Oregon Administrative Rules › Chapter 340 - DEPARTMENT OF ENVIRONMENTAL QUALITY › Division 43 - CHEMICAL MINING › Section 340-043-0120 - Guidelines for the Design, Construction, Operation and Closure of Chemical Mining Operations: Guidelines for Design, Construction, and Operation of Heap-Leach Facilities

Current through Register Vol. 63, No. 7, July 1, 2024
(1) This
			 section applies to heap-leach facilities using dedicated, or expanding, pads.
			 Heap-leach facilities using on-off, reusable pads may require variations from
			 these rules; they shall be approved on a case-by-case basis by the
			 Department.
(2) The heap-leach
			 facility (pad and associated ponds, pipes and tanks) shall be sized to prevent
			 flooding of any of its components.
(3) Table 1 of this Division establishes
			 minimum capacity-sizing criteria for the leach-pad and ponds. The pad and ponds
			 may be designed to act separately or in conjunction with each other to obtain
			 the required storage volumes. Other design criteria may be used, with
			 Department approval, if local conditions warrant. The best available climatic
			 data shall be used to confirm the critical design storm event and estimate the
			 liquid levels in the system over a full seasonal cycle. The liquid mass balance
			 may include provision for evaporation.
(4) The heap leach pad liner system shall be
			 designed, constructed, and operated to meet the following criteria:
(a) A primary liner consisting, at a minimum,
			 of a continuous flexible-membrane of suitable synthetic material shall be
			 provided. This liner shall function together with the process chemical
			 collection system installed immediately above this liner (see section (8) of
			 this rule) to remove process chemicals from the heap;
(b) A leak detection system shall be
			 installed immediately below the primary liner for the purpose of detecting loss
			 of process solutions by leakage through the primary liner. The leak detection
			 system shall be capable of detecting leakage through the primary liner of 400
			 gallons/day-acre within ten weeks of leak initiation. The leak detection system
			 shall consist of appropriately sized collection piping placed within a minimum
			 thickness of 12 inches of permeable material (minimum permeability of 10-2
			 cm/sec) that is capable of withstanding the anticipated weight of the heap
			 without loss of function;
(c) A
			 secondary liner shall be placed below the leak detection system to provide
			 assurance that any leakage through the primary liner during the operation of
			 the heap and following closure of the heap is not released to the environment.
			 The secondary liner shall be of a composite design with a continuous
			 flexible-membrane of suitable synthetic material in direct contact with an
			 engineered, stable, low permeability soil/clay bottom liner (maximum
			 permeability of 10-7 cm/sec) with a minimum thickness of 36 inches;
(d) Each liner system component described in
			 subsections (4)(a)-(c) of this rule addresses a specific need and purpose with
			 respect to environmental protection. For purposes of evaluating alternative
			 facilities and methods of control under OAR 340-043-0050(2), an alternative may
			 be approved if the level of environmental protection intended by each separate
			 liner system component is achieved either within the individual component or on
			 a cross component basis.