LAWRENCE LIVERMORE NATIONAL LABORATORY
BIG TREES PARK 1998 SAMPLING
Overall Data Quality • During the sampling, approximately 10% of the samples were sent to the Georgia Institute of Technology (Georgia Tech)2 in Atlanta for independent analysis of Pu 238 and Pu 239/240 by alpha spectroscopic techniques, and for Americium 241 (Am 241) by low energy X-ray analysis with verification as needed by alpha spectroscopy. ATSDR also requested that the laboratory analyze samples by gamma spectroscopy for additional products that might be present in the soil samples. Another set of samples from the same locations was supplied to LLNL for analysis by their laboratories. A third set consisting of all samples collected was supplied to General Engineering Laboratory, the prime laboratory for sample analyses, under contract to DOE. The data quality review process for this health consultation only allows for an intercomparison of samples evaluated by the three laboratories. Therefore, only Pu 238, Pu 239/240, and Am 241 were considered. Metals were not included in the intercomparison.
The quality of the data collected during the 1998 sampling of Big Trees Park was very good. Comparisons of the results from the three reporting laboratories were in close agreement with respect to the reported Pu 239/240 values. ATSDR and the regulatory agencies therefore believe that the results for the remainder of the samples are a true representation of environmental conditions in Big Trees Park. Figure 1 shows the reported values from each laboratory for the major radionuclide of concern, Pu 239/240, expressed as Pu 239. Figure 1 illustrates that the analyses of most of the samples were very similar in all three laboratories. Furthermore, an analysis of variance (a statistical analysis) of the results of these samples suggests that these measured values are identical to one another.
After the agencies involved with the quality assurance process were satisfied with the acceptability of the data set, the final data sets were distributed to the regulatory agencies and to ATSDR. These results have been used in the development of this public health consultation. Lawrence Livermore National Laboratory also posted the results on their World Wide Web site at the following addresses: http://www-envirinfo.llnl.gov/ or http://www-erd.llnl.gov/bigtrees/.
Overall, LLNL and EPA collected 379 samples for Pu 238 and Pu 239/240 analyses. Of these, 117 samples were also used for Am 241 analysis, and 101 samples for metals analysis. These samples included duplicate samples which served as internal checks on laboratory procedures. The metals included in the analysis were those commonly found in sewage sludge--chromium, copper, lead, nickel, and zinc .
The sampling plan required a reporting level of Pu 239/240 at 0.005 picocuries per gram (pCi/g) equivalent to 2 × 10-4 becquerels per gram (Bq/g). This value approaches the regional background as determined by LLNL and other reports as referenced in the sampling plan [1, 2, 4, 7]. The background values as reported by LLNL and based on approximately 200 samples, show a typical environmental distribution of Pu 239/240 with an estimated geometric mean concentration3 of 0.0026 pCi/g (1 × 10-4 Bq/g) ; Gallegos reported Pu 239/240 levels ranging from 1.2 × 10-4 Bq/g (3.2 × 10-3 pCi/g) to 2 × 10-4 Bq/g (5.4 × 10-3 pCi/g) upwind and downwind from LLNL, respectively . Furthermore, converting data collected by Hardy  into the more common units of picocuries per gram from millicuries per square kilometer by using standard values for soil density, one estimates the plutonium concentration at 2.2 × 10-4 Bq/g (6 × 10-3 pCi/g); this also agrees with LLNL data. Other estimates of background concentrations of Pu 239/240 suggest regional differences exist--possibly related to weather conditions and soil disturbing activities. These activities have been shown to alter radionuclide concentrations in soil . Because of uncertainties involved with radiological detection at extremely low levels, ATSDR health physics staff members use a value 3 to 5 times greater than the suspected background values as an indicator of significance. Therefore, the reporting level of 0.005 pCi/g (2 × 10-4 Bq/g), a value twice the reported background expressed as the geometric mean, is considered valid for the purposes of the sampling plan.
Analytical processes report a minimum detectable activity or level (MDA or MDL). Table 1 summarizes the numbers of samples, the number of samples in which the MDA value was above the reporting level, and the number of samples in which the detected activity was below the MDA. The MDA is a variable that depends on sample characteristics and instrument operational restraints (background, counting time, and so on). Detector instrumentation and its computer-related programs can report values below the MDA once these restraints are factored into their operations. The computer-estimated values below the MDA are usually reported as either the MDA or as nondetects, indicating no activity in the sample under investigation.
The following information was found through reviewing all samples collected from Big Trees Park as an entire group. The highest concentrations of radionuclides detected and their locations were as follows: (A) Pu 238 detected at 8.57 × 10-2 ± 0.018 pCi/g (3.17 × 10-3 Bq/g) in grid location G0103 (10-centimeter [cm] depth); (B) Pu 239/240 at 0.774 ± 0.11 pCi/g (2.9 × 10-2 Bq/g) in grid location G0103 (10-cm depth); and (C) Am 241 at 0.205 ± 0.066 pCi/g (7.6 × 10-3 Bq/g) in grid location G0104 (5-cm depth). For comparison, the EPA Region IX preliminary remediation goal is 2.5 pCi/g for Pu 239/240. As a screening level indicator for the evaluation of additional actions, the National Council on Radiation Protection and Measurements (NCRP) recommends a level of approximately 51 pCi/g for each of these radionuclides in a park scenario . The most stringent NCRP value is 7.8 pCi/g for a sparsely vegetated rural area.
|Total number of
|Number below MDA
|Am 241†||117||12||105 (90)|
|Pu 238‡ (0.005 pCi/g)||379||34||287 (76)|
|Pu 239/240‡ (0.005 pCi/g)||379||94||213 (56)|
* Numbers include field replicates on approximately 10% of
the samples initially collected.
† Analysis performed by low energy gamma spectroscopy and alpha spectroscopy.
‡Analysis performed by alpha spectroscopy that is specific for the listed radionuclide.
Pathway Analyses-- Radiological Considerations
Air pathway · The soils samples used to evaluate the air pathway were collected from the grid locations (coded GXXX where XXX represents the grid coordinate numbers). Collection depths ranged from 5 centimeters to a depth of 40 centimeters. The analysis of these samples was for Pu 238, Pu 239/240, and Am 241. Only those samples that met the criteria previously discussed were used in the analysis; a total of 111 samples from all depths met ATSDR's pre-established criteria.
Several issues must be considered in evaluating the air pathway. Among these issues are (1) the size and location of the grid: that is, whether there is sufficient separation of the sampling locations to give an adequate spatial distribution of samples; (2) a comparison of the grid with other locations within the park; and (3) a comparison of the grid locations with other Livermore Valley sampling locations considered background and listed in the sampling plan .
The air pathway analysis was performed by evaluating the plutonium concentration in the grid area using the 5-cm samples. These samples compared the plutonium distribution at 5-cm depths from other locations in the park, comparing the 5 cm-depths to the 10-cm and 20-cm depths, and from five other locations near the laboratory and south of the laboratory as listed in the sampling plan . These samples, listed in the sampling plan, are coded ERCH (near Mines Road), HOSP (near the Veterans Hospital on Arroyo Road), MET (northwest corner of the laboratory property), MESQ (near Vasco Road on the LLNL property), and RRCH (north of Interstate 580 near Vasco Road).
In investigating small numbers of samples in the analysis, ATSDR used statistical tools called the t-test and the F-test . A t-test evaluates the averages or mean of two sets of samples to determine if they are similar. One result of the t-test is the calculation of a "t value" that can be compared with a tabulated value. The tabulated value, called the critical value, is found in books on statistics, and it is used in business, scientific disciplines, and other disciplines requiring a statistical analysis. If this "t value" is less than the tabulated value, then no difference between the averages of the values evaluated exists. Similarly, the F-test is a procedure to determine if the variations within (or ranges of) the two sets of sample measurements are significantly different. If the measured "F value" is greater than the tabulated critical value, then the chance is small that the two sets of samples are from the same source or process . The grid sample values also were entered into a geographical information system (GIS) to display the spatial configurations to determine whether a distribution pattern could be visualized.
During the initial planning for the park sampling, the sampling rationale was that the distribution pattern of the results on the grid could indicate a pathway, and that uniformly and generally elevated levels throughout the park (including the grid and other parts of the park) might suggest an air pathway. Because of this, ATSDR thought other locations within the park besides the grid could have been impacted by air releases. Therefore, ATSDR decided to evaluate the grid samples not only within the park but also with air monitoring locations upwind and downwind in and around Livermore. These sampling locations included the five previously mentioned locations (ERCH, HOSP, MET, MESQ, and RRCH) plus locations to the east, east northeast, and northeast of the laboratory at distances from the laboratory fence line to 2 kilometers from LLNL.
Based on a recent report of the wind directions in the Livermore Valley , little wind, if any, is from the north; therefore the ERCH samples could represent a background location. The HOSP samples, north and west of the ERCH samples, could also be considered similar to the background samples. The MET and MESQ samples are at the northwest and west boundaries of LLNL, respectively, and these samples could be expected to be impacted by air releases when the wind blows from easterly to westerly directions. The RRCH location is a downwind direction when the wind blows from the south across the laboratory property.
The results of the analyses of these data are given in Table 2. Those samples at the laboratory boundary, MET and MESQ, have reported plutonium concentrations lower than the concentrations in the soil samples collected in the park. Plutonium is a dense material that settles from the atmosphere close to its source. If air dispersion were the process by which plutonium was deposited in the park, the MET or MESQ sampling stations would have higher soil concentrations than those in the park. This was not so--as the park soil samples showed greater average concentrations of plutonium than the MET or MESQ locations. This indicates that the air pathway is unlikely.
Furthermore, the analysis indicates that the average plutonium concentration in soils from the top 5 centimeters at the grid locations is not significantly different from the average plutonium soil concentrations collected from the other 5-centimeter samples from areas within the park. Nor are they different from the soil samples collected at 10 centimeters in the grid area, nor from soils collected in the top 45 centimeters of the tree well areas. This indicates there was not an air pathway to the grid area alone. However, the F-test results showed that the grid locations have much more variability than the other park areas. In the grid area, the range of Pu 239 was 2.84 × 10-3 to 5.94 × 10-1 pCi/g. In the remainder of the park, the range of Pu 239 was 6.1 × 10-4 to 5.82 × 10-2 pCi/g. This distribution which covers 2 orders of magnitude (varies by a factor of 100) would not be expected if the plutonium had been deposited via the air pathway as air dispersion would be more uniform. At other areas, both in the park and outside the park, the 5-centimeter depth grid samples were significantly different.
In areas downwind of the laboratory most of the time, the concentrations of plutonium in soils are lower than those concentrations found in the park at a depth of 5 centimeters. In 1980, the CDHS collected soil samples from areas east, northeast, and east northeast at a distance of up to 2 kilometers from LLNL, approximately the same distance that Big Trees Park is from LLNL. These compass directions are downwind of LLNL most of the time . The geometric mean concentration of Pu 239/240 from the locations east of LLNL was 0.0068 pCi/g (2.5 × 10-3 Bq/g) as compared with the geometric mean of 0.017 pCi/g (6.3 × 10-4 Bq/g) for the top 5 centimeters throughout the park. The concentration of Pu 239/240 in the east direction ranged from a high of 0.0292 pCi/g (at the fence line) to 0.0025 pCi/g (at 2 kilometers) (0.0012 to 9.3 × 10-5 Bq/g). This also would suggest that the plutonium in the park is not the result of atmospheric deposition from LLNL activities. The samples collected from the northeast locations were near the reporting values for the 1998 sampling: that is, 0.005 pCi/g (0.00018 Bq/g). Those samples collected in the east northeast directions showed a maximum value of about 3 times the reporting level.
The GIS spatial analysis showed that the plutonium is not uniformly distributed within the grid area and that these values did not fit a into a pattern that would be expected from atmospheric distribution. In fact, the spatial analysis showed that within the grid areas, the concentrations of plutonium varied by almost two orders of magnitude at the surface.
Is the plutonium in the park the result of atmospheric fallout? The question has been raised as to whether the plutonium in Big Trees Park is the result of atmospheric nuclear testing. All nuclear weapons detonated in the atmosphere release various amounts of plutonium radioisotopes at different isotopic ratios. Over time, these ratios vary as the material decays. An analysis of the plutonium and americium found in the park can be compared with these measured fallout levels. The ratios of the values in the park and those found in fallout are given in Table 3. Analysis of these values indicates that the plutonium in the park may not be the result of atmospheric fallout because the ratios are 4 to 15 times higher than values normally associated with fallout deposition.
Conclusion: Based on the analyses of the grid samples and a comparison of the samples with areas where air deposition is known to have occurred, ATSDR does not believe that plutonium in Big Trees Park is the result of air deposition. Our reasoning is as follows: (1) the park is in the downwind direction approximately 5% of the year yet the plutonium concentrations in the park are greater than the sampling locations downwind the majority of the year; (2) the plutonium concentrations in the park are higher than the laboratory fence line monitoring stations MET and MESQ which are downwind approximately the same amount of time as Big Trees Park; and (3) if the plume from the facility did not impact MET and MESQ locations because of its elevation but did impact the park, the spatial distribution in the park would be more uniform.
Arroyo Seco Pathway • Samples collected to test the hypothesis that plutonium was released to the former Arroyo Seco channel are coded beginning with B-FAS. The hypothetical pathways for plutonium entering the arroyo would include bulk flow (overland flow) from the southeast corner of the laboratory or via a possible sewer line rupture. If plutonium were released to the arroyo, samples collected in the former arroyo channel or the current channel would indicate this as the pathway by which plutonium reached the park. The results of the samples from the previous arroyo channel were below the MDA; the highest computer-estimated value was 0.00345 pCi/g (1.3 × 10-4 Bq/g) for Pu 238 and 0.00229 pCi/g (8 × 10-5 Bq/g) for Pu 239/240. Americium 241 was not detected.
Duplicate samples were collected at each of the sample locations in the current Arroyo Seco channel (coded SSS-AS). The highest Pu 238 computer-estimated value detected was less than the MDA; that value was 0.00269 pCi/g (1 × 10- 4 Bq/g). For Pu 239/240, of the two samples collected at a depth of 25 centimeters below the surface downstream from the concrete channel, one sample was identified at a concentration of 0.0432 pCi/g (1.6 × 10-3 Bq/g) and the duplicate was below the MDA. Pu 239/240 was only detected in one other sample at this depth, and that sample location was also downstream of the concrete channel. The duplicate for that sample was below the MDA as well. Samples obtained from the arroyo immediately downstream from the LLNL outfall near East Avenue and Building 111 on LLNL property, and upstream of the outfall showed no plutonium activity; that is, all were below the MDA. Furthermore, all samples collected at a depth of 5 centimeters were either below the reporting level or less than the MDA.
|Location||t-test value*||critical t value†||NS††||F-test value‡‡||critical F value§||NS††|
|Other park locations¶||1.9||-2.03 to 2.03||NS||46||8.6|
|Tree well**||1.1||-2.03 to 2.03||NS||35||2.7|
|Outside tree well**||2.8||-2.04 to 2.04||>100||2.9|
|Grid (10 cm)||-0.5||-2.02 to 2.02||NS||0.56||0.54|
|Grid (20 cm)||2.14||-2.03 to 2.03||20||2.0|
|HOSP||2.7||-2.04 to 2.04||>100||3.1|
|MESQ||2.9||-2.04 to 2.04||>100||3.4|
|MET||2.9||-2.04 to 2.04||>100||3.4|
|ERCH||2.8||-2.04 to 2.04||>100||4.5|
|RRCH||2.8||-2.04 to 2.04||>100||3.8|
* The t value represents the value that defines how the means
(averages) differ. A negative t value shows the grid average
was lower than the other areas to which it was compared.
† The critical T value is the 95% confidence interval in which the t-value must fall for the samples to be considered identical.
‡The f value represents the value that defines the ratio of the variances.
§ The critical F value, the maximum value, which shows that the ratio of variances is caused by chance alone.
¶ Comparison of other soils samples in the park at a depth of 5 centimeters.
** Comparison of soils collected from 0 to 45 centimeters.
†† Shows sample is not significantly different at the 95% confidence level.
|Ratio||Big Trees Park (all samples)*||Fallout†|
|Am 241/Pu 239+240||1.22||0.33|
|Pu 238/Pu 239+240||0.53||0.065
(0.036 in Northern Hemisphere)
* Samples that met ATSDR requirements for acceptable samples.
† Data from Efurd, DW, et al. .
Conclusion: Based on the sampling results, the current Arroyo Seco channel does not appear to be the source of plutonium in Big Trees Park. Although two samples suggest the presence of plutonium, the duplicate samples do not validate these apparently elevated levels. This suggests either a random deposition of plutonium from areas currently in the park, a random error associated with plutonium deposition, or a possible error in the laboratory analysis. Nonetheless, no other samples collected in the arroyo at either 5-centimeter or 25-centimeter depths contained plutonium above the detection level. Data do not suggest that plutonium ever entered the Arroyo Seco from the LLNL outfall in the southwest corner of the site, from overland transport from the southeast corner of the facility to surface collection areas that enter the outfall areas near Building 111, or from any reported sewer line break.
Sewage Sludge Pathway · The investigation of this pathway was through analysis of samples collected around the ornamental trees. These samples, coded TR, were collected around 10 trees and at depth intervals of 0 to 45 centimeters, 45 to 90 centimeters, and 90 to 135 centimeters. The circular area dug out for the planting of each tree is called the tree well. The soil samples were taken from both inside and outside the tree well areas. If soil amendments containing sewage sludge were added during the planting, the radionuclide concentrations inside the tree wells could be compared with the soils from similar depth intervals outside the wells.
For samples to be valid for analysis, two criteria had to be met. First, the detected concentration had to be greater than the MDA; second, the detected concentration had to be greater than the 2 sigma error of the measurement. Tree well samples and samples from outside the tree well that do not meet these criteria can be considered indistinguishable.
Upon analysis, 8 ornamental trees fit the criteria for one or more of the radionuclides under consideration. It is interesting that only the top 0 to 45 centimeter samples from each tree suggested the presence of elevated concentrations of radionuclides. The ratios associated with these trees are shown in Table 4. For those Pu 239/240 samples within the tree wells, the 2 sigma error average was less than 25%, indicating the detected concentration was significantly higher than the MDA. Conversely, outside the tree well, the 2 sigma error averaged 67%, suggesting that these samples are more closely associated with nominal background concentrations.
Conclusions: From this analysis, the following information can be deduced:
- The ratios of radionuclides at depths greater than 45 centimeters within the tree wells as compared to areas outside the tree wells are not significantly different from background.
- Plutonium or americium radionuclides do not increase with depth.
- The concentrations of these radionuclides at depth (greater than 45 centimeters) are indistinguishable from background levels, indicating that no significant migration of radioactive materials has occurred.
- Sewage sludge containing plutonium radionuclides was most likely applied to these ornamental trees as the area outside the tree wells is not contaminated.
|Tree||Pu 238 ratio||Pu 239/240 ratio||Am 241 ratio|
* NS indicates the criteria for evaluation were not met; therefore,
these ratios are not considered significantly different.
†For this tree, the criteria for evaluation were met, but the ratio was not elevated.
Evaluation of Other Sampling Locations
Eastern Extension of Big Trees Park · Soil samples collected from the eastern extension of Big Trees Park (coded BPE) did not contain any Pu 238 above the reporting limit. One sample, obtained from a depth of 40 centimeters, was above the MDA with a reported concentration of 0.0019 pCi/g (7 × 10-5 Bq/g). Twenty-five soil samples were analyzed for Pu 239/240; all values were below the reporting level, but 7 samples were above the MDA. Of the 7 samples, duplicate samples were collected in 7 instances. The duplicates were below the MDA. Table 5 gives the synopsis of the information for these samples.
Disked Area · Four samples (coded DISK) collected in this area were analyzed for plutonium radionuclides. The results of the Pu 238 analysis show that no Pu 238 was found above the detection limit. The analysis of samples for Pu 239/240 showed that all samples were below the reporting limit; however, one sample was above the MDA. That sample had an associated uncertainty of approximately 75% and is questionable with respect to its reported value.
Playground · Pu 238 was not detected in soil samples from the playing field (coded PLAY) above the reporting value of 0.005 pCi/g (2 × 10-4 Bq/g) with most samples being reported at less than the MDA. The few samples in which the value was greater than the MDA also were suspect as the associated uncertainty of the measurement was more than 70%. Fifteen soil samples were collected for Pu 239/240 analysis, and one sample from a depth of 40 centimeters exceeded the reporting limit and one sample from 5 centimeters was essentially at the reporting limit. Sample duplicates did not contain Pu 239/240; that is, the reported values were below the detection limit.
|Sample Location (depth in centimeters)||Pu 239/240 (picocuries per gram)||Minimum Detectable Activity (picocuries per gram)||Reporting Limit (picocuries per gram)|
|L-BPE01 (5)||0.000996 ± 0.00165
0.0399 ± 0.00958
|L-BPE01 (20)||-0.000469 ± 0.00094
0.0121 ± 0.00478
|L-BPE02 (5)||0.0429 ± 0.00895
0.00175 ± 0.00145
|L-BPE02 (10)||0.000308 ± 0.000617
0.00467 ± 0.00251
|L-BPE02 (20)||0.00395 ± 0.00259
0.000655 ± 0.00124
|L-BPE02 (30)||0.00492 ± 0.00253
0.000675 ± 0.000958
|L-BPE03 (10)||0.00416 ± 0.00291||0.00367||0.005|
* Values in italicized type represent duplicate samples that were not above the MDA.
Pathway Analyses--Metals Considerations
Samples for metals analysis were collected from the ornamental trees area and the grid area. In the ornamental tree area, samples were collected from inside and outside the tree wells. All metals were detected above the MDA. ATSDR believes that if sludge had been used as a soil amendment, the amendment would be used in the tree well area--either as a mulch-type material applied to the surface around the tree trunk or uniformly mixed in with soil in which the tree was planted. Therefore, the ratio of individual metals at each depth in the tree well area compared with the metal concentrations at the same depths outside the tree well area should answer the question whether a soil amendment such as sewage sludge was used.
Sampling was conducted around 10 trees and at depths of 0 to 45 centimeters, 45 to 90 centimeters, and 90 to 135 centimeters. To evaluate the results, a ratio was calculated by dividing the concentration of the individual metals in the tree well at a specific depth by the concentration of the same metals at the same depth outside the tree well. If the concentration inside the tree well is higher than the concentration outside the tree well, the ratio is greater than 1.0, and the higher the ratio, the higher the concentration inside the tree well. If the ratio is greater than 2.0, ATSDR considered the concentration inside the tree well to be significantly different that the concentration outside the tree well. Many trees did not show significant differences in metals concentrations between the tree well and outside the tree well--at any depth. Table 6 shows the results of the comparison of tree 3, the tree with the greatest differences. Only the concentrations of the metals in the top 45 centimeters of soil in the tree well were elevated; concentrations in the samples at the deeper depths are not elevated. This is reflected in the ratio of metals concentrations shown in Table 5 as well. These data suggest that sewage sludge was added to the surface soil, at least around this tree, as the concentration in the top 45 centimeters of soil is about 8.5 to 10 times that found outside the tree well.
* The ratio is the concentration inside the tree well as compared to the concentration outside the tree well.
Metals analysis of samples collected from the grid area suggests that the concentrations of metals in this area are similar to the metals concentration in those samples collected outside the tree wells. Soil samples from the grid collected from depths ranging from 5 to 40 centimeters exhibited the same concentrations as soil samples collected at a minimum depth of 0 to 45 centimeters from outside the tree wells. Conversely, the metals concentrations in grid samples were lower than the metals concentration of the soil samples collected from within the tree wells. This also suggests that sewage sludge may have been added at the time of tree plantings as a soil amendment.
Health impacts of heavy metals in Big Trees Park
The public health impacts of radiological material in Big Trees Park has been evaluated in a previous health consultation . This health consultation is evaluating the health impacts of heavy metals associated with Big Trees Park. ATSDR has established environmental media evaluation guides (EMEG) for many common heavy metals found in the environment. EMEGs represent the concentration in an environmental media below which no adverse health effects are expected to occur. For the heavy metals reported in Big Trees Park, the only EMEG established is for zinc. The EMEG for zinc is 600 milligrams per kilogram or 600 parts per million (ppm). The highest concentration of zinc reported was about 74 ppm, considerably less than the EMEG. Another evaluation guide used by ATSDR is the reference media evaluation guide (RMEG). The RMEG listed for nickel is 40 ppm for chronic ingestion by a pica child (a child with high hand-to-mouth activity). Although 40 soil samples from Big Trees Park exceeded this RMEG, only 2 samples collected from the grid were at the surface (5-centimeter depth). However, throughout the entire park, the average nickel concentration was less than this RMEG.
Conclusion: Based on the above levels and frequency of exposures, ATSDR does not believe that metals in the park would cause any adverse health effects based both on its site wide concentrations and depth of contamination as well as those sampling locations showing elevated (hot spot) concentrations.
Is there a need for additional sampling in the Livermore Valley? As previously discussed, sewage sludge containing plutonium released from LLNL may have been distributed on demand to the community. The log book showing who received this sludge has not been found as reported by CDHS-EHIB . In May 1973, LLNL collected soil samples from the yards of three houses whose occupants (individuals associated with the laboratory) had received the sludge. These individuals knew where the sludge had been placed; they also knew of any soil-disturbing activities that had taken place since the sludge had been added to the yards. Table 7 shows the results of the 1973 sampling.
|Sample location and depth in centimeters||Pu 238 ± 2 sigma (%)†||Pu 239/240 ± 2 sigma (%)†|
|Location 1: 0-1||0.0233 ± 10||0.324 ± 9.8|
|Location 1: 1-25||0.00023 ± 11.6||0.00412 ± 7.4|
|Location 2: 0-1||0.243 ± 13||1.84 ± 13|
|Location 2: 1-25||0.0964 ± 9.1||0.784 ± 9|
|Location 3: 0-1||0.000923 ± 19||0.00797 ± 8.8|
|Location 3: 1-25||0.00013 ± 46||0.00168 ± 15|
* Concentrations expressed as pCi/g.
† The uncertainty is expressed as a percentage. For example, 10 ± 1 is expressed as 10 ±10%.
At Location 2, where the highest concentration of Pu 239/240 was detected, the concentration is below the EPA preliminary remediation goal of 2.5 pCi/g and below 51 pCi/g, which is the concentration at which NCRP recommends additional action . The low levels of concentrations in these three yards indicate that no additional sampling is warranted and that there is no need for additional activities.
ATSDR bases this conclusion on the following factors. The contamination that was higher than nominal background concentrations occurred in the top centimeter of soil (the top 3/8 inch of soil). In the 25 or more years since the sludge was distributed, a number of events could have taken place at these residences including (1) exterior remodeling; (2) extensive landscaping; (3) general yard maintenance activities; and (4) change of owners with the new owners not knowing if sludge had been used. Because of these possible activities and the effects of normal weathering (such as soil erosion), any sampling locations would be very difficult to identify, and if Big Trees Park and the laboratory employees' yards are any indication, the plutonium that might be detected would probably be below the concentrations established as action levels.