CASE STUDIES AND VAlUE OF RESEARCH
DBP Minimization Strategies
Michael Hotaling, newport news, Virginia
Newport News Waterworks (Waterworks) treatment choices over the last thirty years have been driven primarily by
compliance with the family of DBP regulations. The following graphic displays the annual average total trihalomethane
The Compliance Graph: December, 1981–June, 2009
0.160 Raw Water Chlorination
D-81 D-83 J-86 J-88 J-90
J-92 J-94 F-98 M-00 M-02 J-96
M-04 M-06 D-07
Quarterly Compliance Samples
1979 TTHM Limit D/DBP Stage 1
2001 Limit “-20%”
(TTHM) concentration and subsequent treatment choices made to reduce those levels.
After the initial maximum contaminant level (MCL) of 100 µg/L for TTHM became effective in the early 1980s, raw
water chlorination was no longer a viable strategy. Several Water Research Foundation projects had shown that it was
possible to reduce TTHM concentration by removing precursors prior to the application of chlorine, so the application
point for chlorine addition was relocated from the raw water to the filter influent (post coagulation and settling).
The intermediate chlorination strategy was successful in keeping Waterworks narrowly in compliance with the TTHM
MCL, but the promulgation of the Stage 1 Disinfectants/Disinfection By-Products Rule (DBPR) in 1998 necessitated
further changes. Again, Foundation research was key in leading Waterworks to the use of chloramination, wherein
ammonia is added to the process to react with free chlorine to form monochloramine. Foundation research, together
with pilot testing, gave Waterworks confidence the chloramination would insure compliance with Stage 1 by providing:
• Knowledge of the formation rates of TTHMs and 5 haloacetic acids (HAAs) while in contact with free chlorine.
• Estimates of the chloramine decay rate in the distribution system.
• Formulation of a successful nitrification control strategy.
At the time, the Agreement-in-Principle set a placeholder MCL of 40 and 30 µg/L on an annual average for TTHM and
HAA5, respectively. While chloramination was adequate to meet the 80/60 limit of Stage 1, it would be unable to meet
a potential 40/30 limit for Stage 2.