Sequestering Case History
Southern Indiana Water System on the Ohio River
A medium size Indiana municipality on the Ohio River had been successfully sequestering iron and manganese with polyphosphate for several years. Within a five-week period between WSU service visits, the city offices were receiving dirty water complaints for some unknown reason. This study will show Water Solutions Unlimited’s ability to quickly analyze a problem, their knowledge of Ohio River water quality and chlorine demand, and their understanding of the principles of sequestering helped alleviate municipal complaints.
Background
This municipality has three distinct well systems that feed directly to the distribution system. Some wells are influenced by small amounts of ammonia (0.06 mg/L ammonia as NH3-N). There is some iron present (0.3-0.5 mg/L as Fe), but the main contaminant was manganese (0.15-0.25 mg/L).
Solution
The dirty water problems began developing just prior to WSU’s next regular service call. This was very fortunate for the water superintendent and Water Solutions Unlimited.
We first interviewed the superintendent and found that he had to increase the chlorine feed rates when he felt he was losing his free chlorine residual in the distribution system. We checked the operator log books and confirmed that the applied chlorine had increased from the previous 1.0-1.2 mg/L level, to approximately 3.0 mg/L. The phosphate feed rate was also checked and found to be in the proper control range. The ammonia was rechecked and it had not increased so we knew that it was not the reason for a change in the chlorine demand. We went with the operator and flushed several hydrants in the areas with the biggest number of complaints. The color of the water coming out of the hydrants confirmed our suspicions concerning an over feed of chlorine.
We recommended that the chlorine be turned down and the system flushed as soon as possible. This, at first, seemed contradictory to normal logic. WSU explained their reasoning and their recommendations were implemented. Within three days the water was clear throughout the system and complaints went to zero. The free chlorine residuals were 0.3 mg/L or higher at the ends of the distribution system. WSU personnel checked back by phone twice a week for three weeks and then rechecked the log books, ran chlorine and phosphate tests, and inspected hydrants in the system on their next regular service call. The superintendent appreciated the service and now has a better understanding of applied chlorine and the need to check it and the applied phosphate feed rate each day.
Summary
This case history points out several important distinctions about Water Solutions unlimited:
We have an excellent understanding of:
1. Ohio River chlorine demand.
2. How to systematically troubleshoot a problem.
3. The importance of regular service calls
4. An excellent understanding of sequestering and how chlorine affects these programs.