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TID votes to expand Lateral 8 Regulating Reservoir in Hilmar
Directors decide to postpone decision on reservoir lining

Whether or not Turlock Irrigation District would move forward in allocating over $900K to reservoir lining was a source of contention between the Board of Directors on Tuesday as they discussed the planned expansion of the Lateral 8 Regulating Reservoir.


“I think there’s just a good benefit of the project, I just haven’t been sold on that concrete liner on the bottom,” said Director Joe Alamo. “I’m not going to vote for something I’m not sold on. We’re making some assumptions here and there might be some huge change in the area.


“We can always line it any year you want, there’s not a rush to line it right now brand new in my opinion,” continued Alamo.


 “It sounds to me like you’re trying to outguess these guys who are engineers,” responded Director Charles Fernandes. “You have to take their word on some things.”


According to TID Civil Engineering Department Manager Brad Koehn the ground of the proposed reservoir expansion contains poorly graded sand, a historically high groundwater table and high permeability within one mile of the Merced River.


“That isn’t so much a downside to recharge, that is a downside to increasing that historic groundwater level,” said Koehn.


If the reservoir remains unlined, Koehn said that pumping would occasionally return lower quality groundwater and will have an impact or perceived impact to local groundwater levels. A lined reservoir would include lower maintenance costs, limit water lost from the system, and minimize local impacts to groundwater.


TID staff recommended a three-inch concrete liner for the bottom of the reservoir, which would cost an estimated $915,000. The permeability would be 0.003 feet a day, or approximately 0.03 cubic feet per second or 15 acre-feet during an average year.


However, strong opposition from Alamo prompted the rest of the Board to remove the stipulation regarding reservoir bottom lining in order to allow TID to move forward with the rest of the project.


“I think if we’re going to do the project, we’re going to have to line it,” added Director Michael Frantz. “I still am a little unconvinced that we need to do it at all, but you are following our general Board direction of trying to save water during the drought year so I have a hard time being critical of the hard work you’ve put into this project.”


The topic of reservoir lining was included in the greater Lateral 8 Regulating Reservoir Expansion plan. In April TID completed construction of the Lateral 8 Regulating Reservoir, which is located near the end of the Highline Canal in Hilmar. The project, which was constructed by renovating an old waste water treatment facility, goes in conjunction with the Lateral 8 Total Control Channel Pilot Project to capture spillage and deliver only the amount of water that is needed for customers.


Given the success of the existing reservoir during the 2015 irrigation season, the Irrigation Capital Planning Team chose to implement plans to enlarge the facility. TID owns approximately 25.5 acres of property on which the current seven-acre reservoir sits, and the original design also included elements to facilitate an expansion of the reservoir to cover the entire property.


Koehn said project benefits include increasing storage capacity from 29 acre-feet to 130 acre-feet, allowing the ability to start entire irrigation heads from the reservoir without modification to ordered flows from Turlock Lake and increase in operational flexibility.


The expansion would also allow for the capture of a majority of the spills on the Highline Canal at approximately 9,000 acre-feet, which is a significant increase from what the current facility is capable of at approximately 2,500 acre-feet during an average year.


“Eighty percent of the volume spilled would be able to be captured and utilized by the reservoir,” said Koehn.


The reservoir would operate in the same fashion as the existing facility with an increased potential output flow to both Lateral 7 and Lateral 8 facilitated by the installation of two additional pumps at the pumping station. The modifications will also allow for expanded service benefits to customers below the reservoir.


Koehn said that in addition to the high levels of success from the pilot project, other driving factors for the Lateral 8 Regulating Reservoir expansion include the ongoing drought, the ability to save more water towards TID’s continued commitment to water savings, and the cost to benefit ratio of expansion exceeds the original Lateral 8 Regulating Reservoir.


The capital investment cost for this project is estimated at $3.5 million.


TID contracted MWH in August to provide an environmental review of the project to determine if any mitigation measures would be necessary. This review indicated that an Initial Study and Mitigated Negative Declaration was the proper procedure for the site conditions pursuant to the California Environmental Quality Act.


MWH finished the Initial Study and Mitigated Negative Declaration in October and TID staff submitted a Notice of Intent to adopt the declaration later that month. At the end of the public review period, there were no responses from concerned agencies or members of the public.