Application of Critical Control Points and Geometric Information System Automation for Investigation of CECs in Potable Reuse

Potable reuse, whether direct or indirect, relies on a multi-barrier system approach to purify wastewater. A key part of the multi-barrier system is source control.In 2015, the Orange County Water District (OCWD) will complete an expansion of the Groundwater Replenishment System (GWRS). The $142.7 million project will create an additional 30 million gallons per day of new water supplies to serve north and central Orange County bringing the total production of the GWRS to 103,000 acre feet per year (AFY), enough water for 850,000 people.Since startup occurred in 2008, the Orange County Sanitation District expanded its source control program to protect the GWRS. Refinement of the program has been ongoing to better respond to water quality goals in a service area that has over 2.5 million people and a 479-square-mile area in central and northwest Orange County.Refinements include development of a geometric network in a geographic information system. The geometric network facilitates visualization, analysis, and interpretation of data to understand relationships. The geometric network can be used in conjunction with mass balances developed from flow and analytical laboratory data.Recently, these new tools were put to the test to investigate the source of 15 pounds of CECs being discharged within the 463-square-mile service area. Elevated levels of 1,4-dioxane were measured tributary to its facilities. While levels were below regulatory limits, OCSD launched an investigation. OCSD utilized an algorithmic approach to save resources while locating the sources of the discharge.Of particular relevance in this case study is the use of a first order Kalman filter to reduce the noise inherent with a service area of this size. The Kalman filter can be applied to direct potable reuse projects which may use real-time data of critical control points. Both noise reduction and prediction inherent in the Kalman filter can enhance the operator’s ability to make decisions regarding control of the process.The investigation successfully reduced the 1,4-dioxane loading to background levels, confirmed the joint agency response plan and tools, and set a framework for future potable reuse projects in consideration of critical control points and direct potable reuse.