HAZARDOUS WASTE REGULATORY APPLICABILITY FOR ARSENIC RESIDUALS

The disposal of toxic, arsenic laden residuals will significantly impact the decision making process for the selection of an arsenic removal process. Historically, activated alumina (AA) and ion exchange (IX) with regeneration were thought to be the optimal removal processes for arsenic. However, the handling of arsenic laden residuals from these processes must comply with the provisions of the Resource Conservation and Recovery Act (RCRA). From a treatment system implementation standpoint, it is imperative that the applicable disposal regulations for arsenic residuals be understood so that the selection of the most appropriate technology can be made.Under RCRA a residual from an arsenic treatment facility may be defined as being hazardous waste if it has a toxicity characteristic (TC). For arsenic, the hazardous waste TC criterion is 5.0 mg/l as defined in Title 40 of the Code of Federal Regulations (CFR), Part 261.24. For liquid wastes with less than 0.5% solids, the 5 mg/l criterion is applied to the dissolved concentration of arsenic in the liquid. For liquids, sludges, or solids with a solids concentration greater than 0.5 %, the Toxicity Characteristic Leaching Procedure (TCLP) is used. If the concentration of arsenic in the leachate is greater than 5 mg/l, the liquid, sludge, or solid is defined as a hazardous waste.The IX and AA processes will generate both liquid and solid residuals. The waste brine will have a high concentration of arsenic and TDS. Most IX and AA facilities with on-site regeneration will be classified as large quantity hazardous waste generators, and possibly, hazardous waste treatment, storage and disposal facilities. This is because the waste brine mass will exceed 1000 kg per month.RCRA applicability for on-site treatment and handling of liquid arsenic residuals from IX and AA processes will be discussed in this paper. Regulations pertinent to hazardous waste treatment, storage and disposal sites for drinking water facilities that render arsenic residuals non-toxic will be presented. The appropriate facility construction, record-keeping, safety, and operator training requirements will also be discussed. The impact of these RCRA regulations on AA and IX processes with on-site regeneration will affect the selection of an arsenic removal process by utilities.