Reading a borehole log in five minutes
Depth, hatch, description, samples and water: what each column on the sheet tells you (sample note).
What lies under the site, and what to do about it
Marlbank Environmental (sample) investigates land, water and wildlife for developers, architects and landowners: desk studies, boreholes, lab results, ecology surveys and the reports the planning officer asks for.
Most desk studies are reported in 10 working days (sample).
Borehole BH01, former bus depot, Mill Lane (sample)
Drilled on 14 May to 8.00 m with a cable percussion rig. Ground level 42.10 m. Logged by R. Okoye (sample).
Depth (m)
Layer as logged
Samples and tests
What it means for the site
0.00–0.30 m
Topsoil
Dark brown sandy topsoil with grass roots.
S1 at 0.10 m: metals and an asbestos screen
Fit to reuse in the new gardens if the lab results stay below the screening levels (sample).
0.30–1.80 m
Made ground
Grey-black ash, brick, clinker and broken concrete. Diesel odour from 0.90 m.
S2 at 0.90 m: hydrocarbons, PAHs and metals. Gas reading 85 ppm
Hydrocarbons above the level for homes with gardens. Dig out or cover with clean soil before building (sample).
1.80–4.50 m
Clay
Firm brown silty clay, mottled grey. Water struck at 3.20 m , rose to 2.60 m in 20 minutes.
S3 at 2.50 m: no odour, kept for testing
A tight layer that slows anything in the made ground on its way down to the gravel.
4.50–7.20 m
Sand and gravel
Wet orange-brown sand with flint gravel.
Monitoring well screened from 4.50 to 7.00 m; water sampled every month
The groundwater that feeds the brook downstream. We check that it stays clean (sample).
7.20–8.00 m
Mudstone
Weathered grey mudstone. End of hole at 8.00 m.
None
Bedrock, nothing to report. The hole above the well was sealed with bentonite.
Topsoil Made ground Clay Sand and gravel Mudstone ▽Water struck ▼Water level after 20 minutes
Depths in metres below ground level. The core is drawn to scale; the rows say what the drill found and what it means for the new homes planned on the site (sample log).
What we investigate
Four kinds of work, often on the same site. One team does them, so the ecologist and the driller plan their visits together.
Desk study, boreholes and trial pits, lab tests and the risk assessment the council asks for, then the remediation plan and the sign-off report.
Desk study in 10 working days; drilling usually within three weeks (sample).
Preliminary ecological appraisals, bat, bird, newt and reptile surveys in their seasons, and the mitigation plan for the planning application.
Appraisal visits all year; species surveys only in their season.
Monitoring wells, water sampling, soakaway tests and flood risk notes for sites where water decides the design.
Monitoring visits monthly or quarterly (sample).
Waste and water permits, site waste plans, dust and noise plans for construction, and replies to the regulator.
First advice call within a week (sample).
From desk study to sign-off
The order a land contamination condition is cleared in. Many sites stop after step one or three, when the ground turns out to be clean.
1
Desk study
Old maps, records and a walk round the site. It says what might be in the ground and where to look.
Read by the planning officer
2
Ground investigation
Boreholes and trial pits where the desk study points, samples to an accredited lab (sample).
Logged on site, one sheet per hole
3
Risk assessment
Lab results set against the levels for the new use: homes with gardens, offices or open space.
Read by the contaminated land officer
4
Remediation strategy
What will be dug out, covered or treated, and how each step is checked.
Agreed with the council before work starts
5
Verification report
Photos, records and test results that show the plan was carried out.
Discharges the planning condition
When ecology surveys can be done
Wildlife surveys only count in their season. Miss the window and the planning decision can wait a year, so book in winter for a spring application.
Preliminary ecological appraisal
All year; best from April to September, when plants can be named
Bat roost surveys
Inspection all year; emergence surveys from May to September, at dusk and dawn
Breeding birds
March to August, early in the morning
Great crested newts
Mid-March to mid-June for pond surveys; water samples from mid-April to June
Reptiles
April to June and September, on mild mornings
Badgers
All year; easiest from February to April, before the undergrowth grows
Recent projects
Mill Lane, Springfield. 46 homes planned (sample).
What we found. Ash and clinker made ground to 1.80 m with diesel in it near the old fuel tanks; clean clay and groundwater below.
What happened next. The made ground under the gardens was dug out and replaced with 600 mm of tested clean soil. The condition was discharged in March (sample).
Old dye works by the river
Riverside, Springfield. A new public park (sample).
What we found. Metals in the river bank and a culvert full of silt; bats in the boiler house roof.
What happened next. The bank was capped and planted, the culvert cleared, and a bat loft kept in the boiler house when it became a café (sample).
Barns at Hollow Farm
Four homes in converted barns (sample).
What we found. A small summer roost of common pipistrelle bats in one barn and swallow nests in another.
What happened next. Work started in October after the bats left, under a licence, with new roost spaces under the ridge tiles (sample).
Fees
Fixed fees for the first steps, so you can plan the budget before the ground is opened. Larger sites are quoted on the site plan.
Desk study
Historical maps, records, a site walkover and the report for the planning application.
10 working days
from $1,450
Ground investigation
Four to six boreholes or trial pits, lab tests, logs and the risk assessment.
3 to 5 weeks
from $6,800
Preliminary ecological appraisal
A habitat survey, a records search and the list of any species surveys needed.
2 weeks
from $850
Bat emergence survey
Two surveyors at dusk or dawn with detectors; the season decides the dates.
per visit
$480
Groundwater monitoring visit
Water levels, a gas reading and samples from up to three wells.
per visit
$390
Example prices, before tax and lab costs over the usual suite.
Questions before you book
The planning permission has a contamination condition. Where do I start?
With a desk study. It is often all the council needs for a site with a clean history, and it tells you whether drilling is needed and where.
How long does a ground investigation take?
About three to five weeks from booking to report: a day or two of drilling, two weeks for the lab and a week for the report (sample).
Can you survey for bats in winter?
We can inspect buildings for signs of bats all year, but emergence surveys only count from May to September. If your application is in spring, book the survey in winter.
Do you need to be on site when the builders start?
Sometimes: to watch the dig-out of contaminated soil, to check clean cover depths or as ecological clerk of works. It is set out in the strategy the council agrees.
Will you tell me if the site is clean?
Yes. If the desk study or the first holes show nothing of concern, the report says so and we do not sell you more work.
Field notes
Book bat surveys in winter, not in May
Why a spring planning application needs its ecology booked months before the season opens (sample note).
What a contamination condition asks for
The four parts of the usual land contamination condition, in the order you will meet them (sample note).
Send us the site address
We check the old maps and the planning record before we reply, so the quote fits the site. Most quotes go out within two working days (sample).