The Bromide Problem in Fayetteville

Authors:

  • Michael Wang - Hazen and Sawyer

A plot of SRAA TTHM and HAA5 (4/2008 to 1/2012).

PWC Fayetteville owns and operates two water treatment facilities: the 40 mgd capacity P.O. Hoffer WTF and 18 mgd Glenville Lake WTF. Hoffer WTF gets its raw water from the Cape Fear River while Glenville Lake can draw raw water from Cape Fear River or Glenville Lake.

PWC has made a series of treatment and process improvements in the last ten years to comply with emerging water quality regulations. In 2003, PWC switched from free chlorine to chloramines. In 2008, PWC switched its primary coagulant from alum to ferric sulfate. As a result, PWC has been fully compliant with the DBP regulations with TTHM/HAA5 well below the 80/60 ppb limits.

The Stage 2 D/DBP Rule became effective for PWC in Q2 2012. PWC was surprised with the Q2 2012 DBP results. The TTHMs at the ten monitoring sites ranged from 74 to 96 ppb.

The speciation showed a high percentage of brominated THMs, possibly indicating the presence of bromide. The average percentage of chloroform (as part of total THM) was only 18 percent.

A series of raw water bromide and WTF TTHM samples were collected by PWC in July and August 2012, which confirmed the presence of bromide in raw water and a high percentage of brominated THMs.

PWC is currently conducting a one-year quarterly bromide sampling (in conjunction with H&S and NCSU) in the Cape Fear and Haw Rivers, upstream of the Fayetteville intakes. This investigation will help identify possible source(s) of bromide addition into the Haw and Cape Fear Rivers.

Meanwhile, PWC/Hazen and Sawyer is also investigating ways to reduce free chlorine contact time at Hoffer WTF to minimize TTHM formation. PWC/Hazen and Sawyer is also evaluating treatment technologies to either remove bromide from the raw water or remove DBP precursors prior to final chlorination to reduce TTHM formation.

Results from the above investigations will be presented in this paper.

For the full paper, please contact the author at mwang@hazenandsawyer.com.

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