2007 276 0.000 0.000 0.003 0.05 0.29 2.5
2008 285 0.000 0.003 0.040 0.10 0.39 2.4
Change in Percentile Value Over Time2   - - - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6d) Data not available

(Figure 6e) Hawkes Bay Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 20 0.029 0.048 0.190 0.61 4.13 5.6
1996 6 0.060 0.077 0.090 0.29 1.65 2.2
1997 39 0.020 0.057 0.300 1.07 5.39 31.5
1998 43 0.014 0.073 0.190 1.75 5.40 28.0
1999 42 0.013 0.070 0.230 0.88 10.44 27.0
2000 40 0.015 0.095 0.180 1.39 9.90 27.0
2001 43 0.009 0.050 0.145 0.77 8.54 23.0
2002 38 0.010 0.045 0.221 0.94 7.61 25.0
2003 43 0.003 0.023 0.100 0.57 3.76 18.8
2004 41 0.003 0.020 0.110 0.88 4.63 24.8
2005 42 0.006 0.030 0.125 0.77 4.95 24.8
2006 43 0.005 0.033 0.090 1.02 6.78 20.9
2007 43 0.004 0.033 0.093 1.06 7.55 28.2
2008 43 0.003 0.027 0.090 1.33 7.28 27.0
Change in Percentile Value Over Time2   -0.002 -0.003 -0.010 - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6f) Manawatu-Wanganui Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 2 0.070 0.071 0.151 1.52 12.68 21.0
1996 2 0.033 0.070 0.160 1.17 9.25 16.0
1997 2 0.035 0.078 0.300 1.85 11.68 20.9
1998 5 0.031 0.060 0.395 1.72 12.46 32.0
1999 5 0.031 0.070 0.315 1.99 14.90 32.5
2000 4 0.030 0.066 0.208 1.63 17.67 29.2
2001 4 0.028 0.060 0.510 1.37 11.21 27.5
2002 6 0.045 0.120 0.410 2.80 18.10 28.1
2003 4 0.058 0.310 1.190 5.50 18.04 19.0
2004 3 0.033 0.110 0.470 9.24 20.40 27.7
2005 2 0.653 1.580 4.225 19.91 28.23 29.4
2006 15 0.044 0.177 0.744 3.02 10.35 33.9
2007 2 0.070 0.171 0.872 9.69 24.80 25.5
2008 2 0.037 0.047 0.059 0.78 1.36 1.5
Change in Percentile Value Over Time2   - - 0.053 0.27 - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6f) Manawatu-Wanganui Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 2 0.070 0.071 0.151 1.52 12.68 21.0
1996 2 0.033 0.070 0.160 1.17 9.25 16.0
1997 2 0.035 0.078 0.300 1.85 11.68 20.9
1998 5 0.031 0.060 0.395 1.72 12.46 32.0
1999 5 0.031 0.070 0.315 1.99 14.90 32.5
2000 4 0.030 0.066 0.208 1.63 17.67 29.2
2001 4 0.028 0.060 0.510 1.37 11.21 27.5
2002 6 0.045 0.120 0.410 2.80 18.10 28.1
2003 4 0.058 0.310 1.190 5.50 18.04 19.0
2004 3 0.033 0.110 0.470 9.24 20.40 27.7
2005 2 0.653 1.580 4.225 19.91 28.23 29.4
2006 15 0.044 0.177 0.744 3.02 10.35 33.9
2007 2 0.070 0.171 0.872 9.69 24.80 25.5
2008 2 0.037 0.047 0.059 0.78 1.36 1.5
Change in Percentile Value Over Time2   - - 0.053 0.27 - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6g) Marlborough Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 1 0.010 0.010 0.010 0.01 0.01 0.0
1998 4 0.013 0.020 0.020 0.04 0.10 0.1
1999 4 0.004 0.018 0.052 0.23 0.52 0.6
2000 3 0.072 0.099 0.198 0.46 0.88 1.0
2001 5 0.020 0.024 0.049 0.06 0.43 0.6
2002 4 0.000 0.001 0.022 0.04 0.54 0.7
2003 4 0.002 0.003 0.012 0.02 0.06 0.1
2004 6 0.000 0.002 0.022 0.19 0.55 0.6
2005 13 0.001 0.005 0.010 0.06 0.56 0.6
2006 6 0.000 0.000 0.009 0.12 0.55 0.6
2007 6 0.000 0.009 0.015 0.09 0.62 0.8
2008 6 0.000 0.000 0.011 0.11 0.67 0.9
Change in Percentile Value Over Time2   -0.001 -0.001 - - 0.032 0.053

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6h) Northland Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 3 0.0000 0.000 0.010 0.11 0.32 0.4
1997 5 0.0074 0.040 0.105 0.41 0.95 1.2
1998 6 0.0230 0.060 0.170 0.87 1.65 1.9
1999 6 0.0262 0.060 0.370 0.61 1.60 1.6
2000 6 0.0360 0.050 0.150 0.41 1.24 1.5
2001 8 0.0251 0.060 0.505 1.35 21.87 46.9
2002 11 0.0059 0.040 0.800 2.29 49.88 63.0
2003 20 0.0003 0.003 0.040 1.25 23.08 48.7
2004 25 0.0004 0.003 0.065 0.76 4.98 84.6
2005 25 0.0003 0.003 0.050 0.90 4.56 85.7
2006 24 0.0003 0.003 0.055 0.95 9.81 65.4
2007 27 0.0001 0.003 0.038 0.82 8.90 74.8
2008 26 0.0003 0.004 0.045 0.70 10.77 66.0
Change in Percentile Value Over Time2   - - - - 0.74 7.5

(Figure 6i) Otago Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 10 0.010 0.010 0.010 0.01 0.01 0.0
1997 10 0.009 0.011 0.020 0.04 0.07 0.1
1998 10 0.008 0.010 0.018 0.08 0.10 0.1
1999 8 0.004 0.009 0.015 0.04 0.09 0.1
2000 6 0.023 0.036 0.056 0.11 1.15 1.7
2001 5 0.001 0.003 0.006 0.02 0.05 0.1
2002 41 0.000 0.000 0.001 0.06 1.20 2.6
2003 47 0.000 0.000 0.001 0.06 1.96 7.0
2004 41 0.000 0.001 0.005 0.11 0.81 5.7
2005 41 0.000 0.000 0.000 0.04 1.05 4.7
2006 22 0.000 0.001 0.010 0.05 1.14 4.0
2007 26 0.001 0.004 0.022 0.11 1.81 7.9
2008 51 0.000 0.001 0.015 0.13 2.93 18.7
Change in Percentile Value Over Time2   -0.001 -0.001 - 0.005 0.169 0.767

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6j) Southland Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 0            
1998 6 0.0000 0.000 0.01 0.03 0.6 1.1
1999 4 0.0001 0.001 0.02 0.60 1.6 1.7
2000 4 0.0128 0.030 0.03 0.15 0.6 0.8
2001 3 0.0140 0.014 0.01 0.01 0.7 0.9
2002 4 0.0000 0.000 0.00 0.04 0.5 0.7
2003 4 0.0000 0.000 0.01 0.29 166.1 255.0
2004 4 0.0009 0.003 0.04 0.12 0.6 0.8
2005 28 0.0002 0.004 0.01 0.05 0.9 6.0
2006 24 0.0011 0.003 0.01 0.02 5.5 19.0
2007 28 0.0003 0.003 0.01 0.03 8.0 32.0
2008 27 0.0024 0.009 0.08 1.57 44.0 142.2
Change in Percentile Value Over Time2   - - - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6k) Taranaki Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 6 0.003 0.035 0.093 0.445 5.61 21.0
1996 4 0.006 0.023 0.045 0.105 0.69 1.0
1997 3 0.006 0.018 0.080 0.119 1.56 2.8
1998 3 0.040 0.045 0.070 0.115 1.92 3.4
1999 2 0.000 0.001 0.020 0.084 1.82 3.2
2000 2 0.005 0.029 0.063 0.108 1.58 2.8
2001 2 0.003 0.020 0.075 0.085 2.20 3.6
2002 2 0.022 0.043 0.075 0.243 1.89 3.2
2003 2 0.000 0.015 0.021 0.201 1.97 2.9
2004 2 0.000 0.001 0.025 0.093 1.86 2.8
2005 2 0.018 0.038 0.040 0.119 1.47 2.2
2006 2 0.001 0.018 0.030 0.250 2.18 3.2
2007 2 0.043 0.113 0.200 0.205 0.21 0.2
2008 2 0.033 0.055 0.165 0.460 0.54 0.6
Change in Percentile Value Over Time2   - - - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6l) Tasman Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 8 0.0057 0.025 0.12 0.96 1.15 1.18
1996 10 0.0010 0.010 0.04 0.56 1.31 1.31
1997 10 0.0000 0.001 0.01 0.58 2.68 3.65
1998 9 0.0003 0.001 0.02 0.50 2.61 3.50
1999 10 0.0005 0.017 0.03 0.41 2.37 3.40
2000 10 0.0008 0.008 0.03 0.67 2.28 3.00
2001 10 0.0003 0.002 0.02 0.40 2.89 3.70
2002 13 0.0001 0.003 0.02 0.57 1.86 3.05
2003 16 0.0003 0.010 0.03 0.31 3.03 3.40
2004 16 0.0000 0.001 0.02 0.16 2.76 2.95
2005 16 0.0001 0.007 0.02 0.28 2.91 3.10
2006 16 0.0011 0.009 0.03 0.24 3.68 4.65
2007 16 0.0000 0.000 0.01 0.20 3.83 6.00
2008 16 0.0001 0.001 0.02 0.26 3.41 5.09
Change in Percentile Value Over Time2   - - - -0.036 0.156 0.198

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6m) Waikato Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 3 0.009 0.020 0.030 0.06 0.09 0.1
1996 17 0.000 0.001 0.010 0.08 0.37 0.8
1997 6 0.020 0.020 0.020 0.02 0.02 0.0
1998 6 0.002 0.004 0.008 0.02 0.03 0.0
1999 6 0.000 0.000 0.000 0.02 0.85 1.4
2000 6 0.001 0.014 0.020 0.03 0.48 0.8
2001 22 0.000 0.000 0.000 0.00 0.25 1.2
2002 15 0.000 0.000 0.000 0.03 0.49 2.9
2003 6 0.000 0.000 0.002 0.05 0.21 0.3
2004 0            
2005 3 0.506 0.860 1.280 1.57 2.89 3.2
2006 6 0.032 0.055 0.111 0.30 0.54 0.6
2007 13 0.000 0.000 0.000 0.03 0.88 2.3
2008 73 0.000 0.000 0.000 0.00 0.81 35.0
Change in Percentile Value Over Time2   - - - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6n) Wellington Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 13 0.0200 0.038 0.075 0.898 3.93 7.0
1996 19 0.0110 0.030 0.090 0.218 2.46 7.8
1997 28 0.0049 0.020 0.085 0.550 2.37 4.4
1998 43 0.0100 0.076 0.575 3.348 7.61 13.8
1999 43 0.0155 0.081 0.248 2.493 8.19 12.3
2000 43 0.0068 0.040 0.130 2.173 6.95 11.9
2001 41 0.0022 0.020 0.105 2.483 9.10 13.4
2002 41 0.0037 0.029 0.117 2.633 8.69 13.9
2003 41 0.0006 0.004 0.060 1.738 7.93 13.0
2004 25 0.0000 0.000 0.020 0.170 2.13 13.7
2005 59 0.0000 0.000 0.000 0.030 0.97 14.7
2006 59 0.0000 0.000 0.000 0.021 0.92 17.1
2007 25 0.0002 0.002 0.025 0.270 1.84 16.8
2008 25 0.0002 0.001 0.028 0.170 2.74 15.0
Change in Percentile Value Over Time2   -0.001 -0.003 -0.009 - - 0.689

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 6o) West Coast Region calculated percentiles and maximum values for iron in groundwater (in mg/L), based on site-specific median values.

Parameter n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 0            
1998 6 0.003 0.012 0.048 0.12 0.54 0.68
1999 7 0.008 0.015 0.070 0.09 0.33 0.43
2000 7 0.011 0.024 0.038 0.11 0.35 0.44
2001 7 0.000 0.001 0.021 0.12 1.39 1.90
2002 6 0.000 0.004 0.037 0.09 0.70 0.90
2003 7 0.001 0.002 0.027 0.10 0.44 0.56
2004 8 0.005 0.010 0.045 0.10 0.27 0.29
2005 8 0.008 0.033 0.055 0.17 0.44 0.47
2006 8 0.005 0.013 0.035 0.08 0.28 0.40
2007 8 0.005 0.008 0.023 0.05 0.09 0.10
2008 8 0.021 0.035 0.040 0.08 0.13 0.13
Change in Percentile Value Over Time2   - - - - -0.04 -0.05

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.