Evaluation of approaches to determine mixing and assimilation of reuse effluent.
As of now, California agencies cannot discharge to surface water supplies that are used as a drinking water
source, but that is expected to change very soon. The California Division of Drinking Water is currently
developing draft regulations to address this topic. Some of these agencies may be interested in developing
models to predict how contaminants will move through reservoirs and how they can estimate residence time,
which will be a component of the regulations. They will need models to show how the discharges, primarily
composed of RO permeate, will dilute out in the reservoirs.
The City of San Diego's plan to discharge to the San Vicente Reservoir is one example that has already being
studied in considerable detail with reports submitted in the Fall of 2012.
There are other agencies considering similar plans. Two additional agencies are:
(1) In partnership with the City of Wichita Falls, Texas, the Tarrant Regional Water District is investigating the
feasibility of conjunctively managing surface and groundwater supplies by augmenting reservoirs with treated
(2) The Laguna Madre Water District (LMWD), located on the south Texas Gulf Coast "is evaluating alternatives to
reuse effluent from the Port Isabel Wastewater Treatment Plant to improve reliability of water supply.
A scoping proposal will be developed for the 2017 S&T research cycle. The 2017 research is anticipated to
address the following question: In the event that reuse water will be incorporated into each reservoir to meet
water supply needs, what is the most appropriate and verifiable modeling approach, for each type of reservoir,
that can determine environmental impacts and ultimately be used to set a limit, if any on the amount of reuse
water that could be contributed to the water supply?
Need and Benefit
As reuse water becomes an ever-larger component of water resource planning, issues associated with measuring
and modeling the mixing and dispersion of reuse water will become more prominent. The current multi-year
drought, now in its 15th year, has reduced reservoir capacity to historic lows not seen since the impoundments
were first constructed. To cite two examples:
1) Lake Mead is currently at a level of 1,075 feet, with an estimated storage capacity of 9,608,000 acre-feet, or
37% of full pool .
2) San Vicente Reservoir as of early June 2015, was reported to be 36% full with a depth of 193 feet.
Contact the Principal Investigator for information about partners.
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Evaluation of approaches to determine mixing and assimilation of reuse effluent. (final, PDF,
By Douglas Blatchford
Publication completed on September 30, 2016