AWWA ACE62970

This slide presentation outlines a study to: define the term "Consecutive Systems" (CS) - water system purchasing water from another system, earlier regulation non-specific, and specific under Stage 2 DBP Rule; DBP control strategies for CS - characterize DBPs in CS and WS based on historical surveys and sampling survey, develop a hold study protocol for CS, understand impact of storage facility operation, evaluate booster disinfection; and, answer the following questions: how does a WS and CS set water quality goals at the point of purchase; what is the best management practice for water age in CS; and, what are the feasible options for WSs to assist CSs for complying with DBP Rule? The project approach included: historical survey; sampling survey; development of hold study approach; bench-scale evaluation of disinfection strategies; evaluation of storage facilities; and, AwwaRF Reports. Summary of the utility survey included: large portion of the contacted utilities participated on this survey; utility survey provided valuable information on disinfection practices for both WSs and CSs; WS with source water of higher TOC or bromide (DBP precursors) practiced non-Cl₂/Cl₂ system; and, equal number of WS either practiced Cl₂/Cl₂ and/or Cl₂/NH₂Cl, whereas larger portion of CSs practiced Cl_2M/NH₂Cl. Summary of DBPs precursors included: for both WSs and CSs meeting the 80% MCLs (64 µg/L) of TTHMs will require finished water TOC ¿¿¿¿¿¿¿ 3.0 mg/L; for both WSs and CSs meeting the 80% MCLs (48 µg/L) of HAA5 will require finished water TOC ¿¿¿¿¿¿¿ 4.0 mg/L. Summary at distributions included: for both WSs and CSs dominant DBP in distribution is TTHMs; the dominance of TTHMs is greater for Cl₂/NH₂Cl system to Cl₂/Cl₂ system; TTHMs and HAA5 growth (i.e., of finished to distributed water) is similar for Cl₂/Cl₂ system but reduces for Cl₂/NH₂Cl system; HAA5 slightly decreases in distribution system; and, no significant relationship were found on this survey for DBPs with water age. Includes tables, figures.