The role of proprietary products in delivering treatment of surface water runoff as part of SuDS
When considering the treatment of surface water runoff as part of a SuDS design, the designer should always start by looking at the use of vegetative SuDS due to their multiple benefits. However, proprietary products are a useful extension to the SuDS “toolkit” and in many circumstances they can assist in delivering an appropriate design for mitigating pollution risks from the site.
The SuDS Manual accepts that proprietary products can play their part in delivering water quality design standards ‘where design performance is demonstrated’. There are a number of standard testing codes of practice used by manufacturers – the New Jersey NJDEP (June 2017), the German DiBT , and (as from December 2016) a new British Water Code of Practice for Proprietary Product Testing. The aim of the new British Water code is to give regulators, designers, specifiers and local authorities consistent information on product performance. Naturally, scheme designers and manufacturers are now questioning how proprietary product test results should be interpreted alongside the pollution mitigation indices suggested by the SuDS Manual’s Simple Index Approach (SIA) for non-proprietary SuDS components.
The SIA approach, based on SuDS performance evidence, was not developed to specifically align with proprietary product test method results. Therefore, although any data that demonstrates removal efficiencies for specified loads and flow rates will be very valuable in supporting claims of product performance and in providing reassurance to designers that the receiving environment will not be put at risk, there is no direct relationship that can be recommended at this time.
Keep an eye out for a longer briefing note on this issues coming soon.
If you are interested in discussing this further, please get in touch with Richard Kellagher or Bridget Woods Ballard at HR Wallingford.