Secondary Containment — Design and Implementation Best Practices

Secondary Containment — Design and Implementation Best Practices

Overview

Designing secondary containment is an exercise in practical engineering and operational alignment: quantify the risk, choose compatible materials, size containment for credible releases, and ensure the system can be inspected and maintained. The objective is to prevent an escaped pollutant from leaving the facility or entering sensitive receptors such as storm drains or groundwater.

Step 1 — Risk assessment and inventory

Start by cataloging all stored and processed liquids or solids that might escape: container types, volumes, physical properties (density, volatility), chemical hazards, and temperature. Identify the largest single container and groupings of containers that could fail simultaneously. Consider human factors and likely failure modes—overfills, transfer hose failures, corrosion, vehicle impacts—and how each scenario would evolve.

Step 2 — Establish design capacity

Containment capacity is typically based on credible worst-case releases. Common practices include designing for the volume of the largest container plus freeboard or for a percentage of total stored volume. Practical design often uses one of these rules as a baseline but adapts after risk assessment. Ensure freeboard to accommodate precipitation if the containment is outdoors, or provide diversion and covers to exclude stormwater if drainage would otherwise require treatment.

Step 3 — Material selection and chemical compatibility

Choose liner and construction materials resistant to the stored substances. For aggressive chemicals, use HDPE or compatible thermoplastics; for petroleum and solvents, select materials rated for hydrocarbon exposure; for acids or bases, pick appropriate coatings or alloys. Consider UV exposure for outdoor liners and stress cracking for thermoplastics. A compatibility matrix and supplier chemical-resistance documentation are essential tools in this step.

Step 4 — Structural and hydraulic design

Consider loads (weight of stored product and any vehicles), environmental loads (snow, wind), and seismic factors where relevant. Design slopes and floor finishes to direct spilled material toward a safe collection point. If drains are necessary, design them with manually operated valves, locked cap systems, or pump-back arrangements to ensure no inadvertent discharge occurs to sanitary or storm sewers. Incorporate access points for recovery pumps and cleaning.

Step 5 — Leak detection and monitoring

Early detection reduces response time and cleanup volumes. Options range from visual inspection lanes and sumps with sight glasses to electronic sensors that detect liquid presence, level, or hydrocarbon vapors. For double-walled systems, continuous interstitial monitoring with alarms and remote reporting provides rapid notice. Ensure sensor placement considers likely leak locations.

Step 6 — Operational integration and emergency planning

Design secondary containment to work with standard operating procedures. Provide clear access for personnel and emergency responders, space for spill kits, and instructions for isolation and recovery. Update site emergency response plans to include containment activation, sample collection, and disposal procedures. Train staff on what to do when an alarm trips and how to safely recover material.

Step 7 — Testing, commissioning, and documentation

After construction, perform commissioning tests such as hydrostatic or water-hold tests for bunds and lined areas to check for leaks, and calibrate sensor systems. Document test results, as-built drawings, and operational manuals. Maintain an inspection log with dates, observations, and corrective actions to meet regulatory and insurance requirements.

Practical design features to consider

• Visible overfill protection and automatic shutdowns for fill operations.

• Dividing walls in large bunds to limit the number of containers whose failure would fill the entire basin.

• Removable grates or raised walkways to allow frequent inspections without disturbing containment integrity.

• Sloped floors and low-point sumps sized to allow mechanical recovery with standard pumps.

• Secondary containment for transfer areas and loading racks where spills are most likely.

Example calculation

If a facility stores 20 drums of 205 liters (approximately 55 gallons) each, the total inventory is 4,100 liters. A conservative containment design might aim to hold the largest single container (205 L) plus contingency, or 110% of the largest container for single-tank rules; for drum storage, many operators design for at least 25% of aggregate volume or the largest container, depending on jurisdiction. Clear calculation and documentation are important to justify the chosen approach.

Maintenance and lifecycle considerations

Design should anticipate inspection and repairs: select coatings and joints that can be repaired easily, provide access points and spare liner materials, and plan for periodic sensor calibration. Lifecycle planning ensures the containment remains effective as operations and inventories evolve.

Regulatory alignment

Many jurisdictions specify containment requirements for particular materials or thresholds. Engage environmental and safety authorities early in design to ensure the system meets permit conditions. Consider also fire codes, local stormwater regulations, and waste management rules governing collected spill disposal.

Summary

Well-designed secondary containment balances technical requirements and operational realities. By starting with a risk-based inventory, choosing chemically compatible materials, sizing capacity appropriately, providing effective detection and access, and integrating the system into daily operations and emergency plans, facilities can achieve robust protection with predictable lifecycle costs.