Perchlorate is a naturally occurring and man-made synthetic “anion” (negatively charged ion) commonly associated with the solid salts of ammonium, potassium, and sodium perchlorate. Synthetic perchlorate is used in the manufacture of fireworks, explosives, flares, ammunition, and rocket propellant.
Two states have mandated maximum contaminant levels for perchlorate: 6 micrograms per liter in California and 2 micrograms per liter in Massachusetts. Other states have guidelines ranging from 1 to 18 micrograms per liter.
If a residential well is located in a region known to have this type of industrial activity, the groundwater may have been impacted. Also, some types of fertilizers have been linked to perchlorate presence. You can contact a local environmental regulatory agency or the USEPA to ask about industrial pollutants in soil and groundwater in your area.
Disinfection of wells using household bleach also could introduce perchlorate into groundwater. The level of perchlorate in bleach will increase as the bleach ages or is stored at elevated temperatures. The National Ground Water Association (NGWA) recommends that only disinfectants certified for use in drinking water be used to disinfect private household wells.
- Explore with a qualified water well system professional the feasibility of retrofitting the well to block off the perchlorate-producing zones.
- Build a new well system that isolates the likely perchlorate-producing zones of groundwater.
- Install appropriate water treatment technology.
Reverse osmosis (RO): This is a process for removing dissolved ions from water, in which water is forced through a semipermeable membrane, retaining most ions while transmitting the water. Some NSF-certified reverse osmosis technologies have reduced perchlorate levels from as high as 130 micrograms per liter down to 4 micrograms per liter or less.
Most RO units can be fouled by low concentrations of slightly soluble minerals such as calcium, magnesium, iron, and manganese—so some pretreatment of the water may be required.
With RO units installed at the point where water is being used, such as at the tap, a minimum of three gallons of wastewater is discharged for every gallon of treated water. Often the wastewater can be used for non-drinking purposes.
Maintenance of RO units involves replacement of pre- and post-filters as well as the membrane, which can last three years or more.
Ion exchange: This is a physical/chemical process in which ions are exchanged between a solution phase and a solid resin phase. An ion exchange system can be installed at the point of water use or where the water enters the house.
Pre-filtering of water using sediment filtration is recommended as a precaution to prevent sand, silt, and clay particles from clogging the resin bed. Also, the system should be designed to backwash with non-contaminated water.
Know the maintenance requirements of an ion exchange system and make sure maintenance takes place at recommended intervals or when conditions indicate.
For more information on treatment, contact two organizations that certify home drinking water treatment systems: the National Sanitation Foundation (NSF) at www.nsf.org and the Water Quality Association at www.wqa.org.