Soil sampling
A site visit, selection of sampling locations, recording of conditions and preparation of samples for laboratory testing.
Properly documented sampling links the test result to a particular area, depth and time. The sampling plan is determined before the visit, accounting for site heterogeneity and the suspected problem.
Subject of examination
- A sampling grid or targeted locations
- Depths, soil horizons and control zones
- Sample identification, packaging and transfer
Sample questions for the expert
- Which zones of the site must be examined separately?
- Which control samples are needed for comparison?
- What information must be recorded during sampling?
- Does the sampling performed allow the results to be used for the questions posed?
The final questions are formulated according to the objects and circumstances of the particular task.
What to prepare
- A site plan and locations of suspected sources
- The history of use, soil deliveries and soil movement
- Previously obtained reports and records
- Laboratory requirements for parameters and samples
How the examination is conducted
The documents record location, depth, conditions, soil appearance and sample identifier. The sample preparation method and storage conditions are agreed with the laboratory service provider that actually performs the tests.
Scope and limitations
A mixed sample may conceal local contamination or differences between horizons. Decisions on mixing, sample numbers and transport are made according to the task and method.
What the deliverable records
Sampling records and sample information sufficient to verify provenance and interpret subsequent test reports are provided.
A site map before sampling: what helps select locations
Before the site visit, it is useful to mark on one plan areas that may have formed differently: natural soil cover, fill, material storage, an area after earthworks, a depression in the terrain and the zone of suspected impact. This plan helps discuss an examination programme suited to the area, rather than choosing the same set of locations for every site.
For each distinct area, state which information is documented and which is based on the owner's account. The date of soil delivery, machinery routes, former garden-bed locations or changes to drainage may affect interpretation. If the exact location of the event is unknown, mark the presumed area and the basis for that assumption.
How to preserve the link to the location
- Use the same zone labels and stable reference points in photographs and on the plan.
- Keep original photographs taken before grading, layer removal or soil movement.
- Mark previously examined locations separately and attach the corresponding records, not only laboratory results.
- Disclose inaccessible areas, coverings and places where soil conditions have already changed.
The boundary of a land parcel may differ from the boundary of a homogeneous soil unit. Comparison zones are selected to suit the question being investigated. The basis for selecting locations differs for contamination, delivered-soil quality and fertility assessments. It is therefore advisable to prepare a plan and site history before agreeing on sampling; specific quantities, depths and transfer conditions are set by the plan, not a generic instruction.
Describe the task
Specify the site area, address/district, what needs to be proved and which documents are already available.