A new at­tempt to clean Je≠er­son Me­mo­rial dome

The Park Ser­vice is test­ing a process that beams a laser on biofilm

The Washington Post Sunday - - COMMUTER - BY MARTIN WEIL martin.weil@wash­post.com

It’s not mold, or soot, or au­to­mo­tive ex­haust. Rather, of­fi­cials say, it is biofilm, an un­ap­pe­tiz­in­glook­ing smear of mi­cro­scopic or­gan­isms splotched over the dome of the Jef­fer­son Me­mo­rial.

The in­stantly no­tice­able blackand-gray stain does noth­ing for the ap­pear­ance of the 74-year-old mon­u­ment. Last week, as part of its search for a way to get rid of the biofilm, the Na­tional Park Ser­vice said it had started test­ing a process called laser ab­la­tion.

Laser ab­la­tion re­moves ma­te­rial from stone by beam­ing a laser on it. The stone ab­sorbs en­ergy and grows warm. As its tem­per­a­ture rises, the of­fen­sive gunk loosens its grip and evap­o­rates.

Scaf­fold­ing has been erected on the east­ern side of the dome, ris­ing to near its top. It is vis­i­ble to mo­torists and pedes­tri­ans in the area of the Ti­dal Basin in South­west Washington and pre- sum­ably from such van­tage points as the White House.

Biofilm is not unique to the Jef­fer­son Me­mo­rial or to Washington. But it thrives on the mon­u­ment’s dome, the Park Ser­vice has said, be­cause rain has slowly pit­ted the stone, pro­vid­ing the ubiq­ui­tous or­gan­isms with an ideal en­vi­ron­ment in which to grow.

Biofilm con­tam­i­na­tion at the Jef­fer­son was first spot­ted in 2006, the Park Ser­vice said.

But it has become pro­gres­sively worse since then at the me­mo­rial, which hon­ors the coun­try’s third pres­i­dent and the prin­ci­pal au­thor of the Dec­la­ra­tion of In­de­pen­dence.

To first-time visi­tors, or to Washington-area res­i­dents who have not seen the me­mo­rial in a while, the dome might ap­pear to be some­thing of an eye­sore, sug­ges­tive of gloom and de­cay or the af­ter-ef­fects of a ma­jor fire.

A va­ri­ety of tech­niques have al­ready been tested, the Park Ser­vice said, in­clud­ing chem­i­cal treat­ments de­signed to kill the of­fend­ing mi­crobes. But the chal­lenge is one typ­i­cally faced in such restora­tions: re­mov­ing the stain while sav­ing the stone.

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