Bare Liner Surveys: Pre-Service Leak Detection (ASTM D7002)
Bare Liner Surveys: Your Final Quality Assurance Check
Detect Installation Defects Before Your Geomembrane Is Covered – Water Puddle & Spark/Arc Testing Methods
What Is a Bare Liner Survey?
A bare liner survey is an electrical leak location test performed on exposed geomembranes before they are covered with soil, drainage layers, water, or geotextile. This pre-service leak detection process provides the final verification that a liner system is free of defects following installation and seaming.
Bare liner surveys are conducted after all welding and traditional construction quality assurance (CQA) testing are complete, but before the geomembrane is placed into service. At this stage, the liner is fully accessible, making defect detection and repair fast, accurate, and cost-effective.
The primary method used is the ASTM D7002 water puddle test, which applies electrically charged water across the liner surface to identify leaks. For certain applications, spark testing (conductive liner) geomembrane systems (ASTM D7240) may be used as an alternative or arc testing (non-conductive) geomembrane systems (ASTM D7953).
As the most critical QA step in liner installation, a bare liner survey is the last opportunity to find and repair defects easily, before repairs become exponentially more expensive and disruptive.
Why Bare Liner Surveys Are Critical
Even the most experienced installers and rigorous CQA programs cannot eliminate all defects. Seam irregularities, punctures, and installation damage commonly occur during geomembrane deployment, often without visual indicators.
Traditional CQA methods, such as air lance, vacuum box, or ultrasonic testing, primarily focus on seams and are typically sample-based, meaning large portions of the liner surface are never tested. As a result, critical defects can remain undetected.
A bare liner survey provides 100% surface testing, ensuring both seams and field sheets are evaluated. Repairs made at this stage are simple and inexpensive. Once the liner is covered, however, locating and repairing leaks may require excavation, material removal, system shutdowns, and regulatory involvement.
Industry experience shows it is common to find multiple leaks per acre on liners that otherwise appear perfectly installed. Studies also demonstrate that traditional CQA can miss a significant percentage of defects. Repairing leaks after covering can cost many times more than repairing an exposed liner.
Beyond cost savings, bare liner surveys provide:
- Regulatory confidence and documented due diligence
- Assurance the containment system will perform as designed
- Environmental protection before waste or liquids are introduced
- Reduced long-term liability and operational risk
When to Schedule a Bare Liner Survey
✓ After all seaming and welding is complete
✓ After traditional CQA testing
✓ Before protective soil or drainage layers are placed
✓ Before ponds or tanks are filled
✓ As the final step in construction QA
✓ Before the installer demobilizes
✓ While repair crews and materials are still on-site
Water Puddle Method (ASTM D7002)
The ASTM D7002 water puddle method is the most widely used and sensitive form of pre-service leak detection for exposed geomembranes.
How It Works
An electrically charged layer of water is applied to the liner surface and pushed ahead of a squeegee. A power supply is connected to an earth ground or conductive layer beneath the liner. When water contacts the ground through a defect, an electrical circuit is completed, triggering an audible signal.
The Process
- Technician walks a systematic pattern across the liner
- Water is pushed in a 6-8 foot swath using a squeegee
- Electronic equipment continuously monitors current flow
- Leaks are immediately detected and marked
- Photos and coordinates are recorded
Experienced crews can survey multiple acres of liner per day, depending on site conditions.
Detection Capability
- Detects leaks as small as 1 mm
- Identifies punctures, tears, knife cuts, seam defects, and cracks
- Proven performance for over 30 years
- Considered the most sensitive exposed liner leak detection method
Site Requirements
Soil surveys conducted by LLSI offer exceptional sensitivity and reliability:
- Clean liner with no standing water
- Conductive subgrade (clay, GCL, or moist soil)
- No unintended grounding from penetrations
- Installation complete
- Safe weather conditions (no lightning or heavy rain)
Spark Testing Method (ASTM D7240)
Spark testing geomembrane systems is an alternative bare liner survey method used when water puddle testing is not practical.
Overview
This method uses high-voltage, low-current electrical energy and does not require water. A conductive layer manufactured to the underside of the geomembrane allows an electrical arc to form at breach locations.
How It Works
A conductive wand or brush is passed over the liner surface. When a defect is encountered, a visible spark and audible alarm indicate the leak location, which is immediately marked.
When Spark Testing Is Preferred
- Multiple penetrations in a small area
- Very dry subgrade conditions
- Geomembranes with conductive backing
- Certain double-lined systems where there is no conductive material between the layers
- Tanks, roofs, and vertical surfaces
Advantages
- No water required
- Works on short vertical surfaces
- Can be performed in freezing conditions
Arc Testing Method (ASTM D7953)
Arc testing geomembrane systems is an alternative bare liner survey method used when water puddle testing is not practical and a conductive liner is not present.
Overview
This method uses high-voltage, low-current electrical energy and does not require water. It relies on a subgrade in intimate contact with the geomembrane or a conductive geotextile beneath the geomembrane being tested. This conductive layer allows an electrical arc to form at breach locations.
How It Works
A conductive wand or brush is passed over the liner surface. When a defect is encountered, a visible spark and audible alarm indicate the leak location, which is immediately marked.
When Arc Testing Is Preferred
- Multiple penetrations in a small area
- Water is not readily available
- Moist subgrade or conductive geotextile is present
Advantages
- No water required
- Works on short vertical surfaces
Bare Liner Survey Applications
Bare liner surveys are used across a wide range of industries, including:
Landfills – Cell bases, final covers, and double-lined systems
Ponds & Impoundments – Before filling ponds, canals, and tanks
Mining – Heap leach pads, solution ponds, tailings facilities
Industrial – Secondary containment, process tanks, roof membranes
Agriculture – Irrigation ponds and waste lagoons
Any project requiring confidence in liner integrity before covering benefits from exposed geomembrane testing.
Common Defects Found
- Seam Issues: incomplete bonding, skip welds, contamination
- Physical Damage: tool punctures, tears, dragging damage
- Manufacturer Defects: pinholes and material flaws
- Installation Damage: stress cracking, boot traffic, equipment tracking
Advantages Over Traditional CQA Methods
Traditional methods:
- Test only seams
- Are sample-based
- Miss field sheet defects
Bare liner surveys:
✓ Test 100% of the liner
✓ Detect seam and field defects
✓ Faster and more sensitive
✓ ASTM-standardized
✓ Provide complete peace of mind
Best practice: Use traditional CQA during installation and a bare liner survey as final verification.
Soil Survey vs Other Leak Detection Methods
1. Pre-Survey Inspection
-
- Verify liner installation complete
- Check subgrade conductivity
- Identify any ground penetrations
- Plan survey logistics
2. Equipment Setup
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- Connect power supply to ground
- Fill water tank (water puddle method)
- Test and calibrate equipment
- Establish systematic coverage pattern
3. Survey Execution
-
- Systematic coverage of entire liner
- Real-time leak detection
- Immediate marking of each leak
- leak coordinates and photos
- Field notes on leak characteristics
4. Documentation & Reporting
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- Marked site map with all leak locations
- Detailed report with findings
- Photos of each defect
5. Repair Verification
-
- Retest repaired areas
- Confirm all leaks addressed
- Final sign-off documentation
Timing Considerations
- Schedule Early: Book survey before demobilizing installer
- Critical Path: Survey typically takes 1-3 days, depending on size
- Repair Time: Allow half a day for repairs after survey
- Verification: Retests takes minutes, not days
- Don’t Rush: Last step before covering – worth doing right
- Mobilization: We can deploy quickly (48-72 hours notice)
- Project Coordination: Work closely with contractor to avoid delays
Cost-Benefit Analysis
A bare liner survey is a small upfront investment that prevents major downstream costs. A typical survey may cost only a fraction of the installation cost and take only days to complete. Repairs are simple and inexpensive while the liner is exposed.
Finding leaks later can involve:
- Excavation and material replacement
- Weeks of downtime
- Regulatory delays and fines
- Environmental remediation costs
ROI Example: A $8,000 survey finds 6 leaks repaired for $500. Post-cover repairs could exceed $80,000, a 100:1 return on investment.
The LLSI Bare Liner Survey Advantage
- Pioneered the Method: Involved in developing ASTM D7002 standard
- Unmatched Experience: Thousands of acres surveyed since 1992
- Equipment Expertise: Multiple survey systems ready for deployment
- Rapid Response: Can mobilize within 48-72 hours
- Weather-Ready: Survey in conditions others can’t
- Efficient Coverage: Experienced crews maximize productivity
- Thorough Documentation: Comprehensive reports
- Repair Verification: Retest at no additional charge
- Quality Assurance: Rigorous protocols ensure no leaks missed
Frequently Asked Questions
When should I schedule the bare liner survey?
A bare liner survey should be scheduled after all geomembrane installation and seaming are complete and after traditional CQA testing, but before any soil, drainage layers, or water are placed over the liner. This timing ensures the liner is fully accessible and allows any detected defects to be repaired quickly and cost-effectively before the system is put into service.
How long does a survey take?
Survey duration depends on liner size, site conditions, and the testing method used. Most projects are completed within 1–3 days. Large or complex facilities may require additional time, while smaller areas can often be surveyed in a single day. Repair verification typically takes only a few minutes once repairs are completed.
What if you find leaks?
If leaks are detected, they are immediately marked, documented and photographed. Your installer or repair crew can address the defects right away while the liner is still exposed. After repairs are completed, LLSI performs verification testing to confirm that all leaks have been successfully repaired before final sign-off.
Do we need to delay construction?
In most cases, no. Bare liner surveys are designed to integrate seamlessly into construction schedules. Because repairs are fast and localized, they typically do not impact project timelines. Early coordination with LLSI ensures the survey fits smoothly into your critical path without delays.
Can you survey in the rain?
Not ideal. The ASTM D7002 water puddle method can be performed in a light drizzle, but not moderate or heavy rain. Lightning will require temporary suspension for safety reasons. Spark and Arc testing requires the liner to be completely dry and free of debris.
What about textured liners?
Bare liner surveys are effective on both smooth and textured geomembranes. The water puddle method works well on textured liners, and spark testing is also highly effective for vertical slopes, and specialty applications.
Do we still need traditional CQA?
Yes. Bare liner surveys are not a replacement for traditional CQA testing, but rather the final verification step. Traditional methods, such as air lance or vacuum box testing, are essential during installation, while bare liner surveys provide 100% surface coverage as the last quality assurance check before covering.
How much does a bare liner survey cost?
Costs vary based on liner size, site conditions, and testing method. However, bare liner surveys represent a small investment compared to the cost of post-cover leak repairs, which can be 50–100 times more expensive. Most clients find the survey delivers an exceptional return on investment by preventing future excavation and downtime.
What if we’re on a tight schedule?
LLSI specializes in rapid mobilization and can typically deploy crews within 48–72 hours’ notice. Our experienced technicians work efficiently to complete surveys quickly without compromising accuracy, helping projects stay on schedule even under tight deadlines.
Can you survey partial installations?
Yes. Bare liner surveys can be performed on partial or phased installations, provided the tested area meets the electrical and site requirements. This is especially useful for large projects where construction progresses in stages.
What information do you need from us?
To plan your survey efficiently, we typically need:
- Project location and liner type
- Area size and layout drawings
- Subgrade or conductive layer details
- Construction schedule and readiness confirmation
- Site access and safety requirements
This information allows us to mobilize quickly and avoid delays.
How do you mark leak locations?
Each leak is marked directly on the liner surface using clearly visible, non-damaging markers. Locations are also documented with coordinates, photographs, and detailed field notes, ensuring repair crews can easily locate and fix each defect.
ASTM D7002 Standard
ASTM D7002 defines procedures for electrical leak detection using the water puddle method on exposed geomembranes. The standard establishes sensitivity requirements, survey protocols, and quality assurance measures. It is widely accepted by regulators and engineers as the industry benchmark for pre-service leak detection.
Regulatory Compliance
LLSI soil surveys support state environmental agency requirements and EPA landfill CQA guidelines. Our third-party testing provides defensible documentation for permit compliance, closure approvals, and regulatory review.
Water Puddle vs Spark Testing vs Arc Tesgin
| Feature | Water Puddle (D7002) | Spark Test (D7240) Arc Test (D7953) |
| Detection Size | 1mm+ leaks | 1mm+ leaks 1mm+ leaks |
| Speed | Faster | Moderate Moderate |
| Water Required | Yes | No No |
| Best Applications | Most projects | Multiple penetrations Multiple penetrations |
| Vertical Surfaces | Excellent on Slopes | Short Vertical Walls Short Vertical Walls |
| Cost | Similar | Similar Similar |
| Weather | Light Drizzle | Dry and Clean Dry and Clean |
Pre-Survey Checklist for Clients
- All seaming/welding complete
- Traditional CQA finished
- Liner clean and free of debris
- Standing water removed
- Repair crew and materials available
- Site access arranged
- No active construction in area being tested
- Adequate notice provided to LLSI
Request a Bare Liner Survey Today
Don’t cover uncertainty.
Schedule a bare liner survey with Leak Location Services, Inc. and ensure your geomembrane system performs as designed, before it’s too late.
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