BS 6297:2007+A1:2008
$167.15
Code of practice for the design and installation of drainage fields for use in wastewater treatment
| Published By | Publication Date | Number of Pages |
| BSI | 2008 | 44 |
This code of practice gives recommendations and guidance on the design and installation of drainage fields and infiltration systems for use in wastewater treatment. It is applicable to systems for handling discharges from domestic and commercial sources from single households upwards. These sources are typically septic tanks and package treatment plants.
General guidance is given on good design and installation practices. Particular requirements are determined by local conditions. The recommendations are supplemented, as required, by specialist advice.
NOTE Attention is drawn to the environmental regulators Pollution Prevention Guidelines Note 4 [2] and building regulations and standards (see Annex B). These require an adequate system of drainage to carry foul water from appliances within the building to one of the following, listed in order of priority:
public sewer
a private sewer communicating with a public sewer
either a package wastewater treatment plant or septic tank, with a discharge to a properly designed drainage field.
Only where it can be demonstrated that the cost and/or practicability of connection to the public foul sewer is not feasible will alternative options, including use of drainage fields, be considered acceptable.
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 3 | Contents 1 Scope 1 2 Normative references 1 3 Terms and definitions 2 4 Drainage fields 4 5 Preliminary planning, site investigation and assessment 5 6 Detailed system design 12 7 Components 20 8 Construction of drainage field 22 9 Maintenance 24 Annexes Annex A (informative) Plants as drainage indicators 25 Annex B (informative) Regulatory requirements 27 Bibliography 34 List of figures Figure 1 – Trial hole 9 Figure 2 – Cross-section of typical percolation test hole 13 Figure 3 – Worked example showing percolation test results and calculation of Vp 13 Figure 4 – Cross-section of an infiltration trench, example with three trenches 16 Figure 5 – Infiltration trench, alternate layout examples 17 Figure 6 – Undulating sites 19 Figure 7 – Installation of drainage fields on a sloping site (numbered contour lines) 19 Figure 8 – Sloping sites with a critical cross-section 20 Figure 9 – Typical sample chamber design 22 Figure C.1 – Typical cross-section of an infiltration mound with a pump feed 30 Figure C.2 – Typical horizontal flow reed bed treatment system 32 Figure C.3 – Typical vertical flow reed bed treatment system 33 List of tables Table 1 – Required information for site assessment 7 Table 2 – Features influencing the location of wastewater treatment equipment, drainage fields for a single dwelling, good practice and guidelines 8 Table 3 – Subsoil characterization 10 Table 4 – Floor area to linear trench length 14 Table A.1 – Plants which indicate poor drainage conditions throughout the year 25 Table A.2 – Plants which indicate good drainage conditions throughout the year 26 Table A.3 – Other plants that indicate soils with poor drainage qualities 27 |
| 5 | Foreword |
| 7 | 1 Scope 2 Normative references |
| 8 | 3 Terms and definitions 3.1 biological layer 3.2 connection pipe 3.3 disposal area 3.4 distribution chamber 3.5 distribution layer 3.6 distribution pipe 3.7 dosing chamber 3.8 drainage field 3.9 end connection 3.10 filter material 3.11 granular fill material 3.12 infiltration |
| 9 | 3.13 infiltration pipe 3.14 infiltration system 3.15 infiltration trench 3.16 land drain 3.17 geotextile membrane 3.18 pre-treated effluent 3.19 soakaway 3.20 subsoil 3.21 topsoil 3.22 upstream system 3.23 water table 3.24 trial hole 3.25 percolation test hole |
| 10 | 4 Drainage fields Poor design and/or installation of a drainage field in an inappropriate location can lead to public nuisance, cause damage to the environment, and cause harm to human health. It is essential that regular maintenance of the septic tank or wastewater treatment plant is carried out, and the owner should r… |
| 11 | Rainwater or surface water soakaways permit the rapid dispersal of water without any further treatment of pollutants. These are not appropriate for the disposal of wastewater effluent. 5 Preliminary planning, site investigation and assessment 5.1 General The effectiveness of a drainage field to treat and disperse effluent is influenced by groundwater levels and soil moisture conte… 5.2 Preliminary planning The regulator requires a risk-based assessment, which considers the volume, location and sensitivity of the site. This might inv… 5.3 Site investigation 5.3.1 Detailed site investigation |
| 12 | 5.3.2 Protection of drinking water sources Serious and long-term pollution can occur to groundwater from inappropriately installed drainage fields. The distance can be significantly increased depending upon the size of the discharge, environmental sensitivity and local site characteristics. |
| 13 | 5.3.3 Visual site inspection Table 1 Required information for site assessment |
| 14 | Table 2 Features influencing the location of wastewater treatment equipment, drainage fields for a single dwelling, good practice and guidelines 5.4 Assessment 5.4.1 Trial hole A trial hole is distinguishable from a percolation test hole used to establish soil porosity and trench requirements. |
| 15 | Figure 1 Trial hole |
| 16 | 5.4.2 Soil characteristics and site geology Records and documents will provide useful background information on the classification of the soil in relation to its likely dra… Suitable soil conditions include well-drained and well-aerated subsoils, including sand, chalk, sandy loams and clay loams. Less… Table 3 Subsoil characterization Well-drained and well-aerated subsoil can appear brown, yellow or reddish in colour. Poorly drained or saturated subsoil is ofte… |
| 17 | 5.4.3 Water table 5.4.4 Plants as drainage indicators 5.4.5 Influent parameters 5.4.6 Site characteristics |
| 18 | 6 Detailed system design 6.1 Estimating drainage field area 6.2 Percolation test procedure 6.2.1 General 6.2.2 Test method |
| 19 | Figure 2 Cross-section of typical percolation test hole Figure 3 Worked example showing percolation test results and calculation of Vp |
| 20 | The minimum value of 15 ensures that untreated effluent cannot percolate too rapidly into the ground, potentially resulting in the pollution of groundwater. Where Vp is above the limit of 100 effective treatment is unlikely to take place in a drainage field as there will be inefficient soakage in this location, which may lead to wastewater ponding on the surface. 6.3 Calculating trench area and trench length The layout of the trench network will depend upon the soil porosity and the availability of land. Table 4 Floor area to linear trench length |
| 21 | 6.4 Trench depth 6.5 Effluent distribution 6.6 Drainage field layout |
| 22 | Figure 4 Cross-section of an infiltration trench, example with three trenches |
| 23 | Figure 5 Infiltration trench, alternate layout examples |
| 24 | 6.7 Other design parameters 6.8 Dealing with difficult sites and ground conditions Ground characteristics can vary significantly across a site and sloping sites need particular consideration. |
| 25 | Figure 6 Undulating sites Figure 7 Installation of drainage fields on a sloping site (numbered contour lines) |
| 26 | Figure 8 Sloping sites with a critical cross-section The regulator will require a risk-based assessment which will consider the volume, location and sensitivity of the site. This mi… 7 Components 7.1 General 7.2 Distribution pipe |
| 27 | 7.3 Infiltration pipe 7.3.1 Pipe design 7.3.2 Infiltration pipe diameter 7.3.3 Infiltration pipe perforation 7.4 Granular fill material 7.5 Geotextile membrane 7.6 Effluent pumping systems Effluent pumping systems may be used to transport effluent to remote drainage fields, to raise effluent from deep systems and/or for pressure infiltration systems. With regulator approval, some pump station designs may be suitable for providing access to a sample chamber 7.7 Chambers |
| 28 | Figure 9 Typical sample chamber design 8 Construction of drainage field 8.1 Inspection and distribution chambers |
| 29 | 8.2 Infiltration trenches 8.2.1 Trench excavation 8.2.2 Trench dimensions 8.3 Installation of infiltration pipes 8.3.1 Inspection of infiltration pipes 8.3.2 Preparation of infiltration trench 8.3.3 Infiltration pipes |
| 30 | 8.3.4 Installation of end connection pipes and ventilation fittings An independent ventilation pipe on the drainage system will be required in certain circumstances, for example, long or complex drainage layouts. Local authority building control can provide advice. 8.3.5 Backfilling 8.3.6 Covering 8.3.7 Health and safety 9 Maintenance 9.1 General 9.2 Regular checks |
| 31 | Annex A (informative) Plants as drainage indicators Table A.1 Plants which indicate poor drainage conditions throughout the year |
| 32 | Table A.2 Plants which indicate good drainage conditions throughout the year |
| 33 | Table A.3 Other plants that indicate soils with poor drainage qualities Annex B (informative) Regulatory requirements B.1 Introduction |
| 34 | B.2 Land use planning and planning permissions B.3 Regulation of wastewater discharges |
| 35 | B.4 Regulation of wastewater discharges in the UK Annex C (informative) Alternative disposal methods C.1 General C.2 Design and construction of drainage mounds |
| 36 | Figure C.1 Typical cross-section of an infiltration mound with a pump feed C.3 Construction of drainage mounds |
| 37 | C.4 Constructed wetlands/reed beds |
| 38 | Figure C.2 Typical horizontal flow reed bed treatment system |
| 39 | Figure C.3 Typical vertical flow reed bed treatment system |
| 40 | Bibliography [1] CEN/TR 12566-2:2005, Small wastewater treatment systems for up to 50 PT – Part 2: Soil infiltration systems. [2] Environmental Agencies, Pollution Prevention Guidelines Note 4 (PPG4), Disposal of sewage where no main drainage is available, 2005. [3] British Water, Code of practice, Flows and Loads – 2, Sizing criteria, treatment capacity for small wastewater treatment systems (package plants), London, 2004. [4] GREAT BRITAIN. Construction (Health, Safety and Welfare) Regulations 1996, SI 1996/1592. The Stationery Office: London. [5] GREAT BRITAIN. Construction (Design and Management) Regulations 1994, SI 1994/3140. The Stationery Office: London. [6] GREAT BRITAIN. Confined Spaces Regulations 1997, SI 1997/1713. The Stationery Office: London. [7] DETR circular 03/99, WO circular 10/99, Planning requirement in respect of the use of non-mains sewerage incorporating septic tanks in new development, 1999. [8] GREAT BRITAIN. Water Resources Act 1991 as amended by the Environment Act 1995. [9] NORTHERN IRELAND. Water (Northern Ireland) Order 1999, SI 1999/662 (N.I. 6). [10] SCOTLAND. Water Environment (Controlled Activities) (Scotland) Regulations 2005, SSI 2005/348. [11] N Grant and J Griggs, BR420, Reed beds for the treatment of domestic wastewater, Building Research Establishment (BRE), 2001. [12] N Grant and J Griggs, GG42, Good Building Guide No. 42, BRE, 2000. [13] PF Cooper et al, Reed Beds and Constructed Wetlands for Wastewater Treatment, WRC plc, 1996. |
