Newsletter September 2023

September 6, 2023

Residential developments which are located sufficiently far away from public drainage systems (typically taken as 30m for each dwelling within a development), may find it difficult to make sewerage connections to dispose of foul water effluent.

In these cases, the UK Environment Agency has provided guidance on acceptable ways to discharge small sewerage to surface water under the General binding rules: small sewage discharge to a surface water.

This document explains how to meet the general binding rules if a septic tank or small sewage treatment station is planned to release wastewater to a surface water asset such as:

  • Rivers
  • Streams
  • Estuaries
  • Lakes
  • Canals
  • Coastal waters

If your property meets all the general binding rules, The Environment Agency states that you will not need a permit to discharge small sewage wastes to surface water.

Some of the key questions to ask when planning to make such a discharge include but are not limited to:

  Is the volume of discharge less than 5 cubic metres or less per day in volume?
Refer to the daily discharge calculator Sewage discharges: calculator for domestic properties – GOV.UK (
2.  Is the sewage only from domestic use?
3.  Can you confirm that the sewage does not cause pollution to surface water or ground water?
4.  Has the sewage been treated via a treatment plant that complies with BS EN 12566 for small sewage treatment plants?
5.  If your discharge will be into tidal waters, is the outlet below the mean spring low water mark?
6.  Can you confirm that the discharge is not within 30 metres of a public foul sewer?
7.  Does your surface water discharge point normally have flow throughout the year?
8.  Can you confirm that your discharge will not be into an enclosed lake or pond?

It is always advisable to review the latest UK Government and Environment Agency requirements prior to carrying out any discharges to surface water, to ensure that you comply with ALL of their requirements.

I am a civil engineer with over 10 years’ experience.  I hold a BEng Hons and a MSc in Civil and Structural Engineering from the University of Bradford and a MSc in Civil and Construction Management from the University of Derby.

I am a Member of the Institution of Civil Engineers (ICE) and am working towards my Chartership Status.  I am also an active member of Women’s Engineering Society (WES) and am passionate about promoting women in this exciting engineering field.

At Civilistix, I am responsible for the pre-planning stage of our projects which include SuDS Drainage Strategies, Pre-planning Drainage Works and Flood risk Assessments over a variety of sectors.  I work closely with many developers, planning consultants and clients to assist them with sustainable and cost-effective solutions.

I am actively involved in raising awareness of environmental issues including those related to the energy industry and climate change.  I am passionate about sustainable development and have provided material for Websites that focus on these issues.

In my spare time, I enjoy walking my dog and socialising with friends and family.

Dorothea has recently married, and we at Civilistix couldn’t be happier for her.  We wish her and her husband many years of happiness together!

Civilistix Consulting Engineers were appointed to prepare a detailed drainage and external hardstanding engineering package to help deliver 2no. blocks, 4 and 5 stories in height providing 22no. residential units.

The existing brownfield site consisted of commercial businesses, which were demolished along with all existing statutory infrastructure and the existing drains were grubbed out.

Our fully coordinated drainage solution utilised a gravity drained foul water network for both proposed units. The proposed storm water network utilised a gravity drained pipe network where runoff was attenuated via a lined attenuation tank before entering the public sewer infrastructure. We were tasked to apply to Thames Water Utility, on behalf of the client, to agree private connections made to the public drainage infrastructure.

We were tasked to provide finished ground levels and set proposed Finished Floor Levels (FFL’s) for the proposed developments within the private boundary extents.

Our fully coordinated external works package included level design, kerb layout design and full depth construction details for proposed hardstanding.

Challenges overcome:

  • All proposed drainage had to be located internally due to limited external space within the site red line boundary.
  • Coordination of proposed drainage alignments with proposed external landscaping and structural package.

Green roofs are gaining popularity for both environmental and aesthetic reasons.

In essence, Green roofs are roof structures that cover the roof of a building with green vegetation and landscaping with an unrestricted high-level outflow to the below ground drainage network.

Blue roofs are roof structures that also cover the roof of a building with green vegetation and landscaping (indifferent to green roofs in this regard), but with a restricted high-level outflow to the below ground drainage network. Because of this, blue roofs require attenuation storage often in the form of a shallow reservoir or storage crate type arrangement at their base and below the vegetation layer.

Green and Blue roofs can be used as an integral part of an overall Sustainable Urban Drainage System (SuDS) providing interception losses and attenuation respectively, thereby reducing water runoff and minimizing the risk of flooding and sometimes providing bespoke attenuation solutions on congested sites.

Unlike conventional roof systems, green roofs require increased maintenance which should be carefully considered as part of design, including ensuring safe access for routine maintenance and inspection. A typical maintenance regime for a green or blue roof is as below:

  1. Roof inspection – (annually and after severe storms). Inspect roof components, soil substrate, drain inlets and the underside of roof structure (inspect for leaks).
  2. Irrigation – In case of very dry conditions, it is important to provide water for the green/blue roof. An irrigation system may be needed, depending on the climate.
  3. Litter and debris removal will be required regularly.
  4. Replace dead plants as required (annually).
  5. Mow grasses, manage planting and prune shrubs (six months or more depending on the climate and the growing season).

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