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Figure 8. Year-by-year changes in regional percentiles for electrical conductivity in groundwater.

All Y axis scales in μS/cm. Numbers above X axes show the number of sites at which median values could be calculated for the region and calendar year of interest.

Figure 8. Year-by-year changes in regional percentiles for electrical conductivity in groundwater

Figure 8. Year-by-year changes in regional percentiles for electrical conductivity in groundwater

Figure 8. Year-by-year changes in regional percentiles for electrical conductivity in groundwater

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 2 333 423 535 648 738 760
1997 3 212 260 355 491 638 675
1998 21 202 254 294 433 662 3790
1999 9 164 229 288 583 2009 3110
2000 9 196 223 285 395 620 750
2001 21 173 221 280 410 662 725
2002 22 166 220 280 401 618 740
2003 21 165 224 308 426 711 3570
2004 18 216 282 388 466 743 3530
2005 22 208 274 333 443 726 761
2006 21 188 266 314 460 715 745
2007 22 173 267 307 441 711 771
2008 23 149 223 325 443 663 859
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 8b) Bay of Plenty Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 46 90 140 234 497 1153 2240
1996 53 83 117 239 477 905 1440
1997 59 86 114 226 465 988 27700
1998 58 90 115 211 440 1094 1980
1999 15 84 173 340 400 1135 1796
2000 12 99 116 287 363 852 878
2001 12 91 100 275 367 840 877
2002 41 94 169 241 518 1030 2752
2003 22 81 102 240 363 901 927
2004 49 86 114 208 427 1242 27300
2005 45 88 138 233 490 2030 27300
2006 53 86 105 206 421 1247 28000
2007 44 79 102 195 391 1167 2023
2008 46 82 110 212 408 1586 27860
Change in Percentile Value Over Time2   - - -3.3 - - -

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 8c) Canterbury Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 182 83 113 145 190 329 750
1996 211 86 121 160 200 332 677
1997 241 86 121 162 200 329 1300
1998 251 86 120 162 200 334 680
1999 265 90 128 170 220 409 1100
2000 271 100 157 184 239 533 1278
2001 253 91 144 185 244 546 875
2002 277 96 140 190 259 578 980
2003 256 110 160 210 310 704 6000
2004 262 98 150 200 270 625 2665
2005 272 89 139 180 240 444 4500
2006 269 100 150 190 250 448 1300
2007 274 100 140 180 240 419 1400
2008 278 110 150 200 255 453 2130
Change in Percentile Value Over Time2   1.6 2.7 3.5 5.0 11.7 87.5

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 8d) Data not available

(Figure 8e) Hawkes Bay Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 22 140 170 230 290 508 725
1996 8 165 175 223 280 475 525
1997 41 116 170 241 360 1432 2548
1998 44 107 160 242 454 1351 2614
1999 43 117 161 270 428 1475 2603
2000 42 132 170 247 467 1608 2731
2001 44 122 167 242 480 1256 2631
2002 40 126 164 256 522 1380 2595
2003 44 129 169 270 516 1234 2625
2004 36 125 163 237 464 1554 2593
2005 42 118 168 261 467 1271 2583
2006 42 115 168 253 482 1292 2607
2007 45 116 171 254 536 1278 2680
2008 44 127 179 274 546 1218 2655
Change in Percentile Value Over Time2   - - 2.8 16.8 - -

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 8f) Manawatu-Wanganui Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 7 117 298 340 497 681 717
1996 8 117 302 347 504 638 660
1997 8 137 305 347 506 661 764
1998 22 116 223 330 525 832 6215
1999 27 108 229 322 469 702 5825
2000 19 97 201 323 517 818 6115
2001 18 130 278 385 543 860 6135
2002 8 254 444 520 590 1024 1155
2003 11 274 420 530 640 892 1110
2004 3 270 472 501 620 985 1190
2005 3 249 474 510 580 858 990
2006 3 267 361 462 588 5860 5930
2007 1 492 492 492 492 492 492
2008 2 288 306 328 366 396 403
Change in Percentile Value Over Time2   18.8 15.3 - - - -

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 8g) Marlborough Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 2 105 163 235 308 366 380
1998 5 73 93 190 258 286 295
1999 6 88 135 150 243 283 300
2000 7 104 150 160 260 466 590
2001 12 70 110 195 310 473 570
2002 8 135 204 285 369 402 411
2003 8 130 214 308 378 415 420
2004 5 90 182 330 363 410 422
2005 20 74 121 189 321 457 615
2006 19 72 126 200 271 533 684
2007 12 78 128 155 270 601 715
2008 22 70 129 179 274 654 750
Change in Percentile Value Over Time2   - - - - 26.0 33.6

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 8h) Northland Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 4 452 545 559 569 914 1000
1996 6 254 374 458 569 661 697
1997 3 362 475 526 534 544 547
1998 3 410 476 517 532 538 539
1999 7 138 244 348 529 615 680
2000 6 134 284 341 460 1401 1871
2001 10 146 382 432 588 829 1175
2002 13 150 381 548 618 1893 5183
2003 25 112 211 458 573 1345 4449
2004 33 115 282 453 555 986 4419
2005 32 144 307 491 591 1098 3965
2006 33 142 346 526 709 2166 4216
2007 38 139 255 495 674 1911 4499
2008 39 146 242 484 688 2398 4358
Change in Percentile Value Over Time2   -0.001 - - 0.01 0.08 0.58

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 8i) Otago Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median va

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 30 107 208 323 745 1434 1552
1996 36 86 180 482 1187 1909 2020
1997 52 3 199 369 1132 2083 2590
1998 79 91 178 343 1042 2015 4580
1999 82 101 167 338 1008 2469 9160
2000 94 91 157 276 853 4809 113716
2001 99 75 159 256 584 1423 2113
2002 93 82 150 268 565 1569 2220
2003 91 86 155 257 583 1460 2160
2004 90 85 160 246 498 1445 2085
2005 91 90 154 220 518 1435 1860
2006 91 70 129 182 390 1315 2035
2007 89 74 134 195 367 1532 2510
2008 71 91 169 258 447 1730 88571
Change in Percentile Value Over Time2   - -4.6 -16.2 -62.3 - -

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 8j) Southland Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 0            
1998 7 164 191 208 235 250 250
1999 5 152 166 200 215 246 255
2000 19 142 178 230 258 514 825
2001 23 115 177 224 269 389 516
2002 27 133 166 230 275 513 765
2003 28 119 161 208 265 498 707
2004 24 131 158 224 270 412 510
2005 30 100 155 201 257 451 547
2006 30 126 168 212 256 310 508
2007 34 114 158 212 269 402 489
2008 47 133 174 225 272 422 834
Change in Percentile Value Over Time2   -4.0 - - - - -

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 8k) Taranaki Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 64 142 286 361 698 1267 1920
1996 57 108 299 405 764 1245 1930
1997 62 111 280 359 680 1067 1890
1998 70 111 282 351 669 1301 2830
1999 56 144 275 328 628 1449 2845
2000 41 116 282 432 747 1320 2560
2001 45 151 264 365 712 1075 1725
2002 51 149 264 366 716 1668 4990
2003 34 175 264 365 798 1262 25000
2004 33 133 242 368 742 969 6130
2005 49 174 254 323 590 1010 1370
2006 57 118 223 307 491 971 3760
2007 52 147 253 377 714 2781 3430
2008 44 10 245 566 823 2950 4730
Change in Percentile Value Over Time2   - -3.7 - - - -

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 8l) Tasman Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 8 220 228 328 408 611 660
1996 10 210 220 265 350 592 650
1997 10 186 211 258 344 549 580
1998 16 165 195 215 286 532 650
1999 10 200 211 260 351 614 720
2000 10 212 223 275 359 605 690
2001 10 205 238 275 348 531 565
2002 16 140 207 223 298 491 614
2003 16 149 193 220 301 498 640
2004 16 150 209 225 310 464 518
2005 16 148 208 235 325 492 566
2006 16 153 192 222 326 408 439
2007 16 144 197 223 313 465 550
2008 16 141 198 224 320 491 673
Change in Percentile Value Over Time2   -5.7 -2.0 -4.1 -3.5 -12.0 -

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 8m) Waikato Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 49 88 148 209 261 342 412
1996 53 79 130 187 244 393 425
1997 54 91 139 211 264 373 529
1998 42 117 170 231 300 447 600
1999 38 106 163 219 247 391 630
2000 34 113 168 220 270 408 620
2001 43 88 133 214 267 401 625
2002 62 67 123 178 253 367 645
2003 99 81 129 193 270 419 660
2004 100 76 132 194 284 411 671
2005 107 74 125 196 260 406 622
2006 113 74 121 184 259 411 642
2007 110 74 118 178 239 384 1300
2008 115 79 126 199 270 443 6200
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 8n) Wellington Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 16 90 128 184 266 351 364
1996 23 100 130 178 272 344 350
1997 24 100 120 189 272 502 674
1998 25 100 133 191 265 482 644
1999 25 94 133 182 264 478 710
2000 25 106 130 181 268 481 638
2001 25 106 134 199 260 466 771
2002 25 112 140 195 267 474 639
2003 49 101 163 232 333 654 1440
2004 51 108 166 226 334 738 1200
2005 71 96 140 198 306 717 1370
2006 70 95 139 198 318 722 1480
2007 69 95 139 198 320 712 1355
2008 69 94 140 190 325 663 1350
Change in Percentile Value Over Time2   - 1.1 - 4.8 28.1 87.0

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 8o) West Coast Region calculated percentiles and maximum values for electric conductivity in groundwater (in μS/cm), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 0            
1998 6 72 79 93 108 110 110
1999 7 63 66 75 84 86 86
2000 7 55 62 70 83 88 88
2001 7 65 78 99 103 108 109
2002 4 87 96 101 103 104 104
2003 7 80 93 104 114 145 159
2004 7 51 61 72 75 78 79
2005 8 61 81 97 105 111 111
2006 8 61 66 69 74 84 88
2007 8 63 68 82 95 117 129
2008 8 70 80 90 106 123 129
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.