- Contaminated Land
- Site Investigation
- Soil and Landscape Science
- Environment Impact Assessment
- Environmental Permitting Regulations
- Waste Management
- Japanese Knotweed Survey
- Geotechnical Investigation
Voelcker Topsoil Standard
The details below provide a summary of the thresholds for physical and chemical parameters presented in Tables 2 & 3 of the specification presented by Voelcker et al (1989) A Guide to Specifying Topsoil: Part 2, published in Landscape Design.
Soil Reaction & Salinity
- pH Value 1:2.5 (w/v) soil-water extract. 5.5 – 7.8
- Electrical Conductivity 1:2.5 (w/v) soil-water extract <1500 µs/cm
Soil Texture
- Sand (0.05-2.00mm) Max 75% - Min 20%
- Silt (0.002-0.05mm) Max 60% - Min 5%
- Clay (<0.002mm) Max 30% - Min 5%
Stone Content
- Maximum size in any direction 50mm
- Maximum content 2mm-50mm 35% (dry weight)
- Maximum content 2mm-5mm 20% (dry weight)
Nutrient Status
- Organic Matter (Walkley Black Method) Not less than 4%
- Total Nitrogen (N) (Kjeldahl) Not less than 0.2%
- Extractable Phosphorus (P) (MAFF RB427) Not less than 45ppm
- Extractable Potassium (K) (MAFF RB427) Not less than 240ppm
- Extractable Magnesium (Mg) (MAFF RB427) Not less then 80ppm
It should be noted that the authors of this specification indicate that whilst it is a suitable means of assessing the suitability of soils for general landscape planting it is not intended as a definitive specification for all uses.
In the specification the authors also indicated that in some cases it may be necessary to determine phytotoxic (those potentially toxic to plant life) and zootoxic elements (those potentially harmful to human health), which made up Table 1 of the specification. These consisted of copper, nickel, zinc, boron, arsenic, cadmium, chromium, lead and mercury. At the time when the specification was created the thresholds for these elements were based upon those presented in the Department of the Environment’s publication: Guidance on the assessment and redevelopment of contaminated land (ICRCL 59/83), which has since been withdrawn.
Current guidance within the UK policy framework for assessing potential risks of harm from contaminants in surface soils are contained within the Contaminated Land Reports and the CLEA models produced by DEFRA & the Environment Agency (2002).