Note: Topsoil spoil heaps should not exceed 3 m in height, including topsoil existing on site, and should be used within 12 months (reference BS 4428:1989 Code of practice for general landscape operations).
This guidance is intended for situations where there is a prior agreement to reuse site claimed soils. If this is not agreed then Section 5 of the BS (sampling of topsoil) will apply. This guidance is intended to assist in formulating a Working Methodology Statement for Planning purposes. (All references are taken from the BS).
Sampling
Laboratory certification is required for both topsoil and subsoil.
Regardless of whether the soil source is “site won” or imported, an agreed representative number of samples (based on the volume of soil being used) shall be Laboratory tested to evidence compliance with the requirements of BS3882: 2015 (multipurpose topsoil) and BS9601: 2013 (multipurpose subsoil). The subsequent Laboratory Certificates must be submitted to the LPA for approval prior to any filling operations.
If the soil is being imported from an external source, then proof of actual delivery of the certified soil must be evidenced by the submission of the site delivery tickets to the LPA.
BS Introduction
Topsoil provides the function of supporting the growth of vegetation. Topsoil is a dynamic and fragile material, which when managed appropriately, fulfils its function, but is easily damaged by mishandling. It is important that topsoil is lifted, transported, stored and spread carefully over a non-compact substrate. Damage during handling can result in a rapid deterioration in the functions topsoil provides.
Annex A (informative)
Recommendations for stripping, handling and preparing topsoil
A.1 General
Soils generally lose strength and become less resistant to damage as they become wetter; therefore, it is essential that they are stripped, handled and trafficked only in the appropriate conditions of weather and soil moisture, and with suitable machinery. If sustained heavy rainfall (e.g. >10 mm in 24 h) occurs during soil stripping operations, work should be suspended etc., a detailed stripping plan showing soil units to be stripped, haul routes and the phasing of vehicle movements.
Topsoil and subsoil should be stripped separately and they should be kept separate. Topsoils of different quality should also be kept separate from each other.
A.2 Preparation of the receiving area and spreading topsoil
The depth of topsoil spread should not normally exceed 300 mm. Suitable (loosened) subsoil should provide the remainder of the minimum rooting depth. The minimum rooting depth should be normally:
- 450 mm for grass,
- 600 mm for shrubs and
- 900 mm for trees.
(Subsoil in accordance with BS8601: 2013 specification subsoil.)
Prior to spreading topsoil, the receiving area should be de-compacted to increase permeability.
Note 1: The functioning of topsoil within a landscape depends not only on the quality of the topsoil but also on the care given to the preparation of the receiving area, which will often have been compacted by the passage of vehicles or storage of materials.
Note 2: It is particularly important that the topsoil is not over-compacted during spreading. Over compaction prevents plant root growth and function, and reduces water attenuation and the ability of excess water to drain away. It is one of the most common reasons for plant failures in landscape schemes, and it increases the risk of erosion and runoff. Placement of soil by tracked hydraulic excavators working in strips from ground not yet loosened (the “loose-tipping” method) is a way to avoid this. This method is illustrated in Figure A.2 (in BS doc).
If over-compaction of subsoils occurs they should be loosened using ripping equipment before receiving topsoil; ripping should only be done when the subsoil is sufficiently dry that it shatters. In small confined areas, such as in gardens and narrow landscaping strips, the use of a small tracked excavator with a “tine attachment”, or hand cultivation, should be used. Care should be taken to avoid overworking soils, especially with inappropriate machinery, as this can damage soil structure and increases the risk of erosion and runoff.
All stones and other objects larger than 75 mm brought to the subsoil surface by ripping should be removed from the prepared surface.
Note 3: Further guidance on the management, preparation and handling of soils is provided in the Defra publication Construction code of practice for the sustainable use of soils on construction sites [N.1].
A.3 Stones
Stone size and shape can be important factors (see Table A.1of BS) in relation to ultimate land use. For example, large stones, especially sharp stones, are of greater detriment in playing field soil than in planting areas.
Recommended maximum stone size for different land uses
Land use /Maximum stone size (mm):
- Planting areas 50mm
- Tree planting 50 mm
- Informal recreation 20 mm
- Formal recreation 20 mm
- Native habitats 50 mm
- Agriculture 50 mm
Note 4: Further guidance on the specific quality of topsoil for formal recreation is provided in the SAPCA publication The SAPCA Code of practice for the design, construction and improvement of natural sports turf [10].
Normative references
Standards publications
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies:
- BS 7755-3.7:1995, Soil quality – Part 3: Chemical methods – Section 3.7: Determination of total nitrogen – Modified Kjeldahl method
- BS EN 12579:2013, Soil improvers and growing media – Sampling
- BS EN ISO 3696:1995, Water for analytical laboratory use – Specification and test Methods
- BS ISO 10390:2005, Soil quality – Determination of pH
- BS ISO 11277:2009, Soil quality – Determination of particle size distribution in mineral soil material – Method by sieving and sedimentation
- BS ISO 16729:2013, Soil quality – Determination of nitric acid soluble fractions of Elements
Other publications
[N1]DEPARTMENT FOR ENVIRONMENT, FOOD AND RURAL AFFAIRS. Construction code of practice for the sustainable use of soils on construction sites.
London: DEFRA, 2009.
Note: This document is for guidance only and is not intended as a substitute for BS3882:2015 Specification for topsoil Environment & Design Group.
