Based on the information provided, the patterns of atrazine concentrations in groundwater may include the following:
B. Atrazine concentrations in groundwater were highest during July and early August. C. Atrazine in the river water can contaminate groundwater great distances from the original source of the herbicide. D. Atrazine was present in groundwater throughout the year, regardless of the distance from the river.
A does not seem to be a valid pattern if the hypothesis suggests that contaminated river water is moving into the aquifer, likely resulting in higher concentrations closer to the river. Thus, the selected patterns are B, C, and D.