Quick answer: Muddy water pumped from a trench or excavation is a pollutant. Before it leaves site, reduce the silt at source, let it settle where you can, and pass what you pump through a dewatering sediment filter on the end of the hose. Just as important, make sure you have permission for wherever the water ends up. A surface water drain usually leads straight to a stream or river.
Why silty water matters
Silt looks harmless, but in a watercourse it smothers the riverbed, harms fish and invertebrates and carries other pollutants with it. On land it blocks gullies and drains and leaves a mess on roads and pavements that someone has to clean up.
Discharging polluted water can lead to enforcement action and fines, as well as vacuum tanker and drain jetting bills. The cost of doing it properly is small by comparison.
Check where the water can go
Before you start pumping, find out what the discharge point is and whether you can use it.
- Surface water drains and gullies usually discharge to a watercourse, so treat them as if they were the river.
- Discharging to a watercourse or surface water drain may need an environmental permit, or you may need to meet the conditions of a regulatory position statement. Check with the Environment Agency (or Natural Resources Wales, SEPA or NIEA) first.
- Discharging to a foul sewer needs the water company’s permission.
- Discharging to land, such as a grassed area well away from drains and watercourses, is often the simplest option for small volumes, if the ground can take it.
If you’re unsure, ask before you pump, not after.
Four ways to keep silt out of the discharge
1. Reduce silt at source
Less silt in the water means less to deal with. Keep the pump out of the mud: stand it on firm ground or a hard base, and where the sediment can stay put, don’t stir it up. Divert clean surface water away from the excavation so you’re not making more dirty water than necessary.
2. Choose the pump to match the job
If you want the sediment left behind, a vortex site pump such as the EVAK Drainox without an agitator is the better choice. If the silt has to come out, an agitator pump such as the EVAK Trenchman will lift it, which means more silt in the hose and a greater need for a filter. Our guide to agitator pumps for silty water explains the difference.
3. Settle it first
Where space allows, pump into a settlement tank or lagoon and let the solids drop out, then pump the clearer water off the top. Time does most of the work.
4. Filter it at the discharge
A dewatering sediment filter is a large geotextile bag that connects to the end of the pump hose. Water passes through the fabric and the sediment stays inside.
We stock three versions. All measure 150 × 35cm and are designed for use with a 2 inch pump.
| Filter | Captures | Max flow | Best for |
|---|---|---|---|
| Economy Sediment Filter | Sediment to 100µm, holds 20kg | 450 L/min | Small, low-risk jobs; single or occasional use |
| Heavy Duty Sediment Filter | Sediment to 150µm, holds 20kg | 450 L/min | Repeated use; empty and reuse up to 20 times |
| Oil & Sediment Dewatering Filter | Sediment to 150µm (20kg) plus up to 2.5 litres of oil | 300 L/min | Excavations where oil or fuel contamination is possible |
Only the Oil & Sediment filter has a hydrocarbon detector. The standard filters don’t detect oil.
Using a sediment filter
- Lay it flat on stable, gently sloping ground or grass, where the filtered water can run away from the excavation and not back into it.
- Connect with layflat and a hose clip. Layflat hose suits the job; see layflat vs suction and delivery hose.
- Watch it fill. When the bag becomes hard, or it’s difficult to pump through, the filter is full.
- Match the pump to the filter. Each bag is rated for a 2 inch pump, up to 450 L/min (300 L/min for the Oil & Sediment filter). For larger volumes, run several filters in parallel from a manifold.
- Empty and reuse the Heavy Duty and Oil & Sediment filters once they’ve drained. On the Oil & Sediment filter, replace it when the hydrocarbon detector turns dark blue.
- Dispose of collected sediment properly. If it’s contaminated, it’s waste and must be handled as such.
A note on oil
If there’s any chance of fuel or oil in the water, from plant, an old tank or contaminated ground, use the Oil & Sediment filter and watch the detector. Water with a visible oil sheen should not be discharged without proper treatment, whatever filter you use.
Order online, or by phone. Order by 2pm for next working day dispatch.
