Foul and Surface Water Drainage Strategies
Usually required for larger sites, we undertake design and negotiations with statutory undertakers in order to reach agreement on adoptable systems.
Surface Water Drainage Systems
The Planning Practice Guidance defines the hierarchy for management of surface water. The primary focus is to enable the surface water to infiltrate to ground. If this is not possible due to site conditions the order of preference for management of surface water is disposal to a surface water body, disposal to a surface water sewer, highway drain, or other drainage system, with the least favourable method being disposal to a combined sewer. An infiltration test is required to confirm the ability to infiltrate to ground. A topographical survey is preferable to confirm all other proposed surface water drainage solutions as this allows for accurate calculation of the likely drainage route of the surface water and thus the rate of surface water runoff.
Where required, we will obtain an agreement with the statutory undertaker regarding the rate of runoff from the site that will be accepted into their sewer network. Once agreed, this will define the extent of onsite storage required. Sizing of the onsite surface water network and associated storage will be carried out using industry standard software. Additionally, software is used to confirm the continuity between drainage network, foul network and road network design ensuring that each is designed to adoptable standards and detecting any clashes.
Foul Drainage Systems and Treatment Plans
In order to design a foul drainage system for a new site, details of the extent of the proposed development and intended uses are required to carry out an assessment of the expected foul water discharge using Sewers for Adoption, Seventh Edition. This information will be used alongside industry standard software in order to determine the on-site pipe size and gradient. Appropriate connection points to nearby existing sewers are then determined. These are proposed to the statutory undertaker’s Developer Services department and an agreement reached. If it is not possible to discharge from site by gravity, we can provide advice regarding the appropriate pumping station package and a proposed location in consultation with the statutory undertaker.
In some cases, where there are no public sewer services, it is necessary to provide sewerage disposal using private systems such as cesspools, soakaways and private treatment plants. We can provide advice on the type of treatment to be used and the most appropriate method of disposal of the waste. We will obtain consents from the Environment Agency, where necessary, to discharge the treated effluent to ground or to a nearby watercourse.