Rapid encroachment of suburban development on former agricultural lands has greatly increased the potential for human exposure of arsenic, a group A carcinogen used extensively as pesticide prior to the 1990s. Environmental concern due to its toxicity and carcinogenicity requires the development of cost effective technologies capable of lowering bioavailable arsenic concentrations in soils to acceptable levels. Remediation of arsenic can be performed by ex-situ or in-situ methods. Ex-situ treatments are extremely expensive and generally result in destruction of the ecosystem undergoing remediation. Therefore, a novel in-situ remdiation technique - application of drinking water treatment residuals (WTRs) was evaluated in reported study. WTRs can be classified as a byproduct of drinking water treatment plants, which possess amorphous structure and generally have high positive charge. Because arsenic is chemically similar to phosphorus, the oxyanions arsenate and arsenite may have the potential to being retained by the WTRs. Thus, it is hypothesized that WTRs retain arsenic irreversibly, thereby reducing its biavailability. As the mobility of arsenic is controlled by adsorption reactions, knowledge of adsorption of arsenic by the WTRs is of primary relevance. Because arsenic adsorption appears to be influenced by the variable pH-dependent charges developed on the soil particle surfaces, the effect of pH is of critical importance. Furthermore, the sorption of arsenate onto particle surfaces can be significantly affected by the presence of competing ligands and complexing metals. In the reported study, arsenic adsorption envelopes in the presence of competing ions as a function of pH and solid solution ratios were constructed, varying initial As concentrations between 375 and 3000 mg/L. Solid/solution ratios used during the study were 1:5, 1:10 and 1:20 and pH was varied between 3 and 10. Effect of phosphate, sulfate, and selenate as competing ions were evaluated.