Radon in Water. Topic 10 - Audio 80

Transcription

1 Topic 10 - Audio 80 The measurement of radon in water as well as some concerns relative to mitigation was covered in the measurement section (if needed please review Measurement Course). The vast majority of radon comes from soil gas Homes with groundwater supplies can have elevated radon in well water Concern is with additional amount of radon that enters the air 10,000 pci/l in water can yield around 1 pci/l into air On the average, radon from water does not constitute a large portion of radon in homes. Typically, reducing radon from soil gas has the largest impact on indoor radon levels. A home on a well or groundwater supply can present a large amount of radon. Identify water source (groundwater or not) during diagnostics Home may not have been tested while water was being used. Although an ASD can reduce radon laden soil gas, it will do nothing for reducing radon in water. Consider including exclusion or specific wording regarding radon from other sources like water. To reduce radon from water requires skills that are not taught in this course. Plumbing Water quality maintenance Disinfection systems If you do not have these skills or qualifications find someone who does, if you are working in an area of high frequency of radon in water concerns. Radon in water concerns follow EPA zone map. 1

2 Topic 10 - Audio 81 Radon Rule of Safe Drinking Water Act Applies to: Radon in Drinking water not in effect as of September 2005 Applies to: Community Water Systems Using ground water or mixed ground and surface water 15 service connections, or more than 25 people served Does not apply to: Private wells CWS systems only serving: schools, office buildings, campgrounds, restaurants, highway rest stops. Maximum Contaminant Level (MCL) established at 300 pci/l Releases average of 0.03 pci/l in air More stringent than outdoor air at 0.4 pci/l air Alternate Maximum Contaminant Level: 4,000 pci/l air Was to be established if MCL for water would result in lesser risk from water than from outdoor air. With a radon in water to radon in air transfer factor of 10,000:1 4,000 pci/l water is equivalent to 0.4 pci/l air To comply with an AMCL, a state or local municipality must have an approved multi-media program. Designed to achieve risk reductions greater than if MCL alone was implemented, such as reductions from soil gases and other sources. Recognizes cost-effectiveness of reducing radon from soil Can be done statewide or on a district by district basis. Note: If radon is a concern, other heavy metals may also need to be treated (radium/uranium) 2

3 Topic 10 - Audio 82 Surface water typically does not present a radon in water concern Radon off gases Residence time long enough for radon to decay to decay products Ingestion of trace RDPs not considered to be a significant health concern. Storage as a mitigation techniques Impractical for a residence Very large holding tank ~ 7,000 gallons Occurs in many public water supplies where groundwater is pumped to atmospheric storage/head tank Allows radon to off gas as well as provides a certain residence time Residence time goes down as usage goes up Homes at far ends of distribution network can have less radon. 3

4 Topic 10 - Audio 83 Carbon tank inserted into pressure line after existing pressure tank. Does not require water to be re-pressurized. Radon absorbed onto charcoal Radon breaks down into RDPs that are retained on charcoal. Radon and short-lived RDPs emit gamma that can escape tank Gamma can be significant, where shielding may be necessary. 1 mr/hr per 10,000 pci/l in water. Generally not recommended for radon in water greater than 10-20,000 pci/l as a means to limit gamma. Charcoal has unlimited life for absorbing radon, because the concentration gradient between the radon in water and the surface of the charcoal is maintained because radon is changing into radon decay products. Life generally a function of clogging of bed or limit on build-up of long-term radon decay products (lead 210). Bed typically preceded by filter There is a software program included on the resource CD that can assist in calculating the amount of gamma while in operation as well as the residual amount that would be in spent carbon. Check for updates at: Approximately 1 cu. ft. carbon necessary for 95% reduction in home using 150 gallons per day. Backwashing can reduce reduction efficiency. Can provide other improvements to water quality. GAC Bed gamma Gamma is released from tank during operation According to ICRP & NCRP public should not be exposed to more than 100 mrem or 1 msv per year. Falls off rapidly after being taken out of service. Residual gamma can present disposal problems EPA suggests materials in excess of 2,000 pci/g be disposed in low level radioactive waste facilities. 4

5 Topic 10 - Audio 84 Water from well sprayed into tank Air strips out radon No gamma concerns as there is with Granular Activated Charcoal (GAC) An additional pressure tank and pump needed to distribute water throughout building Water Quality Concerns Blowing air through drinking water could introduce bacteria and other organisms. Install filter and insure air source is clean Withdrawing air from basement can cause combustion appliance backdrafting. Water can become stagnant and allow bacteria to grow during periods of non-use. Pre or post-disinfection with chlorine or post-disinfection with ultra-violet light. Discharge Points Route to prevent exposing people to high radon Air at 100% humidity Condensation can be problem Avoid traps in vent Insulate to reduce freeze potential Protect discharge from entry of foreign material and critters Maintenance Hardness can foul system Routine cleaning may be needed or a softener installed. Maintenance of disinfection system if needed. Installing this as well as a GAC system requires special knowledge about water quality and plumbing. This section is an overview only!!! 5

6 Topic 10 - Audio 85 Advice: If you are looking at a radon in water concern get a full analysis and verify that there are not other heavy metal problems. Look at maintenance issues of systems including cleaning. Become good friends with a plumber. Although prevalent in the northeast, radon in water concerns occur in several parts of the country. If home is on a well, it is recommended that both radon in air and radon in water tests are conducted. Granular Activated Charcoal When radon in water levels are low. Less than 20,000 pci/l of water is reasonable Less than 5,000 pci/l of water is prudent Gamma is emitted from carbon, so placement to reduce exposure is critical. After taking out of service, gamma drops off exponentially. Provided they are used on low levels of radon in water and after the carbon has set for 30 days, it can be disposed of like normal household trash (according to Mr. Stilwell). Can provide other benefits in improving water quality. Aeration Most common method Careful attention should be given to maintaining water quality Post-aeration disinfection may be needed. Air source can bring in a lot of crud -use filters on air supply. If air source is from basement, be careful of increasing negative pressure that can increase radon from soil gas as well as backdraft appliances. Treat system like an ASD system and conform with the EPA RMS Use auxiliary blower to keep vent under negative pressure. Install blower outside of envelope of house Terminate vent just like an ASD system. Qualifications Most areas require individual be licensed as a plumber If you are not a plumber work with one. 6