Low-cost detection system pinpoints I&I for South Carolina utility
The Berkeley County (S.C.) Water and Sanitation Authority (BCWS) is responsible for providing approximately 39,000 customers with clean drinking water, along with proper disposal of the community’s solid waste and wastewater. Over the years, its employees have earned a reputation for service excellence, fiscal responsibility and environmental stewardship.
One of the areas under the watchful eye of the BCWS is a lakefront development known as Land O Pines located within the Town of Moncks Corner. The BCWS wastewater group began noticing that immediately following a major rain event, the volume at the pump station servicing the Land O Pines community would nearly triple.
Not only was this additional volume increasing processing costs, but it was also placing an added strain on the equipment required to transport the wastewater downstream towards the treatment facility. The added workload on items such as pumps would eventually result in the need for increased maintenance and reduce the anticipated lifespan of the equipment.
Tommy Harris, superintendent of wastewater collection for the county, decided that it would be operationally and economically beneficial if the cause of the increases in wastewater flows was located and ultimately eliminated. Since Harris and his team had already concluded that the huge jumps in volume during major storm events were caused by the effects of inflow and infiltration (I&I), they now needed to find a cost-efficient method for locating the source of I&I hiding within the 2.1 linear miles of collection infrastructure. The method selected was iTracking from Eastech.
On August 28, 2012, working side-by-side with a factory technician from Eastech, five iTracker I&I micro detection monitors were installed in designated manholes within the 2.1 linear miles of the collection system (see map). Each unit was commissioned in 15 minutes without the requirement for confined space entry. The five iTrackers immediately began monitoring the five independent mini-basins within the 2.1-linear-mile major basin.
After two weeks of surveillance that included a major 5-in. cumulative rain event, the five iTrackers revealed the exact volumetric changes between dry- and wet-weather events within each of the five mini-basins under investigation. It was evident from the recorded data that the 2,200-linear-ft mini-basin designated as 129 was responsible for approximately 80% of the suspected peak rainfall-derived I&I (RDII). Due to the effects of the 5-in. rain event on August 28 through 30, the average daily flow over the two week surveillance period within mini-basin 129 increased by 7,670 gal per day when compared to the average dry-day flows. Peak-period RDII at mini-basin 129 increased flows from 13 gpm to 58 gpm.
As can be seen from the graph, levels increased from an average dry-day level of 1.25 in. to a peak during the storm of 2.65 in. This resulted in a volumetric increase in flow of 4.48 times, or 45 gpm. An analysis of the iTracker at the culmination of manhole 1345, located just prior to entering the pump station, showed that the peak volume during the August 29 storm increased 2.51 times – 37 gpm to 93 gpm. The iTracker at 1345 confirmed the BCWS wastewater group’s initial calculation of an approximate tripling in flow during a major rain event.
Throughout the two-week surveillance period, there was not a single incident of lost data, nor were there any requirements for sensor maintenance.
Frank Sinclair is president of Eastech Flow Controls. Sinclair can be reached at [email protected].