The Maryland Department of the Environment has ruled out two possible sources of bacteria in the Union Bridge water supply, and the agency now plans to check a suspected sinkhole near the well on Locust Street.
Treated water from the well is safe to drink, an MDE spokesman said when tests started in September. But the agency wants to know the source of bacteria in the untreated water.
Dye tests showed no infiltration from the town's sewer system, which is "very good news," said John W. Grace, an MDE public health engineer.
Tests also showed no infiltration from Little Pipe Creek or Sams Creek, but Mr. Grace said the results might have been different if the streams hadn't been tested at a time of very low flow.
Mr. Grace said water test workers spotted an area near the well that appeared to be absorbing a lot of surface water.
They reported a possible sinkhole, which MDE plans to check.
A sinkhole could contribute to well water contamination because it allows surface water to go into aquifers without filtering out bacteria the way layers of soil would, Mr. Grace explained.
If the sinkhole is allowing bacteria to enter the well, MDE will try to fill the hole, according to Mr. Grace.