What did we consider?
One of the first things that Geo-Environmental asked for was details of whether any infiltration testing had been undertaken. The information provided by the client showed a poor soakage rate, but when Geo-Environmental cross checked this against their geological records, they discovered that if the client had increased the depth of the trial pit by 1.7m they would have been through the superficial layer of clay and into the sandstone in the underlying bedrock and that the infiltration rate would be much improved.
The client redid the infiltration test with our suggested depths and our advice proved to be true – new improved infiltration rates were achieved. As storm drainage is sized from these calculations, this meant that the size and complexity of the drainage solution for storm water was reduced, immediately saving money.
Given the issues that the client had encountered with their previous drainage engineer, we undertook a review of the existing drainage plans. During our review of your information, we noted that whilst the architects drawing shows storm and foul drainage in the plan, no pipe size and/or gradients and depths where detailed. In addition the layout also doesn’t show any gullies/channels and the level information provide was also limited. This missing detailed information would be required to enable construction of the external works.