Engineers investigating soil to determine why San Francisco tower is sinking

SAN FRANCISCO (KGO) -- Engineers are digging into the soil to find out why San Francisco's Millennium Tower is sinking.

The first of three holes will be bored into the bedrock and equipment will then be lowered into the holes to measure movement.

RELATED: SF skyscrapers to be examined following Millennium Tower tilting

Engineers hope data will then show why the 58-story tower has sunk 16 inches and tilted two inches since it was completed in 2009.

WATCH VIDEO: Luxury skyscraper Millennium Tower sinking in downtown SF

Experts only expected it to settle four to six inches in all.

The data collected by the soil engineers could ultimately determine who's to blame and who could possibly be forced to pay millions to solve the problem.

The testing is expected to take a month and then we may get some conclusions in five to six months.

Click here to read the subpoena formally filed by San Francisco City Attorney Dennis Herrera.

Click here for a look at more stories and videos about the Millennium Tower in San Francisco.