EPA considers a sludge to be generated at the moment of deposition at the bottom of the unit ("point of generation"). Toxicity characteristic (TC) waste may be generated from non-hazardous wastewater when hazardous constituents in wastewater become concentrated in solution or when hazardous constituents in wastewater settle and become concentrated in a sludge. Once the TC waste is generated and stored or disposed in the unit, the unit is subject to Subtitle C regulations (Memo, Lowrance to Leopold; March 8, 1991 (RCRA Online #11588)).
In addition, EPA considers hazardous waste generated when it is first produced or first becomes subject to regulation, not when the generator first analyzes the waste (Memo, Lowrance to Axtell; April 21, 1989 (RCRA Online #11424)).
Once a hazardous waste is generated it must be stored in accordance with 40 CFR §262.34. RCRA allows generators to accumulate hazardous waste on site without a permit as long as the generator complies with certain management standards for the accumulation unit(s) and for the facility, such as a contingency plan and personnel training requirements. The length of time a generator is allowed to accumulate waste varies depending on the generator's classification. For example, large quantity generators (LQG) can store waste on site for up to ninety days. LQGs may accumulate hazardous wastes only in containers, tanks, containment buildings, or on drip pads. While these units do not need RCRA storage permits when used for generator accumulation, they must comply with certain storage standards, such as release detection and prevention requirements and the unit specific standards (40 CFR Part 265).
The documents cited above are available at the following URL: www.epa.gov/rcraonline