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Summary of Radon Surveys in North Dakota 1988-1993
SUMMARY AND CONCLUSIONS During 1988-1993, the North Dakota State Department of Health and Consolidated Laboratories, in partnership with the Environmental Protection Agency, Region VIII, conducted five surveys of radon in North Dakota. The five surveys, homes, clusters of homes, day cares, schools, and homes of WIC recipients, are represented in various tables and graphs which will aid in a better understanding of radon in North Dakota. The cluster survey is not included in certain tables and graphs as less than half of the counties in the home survey exhibited radon concentrations greater than 20 pCi/l. The fact that a neighbor of the "cluster home" had a radon concentration greater than 20 pCi/l a year earlier does not allow all homes in North Dakota an equal chance to be selected. The home survey of 1988 gave a glimpse of the concentrations to come. With 63% of the samples greater than 4 pCi/l, the EPA "action level," North Dakota has a radon problem. Iowa is the leader in the Nation at 71% of samples greater than 4 pCi/l. The day care survey found many of day cares with concentrations greater than 4 pCi/l. Since 85% of the day cares tested were in homes, the 15% of day cares located in large buildings did not lower the overall average and, therefore, the day care results are almost a copy of homes results. The schools survey was a very nice surprise. The comparatively low arithmetic mean radon concentration combined with the less than 8% of the classrooms greater than 4 pCi/l was certainly good news to already financially strapped school districts. The results of the WIC home survey closely resembles the results from the home survey and the day care survey. The statistics for all surveys is found in Table 16. TABLE 16 STATISTICS FOR ALL SURVEYS 1988-1993 ARITHMETIC
NUMBER ARITHMETIC STANDARD PERCENTAGE OF SAMPLES
OF MEAN IN DEVIATION GREATER THAN
SURVEY SAMPLES pCi/l IN pCi/l 4 pCi/l 20 pCi/l
Home 1596 7.4 9.4 62.5 5.0
Cluster Home 402 18.8 27.2 87.6 29.9
Day Care 1686 5.3 6.9 41.4 3.0
School 8430 1.8 2.5 7.7 0.3
WIC Home 1061 6.1 9.1 48.7 4.0
The arithmetic means of the counties for four of the surveys and how they rank with the other counties in the State are found in Table 17. The lowest ranking number represents the highest concentration. The counties of the Red River Valley and the southwestern part of the State rank higher in radon concentration than do the rest of the counties in the State. TABLE 17 RANKINGS AND ARITHMETIC MEANS FOR COUNTIES HOME DAY CARE SCHOOL WIC HOME ALL
COUNTY SURVEY SURVEY SURVEY SURVEY SURVEYS
-------------- -------------- -------------- ----------- -------
ARITH ARITH ARITH ARITH
MEAN RANK MEAN RANK MEAN RANK MEAN RANK RANK
Bowman 10.7 2 22.7 1 2.5 7 9.0 6 1
Walsh 10.5 3 14.7 2 3.0 4 8.4 7 2
Ransom 8.4 9 11.0 5 5.0 1 13.0 3 3
Billings 8.7 8 - - 2.7 6 4
Adams 9.3 5 13.3 3 2.1 14 6.0 14 5
Grand Forks 11.7 1 11.4 4 1.3 34 9.3 5 6
Stark 8.0 14 3.4 27 4.5 2 6.3 12 7
Hettinger 7.2 17 2.5 38 4.4 3 33.0 1 8
Barnes 8.0 13 8.8 7 2.2 12 4.3 32 9
Sargent 5.5 31 7.5 9 2.9 5 5.6 20 10
Traill 6.8 23 6.5 11 2.0 15 5.8 17 11
Stutsman 7.8 15 4.2 17 1.9 17 6.0 15 12
Pembina 9.4 4 4.2 17 2.2 13 3.8 36 13
McIntosh 7.1 19 6.2 12 2.5 8 4.4 30 14
Cass 7.9 14 7.6 8 1.6 27 5.0 24 15
Emmons 6.6 25 3.6 25 2.3 11 5.7 18 16
Oliver 6.4 26 1.7 24 6.8 10 17
Dickey 5.5 32 4.3 16 1.7 23 6.4 11 18
Mercer 8.1 12 3.5 26 1.7 26 19
Grant 8.1 10 9.1 6 0.1 49 20
Slope 7.0 21 21
Dunn 8.7 7 2.1 43 1.2 36 18.6 2 22
Kidder 4.0 45 3.0 33 2.4 9 6.8 9 23
Divide 8.8 6 3.8 19 0.5 48 4.8 25 24
Ramsey 6.6 24 3.8 20 1.8 20 3.7 37 25
Sheridan 5.0 39 6.2 13 26
Morton 5.6 29 3.7 22 1.6 28 4.7 26 27
Logan 5.7 28 2.6 37 1.2 37 12.0 4 28
Mountrail 7.5 16 4.9 15 1.2 35 3.3 40 29
McLean 5.0 38 3.6 24 1.7 25 5.6 19 30
Nelson 5.3 34 3.2 30 1.8 21 5.4 21 31
Benson 7.2 18 1.9 18 2.6 44 32
Lamoure 5.2 36 4.1 18 2.3 10 2.4 45 33
Towner 8.1 11 6.1 13 1.0 45 2.7 43 34
Sioux 4.9 40 1.8 19 0.0 35
Rolette 5.5 33 2.4 40 1.1 40 7.0 8 36
Cavalier 3.7 49 3.8 21 1.2 38 5.8 16 37
Richland 7.0 20 1.8 45 1.4 31 4.5 29 38
Bottineau 6.0 27 3.4 28 0.7 47 4.6 27 39
Steele 5.2 35 6.9 10 0.9 46 2.9 42 40
Ward 4.2 44 3.2 31 1.3 32 4.6 28 41
McKenzie 3.5 51 2.8 36 2.0 16 42
Griggs 3.3 52 3.3 29 5.2 23 43
Burleigh 4.9 41 3.7 23 1.1 41 4.0 35 44
Eddy 4.6 43 3.0 34 1.6 29 0.0 45
Renville 5.1 37 3.1 32 1.1 42 4.4 31 46
Wells 5.6 30 2.8 35 1.0 44 4.1 34 47
Williams 4.6 42 2.4 41 1.8 22 3.5 38 48
Burke 2.6 53 2.3 42 1.2 39 5.3 22 49
Pierce 3.8 47 2.5 39 1.4 30 3.3 41 50
McHenry 3.6 50 1.9 44 1.3 33 4.2 33 51
Foster 3.7 48 3.5 39 52
Golden Valley 4.0 46 1.8 46 1.0 43 0.0 53
FIGURE 6 - ARITHMETIC MEANS OF COUNTIES IN RADON SURVEYS
FOR NORTH DAKOTA 1988-1993 Another way to visualize the home survey data can be found in Figure 7. Figure 7 shows isoconcentration lines on a map. The isolines were calculated using the data from the home survey. FIGURE7 - NORTH DAKOTA RADON CONCENTRATIONS (pCi/L) STATE
RADON SURVEY 1988 - ALL FLOORS The logarithim of the radon concentrations for each of the five surveys are plotted in Figure 8. FIGURE 8 - LOG NORMAL RADON CONCENTRATIONS FOR ALL RADON SURVEYS IN NORTH DAKOTA 1988-1993
1. On a lognormal plot, all of the surveys form a straight line if the lower radon concentrations are ignored. 2. The school survey radon concentrations are considerably less than the other surveys. 3. The cluster radon concentrations are considerably higher than the rest of the surveys. 4. The radon concentrations for the WIC homes, day cares, and home are very close in value. The precision of radon testing is considered by the EPA to be +25%. The fact that many different contractors and laboratories were involved in doing work for the Department in different years may have added to some of the separations in the lines. The North Dakota State Department of Health and Consolidated Laboratories intends to do one more survey for radon in wells during the 1993-1994 radon testing season. During the period, 1993-2000, the Department and EPA, Region VIII, will concentrate on the targeting of the 15 counties of highest risk by advertising, publicizing, and speaking about radon in those counties, testing school districts that failed to take advantage of the school survey, by increasing the public's awareness and stressing mitigation. TABLE 18 POPULATIONS OF NORTH DAKOTA COUNTIES 1980 1990 POPULATION CHANGE PERCENTAGE OF
CENSUS CENSUS IN PERCENT DURING 1990 POPULATION
COUNTY POP. POP. DECADE IN PERCENT
Adams 3584 3174 - 11.4 0.50
Barnes 13960 12545 - 10.1 1.96
Benson 7944 7198 - 9.4 1.13
Billings 1138 1108 - 2.6 0.17
Bottineau 9239 8011 - 13.3 1.25
Bowman 4229 3596 - 15.0 0.56
Burke 3822 3002 - 21.5 0.47
Burleigh 54811 60031 9.5 9.40
Cass 88247 102874 16.6 16.10
Cavalier 7636 6064 - 20.6 0.95
Dickey 7207 6107 - 15.3 0.96
Divide 3494 2899 - 17.0 0.45
Dunn 4627 4005 - 13.4 0.63
Eddy 3554 2951 - 17.0 0.46
Emmons 5877 4830 - 17.8 0.76
Foster 4611 3983 - 13.6 0.62
Golden Valley 2391 2108 - 11.8 0.33
Grand Forks 66100 70683 6.9 11.06
Grant 4274 3549 - 17.0 0.56
Griggs 3714 3003 - 11.1 0.52
Hettinger 4275 3445 - 19.4 0.53
Kidder 3833 3332 - 13.1 0.52
Lamoure 6473 5383 - 16.8 0.84
Logan 3493 2847 - 18.5 0.45
McHenry 7858 6528 - 16.9 1.02
McIntosh 4800 4021 - 16.2 0.63
McKenzie 7132 6383 - 10.5 1.00
McLean 12383 10457 - 15.6 1.64
Mercer 9404 9808 4.3 1.54
Morton 25177 23700 - 5.9 3.71
Mountrail 7679 7021 - 8.6 1.10
Nelson 5233 4410 - 15.7 0.69
Oliver 2495 2381 - 4.6 0.37
Pembina 10399 9238 - 11.2 1.45
Pierce 6166 5052 - 18.1 0.79
Ramsey 13048 12681 - 2.8 1.99
Ransom 6698 5921 - 11.6 0.93
Renville 3608 3160 - 12.4 0.56
Richland 19207 18148 - 5.5 2.84
Rolette 12177 12772 4.9 2.00
Sargent 5512 4549 - 17.5 0.71
Sheridan 2819 2148 - 23.8 0.34
Sioux 3620 3761 3.9 0.59
Slope 1157 907 - 21.6 0.14
Stark 23697 22832 - 3.7 3.57
Steele 3106 2420 - 22.1 0.38
Stutsman 24154 22241 - 7.9 3.43
Towner 4052 3627 - 10.5 0.57
Traill 9624 8752 - 9.1 1.37
Walsh 15371 13840 - 10.0 2.17
Ward 58392 57921 - 0.8 9.07
Wells 6979 5864 - 16.0 0.93
Williams 22237 21129 - 5.0 3.31
TOTALS 653717 638800 - 2.3 100.07
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Copyright © 2012 North Dakota Department of Health |
The radon
concentration points were calculated by averaging all radon
concentrations in each zip code. The 1596 samples of the study
were averaged and represented by 280 zip code points. These
averaged concentrations for each zip code point were then
countoured to produce this map. 
