ShallowDig Septic Tanks

Shallow dig tanks are designed with a reduced overall height and repositioned inlet/outlet levels, so they can be installed with significantly less excavation than a standard tank of the same capacity. This makes them suitable for sites with a high water table, shallow bedrock, or where deep digging risks structural damage to nearby buildings. The treatment capacity and performance are unaffected — only the installation depth changes.

If a trial hole shows groundwater or solid rock within a metre or so of the surface, a standard-depth tank may not be practical or could float or shift once installed. Shallow dig tanks are also useful where invert levels from the property are already quite high, avoiding costly excessive pipe falls. Your groundworker or installer should confirm ground conditions before you order, as this affects tank choice as much as household size.

Shallow dig septic tanks are available across the same range of population sizes as standard tanks, typically from small 4-6 person dwellings up to larger multi-occupancy properties. Sizing is based on the number of people the property serves, not just bedrooms, so holiday lets and multi-generational households should size up accordingly. We can help you cross-reference household occupancy against manufacturer capacity charts to get this right first time.

Yes — a septic tank only settles solids, so treated effluent still needs to discharge to a drainage field for further treatment in the soil, exactly as with standard-depth tanks. Because ground conditions prompting a shallow dig install (high water table, rock) can also affect drainage field performance, a percolation test is essential before finalising your design. In some cases a raised or mound drainage field is needed alongside the shallow tank.

Most shallow dig septic tanks are manufactured from GRP (glass-reinforced plastic) or high-density polyethylene, both chosen for their strength-to-weight ratio and resistance to corrosion, ground movement and chemical attack from effluent. Despite their reduced height, the tank walls and ribbing are engineered to withstand the same groundwater and soil loading as deeper models. Correct backfill material and compaction during installation is still critical to long-term structural performance.

Yes, our shallow dig tanks are manufactured to meet the relevant British and European standards and comply with the General Binding Rules for small sewage discharges in England and Wales. You'll still need to register the discharge with the Environment Agency (or SEPA/NRW as applicable) if you don't already have consent, and installation must follow the manufacturer's guidelines and current Building Regulations Part H. We supply full installation instructions with every tank to support your building control submission.