(Gillette, Wyo.) Preliminary test results of private wells in Carlile suggest the city’s acid stimulation processes at the Madison Well Field did not cause the problems with private wells in the area of the field.
Last summer, a number of private wells near Gillette’s Madison Well Field, which supplies water to the city, began to produce acidic water and some ran dry.
The Wyoming Department of Environmental Quality has since been trying to determine the cause of the problems and whether or not they’re related to past drilling and acid stimulation at the Madison Well Field.
The DEQ tested 55 wells in the area. Many were found to be unsuitable for drinking, meaning they were in the 3.75 to 6.39 pH range.
The tests also showed traces of sulfuric acid in the water rather than hydrochloric acid, which is what the city used in its acid stimulation process at its wells.
However, discharge activities at the well may have indirectly contributed to the problem. Sulfuric acid can be produced by reactions of water with iron sulfides. Water percolating through the soil and formations may have reacted with the iron sulfides and produced the sulfuric acid in the water.
One possible source of the surface water, besides natural precipitation, is the water that was discharged as part of tests after the wells were complete.
This discharge was drained into an erosion-controlled area and was permitted by the state, according to Gillette spokesperson Geno Palazzari.
None of the hydrochloric acid used in the stimulation process was ever discharged. The mixture, which also contains bleach and water, was pumped back out, transported off-site, and disposed at a disposal facility.
Lowering the water table can also raise the acidic levels.
These results and what they mean for the City of Gillette were presented Tuesday night at the Gillette City Council work session.
“At the end of the day, in all likelihood…there’s been a combination of events,” said Kevin Frederick, water quality division administrator with the DEQ, told the council members present.
Some uncertainty remains, but Frederick said at this point, the tests are pointing to other causes than the city’s drilling and stimulation activities.
However, the DEQ is reviewing the engineering logs to confirm the integrity of the well casings at the most recently drilled wells. Results of the review are expected soon and are an important hurdle in the city moving forward with the Madison Water Supply project.
The well integrity “is the most immediate question we’re trying to resolve,” Frederick said.
Mayor Louise Carter-King stressed the importance of releasing the results as soon as possible. The city wants to begin utilizing the most recently stimulated wells so as to be prepared for irrigation season this summer.
“I’m sure you’re aware why we’re anxious to have something resolved,” the mayor said.
One of the impediments to identifying a source of the problems is a lack of baseline tests on the private wells, which would give more of an indication as to the time frame in which water pH levels began to drop.
The DEQ is conducting interviews with the private well owners to get a better idea when the problems first arose. This might help close some of the gaps in data.