Method 3060 is an alkaline digestion procedure for extracting hexavalent chromium  [Cr(VI)] from soluble, adsorbed, and precipitated forms of chromium compounds in soils, sludges,  sediments, and similar  waste materials.  To quantify total Cr(VI) in a solid matrix, three criteria must  be satisfied:

(1) the extracting solution must solubilize all forms of Cr(VI),

(2) the conditions of the  extraction must not induce reduction of native Cr(VI) to Cr(III), and

(3) the method must not cause  oxidation of native Cr(III) contained in the sample to Cr(VI). 

Method 3060 meets these criteria for a wide spectrum of solid matrices.  Under the alkaline conditions of the extraction, minimal reduction  of Cr(VI) or oxidation of native Cr(III) occurs.  The addition of Mg²⁺   in a phosphate buffer to the alkaline solution has been shown to suppress oxidation, if observed.  The accuracy of the extraction  procedure is assessed using spike recovery data for soluble and insoluble forms of Cr(VI) (e.g.,  K₂Cr₂O₇   and  PbCrO₄ ),  coupled  with  measurement  of  ancillary  soil  properties,  indicative  of  the potential for the soil to maintain a Cr(VI) spike during digestion, such as oxidation reduction potential  (ORP), pH, organic matter content, ferrous iron, and sulfides.  Recovery of an insoluble Cr(VI) spike  can be used to assess the first two criteria, and method-induced oxidation is  usually not observed  except in soils high in Mn and amended with soluble Cr(III) salts or freshly precipitated Cr(OH)₃ .