GEO-113: ENVIRONMENTAL GEOLOGY

RADON LECTURE NOTES

 

 

Produced as part of the decay scheme of uranium 238:

 

Uranium 238 ---> Thorium  ---> Radon 222---> Polonium ---> Lead ---> Bismuth ---> Lead 206

 

Radon 222 has a half-life of 3.8 days so it quickly transforms to polonium, bismuth, and lead. Only isotope in the decay scheme that is a gas and, therefore, mobile.

 

Radon concentration measured in picocuries per liter of air (pci/liter). One pci = 2-3 atoms of radon decaying each minute.

 

 

I. Radon and Lung Cancer

 

Found everywhere in low concentrations. No environment on earth is radon free. Outdoor air averages 0.2 pci/liter and indoor air averages 1.2 pci/liter (or about 150,000 decays per minute in a typical room). Radon itself is not the problem since it is a gas and can easily be flushed out of lungs. However, the radioactive decay products of radon, polonium, bismuth, and lead, are absorbed onto dust and smoke particles and these get stuck in lungs.

 

When these decay products of radon themselves decay, they bathe the inner lining of the lungs with radiation, predominantly alpha radiation. Over time (lifetime exposures), this can lead to the production of lung cancers.

 

Estimated that of the 150,000 lung cancer deaths in this country every year, approximately 15,000 of them may be attributable to excessive radon exposure.

 

 

II. Radon Exposure, Mortality, and Risk

 

Mortality (dose-response) rates based upon studies of uranium miners in the 1950s and 1960s. However, the effects of other carcinogens (i.e., rock dust and smoking) the miners may have been exposed to is uncertain. USEPA suggests lowering your exposure levels to less than 4 pci/year. This is a rather arbitrary number. Does not mean it is safe if the value is less and dangerous if the value is more. It is meant to be a target value that can be reasonably attained in the home environment. Presently exceeded by as many as 5 million homes in the U.S.

 

Mortality rate is usually expressed as deaths/100 over a lifetime of exposure (70 years 75% of the time). Does not tell you when the deaths occurred, just an estimate of how many.

 

4 pci/liter: 3% average mortality

20 pci/liter: 15% average mortality

200 pci/liter: 50% average mortality

 

Houses with upwards of 2000 pci/liter have been measured! Even these can be dangerous in the short term (10 years or less). Although these mortality rates seem very high, they are similar with those for things we accept as part of our everyday lives.

 

10 pci/liter is roughly equivalent to the risk of smoking 1/2-1 pack of cigarettes/day or having 500 chest x-rays/year.

 

Can also express risk as a loss of life expectancy. Tells you, how much something shortens the average (not your) life expectancy. Doesn't say when any individual will die. 15 pci/liter lowers the average life expectancy by one year (10% mortality). Smoking a pack a day reduces it by 6 years. Being 25 pounds overweight reduces it by 2 years. Automobile accidents reduce it by 2/3 years. Home and work accidents reduce it by about 100 days.

 

Radon is dangerous, but no more so than things we do as a regular part of life. On the other hand, we ban substances with mortality rates 10-100,000 less than radon (chemicals that have a one-in-a-million chance of causing cancer are banned). Our perception of risk and how we react to it often is very different than the risk we actually face.

 

We will only know the true risk from radon after we have followed thousands of people over their lives, measured the radon levels they have been exposed to (and for how long), and determined their cause of death. Known as a longitudinal study. May take another 50-75 years. Preliminary results suggest the risk has been slightly overstated, particularly at the low end of the exposure range (less than 10 pci/liter). There may be non-linear dose/response relationship at those levels. A threshold exposure level of about 10 pci/liter may be required.

 

 

III.    Radon in the Home

 

Radon enters the home usually through the basement. May also enter from uranium-bearing rocks and from radon dissolved in well water that has flowed through uranium-rich rocks underground.

 

Radon flows from the surrounding soil into the basement because the air pressure in the basement is less than the air pressure in the soil. This is because air in homes typically rises from the lower levels to the attic. Known as the stack effect. Radon-rich soil gas flows into the basement through cracks in walls or floor, spaces around utility (water, sewer, and electric) lines, porous cinder block, French drains, or open sump pumps.

 

Since radon is heavier than air, radon tends to collect in the lower levels of the house. Typically, radon levels decrease by 50% for every level you go up in the house. High basement levels may not mean high levels in the upper floors where you spend your time.

 

The more airtight and energy efficient the house the higher the radon levels may be. Typically, radon levels are 30% higher in winter than the yearly average and 30% lower in the summer. This is due to the house being more airtight in the winter (doors and windows closed and insulated) than in the summer (doors and windows open more often).

 

So where and when you measure radon levels and how you spend your time in your home may change how you view your risk from radon. For example, a 10 pci/liter level measured in January in an unfinished basement may not be viewed as a problem, whereas the same level measured in the family room in June may be seen as a great risk. Each situation has to be evaluated individually and you have to decide how much risk you or your family is willing to accept. However, first need to have an idea of the radon levels before deciding how to react and what to do, if anything, to remedy the situation.

 

 

IV.    Measuring Radon Concentrations

 

Three general methods for determining radon levels in the home.

 

1)    Air "Grab Bag" Sample: A sample of air is collected and measured. Provides a quick snapshot of the radon level in one place of the home at a given time. Usually done by an environmental consulting firm. May cost a few hundred dollars, but is useful if a quick result is needed. Does not provide long-term exposure information.

 

2)    Activated Charcoal Canister: Place a metal or plastic canister filled with activated charcoal in a room (or rooms) for 3-7 days. After exposure, the canister is sealed and sent to the lab for measurement. Results usually returned in 2-3 weeks. Homeowner can purchase canisters at most home supply stores for $15-25 and includes postage and lab costs. Provides a fairly accurate method (+/- 20%) of the time-averaged radon levels.

 

1)    Alpha Track Detectors: Canisters with a material that records the decay tracks of radon and daughter products are placed in the room (or rooms) for 1-3 months. After exposure the canister is sealed and sent to the lab for counting. Provides an accurate  (+/- 10) long-term seasonal average of radon levels. Canisters typically cost $75-100, including postage and counting costs.

 

Once an accurate and repeatable result has been obtained, the homeowner can decide what to do, if anything, to lower the radon concentrations to acceptable levels.

 

 

V.   Radon Remediation Methods

 

Four general strategies for reducing radon levels: ventilation, sealing entry points, reducing the stack effect, and sub-slab ventilation. Which strategy or strategies are to be used depends on initial radon levels, radon reduction desired, house construction or design, local climate, and budget.

 

1)    Ventilation: Providing more fresh air into the home can significantly lower radon levels. Can be done passively (open doors and windows) and actively (fans). May be of limited use in very cold or tropical climates. Typically very low costs involved.

 

2)    Sealing Entry Points: Seal off all points of radon entry into the home. May include sealing cracks in basement walls and floor, sealing off French drains, capping open sump pumps, sealing gaps around utility pipes and conduits, and waterproofing porous cinder block walls. Typically cost $100 - $1,000, depending on the amount of sealing that needs to be done.

 

3)    Reducing the Stack Effect: Try to minimize the air pressure reduction in the lower levels of the home. Can be done by reducing air circulation from the lower to upper levels of the house by sealing air pathways between floors.  Also use outside air instead of inside air (which is then exhausted to the outside) for clothes dryer, furnace, wood stove, or fireplace. Typical costs are $1,5000 or less.

 

4)    Sub-Slab Ventilation: Evacuate radon-rich soil gas from beneath and around the basement. Usually do this by sinking perforated pipes beneath the basement slab (floor) and attaching an exhaust fan to vent the soil gas to the outside. Also lowers air pressure in the soil so that the airflow is now from the basement to the surrounding soil. Cost is typically $5,0000 or less. Can be incorporated as part of the basement water control system and is much cheaper if done during the home's original construction.

 

Often multiple strategies are employed to realize the maximum reduction in radon levels. Radon reductions of 98% or more are possible, particularly if sub-slab ventilation is utilized. However, at some point further reductions may become very expensive.

 

 

VI.    Radon Levels in New Jersey

 

Depends on the local geology, including rock type, composition, and structures (fractures, bedding, porosity, permeability, and faults). These may change dramatically over fairly short distances (tens of feet). Therefore, can not depend on general levels in your area or your neighbor's level to predict what the particular radon level in your house is going to be. Need to measure each home.

 

New Jersey divided into four major geological provinces.

 

1)    Valley and Ridge (Paleozoics): Generally high values. 25% of the homes or more may have values above 4 pci/liter. Average is 8.2 pci/liter

2)    Reading Prong (Precambrian Highlands): Generally high values. 25% or more of the homes may have values above 4 pci/liter. Averages 8.1 pci/liter). Some very high hot spots (1000+ pci/liter).

3)    Piedmont (Newark Basin): Generally elevated values. 10% or more of the homes may have values above 4 pci/liter. Averages 4.2 pci/liter with locally higher levels (50-200 pci/liter).

4)    Coastal Plain (subdivided into inner and outer zones): Generally low levels, particularly in the outer (southern) coastal plain. Averages 1.5-2.5 pci/liter with less than 10% of the homes above 4 pci/liter.