People are learning: The groundwater issue is not one-size-fits-all.

While the drought brings renewed attention to the water stored beneath the ground and heightened concern about over-pumping the resource, there is great variability in groundwater quantities and levels in the Sacramento Valley.

And some areas are in more trouble than others.

But pinning down a broad statement that encompasses the entire issue is difficult, as groundwater levels can vary depending on soil type, the presence of surface water and proximity to rivers and streams.

"It's a location-based discussion. Areas where there is demand every year, like orchards, and areas where there's no surface water available, those areas are seeing big drops in groundwater this year," said Thad Bettner, general manager of the Glenn-Colusa Irrigation District. "Areas with surface water, like us, are doing pretty well."

One of the prime examples of surface water's effect on groundwater can be seen in Yuba County.

Prior to the construction of canals delivering water from New Bullards Bar to south Yuba County, the groundwater levels were plummeting, dropping 100 feet from 1950-80.

In the early 1980s, the Yuba County Water Agency began delivering surface water to those areas to offset the groundwater use. Since then, the groundwater has returned to historical levels, although it has declined somewhat during the past few drought years, said Scott Matyac, water resources manager for YCWA.

Conversely, the areas in the Sacramento Valley that have seen the most dramatic drops in groundwater levels are in the western areas of the valley, where there is virtually no surface water available, Bettner said.

In this area, south of Orland, water levels have dropped up to 112 feet in the last 10 years, including declines of up to 50 feet from 2013-14, according to monitoring wells operated by the Department of Water Resources.

Groundwater levels have similarly declined near Arbuckle in Colusa County.

Gaps in knowledge

So, clearly, the presence of surface water affects groundwater levels. Soil types also matter. Finer soils don't transmit water as quickly as coarser soils. But what about the issue is still unknown?

Bettner said there needs to be better data about where wells are and how much water they are pumping.

"We have new demands that are being added to the system," Bettner said. "We've put in a lot of orchards in the past decade, and that is all groundwater supply. The question is, where is that water ultimately coming from that's paying for that new demand."

Groundwater, after all, was once surface water that percolated through the ground.

"The water just doesn't regenerate itself underground. It's coming from somewhere," Bettner said. "Is there a creek that is now dry because all the water is getting sucked out of the creek to recharge the groundwater? Is it coming from Sacramento River tributaries? Those are the questions that groundwater users are going to have to really sit down and have a hard conversation about."

The surface water to groundwater connection

New research is showing increased groundwater pumping is having a negative effect on surface water supplies.

Maurice Hall, senior hydrologist for the Nature Conservancy, has been leading a study that uses thousands of well readings from the Department of Water Resources' C2VSIM system, which records groundwater levels in the Central Valley from 1922-2008.

Generally, the model shows groundwater levels in the Sacramento Valley are going down overall, Hall said.

As groundwater levels have dropped, so has the rate at which the groundwater recharged streams that feed into the Sacramento River, Hall said.

What's more, those streams are now leaching into the ground at a greater rate than they are being recharged, Hall said.

This suggests that, more and more, groundwater withdrawals are affecting surface water.

Hall said it's an under-appreciated issue in the groundwater discussion. Pumping groundwater is just another way of diverting surface water. It's just a diversion that takes place over time and is delayed from the moment in occurs.

This fact raises troublesome issues. Groundwater pumping, which is not regulated, could in time affect someone's surface water rights, which are regulated.

CONTACT reporter Andrew Creasey at 749-4780 and on Twitter @AD_Creasey.

Misconceptions, legitimate concerns over valley groundwater

Like most complex issues, there are misconceptions about groundwater in the Sacramento Valley.

One of the biggest misconceptions in Yuba County is the belief water pumped from the valley affects the water stored in the fractured rock aquifers in the foothills.

This is simply not true, said Scott Matyac, water resources manager for the Yuba County Water Agency.

Yuba County has two separate aquifer systems, one in the valley and one in the foothills. They don't connect, and one does not affect the other, Matyac said.

"The water that exists in the cracks in the foothills — that stays there until someone wants to pump it," Matyac said. "It doesn't flow from the cracks anywhere."

The valley aquifer is an alluvial aquifer — it was formed by sand and gravel running down from the mountains. The water sits in that aquifer as a well-connected pool that can be managed regionally, said Curt Aikens, general manager of YCWA.

The wells in the foothills puncture into fractured rock aquifers, which are formed when water trickles into existing cracks and fractures in the rock. Those aquifers are more volatile and fluctuate in volume and quantity throughout the region.

The misconception is so profound it sparked an initiative to halt the sale of groundwater to areas outside of Yuba County. The initiative was filed by two Camptonville residents who insist their well levels drop when valley pumps are turned on.

Other misconceptions, but also legitimate concerns, involve what are called "cones of depression." These cones are formed when groundwater pumps are turned on. The force of the suction creates a cone surrounding the wells that draws down the water levels immediately surrounding the well.

Such cones of depression have sparked concern from residents with shallower domestic wells living near larger, deeper irrigation wells. But the level of the impact is situational.

"It's not uncommon for the groundwater at a well to drop 50 feet while it's operating," Matyac said. "Once the pumping ceases, it recovers to the same level as before the pump was turned on. The effect on a surrounding well is directly proportional to the distance from the well that's pumping."

The size of the cones varies, said Curt Aikens, general manager of YCWA.

"If you have a good well at the right depth, you cannot have much of an impact," Aikens said. "If you have shallower wells that are closer together, it can have an impact. So it's really situational."

These cones can be at the root of skepticism when YCWA uses spring-to-spring groundwater levels to say that the drought has had a minimal impact on groundwater levels. The aquifer has dropped between 3 feet and 5 feet each year, a relatively minor amount given that the aquifer ranges in depth between 200 feet and 700 feet, Matyac said.

But wells being affected by cones of depression could see more drastic changes at certain times in the year.

"The public will hear from the water agency that the long-term trend in the basin is that the dry weather is causing just minor changes," Matyac said. "But then they might hear from a neighbor that their wells has dropped 30 feet in the summer. But they don't understand that that's a temporary condition that will change throughout the season as the groundwater recharges and pumping changes."

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