N.M. Admin. Code § 20.6.7.28

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

Section 20.6.7.28 - WATER QUALITY MONITORING REQUIREMENTS FOR ALL COPPER MINE FACILITIES

The following water quality monitoring requirements apply to all copper mine facilities unless otherwise specified.

A.Monitoring wells - location proposals. An applicant for a new, renewed or modified discharge permit or permittee shall submit a plan for department approval identifying the proposed location of monitoring wells required pursuant to Subsection B of this section, and shall include the following information.

(1) The location of each monitoring well relative to the unit of the copper mine facility it is intended to monitor shall be indicated on the scaled map required by Subsection J of 20.6.7.11 NMAC.

(2) The ground water flow direction beneath the copper mine facility used to determine the monitoring well location(s), including supporting documentation used to determine ground water flow direction.

B.Monitoring wells - required locations. A permittee shall monitor ground water quality as close as practicable around the perimeter and downgradient of each open pit, leach stockpile, waste rock stockpile, tailings impoundment, process water impoundment, and impacted stormwater impoundment The department may require additional wells around the perimeter of mine units that are underlain by areas where ground water flow directions are uncertain, including fracture flow systems, and around copper mine units that have the potential to cause ground water mounding. The department may require additional monitoring wells at any other unit of a copper mine facility that has the potential to cause an exceedance of applicable standards as additional permit conditions in accordance with Subsection I of 20.6.7.10 NMAC. Monitoring wells shall be located pursuant to this section to detect an exceedance(s) or a trend towards exceedance(s) of the applicable standards at the earliest possible occurrence, so that investigation of the extent of contamination and actions to address the source of contamination may be implemented as soon as possible.

(1) Use of existing monitoring wells. A monitoring well in existence before the effective date of the copper mine rule shall be deemed to be in an approved location for ground water monitoring purposes provided the following requirements are met:

(a) the monitoring well location was previously approved by the department; and

(b) the monitoring well is constructed as previously approved by the department; or

(c) if the monitoring well and construction was not previously approved by the department, the applicant or permittee can demonstrate that the well meets the location and construction requirements of this section.

(2)Ground water monitoring - leach stockpiles, waste rock stockpiles, tailings impoundments. A permittee shall install monitoring wells around the perimeter and downgradient of each new leach stockpile, waste rock stockpile and tailings impoundment located outside of the open pit surface drainage area, including its leachate and solution capture and containment systems, to adequately monitor ground water that may be impacted by water contaminants from those units. Each monitoring well shall be installed as close as practicable to the proposed leach stockpile, waste rock stockpile or tailings impoundment, including its leachate and solution capture and containment systems, taking into account surface topography, hydrogeologic conditions, geologic controls, infrastructure, engineering design plans, depth to ground water, working distance and safety.

(a) For a new copper mine facility, the monitoring well networks shall be installed at least 180 days before emplacement of ore, waste rock or discharge of tailings at an individual leach stockpile, waste rock stockpile or tailings impoundment to allow sampling prior to discharge.

(b) A permittee constructing a new leach stockpile, waste rock stockpile or tailings impoundment at an existing copper mine facility, or expanding the footprint of an existing leach stockpile, waste rock stockpile, or tailings impoundment, shall install the monitoring well networks required to monitor ground water around and downgradient of the leach stockpile, waste rock stockpile or tailings impoundment before emplacement of ore, waste rock or discharge of tailings unless an existing monitor well network adequately monitors water quality in the area of the new leach stockpile, waste rock stockpile or tailings impoundment.

(3)Ground water monitoring - process water and impacted stormwater impoundments. A minimum of one monitoring well shall be located downgradient and within 75 feet (measured as horizontal map distance) or as close as practicable taking into account surface topography, hydrogeologic conditions, infrastructure, working distance and safety of each new process water or impacted stormwater impoundment located outside of an open pit surface drainage area.

(a) For a new copper mine facility, monitoring wells shall be installed at least 90 days before discharging to an individual process water or impacted stormwater impoundment at the copper mine facility to allow for sampling prior to discharge.

(b) A permittee constructing a new process water or impacted stormwater impoundment at an existing copper mine facility shall install the monitoring well(s) required to monitor ground water downgradient of the impoundment before discharging process water to the impoundment, before collecting impacted stormwater in the impoundment unless an existing monitor well network adequately monitors water quality in the area of the new impoundment.

(4)Ground water monitoring - open pit. A permittee shall install a sufficient number of monitoring wells around the perimeter of an open pit to monitor ground water quality and the hydrologic gradient around the pit. For a new open pit, an applicant or permittee shall submit a monitor well network installation plan to the department for approval. The plan shall include proposed locations of monitoring wells, a statement of the reasons for selection of the monitoring well locations, and a schedule for installation.

(5)Ground water monitoring - upgradient of each potential contaminant source. A minimum of one monitoring well shall be located upgradient of each new leach stockpile, waste rock stockpile, tailings impoundment, and process water and impacted stormwater impoundment at a copper mine facility to establish upgradient ground water quality conditions not likely to be affected by each contamination source that is being monitored. If an applicant or permittee has existing monitoring wells located appropriately to obtain sufficient background data at a copper mine facility and establish and monitor upgradient conditions, the department may waive the requirement for additional upgradient wells.

(a) For a new copper mine facility, upgradient source monitoring wells shall be installed a minimum of 180 days before emplacement of ore, waste rock or discharge of tailings or other water contaminants at an individual leach stockpile, waste rock stockpile, tailings impoundment or other impoundment.

(b) A permittee constructing a new leach stockpile, waste rock stockpile, tailings impoundment or other impoundment at an existing copper mine facility shall install the monitoring well(s) required to monitor ground water quality upgradient of a leach stockpile, waste rock stockpile, tailings impoundment or other impoundment before emplacement of ore, waste rock or discharging of tailings or water contaminants into the individual source required to be monitored.

(6)Ground water monitoring - upgradient of the copper mine facility. A sufficient number of monitoring wells shall be located upgradient of all potential ground water contamination sources at a copper mine facility to establish upgradient ground water quality conditions that are not affected by any potential contamination sources at the copper mine facility. For a new copper mine facility, upgradient monitoring wells shall be installed at least 180 days before emplacement of ore, waste rock or discharge of tailings or other water contaminants at an individual leach stockpile, waste rock stockpile, tailings impoundment or other impoundment.

C.Monitoring wells - identification tags. A permittee shall clearly identify all monitoring wells required by the copper mine rule with a permanent well identification tag that contains well identification nomenclature included on the scaled map required by Subsection J of 20.6.7.11 NMAC.

D.Monitoring wells - construction and completion. A permittee shall construct monitoring wells pursuant to 19.27.4 NMAC and the following requirements unless the department approves of an alternate monitoring well construction and completion design based upon site-specific hydrogeologic conditions.

(1) All well drilling activities shall be performed by an individual with a current and valid well driller license issued by the state of New Mexico pursuant to 19.27.4 NMAC.

(2) The well driller shall employ drilling methods that allow for accurate determinations of water table locations unless otherwise approved by the department in advance of drilling. All drill bits, drill rods, and down-hole tools shall be thoroughly cleaned immediately before drilling. The borehole diameter shall allow a minimum annular space of two inches between the outer circumference of the well materials (casing or screen) and the borehole wall to allow for the emplacement of sand and sealant.

(3) The well shall be developed so that formation water flows freely through the screen and is not turbid, and sediment and drilling disturbances are removed from the well to the maximum extent practicable.

(4) Unless otherwise approved by the department, schedule 40 (or heavier) polyvinyl chloride (PVC) pipe, stainless steel pipe, or carbon steel pipe shall be used as casing. The casing shall have an inside diameter not less than two inches. The casing material selected for use shall be compatible with, and chemically inert with respect to the anticipated chemistry of the ground water and appropriate for the contaminants of interest at the copper mine facility. The casing material and thickness selected for use shall have sufficient collapse strength to withstand the pressure exerted by grouts used as annular seals and thermal properties sufficient to withstand the heat generated by the hydration of cement-based grouts.

(5) Casing sections shall be joined using welded, threaded, or mechanically locking joints. The method selected shall provide sufficient joint strength for the specific well installation.

(6) The casing shall extend from the top of the screen to at least 18 inches above ground surface. The top of the casing shall be fitted with a removable cap, and the exposed casing shall be protected by a locking steel well shroud. The shroud shall be large enough in diameter to allow easy access for removal of the cap. Alternatively, monitoring wells may be completed below grade. In this case, the casing shall extend from the top of the screen to between six and twelve inches below the ground surface; the monitoring wells shall be sealed with locking, expandable well plugs; a flush-mount, watertight well vault that is rated to withstand traffic loads shall be emplaced around the wellhead; and the cover shall be secured with at least one bolt. The vault cover shall indicate that the wellhead of a monitoring well is contained within the vault.

(7)Well Screen.

(a)For water table monitoring wells. A maximum 20-foot section of continuous well screen shall be installed across the water table with at least five feet of well screen placed above the water table interface to allow for seasonal fluctuations. The department may approve a greater screen length based on the hydraulic properties of the aquifer, the hydrogeologic setting, predictable water level decline rates, or the depth of the well. Screen shall consist of continuous-slot, machine slotted, or other manufactured schedule 40 (or heavier) PVC or stainless steel. Screens created by cutting slots into solid casing with saws or other tools, other than as performed by the manufacturer, shall not be used. The screen material selected for use shall be compatible with the anticipated chemistry of the ground water and appropriate for the contaminants of interest at the copper mine facility. The screen slot size shall be selected to retain 90 percent of the filter pack.

(b)For deep or confined aquifer monitoring wells. Monitoring wells installed in confined aquifers or below the water table elevation of the shallowest aquifer to monitor ground water conditions in different aquifers at depth shall be installed with a maximum ten foot section of continuous well screen. The department may approve a greater screen length based on the hydraulic properties of the aquifer, the hydrogeologic setting, or the depth of the well. The top of the screen shall be placed at the location of the geologic boundary between the top of the aquifer and the bottom of confining aquifers. Screen shall consist of continuous-slot, machine slotted, or other manufactured schedule 40 or heavier PVC or stainless steel. Screens created by cutting slots into solid casing with saws or other tools shall not be used. The screen material selected for use shall be compatible with the anticipated chemistry of the ground water and appropriate for the contaminants of interest at the copper mine facility. The screen slot size shall be selected to retain 90 percent of the filter pack.

(8) Screen sections shall be joined using welded, threaded, or mechanically locking joints. The method selected shall provide sufficient joint strength for the specific well installation and shall not introduce constituents that may reasonably be considered contaminants of interest at the copper mine facility. A cap shall be attached to the bottom of the well screen.

(9) Casing and well screen shall be centered in the borehole by installing centralizers near the top and bottom of the well screen.

(10) A filter pack shall be installed around the screen by filling the annular space from the bottom of the screen to at least two feet above the top of the screen with clean silica sand using methods that prevent bridging. The filter pack shall be properly sized to exclude the entrance of fine sand, silt, and clay from the formation into the monitoring well. All filter pack placed deeper than twenty feet below land surface shall be placed by tremie pipe. The well shall be surged or bailed to settle the filter pack and additional sand added, if necessary, before the bentonite seal is emplaced.

(11) A bentonite seal shall be constructed immediately above the filter pack by emplacing bentonite chips or pellets, three eighths of an inch in size or smaller, in a manner that prevents bridging of the chips/pellets in the annular space. All bentonite seals placed deeper than twenty feet below land surface shall be placed by tremie pipe. The bentonite seal shall be a minimum of three feet in thickness and hydrated with clean water. Adequate time shall be allowed for expansion of the bentonite seal before installation of the annular space seal.

(12) The annular space above the bentonite seal shall be sealed with cement grout or bentonite-based sealing material acceptable to the state engineer in accordance with 19.27.4 NMAC. All annual sealing materials placed deeper than twenty feet below land surface shall be placed by tremie pipe. Annular space seals shall extend from the top of the bentonite seal to the ground surface for wells completed above grade, or to a level three to six inches below the top of casing for wells completed at or below grade.

(13) A concrete pad with a minimum two-foot radius and a minimum four-inch thickness shall be poured around the shroud or well vault and wellhead. The concrete and surrounding soil shall be sloped to direct rainfall and runoff away from the wellhead.

E.Monitoring wells - office of the state engineer requirements. A permittee shall obtain any well permits required by the office of the state engineer prior to well drilling.

F.Ground water sample collection procedure. A permittee shall perform all ground water sample collection, preservation, transport and analysis according to the following procedure.

(1) Depth to ground water shall be measured from the top of well casing at point of survey to the nearest 0.01 feet using an electronic water level indicator consisting of dual conductor wire encased in a cable or tape graduated to 0.01 feet, a probe attached to the end of the conductor wire, and a visual or audible indicator; pneumatically or by using a fiberglass or steel measuring tape using the chalk method, or other method approved by the department.

(2) Monitoring wells shall be purged before sample collection by one of the following methods, unless otherwise approved by the department.

(a) Three well volumes of water shall be purged from the well using conventional methods before sample collection.

(b) The monitoring well shall be purged using low-flow purging methods as approved by the department until measurements of indicator parameters have stabilized. Low-flow purging shall be conducted with a low-flow pump using a low-stress approach, micro-purge method or minimal drawdown method. Indicator parameters shall be measured periodically during purging. A parameter stabilization log shall be kept during each sampling event for each monitoring well and include: date; water quality indicator parameter measurements; time for all measurements; and the purge volume extracted.

(c) For low yield wells, the well shall be purged of all available water.

(3) Following purging and immediately before sample collection the following field parameters shall be measured and recorded: pH, specific conductance, and temperature.

(4) In-line flow-through cells shall be disconnected or by-passed during sample collection, if used during purging.

(5) Samples from the well shall be obtained, prepared, preserved and transported to an analytical laboratory for analysis pursuant to the methods authorized by Subsection B of 20.6.7.29 NMAC.

G.Ground water sampling - existing copper mine facilities. For existing copper mine facilities a permittee shall collect ground water samples from all monitoring wells, seeps and springs for the analytes and at the frequency specified in an existing discharge permit. A permittee shall submit to the department semi-annual monitoring reports containing the information required in Section 20.6.7.29 NMAC.

H.Ground water sampling - reduction of sampling analytes. A permittee may request approval from the department to reduce the sampling frequency of individual water quality analytes. The basis for consideration of reduction of sampling frequency may include a demonstration that the analyte is not present in the impoundment or mine unit being monitored, or could not be generated from the materials present through degradation, oxidation, decay or any other expected process. A permittee may also request approval from the department to reduce sampling frequency of an individual analyte if it has not been detected in a particular monitoring well, is consistently below the applicable standard, or is stable and predictable for eight consecutive quarters. Ground water sampling analyte lists and the frequency of sampling shall be reevaluated upon permit renewal.

I.Ground water sampling - new monitoring wells. A permittee shall submit to the department for approval a proposal for quarterly ground water sampling from each newly installed monitoring required pursuant to this section. Sampling analyte lists shall be based on the geochemical characteristics of the solution or material contained in the impoundment or mine unit intended to be monitored, including constituents that can be generated from the materials present through degradation, oxidation, decay or any other expected process. Proposed analytes shall include field parameters as required in Subsection F of this section, alkalinity-bicarbonate, alkalinity-carbonate, metals, and other analytes from Section 20.6.2.3103 NMAC as applicable.

(1) Samples shall be collected from each newly installed monitoring well required pursuant to this section for a copper mine facility before emplacement of ore, waste rock or discharge of tailings or other water contaminants at an individual leach stockpile, waste rock stockpile, tailings impoundment or other impoundment.

(2) For copper mine facilities installing a new monitoring well during the term of a discharge permit, during construction of a new impoundment, or as a result of required corrective actions, samples shall be collected from the newly installed monitoring wells within 30 days of well completion and prior to commencing operation of the newly constructed unit as applicable.

J.Monitoring well survey and ground water flow determination. The permittee shall survey or otherwise locate monitoring wells and provide location information as required by this section. The coordinate location (northing and easting) shall be provided in the established coordinate system for the copper mine facility with an accuracy (rounded to the nearest foot/tenth meter) and shall also be provided to the department in one of the following coordinate systems: NM state plane (NAD 83) to the nearest foot, UTM (NAD 83) to the nearest tenth of a meter, or latitude/longitude (Lat/Long - WGS84) to the nearest tenth of a second. Elevation of the ground surface at the well location shall be provided to the nearest foot above mean sea level. Elevation of the water level measuring point shall be provided to the nearest hundredth of a foot above mean sea level. The water level measuring point for monitoring wells shall be clearly marked on the casing. Depth to ground water at each monitoring well location shall be measured from the point of survey to the nearest hundredth of a foot in all surveyed wells pursuant to Subsection F of this section, and the data shall be used to develop a map showing the location of all monitoring wells and the direction and gradient of ground water flow at the copper mine facility.

K.Monitoring well completion report. A permittee shall submit to the department a monitoring well completion report for all newly installed monitoring wells. The report shall be submitted within 60 days of completion of installation of the monitoring well. The report shall contain the following information.

(1) Construction and lithologic logs for the new monitoring wells including well record information specified by 19.27.4 NMAC.

(2) Depth to ground water measured in each new monitoring well.

(3) Survey data and a survey map showing the locations of each new monitoring well and a ground water elevation contour map developed pursuant to Subsection L of this section.

(4) Analytical results of ground water samples collected from the new monitoring wells, including laboratory quality assurance and quality control summary reports, and field parameter measurements.

L.Ground water elevation contour maps. A permittee shall develop ground water elevation contour maps on a semi-annual basis using data associated with all monitoring wells installed in the appropriate geologic formation and as required pursuant to this section. Top of casing elevation data, obtained from monitoring well surveys completed pursuant to this section and quarterly depth to ground water measurements in monitoring wells shall be used to calculate ground water elevations at monitoring well locations. Ground water elevations between monitoring well locations shall be estimated using common interpolation methods. Ground water elevations shall be expressed in feet. A contour interval appropriate to the data shall be used. Ground water elevation data used to create potentiometric maps shall be limited to data collected during the quarter being reported. Ground water elevation contour maps shall depict the ground water flow direction, using arrows, based on the orientation of the ground water elevation contours, and the location and identification of each monitoring well and monitored structure or impoundment. A permittee shall submit ground water elevation contour maps to the department in the semi-annual monitoring reports, and submit annually a map showing the extent of the existing open pit surface drainage area as defined in Paragraph (43) of Subsection B of 20.6.7.7 NMAC.

M.Perennial stream sampling and reporting - routine. A permittee shall submit to the department for approval a proposal to collect quarterly surface water samples from each perennial surface waters of the state within a copper mine facility as necessary to monitor potential ground water inflow to the perennial surface water. Analytes to be sampled and analyzed shall be based on the geochemical characteristics of the solution or material contained in the impoundment or mine unit closest to or most likely to effect the perennial stream being sampled. A permittee shall submit to the department in the semi-annual monitoring reports the field parameter measurements, the analytical results (including the laboratory quality assurance and quality control summary report) and a map showing the location of each sampling location in relation to the copper mine facility.

N.Process water, tailings slurry, impacted stormwater, seep, and spring sampling and reporting. An applicant for a new, renewed or modified discharge permit or permittee shall submit for department approval a sampling and analysis plan to monitor quarterly the quality of process water, tailings slurry, impacted stormwater, seeps and springs at a copper mine facility. Proposed analytes shall include field parameters as required in Subsection F of this section, alkalinity-bicarbonate, alkalinity-carbonate, metals, and other analytes from Section 20.6.2.3103 NMAC as applicable.

N.M. Admin. Code § 20.6.7.28

20.6.7.28 NMAC - N, 12/1/13