Page 5 - WM Donald Newsletter - Edition Four

At Grandhome, a new community taking shape in the Bridge of Don, a key design factor is the provision of potable water. The Water Impact Assessment undertaken by Scottish Water determined there was sufficient capacity in the existing main that passes the site for around 400 dwellings. Above this number and the local water network would be ‘stressed’.It is projected there will eventually be around 3,000 properties on the site, so a dedicated reservoir is being constructed to take over the water supply duties in due course.Hard LandscapingCountesswells is a 300 acre development. The sewage infrastructure has been designed such that all sewage pipes drain towards a single point on site. At this location. W M Donald has built a 7m deep wet well to hold the sewage, alongside a dry well in which two pumps and associated electronic controls are housed. The pumps – a duty and a standby – pump the sewage 4km through 225mm polyethylene pipework laid by W M Donald to the nearest public gravity sewer. The pumps switch on a daily basis from duty to standby so that they wear at equal rates.But, what happens if both pumps fail simultaneously? To cover this eventuality, W M Donald has buried two emergency sewage storage tanks with a collective capacity of 90,000 litres. The tanks give Scottish Water at least 24 hours to restore normal operations.The design engineer at Countesswells is Fairhurst (see article on page 8) and the mechanical and electrical engineering sub-contractor was Ferrier Pumps.In the meantime, to ensure consistent 3 bar water pressure to homes W M Donald is installing two large aboveground water tanks and a pumping station. In addition to two variable speed pumps – a duty pump and a standby – a third pump has been installed to maintain the flow rate to hydrants for firefighters should they ever be needed on site. A similar set of circumstances also apply to the Chapelton of Elsick development which will eventually need to construct a dedicated reservoir to ensure there is sufficient water available to residents.As at Countesswells, the design engineer on the Grandhome project is Fairhurst.Hard LandscapingHard Landscaping5