Septic Tank. Installation Guidelines

Transcription

1 Septic Tank Installation Guidelines

2 INSTALLATION GUIDELINES FOR WPL SEPTIC TANKS These guidelines represent Best Practice for the installation of spherical SEPTIC tanks. It must be noted, however that these guidelines are of a general nature. It is the responsibility of others to verify that they are appropriate for the specific ground conditions and in-service loads of each installation. Similarly, a qualified specialist (i.e.: civil engineering consultant or certified installer) must be consulted regarding the design of an installation. SEPTIC TANK SELECTION The number of people using the facility, and the level at which it is to be installed governs the tank model selected. We supply 1.0m invert 1.5m invert depth available to order. Capacity (Litres) No. People (200l/head/day) Diameter (mm) Overall Height (mm) Before specifying or installing of a Septic tank you should consider the following points: A septic tank system comprises a septic tank, a suitable cover and frame and a subsurface irrigation/distribution system (soakaway system). If there is insufficient area or the ground is not suitable for the construction of an effective sub-surface irrigation system a septic tank will not function and some other means of sewage disposal must be used. Septic tanks are not suitable for chemical toilet waste or silage effluent. A septic tank discharge requires permission from the Environment Agency (England & Wales), the Scottish Environmental Protection Agency or Local Authority Public Health Department (Ireland). Planning permission and Building Regulation approval may be required. Building

3 regulations require the tank/system to be sited to avoid contamination of water supplies. We recommend that septic tanks should be sited at the maximum practical distance from the property. Where possible they should be sited a minimum of 15m from any dwelling and 25m is suggested in the regulations. Roof and surface water drains must not be connected to any tank system, they should be connected to a separate soakaway. BEFORE INSTALLING A WPL SEPTIC TANK Ensure Building Regulation approval. Ensure ground porosity is suitable. Inspect tank for damage before installation. Tanks have been fully tested before despatch. Once the tank has been installed, we cannot accept claims for damage. Check that you have correct invert drain depth (neck height) of tank. Ensure access for desludging tanker. Check orientation and heights of inlets and outlets. Check that the tank is suitable for its application. Septic Tanks should not be used for silage effluent, chemical toilet waste or any other chemical. DO: Use the correct backfill material. Site tank at the furthest practical location from habitable dwellings. Most building regulations recommend a minimum of 15m, some require 25m. Fit the correct cover & frame. Consider drainage falls, generally 1 in 60/70 between house and tank and max 1 in 200 for irrigation system. Lift the tank using ropes or slings through both of the shackles fitted either side of the neck. DO NOT: Subject the tank to impact or contact with sharp edges. Add neck extensions to the tank or build a brick manhole above the tank neck (as this increases burial depth of the tank). We do not recommend extending the neck of the Tank under any circumstances. Install tank deeper than the depth that the fitted neck will allow. Install in trafficked areas. Site the tank so that it is subjected to excess ground pressure or applied loads. Lift using only one of the shackles. Fill an unsupported tank.

4 INSTALLATION GENERAL 1/ When units are installed in unstable ground conditions where movement may occur, the connecting pipework should be designed to minimise the risk of differential damage. 2/ Consideration should be given to any loads applied to the unit due to invert depths in excess of 1000mm. Site conditions should be taken into consideration and the backfill designed to account for any extra loads that may be applied. 3/ Care should be taken where the excavation will not maintain a vertical wall. The use of trench sheets and bracing systems should be utilised from the bottom to the top of the excavation and should not be removed until backfill is complete but before the concrete is fully hardened. 4/ In areas where the water table is above the bottom of the excavation and/or the excavation is liable to flood, the excavation should be de-watered using suitable pumping equipment and this should continue until the installation is complete and the concrete has cured. 5/ Uniformly support the unit during installation to avoid point loads being applied.

5 INSTALLATION OF WPL SEPTIC TANKS Where ground water lies below base of tank at all times and ground is free draining. 1/ Excavate a hole at least 300mm wider and minimum 150mm deeper than the tank plus an allowance for shuttering. 2/ Construct a suitable concrete base slab appropriate to site conditions but minimum 250mm deep. 3/ Lower the tank onto the concrete slab ( using suitable webbing slings and lifting equipment ) ensuring the inlet and outlet pipes are in the correct position. 4/ Ensure tank is upright then ballast with water to maximum 500mm depth. 5/ Place concrete backfill to 300mm depth under and to the sides of the tank ensuring good compaction ( DO NOT use vibrating lances ). Allow initial concrete set prior to proceeding. 6/ Continue adding concrete backfill whilst keeping the internal water level no more than 300mm above the backfill level at all times. Continue until the backfill level is just below the outlet pipe, leaving sufficient room to connect both inlet and outlet pipework. 7/ Connect inlet, outlet and vent pipes when safe to do so. 8/ Trim the tank neck to ground level using a fine toothed saw, do not cut the neck to less than 450mm above the inlet invert 9/ Continue backfilling with concrete over the tank body to the required level building up a shell around the access shaft and pipework. Care should be taken to avoid

6 distortion of the neck when backfilling this area. 10/ Fit cover and frame and apply surface finish e.g turf. 11/ Leave septic tank filled with water, this will be displaced as sewage enters. SITING CONSIDERATIONS Where possible, take advantage of site gradients to minimise the invert depth at the tank inlet, as this will reduce excavation. The tank neck can be trimmed to suit, subject to retaining a minimum of 350mm to provide suction tanker access. The vertical distance from the base of the tank to the ground level of the hard standing area should be less than 5 metres. Avoid sitting tanks in sloping ground as this can cause excessive ground pressure on the tank. Septic tanks are not designed to accept any traffic loads. Tanks should be sited within 30m of a hard standing area to allow ventilation via the soil stack at the head of the drains. The direction of the prevailing wind in relation to the property should be considered when selecting the tank site. We recommend the installation of sample chamber down stream of the septic tank so that the effluent quality and soakaway systems can be checked. MATERIAL SPECIFICATIONS Concrete All references to concrete are for 20 N/mm2 20mm aggregate 25mm slump mix. BS5328 Parts 1-4 Pea Shingle 6mm-10mm rounded pea shingle offering low point loading characteristics is the most suitable material for backfilling tanks Polythene Sheet Building quality 500 gauge CONNECTING PIPEWORK/TRENCHING/ INSPECTION CHAMBERS/VENTILATION Building regulations provide guidance as to the specification of materials used and fitted. It is important that these are consulted and complied with as the operation of the septic tank can be adversely affected. No surface water should be allowed to enter a septic tank system as this impairs its performance and affects the size of unit selected. Notes for Septic Tank Users Do not use septic tanks to dispose of motor oils, grease, paint, chemical toilet waste or similar chemicals. Desludge septic tanks at least annually.

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8 WPL Limited Units 1 & 2 Aston Road Waterlooville Hampshire PO7 7UX United Kingdom Tel:: Fax: enquiries@wpl.co.uk