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COLORADO <br />,; •` Department of Public <br />Health b Environment <br />meq/1 = <br />Concentration in mg1l <br />Equivalent weight in mg/meq <br />Water Quality Assessment <br />Where the equivalent weights are determined based on the atomic weight of the element divided by the <br />ion's charge: <br />Na' = 23.0 mg/meq (atomic weight of 23, charge of 1) <br />Ca" = 20.0 mg/meq (atomic weight of 40.078, charge of 2) <br />Mg" = 12.15 mg/meq (atomic weight of 24.3, charge of 2) <br />The SAR standard is established using the SAR/EC equation, shown graphically in Figure A-2, which is <br />reproduced herein from the Ag Policy. Since the allowable SAR value is tied to the actual EC of the effluent, <br />the EC/SAR equation (SAR = (7.1 * EC) - 2.48) will be the SAR limit in the permit, however the allowable SAR <br />of the effluent will be capped at the value above or 9, whichever is less. Due to the effect of bicarbonate <br />on the available calcium and magnesium, limitations will be expressed as adjusted SAR, which accounts for <br />bicarbonate. This is explained in more detail in the fact sheet and permit documents. <br />Figure A-2: Relative Rate of Water Infiltration as Affected by EC W and SAR with Modification to Show <br />Upper Limit for SAR = 9 <br />20- <br />0 - <br />16- <br />16- <br />W <br />W <br />0 12 - <br />CC <br />r- <br />0 <br />EL <br />o $- <br />O <br />CO 4 - <br />I i 1 e <br />2 3 4 5 <br />Electrical Conductivity (ECW) of Irrigation Water <br />Page 27 of 40 <br />4300 Cherry Creek Drive S., Denver, CO 80246-1530 303-692-2000 www.colorado.gov/cdphe/wgcd I <br />, <br />r <br />, <br />, <br />Maximum <br />SAR = 9 <br />/AMVMfa <br />l <br />I i 1 e <br />2 3 4 5 <br />Electrical Conductivity (ECW) of Irrigation Water <br />Page 27 of 40 <br />4300 Cherry Creek Drive S., Denver, CO 80246-1530 303-692-2000 www.colorado.gov/cdphe/wgcd I <br />