Source of well pollution remains elusive
Preliminary tests have failed to discover the source of contamination of three drinking-water wells in the South “Y” area, the South Tahoe Public Utility District has announced.
Earlier this month, the district ordered tests of soil and shallow groundwater near three wells that have been contaminated, but the investigation has yet to produce solid leads, said Rick Hydrick, the district’s operations manager.
So far, the search has cost $37,500, which is being paid by the El Dorado County Water Agency.
At issue is an industrial solvent often used in dry cleaning, polychlorinate ethylene or PCE, and a controversial fuel additive, methyl tertiary butyl ether or MTBE.
The district discovered PCE contamination in the Clement and Julie wells several years ago, while MTBE showed up for the first time in the Tata Lane well this February.
But the source of the pollution has remained a mystery, despite the drilling of 48 monitoring wells in 22 locations, and the gathering of soil samples at each site.
“We were surprised we didn’t find anything except a little PCE,” Hydrick said. “The fact that PCE is found in deeper groundwater (drawn by the wells), but not in shallow groundwater may mean its a historic contamination and not recent. But MTBE is a ‘floater,’ and I thought we would have found some.”
Either today or Tuesday, the district will launch a second phase in its investigation. By slant-drilling near sewer lines, the district hopes to discover contaminants that may have been dumped in storm drains.
“Now we will do some deeper testing,” Hydrick said. “We will identify some water-bearing strata where the pollutants would travel.”
After the discovery of PCE in two wells, the district built a $564,000 air-stripping plant to remove the solvent from the drinking water. This year, the district closed the Tata Lane well for a month following the discovery of MTBE contamination.
In July, the district reopened the well, blending its water with that of the other two wells before sending it to the treatment plant.
While air stripping has not removed all of the MTBE, the highest levels following treatment, 1.7 parts per billion, were well below the 35 ppb state health limit and also below the 15-25 ppb threshold for detecting taste and odor, Hydrick said. And, the last time the blended water was tested, no trace of MTBE was detected.
The good news, Hydrick said, is the latest monitoring has shown a drop in the amount of MTBE contaminating the Tata Lane well. The highest concentration was found in July, when the amount of MTBE peaked at 26 ppb, but the August level declined to 14 ppb.
“The next reading will be real interesting,” Hydrick said.
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