Section 4.0 Continued
Table 4.6
Shelter 204 Launch Room Ceiling (LRC) Survey Units
Reference Figure 5C
|
Survey Unit |
Description |
|
204 LRC-1 |
Top Ledge East Wall |
|
204 LRC-2 |
South Half of Ceiling |
|
204 LRC-3 |
Top Ledge West Wall |
|
204 LRC-4 |
North Half of Ceiling |
The surveys shall acknowledge the fact that loose contamination was fixed in place by the Air Force. Areas that have been painted will be treated as if there were contamination under the paint and the paint removed prior to surveying for final release. If the paint is left in place over an area that is suspected to have been contaminated with plutonium the material will not be released and will be disposed as radioactive waste.
4.2 Class 2 Areas
Class 2 areas have a potential for radioactive contamination but are not expected to exceed the DCGL. Class 2 areas are beyond the scope of this investigation. The following are identified as Class 2 areas:
· The concrete culvert
· The area between Shelters 211 and 213
· Drain system and electrical bunkers in front of shelters 202, 206, 208, and 210
These areas will be investigated in subsequent studies by others.
4.3 Class 3 Areas
Class 3 areas are impacted areas that are not expected to contain any residual radioactivity greater than the DCGL. The remaining areas inside the BOMARC Missile site may be classified as a Class 3 area. Class 3 areas are beyond the scope of this investigation. These areas will be investigated in subsequent studies by others.
4.4 Reference Coordinate System
A reference coordinate system will be established on all Class 1 areas to facilitate selection of measurement and sampling locations. The grid will consist of intersecting lines, referenced to a fixed site location or benchmark. The coordinate system used in the Final Characterization Report, Reference 2.2, and will be used since it is already laid out.
4.5 Number of Data Points
The number, N, of data points for soil surveys to meet final status survey that are needed from each survey unit will be determined using:
Where Z1-" and Z1-$ are statistical constants from the normal distribution related to the chosen decision level for ", the probability of a Type I error and $, the probability of a Type II error. Sign p is the probability that a random measurement from the survey unit is less than a specified value related to ) and )/F. A maximum grid size of 5 meters will be used when sampling along the perimeter of contaminated areas.
For example, this formula was used to generate the table below of number of data points for the survey units from Section 4.1 where remediation may not be needed. The F value was calculated from the data shown in the reference drawing from the Characterization Report, (DWG-1) Reference 2.2, for the survey units defined in Section 4.1. The value for Z1-" and Z1-$ is 1.64 for the chosen decision error levels, " = 0.05 and $ = 0.05. The number of data points listed below includes the number calculated from the above formula plus 20%, rounded up, to account for missing or unusable data. No data was calculated for survey units that obviously require remediation.
Table 4.7
Survey Unit Number Of Data Points
|
Survey Unit |
F |
O/F |
Sign p |
Number of
Data Points
(N+0.2N) |
|
EZ-1 |
4.3 |
.093023 |
0.81594 |
34 |
|
EZ-2 |
4.46 |
0.89686 |
0.81594 |
34 |
|
EZ-3 |
1.98 |
2.02 |
0.977250 |
15 |
|
EZ-4 |
1.59 |
2.51572 |
0.993790 |
15 |
The number of data points for building or surface surveys, N, that are needed from each reference area or survey unit will be determined using:
N=(Z(1-a)+Z(1-b))2 divided by 3(P(r)-0.5)
where Pr is the probability that a random measurement from the survey unit exceeds a random measurement from background and is related to the relative shift through the tables in References 2.1 and 2.3.
A Stem and Leaf display of data for the survey unit and reference area should be performed to analyze for peculiarities. This data can be used to generate a Quantile Plot of the data for further analysis. A Posting plot should be constructed and reviewed for each survey unit.
5.0 DATA QUALITY OBJECTIVES
As stated above, the null hypothesis (Ho) tested for this plan is that residual contamination exceeds the release criterion. The alternative hypothesis (Ha) is that residual contamination meets the release criterion. The Derived Concentration Guideline Level (DCGL) is 8 picocuries per gram (pCi/g) for soil, debris, and volumetric considerations.
Building structure surfaces have a DCGL of 20 disintegrations per minute per 100 square centimeters (20 dpm/100 cm2), for removable alpha contamination. Building surfaces will also be measured for fixed contamination levels and have a DCGL of an average of 100 dpm/cm2 when averaged over a 1 m2 area. These areas may have a single spot of up to 300 dpm/100 cm2 in the 1 m2 area that is the maximum allowed fixed contamination level. This represents the DCGL for Elevated Measurement Comparison, DCGLEMC for surface surveys.
Evaluation of field sampling data for residual radioactivity present above approved release criteria will be done using two statistical tests. If contamination is present in the background, such as in surface surveys in scaler or ratemeter mode, the Wilcoxon Rank Sum test will be used to determine the DCGLw that is used for comparison for the average concentration over an area. This test would also be appropriate for in-situ soil and material measurements with a gamma radiation measurement device, such as a FIDLER.
When the contaminant is not present in background, as when a gamma spectroscopy system is being used, such as in the soil, the Sign test will be used to determine the viability of the radionuclide specific measurement.
5.1 Decision Errors
Decision errors occur when the decision maker rejects the null hypothesis when it is true, (false positive) called a Type I error, or accepts the null hypothesis when it is false, (false negative) a Type II error. The probability of making a Type I decision error is denoted by alpha (a). This represents the amount of evidence that is needed to abandon the null hypothesis. The probability of making a Type II error is denoted by beta (b). The term (1-b) is the probability of rejecting the null hypothesis when it is false.
The arithmetic mean of n measurements in the survey unit data will be compared to the investigation level to determine if the survey unit is in compliance with the release criterion. The investigation level is the Derived Concentration Guideline Level (DCGL).
A gray region will set up where a consequence of a decision error is minimal with the lower bound of the gray region (LBGR) being initially set at 50% of the DCGL, i.e. 4 pCi/g for soil, 10 dpm/100 cm2 removable alpha and 50 dpm/100 cm2 average fixed. This may be adjusted during the project to provide an acceptable value for the relative shift. The width of the gray region is equal to (DCGL - LBGR) and is referred to as the shift, D. The absolute size of the shift is less important than the relative shift, D/ss , where ss is the estimated standard deviation of the measured values in the survey unit. The value of ss will be chosen for each survey unit separately. If any data from the Characterization Report, Reference 2.2, is useable it may be incorporated into the statistical determination of ss for the survey unit. In survey units where remediation occurs, estimates of data point concentrations from field data will be used from samples within the survey unit to determine a ss for the survey unit under investigation. The field data may include soil samples that are taken at selected points within the survey unit based on professional judgement trying to identify spots of elevated activity. The field sampling data may be taken from areas identified as suspect during the field scan of the area. This ss will be used for determining the number of data points and subsequently the survey design for the final release survey.
The probability that a random measurement from a survey unit will exceed the DCGL when the survey unit median is equal to the LBGR is defined as the Sign p. The Sign p is determined from the relative shift as described above and from Tables in References 2.1 (Table 5.1) and/or 2.3. Each survey unit will determine its appropriate Sign P depending on the ss from characterization data or from on site results, at the appropriate relative shift,D/ss. If the precision of the measurements is good, the size of the gray region should be evaluated to be made smaller. For this project, a and b are equal to 0.05, and the decision error percentile, Z1-a and Z1-b, will be 1.645.
5.2 Surrogate Ratio
The ROD, Reference 2.4, specifies the contaminant of interest is plutonium and that the specific isotopes of Pu-239 and 240 are present at this site. Because multiple contaminants are present at the BOMARC Site, i.e. plutonium and americium, and the measurement of the americium component is easier than the plutonium component, a surrogate measurement ratio is established to demonstrate compliance by measuring just the 241Am gamma. The concentration of 239/240Pu will be determined by using a 239/240Pu to 241Am ratio. The 239/240Pu to 241Am ratio for the BOMARC missile accident site has been determined to be 5.4. This means for every 1pCi/gram of 241Am at the site, there is 5.4 pCi/gram of 239/240Pu. Once the 241Am concentration in a soil sample is determined, the ratio (5.4) will be used to determine the concentration of the 239/240Pu.
Prior to development of the final status survey at least 5 samples will be sent to an off-site laboratory to determine the 239/240Pu to 241Am ratio through alpha spectroscopy. The results of these analyses will be compared to the existing ratio and given to the contracting officer's representative for determination whether or not the ratio should be changed. During the project remediation phase approximately one out of 20 samples will be sent to the off-site laboratory for the 239/240Pu to 241Am ratio confirmation, until a total of 20 samples have been analyzed. These will be combined with the initial 5 samples and continually given to the contracting officer's representative for determination whether or not the ratio should be changed. When the results are received, they will be reviewed to determine if the result at the 90% confidence level overlap the ratio 5.4. If the results do not investigation by the CHP will determine if additional samples and analysis are needed.
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