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Last modified
10/6/2022 12:00:14 PM
Creation date
10/6/2022 11:58:49 AM
Metadata
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Official Documents
Official Document Type
Work Order
Approved Date
09/13/2022
Control Number
2022-175
Agenda Item Number
12.H.1.
Entity Name
Tetra Tech, Inc.
Subject
Work Order 9 for Water Quality Study and Potable Water Treatment Facility Evaluation
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4. Tetra Tech will receive, list, and organize all the data received from the County for use in the study <br />and evaluation. <br />Task 2 — Process and Finished Water Quality Evaluation <br />1. Using the water quality and operating data provided by the County, Tetra Tech will perform <br />membrane projection, chemical addition and blending calculations for the existing treatment <br />plants so that changes in operations can be simulated to determine the effect of operational <br />changes. The calculations will be used to understand how key water quality parameters are <br />changed in each step of the process and how changes to the existing operation will change the <br />finished water quality. <br />2. Values for various corrosion and stability indices will be calculated for the permeate, blended <br />water, finished water and a combination of varying percentages of finished water from each of <br />the two treatment facilities blended to simulate water quality in the distribution system. It is <br />anticipated that the following indices will be calculated: <br />• Langelier Index <br />• Calcium Carbonate Precipitation Potential <br />• Larson Index <br />• Chloride to Sulfate Mass Ratio <br />• Ryznarindex <br />The calculations will be performed using custom spreadsheet tools and the AWWA Tetra Tech <br />(RTW) Model for Water Process & Corrosion Chemistry, Version 2.0. The significance of each index <br />as it relates to corrosion of various metals will be discussed and ways to modify the finished water <br />quality to make it less corrosive will also be discussed. <br />The key water quality parameters and corrosion indices will be summarized in tabular form and <br />graphically as appropriate to compare water quality from the two treatment facilities and how it <br />might change as they are mixed in the distribution system. <br />3. The water quality will be compared to the recommendations in the USEPA "Optimal Corrosion <br />Control Treatment Evaluation Technical Recommendations for Primacy Agencies and Public <br />Water Systems", March 2016 to determine if the existing water quality is consistent with the <br />recommendations for optimum corrosion control for this system. If the recommendations are not <br />consistent with the current operations, changes to achieve optimum corrosion control will be <br />described. Overall recommendations for adjustments to the operation and finished water quality <br />based upon work performed under this task will be summarized. <br />BLK/sl/IRCDUS Evaluation <br />Tt # 200BP Toho -2- 08/31/22 <br />OTETRA TECH <br />
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