Bunded Chemical Tanks — Australian Regulations
If you are dosing chemicals into a water system — bore-water treatment, rural pH correction, livestock supply, irrigation conditioning — Australian regulations require secondary containment to catch the chemical if the dosing tank fails. The standard is AS 1940. The practical answer for most installations is an integrated poly bunded tank.
This page covers what the rules actually say, when bunding is required, and how to specify the right tank for the job.
What AS 1940 actually requires
AS 1940 — The storage and handling of flammable and combustible liquids — sets the framework that most state work-safety regulators apply to chemical storage including water-treatment chemicals. The headline rules:
- Secondary containment must be provided for any storage of dangerous goods above threshold quantities. For Class 8 (corrosive) chemicals — which includes sodium hypochlorite (chlorine dosing), soda ash, alum, and most acids and bases used in water treatment — the threshold is generally 25L for the protected class.
- Containment volume must be at least 110% of the largest single tank, with allowances for rainfall and displacement.
- Containment material must be chemically compatible with the stored substance and physically robust enough to retain the contents for the planned response time.
- Drainage from the bund area must be controlled — no direct path to stormwater, ground, or sewer.
The standard is updated periodically; consult the current edition for the specific clause numbers and the latest threshold values.
When you need a bunded tank vs a separate bund
Integrated bunded tank — the dosing tank ships with a built-in outer skin sized to 110% of the inner volume. One delivery, one fit-out, no separate construction. The right call for:
- New installations.
- Single-tank dosing setups.
- Sites where the tank lives indoors or under cover (no rainfall to drain).
- Retrofit jobs where pouring a concrete bund is not practical.
Separate bund — a poured concrete pad with bund walls, or a bunded tray, that the tank sits inside. The right call for:
- Multi-tank installations where one bund serves several tanks.
- Existing tanks that comply chemically but lack containment.
- Outdoor sites where rainfall handling is built into the bund design.
Sizing the bund
For a single-tank installation:
- 100L dosing tank: bund must hold at least 110L. Indoor, no rainfall allowance needed. Outdoor, add allowance for the design rainfall event (usually 24-hour 1-in-10-year storm depth).
- 200L dosing tank: bund must hold at least 220L, plus rainfall allowance if outdoor.
- 500L dosing tank: bund must hold at least 550L, plus rainfall allowance if outdoor.
For multi-tank installations, the calculation is the largest tank's contents plus a percentage of the remaining tanks (typically 25%, but verify against the current AS 1940 clauses).
Material compatibility
Linear medium density polyethylene (LMDPE) — the standard material for poly bunded tanks — is compatible with the chemicals used in almost every domestic and small-commercial water-treatment application:
- Sodium hypochlorite (chlorine dosing, up to 12.5% concentration)
- Soda ash (pH correction)
- Alum (coagulation)
- Hydrogen peroxide (low-concentration disinfection)
- Citric acid (cleaning)
For chemicals outside this list — high-concentration acids, organic solvents, oxidisers — verify compatibility against the tank manufacturer's chart. Stainless steel (typically 316L) or fibre-reinforced plastic are the common alternatives where polyethylene is not suitable.
Installation considerations
- Indoor location: away from the dosing pump's electrical cabinet, away from drinking-water lines, with access for inspection and refilling.
- Outdoor location: UV-stable poly is a must (most reputable manufacturers use carbon-black masterbatch in the resin). Rainfall management — usually a manual drain valve in the bund — is required.
- Access: clear room around the bund for refilling drums and inspecting the inner tank for cracks or weeping.
- Signage: AS 1940 requires placarding at the installation identifying the chemical class and emergency response actions.
- Spill response kit: every chemical-dosing site needs a spill kit appropriate to the chemical — neutralising agents, absorbent, PPE.
When in doubt
Talk to a licensed plumber or water-treatment contractor before specifying a tank for a regulated installation. Agricultural and rural setups have lighter requirements than commercial or industrial sites. Your local work-safety regulator publishes installation guidance specific to the chemical class and the use case — Safe Work Australia and the state regulators (SafeWork NSW, WorkSafe Victoria, Workplace Health and Safety Queensland, etc.) all maintain current resources.
For the dosing tank itself, browse the pumps and tanks category for current bunded options. For the broader context on bore-water treatment that drives most rural dosing installations, see bore water treatment.
Frequently asked questions
Do I always need a bunded tank for chemical dosing?
Not always — it depends on chemical class, volume, location, and the requirements of AS 1940. In broad terms: any indoor or sensitive-environment chemical-dosing setup using more than 25L of a Class 8 (corrosive) chemical needs secondary containment. Outdoor agricultural setups in low-risk locations sometimes do not. The local council, work-safety regulator, or your installer will confirm what applies on your site.
What is the difference between a bunded tank and a separate bund?
An integrated bunded tank has a built-in outer wall sized to hold the contents if the inner tank fails — usually 110% of nominal capacity. A separate bund is a containment tray, basin, or wall built around a standard tank to achieve the same outcome. Integrated bunded tanks are simpler to install and inspect; separate bunds give more flexibility for retrofits or multiple tanks sharing a containment area.
Why 110%?
AS 1940 specifies the bund must hold at least the volume of the largest tank plus an allowance for rainfall, displacement, and incident response. The 110% rule of thumb covers the standard single-tank case. For multi-tank installations the calculation gets more involved — the bund must contain the largest tank plus 25% of remaining tank capacity, depending on the configuration.
Are poly bunded tanks suitable for all dosing chemicals?
For most water-treatment chemicals — sodium hypochlorite, soda ash, alum, hydrogen peroxide solutions in standard concentrations — yes. Linear medium density polyethylene (LMDPE) is chemically compatible with all of these. For unusual chemistries or high concentrations, check the chemical compatibility chart from the tank manufacturer. Stainless steel or fibre-reinforced plastic (FRP) bunded tanks are alternatives for incompatible chemicals.
Does the bunded tank need to be inspected by anyone?
Yes. Workplace installations subject to AS 1940 typically need annual visual inspections plus periodic integrity testing. Domestic and small agricultural installations have lighter requirements but the bund still has to function — meaning regular checks for cracking, UV degradation, and accumulated rainwater that needs to be drained off. Local work-health-and-safety regulators publish inspection guidance for the installation type.