We pump out and decommission the old tank, install a new septic tank, holding tank or biological wastewater treatment plant (BIO plant), and connect it to the house's existing sewer. A septic tank including the tank and installation costs from €2,200; send a request with a description of the old system.
When an old septic tank has to be replaced, not repaired
- It is a bottomless ring well or a single chamber from which wastewater soaks directly into the ground. That is not a septic tank within the meaning of the regulations.
- The rings have shifted, the joints have crumbled, and groundwater flows into the tank in spring.
- The tank never fills up, because the wastewater escapes into the ground and can reach the well water.
- The metal tank has rusted through, the brick walls are crumbling, and the cover is no longer safe.
- The drain field is clogged, and the septic tank fills up within a few days of pumping.
If there is a single fault (a crack, the cover or the inlet pipe), a repair is often enough: see septic tank repair. Replacement is justified if the tank leaks in several places or the design of the system itself does not meet the requirements.
Cabinet Regulation No. 384, point 2.3: a septic tank is a tank with two or more chambers for settling wastewater, with an overflow to the environment after settling; point 4.4: wastewater from a septic tank is discharged into the environment only through a purpose-built infiltration system; point 18: systems had to be brought into compliance by 31.12.2021. Source: likumi.lv, checked on 30 October 2026.
First, check for a mains sewer
If a mains sewer network has already been built along your street, connecting to it may be better value than a new decentralised system. The regulations required owners of non-compliant systems to connect to a network in the street by 31.12.2023. In Riga, municipal co-financing is available for the connection. For more details, see the page connecting to the mains sewer.
Cabinet Regulation No. 384, point 18: if the system has not been brought into compliance by 31.12.2021 and there is a mains sewer network along the adjacent street, the owner connects by 31.12.2023. Riga municipal co-financing for sewer connections: LV portāls, 2026. Sources: likumi.lv, lvportals.lv, checked on 30 October 2026.
What to replace the old septic tank with
| Solution | When it suits | Price from |
|---|---|---|
| Plastic septic tank with a drain field | Sandy soil, low groundwater, enough space for the field | from €2,200 including tank and installation |
| Biological treatment plant | Clay soil, high groundwater, little space; the treated water can be discharged into a ditch or the ground | plant from €1,750 + installation from €800 |
| Holding tank | Where infiltration is not possible or a mains sewer is coming soon | 2 m³ tank from €800 + installation; regular pumping |
The choice is determined by the soil and groundwater, not by the type of the old system. If the old tank was a septic tank with a field but the plot is clayey, that is most likely where the problem came from. See the page septic tank in clay soil. If you want to convert the old septic tank into a biological treatment plant, see converting a septic tank into a biological treatment plant.
What happens to the old tank
The old tank first has to be pumped out and flushed. No sludge may be left in the ground. Then there are two options:
- Removal: the rings or walls are lifted out and taken away. This is done if the new tank goes in the same place. The bottom of the pit is cleared of contaminated soil and compacted again.
- Backfilling: if the new tank will be elsewhere, the cleaned old tank can be backfilled with sand, after first removing the cover and the top ring so that nothing caves in later.
An empty tank must not be left with an old cover on it: it is a collapse risk for people, animals and machinery.
Order of work
- Site visit We determine how deep the outlet pipe leaves the house (this sets the depth of the new tank), what the soil is like and where machinery can get in.
- Documents For a small wastewater treatment structure of up to 5 m³ per day, an explanatory memorandum to the building authority is usually enough. The exact scope of documents is set by the municipal building authority.
- Emptying the old tank Pumping and flushing before the groundworks.
- Installation Pit, base, new tank, connection pipe from the house, drain field or outlet, backfilling.
- Decommissioning the old tank Removal or backfilling, levelling the area.
- Register A change of system type or a rebuild must be reported to the municipality within a month.
A small wastewater treatment structure (capacity up to 5 m³/d) is a Group I engineering structure whose construction is carried out on the basis of an explanatory memorandum (LV portāls, e-consultation 06.12.2024, referring to Cabinet Regulation No. 253); Cabinet Regulation No. 253, point 94.2. Reporting changes within a month: Cabinet Regulation No. 384, point 15.2; Riga City Council Binding Regulations No. 66, point 6. Sources: likumi.lv, lvportals.lv, checked on 30 October 2026.
How much old septic tank replacement costs
A new septic tank including the tank and installation costs from €2,200. Replacement adds pumping out the old tank (from €75 up to 4 m³, from €90 up to 6 m³) and its removal or backfilling, which we include in the estimate after a site visit. If the new tank will be further from the house, the pipe installation costs extra (from €25/m). The price goes up with lifting out concrete rings, high groundwater, limited access for machinery and a new drain field in place of the old one.