题目选项分析

A chemical spill in Oak City that took place in February tainted the drinking water of nearby communities. Some scientists claim that, because underground aquifers are interconnected, more distant water supplies are also at risk of contamination. This claim is not undermined by the fact that a careful study of the regional water table that same month detected no increase in contaminant levels beyond the immediate vicinity of Oak City, because _______.

【选项】in such a large volume of water, the chemicals dissipated to harmless levels