Ocean HDPE Liner 1.5 MM for Oil Pit Reservoir in Assam: A Detailed Case Study

Ocean Non Wovens supplied and installed 8,160 SQM of Ocean HDPE Liner 1.5 MM to line an oil pit reservoir in Assam. The pit holds crude oil, produced water and hydrocarbon by-products, in a region with heavy monsoon rain, waterlogged ground and the country’s highest seismic hazard rating. This case study covers why 1.5 mm HDPE was chosen, what the site demanded, and how the liner was welded and tested.

Assam’s Upper Brahmaputra basin has produced oil since the 1889 discovery at Digboi, often described as the country’s oldest operating oilfield. That history leaves many sites with old pits and residual contamination, which is why new oil pits are built with an engineered liner.

Project overview

• Project Name: Oil Pit Reservoir
• Location: Assam, India
• Product Supplied: Ocean HDPE Liner 1.5 MM
• Scope: Supply and Installation
• Total Area Covered: 8,160 SQM
• Executed By: Ocean Non Wovens

The reservoir was built as a leak-proof containment structure for crude oil and associated petroleum waste, to meet pollution control requirements.

Why an HDPE liner for an oil pit

Oil pits act as primary or secondary containment for crude oil, drilling mud, produced water and oily sludge. Without an impermeable barrier, these seep into the soil and reach groundwater. HDPE geomembranes are the usual choice for hydrocarbon containment because they combine very low permeability, good resistance to crude oil, acids, alkalis and brine, and field-weldable seams that can be tested along their full length.

Why 1.5 mm rather than 1.0 mm

A 1.0 mm liner is common for water reservoirs. For an oil pit, the thicker sheet gives more margin against puncture from angular subgrade and equipment loads, more tensile and tear strength, and more material to resist slow chemical attack. Under GRI-GM13, the minimum puncture resistance rises from 320 N at 1.0 mm to 480 N at 1.5 mm, about 50% higher.

Typical properties of 1.5 mm smooth HDPE (GRI-GM13 minimums)

Ocean states that its HDPE liner meets GRI-GM13. For a 1.5 mm (60 mil) smooth sheet, the specification sets these minimum values:

Carbon black at 2–3% provides the UV stabilisation needed for an uncovered pit, and the antioxidant package (measured by OIT) protects the polymer against oxidation over its service life. For a specific project, ask for the batch test certificate rather than relying on catalogue values.

Site challenges in Assam

High rainfall and waterlogged ground

Assam averages about 2,818 mm of rain a year, most of it in the June to September monsoon. The site stayed waterlogged for long periods, so the team used temporary dewatering and deployed liner during dry windows. Laying HDPE on a saturated subgrade risks trapped water or vapour lifting the sheet into “whales”, which strain seams and the sheet itself.

Seismic Zone V

Assam lies in Seismic Zone V under IS 1893 (Part 1):2016, the highest category in that code; the 1950 Assam earthquake (magnitude 8.6) was one of the largest recorded anywhere. HDPE meeting GM13 yields at around 12% strain and does not break until beyond 700%, so it can follow moderate ground movement without tearing. Seismic design still has to keep sustained strain in the liner well below yield, mainly through anchor-trench detailing and slope geometry.

Hydrocarbon traces in the subgrade

Pre-installation soil testing found petroleum traces in the subgrade, a legacy of oil activity in the area. The site was remediated before the liner went down so contaminated soil would not compromise the anchoring.

Heat, humidity and thermal movement

Temperatures range from about 6 °C in winter to 38 °C in summer, with relative humidity usually above 80%. HDPE expands and contracts noticeably with temperature, so the crew built in slack during deployment. A liner installed tight on a hot afternoon can bridge across the toe of slopes when it cools and contracts, putting the sheet in tension.

Installation, step by step

Phase 1: Site preparation

The reservoir bed was excavated to design depth and the subgrade compacted to a minimum 95% Standard Proctor density. Sharp stones, roots and debris were removed, and a 150 mm sand cushion was placed as bedding to protect the liner from below.

Phase 2: Panel layout and deployment

Rolls were deployed with spreader bars and manual positioning. The panel layout kept seam length to a minimum, with at least 100 mm overlap for fusion welding. Deployment was done in the morning, when temperatures were moderate, to limit thermal stress.

Phase 3: Fusion welding

Panel joints were welded with dual-track hot wedge machines, which leave two parallel welds with an air channel between them so every seam can be pressure tested. Machine speed was kept between 1.5 and 3.0 metres per minute and wedge temperature between 380 and 440 °C, adjusted for ambient temperature and humidity.

Phase 4: Seam testing

• Air channel pressure test: the channel between the dual welds was pressurised to 200 kPa and held for 5 minutes; a pressure drop of more than 10% meant re-welding.
• Vacuum box test: used on T-joints, patches and extrusion welds. Soapy solution under a clear vacuum box shows leaks as bubbles.
• Destructive peel and shear tests: samples cut from production welds and tested to ASTM D6392.
• Visual inspection: the whole liner surface checked for scratches, thin spots, contamination and damage.

Seams are the most likely leak path in any geomembrane, which is why every metre of fusion seam is tested non-destructively and samples are cut for destructive testing at set intervals.

Long-term performance

Chemical exposure

HDPE resists crude oil well. Prolonged contact with aromatic solvents such as benzene, toluene and xylene can cause swelling and slow loss of properties, so the chemistry of what goes into the pit should be checked against the liner’s chemical resistance data. A high OIT value indicates a strong antioxidant package and longer oxidative life.

UV on exposed slopes

Oil pits in Assam are often left uncovered, so the liner is exposed to sun. Well-dispersed carbon black is the main protection; covered or buried liners last considerably longer than exposed ones.

Maintenance

Ocean Non Wovens recommends the following for this pit:

• Annual visual inspection in the dry season for surface damage, wrinkles or exposed anchor trenches
• Periodic sludge removal, so loads stay within design and the liner can be inspected
• Checking anchor trenches after earthquakes and heavy monsoons
• Prompt repair of damage by extrusion welding HDPE patches
• A maintenance log of all inspections and repairs for regulatory records

Other geosynthetics in an oil containment system

• Geotextiles: non-woven geotextile above and below the liner as a cushion against puncture.
• Geocomposites: drainage geocomposites between primary and secondary liners for leak detection in double-lined designs.
• Geosynthetic clay liners: a GCL under the HDPE forms a composite barrier with a second line of defence.
• Geonets: drainage layers that carry any leakage to a monitoring sump.

HDPE compared with other containment methods

• Concrete-lined pits: higher initial cost, prone to cracking under seismic loading, joints that degrade, and hard to repair in the field.
• Compacted clay liners: typically built to a hydraulic conductivity of 1 × 10⁻⁷ cm/s, far more permeable than HDPE, prone to desiccation cracking in the hot pre-monsoon months, and need much more material.
• PVC liners: lower resistance to hydrocarbons, and plasticiser loss over time reduces flexibility and service life.
• HDPE 1.5 mm: very low permeability, field-weldable for repairs, and widely used in hydrocarbon containment.

Frequently asked questions

What thickness of HDPE liner is used for oil pit reservoirs?

1.5 mm (60 mil) is a common choice for crude oil and petroleum waste pits because it adds puncture, tensile and chemical margin over 1.0 mm. GRI-GM13 sets material properties for each thickness but does not prescribe a thickness for an application; that is a design decision. For comparison, India’s Solid Waste Management Rules, 2016 require an HDPE liner of at least 1.5 mm in sanitary landfills. Thinner liners (1.0 mm) are often used for water reservoirs.

How long does an HDPE liner last in oil containment?

Service life depends mainly on exposure: UV, temperature and the chemicals stored. A GM13-compliant liner with proper carbon black and antioxidants lasts for decades, and covered or buried liners last much longer than exposed ones.

Can HDPE liners cope with earthquakes?

HDPE is ductile, yielding at around 12% strain and breaking beyond 700%, so it can follow moderate settlement and differential movement. Anchor trenches, slopes and pipe penetrations need detailing so the liner is not overstrained during ground shaking.

What quality control tests are done on HDPE seams?

Air channel pressure testing for dual-track fusion welds, vacuum box testing for extrusion welds and detail work, destructive peel and shear testing to ASTM D6392, and visual inspection. All fusion seams should be tested non-destructively, with destructive samples taken at specified intervals.

What regulations apply to oil pit containment in India?

Oily sludge and similar wastes fall under the Hazardous and Other Wastes (Management and Transboundary Movement) Rules, 2016, administered through the State Pollution Control Boards, which set the containment conditions for each facility. HDPE geomembranes meeting GRI-GM13 are the usual specification for these liners.

About Ocean Non Wovens

Ocean Non Wovens manufactures and supplies geosynthetics for oil and gas containment, water reservoirs, chemical storage, railway infrastructure and environmental protection projects across India, with installation teams and post-installation support. Products include HDPE liners, geotextiles, geocells and complete containment systems. See more case studies or contact the team to discuss your project.