I don't know of the regulatory position in England & Wales, but in Scotland, there is a regulatory dislike for "infiltration SuDS " on brownfield sites, with "attenuaton SuDS" (in the form of lined ponds, swales etc) the preferred option. It is still possible to situate infiltration SuDS on brownfield sites, however they have to be situated in areas where they are not going to mobilise contaminants to GW through flushing of water through the soils.
Much of this is down to how the Scottish Govenment & SEPA have chosen to interpret the Groundwater Daugter Directive (GWDD)
My understanding is that in essence, in Scotland, it has been decided to adopt the "Prevent and Limit" principal in relation to new activities (i.e. Prevent entry of Haz Substances to GW, & Limit entry of Non-Haz Substances to GW for NEW activities) and Limit and Limit principal in relation to historic contamination (i.e. Limit entry of Haz Substances to GW, & Limit entry of Non-Haz Substances to GW for contamination arising from historic activities). This recognises that new activities can (and should ) be regulated to prevent discharge of haz substances to the environment hut it is not practical / feesable / economical to apply the same standard to hazardous substances which have already been discharged to the wider environment during historical operations
In practice, this means that existing in-situ historic ground contamination would be permitted to leach haz substances to GW in a greater concentration (as it is falls under the limit principle) than would be permitted by a new activity (say an operational site process (which operates under the Prevent princple). SEPA would consider an infiltration SuDS as a new activity and would be subject to the Prevent principle.
The apprach is outlined in more detail in the SEPA document WAT-PS-10-01 - Assigning groundwater assessment criteria for pollutant inputs
http://www.sepa.org.uk/water/water_regulation/regimes/groundwater/idoc.ashx?docid=512b7d2c-e883-4a7b-8837-21e40ab75950&version=-1
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