How to Test Heap Leach Pad Liners | Full Guide

To fully ensure the anti-seepage effect, the industry primarily adopts the following testing methods:

Seam Testing: For fragile joints, use a vacuum box (applying approximately 35 kPa negative pressure) or a spark tester to check for welding defects inch by inch.

Electrical Leak Location (ELL): This is currently the industry benchmark for inspecting large-area damage. By covering the liner with water or soil and applying voltage, it can accurately locate perforations as small as 1 mm that are invisible to the naked eye.

Seam Testing

Seam testing of heap leach pad geomembranes (usually HDPE or LLDPE with a thickness of 60-100 mil) is responsible for verifying the physical integrity of the anti-seepage system. According to the Geosynthetic Institute (GSI) specifications, testing must cover 100% of all field physical seams. Dual-track hot-wedge welds use air pressure testing (injecting 25-30 psi compressed air, maintaining for 5 minutes, with a pressure drop requirement of less than 2-3 psi); extrusion welds use vacuum box testing (applying -3 to -5 psi negative pressure, continuously observing for 10-15 seconds).

Destructive testing is based on the ASTM D6392 standard. For every 150 meters (approximately 500 feet) of weld completed, a 12×36 inch field sample must be cut and sent to an independent third-party laboratory for shear and peel tension testing.

Non-Destructive Testing (NDT)

The GRI-GM19 standard published by the Geosynthetic Institute (GSI) and the American Society for Testing and Materials (ASTM) specifications provide quantitative regulations for on-site non-destructive testing procedures. All physical seams of the geomembrane liner system (HDPE or LLDPE materials with thickness between 1.5mm and 2.5mm) must undergo 100% verification according to specific specifications.

Dual-track hot-wedge weld testing is performed according to the ASTM D5820 specification. Technicians insert a 16-gauge or 18-gauge hollow steel inflation needle into one end of the hollow air channel, which is approximately 12.5 mm (0.5 inches) wide, between the two parallel welds. The inflation equipment must be equipped with an oil-water separator to deliver clean, dry compressed air into the channel, preventing moisture accumulation inside the air channel.

The calibration accuracy requirements for pressure gauges are extremely high, with the minimum reading on the dial set to 1 psi or 0.1 bar. The dial must carry a calibration certificate recognized by the National Institute of Standards and Technology (NIST), and the calibration date must not be more than 6 months from the test date. For 60 mil thick smooth HDPE geomembrane, the initial inflation pressure is set to 30 psi (approximately 207 kPa).

After reaching 30 psi, the technician closes the valve and cuts off the air source. The compressed air in the channel requires 2 minutes to undergo heat exchange with the surrounding polymer matrix and reach temperature equilibrium. After the equilibrium period ends, the formal 5-minute reading observation period begins. According to engineering specifications, the air pressure drop within 5 minutes must not exceed 2 psi (13.8 kPa).

ASTM D5820 supplementary step requirement: After the pressure maintenance test passes, the operator must pull out the sealing needle or cut the air channel at the other end of the weld (usually 150 meters from the inflation end). The pressure gauge reading drops rapidly to 0 psi, proving that the entire air channel is continuous and unobstructed.

Extrusion welds, patch repair areas, and T-joints, which do not have hollow air channels, must use the vacuum box testing method according to the ASTM D5641 standard. Before the test begins, the operator prepares a surfactant solution in a ratio of 1 part liquid detergent to 10 parts clean water. The prepared solution is evenly sprayed onto the surface of the weld to be tested, significantly reducing the surface tension of the water.

The vacuum box is made of an aluminum alloy frame and a 6 mm (0.25 inch) thick transparent acrylic observation window. The physical dimensions of a standard vacuum box are 750 mm x 250 mm (30 inches x 10 inches). A closed-cell neoprene sponge seal gasket is installed at the bottom of the box to ensure that no external air backflow occurs when the box is in contact with the geomembrane surface.

An electric vacuum pump quickly extracts the air inside the vacuum box through a high-pressure hose. The internal air pressure must drop to a negative pressure range of -3 psi to -5 psi (approximately -20.7 to -34.5 kPa) within 3 seconds. Technicians observe the extrusion weld wetted by the solution through the acrylic window, with the continuous observation time strictly set between 10 and 15 seconds.

If there is a tiny perforation with a diameter of less than 1 mm in the extrusion weld, the negative pressure in the box will force the air under the geomembrane out. As air passes through the soap solution, it forms continuous soap bubbles with a diameter of 1 to 5 mm that are clearly visible to the naked eye. Once a bubble is found, the technician uses a white marker to draw a circle with a radius of 5 cm at the bubble’s location for subsequent repair.

• Quantitative indicators for air pressure testing: Inflation pressure 30 psi, thermal equilibrium 2 minutes, formal test 5 minutes, maximum allowable pressure drop ≤ 2 psi.
• Quantitative indicators for vacuum box testing: Continuous negative pressure value -3 to -5 psi, observation window duration 10-15 seconds, standard solution ratio 1:10.
• Quantitative indicators for spark testing: Applied voltage 15,000-35,000 volts, sweep speed 10-20 cm/s, detection thickness up to 2.5 mm.

For special conductive geomembranes containing a co-extruded conductive carbon black bottom layer, the US Environmental Protection Agency (EPA) recommends using spark testing (based on the ASTM D7240 standard). Technicians hold a detector with a brass wire brush and sweep it evenly over the surface of the extrusion weld at a constant speed of 10 to 20 cm per second. The test voltage generated by the detector is usually set between 15,000 and 35,000 volts.

When the brass wire brush passes over a weld area with micro-pores, the high-voltage current instantly breaks through the insulating polymer material layer to reach the conductive layer at the bottom. The testing instrument produces a visible blue arc and simultaneously triggers an electronic alarm with a volume exceeding 80 decibels. Spark testing can not only detect penetrating holes but also accurately identify un-fused bubbles 2 mm deep from the surface inside the weld.

On-site meteorological conditions greatly affect the accuracy of NDT data. Ambient temperature measurement must use a NIST-calibrated thermometer, fixed 15 cm (6 inches) away from the geomembrane surface. When the ambient temperature drops below 0°C (32°F), the polymer material becomes brittle, and pressure drop readings for air testing must be entered into the system for volume contraction error compensation based on Boyle’s Law.

When field wind speeds exceed 32 km/h (20 mph), the sealing edge of the neoprene gasket at the bottom of the vacuum box will be disturbed by lateral wind pressure, easily leading to an inability to maintain the negative pressure reading at -3 psi. Strong winds also accelerate the natural evaporation of the surfactant solution, making it impossible to form continuous and visible test bubbles during the 15-second observation period. Operators must use a portable anemometer to measure and record field wind speed data once per hour.

After each test, the operator records the test data on the geomembrane surface using a white permanent paint pen in accordance with ASTM D5820 requirements. The standard writing format is: “Date format MM/DD / Technician ID abbreviation / Test category (A=Air, V=Vac) / Initial psi reading / Final psi reading”. Dial readings, along with GPS coordinate system data, must be entered into the Construction Quality Assurance (CQA) electronic database within 24 hours.

Destructive Testing

Destructive testing is strictly performed according to the ASTM D6392 standard, where a 12×36 inch physical sample is cut from the 60-mil or 80-mil geomembrane weld of the heap leach pad. By default, engineering requires sampling once every 500 feet (150 meters) of continuous weld. The sample is punched into standard 1-inch wide strips and placed in electronic tensile equipment for stretching at a rate of 2 inches/minute (50 mm/min).

The test is divided into shear strength and peel strength. Indicators must reach the minimum poundage specified by GRI-GM19 (for example, 60-mil smooth HDPE requires 120 ppi for shear and 78 ppi for peel), and the fracture mode must be a Film Tear, thereby verifying that the physical structure meets the standards.

Sampling Standards

On-site Construction Quality Assurance (CQA) specifications require physical samples to be cut from dual-track hot-wedge welds or extrusion welds. The basic interval for sampling is set at one strip every 500 feet (152.4 meters). The CQA engineer uses a distance measuring wheel to pace along the weld and draws a 12-inch wide, 36-inch long (30 cm × 90 cm) rectangular box on the membrane surface with a white industrial marker when reaching the specified footage.

When drawing lines, the weld is required to pass strictly through the center of the 36-inch long side. The inspector checks the ambient temperature of the day; when the ambient temperature is below 40°F (4°C) or higher than 104°F (40°C), the sampling interval is shortened to 400 feet (122 meters). When an operator is changed, the welding machine is shut down for more than 30 minutes, or work resumes after rain, an additional sample must be taken within the first 10 feet (3 meters) of restarting work.

Sampling personnel use a utility knife with a hooked blade (such as Stanley 11-983) to cut the geomembrane along the marker lines. The hooked blade lifts the upper membrane material, preventing the knife tip from scratching the GCL (geosynthetic clay liner) or compacted soil layer laid below. The cut 12×36 inch sample must be kept clean, avoiding contamination by on-site slag or mud water.

After the sample is cut, the CQA engineer fills in the identification information on the back of the sample. Recorded parameters include multiple specific data points and are completely aligned with the on-site daily welding log.

• Project number and sampling date (e.g., 2026-03-12)
• Unique alphanumeric weld ID (e.g., S-402)
• Sample sequential serial number (e.g., DS-15)
• Operator ID and welder equipment body code
• Ambient temperature during sampling and HDPE membrane surface temperature
• Operating temperature of the heating wedge set by the welder (e.g., 720°F)
• Actual crawler walking speed of the welder (e.g., 6 feet/minute)

After cutting is complete, a 12×36 inch open hole is left on the heap leach pad membrane surface. The installation team cuts an 18-inch × 42-inch oval parent material as a patch to cover the hole. The patch edge leaves a 6-inch (15 cm) overlap allowance from the hole edge. Technicians use a handheld extrusion weld gun to extrude molten polyethylene welding rod along the outer edge of the patch to seal it.

The 36-inch long sample taken is brought to the on-site temperature-controlled testing room. The inspector uses a ruler and a cutter to divide the long sample into three 12-inch × 12-inch (30 cm × 30 cm) square modules.

• Module A: Kept in the on-site testing room, where the tensile mechanical testing process is completed within two hours.
• Module B: Placed in a sealed moisture-proof bag and sent via FedEx to a CQA-approved third-party independent laboratory.
• Module C: Handed over to the mining company owner, stored in a dark and dry archive room for a retention period of 5 years.

After receiving Module A, the on-site testing room enters the specimen preparation stage. Geomembranes are hard in texture and cannot be precisely cut with ordinary blades. The inspector operates a hydraulic press (Clicker Press) equipped with more than 5 tons of pressure, along with a steel rule die specified by ASTM D6392 for punching.

The inner diameter of the steel rule die is set to 1.0 inch (25.4 mm) wide and 6 to 8 inches (150 to 200 mm) long. When punching, the die is placed perpendicular to the weld, requiring the weld to be in the exact center of the specimen. Both ends of the specimen retain a flat gripping area of at least 2 inches (50.8 mm) to be placed in the grips of the subsequent tensile machine.

From a single 12×12 inch Module A, the inspector punches out the specified number of 1-inch wide standard specimens. For extrusion welds, 10 specimens must be prepared: 5 for shear testing and 5 for peel testing. For dual-track hot-wedge welds, since there are two parallel independent welds, the number of specimens prepared increases accordingly.

There is a cavity in the middle of the dual-track hot-wedge weld. Peel testing needs to be performed separately for the inner track and the outer track. Among the specimens punched out, 5 are left untreated for shear testing; the other 10 need to have one end of the dual tracks torn open with hand pliers.

• 5 complete original specimens, ready for shear tensile load.
• 5 specimens with the outer track manually peeled apart, ready for testing outer track peel adhesion.
• 5 specimens with the inner track manually peeled apart, ready for testing inner track peel adhesion.
• All specimen edges are polished with 120-mesh fine sandpaper to remove burrs generated by punching.

Tiny notches on the specimen edges can cause stress concentration during stretching, causing the specimen to break under tension lower than the specified poundage. The polished specimens are placed in a constant temperature room at 70°F ± 4°F (21°C ± 2°C) for 1 hour to eliminate residual thermal stress generated during the cutting and punching process.

After the standing countdown ends, the inspector uses a digital vernier caliper with NIST (National Institute of Standards and Technology) traceable calibration to measure the width and thickness of each specimen. Thickness measurement points are located on the parent material 1 inch (25.4 mm) on both sides of the weld. The average thickness error of 5 specimens in the same group must not exceed ±10% of the nominal thickness value.

If the width of a specimen deviates from the 1.0-inch baseline by more than 0.04 inches (1 mm), the specimen is discarded and needs to be re-punched from the remaining Module A scrap. After all dimensional data is entered into the computer software, the specimen preparation stage ends, and they are kemudian transferred to a tensile testing machine equipped with serrated pneumatic grips.

Tensile Testing

After the on-site or independent third-party CQA laboratory receives the 1-inch wide standard specimen, the technician moves it into a controlled testing environment. A high-precision electronic universal material testing machine (such as an Instron 5960 equipped with a 10 kN load cell) enters standby mode. Before the technician loads the specimen, the environment and physical equipment must meet a set of calibration requirements for specific parameters:

• The testing room temperature is stably maintained at 70°F ± 4°F (21°C ± 2°C).
• The relative humidity of the testing room is locked in the range of 50% ± 5% by the instrument.
• The polyethylene specimen must be exposed in the environment for a full 40 minutes.
• The equipment load cell has an annual calibration certificate according to the ASTM E4 standard.
• The hardware absolute error of the peak tension reading is controlled within ±0.5%.

To prevent smooth membrane material from derailment and slipping during stretching over 200 lbf, pneumatic serrated parallel grips are assembled at both the upper and lower ends of the testing machine. The air compressor inputs a stable air pressure of 80 psi (550 kPa) to the two sets of grip cylinders. The metal jaw surfaces are covered with a 120-mesh silicon carbide coating, applying a constant lateral biting force of 500 pounds to the 1.5 mm thick membrane surface.

According to the ASTM D6392 industrial operating specification, the technician precisely sets the initial geometric physical distance between the upper and lower jaws to 2 inches (50.8 mm). The physical weld section is accurately aligned at the exact center of the two sets of grips’ 50.8 mm span.

The first mechanical loading procedure is the Shear Test, used to measure the structural resistance of two layers of membrane material sliding and peeling in a plane. The main axis of the testing machine lifts vertically upwards, the equipment motor rate control tolerance is ±5%, and the actual running stretching speed is limited between 47.5 mm/min and 52.5 mm/min.

The Bluehill software on the main control computer captures continuous readings at a high sampling rate of 50 Hz, plotting the load-displacement physical tensile curve. High-density polyethylene (HDPE) smooth geomembrane has a hard specification lower limit set for physical destructive strength in the shear direction:

After the shear physical loading process is completed, the test channel switches to Peel Test mode. Technicians use steel pliers to pre-tear the un-fused overlap areas at both ends of the 1-inch specimen and lock the two pieces of membrane into the upper and lower pneumatic grips respectively, forming a 180-degree reversed T-peel geometry. The total width of the dual-track hot-wedge weld is 1.5 inches (38 mm), containing a 0.5-inch (12.7 mm) cavity.

T-peel tears outward at the independent fusion tracks on the inner or outer side. The peak resistance data obtained is generally lower than the shear tension. The peel qualification line for 60-mil specimens stays at 78 ppi (137 N/cm), 80-mil requirements are pushed to 104 ppi (182 N/cm), and 100-mil membrane corresponds to a mechanical peel resistance requirement of 130 ppi (227 N/cm).

Qualification of pure physical values cannot end the determination process; the GRI-GM19 specification introduces a mandatory visual failure mode (Failure Mode) verification procedure. Technicians turn on a 1500-lumen LED inspection light and observe the three-dimensional physical fracture morphology of the 10 torn specimens with a 10x optical magnifying glass.

The location of compliant physical fracture must fall on the original parent material outside the heat-fused area. Four common fracture mode abbreviation codes need to be manually entered by the technician into the dropdown menu of the CQA quality database:

• FT (Film Tear): Parent material fracture, the polyethylene molecular chains are completely pulled apart in the non-heat-affected zone.
• AD (Adhesion Failure): Adhesion failure, the two layers of membrane are smoothly torn apart at the fusion interface.
• AD-BRK: Interface peel accompanied by material pull-apart, where the peel area invading the weld exceeds the 25% red line.
• SE (Seam Edge Break): Abnormal stress fracture occurring right at the weld edge, considered non-compliant.

The computer system executes a comprehensive Boolean logic determination based on the matrix test data of 5 specimens in the same group. Material physical differences of individual 1-inch wide specimens are pre-calculated into a data fault tolerance background model.

In a test set of 5 shear or 5 peel specimens, it is mandatory that 4 pass the table’s ppi lower limit and present an FT fracture mode. The peak tension drop of the remaining 1st specimen is limited to within 20% of the specification’s lower limit, and the separation interface area is kept below 25%.

The high-density data stream output by the device at 50 Hz is eventually compressed by the software into a 150 KB locked PDF electronic test dossier. This data dossier is pushed from the independent laboratory workstation to the supervision company’s cloud server via 256-bit AES protocol. The dossier contains the following validation information:

• Peak digital records of the load cell accurate to 0.01 lbf (0.04 N).
• Unique alphanumeric barcode printed on the polyethylene sample (e.g., S-402).
• Accurate millimeter-level tensile fracture coordinate data for 10 corresponding specimens.
• 10x magnification visual recognition determination codes judged under 1500-lumen lighting.

Handling of Non-Conformance

When the on-site laboratory or a third-party agency reports that a 1-inch wide specimen fails to reach the poundage specified by GRI-GM19 on the tensile machine, or if the fracture mode does not comply with the Film Tear (FT) standard, the CQA engineer immediately initiates a boundary investigation procedure. If a 60-mil HDPE specimen shows a separation area exceeding 25% in the peel test, or if the shear strength is fixed at 115 ppi (below the 120 ppi threshold), the entire 12×36 inch sample is judged as non-conforming.

After non-conforming results are entered into the system, testing personnel notify the field installation supervisor via handheld radio. The supervisor cuts off power to the specific hot-wedge welder (e.g., body ID W-09) that produced the non-conforming weld within 15 minutes. Body ID W-09 is moved out of the heap leach pad 60-mil laying area and sent back to the repair tent for re-calibration.

Technicians perform 100% isopropyl alcohol cleaning on the heating wedge of the W-09 welder and conduct a trial weld on a 3-foot × 10-foot scrap piece. The equipment can only resume geomembrane operations after destructive trial weld data reaches over 125 ppi twice in a row.

For non-conforming welds already laid on-site, the CQA engineer uses a 50-foot fiberglass tape measure to measure in two opposite directions, left and right, along the weld trajectory. The standard investigation starting point is the cross center of the original non-conforming sampling point.

• Extend 10 feet (3.05 meters) east along the weld and draw a new 12×36 inch sampling box with a white industrial marker.
• Extend 10 feet (3.05 meters) west along the weld and draw a second new 12×36 inch sampling box.
• Cut two new samples and divide them into A, B, and C parts. Part A is sent to the on-site constant temperature room to punch out 10 1-inch specimens.

The two sets of boundary samples newly cut must complete electronic tensile machine testing within 60 minutes. If the sample 10 feet to the east reaches 80 ppi in the peel test with 100% FT fracture, the east boundary is successfully locked. If the sample extending west only reaches 105 ppi in the shear test, investigation continues further west.

The installation team measures an additional 10 feet (3.05 meters) west from the second non-conforming position on the west side. Technicians cut a third 12×36 inch sample for the constant temperature room test queue. Steps are repeated, incrementing by 10 feet each time, until conforming samples are obtained at both ends.

After finding the conforming east and west boundary points, the entire section of geomembrane weld between the two points (usually between 20 and 40 feet in length) is officially marked as a rejected zone. The CQA engineer records the GPS coordinates of both ends of the rejected zone in the system, with data point accuracy reaching sub-meter level (error less than 0.3 meters).

Dual-track hot-wedge welds within the rejected zone lose their qualification for containing leachate containing sodium cyanide (NaCN). The contractor must not reheat the original weld or attempt to peel and re-weld it; physical overlay repair methods are mandatory.

The repair team uses industrial heat guns to sweep along the entire length of the non-conforming weld, removing ore dust particles larger than 10 microns attached to the surface. Personnel cut a cap strip of the same HDPE material with a width of 6 inches (152.4 mm) and lay it flat, aligning it with the center line of the non-conforming weld.

The length of the cap strip exceeds the two ends of the non-conforming weld by 6 inches (152.4 mm) each. Technicians use an angle grinder with 80-mesh sandpaper to grind the left and right edges of the cap strip and the underlying parent material. The grinding depth is controlled at 0.5 mm to remove the 0.5 mm oxidation layer, exposing the unaged polyethylene molecular chains inside.

• Within 30 minutes after grinding, technicians operate an extrusion weld gun to apply molten polyethylene with a diameter of 4 to 5 mm along the edge of the cap strip.
• The extrusion weld gun barrel temperature is set to 400°F to 420°F (204°C-215°C) to promote molecular cross-linking between the new welding rod and the parent material.
• Both ends of the repair area are cut into rounded corners with a radius of 3 inches (76 mm) to prevent stress concentration tears at 90-degree right-angle edges.

After cap strip extrusion welding is complete, wait 1 hour on-site for the polyethylene to naturally cool to below 80°F (26°C). The inspector applies a 1:10 diluted soap solution to the entire new weld surface, preparing for a 100% coverage non-destructive Vacuum Test.

The inspector places a vacuum box with a width of 10 inches and a length of 30 inches (25.4 cm × 76.2 cm) with a transparent acrylic observation window onto the soap-covered cap strip weld. Start the 1.5 HP electric vacuum pump connected to the box to extract air inside.

Air pressure inside the box drops to a negative pressure of 3 to 5 psi (20 to 35 kPa) and is maintained for 10 seconds. The inspector observes the 30-inch long weld through the 0.5-inch thick acrylic plate to check for continuous soap bubbles.

If no soap bubbles with a diameter greater than 1 mm are observed within 10 seconds, the inspector opens the relief valve and moves the vacuum box 24 inches (60.9 cm) forward along the cap strip, retaining a 6-inch test overlap area. Repeat the negative pressure extraction until the entire 40-foot cap strip is scanned.

After the entire line passes the vacuum test, the CQA engineer uses a yellow marker to write the March 2026 repair date, weld gun ID W-15, and “VAC-PASS” next to the cap strip. Supervision personnel archive the 40-foot cap strip data into the repair log of the daily electronic quality report.

Post-Installation Phase

Post-installation testing after geomembrane laying is the acceptance procedure to verify the physical integrity of the 60-80 mil HDPE material. Engineers must inject 210-240 kPa (30-35 psi) air pressure into 100% of the hot-wedge dual-track welds according to ASTM standards, with a pressure drop of no more than 14 kPa (2 psi) within 5 minutes considered qualified. For single-track extrusion welds at pipe penetrations and repair points, a negative pressure of 35 kPa (5 psi) must be applied for vacuum box detection.

High-voltage electrical leak location (ELL) will also be performed site-wide to check for tiny punctures as small as 0.5 mm in diameter. All data is summarized into a CQA report as documentation for regulatory agencies such as the US Environmental Protection Agency (EPA) to issue heap leach operation permits.

Non-Destructive Testing (NDT)

For dual-track hot-wedge welds up to 150 meters long, testers inject 210 kPa compressed air and continuously monitor for 5 minutes, with a maximum physical pressure drop of 14 kPa allowed. Single-track extrusion weld areas are bubble-tested using a transparent vacuum box with 35 kPa negative pressure applied. Complex three-dimensional flange connections are inspected with a 20,000-volt DC spark scanner. Site-wide detection considers identifying physical micropores with a diameter of 0.1 mm as the qualification benchmark, with the reading accuracy of all testing equipment controlled within 1%.

When dual-track hot-wedge welders join 1.5 mm to 2.0 mm thick HDPE geomembranes, two parallel solid welds are formed. A continuous hollow channel with a width of 10 mm to 15 mm and a height of 2 mm is reserved between the two welds. Engineers use inflation equipment with a hollow steel needle to pierce and seal both ends of the channel. Inject an initial compressed air pressure of 210 kPa (30 psi). The pressure gauge accuracy reaches a 7 kPa scale standard and possesses a calibration certificate issued by a metrology laboratory every six months.

The testing process follows these standard steps:

• Inflate to 240 kPa in the reserved space and let stand for 2 minutes to wait for the polymer wall’s physical tensile stabilization.
• Release pressure back to 210 kPa and start a stopwatch to record continuous pressure drop data for 5 minutes.
• Insert a second pressure gauge needle at the other end of the channel 150 meters away to verify if the air channel is blocked.

Air pressure readings are significantly affected by site temperature changes. For every 1°C rise or fall in temperature, the air pressure in the 150-meter-long closed channel will produce a physical expansion or contraction deviation of approximately 3.5 kPa. Testers must record the air temperature simultaneously on the log sheet.

For high-temperature environments in desert mines up to 45°C, specifications restrict testing between 12:00 PM and 3:00 PM when the surface temperature exceeds 65°C. Operations are conducted during periods of relatively constant temperature in the early morning or evening (temperature difference less than 1°C within 5 minutes). For non-conforming sections where the pressure drop exceeds 14 kPa, the operator divides the channel into independent sub-intervals of 75 meters or shorter along the weld. By repeatedly inserting inflation needles at different points to apply 210 kPa pressure, the physical coordinate range of the air leak is narrowed down.

In pipe penetration areas, edge corners, and narrow joints where hot-wedge equipment cannot enter, geomembranes use single-track extrusion welding. A single solid weld does not have an inflation channel; therefore, field verification of its surface sealing is conducted via negative pressure adsorption. The physical dimensions of an industrial-grade vacuum box are 900 mm long and 300 mm wide. A 10 mm thick transparent polycarbonate resin observation window with a light transmittance of 90% is installed at the top of the box, with closed-cell neoprene seal strips embedded around the bottom.

Field detection operations are divided into three physical steps:

• Use a grinder to remove the 0.5 mm oxidation layer on the weld surface and spray a 30% surfactant water solution.
• Place the vacuum box and apply 40 kg of human downward weight, turning on the air pump to extract internal air to form a 35 kPa negative pressure.
• Maintain the negative pressure state for a full 10 seconds and observe micro-changes in the solution level vertically through the polycarbonate window.

If no continuously expanding soap bubbles are observed on the liquid surface within the 10-second countdown, that 800 mm long local weld segment is judged to be physically sealed and qualified. The tester releases the valve and moves the vacuum box 750 mm, maintaining a 50 mm test overlap.

Rubber strips at the bottom of the vacuum box are difficult to seal on rough surfaces or complex three-dimensional geometries, such as the flange interface of a 300 mm diameter drainage pipe. For three-dimensional joint areas with a curvature radius less than 200 mm, the high-voltage discharge principle must be used for detection. Before performing spark testing, welding technicians pre-bury a bare brass wire with a diameter of 1.5 mm in the overlap area under the extrusion weld. A portable high-voltage generator applies 20,000 to 35,000 volts of DC high-voltage electricity to an external scanning electrode.

The equipment operating parameters for electromagnetic scanning are as follows:

• Hold a 200 mm long brass brush electrode and scan evenly on the weld surface at a speed not exceeding 150 mm per second.
• Maintain the physical distance between the metal bristles of the detection electrode and the highest point of the extrusion weld between 10 mm and 15 mm.
• When the high-voltage arc passes through a 0.1 mm micro-pinhole to touch the internal copper wire, the instrument’s built-in speaker emits an 85-decibel beep.

In areas where bubbles are generated in the vacuum box or the spark instrument triggers an audible alarm, the inspector draws marks with a white solid highlighter marker. The marked area must extend outward to cover a non-destructive geomembrane area with a radius of 150 mm around the leak point.

Repair technicians use a heat gun to heat the surface within the marked area to over 200°C. Once the polymer shows signs of slight reflective melting, the extrusion weld gun sprays HDPE welding rod in a molten state at temperatures up to 260°C to completely cover the repair boundary. For circular or strip-shaped patches formed by extrusion repair, the center thickness must be 2 mm to 3 mm higher than the surrounding parent material surface. The repair area is naturally cooled in the air for 30 minutes until the surface temperature drops below 40°C before the solution can be reapplied for secondary inspection.

Physical joint data that passes repair and secondary verification is entered into the digital construction quality assurance ledger according to daily progress. The database records the date of each test, the time accurate to the minute, the operator’s ID, and the equipment serial number.

Leak Location

The physical resistivity of 1.5 mm thick HDPE geomembrane is as high as $10^{15}$ ohm·cm, showing extremely strong electrical insulation. The moisture resistivity of the ore soil in the upper and lower layers and the underground base is only $10^2$ to $10^4$ ohm·cm. Testers place electrodes on both sides of the geomembrane and apply DC power, using the physical barrier of the polymer material to cut off the two layers of conductive media. In a 100,000 square meter single work area of a heap leach pad, the geomembrane does not have a conductive path under normal conditions.

The high-voltage generator outputs 200 volts to 1000 volts of DC voltage to specific work blocks. When there is a puncture hole with a diameter of more than 0.5 mm on the insulating membrane surface, water or moist soil will pass through the hole to connect the upper and lower media. The local electric field will then undergo a weak potential shift of 10 millivolts to 50 millivolts, allowing operators to accurately locate the three-dimensional coordinates of the leak point. The instrument’s built-in 24-bit analog-to-digital converter continuously samples potential change data at a physical frequency of 100 times per second.

Before engineers perform large-area scanning, they must create manual calibration benchmarks on-site according to the ASTM D7007 specification. The calibration area is selected in a flat area approximately 50 meters away from the power supply electrode to establish an accurate background electrical noise baseline. The following mandatory procedures are performed before the test:

• Use a hole punch to cut a 3.2 mm diameter circular physical hole in the geomembrane.
• Evenly spray a high-concentration conductive liquid within a 1-meter radius around the hole.
• Connect the high-voltage power equipment and record the initial millivolt reading emitted by the receiving instrument.
• Adjust the instrument’s physical sensitivity threshold until an 85-decibel alarm is clearly triggered.

The puddle method under bare membrane conditions is suitable for the pure membrane construction stage without ore bed cover. A water spray network with a width of 1.5 meters is installed at the bottom of the cart, with a 12-volt micro water pump in front continuously spraying a conductive water film. The cart advances in a straight line on the 1.5 mm thick HDPE surface at a constant physical speed of 0.5 meters per second. Each scan path must maintain a physical width overlap of 150 mm with the previous path.

The puddle method has extremely high requirements for the physical conductivity of water, and the liquid conductivity in the water tank must be greater than 500 microsiemens/cm. If the water source in arid mining areas such as the Atacama Desert in Chile is of high purity, operators need to dissolve 2 kg of sodium chloride per 1000 liters of pure water to increase the ion concentration.

The conductive water film and the base soil form a closed loop, and the high-brightness LED indicator on the cart’s control panel flashes at high frequency 10 cm away from the leak point. The cart has a built-in water tank capacity of 200 liters, supporting continuous 45-minute physical spraying operations when fully loaded.

For areas where a 600 mm thick protective gravel layer has been laid, the physical principle of the puddle method fails. The diameter of gravel particles at the bottom of the heap leach pad is generally between 12 mm and 25 mm, which hinders the continuous spreading of the surface water film. Engineers need to switch the operating mode to the dipole method, establishing a wide-area high-voltage electric field between the heavy gravel layer and the bottom soil.

High-voltage insulated transmission lines connect to a stainless steel grounding rod at a depth of 150 mm below the geomembrane. The positive plate is buried in the 600 mm thick moist gravel layer above. The power output voltage is set to 300 volts to 1000 volts, and the system output current is limited to within 200 milliamperes by a physical circuit breaker. The physical dimensions of the positive plate adopt an aluminum metal conductive mesh 1 meter long and 1 meter wide.

The physical moisture content of the gravel layer determines the coverage radius and accuracy of the dipole method’s detection field. Dry ore fragments cannot conduct a weak current of 200 mA. Engineers deploy an industrial water truck with a displacement of 15,000 liters to flood the work block for 2 hours and maintain the following physical indicators:

• The physical mass moisture content of the surface cover material is maintained between 2% and 5%.
• Standardized measurement grid reference lines with a spacing of 1 meter by 1 meter are laid out site-wide.
• Physical isolation trenches with a depth of 1.2 meters are excavated around the work area to cut off edge stray currents.
• The effective physical detection radius for a single application of voltage is strictly controlled within 75 meters.

Testers hold two titanium alloy insulated probes with a length of 1.2 meters, and the physical distance between the two probes is fixed at 0.5 meters. Along the 1-meter wide grid lines, personnel insert the probes vertically 50 mm into the gravel layer every 0.5 meters. A high-precision voltmeter connected to the top of the probes measures the potential difference between two points in real-time, displaying readings accurate to 0.1 millivolts. Within a standard 8-hour workday, a single team must complete physical insertion and potential reading records for 2,000 nodes.

When the probe set physically approaches a buried puncture point with a diameter of 1 mm, the millivolt reading on the instrument panel shows an exponential leap. From a typical background noise of ±2 millivolts, it instantly climbs to a peak of +45 millivolts. The operator makes a cross-shaped physical positioning mark with quicklime powder at the highest peak. After the two titanium alloy probes are flipped 180 degrees, the voltmeter screen shows an equivalent negative potential value, thereby double-confirming the electric polarity reversal phenomenon.

To exclude physical interference from underground metal pipes, engineers import all node data into a computer to draw a site-wide millivolt potential contour map. Buried 150 mm diameter HDPE leachate main pipes or 300 mm thick clay depressions will trigger potential anomalies similar to leak points.

By comparing with the 50-millivolt peak characteristics of manual calibration holes, the software filters out false-positive waveforms below 15 millivolts. The physical coordinates of the center point where contours are densely concentrated are input into a handheld GPS device, narrowing the excavation error to within 50 mm.

A small crawler excavator removes the 600 mm gravel cover above the marked coordinate point. Handheld flat shovels are used to clear the final 50 mm of fine-grained protective soil at the bottom, exposing the damaged 1.5 mm geomembrane parent material. Repair technicians start a 120 psi high-pressure air gun to blow clean the grit and dust in an area of approximately 200 mm in diameter. Use industrial non-woven fabrics to wipe the film surface until the material friction coefficient returns to the factory state.

If the damage is a mechanical scratch up to 50 mm long, technicians cut a 150 mm diameter circular HDPE solid patch. If it is a tiny puncture with a diameter of 2 mm, technicians operate an extrusion weld gun to spray 260°C molten polymer welding rod to cover it in situ. The welding gun advance speed is stably maintained at a physical movement speed of 300 mm per minute, and secondary verification follows completion:

• The physical width of the extrusion weld reaches 30 mm, and the center area thickness increases by 2.5 mm.
• The patch is left to cool in the air for 30 minutes until the surface physical temperature drops below 40°C.
• A transparent vacuum box covers the top, 35 kPa negative pressure suction is applied, and observation continues for 10 seconds.
• Enter the three-dimensional longitude and latitude data of the repair coordinates into the CQA acceptance ledger for archiving.

Site-wide high-voltage electrical leak location scanning proceeds at a physical rate of 10,000 square meters per day. The 15,000 recorded potential difference data nodes are reviewed and signed by an independent third-party civil engineer. A 300-page data summary document is submitted to the regional office of the US Environmental Protection Agency along with the CQA construction quality acceptance report. After approval, the project officially receives a physical dumping permit to pump a 0.5% concentration industrial sodium cyanide solution into the heap leach pad.