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Solidification/stabilization (S/S) of chromium contaminated soils is influenced by the oxidation state of the chromium. The sum of the hexavalent chromium and trivalent chromium represent the total chromium concentration which is used to determine whether the soil meets the criteria for chromium in the Toxicity Characteristic Leaching Procedure (TCLP) or whether the levels of chromium in applicable extractions are below the drinking water standard. Hexavalent chromium is the more mobile form of chromium and also the more toxic.
Seven vendors and the U.S. Army Engineer Waterways Experiment Station (WES) evaluated SIS treatment of chromium contaminated soils collected from a Superfund site. Physical and chemical tests were conducted on the untreated and treated soils to determine the effectiveness of SIS treatment. Physical tests were conducted by the WES and included the unconfined compressive strength (UCS) , wet/dry durability, permeability, moisture content, Atterbery limits, Proctor density, bulk density, specific gravity, slump, cracking, bleed water, and resistance to penetration. Chemical tests conducted on the untreated and treated soils included the Toxicity Characteristic Leaching Procedure (TCLP), one extraction of the Monofilled Waste Extraction Procedure (MWEP-l), and bulk chemistry analyses. The chemical extractions and bulk chemistry analyses were conducted by personnel from Radian, Inc.