tank dike, Oil & Gas Glossary

A tank dike, also called a firewall, berm, or secondary containment structure, is an earthen, concrete, or engineered barrier constructed around one or more aboveground storage tanks (ASTs) at oil and gas production facilities, tank batteries, terminals, refineries, and chemical storage areas to contain spilled product in the event of tank rupture, overflow, fire, vandalism, or catastrophic failure. The fundamental engineering requirement is that the volumetric capacity inside the dike must exceed the volume of the largest single tank within the diked area, with most regulatory regimes specifying a minimum of 110 percent of the largest tank's nominal capacity to allow for displaced rainwater, freeboard, snow accumulation, and partial occupation of the containment by tank foundations, valves, piping, and ancillary equipment. In Western Canadian Sedimentary Basin upstream operations, AER Directive 055 (Storage Requirements for the Upstream Petroleum Industry) governs tank dike design, construction, inspection, and maintenance for all crude oil, condensate, produced water, and chemical storage tanks at well sites, batteries, gas plants, and pipeline terminals in Alberta, with parallel requirements in British Columbia through BC Energy Regulator (BCER) directives and in Saskatchewan under the Ministry of Energy and Resources. The dike volume calculation must subtract the displacement volume of any tank foundations within the dike but is allowed to assume that secondary tanks within a multi-tank dike will not simultaneously fail with the primary tank, so the containment capacity is sized for the largest tank only, not the cumulative tank volume. Dike walls are typically constructed of compacted earth with an impermeable liner (40 mil to 80 mil HDPE geomembrane, or compacted clay with permeability below 1 times 10 to the minus 7 cm/s) extending up the inside slope of the dike and beneath the tank pad to form a continuous bathtub-style containment, with concrete bulkheads at strategic points and engineered drainage outlets fitted with manually-operated valves locked closed by default and opened only during scheduled rainwater removal under operator supervision. Per AER Directive 055, dike walls must withstand the hydrostatic pressure of full design containment plus a dynamic surge factor of 1.5, must be inspected visually quarterly and assessed annually, and must be maintained free of vegetation, burrowing animals, settlement cracks, and erosion. Related concepts include tank battery for the broader facility, secondary containment for the regulatory category, and bunding for the equivalent British-Commonwealth terminology used in some international standards.

Key Takeaways

Volumetric Containment Requirement: The volume inside a tank dike must hold at least 110 percent of the largest single tank within the diked area, accounting for displaced rainwater, freeboard against wind-driven sloshing, snow accumulation in winter conditions, and the volume occupied by tank foundations and piping; in multi-tank dikes, the capacity is sized for the largest tank only since simultaneous catastrophic failure of multiple tanks is not the design basis under AER Directive 055.
AER Directive 055 Compliance: Alberta upstream tank batteries must comply with AER Directive 055 Storage Requirements for the Upstream Petroleum Industry, which specifies dike design, impermeable liner requirements (40 to 80 mil HDPE geomembrane or compacted clay below 1 times 10 to the minus 7 cm/s permeability), quarterly visual inspections, annual integrity assessments, vegetation control, and rainwater drainage protocols with manually-locked drain valves; parallel requirements apply in BC through BCER and in Saskatchewan through SK Ministry of Energy.
Construction Materials and Cost: WCSB tank dikes are typically built of compacted clay earth with HDPE geomembrane liner extending up the inside slope and beneath the tank pad in a bathtub configuration; typical construction cost for a 400 to 1,000 bbl tank battery dike runs CAD 35,000 to CAD 85,000 for earthwork, liner, drainage outlet, and culvert work, with steel or concrete dike alternatives running 2 to 4 times higher cost but offering longer service life in saline produced water environments.
Drainage and Rainwater Management: Diked areas accumulate rain, snowmelt, and condensate that must be released periodically, controlled through a manually-operated drain valve locked closed by default and opened only after visual inspection confirms no hydrocarbon sheen or contamination; under AER Directive 055, accumulated water that shows hydrocarbon contamination must be vacuum-trucked to an approved Class Ib disposal facility at typical cost of CAD 250 to 400 per m3 hauled rather than discharged.
Inspection and Maintenance Schedule: Quarterly visual inspections check dike walls for settlement cracks, animal burrows (gophers, badgers, foxes are common WCSB threats), erosion, liner exposure, vegetation overgrowth, and damage to drainage valves and gauges; annual integrity assessments include liner integrity verification through visual inspection or holiday testing, volume re-calculation, and documentation review per AER Directive 055 record-keeping requirements with retention for the operating life of the facility.

Dike Volume Calculation and Freeboard Allowance

The standard AER Directive 055 volumetric calculation begins with 100 percent of the largest tank's nominal capacity, adds 10 percent freeboard for wave and wind sloshing, then subtracts the displacement volume of tank foundations, piping racks, and any secondary tanks within the diked area. A typical WCSB tank battery with two 750 bbl (119 m3) crude tanks and a 1,000 bbl (159 m3) produced water tank requires a dike sized for the largest (159 m3) plus 10 percent (15.9 m3) for total minimum containment of 175 m3 within the dike walls. After subtracting roughly 12 m3 of foundation and piping displacement, the actual dike footprint must enclose 187 m3 of containment volume at design freeboard depth.

Liner Systems and Impermeability Standards

AER Directive 055 requires that the diked area be lined with material providing permeability below 1 times 10 to the minus 7 cm/s, achievable through 40 to 80 mil thickness HDPE geomembrane (most common in modern WCSB construction), through compacted clay with proven low permeability via Atterberg limits and proctor density testing, or through concrete with sealed joints. The liner extends from beneath the tank foundation up the inside slope of the dike to at least 150 mm (6 inches) above design containment level, with all seams heat-welded and tested. Holiday testing per ASTM D7240 verifies liner integrity at CAD 3,500 to 8,000 per tank battery liner installation.

Fast Facts

The largest tank dike failure in Canadian history occurred in 1973 at the Brookvale terminal in New Brunswick, where a 30,000 barrel furnace oil tank ruptured during winter conditions and the diked containment held the entire spilled volume successfully but was overwhelmed when the contained oil ignited from a static electricity source, with the dike walls then channeling burning oil through a drainage culvert that had been left unlocked into a nearby creek. The incident spurred regulatory revision across North America to mandate locked drain valves with positive lockout-tagout procedures, a standard now embedded in AER Directive 055 and equivalent regulations in BC, Saskatchewan, and US EPA SPCC requirements.

A tank dike is one component of the broader tank battery facility that includes oil, gas, and water separation, treating, and storage equipment at upstream well sites. The dike provides secondary containment, the regulatory category covering all spill-prevention barrier systems including dikes, double-walled tanks, and impervious slabs under spill prevention control regimes. The British-Commonwealth equivalent term bunding describes the same concept in UK North Sea, Australian, and Norwegian offshore and onshore operations, and the dike interfaces with spill prevention programs documented in Alberta facility licenses and US EPA SPCC plans.

Cardium Tank Battery: Dike Cost and Compliance

Consider a Cardium oil battery operated by Canadian Natural Resources in the Pembina field of west-central Alberta, handling crude from 8 producing wells with daily throughput of 320 bbl/day. The tank battery includes two 750 bbl (119 m3) sales oil tanks, one 1,000 bbl (159 m3) produced water tank, and a 400 bbl (64 m3) crude oil flash tank. The required dike capacity per AER Directive 055 sizes to 110 percent of the largest tank (159 m3 plus 15.9 m3 freeboard = 175 m3), with engineered design adding 12 m3 for foundation and piping displacement, totaling 187 m3 enclosed at design containment depth.

Construction cost in 2024 dollars includes CAD 18,000 for earthwork (clearing, grading, compacted clay subgrade), CAD 24,000 for 60 mil HDPE geomembrane liner with heat-welded seams and holiday testing, CAD 9,500 for drainage outlet with locked manual valve and observation riser, and CAD 6,500 for engineering, surveying, and as-built documentation, totaling CAD 58,000 against an overall battery construction AFE of CAD 1.4 million. Quarterly inspection and annual integrity assessment ongoing costs run CAD 3,200 per year over the 20- to 25-year facility life under AER Directive 055 compliance.