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Phosphate


Background

The Cedar Rapids Utilities Department monitors the levels of lead and copper within its drinking water distribution system in accordance with state and federal requirements. In October 2017 the City completed a Corrosion Control Treatment Evaluation to assess the effectiveness zinc orthophosphate, the corrosion inhibition chemical used by the Utilities Department to prevent the leaching of lead and copper into the drinking water. This assessment concluded that the City’s current practice provided “an optimized treated water chemistry suitable for controlling lead and copper corrosion in a distribution system that has been exposed to phosphate for an extended period of time.” The assessment also concluded that, “Cedar Rapids should consider potential improvements to corrosion control water chemistry in preparation for upcoming changes to the LCR.” LCR stands for Lead and Copper Rule, which is the federal rule requiring the use of corrosion control chemicals within drinking water and the monitoring and control of lead and copper within municipal drinking water.

Cedar Rapids is currently undergoing an evaluation of using an orthophosphoric acid as the corrosion control chemical instead of using the current zinc based chemical and what impacts that would have on the water distribution system in the long run. The impacts will be evaluated through pipe-rig testing with J Avenue and Northwest Plant water using harvested lead service lines (LSLs) from the City’s distribution system. The effectiveness will be determined through measurements of lead and other water quality parameters and the changes of composition of scale layers formed on the interior of LSLs under test. Data collected by these tests will be used to support any revisions to the City’s Optimized Corrosion Control Treatment (OCCT) with the Iowa Department of Natural Resources.


Test Approach
Overview of Pipe-Rig Testing

Pipe-rig testing is accepted by the EPA as an effective way to evaluate corrosion control treatment. These tests consist of long term exposure (6 to 12 months) of LSLs or other lead containing materials to treated water under conditions that simulate usage patterns in premise (private home) plumbing. These patterns typically consist of long periods of little or no flow, when lead can dissolve into the water, interspersed with short periods of use when lead can be transported from the LSL to the tap. Typically the LSLs used in these tests are harvested from the distribution system in order to perform the evaluation on the actual lead scales that line the LSL. By monitoring water lead levels over extended periods of time, the effectiveness of alternative corrosion control treatment strategies can be compared to each other.

Cedar Rapids Pipe-Rig Testing
Pipe-rig testing is being performed on water from both the J Avenue and Northwest Water Treatment Plants with 2 pipe-rigs at each plant. LSL samples used in each plant’s pipe-rig will be harvested from pressure zones solely under the influence of the respective plant. But LSLs may not be the primary sources of lead at the customer’s tap, so non-LSL sources of lead and copper pipes will also be tested using the pipe-rig. Testing will consist of a preconditioning period, where scales in the LSLs disturbed by harvesting are restabilized by exposure to treated water, and a test period where the LSL scales will be exposed to the new condition. It is anticipated that the preconditioning period (current stage) will extend from 3 to 6 months and the test period will take approximately 6-12 months. Each pipe-rig will be capable of testing two corrosion control scenarios and a total of four scenarios can be tested at each plant.

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