Frequently asked questions.

It depends on the size of the site, the number and depth of boreholes or pits, access and the testing needed. A single soakaway test or trial pit for an extension is a small job; a full investigation for a development is a bigger one. Send us the site address and what you're building and we'll give you a clear quote.

Often, yes. Building control may want to know the ground can carry your foundations, especially on clay, made ground or near trees, and if surface water is going to a soakaway they'll usually want a soakaway test. A trial pit or a window sample is often all it takes.

A percolation test checks whether the ground can take the treated water from a septic tank or treatment plant through a drainage field. A soakaway test, usually to the BRE 365 method, checks how quickly surface water from roofs and drives will soak away, so a soakaway can be designed.

Yes. We're based in Wigan and work across Greater Manchester, Merseyside, Lancashire and Cheshire. Tell us where your site is and we'll let you know.

Yes. Where access is too tight even for our compact rig, we use a hand-held window sampling system that recovers samples in the same tubes as the rig.

Often, yes. Building control or your structural engineer may ask for a trial pit or borehole to confirm the soil and its depth before signing off the foundation design, especially on clay, near trees, or on filled or mined ground. It is decided case by case.

Phase 1 is a desk study and site walkover using maps, records and history. Phase 2 is the intrusive work on site: trial pits, boreholes, sampling and testing.

It depends on the size of the site, the number and depth of exploratory holes, access and the testing needed. Send us the address and what you are building and we will give you a clear quote. Our guide on ground investigation costs explains what drives the price.

It depends on the structure and the ground. The borehole needs to go below the depth the foundation loads will affect, and your engineer sets the depth. With cable percussion we can form boreholes up to 60m deep where access and ground conditions allow.

A count of hammer blows to drive a standard sampler 300mm into the ground. It gives an indication of how dense or stiff the ground is and is used in foundation and pile design.

Cable percussion goes deeper, takes larger and better-quality samples, and allows SPTs in deeper soils. Window sampling is quicker and suits shallow investigations and tight access.

Open hole is faster and cheaper, and it is the usual way to prove whether there are voids or broken ground at seam level. Coring is used when you need to see and test the rock itself.

Deep enough to prove the seams of concern and enough sound rock above them, as set out by the coal mining risk assessment or your engineer. There is no single fixed depth.

Only if the boreholes are expected to enter or disturb coal seams, workings or mine entries. We will tell you if your site needs one and allow for it in the programme.

Very likely. Our compact rig is designed for restricted access, and where even that will not fit, we can use a hand-held window sampling system.

Very little. The holes are small in diameter and are backfilled when we finish.

Often, for shallow foundations in typical soils. For piles or deep or variable ground, your engineer may want deeper boreholes.

How the ground's resistance changes with depth, including where it firms up and where there are soft or loose layers. That helps the engineer choose a foundation depth.

No. It gives no samples, so it is used with window samples or boreholes, not instead of them.

Until the probe refuses or reaches the depth required for your project.

Trial pits are quick and good value, and show the ground in detail to a few metres. Boreholes are needed for anything deeper or where a pit is not practical.

Pits are backfilled with the dug material and compacted when we finish. Talk to us about access and reinstatement when you ask for a quote.

Not into an unsupported excavation. We log and sample from the surface or the excavator bucket.

No. A percolation test to Part H and BS 6297 is for septic tank and treatment plant drainage fields. A BRE 365 soakaway test is for rainwater soakaways. Building control will not accept one in place of the other.

Part H guidance says drainage fields should only be used where the average Vp is between 12 and 100. BS 6297 and the Environment Agency general binding rules use a minimum of 15.

At least two days on site, because the test hole has to soak overnight before the timed tests are run.

No. BRE 365 is for rainwater soakaways. A Part H and BS 6297 percolation test is for septic tank and treatment plant drainage fields, and one cannot be used in place of the other.

BRE 365 needs three fill-and-drain cycles on the same or consecutive days, so it is usually a day or two on site, depending on how quickly the ground drains.

The drainage hierarchy moves on to other options, such as a watercourse or sewer connection. Your engineer or building control will advise on the route.

Plasticity tells the engineer how much the clay will shrink and swell. Near trees, that sets how deep the foundations need to go.

It tells the engineer which concrete mix to specify, so the foundations are not attacked by chemicals in the ground.

Get in touch with the details of the samples and the tests you need and we will let you know.

Councils commonly attach conditions requiring a desk study, investigation and, where needed, remediation before work starts, following the Environment Agency's LCRM guidance.

A desk study looks at the site's history to judge whether there is a plausible risk. Sampling and testing then confirm it either way.

Gas levels change with the weather and air pressure, so several visits, including during falling pressure, are needed to understand the site.

Check the address on the Mining Remediation Authority's interactive map, or send it to us and we will check it. The status is set site by site, not by town.

Householder applications are exempt from the automatic requirement, but the council or building control can still ask for one if they think it is needed.

Only if the boreholes are expected to enter or disturb coal seams, workings or mine entries. We will tell you if your site needs one.