There is no regulatory definition of aqueous however, for purposes of the corrosivity characteristic an aqueous waste is defined as the waste for which pH is measurable (Call Center Monthly Report Question; September 1992 RCRA Online #13561). Furthermore, Method 9040C (PDF) (5 pp, 30K) in Test Methods for the Evaluation of Solid Waste, Physical/Chemical Methods (SW-846) is the appropriate test method to determine the pH of a waste. This method is used to measure the pH of aqueous wastes and those wastes where the aqueous phase constitutes at least twenty percent of the total volume of the waste. Therefore, any waste to which this method is applicable must contain at least twenty percent free water by volume (Memo, Bussard to Franzmathes; April 23, 1993 RCRA Online #11738).
The guidance referenced above is available at the following URL: