N.M. Admin. Code § 20.6.7.21

Current through Register Vol. 35, No. 21, November 5, 2024

Section 20.6.7.21 - REQUIREMENTS FOR COPPER MINE WASTE ROCK STOCKPILES

A.Material characterization requirements.

(1)Material characterization and acid mine drainage prediction. All waste rock stored, deposited or disposed of at a copper mine facility shall be evaluated for its potential to generate acid and to release water contaminants at levels in excess of the standards of 20.6.2.3103 NMAC. A plan for determining the potential of the material to release water contaminants, and the method for such evaluations shall be submitted to the department for approval in a material characterization plan that includes the following.

(a) The geologic, mineralogical, physical, and geochemical characteristics of the material stored, deposited or disposed of at the copper mine facility.

(b) A sampling and analysis plan to provide representative samples of the entire range of material stored, deposited or disposed of at the copper mine facility. The plan shall include quality assurance/quality control procedures to be implemented to ensure the validity of the sample results. The plan shall consider the following factors in collecting and establishing representative samples.

(i) lithological variations;

(ii) particle size distribution of each lithology;

(iii) hydraulic conductivity, water content and matric suction relationship for each lithology;

(iv) mineralogical and textural variations;

(v) the nature and extent of sulfide mineralization;

(vi) color variation;

(vii) degree and nature of fracturing;

(viii) variations in oxidation and reducing conditions; and

(ix) the nature and extent of secondary mineralization.

(c) A static testing program using, at a minimum, acid/base accounting, or a department approved equivalent testing method, to evaluate the acid generation and neutralization potential of the material; and meteoric water mobility procedure or other department approved method for whole rock testing to determine water contaminant leaching potential.

(d) If the results of static testing indicate that a material may be acid generating or may generate a leachate containing water contaminants, a kinetic testing program shall be proposed to evaluate reaction rates, provide data to estimate drainage quality, the lag time to acidification of the material, and primary weathering and secondary mineral precipitation/dissolution as it may affect acidification, neutralization and drainage quality. The length of and means of determining when kinetic tests will be discontinued shall be approved by the department prior to implementation of the kinetic testing program.

(e) If the results of the static testing or kinetic testing indicate that the material will be acid generating or generate water contaminants, and the materials will be placed outside of an open pit surface drainage area, a plan shall be submitted to the department to evaluate whether discharges of leachate from the stockpile may cause an exceedance of applicable standards, including an evaluation of the geology and hydrology of the area where the material is to be placed. The plan may include either a department approved model or other department approved demonstration.

(f) If an interceptor system pursuant to Subparagraph (d) of Paragraph (1) of Subsection B of this section or a liner system is proposed for storage or disposal of waste rock, the kinetic testing program is not required.

(2)Material handling plan. A permittee shall manage waste rock that may generate or release water contaminants according to a material handling plan approved by the department. The material handling plan shall address:

(a) segregation of acid generating materials and materials that may generate or release water contaminants and the method for handling, storage or disposal of the materials in a manner designed to prevent an exceedance of applicable standards;

(b) stockpiling of non-acid generating materials for potential use in neutralizing acid generating materials or in reclamation;

(c) blending or layering of material types to maximize the benefit of acid neutralizing material;

(d) any chemical amendments of the waste rock;

(e) a description of any proposed containment system(s) proposed in accordance with Subsection B of 20.6.7.21 NMAC.

B.Engineering design requirements for new waste rock stockpiles. At a minimum, the following requirements shall be met in designing engineered structures for waste rock 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 waste rock stockpiles located outside an open pit surface drainage area. New waste rock stockpiles located outside an open pit surface drainage area shall meet the following requirements unless the applicant or permittee demonstrates through material characterization or implementation of a material handling plan pursuant to Subsection A of this section that the waste rock pile will not cause an exceedence of applicable standards.

(a) Stormwater run-on shall be diverted or contained to minimize contact between stormwater run-on and the stockpiled material.

(b) Seepage from the sides of a waste rock stockpile shall be captured and contained through the construction of headwalls, impoundments and diversion structures as applicable.

(c) Ground water impacted by waste rock stockpiles in excess of applicable standards shall be captured and contained through the construction of interceptor systems as applicable.

(d) The applicant shall submit design plans signed and sealed by a qualified licensed New Mexico professional engineer along with a design report that includes the following.

(i) The proposed areal extent and configuration of the waste rock stockpile.

(ii) The topography of the site where the waste rock stockpile will be located.

(iii) The geology of the site.

(iv) The design of waste rock stockpile seepage collection systems, to be proposed based on consideration of site-specific conditions.

(v) The design of stormwater diversion structures to minimize contact between stormwater run-on and the waste rock 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.

(vi) An aquifer evaluation to determine the potential nature and extent of impacts to ground water from the waste rock stockpile based on the proposed waste rock stockpile design and geochemical characteristics. The aquifer evaluation shall include a complete description of aquifer characteristics and hydrogeologic controls on the movement of leachate from the waste rock stockpile and ground water impacted by the waste rock stockpile based on actual field data.

(vii) A design report for a proposed interceptor system for containment and capture of ground water impacted by the waste rock stockpile based on the aquifer evaluation required in Subparagraph (d) of Paragraph (1) of Subsection B 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 the interceptor system design will capture ground water impacted by the waste rock stockpile such that applicable standards will not be exceeded at monitor 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 waste rock stockpile.

(viii) within 120 days of completion of seepage collection and interceptor 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) of Paragraph (1) of Subsection B of 20.6.7.21 thru Subparagraph (d) of Paragraph (1) of Subsection B of 20.6.7.21 NMAC were incorporated into the design.

(e) If the department determines that the proposed waste rock stockpile, seepage collection and interceptor systems when 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 H of 20.6.7.10 NMAC.

(2)New waste rock stockpiles located inside an open pit surface drainage area. Stormwater run-on shall be diverted or contained to minimize contact between stormwater run-on and the stockpiled material.

C.Construction.

(1)New waste rock stockpiles. Construction of a new waste rock stockpile shall be performed in accordance with the applicable engineering requirements of Subsection B of 20.6.7.21 NMAC and 20.6.7.17 NMAC.

(2)Existing waste rock stockpiles. A waste rock stockpile in existence on the effective date of the copper mine rule is not required to meet the design and construction requirements of Subsection B of 20.6.7.21 NMAC and may continue to operate as previously authorized under a discharge permit unless ground water monitoring of the stockpile pursuant to 20.6.7.28 NMAC requires implementation of corrective action under Subsection A of 20.6.7.30 NMAC. A permit issued for such an existing waste rock stockpile 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.

D.Operational requirements. A permittee operating a waste rock stockpile shall operate the stockpile pursuant to the following requirements.

(1) The stockpile shall remain within the area identified in the approved design plan required in Paragraph (1) of Subsection B of 20.6.7.21 NMAC.

(2) The perimeter of the stockpile and the solution collection systems shall be inspected monthly.

(3) Any evidence of mass instability in the stockpile that could potentially result in a slope failure that may result in an unauthorized discharge shall be reported to the department as soon as possible, but not later than 24 hours after discovery and corrected pursuant to Subsection H of Section 20.6.7.30 NMAC.

(4) Any leaks or spills of leachate outside the waste rock stockpile and any associated containment system shall be recorded and reported pursuant to 20.6.2.1203 NMAC.

(5) 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.

(6) Interceptor system collection rates shall be determined using flow meters installed in accordance with Paragraph (5) of Subsection C of 20.6.7.17 NMAC.

(7) The placement of waste rock shall be in accordance with an operating plan that describes the sequencing of waste rock deposition on an annual basis, operation of seepage collection systems, operation of interceptor systems, operation of systems to return water to the concentrator or other locations as appropriate, and any other water management features.

(8) If an interceptor system to maintain capture of ground water impacted by a waste rock stockpile exists, the permittee shall submit an interceptor system monitoring and evaluation report pursuant to 20.6.7.29 NMAC.

N.M. Admin. Code § 20.6.7.21

20.6.7.21 NMAC - N, 12/1/13