N.M. Admin. Code § 20.6.7.17

Current through Register Vol. 35, No. 23, December 10, 2024

Section 20.6.7.17 - GENERAL ENGINEERING AND SURVEYING REQUIREMENTS

A.Practice of engineering. All plans, designs, drawings, reports and specifications required by the copper mine rule that require the practice of engineering shall bear the seal and signature of a licensed New Mexico professional engineer pursuant to the New Mexico Engineering and Surveying Practice Act, Sections 61-23-1 through 61-23-33, NMSA 1978, and the rules promulgated under that authority.

B.Practice of surveying. All plans, drawings and reports required by the copper mine rule that require the practice of surveying shall bear the seal and signature of a licensed New Mexico professional surveyor pursuant to the New Mexico Engineering and Surveying Practice Act, Sections 61-23-1 through 61-23-33, NMSA 1978, and the rules promulgated under that authority.

C.Engineering plans and specifications requirements. The following engineering plans and specifications and associated requirements shall be submitted to the department for approval with an application for a new, renewed or modified discharge permit, as applicable.

(1)Liner system plans and specifications. An applicant or permittee proposing or required to construct a new or improve an existing liner system required by the copper mine rule or an existing discharge permit, including the repair, modification or replacement of a liner system, shall include the following elements in all liner system plans and specifications submitted to the department.

(a)Construction plans and specifications. Detailed and complete construction plans and specifications and supporting design calculations developed pursuant to this section and 20.6.7.18 and 20.6.7. 20 through 20.6.7.26 NMAC shall be submitted to the department.

(b)Liner system CQA/CQC. The construction and installation of all liner systems and the repair, modification or replacement of a liner system shall be conducted in accordance with a construction quality assurance/construction quality control (CQA/CQC) plan. A CQA/CQC plan shall be included as part of the design plans and specifications. The CQA/CQC plan shall specify the observations and tests to be used to ensure that construction of the liner system meets all design criteria, plans and specifications. All liner system testing and evaluation reports for liner construction and installation, including modifications and replacements shall be signed and sealed by a licensed New Mexico professional engineer with experience in liner system construction and installation. The CQA/CQC plan shall include the following elements.

(i) the identity of persons responsible for overseeing the CQA/CQC program. The person responsible for overseeing the CQA/CQC plan shall be a licensed New Mexico professional engineer with experience in liner system construction and installation;

(ii) an inspection protocol;

(iii) identification of field and laboratory testing equipment and facilities proposed to be used, and calibration methods;

(iv) the procedures for observing and testing the liner, subgrade, liner bedding, and other liner system construction material;

(v) a protocol for verification of any manufacturers' quality control testing and procedures;

(vi) the procedures for reviewing inspection test results and laboratory and field sampling test results;

(vii) the actions to be taken to replace or repair liner material, subgrade, liner bedding, or other liner system construction materials should deficiencies be identified;

(viii) the procedures for seaming synthetic liners;

(ix) the reporting procedures for all inspections and test data; and

(x) the submission of a CQA/CQC report.

(c)Management of process water, solids and sludge or impacted stormwater during liner system improvement. An applicant or permittee proposing or required to improve copper mine facility operational units that requires the use of a liner system, including re-lining or replacement of an existing liner system, shall submit a plan for managing process water, solids and sludges, or impacted stormwater during preparation and construction of the improvement. The plan shall be submitted as part of the design plans and specifications. The plan shall include the following minimum elements.

(i) a plan for handling and disposal of process water, solids and sludges and impacted stormwater discharges during improvement to the impoundment;

(ii) a plan for removal and disposal of process water, solids and sludges or impacted stormwater within the liner system prior to beginning improvement to the liner system;

(iii) a plan and schedule for implementation of the project; and

(iv) if the plan proposes a temporary location for the discharge of process water, solids and sludge, or impacted stormwater not authorized by the effective discharge permit, the applicant or permittee shall request temporary permission to discharge from the department pursuant to Subsection B of Section 20.6.2.3106 NMAC.

(d)Dam safety. An applicant or permittee proposing or required to construct a tailings impoundment shall submit documentation of compliance with the requirements of the dam safety bureau of the state engineer pursuant to Section 72-5-32 NMSA 1978, and rules promulgated under that authority, unless exempt by law from such requirements.

(2)Tank, pipeline, sump or other containment system plans and specifications. An applicant or permittee proposing or required to construct a new tank, pipeline, sump or other containment system for the management of tailings, process water or other water contaminants shall submit detailed and complete construction plans and specifications and supporting design calculations developed pursuant to this section and 20.6.7.23 NMAC. The construction plans and specifications for an improvement(s) or replacement of an existing tank, pipeline, sump or other containment systems shall address the management of solids, waste, process water or other water contaminants generated during preparation and construction of the improvements or replacement. This requirement does not apply to portable or temporary tanks, pipelines, sumps, or other containment systems that are subject to periodic relocation during mining operations.

(3)Process water or impacted stormwater treatment system plans and specifications. An applicant or permittee proposing or required to construct a treatment system during mine operations for process water or impacted stormwater to be treated prior to discharge shall submit detailed and complete construction plans and specifications and supporting design calculations developed pursuant to this section and 20.6.7.18 NMAC.

(4)Impacted stormwater management plans and specifications. An applicant shall submit stormwater management plans and specifications to limit run-on of stormwater and manage impacted stormwater in a manner which prevents water pollution that may cause an exceedance of the applicable standards. The plans and specifications shall be submitted with an application for a new or renewed discharge permit, or as applicable with an application for a modified discharge permit, and shall include the following information.

(a) A scaled map of the copper mine facility showing:

(i) the property boundaries of the copper mine facility and the mining areas;

(ii) all existing and proposed structures;

(iii) existing and proposed final ground surface contours outside of the open pit surface drainage area at appropriate vertical intervals; and

(iv) existing and proposed stormwater containment and conveyance structures, including construction materials, size, type, slope, capacity and inlet and invert elevation (or minimum and maximum slopes) of the structures, as applicable.

(b) A description of existing surface water drainage conditions.

(c) A description of the proposed post-development surface water drainage conditions.

(d) Supplemental information supporting the stormwater management plan including the following information:

(i) hydrologic and hydraulic calculations for design storm events;

(ii) hydraulic calculations demonstrating the capacity of existing and proposed stormwater impoundments;

(iii) hydraulic calculations demonstrating the capacity of existing and proposed conveyance channels to divert stormwater or contain and transport runoff to stormwater impoundment(s); and

(iv) a list of tools and references used to develop the hydrologic and hydraulic calculations such as computer software, documents, circulars, and manuals.

(e) A plan to manage impacted stormwater, and to divert run-on of non-impacted stormwater where practicable. The plan shall include, as necessary, design, construction, and installation of stormwater run-on and run-off diversion structures, collection of impacted stormwater, and a description of existing surface water drainage conditions. The plan shall consider:

(i) the amount, intensity, duration and frequency of precipitation;

(ii) watershed characteristics including the size, topography, soils and vegetation of the watershed; and

(iii) runoff characteristics including the peak rate, volumes and time distribution of runoff events.

(5)Flow metering plans. An applicant or permittee proposing or required to install a flow meter(s) pursuant to the copper mine rule shall submit a flow metering plan to support the selection of the proposed device along with information or construction plans and specifications, as appropriate, detailing the installation or construction of each device. This information or construction plans and specifications proposed by the applicant or permittee shall be submitted to the department with the application for a new discharge permit or a renewed or modified discharge permit if a new flow meter is proposed.

D.New impoundment engineering design requirements. At a minimum, construction of a new impoundment or replacement of an existing impoundment shall be in accordance with the applicable liner, design, and construction requirements of this subsection. These requirements do not apply to tailing impoundments that are subject to the specific engineering design requirements of Paragraph (4) of Subsection A of 20.6.7.22 NMAC.

(1)General design and construction requirements.

(a) The outside slopes of an impoundment shall be a maximum of two (horizontal) to one (vertical) and shall meet a minimum static factor of safety of 1.3 with water impounded to the maximum capacity design level, except where an impoundment is bounded by rock walls or is below the surrounding surface grade.

(b) The dikes of an impoundment shall be designed to allow for access for maintenance unless otherwise approved by the department.

(c) Liners shall be installed with sufficient slack in the liner material to accommodate expansion and contraction due to temperature changes. Folds in the liner material shall not be present in the completed liner except to the extent necessary to provide slack.

(d) Liners shall be anchored in an anchor trench. The trench shall be of a size and setback distance sufficient for the size of the impoundment.

(e) Liner panels shall be oriented such that all sidewall seams are vertical.

(f) Any opening in the liner through which a pipe or other fixture protrudes shall be sealed in accordance with the liner manufacturer's requirements. Liner penetrations shall be detailed in the construction plans and as-built drawings.

(g) All liners shall be installed by an individual that has the necessary training and experience as required by the liner manufacturer.

(h) Liner manufacturer's installation and field seaming guidelines shall be followed.

(i) All liner seams shall be field tested by the installer and verification of the adequacy of the seams shall be submitted to the department along with the as-built drawings.

(j) Concrete slabs installed on top of a liner for operational purposes shall be completed in accordance with manufacturer and installer recommendations to ensure liner integrity.

(2)Impoundment capacity. Impoundments shall meet the following design capacities. Capacity requirements may be satisfied by a single impoundment or by the collective capacity of multiple interconnected impoundments and any interconnected tanks.

(a)Capacity requirements for impoundments that contain leach solutions. Process water systems that impound leach solutions shall be designed for adequate overflow capacity for upset conditions such as power outages, pump or conveyance disruptions and significant precipitation events. Any impoundment that collects leach solutions and is routinely at capacity shall be designed to maintain a minimum of two feet of freeboard during normal operating conditions while conveying the maximum design process flows. The appropriate overflow capacity design shall consider system redundancies such as backup power systems and pumps. The overflow capacity shall be designed to contain the maximum design flows for the collection system for the maximum period of time that is required for maintenance activities or restoration to normal operating conditions while maintaining two feet of freeboard. If the collection system receives direct precipitation run-off with little or no flow attenuation in the upgradient leach stockpile collection system, the overflow capacity shall be sized to contain the runoff from a 100 year, 24 hour storm event in addition to the upset condition capacity. For process water impoundments located within the open pit surface drainage area, the open pit bottom may be utilized for a portion of the permitted impoundment capacity. Impoundments constructed on a leach stockpile such that any overflow would discharge to and be contained by the approved leach stockpile system are not subject to this capacity requirement.

(b)Other process water impoundment capacity requirements. Process water impoundments intended to manage or dispose of process water, other than leach solutions, shall be designed for adequate overflow capacity for upset conditions such as power outages, pump or conveyance disruptions and significant precipitation events. Any impoundment that collects such process water and is routinely at capacity shall be designed to maintain a minimum of two feet of freeboard during normal operating conditions while conveying the maximum design process flows. The appropriate overflow capacity design shall consider system redundancies such as backup power systems and pumps. The overflow capacity shall be designed to contain the maximum design flows for the collection system for the maximum period of time that is required for maintenance activities or restoration to normal operating conditions while maintaining two feet of freeboard. For process water impoundments located within the open pit surface drainage area, the open pit bottom may be utilized for a portion of the permitted impoundment capacity. Impoundments constructed on a leach stockpile such that any overflow would discharge to and be contained by the approved leach stockpile system are not subject to this capacity requirement.

(c)Combination process water/impacted stormwater impoundment capacity requirements.Impoundments, other than impoundments for the containment of leach solutions, intended to dispose of a combination of process water and impacted stormwater shall be designed to contain, at a minimum, the volume described in Subparagraph (b) of Paragraph 2 of this subsection and the volume of stormwater runoff and direct precipitation generated from the receiving surface area resulting from a 100 year return interval storm event while preserving two feet of freeboard. For combination process water/impacted stormwater impoundments located within the open pit surface drainage area, the open pit bottom may be utilized for a portion of the impoundment capacity.

(d)Evaporative impacted stormwater impoundment design requirements. Impoundments intended to manage or dispose of impacted stormwater by evaporation shall be designed to contain, at a minimum, the volume of stormwater runoff and direct precipitation generated from the receiving surface area resulting from a 100 year return interval storm event while preserving two feet of freeboard. For impoundments located within the open pit surface drainage area, the open pit bottom may be utilized for a portion of the impoundment capacity.

(e)Other impacted stormwater impoundment design requirements. Other impacted stormwater impoundment systems shall be designed to prevent overflow resulting from a 100 year return interval storm event while maintaining two feet of freeboard and may use interconnected impoundments, gravity flow conveyances and pumping systems designed to remove water from individual impoundments at rates to prevent overflow during the design storm event. The appropriate overflow capacity design shall consider system redundancies such as backup power systems and pumps. For impacted stormwater impoundments located within the open pit surface drainage area, the open pit bottom may be utilized for a portion of the permitted impoundment capacity.

(f)Conveyance design requirement. Open channel conveyance structures intended to transport stormwater to an impoundment shall be designed to convey, at a minimum, the peak flow from a 100 year return interval storm event while preserving adequate freeboard, but not less than six inches of freeboard. Conveyances shall be designed to minimize ponding and infiltration of stormwater.

(g)Solids settling. An impoundment designed and used for solids settling shall not be used to satisfy the impoundment capacity requirements of this paragraph.

(3)Process water and impacted stormwater long-term storage impoundments. Process water, and impacted stormwater impoundments that store impacted stormwater for longer than thirty days shall meet the following design and construction requirements, except that process water and impacted stormwater long-term impoundments located within an open pit surface drainage area of an existing copper mine facility may be designed and constructed in accordance with the requirements of Paragraph (4) of this subsection.

(a)Liner system. At a minimum, impoundments subject to this paragraph shall be designed and constructed as an engineered liner system consisting of a suitable subgrade and liner bedding overlain by a secondary synthetic liner which is overlain by a leak collection system overlain by a primary synthetic liner, unless an alternate design is approved by the department pursuant to Subparagraph (e) of this paragraph. The liner system shall be installed in accordance with a department approved CQA/CQC plan pursuant to Paragraph (2) of Subsection C of 20.6.7.17 NMAC.

(b)Liner system sub-grade and bedding. The liner system shall be placed upon a stable sub-grade. The sub-grade shall be free of sharp rocks, vegetation and stubble to a depth of at least six inches below the liner. Liners shall be placed on a liner bedding of sand or fine soil. The surface in contact with the liner shall be smooth to allow for good contact between liner bedding. The liner bedding surface shall be sufficiently dry during liner installation such that free or excess water will not hinder the welding of seams. The liner installer shall provide the owner or permittee with a sub-grade and liner bedding acceptance certificate prior to installing the liner indicating acceptance of the earthwork.

(c)Liner type. The primary and secondary synthetic liners for the impoundment 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, exposure and conditions.

(d)Leak collection system. A leak collection system shall be constructed between the primary and secondary synthetic liners for the purpose of collecting and rapidly removing fluids from leaks that may occur in the primary liner so that minimal hydraulic head is maintained on the secondary liner. The leak collection system shall consist of a drainage layer, fluid collection pipes and a fluid removal system to prevent hydraulic head transference from the primary liner to the secondary liner and shall meet the following requirements.

(i) The drainage layer shall be constructed of granular soil materials or geosynthetic drainage net (geonet) with a design slope of at least two percent. Drainage material shall have a coefficient of permeability of 1x10^-2 centimeters/second or greater.

(ii) Perforated fluid collection pipes shall be installed to transmit fluid from the drainage layer to a fluid collection sump(s). Collection pipe material, diameter, wall thickness, and slot size and distribution shall be sufficient to prevent deflection, buckling, collapse or other failure. Collection pipes shall be installed with slopes equivalent to the slope of the drainage layer. Collection pipe systems shall be designed to allow for cleaning of all collection pipes with standard pipe cleaning equipment.

(iii) A fluid removal system shall be installed to remove fluid from the leak collection system. The fluid removal system shall consist of a sump(s), a dedicated pump(s), an automated pump activation system that activates the pump(s) when a specific fluid level is reached in a sump(s), a totalizing flow meter to measure to measure the volume of leachate pumped from the system, and an automated alarm system that provides warning of pump failure. Alternately a gravity drain system may be utilized where practicable and approved by the department.

(e) An applicant or permittee may propose for department approval an alternative design for process water and impacted stormwater long-term storage impoundments that provides the same or greater level of containment as a double synthetically lined system with leak collection.

(4)Impacted stormwater impoundments. Impacted stormwater impoundments that store impacted stormwater for less than 30 days shall meet the following design and construction requirements; except that any such impoundments located within an open pit surface drainage area may not require a liner.

(a)Liner system. At a minimum, an impacted stormwater impoundment subject to this paragraph shall be constructed as an engineered liner system consisting of a compacted subbase overlain by a synthetic liner. The liner system shall be installed in accordance with a department approved CQA/CQC plan pursuant to Paragraph (2) of Subsection C of 20.6.7.17 NMAC.

(b)Liner system subgrade and liner bedding. The liner system shall be prepared and placed upon a stable subgrade. The top surface of the subgrade shall be smooth and free of sharp rocks or any other material that could penetrate the overlying liner bedding or synthetic liner. Liner bedding shall be placed atop the subgrade and shall consist of a minimum of six inches of sand or fine soil to allow for good contact between liner and liner bedding. The liner bedding surface shall be sufficiently dry during liner installation such that free or excess water will not hinder the welding of seams. The liner installer shall provide the owner or permittee with a sub-grade and liner bedding acceptance certificate prior to installing the liner indicating acceptance of the earthwork.

(c)Liner type. Synthetic liners for an impacted stormwater impoundment 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, exposure and conditions.

(d)Wind protection. Liner systems for impacted stormwater impoundments shall be designed and constructed with a weighting system to secure the liner and limit liner damage during periods of extreme wind events when the impoundment is empty.

(e)Alternate design. An applicant or permittee may propose for department approval an alternative design for an impacted stormwater impoundment that provides the same or greater level of containment as the liner system described in Subparagraphs (a) through (d) of this paragraph.

(5)Non-impacted stormwater impoundments. Non-impacted stormwater impoundments located outside the open pit surface drainage area over contaminated areas where the water has the potential to infiltrate and produce a leachate that may cause an exceedance of the applicable standards require a liner system designed and installed in accordance with Paragraph (4) this subsection.

(6)Separation between impoundments and ground water. Impoundments that require a liner pursuant to this subsection shall not be constructed in a location where the vertical distance between the seasonal high ground water level and the finished grade of the floor of the impoundment is less than or equal to four feet unless the applicant or permittee submits an engineering evaluation from a licensed New Mexico professional engineer that demonstrates that the impoundment design will not be affected by shallow ground water conditions.

(7)Spillways. Impacted stormwater impoundments shall have spillways to safely discharge the peak runoff of a 25-year, 24-hour precipitation event, or an event with a 90-percent chance of not being exceeded for the design life of the impoundment. Impoundments intended as primary containment for process water shall not be designed with a spillway that empties onto the ground surface.

N.M. Admin. Code § 20.6.7.17

20.6.7.17 NMAC - N, 12/1/13