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<br />Calculating the Langelier Saturation Index <br /> <br />A simplified procedure for calculating the LSI is given below. Although the LSI cannot <br />predict all corrosion tendencies, it is a useful indicator when used within the boundaries of its <br />applicability and intent. A positive LSI means the water has a tendency to deposit CaC03; <br />a negative LSI means the water has a tendency to dissolve CaC03. An LSI of zero means <br />the water is in equilibrium with respect to CaC03; it will neither deposit nor dissolve <br />CaC03. <br /> <br />The LSI is calculated with Equation 1. <br /> <br />LSI = pH-pHs <br /> <br />(1) <br /> <br />where: <br />pH = <br />pHs = <br /> <br />pH measured at the system temperature <br />pH if water were in equilibrium with CaCO, at the existing calcium and <br />bicarbonate ion concentrations <br /> <br />pHs is defined by Equation 2. <br /> <br />( Ca ) ( Alk ) <br />pHs = K - logte - loglo + <br />40,000 50,000 <br /> <br />5A C~V - 0.31) <br /> <br />(2) <br /> <br />where: <br />K and A are temperature dependent constants found in Table 3 <br />Ca = calcium concentration, mg/! <br />Alk = total alkalinity, as CaCO" mg/! <br />I = ionic strength. <br /> <br />Ionic strength may be roughly estimated by Equation 3 (preferred) or Equation 4. <br />I = 1.6x10'sC <br /> <br />(3) <br /> <br />where: <br />C = conductivity, j.lmhos/cm (j.lS/cm) <br /> <br />1= TDS <br />40,000 <br /> <br />(4) <br /> <br />IIi] BROWN AND CALDWELL <br /> <br />5 <br />