It’s not uncommon for gravity sewers to undergo rehabilitation, only to find that, with the next big storm, the treatment works are yet again overwhelmed with infiltration.
The problem is that traditional methods of condition assessment, such as CCTV, have some obvious limitations. They are heavily reliant on the interpretation of the operators. Change the ground water conditions, or change the operator, and the results are likely to differ. Worse still, some sewer faults are virtually impossible to identify without X-ray glasses.
Electro Scan is a method of testing gravity sewers not unlike electrically testing the continuity of a cable insulation. The sewer is surcharged and a directional electrical current is applied to the column of water. Wherever there is discontinuity in the sewer wall, the current escapes and a potential point of infiltration is located.
Repeatable, quantifiable results
Because Electro Scan is performed under identical conditions each time the results are repeatable, regardless of the operator, time of year or weather conditions.
Larger breaks in the pipe produce larger flows of current, in the same way that they will result in larger levels of infiltration. This means that the relative impact of each break in the pipe can be determined from the spread and amplitude of the peak.
The unique pattern of peaks is repeatable and because they are not affected by operator judgement or ground conditions the results can either be used to plot deterioration over time or pre and post rehab to ensure workmanship is to a water-tight standard.
Capital Maintenance Efficiency
Frighteningly, waste and clean water networks are ageing faster than they are being replaced. However, in WRc’s experience only a very small percentage of these networks require intervention today; as little as 4%.
The questions is – which 4%
With Electro Scan it is possible to answer that question with a very high level of confidence where infiltration is the driver for gravity sewer rehabilitation. By ranking the electroscan peaks in a given catchment it is possible make a proportional judgement on the level of rehabilitation required. By only targeting capital maintenance where it is required within a catchment budgets can be spent more effectively, greatly reducing asset risk, improving the performance of more catchments, and providing a chance of staying ahead of the deterioration of these aging assets.