The City of Fresno, CA with extensive use of galvanized iron pipe (GIP) has historically used groundwater (GW) sources and met drinking water regulations. When Northeast Fresno introduced treated surface water (SW) with a typical water pH of 8.4 to its distribution system in 2016, the city received ~2500 water reports. Additionally, in an attempt to increase GW sustainability, Fresno constructed a new 160-million-dollar SW treatment plant with an 80 MGD capacity, and that would distribute even more SW throughout the city. Given that over 80% Fresno homes presently have GIP service lines and home plumbing, avoiding problems by simply replacing all of the archaic pipe material at a cost of roughly $10,000-15,000 per home is extremely challenging. This study aims at investigating the causes of water discoloration and seeking solutions to reduce its extent by optimizing water chemistry. Laboratory testing showed that the GW was more corrosive to zinc wire (representative of newly installed GIP) and less corrosive to iron wire (representative of aged GIP) compared to SW. For “good” GIP harvested from homes with a relatively high percentage of zinc contacting water, the release of turbidity (&lt;2.1 NTU), iron (&lt;detection limit of 10 µg/L) and zinc levels (&lt;662 µg/L) was relatively low in a range of conditions with both SW and GW. For “bad” GIP harvested from homes with a relatively high percentage of iron surface contacting water, the turbidity, iron and zinc levels after exposure to typical GW for 13.5 weeks were 47-89% lower than the levels after exposure to the typical SW, indicating less likelihood of discolored water with GW. A corrosion control strategy with orthophosphate at 1 mg/L as P and water pH 7.5 reduced problems with turbidity, iron, and zinc release by 36-87% for exposure of “bad” GIP to SW only and alternating SW/GW.

Investigating the relationship between discolored water from galvanized iron corrosion and source water conditions

255th National Meeting (2018)

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