Starting in a couple of weeks, the water from Longview’s taps will originate from a deep aquifer rather than the Cowlitz River, which has supplied the city’s drinking water for decades.

The city of Longview plans to activate the new, $33-million Mint Farm Water Treatment Plant sometime around Jan. 14, Public Works Director Jeff Cameron said last week. The date is tentative because the plant first needs to undergo a 14-day commissioning process, when the city will take over plant operations while the contractor remains on standby. If anything goes wrong, the contractor, Prospect Construction Inc. of Pullayup, can fix it, and the 14-day commissioning clock would start over, Cameron said.

The water turn-on date also depends on final approval from the state Department of Health, which is reviewing the latest water quality data. The DOH already has approved the plant’s construction and its four production wells.

A few dozen water customers throughout Longview have volunteered to serve as “water sentinels” for two months and will notify the city of any changes in the water’s taste, odor or appearance.

The city began looking for an alternative to the Cowlitz River around 2007 because the high amount of volcanic silt in the river was found to be damaging equipment at the old Fisher’s Lane Regional Water Treatment Plant and sediment was threatening to block the plant’s water intake structure.

The Fisher’s Lane plant will be kept operational for several weeks after the Mint Farm plant begins supplying water to Longview utility customers, just in case there’s a big problem at the new plant, Cameron said.

Q: Will the Mint Farm water arrive at my home’s taps the day the plant is turned on?

A: It depends where you live. Customers who live near the Mint Farm Industrial Park in the 33rd Avenue area should begin receiving the well water within an hour. The water might not reach customers in the hills for a week because their water is piped to main zone reservoirs before it’s repumped to the upper zones.

The water source from customer’s taps can be identified by testing for fluoride, Cameron said. To be able to tell the difference, the city stopped feeding fluoride into the Fisher’s Lane plant on Nov. 26. Fluoride, which the city has added to its water supply for decades, will be added to the Mint Farm water when the plant is turned on. Therefore, fluoride will be the marker for Mint Farm water. City staff will regularly sample the water to track the transition of Cowlitz River water to groundwater.

Q: Will the water taste funny?

A: Most customers shouldn’t notice a change in the water’s taste or appearance because the chemistry of the two water sources isn’t dramatically different, Cameron said. Often, any taste in the water has more to do with the customer’s plumbing than the water chemistry.

Before treatment, water from the Mint Farm’s aquifer has a metallic taste and dark color due to the presence of iron and manganese. During the treatment process, green sand filters impregnated with the chemical permanganate and anthracite carbon will remove the manganese, iron and arsenic. (The arsenic, a naturally occurring element in the raw groundwater, is below the level requiring treatment, Cameron said. After treatment, the arsenic levels drop below the level requiring reporting.)

In 2008, the Longview City Council conducted a blind taste test of five water samples, two of which were from the Mint Farm aquifer using different types of filters. Bottled water scored highest in taste and odor and water from the City Hall break room scored lowest. The Mint Farm samples scored in the middle — but most council members admitted they couldn’t tell a difference in taste.

Q: The aquifer lies below some of Longview’s polluted industrial areas, such as the former site of the Reynolds aluminum plant. Could contaminants seep down into the aquifer?

A: It’s extremely unlikely. Between the ground’s surface and the aquifer are about 200 feet of sand, silt and clay. These layers are resistant to water seepage from above.

The city hired Kennedy/Jenks Consultants in 2009 to analyze the groundwater. Samples were taken from one production test well, 17 monitoring wells, wells at the former Reynolds Metals Co. and the Puget Sound Energy Mint Farm Generating Station, the Cowlitz River and the Columbia River. Scientists looked for concentrations of contaminants as small as one part per billion and even one part per trillion. Tests found no evidence that shallow contaminants have seeped into the deep aquifer and that the water is safe to drink.

An environmental firm hired to manage cleanup of the former Reynolds site has performed extensive soil and groundwater testing. Their results mirror those of Kennedy/Jenks: the aquifer’s pressure forces water up to the surface rather than down, Cameron said.

“The surface contamination is not migrating down to the deeper aquifer,” he said.

Q: Where does the aquifer’s water come from?

A: The deep aquifer is recharged by water that seeps through the bottom of the Columbia River and filters through thousands of feet of sand and gravel. The aquifer’s connection to the Columbia provides a near endless supply of naturally filtered water.

Q: Why can’t the city just fix the Fisher’s Lane treatment plant?

A: There’s no guarantee rehabilitating the Fisher’s Lane plant would solve the city’s water supply problem. Volcanic sediment continues to wash into the Cowlitz River from Mount St. Helens, grinding away the plant’s equipment and threatening to clog its intakes.

City officials have said the risks, final costs and time delay to rehabilitate the Fisher’s Lane plant and attempt to solve the sediment problem are much greater than those for the new Mint Farm plant. Also, the Cowlitz River water quality is not “risk free.” Longview is downriver from nine sewage treatment plants with outfalls into the Cowlitz and the river is vulnerable to spills of hazardous chemicals on nearby highways and railroads. In recent years, water testing has revealed high levels of pharmaceutical medications and antibiotics in the state’s waters that scientists haven’t yet figured out how to eliminate.

Q: Why has the city chosen to drill wells at the Mint Farm Industrial Park rather than somewhere with less of a stigma?

A: The Mint Farm is the only area engineers have found where the aquifer has both high water quality and high production, Cameron said.