Naturally Occurring Elements
The groundwater contains small amounts of naturally occurring iron, manganese and arsenic. Iron and manganese are not considered a risk to human health and federal regulations do not require treatment to remove them from drinking water. Many people take vitamin and mineral supplements containing iron and manganese, and when ingested in small concentrations, both can provide a health benefit. However, at the concentrations found in the Mint Farm aquifer, state regulations do require treatment because iron and manganese cause objectionable aesthetic issues like taste, odor, color and a tendency to stain. The City plans to treat for iron and manganese removal in order to produce high quality drinking water and prevent those types of problems.
The groundwater also contains trace amounts of naturally occurring arsenic. For many years, the drinking water standard for arsenic was 50 parts per billion (ppb). In 2004, regulations tightened the drinking water standard for arsenic from 50 to 10 ppb to lessen people's long-term exposure.
The groundwater at the Mint Farm contains approximately 6 ppb of arsenic, roughly one-half the allowable limit. At that concentration, drinking water regulations only require that we notify our customers that arsenic exists above the specified reporting level. Our current water source, the Cowlitz River, also contains arsenic but at lower levels. Although not required, the City plans to treat for further arsenic removal and reduce the arsenic concentration to approximately 2 to 3 ppb.