In many source waters across the United States (US), chloride levels are increasing and this change could be problematic for galvanized iron pipe (GIP) installed in consumers' homes and buildings. The higher levels of chloride might increase the rate of galvanic corrosion between the sacrificial zinc coating and the underlying iron (steel) pipe. There are also concerns that the iron in GIP can accumulate lead on its surface from upstream lead service lines, occasionally causing high lead in water from GIP during scale sloughing and associated red water events.
The role of high chloride and potential mitigation strategies by orthophosphate and alkalinity on galvanic iron-zinc corrosion in GIP were examined by using new iron and zinc wires, and complementary studies with 85-year-old harvested GIP coupons from the Washington Suburban Sanitary Commission (WSSC). Sequential samplings on a constructed pilot-scale test rig with copper – lead – GIP ¬– brass meter configuration were used to evaluate lead source fingerprinting methods (metal co-occurrence, correlating the plumbing configuration to sample profiling data, and evaluation of lead isotope ratios) and role of flow rate.
As chloride concentration increased from 2.6 to 554 mg/L, galvanic current and weight loss of sacrificial zinc increased by about an order of magnitude. Iron leaching also increased by 4.4 times as chloride levels increased by a factor of 12 in WSSC modified water to simulate actual road salt runoff events. Increased orthophosphate or alkalinity could at least partly counter the adverse effects of chloride, as the average iron concentration decreased by 43% as orthophosphate level increased from 3.8 to 11.2 mg/L as P, and average iron concentrations decreased by 32% as alkalinity increased from 50 to 90 mg/L as CaCO3.
Applying fingerprinting methods on sequential samples has the potential to determine whether premise plumbing contains GIP and/or lead pipe. Specifically, the metal co-occurrence fingerprinting technique was successful in identifying the location of GIP by the detection of low-level cadmium, and the lead isotope ratio fingerprinting technique was fairly successful in identifying lead pipe. Additionally, our study found that GIP was not contaminated by an upstream lead pipe after five months of conditioning; hence, water discoloration (iron level > 400 ppb) does not always indicate lead problems from GIP. However, with longer exposure of GIP to lead pipe, the magnitude of the problem might increase. As flow rate increased from 0.9 to 2.4 GPM, the median particulate iron release increased by 3.3 times, and the median particulate lead release (>83% particulate lead) increased by 4.9 times. / Master of Science / In many source waters across the United States (US), chloride levels are increasing and this change could be problematic for galvanized iron pipe (GIP) installed in consumers' homes and buildings. The higher levels of chloride might increase the rate of galvanic corrosion in GIP. There are also concerns that the iron in GIP can accumulate lead on its surface from upstream lead service lines, occasionally causing high lead in water from GIP during scale sloughing and associated red water events.
The role of high chloride and potential mitigation strategies for GIP by adjusting orthophosphate and alkalinity were examined by conducting bench scale testing. Sequential samplings on a constructed pilot-scale test rig with different lead source pipe sections were used to evaluate lead source fingerprinting methods and role of flow rate.
Higher chloride in water increased galvanic current and weight loss of zinc coating as chloride concentration increased from 2.6 to 554 mg/L in the fundamental experiments. Iron leaching also increased as chloride levels increased in the GIP coupon testing. Increasing orthophosphate or alkalinity proved to counter the adverse effects of chloride as the average iron concentration decreased.
Sampling profiles can be useful in determining whether premise plumbing contains GIP or lead pipe by using fingerprinting methods. Iron and lead leaching from GIP increased as the water flow rate increased.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/107261 |
| Date | 01 July 2020 |
| Creators | Mohsin, Hisyam |
| Contributors | Civil and Environmental Engineering, Edwards, Marc A., Pieper, Kelsey Janette, Parks, Jeffrey L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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