CONTRIBUTION OF WATERBORNE RADON TO HOME AIR QUALITY

by: Joel 0. Catlin Arun K. Deb AWWA Research Foundation Roy F. Weston, Inc. Denver, CO 80235 West Chester, PA 19380

ABSTRACT

The American Water Works Association Research Foundation (AWWARF) initiated a study to determine the contribution of waterborne radon to radon levels in indoor household air. The project required selection of three communities with waterborne radon levels in the ranges of 500 to 2,000 pCi/L; 2,000 to 10,000 pCi/L; and greater than 10,000 pCi/L and required the concurrent measurements of airborne and waterborne radon in selected homes. The main objective of the project is to perform a controlled experiment to explore the effect of a centralized water system on indoor radon levels in three communities with widely variant waterborne radon contamination levels.

Various processes, such as diffused bubble aeration, granular activated carbon (GAC), and packed tower aeration (PTA) for - removal of radon were reviewed. Various advantages and disadvantages of each treatment system were identified. Capital costs and annual operating costs for PTA systems for radon removal from water were evaluated.

Improvement in indoor air quality resulting from treatment of waterborne radon in two communities was small. However, in one community a large indoor air radon reduction was achieved by reducing the waterborne radon concentration using a PTA treatment system.

This study was funded by the AWWA Research Foundation (AWWARF) . AWWARF assumes no responsibility for the content of the research study reported in this publication, or for the opinions or statements of fact expressed in the report. The mention of trade names for commercial products does not represent or imply the approval or endorsement of AWWARF. This report is presented solely for informational purposes.

BACKGROUND

RADON OCCURRENCE I N PUBLIC GROUNDWATER SUPPLIES

T h e occurrence of radon i n d r ink ing water s u p p l i e s o r i g i n a t e s from groundwater sources. The radon content i n groundwater may range from around 100 p C i / ~ t o occas ional ly over 1,000,000 pCi/L (Longtin 1990). I n o rde r t o develop r e g u l a t i o n s f o r radon i n d r ink ing water, t h e U.S. Environmental P r o t e c t i o n Agency (USEPA) conducted a survey t o develop a nationwide d i s t r i b u t i o n o f radon i n p u b l i c groundwater supp l i e s . The survey inc luded a sample of 1,000 s i t e s , which were d iv ided i n t o f o u r popula t ion c a t e g o r i e s . A minimum repor t ing l e v e l (MRL) of radon of 100 pCi/L was used i n t h i s survey. The maximum concent ra t ion of radon found i n t h i s survey was 25,700 pCi/L. Only 27.4 pe rcen t of t h e si tes repor ted concent ra t ions of radon l e s s than t h e MEU, of 100 pCi/L.

Population-weighted averages of radon i n groundwater were ca lcu la ted . I t was found t h a t t h e s t a t e s o f Maine, New Hampshire, and Rhode I s l a n d had t h e h ighes t l e v e l s of radon i n t h e na t ion . The population-weighted average f o r radon i n water was 194 pCi/L f o r populat ions g r e a t e r than 1,000. For populat ions l e s s than 1,000, t h e average was 602 pCi/L; whereas t h e o v e r a l l n a t i o n a l average was 249 pCi/L.

INDOOR RADON OCCURRENCE

Radon e n t e r s i n t o a home through cracks and o t h e r openings i n t h e wa l l s and f l o o r s t h a t a r e i n con tac t with t h e s o i l . A nationwide survey of radon concent ra t ions i n indoor a i r w a s conducted by Cohen (1989) a t t h e Univers i ty of P i t t sburgh . This study, with over 100,000 measurements of indoor a i r radon concent ra t ions , found t h a t t h e indoor radon l e v e l s i n a given geographic a rea i s l o g normally d i s t r i b u t e d , wi th a geometric s tandard devia t ion of about t h r e e . Average radon l e v e l s i n main l i v i n g a reas have been found t o be 40 pe rcen t h igher i n win te r than i n summer. Also, t h i s study showed t h a t radon l e v e l s i n rooms below ground l e v e l a r e twice a s high a s i n rooms above ground l e v e l . The nationwide mean radon l e v e l i n l i v i n g a r e a s was found t o be 1 . 7 6 pCi/L. T h e d a t a i n t h i s s tudy showed t h a t North Dakota and Colorado had t h e h ighes t l e v e l s of indoor radon.

I t has been es t imated t h a t about 10 pe rcen t o f a l l homes i n t h e United S t a t e s have radon l e v e l s exceeding t h e USEPA c o r r e c t i v e a c t i o n l e v e l of 4 pCi/L (Skrable 1991) . A major por t ion of t h e s e homes had radon concen t ra t ions i n t he range of 4 t o 20 pCi/L.

RADON TRANSFER FROM WATER TO AIR

When water i s exposed t o t h e atmosphere, some of t h e d isso lved radon i n water w i l l d i f f u s e i n t o t h e a i r . I n genera l , t h e q u a n t i t y o f radon and the r a t e a t which it i s r e l e a s e d from water depend on t h e waterborne radon concen t ra t ion , water temperature, and water usage ( i .e. , t h e degree of a g i t a t i o n t o which water i s s u b j e c t e d ) . Thus, t h e l a r g e s t r e l e a s e s of waterborne radon i n t h e home are due t o t h o s e a c t i v i t i e s and appl iances t h a t spray o r a g i t a t e hea ted water , such a s t a k i n g showers and washing d i s h e s o r c l o t h e s .

Gesell and Pr icha rd (1978) conducted a f i e l d test on t h e number of dwel l ings served by water con ta in ing 1,500 t o 2 , 0 0 0 pCi/L of radon. They found t h a t t h e r a t i o o f radon concen t ra t ion i n a i r t o t h e water concen t ra t ion ranged from 5 x 10" t o 2 x and averaged 1 x 10"'. Hess, Weiffenbach, and Norton ( H e s s e t a l . 1982) made more e x t e n s i v e measurements of t h e radon water-to- a i r exchange i n 85 houses. The r a t i o o f t h e concen t ra t ion of radon i n a i r t o t h a t i n water was found t o be 1.07 x l O " , which is i n good agreement wi th Gese l l and P r i c h a r d (1978).

RADON-IN-WATER HEALTH RISK

Radon i t s e l f , be ing chemical ly i n e r t , is no t hazardous a t environmental concen t ra t ions . The major h e a l t h e f f e c t a s s o c i a t e d with radon arises from t h e i n h a l a t i o n of i t s s h o r t - l i v e d decay products, which a r e chemically r e a c t i v e and may lodge on t h e l i n i n g of t h e lungs (Nero 1990). Alpha p a r t i c l e emissions from polonium-218 and polonium-214 damage t i s s u e nea r t h e depos i t ion s i t e . This i s t h e main mechanism t h a t i n c r e a s e s t h e r i s k o f lung cancer a s s o c i a t e d with exposure t o radon and i t s decay products . T rad i t iona l ly , a i rborne radon is considered t o be a much g r e a t e r r i s k than inges ted radon i n d a i l y l i f e (Crawford-Brown 1991) . A s a r e s u l t , t h e h e a l t h risk of waterborne radon c u r r e n t l y i s based on t h e d i f f u s i o n of radon from water t o indoor a i r .

The USEPA proposed a r e g u l a t o r y s tandard l i m i t i n g t h e concent ra t ion of radon i n d r ink ing water s u p p l i e s . The proposed maximum contaminant l e v e l (MCL) of radon i s 300 pCi/L i n p u b l i c dr inking water s u p p l i e s s e r v i n g more than 25 res idences . Considering t h e normal water use and v e n t i l a t i o n cond i t ions i n an average home, and cons ide r ing t h a t t h e r a t i o of radon i n a i r t o radon i n water i s 1 x t h e proposed MCL of 300 pCi/L i n water i s expected t o c o n t r i b u t e 0.03 pCi/L t o t h e average indoor radon concent ra t ion (Skrable 1991) . Skrable (1991) a l s o mentioned t h a t t h e proposed l i m i t of 300 pCi/L o f radon i n water may cause a f a l s e sense of s a f e t y t o occupants o f homes i f t h e radon concent ra t ion i n water is reduced when i n fact t h e major source of a i rborne radon i s i n f i l t r a t i o n from t h e s o i l . Water supp l i e s wi th high radon concen t ra t ions t end t o occur i n areas

where significant radon entry occurs via soil gas (Tanner 1988).

The USEPA (1986) risk assessment of radon in drinking water is based on inhalation from radon released during water-related activities as the major exposure pathway. This assessment of risk estimated that a water radon concentration of 10 pCi/L would produce a lifetime risk of 1 x lo'* (i.e., there is a chance of 1 death in 1 million population during a life span of 70 years due to lung cancer) .

There can be two significant sources of radon that contribute to the indoor home radon concentration. These sources are soil gas and drinking water. The pathway for health effects from soil gas radon is inhalation, resulting in lung cancer. The pathways for health effects due to radon in drinking water may be inhalation and ingestion, resulting in lung and stomach cancers. For lung cancer from radon in drinking water, the critical pathway is inhalation, whereas for stomach cancer the critical pathway is ingestion. Extensive studies have been conducted to determine the health risk of indoor air radon. Studies have shown that the effect of 300 pCi/L of radon in water on indoor air radon will be negligible, compared with the 4 pCi/L indoor air concentration as an action level. There will be little reduction in the health risk of lung cancer by reducing the waterborne radon concentration from 1,000 pCi/L to 300 pCi/L, when the indoor air radon contribution from soil gas is 3 pCi/L in the air.

RESEARCH STUDY OUTLINE

The American Water Works Association Research Foundation (AWWARF) initiated a project to study the contribution of waterborne radon to radon levels in indoor household air. The project entailed the concurrent measurements of airborne and waterborne radon in selected homes in three small communities before and after the installation of waterborne radon removal systems on community water supply systems.

The selection of these three communities for this study was based on their documented waterborne radon levels in the ranges of 500 to 2,000 pCi/L, 2,000 to 10,000 pCi/L, and greater than 10,0*00 pCi/L.

The objectives of this study are to perform a controlled experiment aimed at exploring the effect of a centralized water treatment system on indoor radon exposures in three communities with widely variant waterborne radon contamination levels, and to produce empirical data regarding radon wacer-to-air transfer coefficients in the home environment.

COMMUNITY SELECTION

In order to develop statistically significant measurements based on different waterborne radon concentrations, it was necessary to carefully identify and select the communities. Three communities were selected that have groundwater with documented radon concentrations in the following ranges: one with 500 to 2,000 pCi/L; one with 2,000 to 10,000 pCi/L; and one with greater than 10,000 pCi/L. Each of the communities are served by a centralized public groundwater supply system. This would allow installation of centralized radon removal equipment. All three communities are located in southern New Hampshire, within a 15- mile radius of each other, and served by small groundwater systems owned and operated by the SNHW Company. These communities have been designated as Community A, B, and C to comply with the confidentiality agreement made with the homeowners.

RADON MEASUREMENTS

This study had not only to generate valid water and air radon measurements, but also to successfully establish a waterborne radon removal system and data base, where differences in pre- and posttreatment indoor air radon concentrations could be attributed to the pre- and posttreatment waterborne radon contribution.

Airborne Radon Measurements

Airborne radon measurements were made using electret-passive environmental radon monitors, (E-PERM). The E-PERM is a device that uses an electrostatically charged Teflon disc, called an electret, to measure the radon concentration in air. Once activated, the electret surface, which has a positive charge, attracts negative ions produced by the alpha particles generated from decaying radon. The radon enters a filtered ionization chamber housing the electret, and negatively charged ions are drawn to the surface of the electret, thereby reducing its surface voltage. The resulting electret surface voltage is read using a portable digital meter (surface potential electret reader, or SPER) before and after exposure to radon. The resulting differential voltage is then used to calculate the average radon concentration present during the exposure period. For a 7-day exposure period, the lower level of detection (LLD) of airborne radon measurements using E-PERM is about 0.3 pCi/L (USEPA 1989). Airborne radon tests were performed in accordance with the USEPA radon measurement protocols (USEPA 1989).

One of the major benefits of using the E-PERM is that it car. be used in areas of high humidity and temperature ( e . g . , laundry

rooms, bathrooms, and k i t c h e n s ) , which a r e not normally recommended f o r radon t e s t i n g . This c h a r a c t e r i s t i c made t h e E- PERM wel l s u i t e d f o r use i n t h i s s tudy. These rooms were important f o r t h i s s tudy because they a r e most l i k e l y t o have radon i n a i r con t r ibu ted from waterborne radon.

The a i rborne t e s t i n g program was based on t h e premise t h a t i f f a c t o r s with t h e g r e a t e s t p o t e n t i a l t o a f f e c t radon measurements can be kept i d e n t i c a l i n t h e pre- and pos t t rea tment t e s t i n g phases, then any s t a t i s t i c a l l y v a l i d d i f f e r e n c e s between pre- and pos t t rea tment r e s u l t s can be a t t r i b u t e d t o d i f f e r e n c e s i n t h e waterborne radon concent ra t ion .

The measurements were conducted between February and Apr i l , 1990. Except t o r a few unusual ly m i l d days, dur ing which no t e s t i n g was done, t h e temperatures were t y p i c a l f o r southern N e w Hampshire f o r t h a t t ime of year . These cond i t ions f o r indoor radon can be considered a worst case scenar io .

Airborne radon monitoring w a s conducted over a 7-day p e r i o d ( t h e t i m e pe r iod between readings) t o measure t h e average home a i r q u a l i t y condi t ions and t o cover a t l e a s t one weekly c y c l e of household a c t i v i t i e s c o n t r i b u t i n g t o waterborne radon r e l e a s e s . Every house tested had a c l o t h e s and a d i s h washer. Water usage w a s monitored by t a k i n g water meter readings before and af ter t h e test.

The concent ra t ion of radon i n indoor a i r i s genera l ly less than i ts equi l ibr ium value. A s a r e s u l t , radon w i l l move from water i n t o t h e a i r according t o Henry's law. Radon has a h igh Henry's c o e f f i c i e n t , which i n d i c a t e s t h a t radon w i l l e a s i l y d i f f u s e from water t o a i r . Release of waterborne radon t o indoor a i r depends on waterborne radon concen t ra t ions , water temperature, and t h e degree of a g i t a t i o n of water. Thus, t h e l a r g e s t r e l e a s e s of waterborne radon i n t h e home a r e due t o a c t i v i t i e s such as t a k i n g showers and washing d i shes o r c l o t h e s .

Radon monitor l o c a t i o n s were s e l e c t e d t o b e s t d i f f e r e n t i a t e between a i rborne radon c o n t r i b u t i o n s from t h e s o i l and from t h e household water. The a i r radon c o n t r i b u t i o n from domestic water should be t h e h ighes t i n a r e a s o r rooms where household a c t i v i t i e s would cause radon/water sepa ra t ion . Radon monitors were placed within each house i n a r e a s with vary ing p o t e n t i a l s f o r radon/water sepa ra t ion . These a r e a s inc luded t h e fol lowing:

Area 1: Areas of high p o t e n t i a l f o r r e l e a s e of radon from water and high p o t e n t i a l f o r a i rborne l e v e l s from s o i l gas (e. g., basement laundry rooms)

Area 2 : Areas of low p o t e n t i a l f o r r e l e a s e o f radon from wafer but with high p o t e n t i a l f o r a i rborne l e v e l s from s o i l gas (e .g . , basement f a m i l y rooms)

Area 3: Areas of high potential for release of radon from water and low potential for airborne levels from soil gas (e.g., first floor kitchens or bathrooms and second floor laundries)

Area 1 (high water and high soil) was chosen to be the laundry rooms located in the basements in Communities B and C. The habitable portions of the typical basement were divided into a family room, a work or storage room, and an enclosed laundry room. The enclosure of laundry rooms helped to isolate them from the rest of the basement.

Basement family rooms were selected as Area 2 (low water, high soil). These areas are typical locations recommended in the USEPA radon measurement protocols for screening tests (USEPA 1990). They have the same potential for soil gas as the enclosed laundry rooms. However, the effect of waterborne radon would likely not be as significant as in the enclosed laundry rooms.

Rooms on an upper floor have a lower potential for elevated radon concentrations due to soil gas because of remoteness from soil gas sources. However, kitchens or bathrooms on the first floor and laundries on the second floor were chosen as Area 3 (high water, low soil), based on the premise that they would be affected mostly by waterborne radon resulting from either dish washing or showering.

For each selected house, E-PERMS were placed in each of the three areas discussed above for a continuous 7-day period before and after the installation and operation of the community-wide radon removal water treatment systems. A 7-day period for indoor air radon measurements was selected to cover the weekly cycle of household water-related activities in a house. In accordance with the USEPA radon measurement protocols, monitors were placed: at breathing height, between 4 and 6 feet above the floor; away from walls, air-moving equipment, registers, and furnaces; and in unobstructed areas.

In keeping with the intent to maintain test conditions consistent in both pre- and posttreatment phases of the testing program, a sketch of each house floor plan was prepared showing the exact locations of the radon monitors as they were placed in the pre-treatment testing phase. The plans were then used to ~ - -

replace the monitors in the same locations for posttreatment testing.

Water Sample Collection and Analysis

Samples of household water were collected for radon analysis concurrently with the placement of the airborne radon monitors for both the pretreatment and oosttreatment testing phzses. Water samples were collected only at the time monitors were

placed. A t o t a l of 242 r e g u l a r water samples and 51 d u p l i c a t e water samples, f o r QA/QC purposes, were c o l l e c t e d . Water samples were taken from t h e cold-water system, us ing t h e submerged v i a l method. Except f o r a few houses t h a t had i r o n removal systems i n opera t ion , none of t h e houses had point-of-entry o r point-of-use water t rea tment systems i n opera t ion . Samples were c o l l e c t e d fol lowing t h e USEPA (1983) p ro toco l s .

WATERBORNE RADON REMOVAL SYSTEMS

I n a s tudy f o r t h e USEPA, Kinner e t a l . (1990) eva lua ted radon removal systems f o r small community' water systems, u s i n g g ranu la r a c t i v a t e d carbon (GAC) and adsorpt ion , d i f f u s e d bubble a e r a t i o n , and packed tower a e r a t i o n (PTA). The performance o f GAC u n i t s may be impaired by accumulation o f i r o n , manganese, and p a r t i c u l a t e s . Furthermore, a GAC system may r e q u i r e p e r i o d i c backwashing. Kinner e t a l . (1990) a l s o mentioned t h a t r e t e n t i o n of r a d i o a c t i v e m a t e r i a l s i n t h e GAC bed may cause t h e GAC t o be c l a s s i f i e d a s a low-level r a d i o a c t i v e waste. Lowry e t a l . (1987) ind ica ted t h a t GAC is a b l e t o absorb a new radon atom on i t s su r face once t h e radon atom previous ly absorbed decays t o i t s progeny. Kinner e t a l . (1990) d i d no t observe any breakthrough, and regenera t ion was n o t requi red . Lowry e t a l . (1991) analyzed d a t a from 121 point-of-entry GAC u n i t s from 1981 t o 1989 and i n d i c a t e d no l o s s of e f f i c i e n c y of u n i t s over 2 t o 6 yea r s of monitoring. It is, bel ieved, t h e r e f o r e , t h a t a GAC bed should t h e o r e t i c a l l y remove radon from dr ink ing water f o r extended per iods . Kinner e t a l . (1990) concluded t h a t t h e i s s u e s of foul ing , gamma exposure, d i sposa l of used GAC, and p o t e n t i a l desorpt ion of radon progeny should be considered be fo re GAC is used f o r radon removal. The l e v e l s of Pb-210 and i t s progeny i n t h e t r e a t e d water should a l s o be a concern when us ing GAC u n i t s (Lowry et a l . 1991) .

Kinner e t a l . (1990) a l s o t e s t e d a d i f f u s e d bubble a e r a t i o n system f o r radon removal. The d i f f u s e d bubble a e r a t i o n system cons i s t ed of polyethylene tanks wi th p l a s t i c d i f f u s e r s l o c a t e d a t t h e bottom of t h e tanks . Aeration w a s provided by a blower. Water was pumped d i r e c t l y from t h e we l l s t o t h e d i f f u s e d bubble system and then pumped t o pressure t anks . A i r t o water (A:W) r a t i o s of more than 5:1 yie lded radon removal e f f i c i e n c i e s of 90 percent t o 99.6 percent . Diffused bubble a e r a t i o n systems, however, w i l l have p o t e n t i a l a i r p o l l u t i o n problems i n a d d i t i o n t o i r o n and manganese p r e c i p i t a t i o n .

Kinner e t a l . (1990) found t h a t t h e packed tower a e r a t i o n (PTA) system was very e f f i c i e n t i n removing radon from water (90 t o 99 percent removal) . Curnrnins (1988) a l s o found t h a t PTA w a s highly e f f i c i e n t . Lenzo (1990) conducted some f u l l - s c a l e p i l o t s t u d i e s and found 96.5 percent removal a t 10 feet packed depth. Untreated water is pumped t o t h e t o p of t h e tower and evenly d i s t r i b u t e d ovez t h e packing of p l a s t i c macer ia ls , while a i r i s

blown irom the bottom upward through the packing. The greater the contact time between the air and water, the greater the opportunity for transferring the volatile contaminant from the water into the upward-flowing air (Lenzo 1990). In the present study, the PTA system was used to remove radon from water in the three communities.

DATA MEASUREMENT

A total of 119 homeowners in the three communities participated in the pre- and posttreatment radon measurements. Community A participated with 19 homes, Community B participated with 85 homes, and Community C participated with 15 homes.

Airborne Radon Data

Airborne radon concentrations in both pre- and posttreatment periods primarily were measured in three locations in each house: the basement family room, the basement or second floor laundry, and the first floor kitchen. In addition, airborne radon was measured in the first floor bathrooms in two homes. A total of 60 pairs of airborne radon data (pre- and posttreatment measurements) were obtained in Community A, 256 pairs in Community B, and 45 pairs in Community C. All of these data were entered into the data base.

A summary of the airborne radon concentrations is shown in Table 1. This table shows high, average. and low airborne radon concentrations broken down by community and by the location in the house. The average radon concentrations in each community was reduced after treatment. These reductions for Communities A, B, and C were 0.1. 0.2, and 2.9 pCi/L, respectively. Low-level detection (LLD) of the E-PERM method of indoor radon measurement is about 0.3 pCi/L.

Because previous measurements of indoor airborne radon have been log normally distributed (c.f., Longtin 1988). the airborne data collected in this study also were assumed to be log normally distributed. A statistical analysis of airborne radon data by community and by each location was conducted.

Waterborne Radon Data

Waterborne radon for each house during ore- and posttreatmenc oeriods were collected. The household waterborne radon concentrations were

The reduction of

entered into the waterborne radon data base.

average household water radon concanizations

TABLE 1

Household Airborne Radon Concentration*

Note:

Pretreatment Posttreatment Location Maximum Average Minimum Maximum Average Minimum SL 1.6 0.6 0.0 1.5 0.5 0.0 BF 9.2 4.1 0.5 7.2 3.7 0.6 FK 1.3 0.5 0.0 1.4 0.5 0.0

Overall 1.8 1.7

BL 3.0 1.1 0.1 BF 7.1 1.3 0.0 FK 2.1 0.8 0.0

FB 0.7 0.7 0.7 Overall 1.1

BL 8.8 4.9 1.1 BF 7.5 4.1 0.9

FK 7.8 3.6 1.8 FB 7.8 6.8 5.7

Overall 4.3

BL = Basement Laundry BF = Basement Family FK = First Floor Kitchen SL = Second Floor Laundry FB = First Floor Bath * = All values given in pCi/L

due to the treatment system for Communities A, B, and C were 1, 166, 2,170, and 20,775 pCi/L, respectively. Waterborne radon removal efficiencies of radon treatment systems installed at the well locations of all communities were measured by analyzing samples for waterborne radon concentration collected from the influent and effluent of the treatment systems. Treatment system efficiency ranges from 95 percent to 96 percent.

ANALYSIS OF DATA

The objective of this analysis was to determine the effect of household waterborne radon on household airborne radon levels under various waterborne radon concentrations. The average household waterborne radon concentrations measured during this study were 1,292 pCi/L for Community A, 2,411 pCi/L for Community B, and 21,295 pCi/L for Community C. If the reduction in airborne radon, due to the reduction in waterborne radon, is low and within the diurnal and other fluctuations of indoor radon concentration, it will be difficult to accurately identify the contribution of the reduction in airborne radon due to the reduction in waterborne radon. This is particularly true when the background indoor radon concentration, due to the soil gas and other sources, is high in comparison with the contribution of waterborne radon to indoor radon.

STATISTICAL ANALYSIS

The data entered into the data base have been analyzed using the following methods:

Matched pair statistical analysis.

Statistical analysis of the reduction in airborne radon concentrations with respect to the reduction in waterborne radon concentrations.

Comparison of the cumulative distribution of pre- and posttreatment airborne radon concentrations.

Matched Pair Analysis

In studies involving data consisting of t w o samples where one cannot assume that the two samples are independent of each other, the data can be analyzed as an ordered pair. Samples of pretreatment household airborne radon measurements and posttreatnient airborne radon measurements taken in the same house at the same locations can be paired together. The paired data are not: independent of each other. Each observation (data point), consisting of pre- and posttreatment airborne radon

concentrations at the same location, will be treated as a matched pair. These matched pairs can be plotted, and the difference in the slope of a linear regression line, passing through the origin, from a slope of 1.0 will indicate the degree to which the pre- and posttreatment data differ. A regression line with a slope not significantly different from 1.0 indicates that the pretreatment and posttreatment data are not significantly different. The statistical hypothesis for this regression model is that the slope of the regression line is not significantly different from 1.0. If this is not the case, then a conclusion can be reached that the pretreatment data are significantly different from the posttreatment data.

Figures 1, 2 and 3 show that the slopes of these lines for Communities A, B, and C are 1.11, 1.03, and 1.87, respectively. Slopes significantly greater than 1.0 indicate a reduction of the airborne radon concentration due to the reduction of waterborne radon concentration, whereas slopes less than 1.0 indicate an increase in the airborne radon concentration. The slopes of the regression lines for all communities are greater than 1.0 indicating a reduction between pre- and posttreatment average airborne radon concentration. The slopes of the regression lines for Communities A and B are 1.11 and 1.03, respectively. The slope of the regression line for Community C is 1.87.

The average household waterborne radon reductions were: Community A, 1,166 pCi/L (from 1,292 pCi/L o 126 pCi/L) ; Community B, 2,170 pCi/L (from 2,411 pCi/L to 241 pCi/L) ; and Community C, 20,775 pCi/L (from 21,295 .pCi/L to 520 pCi/L) .

Data Analysis by Location

The relative effect of the location within the household on the airborne radon concentration was evaluated by matched pair data of airborne radon concentrations segregated for each community by the three household locations. These locations are the basement family room (BF) , the basement laundry (BL), and the first floor kitchen (EK) for Communities B and C, and the basement family room ( B E ) , second floor laundry (SL), and the first floor kitchen (FK), for Community A. In addition, the first floor bathroom (FB) was used for locations in two houses each in Communities B and C.

The overall results of this analysis showed that there is little reduction (less than 10 percent) of posttreatment airborne radon at all locations in Community A and at locations BF and BL in Community B. In Community C, indoor mean air radon concentrations under pretreatment condition were high at all locations ranging from 3.6 to 5.0 pCi/L. The slopes of she regression lines from the matched pair analysis vary from 1.74 to 2.41 indicating reductions of indoor air radon concentrations ac

a l l l o c a t i o n s . A range o f r e d u c t i o n o f 42.5 t o 58.5 p e r c e n t of a i r b o r n e radon was ach ieved a t l o c a t i o n s i n Community C .

I n o r d e r t o assess t h e effects of waterborne radon on i n d o o r a i r radon, it w a s neces sa ry t o estimate t h e c o n c e n t r a t i o n o f t h e average background indoor a i r radon c o n c e n t r a t i o n o f each community. Estimated background a i r b o r n e radon c o n c e n t r a t i o n s i t h e t h r e e communities shows t h a t Community A had a r e l a t i v e l y h igh background radon concen t r a t i on , whereas Community B and C each had indoor background radon c o n c e n t r a t i o n s o f 1 . 0 and 1 . 6 pCi/L, r e s p e c t i v e l y , which a r e lower t h a n t h e n a t i o n a l ave rage l i v i n g area indoor radon c o n c e n t r a t i o n o f 1 .7 pCi/L (Cohen 1989)

Ana lys i s o f Radon Reduction Data

~ l l pos t t r ea tmen t household a i r b o r n e radon d a t a were s u b t r a c t e d f r o m t h e cor responding p r e t r e a t m e n t radon data t o determine t h e r e d u c t i o n i n a i r b o r n e radon a t each l o c a t i o n due t o r educ t ion i n waterborne radon. An a n a l y s i s o f radon r e d u c t i o n d a t a by community and by l o c a t i o n was conducted. These r e s u l t s show t h a t , for communities A, B, and C, average a i r b o r n e radon r educ t ions o f 0.09 pCi/L, 0.19 pCi/L, and 2.92 p C i / ~ were achieved due t o average waterborne radon r e d u c t i o n s o f 1 ,166 pCi/L, 2,170 pCi/Lf and 20,775 pCi/Lf r e s p e c t i v e l y . Indoor radon r educ t ion v a l u e s can no t be f u l l y a t t r i b u t e d t o t h e r e d u c t i o n of waterborne radon c o n c e n t r a t i o n . Other v a r i a b l e s t h a t w i l l c o n t r i b u t e t o t h e s e d i f f e r e n c e s are d i u r n a l radon v a r i a t i o n s , t i m e l a g o f measurements, and accuracy o f measurements.

Analys i s o f D i s t r i b u t i o n o f Data

I n o r d e r t o o b t a i n an o v e r a l l , community-wide d i s t r i b u t i o n o f a i r b o r n e radon c o n c e n t r a t i o n r e d u c t i o n due t o r e d u c t i o n o f waterborne radon f o r each community, a cumula t ive d i s t r i b u t i o n a n a l y s i s o f p re - and p o s t t r e a t m e n t a i r b o r n e radon c o n c e n t r a t i o n s was conducted. Cumulative d i s t r i b u t i o n s o f measured a i r b o r n e radon concen t r a t i on v a l u e s (bo th b e f o r e and a f te r t r e a t m e n t ) f o r communities A, B and C are shown i n F i g u r e s 4, 5 and 6 r e s p e c t i v e l y .

T h i s a n a l y s i s shows t h a t t h e r e was e s s e n t i a l l y no d i f f e r e n c e i n a i r b o r n e radon c o n c e n t r a t i o n due t o wa te r t r e a t m e n t i n Community A, t h e r e w a s a sma l l r e d u c t i o n of radon i n Community B, and i n Community C a l a r g e e r e d u c t i o n o f a i r b o r n e radon was achieved. The cumulat ive d i s t r i b u t i o n a n a l y s i s does no t c o n s i d e r matched p a i r data and does no t r e p r e s e n t t h e e f f e c t o f t h e reduc t ion of waterborne radon on a i r b o r n e radon a t a p a r t i c u l a r l o c a t i o n wi th in a house.

Pretreatment Posttreatment

FIGURE 4 Alrborir Radon Cumulathm Distribution, Community A, Summary

FIGURE 5 Airbonr Radon Cumulative Dlstribution, Community 8, Summary

. . . A A .

A

6

6 A .*

- 6 A . .

b A

. .= A . A

A

. b

. 0-

A .

A

. Â . . . . . . . . Pretreatment

- Posttrcatment A . - .

0 1 2 3 4 5 6 7 1 9 10 11 12 13 14 15 16 17 10 19

FIGURE 5 Airborne Radon Cumulaiiva Oistribution. Community C. Surnrnarv

CONCLUSIONS

The f ind ings i d e n t i f i e d i n t h i s s e c t i o n l e a d t o t h e fo l lowing conclusions:

1. I n Community A, c o n t r i b u t i o n of waterborne radon t o indoor a i r radon is small r e l a t i v e t o t h e c o n t r i b u t i o n from s o i l gas and o t h e r sources . , Thus, water t r ea tmen t system f o r radon removal has l i t t l e effect on indoor a i r radon i n Community A.

2 . I n Community B, average pre t rea tment indoor a i r radon concent ra t ions i n a l l l o c a t i o n s a r e low and a l s o the small d i f f e r e n c e i n pre- and pos t t rea tment indoor a i r radon concentrat ion i n d i c a t e d a small c o n t r i b u t i o n of waterborne radon t o indoor a i r radon.

3 . I n Community C, a r e l a t i v e l y l a r g e reduc t ion of indoor a i r radon between pre- and pos t t rea tment measurements a t a l l l o c a t i o n s ind ica ted a l a r g e c o n t r i b u t i o n of waterborne radon t o indoor a i r radon and t h e e f f e c t i v e n e s s of water t rea tment system i n indoor a i r radon reduct ion .

4 . The e f f e c t of reducing waterborne radon on reducing indoor a i r radon has been found t o be a r educ t ion o f 1 pCi/L of waterborne radon w i l l reduce 1 . 3 x lo-' p C i / L of indoor a i r radon.

5. I n s t a l l a t i o n of water t rea tment systems f o r radon removal i n water f o r Communities A and B con ta in ing radon concen t ra t ion up t o 2 , 4 0 0 pCi/L did not produce any s i g n i f i c a n t improvement i n indoor a i r q u a l i t y .

. Before conducting any s t u d i e s of waterborne radon reduct ion and i n s t a l l a t i o n of waterborne radon removal system, it i s advisable t o conduct indoor a i r radon measurements t o e s t ima te t h e r e l a t i v e con t r ibu t ions o f s o i l gas and waterborne radon t o indoor a i r radon.

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