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Summary of Radon Surveys in North Dakota 1988-1993

  • HOME SURVEY - 1988
  • CLUSTER SURVEY - 1989
  • SCHOOL SURVEY - 1989-1992
  • DAY CARE SURVEY - 1991-1992
  • WIC HOME SURVEY - 1992-1993

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
Click here to see Figure 6 (57K)
This map is a summary of Table 17. The number in the northeast corner of each county is its county ranking as compared to other counties in North Dakota. The four other numbers in each county represent the arithmetic means (pCi/l) in descending order for the following surveys: home, day care, schools, and WIC. Thus, McKenzie County ranks 42nd with average radon concentrations in pCi/l of 3.5 for home, 2.8 for day cares, 2.0 for school, and no report for WIC.

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
Radon Map 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.

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

Radon Graph
Certain relationships are evident:

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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