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REVIEW: "An Evaluation of a Field-Based Aquatic Benchmark for Specific Conductance in Northeast Minnesota" (November 2015). Prepared by B. L. Johnson and M. K. Johnson for WaterLegacy. PREPARER: Susan M. Cormier, Ph D. National Center for Environmental Assessment--Cincinnati, Office of Research and Development, U.S. EPA DATE: February 4, 2016 Introduction The evaluation by Johnson and Johnson (2015) examined the ionic mixtures of mining effluents and their impact on northeast Minnesota waters. The authors made the following inference: Because organisms (benthic macroinvertebrates) are extirpated in Appalachian streams by mineral additions that increase specific conductivity (SC)*1to 300 microsiemens per centimeter (pS/cm) where natural background is 146 pS/cm (U.S. EPA, 2011), then organisms in waters of northeast Minnesota waters are likely to be affected by the same levels given a similar mineral composition. "Northeast Minnesota waters" defined by Johnson and Johnson (2015) refers to a portion of the Northern Lakes and Forests Level III Ecoregion 50 (Omernik, 1987), which includes parts of the Boundary Lakes and Hills (5On), the northern portion of Toimi Drumlins (50p), and North Shore Highlands (50t). The Minnesota Pollution Control Agency (MPCA, 2016) describes the Northern Lakes and Forests on their website: "This heavily forested ecoregion is made up of steep, rolling hills interspersed with pockets of wetlands, bogs, lakes and ponds. Lakes are typically deep and clear, with good gamefish populations. These lakes are very sensitive to damage from atmospheric deposition of pollutants, storm water runoff from logging operations, urban and shoreland development, mining, inadequate wastewater treatment, and failing septic systems" (MPCA accessed 1/5/2016). 1 This review uses conductivity as a measure of ionic concentration rather than as description of an electrical property of water. As ionic concentration increases, conductivity increases. Both specific conductivity and specific conductance are often used synonymously in the open literature indicating normalization or measurement at 25C. Conductivity is a property- of water expressed in units of micro-Siemens per centimeter (pS/cm). Conductance of a sample or electrical component is measured as Siemens (S). All measurements in this review refer to specific conductivity , pS/cm at 25C and background is estimated as the 25th centile o f SC measurements. 1 Sierra Club v. EPA 18cv3472 NDCA Tier 7 ED 002061 00107212-00001 The Johnson and Johnson (2015) evaluation describes the ionic mixture of effluents in northeast Minnesota. In Appalachia (U. S. EPA, 2011) and northeast Minnesota, the ionic mixture is dominated by bicarbonate and sulfate anions and calcium and magnesium cations (Thingvold et al., 1979). This finding is consistent with dominant ions for Ecoregion 50 (including Minnesota, Wisconsin, and Michigan) reported by Griffith (2014), whose study Johnson and Johnson (2015) did not cite. The data set used in the Johnson and Johnson study had a reported mean (note: not the 25th centile) background SC of 68 pS/cm in the defined regions of Ecoregion 50 (parts of 5On, 5Op, and 50t). This is less than the 25th centile SC of the data set used in the development of the central Appalachian benchmark (146 pS/cm). The Johnson and Johnson (2015) report provides evidence that where the SC is high, there are disturbed environments. In particular, the mean and maximum SC in their study area increase below mineral effluent discharges associated with mines in the northeast region of Minnesota. The study also provides evidence that benthic invertebrates are adversely affected where SC is greater than background. Where SC is greater than background, benthic invertebrate diversity and abundance decreases and the proportion of dominant genera increases. Attachment A, Table 1 of Johnson and Johnson (2015) identified the genera occurring in both central Appalachia and northeast Minnesota. Overall, the weight of evidence supports the inference that effluents that increase waterbody SC to more than 300 pS/cm have adverse effects in northeast Minnesota waters. Using effect levels developed in central Appalachia, more than 5% of these shared genera are likely to be extirpated in waters with SC >300 pS/cm. Confirmation using independent data sets Benthic invertebrate and water quality data sets collected by the MPCA had been made available to the U S. Environment Protection Agency (EPA) for research on stressor-response relationships. These data are used here to assess the validity of the Johnson and Johnson's findings. In Ecoregion 50, the MPCA data set consists of 40,585 water chemistry samples collected from less than 2000 sites between 1996-2013, with most of the water chemistry samples collected from repeated sampling in the same location in the same year between June and September. Annual site averages (geometric means) for SC and several other measured water quality parameters were calculated. The mean, median, minimum, maximum, and several quantiles for the population of sites in the data set are shown in Table 1. Sierra Club v. EPA 18cv3472 NDCA 2 Tier 7 ED 002061 00107212-00002 Table 1. Summary statistics of annual geometric mean water chemistry parameters for Ecoregion 50 (MPCA, 1996-2013) prepared for this review. Mean, minimum, 5th-95th quantiles, and maximum are shown. P aram eter SC (pS/cm ) A ik (m g/L , u n filtered ) C hi a (pg/L ) D O (m g/L ) N E b (m g/L ) N O x (m g/L ) O P (filtered, m g/L ) OP (u n filte r e d , m g/L ) T D S (m g/L ) T K N (m g/L ) T N (m g/L ) T P (m g/L ) T ransp (cm ) T S S (m g/L ) T urbidity (N T U ) N M ean 1,409 210 293 78.4 M in 23 7 .9 ^th 64 17.1 1 0 th 83 2 4 .8 2 5 th 135 4 7 .0 5 0 th 222 9 0 .8 U -i 00 7 5 th 142 9 0 th 461 220 9 5 th 567 249 M ax 1 ,4 5 8 363 200 1 ,3 6 2 616 850 149 2 .3 8 .8 0 .0 6 0 .0 9 0 .0 1 5 0 .5 0.1 0 .0 0 0 .0 0 0 .0 0 4 0 .8 1.0 4 .7 5 .8 0 .0 2 0 .0 3 0 .0 2 0 .0 3 0.005 0.006 1.5 7 .5 0 .0 4 0 .0 5 0 .0 1 0 2 .3 9 .0 0 .0 5 0 .0 7 0 .0 1 2 3 .7 1 0 .2 0 .0 7 0 .1 5 0 .0 2 5 5 .2 11.3 0 .1 4 0 .3 4 0 .0 4 5 6 .6 1 1 .9 0 .2 2 0 .6 3 0 .0 7 8 14.6 1 7 .2 1 .2 4 2 0 .8 0 .3 2 3 3 9 0 .0 1 3 0.001 0 .0 0 5 0 .0 0 5 0 .0 0 7 0.011 0 .0 2 0 0 .0 3 7 0 .0 5 8 0 .6 1 165 170 49 62 70 117 200 250 632 0 .7 7 0 .2 0 0 .4 3 0 .5 0 0 .5 9 0 .7 4 0 .9 6 799 0 .8 4 0 .1 2 0 .4 4 0 .5 0 0 .6 2 0 .7 9 1.05 1,151 0.043 0.003 0.015 0.019 0 .0 2 6 0 .0 4 2 0 .0 6 6 1 ,7 6 8 1 ,2 1 7 7 1 .5 6 .4 4 .9 3 3 .6 45 1.0 1.7 2 .0 60 3 .0 79 5.1 99 1 0 .4 223 8.1 0 .6 1.7 1.9 2 .9 5 .9 17.1 307 1.29 1 .4 9 0 .1 0 2 100 2 8 .3 5 2 .2 372 1.54 1.95 0 .1 5 4 100 5 0 .9 1 1 7 .0 780 3.91 2 1 .5 0 .9 1 122 1 ,0 7 6 453 Aik = alkalinity; Chi a = chlorophyll a; DO = dissolved oxy gen; NH3 = ammonia; NOx = oxides of nitrogen; OP = orthophosphate; TDS = total dissolved solids; TKN = total Kjeldahl nitrogen; TN = total nitrogen; TP = total phosphorous; Transp = transparency; TSS = total suspended solids; NTU = nephelometric turbidity units. Background conductivity The 25th centile of all samples from the MPCA data set (years: 1996-2013) was used to estimate the background SC for seven Level III ecoregions in Minnesota (see Figure 1). The estimated background SC for the entire Level III Ecoregion 50 in northeastern Minnesota is 135 pS/cm (90% confidence interval [Cl] 130-140 pS/cm, N = 1,409). A number of the MPCA sampling sites had paired biological and chemical measurements. The 25th centile estimated background SC for sites with paired MPCA biological and chemical measurements was 108 pS/cm (90% Cl 97-116 pS/cm, N= 735). Estimates were not made for the Level IV Ecoregions. Using either data set, Ecoregion 50 has the lowest background SC among the ecoregions in Minnesota (see Figure 1). 3 Sierra Club v. EPA 18cv3472 NDCA Tier 7 ED 002061 00107212-00003 Figure 1. Empirical cumulative distribution function (ECDF) of annual geometric mean conductivity values in ecoregions of Minnesota. The dark horizontal dashed line is the 25th centile of ECDF. Ecoregion 50 is the Minnesota ecoregion with the lowest background SC and is plotted at the far left in turquoise (data: MPCA, 1996-2013). Another water chemistry analysis was published in 2014 by Griffith for the entire Ecoregion 50 extending from northeastern Minnesota through Wisconsin and into northern Michigan. These published results were generated from data sets compiled from several EPA surveys that used probability-based sampling designs (Griffith, 2014). The 25th centile SC for that data set at the Level III Ecoregion 50 was 111 pS/cm (N = 151), which is less than in the Appalachian study data set. In comparison, Table 2 contains values from the Minnesota Environmental Quality Board MEQB (1979), which were collected between 1975 and 1977. This earlier sampling effort is confined to an area of interest consisting of 14 watersheds that are included in the Johnson and Johnson evaluation (2015). The median stream SC is reported as 55 pS/cm. Johnson and Johnson (2015) report a mean of 68 pS/cm using data from a comparable time period. Both values are less than the 25th centile background in Appalachia streams (U.S. EPA, 2011). Based on these independent data sets, it appears that, currently and 40 years ago, the background SC in the study area has been less than the background estimated from the data set used to derive the conductivity benchmark for the combined Appalachian Ecoregions 69 and 70 (U. S. EPA, 2011). This confirms the Johnson and Johnson claim. 4 Sierra Club v. EPA 18cv3472 NDCA Tier 7 ED 002061 00107212-00004 Table 2. Data from Minnesota Environmental Quality Board collected between 1975 and 1977 from streams in "Group C stations" and reproduced here for the reader's convenience Parameters Specific conductivity (pS/cm) (25C) A1(pg/L) As (pg/L) Ca (mg/L) Cd (pg/L) Cl (mg/L) Co (pg/L) Cu (pg/L) Fe (pg/L) F (mg/L) Hg (pg/L) K (mg/L) Mg (mg/L) Mn (pg/L) Na (mg/L) Ni (pg/L) Pb (pg/L) Zn (pg/L) Alkalinity (mg/L))(CaC03) TOC (mg/L) P-total (pg/L) Total Nitrogen (mg/L) SO4 (mg/L) pH Color (Pt-Co scale) Silica (mg/L) Median stream value 55 90 0.8 6.0 0.03 1.6 0.4 1.3 560 310 0.08 0.6 3 35 1.6 1.0 0.5 2.0 19 15 20 0.79 6.6 6.9 90.2 6.3 TOC = total organic carbon; P-total = total phosphorous; Pt-Co = platinum-cobalt. 5 Sierra Club v. EPA 18cv3472 NDCA Tier 7 ED 002061 00107212-00005 Biological effect Extirpation is the loss of a taxon from its normal habitat, such as a portion of a stream or geographic area. For this review, the concentration resulting in extirpation is defined as the SC level above which less than 5% of observations of a genus were made in an ecoregion, an extirpation concentrations (XC95) (U. S. EPA, 2011). Johnson and Johnson (2015, Attachment A, Table 1 of their report) identified the benthic macroinvertebrate genera occurring in both Appalachia and northeast Minnesota streams. They used XC95 values for Appalachian genera to evaluate extirpation of the same genera in northeast Minnesota streams. Using effect levels developed in central Appalachia, more than 5% of these shared genera are likely to be extirpated in waters with SC >300 pS/cm. Because Johnson and Johnson did not use Minnesota data to calculate effect levels for individual genera in northeastern Minnesota streams, there is uncertainty whether the species comprising a genus in Minnesota is similar enough to those in West Virginia for comparison. This point is important because the extirpation concentration (XC95) values represent the effect level for the most tolerant species in that genus. We were able to overcome this limitation for this review because we had a paired biological and SC data from Ecoregion 50 in Minnesota. Using the MPCA data set, we directly calculated XC95 levels for benthic invertebrates in northeastern Minnesota streams. Then, we used these Ecoregion 50-Minnesota XC95 values to predict the SC at which 5% of benthic invertebrate genera are likely to be extirpated. Estimation of specific conductivity (SC) likely to cause extirpation Paired biological and chemical data were analyzed using the MPCA data set from 1996-2013 (see Figure 2) and using the methods described in EPA (2011). XC95 values were calculated for 164 genera (see Table 3) that occurred at >25 sites in the MPCA paired data set (see Figure 2) using the methods in EPA (2011). Although the number of sites was modest (number of samples was 734, number of sites was 596) and the range of SC values is limited, the tolerance range was defined for more than 12% of genera that were analyzed, which allowed confident estimation of the SC that would result in the loss of 5% of genera. Estimation of the specific conductivity (SC) likely to extirpate 5% ofgenera In this review, extirpation of 5% of genera was used as the effect threshold. The SC level predicted to cause 5% extirpation is referred to as the hazardous concentration (HC05) (U.S. EPA, 2011). Using the available data set, the interpolated 5th centile of the ranked XC95 values (HC05) for Ecoregion 50 in Minnesota is 320 pS/cm. Note that even if a genus is not extirpated at the HC05, the abundance or ecoregion occurrences may still be reduced. The 6 Sierra Club v. EPA 18cv3472 NDCA Tier 7 ED 002061 00107212-00006 Minnesota HCos for Ecoregion 50 (320 jiS/cm) is similar to the HCos of the Appalachian study (295 pS/cm). Most samples in the MPCA data set were collected during August and September, and many salt-intolerant genera may not have been collected because they are more likely to be collected earlier in the year. Therefore, this HCos may be higher than would be obtained with a data set that included more mayfly genera which are collected in the spring and tend to be among the more intolerant genera. Also, the estimated HCos is for this review only and it does not represent a benchmark for Ecoregion 50. Additional analyses are recommended to evaluate the seasonal effects in the data set that was used for the estimate. Figure 2. Ecoregion 50 is contained in the orange area in the northeast portion of Minnesota. Circles represent paired biological and water quality sampling sites. There are fewer samples in the area bordering Canada, often referred to as the boundary waters, which are less accessible for sampling. Sierra Club v. EPA 18cv3472 NDCA 7 Tier 7 ED 002061 00107212-00007 Table 3. XC95 values for 164 genera with >25 occurrences in Ecoregion 50 of Minnesota prepared for this review G enus D olophilodes Epeorus Rhyacophila O phiogom phus Serratella B o yeria A g n e tin a Trissopelopia Xenochironom us Larsia Paraponyx Eurylophella Stictochironom us H elisom a Lopescladius Leptophlebia Leucrocuta Labiobaetis P la u d itu s Triaenodes N ilo ta n yp u s N ecto p sy c h e Liodessus P ro c lo e o n C a llib a etis C ryp to ten d ip es Valvata Ancyronyx Elexatoma Atrichopogon A cen tre lla C a rdiocladius G lo sso so m a XC95 p S /c m 191 201 254 272 283 298 302 327 335 338 338 357 361 374 390 416 435 456 464 502 510 529 559 568 620 620 620 626 626 630 650 650 650 Sam ples G enus 82 P ro to p tila 94 P sych o m yia 35 Pycnopsyche 73 C him arra 40 Ephemera 117 E p h em erella 25 N yctio p h yla x 25 P a ra te n d ip e s 36 Pteronarcys 25 Sten o n em a 33 D ixa 151 N eo p lea 46 Stenochironom us 95 X ylo to p u s 60 Elexagenia 43 Stenacron 124 Acroneuria 55 A th erix 38 E nd o ch iro n o m u s 58 Isonychia 50 N eu reclip sis 56 Labrundinia 73 O ecetis 131 P a ra g n etin a 26 Sublettea 35 Tricorythodes 26 E n a lla g m a 45 Parakiefferiella 37 Brachycentrus 29 M acronychus 164 Rheocricotopus 30 Probezzia 191 Psectrocladius X C 95 p S /c m 717 in in 719 719 719 719 719 719 719 736 736 736 736 829 859 867 867 867 867 867 872 872 872 872 872 879 879 882 882 882 912 912 Sam ples G enus 106 Rheotanytarsus 71 Tvetenia 51 N ilothaum a 277 D icra n o ta 44 C h tyso p s 144 C lin o ta n y p u s 30 G am m arus 67 Sigara 82 C era clea 184 N eo p h yla x 28 N ig ro n ia 71 Potthastia 205 S tem p ellin a 64 C h ironom us 32 Z avrelim yia 125 M icrasema 225 Antocha 211 C ryp to ch iro n o m u s 53 D icrotendipes 98 G lyp to ten d ip es 127 Taeniopteryx 198 C o n ch a p elo p ia 329 G yraulus 161 Hydropsyche 28 Lim nephilus 141 N a n o cla d iu s 53 Tanytarsus 134 T hien em a n n im yia 113 Hydraena 159 A blabesm yia 163 Ilelicopsyche 40 M accaffertium 105 M icrotendipes XC95 p S /c m 912 912 1 ,0 0 8 1 ,0 2 9 1 ,1 1 0 1 ,1 1 0 1 ,1 1 0 1,110 1 ,1 3 4 1 ,1 3 4 1 ,1 3 4 1 ,1 3 4 1,134 1 ,1 3 8 1 ,1 3 8 1 ,1 8 2 1,185 1,185 1,185 1,185 1,185 1,353 1,353 1,353 1,353 1,353 1,353 1,353 1 ,3 7 0 1 ,4 1 2 1 ,4 1 2 1 ,4 1 2 1 ,4 1 2 Sam ples 477 347 71 70 38 31 40 52 140 26 101 30 112 86 34 162 123 83 197 47 33 51 107 294 25 140 511 524 86 297 213 244 412 8 Sierra Club v. EPA 18cv3472 NDCA Tier 7 ED 002061 00107212-00008 Table 3. XC95 values for 164 genera with >25 occurrences in Ecoregion 50 of Minnesota prepared for this review (continued) G enus P seu d o ch iro n o m u s Stenelm is Tribelos T hienem anniella M icropsectra P olypedihm C rico to p u s P lem ero d ro m ia Pamchironom us Pentaneura Corynoneura C h eu m a to p syche Plydroptila Isoperla O ptioservus O xyethira P a ra ta n yta rsu s A m n ico la Bezzia C o rd u leg a ster F o ssa ria L epidostom a X C 95 p S /c m 1 ,4 1 2 1 ,4 1 2 1,412 1 ,4 1 7 1 ,4 2 6 1 ,4 4 2 1 ,4 4 7 1,447 1 ,4 4 7 1 ,4 4 7 1,451 1 ,4 5 8 1,458 1 ,4 5 8 1 ,4 5 8 1 ,4 5 8 1,458 1 ,5 2 7 1 ,5 2 7 1 ,5 2 7 1 ,5 2 7 1,527 Sam ples G enus 27 Anacaena 302 A n o p h e le s 66 B a e tis 259 C era to p sych e 275 C la d o ta n y ta rsu s 628 D ubiraphia 508 G yrinus 308 Flyalella 34 hype 56 Sim u liu m 274 Som atochlom 422 Tipula 223 Physa 42 C a en is 401 Acerpenna 233 Aeshna 238 B a etisca 80 B elo sto m a 94 B rillio 29 C a ecid o tea 49 C a lo p te ry x 267 C en tro p tilu m X C 95 p S/cm 1,594 1 ,5 9 4 1 ,5 9 4 1 ,5 9 4 1 ,5 9 4 1,594 1 ,5 9 4 1 ,5 9 4 1 ,5 9 4 1,594 1 ,5 9 4 1 ,5 9 4 1 ,8 1 8 1,825 1,998 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1,998 1 ,9 9 8 1 ,9 9 8 Sam ples G enus 39 D ixella 79 E u kiefferiella 402 F e rrissia 436 H aliplus 97 H ydatophylax 371 Iswaeon 60 Lim nophyes 436 M ystacides 62 O rconectes 463 O rth o cla d iu s 35 Paraleptophlebia 120 P a ram erina 387 P ararne triocnem us 369 Phaenopsectra 251 P o lycen tro p u s 79 Procladius 41 P seu d o clo e o n 75 P tilo sto m is 118 Sialis 39 Stem p ellin ella 259 Synorthocladius 67 X C 95 p S/cm 1,998 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1,998 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1,998 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1,998 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1 ,9 9 8 1,998 1 ,9 9 8 Sam ples 102 198 348 109 88 87 69 95 54 219 217 120 286 187 138 205 82 97 88 330 47 Conclusion The results of the analyses performed for this review support the conclusions of Johnson and Johnson (2015) concerning the effects of SC on benthic invertebrates. 1. Independent data sets from different decades confirm Johnson and Johnson's conclusion that the background SC in Ecoregion 50 in Minnesota is less than the background of the data set used to develop the SC benchmark for Ecoregions 69 and 70 in Central Appalachia. Hence, a benchmark value for SC in Ecoregion 50 is not expected to be greater than the benchmark for central Appalachia, i.e. 300 pS/cm. 9 Sierra Club v. EPA 18cv3472 NDCA Tier 7 ED 002061 00107212-00009 2. Likewise, the inference that 5% extirpation of benthic invertebrates would occur at similar conductivity levels in central Appalachia and Ecoregion 50 in Minnesota was supported by analysis of an independent data set of paired benthic invertebrate and SC data from Ecoregion 50 in Minnesota. We estimated that more than 5% of genera would be extirpated in streams greater than 320 pS/cm. However, additional analyses are needed to evaluate the effect of seasonal collection. 3. Johnson and Johnson evaluated biological effects where SC was greater than background at several mine sites and streams draining in or near the mines. SC associated with discharges and mine pits exceeded 300 pS/cm. For some sites, dilution may reduce the SC below 300 pS/cm in the waterbody, but the data are not shown and may not be available for all sites. In other cases, SC is very high (>1,000 pS/cm) and biological effects have been reported by MPCA. The severity of the effects are consistent with effects expected for increased level of SC. 4. Metal contamination, habitat alteration, temperature, and nutrient enrichment may contribute to biological effects at some of the mine sites. These stressors may exacerbate the effect, but the extirpation due to SC would still occur if these stressors were removed based on removal of other stressors and persistent effects observed in Appalachia when only conductivity was high and other stressors were low or absent (U.S. EPA, 2011; Timpano et al., 2015; Cook et ah, 2015). Johnson and Johnson (2015) make several recommendations based on their findings. These are policy decisions and are not part of this scientific review. Sierra Club v. EPA 18cv3472 NDCA 10 Tier 7 ED 002061 00107212-00010 References Cook, NA: Sarver, EA; Krometis, LH; Huang, J. (2015) Habitat and water quality as drivers of ecological system health in Central Appalachia. Ecol Eng 84:180-189. Griffith, MB. (2014) Natural variation and current reference for specific conductivity and major ions in wadeable streams of the conterminous U.S. Freshw Sci 33(1): 1--17. Johnson, BL; Johnson, MK. (2015) An evaluation of a field-based aquatic benchmark for specific conductance in northeast Minnesota. (November 2015). Prepared for WaterLegacy, St. Paul, MN. MPCA (Minnesota Pollution Control Agency). (2016) EDA: Guide to typical Minnesota water quality conditions. Accessed January 7, 2016. https://www.pca.state.imi.us/qiuck-liiiks/eda-guide-tvpical-miimesota-water-qualitvconditions. MEQB (Minnesota Environmental Quality Board). (1979) The Minnesota regional copper-nickel study 1976-1979. Volume 1. Executive Summary. August 31, 1979. St. Paul, MN: Minnesota Environmental Quality Board, State Planning Agency. Pp. 18. https://d-commons.d.umn,edu/handle/10792/2769, Omemik, JM. (1987) Ecoregions of the conterminous United States. Ann Assoc Am Geograph 77:118-125. Thingvold, D; Sather, N; Ashbrook, P. (1979) Water quality characterization of the copper-nickel water quality research area. St. Paul, MN: Minnesota Environmental Quality Board. Timpano, AJ; Schoenholtz, SH; Soucek, DJ; Zipper, CE. (2015) Salinity' as a limiting factor for biological condition in mining-influenced central Appalachian headwater streams. J Am Water Resour Assoc 51:240-250. DOI: 10.1111/jawr.l2247. U.S. EPA (Environmental Protection Agency). (2011) A field-based aquatic life benchmark for conductivity in Central Appalachian streams. [EPA/600/R-10/023F]. Washington, DC: Office of Research and Development, National Center for Environmental Assessment, http://cfpub.epa. gov/ncea/cfm/recordisplav.cfm?deid=233809. Sierra Club v. EPA 18cv3472 NDCA 11 Tier 7 ED 002061 00107212-00011