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The Portland Water Bureau‘s last effort to keep its five in-town drinking water reservoirs uncovered has failed. The bureau said it received  from the federal Environmental Protection Agency on Wednesday denying its request.

The bureau made every effort to evade the rule, said Administrator David Shaff, even in light of earlier word from the EPA that it would probably stand. “They had indicated pretty strongly that they didn’t think there was any crack in the door, but we told them they could have been clearer in their earlier communications to us,” Shaff said.

In a November 2009 letter to the EPA, Commissioner Randy Leonard, who oversees the bureau, wrote that “considerable confusion exists” as to whether Portland could seek a variance from the rule. The Long Term 2 Enhanced Surface Water Treatment Rule would forbid open reservoirs such as those at Mount Tabor and Washington Park.

A return letter, dated Dec. 16, 2009 cleared up that confusion, saying the open reservoirs are vulnerable to contamination by Cryptosporidium and Giardia. “Neither of the two types of variances available … are applicable in this circumstance,” wrote EPA Assistant Administrator Peter Silva.

Water Bureau officials already have started working to comply with the rule by taking the reservoirs off-line. To replace the storage capacity, the bureau is building new reservoirs at Powell Butte, Kelly Butte and Washington Park.

Separately, bureau officials are making their case for another variance to the same rule. Officials are taking water samples in the Bull Run watershed to show that Portland doesn’t have a problem with Cryptosporidium and shouldn’t have to build a new plant, estimated to cost $385 million, to treat for it.