It was no merry splash of holiday color when a bright-green liquid gushed from a freeway wall onto Interstate 696 in Michigan during Friday’s rush hour.

The green gusher backed up thousands of motorists, requiring first a one-lane closure, then two lanes – likely to last at least through this week. Yet those were comparatively minor problems.

Far more worrisome has been deciding what’s in this grinchy gift, how much area did it contaminate, and why wasn’t this gusher choked off last year when the U.S. Environmental Protection Agency spent $1.5 million cleaning up the source of the pollution.

According to a state of Michigan official at the site Monday, last year’s cleanup removed the “imminent threat” to health and safety. But investigators didn’t figure on the basement of the factory gradually becoming a hidden reservoir of contaminated liquid, growing with rain and groundwater to become a small geyser seeking an outlet.

Read more: yahoo