Freeboard Determination and Management in Hazardous Waste Surface Impoundments

A rule-of-thumb minimum freeboard requirement of two feet (60 cm) has been used in the past for hazardous wa ste sur face impoundments. In many situations, however, this minimum value may not be su fficient to preve nt over topping. Consequently, a procedure was developed tor calculating freeboard values in surface impoundments where the liquid depths are shallow and fetches are short, as is typical In hazardous waste surface impoundments. The procedure takes into account all of the parameters that influence freeboard and presents the information in a format that can be used on a site-specific basis. Additional support information in the full report includes an example calculation of freeboard requirement, site specific data obtained from research using a mass liquid balance, and a listing of the various types of liquid level detec tion equipment
he purpose of the full document is to present all of the information necessary to calculate freeboard requirements on site-specific basis. Section 3.0 presents the procedure for calculating freeboard and provides a discussion of the factors that influence freeboard, such as fetch, liquid depth, wave height and period, wind set-up, and wave run-up. Each factor is discussed and incorporated into the mathematical procedure for determining free board. Section 4.0 presents information on two basic methods for detecting and maintaining a predetermined liquid level . Both methods, active and passive level control, are discussed along with suggested safety margins.
Supplemental material included in the appendices is intended to augment the information presented in the body of the document. The appendices include: (1) the procedure for calculating freeboard using a hypothetical surface impoundment design; (2) data collected from a field study on a liquid mass balance at a surface 1mpoundment; and (3) a discussion of vanous types of liquid level detection equipment that are currently available.