Tacoma Waters

This section summarizes the field studies performed to compare the efficiencies of dechlorination chemicals under identical conditions to evaluate the chemical of choice for various dechlorination applications (18,19). The field tests were conducted at Tacoma Waters, WA, Portland Bureau of Water Works, OR, and East Bay Municipal Utility District (EBMUD), CA. Six dechlorination chemicals were used in solution, tablet, or powder form in these tests (Table 3). In the Tacoma and Portland studies, a 1 % solution of the dechlorination chemicals were introduced into water released from a hydrant. The field studies evaluated the rate of dechlorination, effect of overdosing, and concurrent water quality impacts when stoichiometric or twice the stoichiometric amounts of dechlorination agents were added. In the EBMUD dechlorination studies, bags, or dispensers containing tablets or powders of dechlorination chemicals were placed in the flow path of hydrant water. At all three sites, the water used for the test originated from surface water sources rather than from groundwater sources. Table 3 summarizes the chemicals, forms and dosing rates used in these studies. 

Tacoma Waters, Tacoma, WA Free chlorine Sodinm metabisnlfite Sodinm snlfite Sodinm thiosnlfate Calcinm thiosnlfate Ascorbic acid Sodinm ascorbate 1% solution Stoichiometric concentrations and twice the stoichiometric concentrations needed for dechlorination 1.2 8.9 Surface water 300... 

Phenol is not expected to bioconcentrate significantly in aquatic organisms. Reported log bioconcentration factors (BCF) in fish for phenol include 0.28 for goldfish, (Kobayashi et al. 1979) and 1.3 for golden orfe (Freitag et al. 1984). The highest mean level of phenol detected in bottom fish from Commencement Bay in Tacoma, WA, was 0.14 ppm (Nicola et al. 1987). The levels of phenol in the water or sediments were not stated. 

Fig. 1. Chlorine concentrations at Tacoma City Water when stoichiometric concentrations of dechlorination chemicals were added to neutralize chlorine in potable water from a hydrant. The water traveled a distance of about 450 ft after 250 s.

Portland Bureau of Water Works uses combined cWorine for disinfection. The tests conducted at Portland were similar to those at Tacoma, except in the following aspects Tests using all the chemicals, except sodium sulfite, were conducted at stoichiometric concentrations only a 100 ft hose, rather than a diffuser, was provided for mixing of chemicals with the water the released water traveled along a well-paved surface for 1000 ft prior to discharging into a storm drain leading to a storage pond. 

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