Full Description

Small water systems face challenges complying with existing regulations including theStage 1 Disinfectants/Disinfection Byproducts Rule (D/DBPR) and will face increasedchallenges when the Stage 2 D/DBPR becomes effective. There will be additionalchallenges for surface water supplies that contain natural organic matter (NOM) withcharacteristics that produce DBPs exceeding the total trihalomethane (TTHM) or the fiveregulated haloacetic acid (HAA5) maximum contaminant levels (MCLs). In additionsome source water characteristics and other treated water quality goals may interferewith DBP control strategies. This presentation describes the Calaveras County WaterDistrict (District) Jenny Lind Domestic Water System (JLDWS) experience with theStage 1 D/DBP Rule. Specifically, the JLDWS exceeded the HAA5 running annualaverage (RAA) MCL of 60 g/L during 2005. the raw water treated at the Jenny Lind Water Treatment Plant(JLWTP) has been more difficult to treat due to a relatively high manganeseconcentration in its source water, and a higher than normal TOC level during the past4 years associated with a three-year drought followed by a higher than normal rainfallduring the winter in 2004 and 2005. The JLWTP operators have used ozone, chlorineand potassium permanganate for pre-oxidation, and use polyaluminum chloride (PACl)or PACl blended with polymer for coagulation. The treatment process includes contactclarification and filtration in five modular treatment units. Chlorine is added to the filteredwater between the water treatment units and two on-site clearwells. Distribution system strategies include seasonally reducing the volume in the storagetanks located throughout the JLDWS to reduce the maximum water age. The TTHM andHAA5 monitoring frequency was also increased from quarterly to monthly to reduce therisk that a single laboratory result could create a compliance problem. A bench scaleevaluation of TTHM and HAA5 formation as a function of time conducted in October2005 indicated that the water age should be less than 3 days to facilitate compliance with the HAA5 MCL. Potential process modifications included optimizing operation ofthe existing ozone system, evaluating use of chlorine dioxide for pre-oxidation, using granular activated carbon(GAC) filter media to remove the TOC fraction associated with UV254 absorbance andhigh SUVA values, and/or switching to chloramines as a final disinfectant. Includes 5 references, table, figures.

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 10File Size: 1 file , 540 KB