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City
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Source Number: 2.1.2 Source Description PEER Consultants and CH2M HILL. Cycle Test No. 1, Data Package at the Rome Avenue Park. Prepared for the City of Tampa Water Department, Tampa, Florida. August 1996. Key Words Executive Summary Total Trihalomethanes (THM) were observed to decrease with residence time in the storage zone. Average THM concentration during recharge was in a range of 53 to 91 milligrams per liter (mg/l), averaging about 75 mg/l. After about one week at the beginning of recovery, THM concentrations were below 60 mg/l and were below 10 mg/l by the end of recovery. Other tracers in the water, such as fluoride and sulfate, confirm that the reduction process is not dilution alone, since recovered water with low THM concentrations still consisted primarily of the recharged drinking water. These findings are consistent with data from other sites, as published by the American Water Works Association Research Foundation's Aquifer Storage Recovery of Treated Drinking Water (1996), indicating that disinfection byproducts (DBP) attenuate during ASR storage due to natural microbial processes occurring in the aquifer. THMs decline to zero concentrations due to anaerobic bacterial processes over a period of a few weeks, and their formation potential also declines. Haloacetic acids (HA) and their formation potentially disappear due to aerobic bacterial processes within a few days of storage. Other mechanisms such as adsorption may contribute to DBP reduction; however, microbial mechanisms are believed to be predominant. The data are pertinent to the current literature search since they demonstrate the occurrence of natural subsurface microbiological processes in Florida hydrogeologic settings. In this case, the effect pertains to the reduction of DBP concentrations, not pathogenic bacteria. The recharge water was treated drinking water, so all pathogenic bacteria had been removed. Following are other pertinent data contained in the reports: Recharge water, including THMs, arrives at the storage zone monitoring well at a distance of 190 feet from the ASR well within approximately one week. Concentrations are approximately 20 to 40 mg/l lower than the recharge water, peaking at about 50 parts per billion (ppb). Concentrations rapidly decline with residence time in the aquifer. Chlorine residual in the recharge water ranged from 1.5 to 2.5 mg/l. Chlorine residual in the recovered water was initially 0.2 mg/l, then declined to less than 0.2 mg/l. Total coliform was observed in the observation wells, with many samples characterized as "Too Numerous to Count." It is hypothesized that the recharge water stimulated downhole microbial activity for indigenous microbiota, reflecting the increase in carbon, nitrogen and phosphorous in the recharge water. Total coliform was observed in a few samples from the water recovered from the ASR well. No fecal coliform concentrations were observed. In the ASR well, iron concentrations gradually increased during recovery, from approximately 0.1 mg/l to 0.3 mg/l. The carbon steel well casing construction may partially influence these results. Graphics and
Tables Table
1 - Well TPW-1 Water Quality Data Contact Information Mr. Mark B. McNeal,
P.G. Source Documents |
