New Mexico Administrative Code › Title 20 - ENVIRONMENTAL PROTECTION › Chapter 6 - WATER QUALITY › Part 7 - GROUND WATER PROTECTION - SUPPLEMENTAL PERMITTING REQUIREMENTS FOR COPPER MINE FACILITIES › Section 20.6.7.20 - REQUIREMENTS FOR LEACH STOCKPILES AND SX/EW PLANTS

Current through Register Vol. 35, No. 13, July 16, 2024
A.
Engineering design
				requirements.
At a minimum, the following requirements shall be met in
				designing leach stockpiles at copper mine facilities unless the applicant or
				permittee can demonstrate that an alternate design will provide an equal or
				greater level of containment.
(1)
New
				leach stockpiles.
New leach stockpiles shall meet the following
				requirements.
(a)
Liner system.
A new leach stockpile shall be placed on an engineered liner system consisting
				of a subgrade and compacted earthen liner overlain by a synthetic liner which
				is overlain by a solution collection system designed to transmit process fluids
				out of the leach stockpile. The liner system shall be approved by the
				department prior to installation and shall be installed in accordance with a
				department approved CQA/CQC plan pursuant to Paragraph (1) of Subsection C of
				20.6.7.17 NMAC.
(b)
Liner
				system subgrade and earthen liner.
A liner system earthen liner shall be
				prepared and placed upon a stable subgrade. The prepared earthen liner shall
				consist of a minimum of 12 inches of soil that has a minimum re-compacted
				in-place coefficient of permeability of 1x10-6
				cm/sec. The top surface of the earthen liner shall be smooth and free of sharp
				rocks or any other material that could penetrate the overlying synthetic
				liner.
(c)
Liner type.
A synthetic liner for a leach stockpile shall provide the same or greater level
				of containment, including permeability, as a 60 mil HDPE geomembrane liner
				system. The liner system's tensile strength, tear and puncture resistance and
				resistance to degradation by ultraviolet light shall be compatible with design
				loads, exposures and conditions. A licensed New Mexico professional engineer
				with experience in liner system construction and installation shall identify
				the basis for the geomembrane composition and specific liner based upon:
(i) the type, slope and stability of the
				subgrade;
(ii) the overliner
				protection and provisions for hydraulic relief within the liner
				system;
(iii) the load and the
				means of applying the load on the liner system;
(iv) the compatibility of the liner material
				with process solutions applied to the leach stockpile and temperature extremes
				of the location at which it will be installed; and
(v) the liner's ability to remain functional
				for five years after the implementation of closure of the leach stockpile.
(d)
Solution
				collection system.
A solution collection system shall be constructed in
				an overliner protection and drainage system. The solution collection system
				shall be designed to remain functional for five years after the operational
				life of the leach stockpile. The overliner protection shall be designed and
				constructed to protect the synthetic liner from damage during loading and
				minimize the potential for penetration of the synthetic liner. A sloped
				collection system shall be designed that will transmit fluids out of the
				drainage layer of the leach stockpile. The collection system shall be designed
				to maintain a hydraulic head of less than the thickness of the drainage layer
				but the drainage layer shall not exceed five feet in thickness. Any penetration
				of the liner by the collection system through which a pipe or other fixture
				protrudes shall be constructed in accordance with the liner manufacturer's
				requirements. Liner penetrations shall be detailed in the construction plans
				and as-built drawings.
(e)
Solution containment systems.
PLS flows exiting the leach
				stockpile shall be collected, contained and conveyed to a process water
				impoundment(s) or tank(s) using pipelines or lined conveyance
				systems.
(f)
Alternate
				design.
An applicant may propose and the department may approve an
				alternative design for a leach stockpile located within an open pit surface
				drainage area provided that the stockpile and solution capture systems are
				designed to maximize leach solution capture considering the site-specific
				conditions of the open pit, underlying geology and hydrology, and leach
				solutions will not migrate outside of the open pit surface drainage area.