Test results for DDT prove negative | TahoeDailyTribune.com

Test results for DDT prove negative

Gregory Crofton

Tests that showed small amounts of the pesticide DDT in a Tahoe Keys dredging operation turned out to be false, said Jill Southerland, administrator of the Tahoe Keys Property Owners’ Association.

Water tests that were required before the dredging operation could begin showed the presence of DDT, a pesticide banned in the United States more than 30 years ago, as well as other pesticides, said Doug Smith, a senior engineering geologist for the Lahontan Regional Water Quality Control Board.

The “false positive” that occurred for DDT likely occurred because California law requires testing to such an infinitesimal level that test results can vary between laboratories and change with subsequent testing, said Dominic Meo III, a consultant from Geotechnical Support Services who is overseeing the dredging work.

To eliminate any pesticide from water being returned to the lake, and to comply with state law, the property owners’ association added a $40,000 carbon filter to a system it is using to clear sand from Tahoe Key’s west boat channel.

After a number of delays, the dredging operation finally began Aug. 21. But work to clear the channel is going more slowly than anticipated.

Now instead of two weeks, the operation could take four weeks to complete because the sand in the channel is coarser than expected and that has created pumping problems. Also having to dredge in shallow water has caused suction digging to take longer, Meo said.

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The dredging process taking longer than expected, combined with the need for the carbon filter, will increase the cost of the project by about $60,000, Meo said. The original cost estimate for the work was $470,000.

– Gregory Crofton can be reached at (530) 542-8045 or by e-mail at gcrofton@tahoedailytribune.com