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Case Study of the City of Carlsbad and Surrounding Areas’ Experience with Integrating Desalinated Seawater Supply in Municipal Distribution Systems

Project: 15-06
RFP Open Date: August 4, 2015
RFP Close Date: September 8, 2015

Program: Principal
Funding Available: $200,000
In-Kind Requirement: At least 25% ($66,666) of the total project costs

Project Manager: Kristan Cwalina

Background

A change in the water source could potentially cause water quality problems in the distribution system, and the introduction of desalinated seawater as a new water source may accelerate the rate of corrosion, trigger taste and odor issues as well as other aesthetic challenges, and impact the stability of disinfectants in the distribution system.  Seawater contains elevated levels of specific constituents not normally found in other water sources, including boron and bromide, which may present a problem for irrigation and water reuse applications and negatively affect consumer acceptance.

The startup of the 50 million gallon per day (mgd) Carlsbad Desalination Plant offers a unique opportunity to study the water quality changes over time as the blend of the desalinated seawater in the distribution system is increased.  This project seeks to document the impacts as the water blend changes are occurring, and also to record any other operational changes during this time as well as the number and types of water quality complaints.  In this manner, the complaints that are solely attributed to the introduction of desalinated seawater can be accounted for properly.

Goals and Objectives

This project will provide independent review of the impacts from introducing desalinated seawater into an existing distribution system, including but not limited to quantifying source water quality changes, water quality effects (e.g. corrosion, disinfectant residual, etc.), and public acceptance.  The project investigators will need to obtain, review, and report on the water quality data collected at the City of Carlsbad and, if possible, other water agencies in this area which will be receiving the desalinated seawater.

Research Approach

The project will review distribution system water quality data collected from the area serviced by desalinated seawater from the Carlsbad Desalination Plant, appropriate distribution system operational data (i.e. demands, pressures, system water quality flushing) and the number and types of customer complaint calls by date, before and after the introduction of the desalinated seawater.  A clear and rational basis must be provided for the selection of the sites where the water quality information will be collected (for example, by pressure zones, regulatory compliance points, average and longest detention times, etc.), and a minimum of three sites should be selected within each service boundary area (for example, city or water district boundary).

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