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Regulation No. 31 Table III Metal Parameters: Calculator for Hardness-based Equations
(updated February 26, 2021)
Download this document as an Excel file for personal use.
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This table shows the hardness-based table value standards calculated at hardness values ranging from 25 - 400 mg/L (Columns D - N).
It also includes a calculator to generate standards using a site-specific hardness value (Column O).
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Hardness values to be used in equations are in mg/L as calcium carbonate (CaCO3) and shall be no greater than 400 mg/L. The exception is for aluminum, where the upper cap on calculations is a hardness of 220 mg/L.
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If data for hardness as CaCO3 are not available, hardness can be calculated using calcium and magnesium data in the "Hardness Calculator" tab.
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Source: Regulation No. 31 - The Basic Standards and Methodologies for Surface Water
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To generate the standards for a given site, enter the site-specific hardness value (as CaCO3) here: 250
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ParameterEquationMean Hardness in mg/L as CaCO3a
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255075100150200220250300350400Site-specific Hardness
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Aluminum (µg/L, total recoverable)b
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Acute
e(1.3695*ln(hardness)+1.8308)
5121,3242,3073,4215,9608,83810,07110,07110,07110,07110,07110,071
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Chronic
e(1.3695*ln(hardness)-0.1158)
731893294888511,2621,4381,4381,4381,4381,4381,438
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Cadmium (μg/L, dissolved)c,d
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Acute(warm)
cfa*e(0.9789*ln(hardness)-3.443)
0.751.432.092.744.005.235.726.447.648.829.996.44
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Acute(cold)
cfa*e(0.9789*ln(hardness)-3.866)
0.490.941.371.792.623.433.754.225.005.786.544.22
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Chronic
cfc*e(0.7977*ln(hardness)-3.909)
0.250.430.580.720.971.211.301.431.641.842.031.43
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Chromium III (μg/L, dissolved)
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Acute
e(0.8190*ln(hardness)+2.5736)
1833234505707941005108712071401159017731207
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Chronic
e(0.8190*ln(hardness)+0.5340)
24425974103131141157182207231157
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Copper (μg/L, dissolved)
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Acutee(0.9422*ln(hardness)-1.7408)3.67.010.213.419.725.828.231.937.843.849.631.9
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Chronic
e(0.8545*ln(hardness)-1.7428)
2.75.07.09.012.716.217.619.622.926.129.319.6
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Lead (μg/L, dissolved)c
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Acute
cfa*e(1.273*ln(hardness)-1.460)
13.9304765100136151172209245281172
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Chronic
cfc*e(1.273*ln(hardness)-4.705)
0.541.171.842.523.905.315.876.728.139.5410.96.7
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Manganese (μg/L, dissolved)
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Acutee(0.331*ln(hardness)+6.4676)188123702713298634173761388240514305453247384051
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Chronice(0.331*ln(hardness)+5.8743)104013091499165018882078214522382379250426182238
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Nickel (μg/L, dissolved)
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Acutee(0.8460*ln(hardness)+2.253)14526036746866084291210171186135115131017
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Chronic
e(0.8460*ln(hardness)+0.0554)
162941527393101113132150168113
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Silver (μg/L, dissolved)
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Acute0.5*e(1.72*ln(hardness)-6.52)0.190.61.22.04.16.697.99.813.417.522.09.8
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Chronic(trout)e(1.72*ln(hardness)-10.51)0.010.020.050.080.150.250.290.360.500.650.810.36
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Chronice(1.72*ln(hardness)-9.06)0.030.10.20.30.61.11.21.52.12.83.51.5
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Uranium (μg/L, dissolved)e
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Acute
e(1.1021*ln(hardness)+2.7088)
521111917502402375651575728659580629555110706595
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Chronic
e(1.1021*ln(hardness)+2.2382)
3266991093150123463221357841195036596869154119
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Zinc (μg/L, dissolved)f
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Acute
0.978*e(0.9094*ln(hardness)+0.9095)
4585123160231301328368435500564368
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Chronic(sculpin)e(2.140*ln(hardness)-5.084)6.12764118----------------
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Chronic
e(0.9094*ln(hardness)+0.6235)
346593121175228248279329379428279
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Notes:
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a Hardness values to be used in equations are in mg/l as calcium carbonate and shall be no greater than 400 mg/l. The exception is for aluminum, where the upper cap on calculations is a hardness of 220 mg/l.
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b Where the pH is equal to or greater than 7.0 in the receiving water after mixing, the chronic hardness-dependent equation will apply. Where pH is less than 7.0 in the receiving water after mixing, either the 87 µg/l chronic total recoverable aluminum criterion or the criterion resulting from the chronic hardness-dependent equation will apply, whichever is more stringent.
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c Acute (cfa) and chronic (cfc) conversion factors for cadmium and lead are provided in the table below.
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d The acute(warm) cadmium equation applies to segments classified as Aquatic Life Warm Class 1 or 2. The acute(cold) cadmium equation applies to segments classified as Aquatic Life Cold Class 1 or 2.
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e When applying the table value standards for uranium to individual segments, the Commission shall consider the need to maintain radioactive materials at the lowest practical level as required by Section 31.11(2) of the Basic Standards regulation.
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f The chronic zinc equation for sculpin applies in areas where mottled sculpin are expected to occur and hardness is less than or equal to 102 mg/L CaCO3. The regular chronic zinc equation applies where mottled sculpin are expected to occur, but the hardness is greater than 102 mg/L CaCO3. The regular chronic zinc equation also applies where mottled sculpin are not expected to occur.
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Conversion Factors (cf) Used in the Table Above
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Cadmiumcfa
1.136672-(ln(hardness)*0.041838)
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Cadmiumcfc
1.101672-(ln(hardness)*0.041838)
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Leadcfa
1.46203-(ln(hardness)*0.145712)
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Leadcfc
1.46203-(ln(hardness)*0.145712)
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