Utilizing Industrial Ash to Stabilize Arsenic in Soil Contaminated From Chromated Copper Arsenate (CCA) Treated Wood

From 1980 to 1985, Shelby Wood Specialty Inc. operated on a 0.8 hectare site in Tenaha, Texas. As part of their operation, chromated copper arsenate (CCA) was used to pressure treat wood products. During the company's operation, CCA leached from stockpiled wood products contaminating nearby soil. A soil column study was performed to test what type and concentration of industrial fly ash would effectively stabilize arsenic in CCA contaminated soils. The types of fly ash used were wood fly ash, Class C coal fly ash, and Class F coal fly ash. Each ash type was tested at 0, 4, 10, 16, and 22 percent of soil volume. Weekly rain simulations were performed for 7 weeks by treating the columns with a 250 ml synthetic rain solution. Arsenic mobility was measured using Inductively Coupled Plasma (ICP) analysis, with a detection limit of 0.0265 ppm for arsenic, of leachate samples collected from the treated soil columns. A two way analysis of variance (ANOVA) of data showed a significant interaction between time and treatments (P<0.0001). Arsenic concentrations in leachate from wood fly ash treatments generally increased with increasing ash concentrations, whereas Class C coal fly ash showed increasing arsenic concentrations with decreasing ash concentrations. Class F coal fly ash did not indicate any trend for any treatment. Due to an elevated soil pH of 8.1 at the contaminated site treatments were found to be ineffective for this site. Arsenic has been found to be less soluble at mid-range pH. Therefore, the soil pH on the site may have effectively reduced arsenic mobility. Increased arsenic in wood fly ash leachate however was detected and attributed to mobilization by organic carbon in the fly ash. Although ash stabilization was ineffective on this site, the ability for fly ash to act as a stabilizing medium may be correlated to the liming efficiency of the ash. Therefore, a second experiment was conducted to test the liming effectiveness of each ash type. For this experiment, 10 percent by soil volume of each ash type was mixed with a moist sandy loam soil (pH 5.1) and hydrogen ion concentration was measured once every 3 days over a 12-day period. A two-way ANOVA of data showed no significant interaction to occur between time and treatment (P=0.5304). All ash treatments were significantly different from the control (P<0.0001), but not each other. Although not significantly different, general trends showed Class C coal fly ash was the most effective liming agent tested, having a greater effect on soil hydrogen ion concentration than both the wood and Class F coal fly ash. This may be due to higher calcium carbonate and magnesium carbonate content in the Class C coal fly ash as compared to the wood fly ash and Class F coal fly ash which ranked second and third in liming equivalency, respectively.