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Manteca exploring selling treated wastewater
wasteewater copy
The Manteca wastewater treatment plant is on West Yosemite Avenue. - photo by Bulletin file photo

What you send down the drain could help reduce future costs to operate the Manteca wastewater treatment system.
An “independent party” has approached the city recently about securing the rights to Manteca’s treated wastewater that is currently being returned to the San Joaquin River. That request follows on the heels of an inquiry during the drought by another local agency that also wanted to buy the city’s treated wastewater.
The potential sale of wastewater, treatment plant capacity, the handling of industrial wastewater from Eckert’s bell pepper cleaning process, possibly treating Oakwood Lake wastewater, and the potential of Manteca’s facility becoming a regional treatment plant are part of a status report the Manteca City Council will receive when they meet Tuesday at 7 p.m. at the Civic Center, 1001 W. Center St.
Tuesday’s presentation has been billed as a presentation “intended to inform council on current issues and lay the foundation for further planning and development of the city’s wastewater capacity and assets.”
The five wastewater issues are listed on the agenda as an update on wastewater planning efforts underway and anticipated. What isn’t a part of the discussion the Public Works Department is making to the council is using recycled wastewater to supplement treated domestic water to irrigate large swaths of public landscaping and parks.
Not only is Manteca requiring developers to put purple pipe in the ground to use recycled wastewater for irrigation but one of the big selling points on investing in a gravity flow line that was just installed under the 120 Bypass as part of an $8 million city investment was eventually repurposing the existing forced pumped sewer main to send recycled wastewater by gravity to as far east as Woodward Park.
While a separate study is being down on reclaimed wastewater use, such an effort obviously would impact the city’s ability to sell treated wastewater.
The city could realize significant income from selling treated wastewater. Lodi in 2009 inked a deal with the Northern California Power Authority to buy recycled wastewater for a natural gas lower plant that represents $1 million annually for that city. That said selling it takes water away from being used for non-potable uses in Manteca.
Given the growing pressure on water supplies harnessing treated wastewater for purposes in Manteca could prove critical in future years as the city grows. It also could reduce significant expenses.
If treated wastewater can be used in ways to reduce per capita use of treated domestic water it would delay the need for expensive well work and expansion of the regional surface water treatment plant. At the same time it can stretch the city’s investment in current resources.
On Tuesday’s agenda, as an example, there is an item to award a bid to equip two new water wells at a cost of $5.8 million. That is in addition to the cost of drilling them.

Council directed staff
to explore possibility of
selling treated wastewater
to SSJID for farm use
Back in April of 2014 council directed staff to explore working with the South San Joaquin Irrigation District to see if 7 million gallons of treated wastewater the city releases back into the San Joaquin River could instead be diverted for local farm use.
The city’s treatment plant processes enough water to support 90,000 people — the current population of Manteca and part of Lathrop that send wastewater to the facility.  City ratepayers were pay nearly $2 million a year to treat it in 2014 — including $1.2 million in power costs. It is now essentianlly given away free to downstream users.
State law gives cities the ability to sell “rights” to the fresh water they create from the treatment of wastewater. Other valley cities have taken advantage of the law to either sell it for agricultural irrigation or trade it for upstream water. Stockton was one of the cities that made such a deal.
It was estimated in 2014 that Manteca could get anywhere from $100,000 to $400,000 a year selling that water by the acre foot depending upon the market and water conditions.
But that isn’t where the real money is.
If Manteca-Lathrop reuses the water it would continue to assure economic prosperity in drought periods or as continued growth and demand outstrips available water supplies.
Treated wastewater is now at such a high quality for cutting edge plants such as the one serving Manteca that some Californians are already drinking and showering using treated wastewater.
That’s been the case in San Diego since 2012 when a pilot treatment plant went into operation that put a portion of San Diego’s treated wastewater through one additional treatment process. The $13 million plant now produces a million gallons of water a day for municipal use to support the equivalent needs of 12,825 people. By 2020, San Diego expects to have 7 percent of all municipal water for drinking as well as other residential and commercial uses come from the city’s wastewater treatment plants.
Treated wastewater has been used for years on crops such as lettuce in the Salinas Valley, for manufacturing processes that require highly clean water, and to irrigate golf courses in Palm Springs.
Orange County has used a slightly different approach. They are injecting treated wastewater directly into the underground aquifer that communities in the region pump water from for domestic use. The recharging already accounts for 20 percent of the aquifer’s water.
DeBrum in 2014 said he viewed the water being returned to the San Joaquin River as the equivalent of Manteca tossing away money. He also believes the city should make every effort to help make sure there is adequate water for local agriculture given how SSJID has worked to secure and protect water rights for municipal use.
Recycled wastewater figures heavily in the Manteca Urban Water Master Plan that was adopted three years ago by the City Council
The plan notes that based on water use projections against the safe annual groundwater pumping yield of 13,570 acre feet and the maximum 11,500 acre feet from the first phase of the surface water treatment, the city would need to have the second phase of the treatment plant located on Dodds Road 16 miles northwest of Manteca near Woodward Reservoir in place by 2031. The second phase would give Manteca 7,000 acre feet of additional water for a combined capacity of 32,250 acre feet of water in a normal year.
The city anticipates using the full current phase one allotment of 11,500 acre feet by 2020 and then working up toward the groundwater safe yield rate until the second phase is in place. The safe yield is likely to be cast in stone by the state-mandated groundwater sustainability law that restricts pumping to the amount that is replenished each year in an aquifer. That means additional groundwater could not be taken out to support growth unless it is replaced on an annual basis.

Recycled water
becomes essential
by the year 2040
Meanwhile projections to ramp up the use of recycled water to the point in 2040 when 2,240 acre feet of such water is excepted to be used for public landscaping and the golf course will mean Manteca will need 27,530 acre feet of water from the surface treatment plant and groundwater to serve anticipated growth.
That is enough water to meet the needs of 127,740 residents in 2040 that Manteca is expected to have based on historic annual growth rates of 2.3 percent. That is 49,740 more residents than the current population.
When the second phase is finished at the treatment plant and coupled with groundwater Manteca would have a 4,720 acre foot cushion. Although not stated in the report given it looks out only 25 years, that cushion should it all be used on based on per capita annual water consumption numbers in the report could support up to another 20,000 residents for a population of just under 150,000.
Given the state mandate on groundwater pumping to essentially take no more from a basin than is replenished in a given year, Manteca would only have three other ways to further increase water availability for growth: Harnessing stormwater in some manner, using treated wastewater to recharge aquifers or reduce portable water for irrigation, or more effective water conservation.
If Manteca maintains per capita usage that they had in 2015 of 139 gallons a day, the city’s water use forecast will be extremely conservative given the plan is built on a state target of 179 gallons of water a day being used by every Manteca residents on a per capita basis. By comparison Manteca’s average daily use between 2003 and 2007 was 221 gallons per capita.
Manteca has 17 potable water wells and 31 irrigation wells that draw from aquifers that extend down to 600 feet. At 600 feet and lower there are more water tables but they have salt water.

To contact Dennis Wyatt, email