Public Works Discusses Wastewater Plant Upgrade/Expansion Options at NRC Monthly Meeting

On their regularly scheduled monthly meeting on Monday, May 24, the Davis Natural Resources Commission (NRC) heard from Mike Lindquist, a civil engineer with the City of Davis Department of Public Works, on various wastewater treatment plant upgrade options currently being considered by the City.

Currently, Davis processes about 5.5 million gallons per day (mgd) of wastewater and discharges secondary treated waste water to wetlands eventually emptying into the causeway under permit from the Sacramento Regional Water Quality Control Board (RWQCB). Mr. Lindquist explained that the city is not currently meeting wastewater discharge requirements for certain minerals such as selenium as well as for total dissolved solids in the wastewater. Although the current limits are not being enforced because the City has obtained temporary waivers from the RWQCB in the past, these will certainly expire at some point in the future which could result in fines of up to $10,000 per day. Mr. Lundquist did not specify a deadline by which these upgrades must occur.

Mr. Lindquist went on to describe three options currently being considered by the city to meet their discharge standards. He indicated the city is extensively evaluating each of the treatment options as to its cost effectiveness with the ultimate goal of achieving compliance with the least economic impact on Davis ratepayers. He acknowledged, though, that all of the treatment options will entail significant capital and/or operational expenses that would eventually be borne by the ratepayers.

2) Reclamation of the Wastewater for Agricultural Purposes – This option is still being considered but Mr. Lindquist stated that prior discussions with the Conaway Ranch as an eventual recipient and user of this water have not been productive and the ranch is currently on the market for sale. He stated that approximately 4,000 acres of land would otherwise be required for this option to be feasible of which 400 acres would be used for storage of wastewater during the rainy season for irrigation use during the dryer, growing part of the year. He further indicated that such acreage had not yet been committed by any area farmer(s) and that there were logistical and operational difficulties in pursuing this option. These included identifying and negotiating with prospective partners to accept this water on a long term basis and managing the wastewater stream such that it meets the statutory requirements of use of such water for agricultural purposes. He did not provide an estimate of the costs of such a project but added that some treatment plant upgrades would be required in addition to the costs of laying a pipeline from the current treatment plant to the eventual agricultural site selected for use

3) Use of Excess Capacity in Woodland Wastewater Treatment Plant – The 3rd option discussed by Mr. Lindquist was a possible joint venture with the City of Woodland to pump either raw or partially treated wastewater to Woodland’s existing wastewater treatment plant. This plant is currently underutilized following a recent expansion in anticipation of population growth in Woodland that had not materialized (e.g. the slow build-out of the Spring Lake residential subdivision among other projects). He noted that the current Woodland waste treatment plant was permitted to discharge up to 10 mgd but was currently only discharging approximately 6.5 mgd. Thus, there is unutilized capacity in the plant which might be used for treatment of Davis wastewater possibly to the financial benefit of both cities. He indicated that this option was subject to extensive engineering study and future negotiations with Woodland. If pursued, it would likely entail formation of a Joint Powers Authority conceptually similar to the current JPA exploring the possibility of importing Sacramento River Water to both cities. He said there currently was insufficient information to determine a price tag for pursuing such an option but that it would entail expanding the Woodland plant and laying a pipeline from Davis to Woodland. Costs for pumping the wastewater from Davis to Woodland would also be significant but were not specified.

Author’s Note – There was not any material discussion by Mr. Lindquist about wastewater conservation measures being considered by the City. This was somewhat surprising because wastewater conservation practices are almost always considered the most cost-effective and lowest cost impact to ratepayers. This is because every gallon of wastewater avoided not only saves the cost of treating that gallon of wastewater at a treatment plant but also the cost of delivering the potable water to the customer in the first place.

Davis is far behind the curve in wastewater conservation compared to many Southern California communities whose residents per capital wastewater discharge is about half of that generated by the average Davis resident. In addition to aggressively promoting and subsidizing standard off-the-shelf wastewater conservation practices (low flow toilets, shower heads, and faucets for example), it is this author’s opinion that substantial future treatment savings can also be realized by regulating water softener use in the City.

For instance, many Southern California communities regulate softeners by requiring them to be of a more efficient design than many older softeners currently in use. Newer, more efficient models greatly reduce the volume of salt and brine water now sent down the sewer system to the treatment plant.  The absence of any such regulations in Davis means that companies like Culligan have no incentive to promote wise softener use in Davis because they charge by the bag of salt delivered to the customer’s door. The more inefficient is a softener, the more salt and brine is washed down the drain as regeneration waste, the more profit the softener service company makes on replacing that wasted salt, and the more the utility ratepayers have to pay to remove that salt from the wastewater stream before eventual discharge into the environment. In effect, inefficient, outdated softeners produce more profit for Culligan and other softener service companies at the direct expense of the entire Davis wastewater ratepayer base.

Initial estimates show that it is possible that 5,000,000 lbs of salt a year or more could be removed from the Davis wastewater stream if softeners were properly regulated in Davis as is now specifically allowed under new state law. Since salt removal is one of the most expensive types of tertiary treatment, substantial capital and operating cost savings could accrue to the Davis ratepayers if the City’s Department Public Utilities has the foresight to address the problem of softeners and implement an aggressive wastewater conservation options before finalizing final wastewater treatment plant design.