Watercourse advice note (Aylesbury Vale area)
5. Preventing pollution
Key principle 13: Developments should avoid pollution by incorporating mitigation or design solutions during and after construction. Consult the Environment Agency for advice on measures necessary to prevent pollution of surface and ground water.
5.1 Oil, silt and sediment
Pollution can come from a range of sources and should be considered during all phases of a development, design, construction and lifetime. Practical ‘how to’ measures to reduce and avoid water pollution during construction and on completed sites include:
- bund oil tanks and other potential pollutants
- store oils, chemicals and other potential pollutants away from water bodies and surface water drains
- avoid silt and sediments entering freshwater habitats as they can damage habitat and wildlife – for example, smothering fish eggs and aquatic insects
- site compounds away from watercourses and out of the floodplain
Further guidance on controlling sediments during construction can be found within the CIRIA Contaminated sediments: a guide for risk assessment and management document. (Dennis, I, Challinor, S, Page, C, Walentek, M (2019). Contaminated sediments: a guide for risk assessment and management (C781), CIRIA).
5.2 Septic tanks
Septic tanks and small sewage treatment plants are likely to be a major and underestimated source of pollution. Systems are often located in unsuitable areas, on unsuitable soils and are often improperly managed. (Withers, P. et al (2013)., ‘Do septic tank systems pose a hidden threat to water quality?’. Front Ecol Environ. 12(2): 123–130, doi:10.1890/130131) Poorly performing systems can release raw sewage and pollute ground water, rivers and streams. It is advised to:
- connect to the main sewer network where possible
- if it is not possible to connect to the main sewer network, consider using a central combined sewage treatment system for multiple housing developments
- ensure homeowners are left with full details on the make and size of their sewage treatment system, and instructions on how best to maintain it
- ensure newly installed sewage treatment systems have spare capacity to deal with future extensions to the new build
Further guidance can be found within the government's General Binding Rules for small sewage discharge to a surface water (Environment Agency 2020) and RTCT Septic Tanks Guidance. (Dennis, I, Challinor, S, Page, C, Walentek, M (2019). Contaminated sediments: a guide for risk assessment and management (C781), CIRIA.)