Surface water project or no surface water project, Davis public works staff members have always assumed they would need to retrofit the city’s deep wells to step up treatment for manganese, a naturally occurring element that poses no health risks, but that can oxidize and turn plumbing fixtures black.
They just didn’t think they would have to do it this soon.
A string of emails between public works staffers and the City Council was forwarded to The Enterprise this week, detailing circumstances that resulted in the city shutting down one of its highest-producing deep water wells due to a recent dramatic spike in manganese levels.
On Feb. 5, a sample was pulled from Well 30 in West Davis showing levels of manganese at 2,400 parts per billion, far exceeding the 50 ppb maximum contaminant limit set by the state.
The city then took a second, separate sample on Feb. 22 that read 1,700 ppb, subsequently forcing the city to cut the well off from the water supply.
“Manganese is naturally occurring and considered a secondary constituent, not a primary health hazard,” explained Herb Niederberger, the city’s general manager of utilities, development and operations, in his email to City Manager Steve Pinkerton.
“Its impact on water quality is typically aesthetic as it rapidly oxidizes in the presence of chlorine and will stain plumbing fixtures a dark brown or black. … Because there is no treatment, this well is now off-line.”
With the mail-only election on the surface water project ending Tuesday — and with the campaign putting the city’s groundwater supply under much public scrutiny — The Enterprise questioned the city manager about the timing of the release of this information.
But Pinkerton said Wednesday there was no consideration of the water project when he forwarded the news to the City Council.
“Losing a well is a very big deal and the sort of thing I would pass on to the council in a timely manner,” Pinkerton said in a text message Wednesday.
Meanwhile, Walt Sadler, a Davis Water Advisory Committee member and licensed water treatment operator with surface and groundwater experience, said he has questions about the way the city obtained the well samples. Sadler opposes Measure I.
“I’ve never seen manganese levels this high,” he said. “Unless the bottom of the sample bottle is filled with a whole bunch of rust.”
Sadler wonders about the protocols the city followed when testing the well water, especially whether the sample was tested for total and dissolved or field filtered, if the well had been continually operating before the sample was drawn or if the well was sufficiently purged prior to the sample being drawn, among other questions.
Dianna Jensen, the city’s principal civil engineer, could not be reached before press time to respond to Sadler’s questions.
Water agencies are required by the Department of Public Health to sample wells annually and monitor various constituent levels to ensure drinking water quality and safety.
Should a well begin to show signs that a certain constituent is edging closer to the maximum contaminant level, samples are taken more frequently to keep even closer watch.
Reached earlier Wednesday, Jensen said Well 30 was already on a quarterly sampling schedule because manganese levels had been nearing the 50 ppb limit.
Niederberger told the City Council at its meeting Tuesday that the loss of the deep well, which sits near Lake Boulevard in West Davis, would not result in lower water pressure throughout the city’s water distribution system.
He did say, however, that any further reductions in well water supply could mean lower pressure this summer.
“We could place this well on standby and use it up to 15 days this summer,” Niederberger said in an email. “But we would be required to notify the community every time the well is used.”
Complicating the issue, Well 33 is also being monitored quarterly for manganese. The latest reading had levels up to 45 ppb.
Jensen said if that number climbs over 50, the city will have to track the annual running average to see if the well needs further attention.
Additionally, the city temporarily shut down another deep well, 32, in November due to high levels of manganese and was forced to build a treatment facility there for the contaminant.
The city has four operational deep wells, not including Well 30, numbered 28, 31, 32 and 33. A fifth deep well, Well 34, has been drilled, but has not yet been equipped with a pumping station. A sixth deep well is planned for drilling at the former Well 29 site sometime in the next 10 years, according to Jensen.
But while the city has seen several of its deep wells get hit by manganese, Graham Fogg, a UC Davis professor of hydrogeology, said just because one well shows signs of higher contamination doesn’t mean others will.
“It’s not surprising in these wells, when they pump they draw in water from considerable distances, possibly from other levels above and below,” Fogg said Wednesday. “It may have taken a while for that high-manganese water to get into that particular well. (But) it doesn’t mean that every deep well will have that problem.”
Regardless, Jensen said Tuesday the city always has known it would have to treat all of its wells for manganese as part of maintaining its deep well system, even if Measure I passes on Tuesday.
To retrofit a well with manganese treatment equipment, Niederberger projects it would cost about $2.6 million per site, the same cost for the treatment facility placed at Well 32 last year. If the city is considering treating all of its deep wells for manganese, he told the council Tuesday, then perhaps rerouting all the water to one central treatment facility would be more cost-effective.
The city also has other ways it can reduce the amount of manganese found in the deep wells in question. Jensen and Fogg both pointed to possibly analyzing the adjacent ground to determine where the manganese water is coming from and then subsequently attempting to block those sources off.
When Well 32 exceeded maximum limits, the city spent $16,600 to perform such a process. However, in the end, the effort was unsuccessful.
“The intermingled screened areas that produce high manganese in this well made physically blocking off these areas difficult,” Jensen explained. “And we were concerned about the manganese traveling down the outside of the well in the gravel pack and being pulled into the well from another screened zone.”
Will Arnold, campaign manager for Yes on Measure I, believes the recent development pokes holes in one of No on Measure I’s fundamental arguments against the project.
“I think this is a pretty big deal,” Arnold said in a text message. “The other side is saying, one, the deep aquifer is pristine and, two, we can meet our water needs with just the deep wells. The latter is predicated on all our deep wells running 24/7 at (maximum) capacity. That is clearly not a realistic scenario.”
Mike Harrington, spokesman for No on Measure I, however, remains unconvinced.
“The No on I Committee is very skeptical of the city’s water staff deciding that one of the deep aquifer wells needs to be turned off temporarily,” Harrington said Wednesday. “There’s been a breakdown in trust in the city with the way they behaved about the water project and the water rates. Do we trust the city to tell us that Well 30 is actually defunct and negatively affects the deep aquifer availability? The answer is no.”
— Reach Tom Sakash at firstname.lastname@example.org or 530-747-8057. Follow him on Twitter at @TomSakash