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For low to medium risk sites, the indices
approach for discharge to surface waters is
reasonably simplistic to apply.

A level of understanding of the site’s soil and
underlying geology is required to undertake Detailed Design
the infiltration risk screening assessment. The
screening assessment will determine whether
it will be permissible to infiltrate and the
indices approach is applied to define the level

of treatment required prior to the point of
infiltration.

Discussion will be required with EA where the
SPZ areas identified on the EA website:
site overlies Source Protection Zones 1 or 2 or http://apps.environment-agency.gov.uk/
where contamination is identified on
wiyby/37833.aspx
brownfield sites.

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Design Notes:
On freely draining sites where insufficient treatment is provided at the first stage of treatment
source control, initial SuDS components may require lining to prevent direct infiltration
carrying pollutants into underlying geology.

On low to medium risk sites permeable pavement will provide sufficient treatment prior to
infiltration into the ground via the pavement subbase.

The Royal Borough of Kensington & Chelsea SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates