City of Davis

The City of Davis is responsible for providing water, sewer, drainage and other services to its residents, businesses and public properties. Providing these services requires investments in maintaining the existing infrastructure, replacing old or worn-out components as needed, and planning for current and future needs of the community, as well as for meeting all state and federal water quality regulations.

This page was developed in order to explain the surface water project and the rates that were adopted by the City Council to support the project. Currently, groundwater is the sole source of all City water supplies. As early as 1989, the City recognized that it would be required to pursue an alternative drinking water supply in order to meet the community’s long term needs and continue to meet State and Federal water quality regulations. Many alternatives have been analyzed in the ensuing years. But supplementing our supply with water from the Sacramento River was determined to be the most economical way to meet all of the project objectives. These objectives include the ability to continue to provide a reliable water supply to meet existing and future needs, improve water quality for drinking water purposes, and improve the quality of treated wastewater effluent.

The timing of this project is driven by regulatory issues both for wastewater (definite) and for drinking water (anticipated). What exactly is the connection between water and wastewater? Everything that goes down the drain in our households ends up at the wastewater plant for treatment. This plant is designed to treat the waste that is added by the customer as well as minerals and organics that naturally exist in groundwater. There are some naturally occurring elements, such as selenium, that the normal waste treatment process does not remove. Selenium is a problem for the environment because if it is ingested by birds, it causes the shells of their eggs to become abnormally fragile. Read more about selenium here.

The State’s Regional Water Quality Control Board has set the City of Davis’ WWTP (Waste Water Treatment Plant) effluent discharge selenium limit at 4.4 micrograms per liter (µg/l). Although our deep wells have tested at less than 2.0 µg/l, our intermediate wells contain selenium at concentrations up to 52 µg/l. It is clear that we need to move away from our reliance on the intermediate aquifer to consistently comply with our WWTP selenium limit of 4.4 µg/l.

Another constituent of concern is total dissolved solids (TDS), also referred to as Electrical Conductivity (EC). Our intermediate wells are high in EC and we may not be able to meet our 2012 permit requirements for EC if we continue to pump water from this intermediate aquifer.

The graphic below highlights upcoming regulatory dates and issues that the City must consider for its drinking water and wastewater infrastructures. The importance of the overland flow being removed at the WWTP in 2017 is that the overland flow appears to reduce the selenium in the effluent.

The project will supplement Davis’ water supply with surface water from the Sacramento River. The plans include a jointly-owned (with Reclamation District 2035) and operated intake on the Sacramento River, raw water pipelines connecting the intake to a new regional water treatment plant, and separate pipelines delivering treated water to Woodland, Davis and UC Davis. Improvements to existing water supply systems will vary for Woodland and Davis, but the improvements specifically for Davis include new distribution pipelines.

The project will divert up to 45,000 acre-feet of water per year from the Sacramento River. Water rights were granted in March 2011, and will be subject to conditions imposed by the state. Water diversions will be limited during summer and other dry periods. To supplement our surface water during dry periods, an additional 10,000 acre-feet water right was purchased from Conaway Ranch. Groundwater will continue to be used by Woodland and Davis to supplement the supply when demand for water cannot be met with surface water alone. One acre-foot of water equals 325,851 gallons.

The City began planning to improve its water system infrastructure in 1989 when a Water Master Plan was developed and approved by the Davis City Council. The planning horizon was 2040 and objectives were to improve water quality and supply reliability. Up until this point, only intermediate depth wells had been used to supply water to the City. The plan’s recommendations were to develop only deep wells while investigating the option of bringing treated surface water to the City to eventually replace the intermediate well supplies. The City started using its first deep well in 1992.

During the 1990s the City began investigating the quality and reliability of the deep aquifer and evaluated various water supply options. UC Davis had already been relying on the deep aquifer for its potable (drinking) water system for many decades. A water supply evaluation was completed and the first of two deep aquifer studies was completed that showed the deep aquifers were connected and that we would be impacting UC Davis by drilling more deep wells.

During the time that Davis and UC Davis were involved in this investigation, other entities in Yolo County were also pursuing long term water supply solutions. The Yolo County Flood Control & Water Conservation District filed a water right application for Sacramento River area-of-origin water supplies (1994) with the State Water Resources Control Board to keep the surface water option available to the City and the other entities included in the Application.

In the 2000s the City and UC Davis developed a Water Supply Feasibility Study that evaluated the following resource combinations: 100% reliance on groundwater, 100% reliance on surface water, and conjunctive use of both surface and groundwater supplies for the City’s water future. This study concluded that a conjunctive use water supply system would provide the highest quality water and provide the most reliability at a cost higher than the current untreated intermediate depth well supply. A second deep aquifer study, completed in 2005, evaluated the characteristics of the deep aquifer from a long term water supply reliability perspective. The conclusions were that

• the City would impact UC Davis by relying on the deep aquifer for 100% of its potable drinking water supplies
• deep wells would likely require wellhead treatment
• further study and environmental impact analysis of the deep aquifer would be required before the City could commit to the deep aquifer as its sole water supply

The Davis-Woodland Water Supply Project Environmental Impact Report (2007) was completed to select the preferred project should the entities involved pursue a surface water supply project for the three entities involved (the Cities of Woodland and Davis and UC Davis). The EIR was approved and certified by the City Council on October 16, 2007 and a Joint Powers Authority, known as the Woodland-Davis Clean Water Agency (2009), was created to deliver the preferred surface water supply project recommended in the 2007 EIR. The Agency, although comprised of representatives from Davis and Woodland, is a separate legal entity.

The 1994 application for water rights was successful in securing water supplies from the Sacramento River in 2011. Additional necessary summer water supplies were purchased from the Conaway Preservation Group in 2010. Together these surface water supplies yield enough water to serve most of the water needs for the City of Davis, City of Woodland and UC Davis out to 2050.

The actions described above culminated in the City Council’s adoption of the five year water rate plan in September 2011. The water rates adopted would support building the regional and local facilities required to deliver treated surface water to Davis residents by 2016.

For more detail on past actions, visit Water Supply Timeline which shows the various water studies and reports completed between 1989 and 2011.

There has been discussion about what would happen if we were to delay the surface water project for a few years in order to increase rates more slowly. There are three main alternatives to analyze delaying pursuit of surface water: 1) Rely more heavily on the deep aquifer; 2) Rely more heavily on our intermediate aquifer; or 3) Do nothing. We would also need to evaluate the repercussions on the surface water project if it is delayed.

1. The Deep Aquifer

   We currently operate five wells in the deep aquifer and we have one deep well drilled that is still awaiting surface improvements (the pump station and manganese treatment system). The deep aquifer is between 700 and 1600 feet below ground surface. We have lost one deep well due to structural failure.

   We would likely need to construct five or six new deep aquifer wells to meet our water demands for the next 10 years, if we did not use any intermediate wells. Any new wells constructed now will no longer be needed after a surface water project comes online in the future and represent a sunk (lost) cost. Before any final determination of amount of wells, our hydraulic model would need to be modified to test how many wells are needed to ensure adequate supply and pressure.

   For More Information on This Topic Click on the Links Below:

   Davis Well Replacement EIR -additional information on potential subsidence
   
   Information on Manganese
   

   Any additional wells drilled in the deep aquifer would require a new EIR and discussions with UC Davis. Concerns with increasing our pumping rates from the deep aquifer on a long term basis include potential subsidence that could permanently damage the aquifer and impact UC Davis. Also, it appears that any new deep well will, at a minimum, require manganese treatment.

   The deep aquifer has fairly high Boron concentrations (720-960 ppb). The Wastewater Treatment Plant is required to do a site specific study in 2015 that includes Boron and we will likely see a recommended effluent limit to be issued with our 2017 permit. The generally accepted level of Boron that is protective for all agricultural crops is 700 ppb. While our future limit is unknown at this time, it is likely to be at or near 700 ppb.

2. The Intermediate Aquifer

   We currently operate 15 intermediate aquifer wells. The intermediate aquifer is between 200 and 600 feet below ground surface. There are two majors issues with continuing to rely on the intermediate aquifer, one is the structural integrity of the wells (some are over 50 years old), and several water quality constituents are becoming a problem.

   If any of these older wells need to be abandoned due to structural failure, we will be faced with analyzing whether or not the capacity from the lost well needs to be replaced. With the total pumping capacity we will have from our deep aquifer, we may have the flexibility to abandon several of our intermediate wells and still maintain enough capacity to meet demand for today’s water use.

   The water quality issues we face with the intermediate aquifer include both drinking water regulations and wastewater regulations. On the drinking water side, in the past we have had to abandon wells due to high nitrates and high total chromium. We are currently conducting enhanced monitoring of 5 intermediate wells because the nitrate levels have been rising.

   As for chromium, the Office of Environmental Health Hazard Assessment (OEHHA) has set a Public Health Goal for hexavalent chromium at 0.02 parts per billion (ppb). You can find the details of this report on the following web site http://oehha.ca.gov/water/phg/pdf/Cr6PHG072911.pdf. The California Department of Public Health (CDPH) has two years to set a maximum contaminant level (MCL). It is likely that at least 12 of our 15 wells will require treatment in order to meet the final MCL. For more information on hexavalent chromium in our water, please visit information on hexavalent chromium.

   The water quality issues for our waste water effluent were touched upon in the above discussion on regulatory issues. The two main constituents of concern are selenium and total dissolved solids (TDS), although Boron may potentially be an issue as well. In order to continue to use all 15 intermediate wells, and meet the WWTP’s selenium limit after 2017, we would have to remove selenium at the well head. The process for this is expensive, energy intensive, and creates brine that is difficult to dispose of. And while we do not currently have a limit for TDS at the WWTP, the limit could be set at a level that would require well head treatment similar to that of selenium and create the same issues.

3. Do Nothing

   If we “Do Nothing”, which in this case means operating our system as we currently do, we increase our risk in several areas. As mentioned above, several of our intermediate wells are likely reaching the end of their life span, and this increases our risk in meeting water demands. And when the hexavalent chromium limit is set, we are looking at potentially very expensive well head treatment. This increases our risk of being fined by CDPH for not complying with an MCL, or worse, they could make us stop pumping. Additionally, the fines which would be imposed should we exceed selenium limits set on wastewater effluent, are also expensive.

   Much of the risk is difficult to categorize without knowing the length of delay we would face before surface water is on-line. It is important to remember that changes in our water system infrastructure take time. If we lose an intermediate well tomorrow due to a structural failure, it would be a minimum of twelve months, at a high cost to expedite the process, before we could replace the well. And then, ultimately, this is a lost investment because it is a well we would not need once we have surface water.

   Infrastructure investment is part of any water system. Delivering water, to sustain current and future health and safety, provides an essential service to the City. Planning and preparation must be factored into the management of a city water system.

The following table shows the constituents of concern and the levels found in the different water supply sources.

And finally, what are the issues for the current surface water project if it is delayed for a period of time? One of the main issues we are facing is increased cost. The City of Woodland has made it clear that they cannot delay. This potentially means they would need to move ahead without the City of Davis, and if we should decide to join them later, there would be a buy-in cost that would ultimately be a higher cost to us than if we stayed on course, participating now.

If the Woodland Davis Clean Water Agency decides they can wait one year, there are risk factors associated with this; construction cost for the treatment plant may increase; Design Build Operate teams that are proposing on the project may wonder if this is a credible project to pursue; the Regional Board Water Quality Control Board may evaluate our wastewater limits with a more strict view RWQCB Q&A; there may be potential intermediate Reverse Osmosis treatment (see table 2 of Summary of Alternatives); construction cost of current water intake facility on the river will likely increases costs.; we will begin to pay for the Conaway Preservation Group water right in 2016, even if it will not yet be put to use WDCWA Water Agreement; we risk the potential to lose grant funding opportunities.

The City provides water service to the community and charges customers through water rates to pay for water system costs. Water rates are designed to generate enough revenue to pay for the costs of maintaining, operating, replacing, and upgrading the water system over time. In most years annual water rate adjustments are relatively low. From time to time, when large capital investments are required, water rate increases can be much higher. The water rates adopted by the City Council in September 2011 Rate Information reflect higher than normal rate increases to pay for the City’s share of the regional water supply project. This project would replace the water supply capacity of the City’s existing intermediate depth wells.

Water rates consider the number and type of accounts, customer water demands, the costs required to operate and maintain the water system, and capital improvements required to repair, replace and/or upgrade the water system facilities. As water infrastructure ages over time, the City must plan for the eventual replacement of those facilities prior to failure so there is no interruption in water service. Therefore water rates must consider current costs as well as future costs to keep facilities operating while meeting all regulatory requirements. The City currently has a water rate structure which includes a fixed base rate (based on meter size) and a two-tier consumption charge. This means that on a customer utility bill there are fixed rates based on meter size and a variable rate based on actual water use. The amount of the charges for water use will vary from bill to bill, and will be higher if a customer has some of their water use in the second tier. The sample bill indicates where on your bill to find your water charge information. The tier cutoff points have been changed on the City’s five year rate plan adopted in September 2011 to reflect the trend of lower water demands in Davis.

The general principle of water rates is to charge customers for their costs of service. In a metered water system this means that higher water users pay more for service because they use more water and water facilities must be sized to meet demands during peak demand periods.

One of the big challenges of setting water rates is accurately forecasting customer water demands. Factors that influence water demand include: weather (irrigation increases in hot weather), economic factors, customer water use efficiency (upgrade to efficient plumbing fixtures), and the City’s rate structure (higher water rates motivate people to conserve). The City’s annual water production dropped from 14,758 acre-feet in 2007 to 11,954 acre-feet in 2010.

There are many factors involved both in pursuing new infrastructure projects and in setting utility rates to create enough revenue to pay for these projects as well as for routine operations and maintenance, and repair and replacement projects. We hope the information provided here will answer some basic questions, and that the links provide more detailed information for those that are interested. Additional questions have been answered in a Frequently Asked Questions.

If you have further questions on the rates or on the project, please contact the Water Division Manager, Dianna Jensen or the Interim Public Works Director, Bob Clarke at (530) 757-5686 or water@cityofdavis.org.