Good practice for sampling strategies are described in the following guidance documents:
- BS10175
- CLR4
- R&D66.
BS10175 recommends a minimum sampling density of 10m to 25m centres for non-targeted main investigations.
CLR4 introduces calculations to determine the minimum number of samples (N) for sampling strategies to find contamination hotspots based on the hotspot area (a) as a percentage of the site area (A) and using a factor (k) which is dependant on the anticipated hotspot shape (circular, plume, or elliptical). The equation is:
N = k x (A/a)
This results in the following sample densities:
| Hotspot Area (%) | Number of Samples (N) | ||
| Circular | Plume | Elliptical | |
| 2 | 54 | 63 | 75 |
| 3 | 36 | 42 | 50 |
| 4 | 27 | 32 | 38 |
| 5 | 22 | 25 | 30 |
| 10 | 11 | 13 | 15 |
| 15 | 7 | 9 | 10 |
| 20 | 6 | 7 | 8 |
| 30 | 4 | 5 | 5 |
| 40 | 3 | 4 | 4 |
| 50 | 3 | 3 | 3 |
| 60 | 2 | 3 | 3 |
| 70 | 2 | 2 | 3 |
| 80 | 2 | 2 | 2 |
| 90 | 2 | 2 | 2 |
| 100 | 2 | 2 | 2 |