11 Halls Farm Close Winchester Hampshire SO22 6RE
The documents submitted show1. The onsite surface water infiltration/percolation rate test results (conducted to comply with BRE Digest 365 requirements) and the hydraulic calculations for the required soakaway (the soakaway's dimension) based on the infiltration rate test results2. The soakaway location as shown on a site plan with surface water drainage from the new house.3. The design of the soakaway to meet the required dimensions.Note that the Soakaway calculations and design satisfy the WCC Drainage Engineer's detailed requirements that the surface drainage solution must meet as follows:i.e. WCC Drainage Engineer's Comments:An indicative layout plan (sketch) for both foul and surface water drainage has been presented. Ihave the following observations:I agree with the plan to connect wastewater to the current sewer system. I have no problem withfoul drainage after the application for the connection has been submitted to Southern Water andthe building standards have been met.For surface water drainage, neither the size of the soakaway nor its correct design have beenprovided. We require a tested infiltration rate for the location, as well as hydraulic calculations forthe size of the soakaway, which could cater the development's runoff during any extreme stormevents up to and including 1 in 100-year, with a 45% allowance for climate change and a 10%provision for urban creep. This ensures that the house will not flood throughout the development'sdesign lifespan, nor will it increase the risk of flooding elsewhere around the area in such events.To confirm the above, infiltration testing in accordance with the approach provided in BRE Digest365 is required and provide hydraulic calculations based on the tested infiltration rate.