DISINFECTION BY PRODUCTS IN ALASKAN WATER SYSTEMS by Lee Johnson, P.E. ADEC Drinking Water Program Northern Program

COMPARISON OF TOTAL SYSTEMS AND SYSTEMS WITH DBP ISSUES

SYSTEMS THAT DISINFECT

DISTRIBUTION OF WATER SYSTEMS WITH DBP ISSUES

IS SOURCE TYPE THE ISSUE?

IS FILTRATION TYPE THE ISSUE?

CONVENTIONAL FILTRATION PACKAGE PLANT

DIRECT FILTRATION

BAG FILTER SYSTEM

CARTRIDGE & BAG FILTER SYSTEM

MEMBRANES & DIATOMACEOUS EARTH  Membranes are classified as Alternate Filtration under LT1  Membrane filtration systems are meeting the DBP mcl’s  Only 1 DE filtration plant in Alaska. DE plant is meeting the DBP mcl’s.

MAXIMUM DBP’S BY FILTRATION TYPE

IS THE ISSUE TTHM’s OR HAA5’s?  Approximately 36 systems are currently exceeding standards or have had samples over the limit.  11% have only TTHM issue.  8% have only HAA5 issue.  81% have both a TTHM and HAA5 issue.

IS DETENTION TIME THE ISSUE?  Of the 36 systems evaluated only 6 were fill and draw.  Fill and draw systems are those that do not routinely filter on a daily basis but rather filter to storage and meet distribution demand off storage.  Time periods between filtering can range from every few days to a year or more.

LONG DETENTION TIMES?

WHAT HAVE SYSTEMS BEEN TRYING?  Controlling detention times –Converting treated water storage to raw water storage –Flushing distribution system  Controlling disinfection levels  Cleaning raw water reservoir  Trying different coagulants/flocculants  Piloting new filtration technology  GAC filter media  Different disinfectants  Adding PAC  Looking at other water sources