Policy and technical guidance for conversion of sediment concentration from parts per million (ppm) to milligrams per liter (mg/L) In Reply Refer To: August 9, 1993 Mail Stop 415 OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 93.21 SUBJECT: Policy and technical guidance for conversion of sediment concentration from parts per million (ppm) to milligrams per liter (mg/L) Beginning with the 1972 Water Year, conversion factors given in Techniques of Water-Resources Investigations (TWRI), Book 5, Chapter C1, page 4, "Laboratory theory and methods for sediment analysis," were superseded by conversion factors given in a new table in Quality of Water Branch Technical Memorandum No. 72.10. Since Memorandum 72.10 was issued, there have been a few instances where Water Resources Division (WRD) sediment laboratory computer programs have produced different concentrations, expressed as mg/L, than those computed following guidelines in Memorandum 72.10. The differences apparently result from the use of different rounding and interpolation methods. The reported differences have been small, but their occurrence indicates that guidelines are needed to ensure that concentration data are processed uniformly throughout WRD. The purpose of this memorandum is to provide guidelines for the use of standard conversion factors to convert sediment concentrations, expressed in parts per million (ppm), to milligrams per liter (mg/L). The following equation should be used as the primary method for converting concentrations, expressed in ppm, to values expressed in mg/L. The equation provides an exact solution which is suitable for laboratory computer programs. Table 1, which is a revised version of the two tables in Memorandum 72.10, is also acceptable for use under most conditions (see assumptions under which Table 1 was derived). Interpolation is required for values that are outside of the concentration ranges given in the table. The equation for converting ppm to mg/L is: Milligrams per liter Ds x Dw x 1,000,000 C = -------------------- = --------------------------------- Parts per million Ds x 1,000,000 - [(Ds - Dw) x ppm] where C = conversion factor (The concentration, in ppm is multiplied by C to obtain concentration, in mg/L) Ds = density of sediment, in grams per cubic centimeter Dw = density of water, in grams per cubic centimeter ppm = sediment concentration, in parts per million For sediment with a specific gravity of 2.65, The equation reduces to: Milligrams per liter 2,650,000 C = -------------------- = ------------------------ Parts per million 2,650,000 - (1.65 x ppm) Table 1.--Conversion factors for sediment concentration: Parts per million to milligrams per liter. (Revised from Quality of Water Branch Technical Memorandum No. 72.10) [The factors are based on the assumption that the density of water is 1.00, the range of temperature is 0-20o C, the specific gravity of sediment is 2.65, and the dissolved solids concentration is less than 10,000 ppm.] __________________________________________________________________ Concentration C Concentration C range (ppm) range (ppm) __________________________________________________________________ 0- 7,990 1.00 327,000 336,000 1.26 8,000 23,700 1.01 337,000 346,000 1.27 23,800 39,200 1.02 347,000 356,000 1.28 39,300 54,300 1.03 357,000 366,000 1.29 54,400 69,200 1.04 367,000 375,000 1.30 69,300 83,700 1.05 376,000 385,000 1.31 83,800 98,000 1.06 386,000 394,000 1.32 98,100 112,000 1.07 395,000 403,000 1.33 113,000 126,000 1.08 404,000 412,000 1.34 127,000 139,000 1.09 413,000 421,000 1.35 140,000 153,000 1.10 422,000 429,000 1.36 154,000 166,000 1.11 430,000 438,000 1.37 167,000 178,000 1.12 439,000 446,000 1.38 179,000 191,000 1.13 447,000 455,000 1.39 192,000 203,000 1.14 456,000 463,000 1.40 204,000 *216,000 1.15 464,000 471,000 1.41 *217,000 227,000 1.16 472,000 *479,000 1.42 228,000 239,000 1.17 480,000 487,000 1.43 240,000 251,000 1.18 488,000 495,000 1.44 252,000 262,000 1.19 496,000 502,000 1.45 263,000 273,000 1.20 503,000 510,000 1.46 274,000 284,000 1.21 511,000 517,000 1.47 Table 1.--Conversion factors for sediment concentration: Parts per million to milligrams per liter. (Revised from Quality of Water Branch Technical Memorandum No. 72.10) (Continued) [The factors are based on the assumption that the density of water is 1.00, the range of temperature is 0-20o C, the specific gravity of sediment is 2.65, and the dissolved solids concentration is less than 10,000 ppm.] __________________________________________________________________ Concentration C Concentration C range (ppm) range (ppm) __________________________________________________________________ 285,000 295,000 1.22 518,000 525,000 1.48 296,000 306,000 1.23 526,000 532,000 1.49 307,000 316,000 1.24 533,000 539,000 1.50 317,000 326,000 1.25 --- --- --- _________________________________________________________________ *Revised from Quality of Water Branch Technical Memorandum 72.10 Charles W. Boning Chief, Office of Surface Water WRD DISTRIBUTION: A, B, FO, PO