Mon, 16 Apr 2012 14:01 UTC
A retired marine geologist with the U.S. Geological Survey, Wolf said he has seen what is happening in eastern Shasta County before. After the 1989 Loma Prieta earthquake, water well levels in the area of the quake fell significantly, he said.
Following the 6.9 magnitude quake in the Santa Cruz Mountains, Wolf wrote a paper for the USGS about the effects the quake had on surface and groundwater.
"The correlation is there. The behavior is identical," said Wolf, who has lived in the tiny eastern Shasta County community of Cassel since 2001.
Back in October, 131 earthquakes hit the Lassen Peak area. Most were less than 2.0 in magnitude. But since then the water table has fallen significantly, Wolf said.
Pete Amos said his pump had been submerged 40 feet the entire 24 years he has lived in Cassel. But a couple months ago he ran out of water. When the pump company measured his water level, it had fallen to 54 feet, he said.
"We've never had a water problem before. We never thought about the water table going down," Amos said.
Terry Briggs, who owns Gallagher Pump in Fall River Mills, said what is going on in Cassel is unusual. He said the drop in the water table in eastern Shasta County is the most dramatic he has seen in the past 10 to 15 years.
"It always moves up and down a little bit, but this was way more," Briggs said.
Since January, he has had to help homeowners whose water tables have dropped below their pumps.
Briggs said he isn't sure why the water level is dropping. Seismic activity may be affecting wells. Rainfall levels also affect the water level, he said. And Cassel, like the rest of the north state, went through a dry winter.
Wolf said the seismic activity further fractures the rocky, volcanic soil, allowing the water to flow deeper into the Earth.
Every time a small quake rattles the area around Lassen Peak, his toilet fills with dirty, silted water, he said. That is the silt that is broken loose from the volcanic soil underground, he said.
Officials at the USGS said they are hesitant to draw a correlation between the quakes and the drop in the water level in Cassel.
Steven Ingebritsen, a research hydrologist with the USGS, said he respected Wolf and knew of his work studying the Loma Prieta quake.
But Ingebritsen said the earthquakes were too far away to cause the water table to fall in the Cassel area. A magnitude 3.0 quake can affect water table levels in an area of about 6 miles; a magnitude 4.0 quake would affect groundwater up to about 18 miles away; and a 5.0 magnitude quake would affect wells in a 62-mile radius, Ingebritsen said.
The swarm of quakes that hit the Lassen Peak area last fall were too small to be causing problems in the Cassel area, some 45 miles away, he said.
Whatever caused the water table to drop, Wolf thinks homeowners in the area should learn a lesson from it and drill their water wells deeper to avoid the problems residents are seeing this year.
He thinks the seismic activity also may be related to other soil problems in the area, including a sinkhole that developed March 14 in the side of a holding pond Pacific Gas and Electric Co. uses in a Hat Creek Hydroelectric project in the Cassel area.
Pacific Gas and Electric Co. spokesman Paul Moreno said a sinkhole 3 feet wide and 4 feet deep developed at Hat 1 Forebay this month, so they drained the pond.
He said PG&E hired a soil scientist to investigate the cause of the sinkhole, but they have reached no conclusions, Moreno said.
"They don't know what caused the problem. Maybe there's a connection between the water table falling and the sink hole," Wolf said.
He said 858 fish had to be rescued and hauled to nearby Cassel Pond. Hat 1 Forebay will remain closed until May, he said.
Sinkholes also have developed at nearby Baum Lake, Moreno said. The Baum Lake sinkholes were caused by underground lava tubes, which are underground tunnels formed by ancient lava flows. Subway Cave, near the intersection of highways 89 and 44 in Hat Creek, is a lava tube big enough to stand up in.
Moreno said the sinkholes develop when the earth berms on the lakeshore erode away and are basically sucked down toward an underground lava tube.
He didn't know the size of the lava tubes that damaged Baum Lake. He said sinkholes sometimes are caused by rodents digging in the berms.
About 30 miles to the west, Paul Schoen is dealing with his own lake problem. He said his 60-acre Arthur Lake has been leaking water out of the bottom for many years.
He has hired consultants to find out why the lake is draining. They concluded the volcanic rocks below the surface have cracked and the lake drains from the bottom, said Dennis Possehn, a registered forester Schoen hired to help him solve his lake problem.
"Something's changed over the long term," Possehn said. "In the spring the lake is full, but by the end of the summer all the water is gone."
Schoen applied with the state Water Resources Control Board for permission to store more water in the lake and fill in the "holes" at the bottom of the lake.
Possehn said they have been exploring putting polyurethane foam over the rocks and pouring concrete over that to fill in the cracks.
Schoen said he didn't think what was happening with his lake was unusual, especially for the rocky, volcanic soil in the area. Wolf also wasn't sure the draining at Arthur Lake was related to what was happening in Cassel.
He did wonder if subsidence discovered in a parking lot in Lassen Volcanic National Park was related to seismic activity in the area.
Ingebritsen hadn't heard about a parking lot, but said there have been some problems found on the road through Lassen National Park. He said the road is hot and soft in the area around The Sulphur Works, in the southwest part of the park.
But he said he didn't think the seismic activity or heat under the road indicated Lassen Peak, an active volcano, was moving toward an eruption.