GrokSurf's San Diego

Local observations on water, environment, technology, law & politics

Questions arise about the San Vicente Reservoir limnology study

Posted by George J Janczyn on September 27, 2011

Limnology [lim-nol-uh-jee] Noun. The scientific study of bodies of fresh water, as lakes and ponds, with reference to their physical, geographical, biological, and other features.


San Diego’s Water Purification Demonstration Project is well underway now (aka Water Reuse Program). The project aims to assess the viability of advanced treatment and purification of reclaimed water as a supplemental source of drinking water.

The plan under investigation envisions that the purified reclaimed water will be blended with raw imported water in the San Vicente Reservoir and retained for a specified period of time to create an “environmental buffer” effect. Then the reservoir water would be piped to a water treatment plant to distribute as drinking water.

The project has under contract a limnology study to determine if the San Vicente Reservoir can provide sufficient detention time for the treated reclaimed water before it enters the potable distribution system. The study relies on modeling techniques — sophisticated ones to be sure — to predict the dynamics of water transit through the reservoir.

The question is: can the limnology study accomplish its task through modeling techniques alone?

That’s one question that San Diego physicist and fluid dynamicist Dr. Burton Freeman has been studying. Freeman examined the limnology study methodology and believes he found serious shortcomings. He documented them and asked for comments from Jeffrey Pasek, Public Utilities Dept. (PUD) Watershed Manager, Marsi Steirer, Assistant Director at PUD, Dr. Michael Anderson of the Water Purification Demonstration Project’s Independent Advisory Committee; Dr. Imad Hannoun, the Project’s limnology modeling consultant; and others.

Dr. Freeman agreed to let me publish his review here (may not display properly on mobile devices):


If Scribd doesn’t display the document, here’s a link to the PDF version.

I think Dr. Freeman raised some very pertinent questions, but the official response to Dr. Freeman’s review from PUD’s Jeffrey Pasek was:

“A full Project Report for the Water Purification Demonstration Project will be presented to the City Council in late 2012. The Limnology and Reservoir Detention Study of San Vicente Reservoir [including the modeling work] will be part of this report. At that time there will be opportunity for public review and comment on the report. Until then, sub-portions or internal drafts of the Project Report will not available for public review. When the draft of the full report is released, we would be please to meet with you and get your input.”

That’s pretty clear: no public input or review of the study process until they issue their full draft report late next year, although Jim Peugh, chair of the Independent Rates Oversight Committee, indicated a willingness to allow Dr. Freeman to give a presentation to the committee or a subcommittee, which may happen.



Dr. Freeman’s points are important to be considered for the project as envisioned, but my own question about the project has been on a slightly different track: is there really a need for detention time at all?

Many scientific studies have already demonstrated that the advanced treatment process produces extremely high quality purified water…significantly better than the imported raw water that we use. So pure that it needs to be diluted somewhat for good mineral balance. Blending it in the reservoir with imported raw untreated water seems like the perfect solution.

A bay in the San Vicente Reservoir. Water cascades down the fill chute from the San Diego Aqueduct tunnel portal. Water level has been drawn down while the dam raise project is underway. The new water level will be noticeably higher than the bathtub ring indicates.


But what reason, other than fears about public perceptions about potable reuse, to require a lengthy detention time in the reservoir before it can be used? And what if the limnology study reveals that the treated water mixture will reach the reservoir’s intakes leading to the treatment plant sooner? Does that kill the whole project? I don’t think that’s acceptable.

Surely a reliable multi-barrier failsafe mechanism can be designed to make sure that any malfunction/contamination that may occur in the water purification process will immediately block tainted water from reaching San Vicente Reservoir.

In any case, San Vicente Reservoir has been drawn down considerably because of the construction to raise the dam and increase the reservoir size. After construction, it will take several years to refill to the enlarged capacity. That means there is no way to use real-time data about water currents and other factors that will affect the water added to the reservoir, and the relatively scant historical data about the reservoir may not be relevant because it’s based on the smaller reservoir’s size.

Dr. Freeman’s questions should be taken seriously…(and mine, too!).


6 Responses to “Questions arise about the San Vicente Reservoir limnology study”

  1. Limnology doesn’t scare me! But honestly I think the idea of reclaimed water has seriously been tainted in the eyes of the public by the label given to it in the media – Toilet to Tap – and it’s going to take more non-biased public education to get them to swallow it.

    Keep up the good work George!

    • Still, public opinion has changed considerably over the past few years. Plus the media (at least some, like the Union-Tribune) dropped negative labeling and editorials, and even Mayor Sanders is no longer against the idea. If people want to label potable reuse with derogatory terms to evoke images of drinking sewage that’s up to them, but informed people will know what the score is. With groups like the Water Reliability Coalition spreading solid information and the Public Utilities Department giving tours and educational forums, I think San Diego has a good chance at making this succeed.

  2. Dr. Charles Freeman said

    Thank you George. Excellent article Dr. B. Freeman.

  3. The article is very encouraging. For ten years I have been writing letters to the editor of the UT attempting to discourage the use of the term toilet to tap, and encouraging our city leaders to begin the process of making San Diego water independent. The book I am writing (getting close to publishing it) is all about the socio-economic results of bad public water policy, using actual data and history and weaving a fictional story around it to make it more interesting. The mountain we all have to climb and conquer is the California Department of Health. The CDH has not even begun to consider direct potable reuse despite the water stress crisis we are into. Thanks for taking the lead in this effort. Keep up the good work.

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