2001 AIRNET Data Evaluation

Overview

Upon receiving the analytical chemistry data for biweekly and quarterly data, AIRNET personnel calculated air concentrations and reviewed them to determine if any values indicated an unplanned release. Two action levels have been established: investigation and alert. Investigation levels are based on historical measurements and are designed to indicate that an air concentration is higher than expected. Alert levels are based on dose and require a more thorough, immediate follow-up.

In 2001, a number of air sampling values exceeded investigation levels. When a measured air concentration exceeds an investigation level, the AIRNET team verifies that the calculations were done correctly and that the sampled air concentrations are likely to be representative, i.e., that no cross contamination has taken place. Next, we work with personnel from the appropriate operations to assess potential sources and possible mitigation for the elevated concentrations.

Plutonium

2001 Plutonium Findings & Analysis

• Plutonium-239 First Quarter
• The ambient concentration of Pu-239 at site 66, Los Alamos Inn - South, exceeded the "Investigate" level (which has been adopted from site 07) and was above its uncertainty. This concentration, 5 aCi/m3, is about 0.3% of the EPA public dose limit. Plutonium from the historical TA-1 activities on the hillside below site 66 appears to be the cause of the detectable concentrations at this new sampling location.
• TA-21 Plutonium-239 Fourth Quarter
• Site 71 at TA-21 had Pu-239 results significantly above its "investigate" action level with a concentration of 26 aCi/m3. The increased result may be due to resuspension of historical soil contamination or disconnecting and cleaning up some of the systems within building 344 in preparation for "formal" D&D activity. The concentration is about 0.001% of the DOE DAC for worker exposure standard of 2,000,000 aCi/m3.

Tritium

2001 Tritium Data Findings & Analysis

• TA-16: July 16
• Two adjacent sample sites near TA-16 exceeded their IAL. The higher measured emissions at these locations may be due to the tritium contaminated materials stored nearby or to increased emissions from the Weapons Engineering Tritium Facility at TA-16. The concentrations correlate closely in time and location with routine calibration exercises at TA-16. If the highest concentration (8 pCi/m3) were an annual average, it would be equivalent to less than 1% of the EPA dose limit, which corresponds to 1500 pCi/m3.
• TA-21: July 2
• The tritium concentrations for stations 9, 20, 62, and 71 exceeded their IAL and correlate very closely in time and location to planned HTO emissionsat TA-21-209 of about 21 curies during 19 June-03 July 2001. Typically, TA-21 HTO emissions are smaller than this amount. If the maximum concentration (19 pCi/m3) were an annual average, it would be equivalent to about 1% of the EPA dose limit which is 1500 pCi/m3. As a two-week average it represents about 1/26 of 1% of the EPA public dose limit.
• TA-21: July 16 and July 30
• One sample site at TA-21, site 20, exceeded its IAL over two consecutive sampling periods. The concentrations correlate closely in time and location to HTO emissions at TA-21-209 of about 46 curies during July 2001. If the highest concentration (19 pCi/m3) were an annual average, it would be equivalent to approximately 1% of the EPA dose limit, which corresponds to 1500 pCi/m3.
• TA-33: August
• Two sample sites near TA-33 exceeded their IAL for the August 27 sampling period. The concentrations correlate closely in time and location to planned HTO emissions at TA-33 of about 33 curies during 14 August-28 August 2001. If the highest concentration (12 pCi/m3) were an annual average, it would be equivalent to less than 1% of the EPA dose limit, which corresponds to 1500 pCi/m3.
• TA-41: May
• During the first week of May 2001 there was a planned release of tritiated water from D&D activities at TA-41 of about 12 curies. Typically, TA-41 HTO emissions are less than 10% this amount. Several nearby AIRNET stations (08, 60, and 66) recorded ambient air concentrations of tritium above investigation levels with a maximum concentration of 22 pCi/m3. If this concentration were an annual average it would be less than 2% of the EPA dose limit which is 1500 pCi/m3. As two-week averages they represent about 1/26 of 2% of the EPA public dose limit.
• TA-41: July 2
• The tritium concentrations for four stations 8, 60, 66 (and possibly 62) exceeded their Investigation Action Levels (IAL) and correlate very closely intime and location to planned tritiated water emissions at TA-41 of about 25 curies during 19 June-03 July 2001. Typically, TA-41 HTO emissions are less than 10% this amount. If the maximum concentration (44 pCi/m3) were an annual average, it would be equivalent to about 3% of the EPA dose limit which is 1500 pCi/m3. As a two-week average it represents about 1/26 of 3% of the EPA public dose limit.
• TA-41: July 16th and 30th, August 13th and 27th
• Five sample sites near TA-41 (8, 60, 61, and 66) exceeded their IAL over four consecutive sampling periods. The concentrations for stations 8, 12, 60, 61, and 66 correlate closely in time and location to planned HTO emissions at TA-41 of about 24 curies during 03 July-31 July 2001. Additional HTO emissions of about 12 curies were released during 31 July-28 August 2001. If the highest concentration of these 20 measurements (60 pCi/m3) were an annual average, it would be equivalent to 4% of the EPA public dose limit, which corresponds to 1500 pCi/m3.
• Area G
• Each year, as the ambient temperature increases, the tritium concentrations at TA-54 increase due to the diffusion of the tritium from the stored waste. Because this effect is a known, repeated phenomenon, a moving average is used to determine if unexpected results are being measured. At site 35, which is located next to tritium waste disposal shafts, this temperature effect is accentuated. During sample periods ending July 30th, August 27th, and September 24th, airborne tritium levels at this site exceeded the moving-average action levels. The maximum two-week concentration at Site 35 was 7316 pCi/m3. These investigate concentrations peaked at approximately twice the highest values previously recorded in other years. After an investigation, no specific explanation for these new peaks was identified. Weather conditions, a "wave" of tritium diffusion through the soil, or physical changes in the buried waste containers may have caused this increase. The annual mean concentration at this site, 1826 pCi/m3, is only 0.01% of the DOE DAC for worker exposure, which is 20,000,000 pCi/m3.

Uranium

2001 Uranium Data Findings & Analysis

For natural uranium, the natural isotopic abundances of uranium-238 and uranium-234 are normally in radioactive equilibrium, with a measured uranium-238 to uranium-234 isotopic activity ratio of 0.993. Thus, activity concentrations of these two isotopes are effectively the same in particulate matter derived from natural sources. Because known LANL uranium emissions are enriched (excess uranium-234 and -235) or depleted (excess uranium-238), comparisons of isotopic concentrations can be used to identify LANL contributions. For purposes of this review, excess isotopic concentrations are considered to be present when the difference in concentrations is statistically different (more than three standard deviations).

• AIRNET Sites with Excess Uranium Plot (pdf).

A number of uranium measurements exceeded action levels during 2001. In most cases, the follow-up investigation demonstrated that natural uranium associated with higher levels of suspended particulate matter produced the elevated uranium concentrations except for the depleted uranium concentrations discussed in this section. Even though there were a number of sites with excess uranium-238, all concentrations, with the exception of site 77, were less than the 2001 maximum natural uranium concentration (the county landfill site 32) and much less than the highest natural concentration during the past five years. Therefore these concentrations per se do not raise any public health concerns beyond that posed by natural uranium. Fifteen sites (09, 14, 17, 20, 23, 30, 35, 47, 49, 51, 62, 71, 76, 77, and 78) had at least one quarter with excess uranium-238.

No excess uranium-234 was measured during 2001.

Americium/Plutonium

2001 Americium and Plutonium Data Findings & Analysis

Am-241 and Pu-239 action levels at site 34 were exceeded for all four quarters of 2001. In addition, one quarterly sample at Area G exceeded its Pu-238 investigate concentration. The concentrations of all three radionuclides at this site have been higher since early 1999. High concentrations for more than two years and the absence of similar increases at other locations in the eastern part of Area G indicate that these "investigate" concentrations remain localized and are caused by nearby activities. These concentrations are less than 0.01% of the DOE workplace exposure standards.

During the fourth quarter of 2001 the Pu-239 concentration at site 50 was 23 aCi/m3. This sampler is located in Area G, but the analytical results over the last several years have been on the order of 0-5 aCi/m3. It is not known what caused this increase. This concentration is about 0.001% of the DOE workplace exposure standards.