Current through Register Vol. 35, No. 11, June 11, 2024
Section 20.6.7.22 - REQUIREMENTS FOR COPPER CRUSHING, MILLING, CONCENTRATOR, SMELTING AND TAILINGS IMPOUNDMENT UNITSA.Engineering design requirements. At a minimum, the following requirements shall be met in designing crushing, milling, concentrating, smelting and tailings impoundment units 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 crushing and milling units. New crushing and milling units, including associated ore storage, except when located within the open pit surface drainage area, shall be designed to contain and manage all materials containing water contaminants that have the potential to migrate to ground water and cause an exceedance of applicable standards on concrete or low permeability surfaces approved by the department.(2)New concentrator units. New concentrator units shall be designed to contain and manage in tank and pipeline systems designed and operated pursuant to 20.6.7.23 NMAC all materials containing water contaminants that have the potential to migrate to ground water and cause an exceedance of applicable standards. Tailing and concentrate thickener tanks may be constructed with concrete or low permeability bottoms consisting 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 tank designs shall be based on plans and specifications signed and sealed by a licensed New Mexico professional engineer. For low permeability bottoms, such plans and specifications shall describe how process rates, material density and settling rates were considered in the design to minimize infiltration such that water contaminants in the tank will not migrate to ground water and cause an exceedance of applicable standards.(3)New smelting units. New smelting units shall be designed to contain and manage on impermeable surfaces all materials, including associated slag and flue dust, containing water contaminants that have the potential to migrate to ground water and cause an exceedance of applicable standards.(4)New tailings impoundments. Tailings impoundments shall be designed according to the following requirements.(a) Stormwater run-on shall be diverted and/or contained to minimize contact between stormwater run-on and the tailing material.(b) Seepage from the sides of a tailing impoundment shall be captured and contained through the construction of headwalls, impoundments and diversion structures as applicable.(c) Ground water impacted by the tailing impoundment in excess of applicable standards shall be captured and contained through the construction of interceptor systems designed in accordance with Subparagraph (d) of Paragraph (4) of Subsection A of 20.6.7.22 NMAC.(d) The applicant shall submit design plans signed and sealed by a licensed New Mexico professional engineer along with a design report that includes the following. (i) The annual volumes and daily maximum design rates of tailings or other discharge approved by the department to be deposited in the impoundment.(ii) The topography of the site where the impoundment will be located.(iii) The geology of the site.(iv) The design footprint of the tailing impoundment.(v) The design of tailing seepage collection systems, to be proposed based on consideration of site-specific conditions.(vi) The design of stormwater diversion structures to minimize contact between stormwater run-on and the tailing material. The design shall consider the amount, intensity, duration and frequency of precipitation; watershed characteristics including the area, topography, geomorphology, soils and vegetation of the watershed; and run-off characteristics of the watershed including the peak rate, volumes and time distribution of run-off events.(vii) An aquifer evaluation to determine the potential nature and extent of impacts on ground water from the tailings impoundment based on the proposed tailings impoundment design. The aquifer evaluation shall include a complete description of aquifer characteristics and hydrogeologic controls on movement of tailing drainage and ground water impacted by the tailings impoundment.(viii) A design report for a proposed interceptor system for containment and capture of ground water impacted by the tailings impoundment based on the aquifer evaluation required in Subparagraph (d) of Paragraph (4) of Subsection A of this section. The design report shall include, at a minimum construction drawings and interceptor system performance information, recommended equipment including pumps and meters, recommended pump settings and pumping rates, methods for data collection, and a demonstration that the permittee has adequate water rights to operate the system as designed. The design report shall include a demonstration that interceptor system design will capture ground water impacted by the tailings impoundment such that applicable standards will not be exceeded at monitoring well locations specified by 20.6.7.28 NMAC. The interceptor system shall be designed to maximize capture of impacted ground water and minimize the extent of ground water impacted by the tailings impoundment.(ix) Within 120 days of seepage collection and interceptor well system construction, or liner system installation a final report shall be submitted to the department that includes complete as-built drawings and a summary of how the items in Subparagraph (a) thru Subparagraph (d) of Paragraph (4) of Subsection A of 20.6.7.22 NMAC were incorporated into the design.(e) If the department determines that the proposed tailings impoundment, seepage collection and interceptor systems when constructed and operated in accordance with the design plan specified in this paragraph would cause ground water to exceed applicable standards at monitoring well locations specified by 20.6.7.28 NMAC, the department shall require additional controls, which may include but are not limited to, a liner system as additional conditions in accordance with Subsection I of 20.6.7.10 NMAC. (5)New dry stack tailing piles. New dry stack tailings piles shall comply with the material characterization, engineering design, construction, and operational requirements of 20.6.7.21 NMAC, as applicable.B.Construction.(1)New crushing, milling, concentrating, smelting, or tailings impoundment. Construction of a new crushing, milling, concentrating, smelting, or tailings impoundment shall be performed in accordance with the applicable engineering requirements of Subsection A of 20.6.7.22 and 20.6.7.17 NMAC.(2)Existing crushing, milling, concentrating, smelting or tailings impoundments. Crushing, milling, concentrating, smelting and tailings impoundments at an existing copper mine facility in existence on the effective date of the copper mine rule are not required to meet the liner, design, and construction requirements of Subsection A of 20.6.7.22 NMAC and may continue to operate as previously authorized under a discharge permit subject to compliance with the contingency requirements of 20.6.7.30 NMAC so long as they are maintained within the existing footprint. A permit issued for such an existing crushing, milling, concentrating, smelting or tailings impoundment after the effective date of the copper mine rule may include the conditions of the existing discharge permit, which shall not be considered to be "additional conditions" under Subsection I of 20.6.7 NMAC.C.Operational Requirements.(1)Tailings impoundment operating requirements. A permittee operating a tailings impoundment shall operate the impoundment pursuant to the following requirements. (a) The tailings impoundment shall remain within the area identified in the approved design.(b) The perimeter of the tailings impoundment and any associated solution collection systems shall be inspected monthly.(c) Any evidence of instability in the tailings impoundment that could potentially result in a dam failure and an unauthorized discharge shall be reported to the department as soon as possible, but not later than 24 hours after discovery.(d) Any leaks or spills outside the tailings impoundment and any associated containment system shall be recorded and reported pursuant to 20.6.2.1203 NMAC.(e) If seeps occur, they shall be monitored on a monthly basis and an estimate of the seep flow rate shall be made. Monthly records of the seep inspections and flow rates shall be maintained and included in the site monitoring reports.(f) The monthly volume of tailings placed in the impoundment shall be recorded, maintained, and included in the site monitoring reports.(g) Tailings deposition rates shall not exceed the maximum rates approved in the discharge permit.(h) The daily tailings deposition and associated solution system collection rate shall be determined using flow meters installed in accordance with Paragraph (5) of Subsection C of 20.6.7.17 NMAC.(i) The average daily rate and monthly volume of tailings deposited and solution collected shall be recorded, maintained, and included in the site monitoring reports.(j) The placement of tailings and effluent shall be in accordance with an operating plan that describes the following: (i) the sequencing of tailings deposition on an annual basis;(ii) measures to manage the surface impoundment area to maintain adequate freeboard;(iii) operation of seepage collection systems;(iv) operation of interceptor systems;(v) operation of systems to return water to the concentrator or other locations as appropriate; and(vi) any other water management features.(k) If an interceptor system to maintain capture of ground water impacted by a tailings impoundment exists on the effective date of the Copper Rule, the permittee shall submit an interceptor system monitoring and evaluation report pursuant to 20.6.7.29 NMAC. (2)Smelting units. A permittee operating a smelting unit shall operate pursuant to the following requirements.(a) The smelting unit shall remain within the area identified in the discharge permit.(b) Slag and flue dust generated as a result of smelting activities shall be characterized, managed, and properly stored and disposed of.(c) Any leaks or spills outside the containment systems of the smelter unit shall be recorded and reported pursuant to 20.6.2.1203 NMAC.(3)Crushing, milling and concentrating unit operating requirements. A permittee operating a crushing, milling, or concentrating unit shall operate pursuant to the following requirements. (a) The crushing, milling and concentrating operations shall remain within the area identified in the discharge permit.(b) All containment system structures shall be inspected monthly.(c) Any leaks or spills of process water outside the containment system shall be recorded and reported pursuant to 20.6.2.1203 NMAC.20.6.7.22 NMAC - N, 12/1/13