By Ed Schroeder

In mid-2008, my faculty colleague, George Tchobanoglous, and I were asked by the Davis City Council to review the city’s Water Resources Master Plan. George is currently out of the country and therefore comments in this piece are mine alone.

The council was particularly interested in responses to two questions: Do alternative solutions exist that have not been considered, and can water supply and wastewater dispersal issues be addressed in a manner that spreads capital investment over a longer period of time and allows lower rate increases?

We concluded that water supply and wastewater treatment projects for Davis are interrelated and that both needed to proceed. However, we suggested that alternatives to the proposed wastewater treatment plant could be developed that would be considerably less expensive.

Our conclusions were developed from studying the Master Plan and the supporting documents developed over the previous 20 years. We based our review on five guiding principles:

* Security and reliability of the water supply source(s) is of paramount importance to the long-term security of a community;

* Provision of an adequate supply of high quality water is a fundamental responsibility of the city;

* The value of water will rise significantly in the future and water supply options will diminish;

* The planning horizon should be as long as possible; and

* The city must meet applicable requirements for water quality, water treatment and water reuse and/or dispersal.

The water supply and wastewater management issues are tied together because selenium concentrations in the intermediate aquifer are above limits in our discharge permit. Stricter discharge requirements on other minerals such as boron and total salt content are expected in the future to protect groundwater and the Sacramento-San Joaquin Delta.

Additionally, the condition of the city’s wells and the quality of water in the intermediate aquifer is deteriorating. A 2008 National Water Research Institute panel noted that 12 of the city’s 23 wells were more than 30 years old; that a number of intermediate aquifer wells had been taken out of production due to high nitrate, selenium, total dissolved solids and other mineral concentrations; and major investments would be needed to maintain the system.

To improve water quality, the city has developed several new wells in the “deep aquifer” at depths of more than 1,500 feet. The deep aquifer is believed connected to the upper intermediate aquifer and pumping could result in drawing contaminants from higher elevations into the deep wells as well as additional ground subsidence and loss of aquifer capacity. More important is the unknown sustainability of the deep aquifer if the city begins to rely more extensively on water from that depth.

Based on the available information, we concluded, and I continue to believe, that prudence demands developing a surface water supply at this time. The Sacramento River is a high-quality source of municipal water supplies used by Sacramento, West Sacramento, 550,000 people in Contra Costa County, the Metropolitan Water Agency of Southern California and many others.

Competition for surface water is increasing from other users and the demands that maintaining delta water quality place on supplies. Obtaining rights to Sacramento River water may not be possible in the future and the cost of buying water rights is expected to increase dramatically in coming years.

Postponing development will reduce future options and may require more expensive alternatives such as indirect potable reuse of municipal wastewater as is now being done in Southern California and El Paso, Texas, or direct potable reuse now being introduced in Cloudcroft, N.M., and Big Springs, Texas.

— Ed Schroeder is a professor emeritus of civil and environmental engineering at UC Davis. Reach him at [email protected]

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