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intends to take to reduce the concentration of the contaminant and the basis for that decision. Arsenic — The BATs for removal of arsenic in water for large water systems are: activated alumina, coagulation/filtration, electrodialysis, ion exchange, lime softening, oxidation/filtration, and reverse osmosis. Arsenic was detected above the PHG in the local groundwater (Wells 37 and 38). The City is in compliance with the MCL for arsenic. The estimated cost to reduce arsenic levels in local groundwater to below the PHG of 0.004 microgram per liter (tag/1) using ion exchange was calculated. Because the DDW detection limit for purposes of reporting (DLR) for arsenic is 2 tag/I, treating arsenic to below the PHG level means treating arsenic to below the DLR of 2 tag/l. There are numerous factors that may influence the actual cost of reducing arsenic levels to the PHG. Achieving the water quality goal for arsenic could be approximately $1,500,000 per year, or $32 per household per year. Bromate — The BATs for removal of bromate in water for large water systems are: coagulation/filtration optimization, granular activated carbon, and reverse osmosis. Bromate was detected above the PHG in surface water supplied by MWDSC. The City is in compliance with the MCL for bromate. The estimated cost to reduce bromate levels in MWDSC surface water to below the PHG of 0.1 pg/l using reverse osmosis was calculated. Because the DDW detection limit for purposes of reporting (DLR) for bromate is 1 tag/l, treating bromate to below the PHG level means treating bromate to below the DLR of 1 tag/l. There are numerous factors that may influence the actual cost of reducing bromate levels to the PHG. Achieving the water quality goal for bromate could range from approximately $2,610,000 to $22,230,000 per year, or between $58 and $496 per household per year. Coliform Bacteria, Total — The BAT for removal of coliform bacteria in drinking water has been determined by USEPA to be disinfection. The City already disinfects all water served to the public. Chlorine or chloramines is used to disinfect the water because it is City of Santa Ana 6 2019 PHGs Report 75C-9