Designers of soakaways should take a more holistic approach to site investigation, including consideration of contamination and ground risk, according to the latest guidance.
The call comes from the recently published BRE Digest DG365 Soakaway design which updates guidance last issued almost a decade ago.
The guidance document is believed to be the most widely used BRE publication and the new edition includes recommendations from the Environment Agency on climate change and consideration of 1 in 100 year flood events, as well as new recommendations for ground investigation.
“While pollution was mentioned in the 2007 edition of the guidance, it was not part of the site investigation recommendations,” said Harrison Group Environmental principal geoenvironmental engineer Jon Archer. “In contrast, the new publication states that prior to designing the soakaway, the potential for contamination on the site needs to be established. It also recommends that remedial measures need to be included in design.”
Archer added that the new guidance emphasises the importance of desk studies, stating they are preferred even for smallest developments. “It recommends ‘local’ advice is sought on ground and slope stability risk, including flooding- and wash-out-induced settlement, and that these need to be considered in the design,” he said.
“It is clear that developers and their design teams must ensure they commission comprehensive site investigations when designing soakaways,” Archer continued. “This should include a desk study, a well-planned and targeted ground investigation, plus insitu and laboratory testing. Data gathered can be used to develop a ground model that will help mitigate design risk.”