On what basis does the EPA recommend collecting samples for hexavalent chromium in water systems using surface water?

The EPA recommends collecting samples for hexavalent chromium on a quarterly basis in water systems using surface water. This frequency is based on the need to monitor potential contaminants more closely due to the dynamic nature of surface water sources. Such sources can be significantly affected by various environmental factors, including runoff, industrial discharges, and seasonal changes, which can all influence the levels of contaminants like hexavalent chromium.

Quarterly sampling allows for timely detection of any fluctuations in hexavalent chromium concentrations, thereby helping water treatment facilities respond effectively to changes that could pose risks to public health. This proactive approach enhances the ability to maintain compliance with water quality standards and ensures the safety of the drinking water supply.