To validate low arsenic leachability, an extended TCLP test (34) was performed for a sludge sample collected from the top of the well-aerated coarse sand filter; Figure 7 shows the results. While the sludge had approximately 32 mg As/g of dry solids, the arsenic concentration in the leachate was consistently less than 200 µg/L in the pH range of 4.3-6.3.