SPRINGFIELD – The idea that Lane County could be “water poor” is laughable to many people.
After all, this is the wet Willamette Valley, where it rains for nine months and drips for the next three.
Well, not precisely … and wipe that smirk off your face.
In the 1970s and ‘80s, I was Lane County’s hydrogeologist specializing in arsenic and dry wells. I was one of only two county hydrogeologists in the country; the other was from San Diego County.
It all started in the 1960s when a woman in Creswell was suffering from an undiagnosed chronic illness. The symptoms varied from one time to another, and didn’t seem to fit any of the usual disease profiles.
Blood test results revealed near-fatal levels of arsenic.
Lane County Environmental Health (LCEH) officials interviewed her in 1963 and traced her food and drink sources. Her water test revealed arsenic at 2.65 parts per million (ppm). The legal drinking water limit at that time was 0.50 ppm. It is 0.10 ppm today.
She drank a lot of tap water in her coffee. Her husband got most of his water in six-packs imported from Milwaukee, and the children mostly drank sodas.
After that, LCEH staff started testing well water countywide, sticking a red pin on a map when they found arsenic above the drinking water limit, an orange pin at lower levels, and a blue pin with no arsenic.
As pins increased, a pattern emerged: the county’s east side had red pins for about 50% of the tested wells, and the west side had nearly none. A report concluded that groundwater east of a line that split the county from Eugene down through Cottage Grove could be dangerous to drink.
Interestingly, many people with high arsenic levels in their well water reported it as the “best-tasting water.”
Apparently, not all poisons are bitter.
Naturally occurring hazard
Lane officials were among the first in the world to recognize that naturally occurring arsenic could be a groundwater problem in volcanic and other regions. Bangladesh is another prominent area of high arsenic groundwater, discovered after Lane County’s example.
LCEH received reports about wells running dry, salt water in wells, bad-tasting water, neighbors drilling wells that interfered, and neighbors afraid the new five-acre plots going in next door would drain all of their well water.
People realized that the three-gallon per minute (gpm) well they were using for the house didn’t leave much margin and new wells just might be the straw that broke the camel’s back for their water supply — the straw being an apt descriptor, a sucking straw, sucking up the groundwater.
County leaders hired a public health engineer and a hydrogeologist to solve these problems through avoidance, mitigation, engineering, chemistry, or treatment science. They were then charged with crafting a county ordinance to address these issues.
Percentage-wise, nearly everyone in Lane County lives in cities where they get their water from the local rivers. Even though the cities may use wells (Springfield as an example), these wells are in gravel deposits connected to the rivers.
However, most people get water from wells drilled into the bedrock in rural areas, where issues can arise.
Basic background
Let’s start at the beginning. All groundwater and all surface water comes from precipitation: snow, sleet, rain, hail, even fog. Precipitation falls to the ground, evaporating, soaking in, or running off.
If it runs off, we see it running across the ground, in little rivulets, streams, and rivers. How much water is available for running off or soaking in depends on how much precipitation falls, the ability of the ground to absorb water, and the timing of that precipitation.
Timing is essential because if you get all of the year’s precipitation in one day, water will be scarce most of the year.
Still, if you get about the same amount every month, water will seem abundant unless you only get a tiny amount each month. The former describes many deserts worldwide, and the latter represents the Midwest and East, which tend to get about equal amounts of precipitation each month throughout the year.
Too much water at once and the ground loses its ability to absorb the excess water; all the little pores are already full of water. Different soil types can absorb water at different rates – think a boulder field vs. a clay-rich soil vs. exposed bedrock.
One of the most telling things we did to show the effect of the abovementioned factors was to pick three streams with different precipitation amounts and geology and compare them by taking pictures of each stream in the fall before the fall rains had begun.
We chose the fall because in western Oregon, the rainfall is insufficient to keep the soil moist from June through September. This weather pattern, with wet, mild winters and dry, moderate summers, is known as a Mediterranean Climate.
During the summer dry period, surface runoff only occurs with rare storms, so streams flow primarily from groundwater. Small streams are typically dry, with larger ones seeing decreasing flow from late spring into fall. We selected three locations with a 95-square-mile watershed: Coyote Creek southwest of Eugene, the Siuslaw River near Highway 126, and the McKenzie River upstream from McKenzie Bridge. Each has distinct precipitation and geology.
Siuslaw River at Austa
• Siuslaw River at Austa: Moderate flow under 150 cfs. Soils are moderately developed on steep, forested hillsides. The bedrock consists of tight sandstones and shales with few fractures. Some streamside sand and silt deposits help retain groundwater. The area experiences over 80 inches of precipitation yearly, but much runs off due to steep slopes.
• Coyote Creek: No water flow. Stagnant pools. The area has poorly developed clay soils over tight sandstones and shales from the Spencer and Tyee Formations. Limited streamside sand and silt deposits hinder groundwater retention. Located in a rain shadow, it receives less than 50 inches of precipitation annually.
• McKenzie River above McKenzie Bridge: Flow ranges from 500-600 cfs—well-developed forest soils on steep hillsides. Bedrock varies between porous volcanic lava flows and dense ash deposits. Valleys feature streamside sands and gravels. Precipitation exceeds 100 inches annually, with significant snowpack influence.
Annual precipitation affects late fall river flows, but the rock and soil’s ability to store groundwater for gradual release is the primary influence. Heavier winter rainfall typically results in surface runoff. Coyote Creek and the Siuslaw River are “flashy” streams, rising and falling quickly with rain. In contrast, the McKenzie River, though it has steep slopes and more precipitation, is less flashy due to its geology, which retains more groundwater, leading to higher late summer flows.
Addressing the issues
The arsenic problem in western Oregon is linked to groundwater interacting with volcanic ash beds from the Old Cascades, which began erupting around 50 million years ago. These deeply eroded rocks are poorly permeable, causing groundwater to take longer to move through, which increases arsenic levels in the water as it leaches from the rock. The longer the water is in contact with the weathered rock and soils, the more arsenic can be transferred to the water.
Tiny openings slow groundwater movement and store it low for late summer release. Water is a suitable solvent, and arsenic has many chemical forms that are soluble in water. Much of the Old Cascades rocks are about as poorly permeable as the sandstones and shales found in the Coyote Creek valley and the Siuslaw watersheds.
Picture trying to get water to move through cracked concrete. It leaks through, but slowly, compared to concrete rubble.
Thus, groundwater moving through Old Cascades volcanic rocks picks up arsenic above the drinking water limit and sometimes well above it.
So why doesn’t groundwater in the Coyote Creek and Siuslaw River drainages have high arsenic if they are poorly permeable? Their rocks, sandstones, and shales are formed in the ocean environment and do not have appreciable arsenic to be leached into the groundwater.
It should also be noted that a few parts per million (ppm) of arsenic is very little arsenic.
It’s not as if the Old Cascades is a mineable source for arsenic; humans don’t tolerate any arsenic very well.
Volcanic ashes, which are poorly permeable and commonly contain leachable arsenic, exacerbate the problem. This slow groundwater movement results in higher arsenic concentrations.
The issue of wells “going dry” is also related to the poor permeability of volcanic ashes, sandstones, and shales found in western Oregon. In contrast, the loose sand, gravel, and silts along the Willamette and McKenzie rivers provide more abundant water. Dune deposits at Florence store significant water, but fine grain size limits flow rates to tens or a few hundred gallons per minute, and high iron content in the groundwater poses additional challenges.
Defining an aquifer
An aquifer is a geological unit that stores usable water, but in Lane County, suitable aquifers for irrigating a 750-gallon-per-minute (gpm) system covering a one-mile area are scarce. While surface sources can provide this water, few wells can achieve this output. In contrast, a typical household needs only about five gpm, and such wells are typically available in the local bedrock.
If your well produces only two gpm, which is common, you’ll need a storage solution. Households usually consume between 250 and 500 gallons daily, equating to about 0.2 to 0.3 gpm. If you can maintain a flow of 0.25 gpm into a storage tank, you can draw five gpm during peak times. It’s advisable to have a storage capacity three to five times your daily requirement, meaning a tank of at least 1,500 gallons is ideal, not accounting for irrigation needs.
Even a five gpm well should use storage, as bedrock wells can have dissolved iron, causing issues beyond taste. When pumped, the water level may drop, creating pressure changes that can lead to iron precipitation in the rock’s cracks, eventually clogging the well. This is especially true for lower-capacity wells. Gradual pumping can help prevent these issues and extend the well’s lifespan.
In poorly permeable bedrock, the slow water movement limits the potential for one well to drain another, as long as wells are not overcrowded. Three to five acres can provide enough rock volume for a year’s storage.
The High Cascades are known for excellent groundwater storage but are often located away from populated areas. In contrast, the western Old Cascades – which extend from McKenzie Bridge down to Springfield (or from Oakridge to Goshen; Culp Creek to Cottage Grove – are made up of old volcanic materials. They tend to have low permeability and may harbor elevated arsenic levels in groundwater, which frequently exceeds safe drinking standards.
The marine-origin bedrock west of Eugene is low-permeability but generally free of arsenic, although some areas have high salt and iron content.
The bedrock west of Eugene and Cottage Grove is of marine origin and has low permeability but is not arsenic-bearing. However, some areas west of Eugene have high salt content, high iron and manganese, and sulfur.
Of passing interest is Rat Creek, down near Dorena Reservoir east of Cottage Grove, in the late fall, when all the flow in the creek comes from groundwater flows. The water in the creek tests above the drinking water standard for arsenic. That doesn’t bother the animals that use it for a water source, as one of the primary ways arsenic is excreted from the body is through hair and fingernails (hooves). Animals have plenty of hair …
But look out, bald guys!
Ralph Christensen is the former Lane County hydrogeologist.
