8


Vegetation and Foodstuffs


I. BACKGROUND   8.1

II. TREE SAMPLING   8.2

Figure 8-1: Areas Sampled in 1998–1999

III. RESULTS   8.3

Figure 8-2: Vegetation Tritium Concentration vs. Distance from NTLF

Table 8-1: Maximum Tritium Concentration Measured in Wood or
                   Vegetation Materials



8.1      I. BACKGROUND

Sampling of vegetation and foodstuffs can provide information regarding the presence, transport, and distribution of radioactive emissions in the environment. This information can be used to detect and evaluate changes in environmental radioactivity resulting from Berkeley Lab activities and to calculate potential human doses from consuming vegetation and foodstuffs. Possible pathways or routes for ingesting radionuclides include:

DOE guidance indicates that when the annual effective dose equivalent for the consumption of vegetation and foodstuffs is between 0.001 mSv (0.1 mrem) and 0.01 mSv (1 mrem), only a minimal vegetation and foodstuff surveillance program is required.1 Using conservative assumptions, Berkeley Lab’s maximum individual dose attributable to the consumption of locally grown vegetation and foodstuffs was well below the requirement for a minimal monitoring program. Tritium air emissions were identified as the only potentially significant contributor to these pathways.

Tritium emissions can be in the form of tritiated water vapor or tritiated hydrogen gas. The relative dose from an exposure to tritiated hydrogen gas is much less than that from an equal exposure to tritiated water. Nevertheless, in modeling and dose calculations, the Laboratory conservatively assumes that 100% of the emissions are tritiated water vapor to provide a safe overestimate of actual dose.

Tritiated water vapor released to the environment mixes and exchanges readily with atmospheric water (e.g., precipitation, fog, vapor) and with other sources of environmental water (e.g., plant water, surface water, soil water). Within plants, tritium exists as either tissue-free water tritium (TFWT) or organically bound tritium (OBT).

The Laboratory’s Environmental Monitoring Plan2 outlines the current vegetation sampling program. The objective of this portion of the program is to better understand the distribution of tritium in local vegetation.

8.2      II. TREE SAMPLING

Berkeley Lab manages on-site trees and vegetation (and some immediately adjacent to the University of California) as part of a multi-year wildland fire task management program and its maintenance program for a fire-safe landscape.3 In the future, Berkeley Lab is considering thinning nonnative tree stands around Buildings 75, 76, and 77. See Figure 8-1.

Environmental tritium levels have been determined to be above regional background levels near the National Tritium Labeling Facility (NTLF) and to decrease with distance from the facility stack.4 A sampling and analysis plan was developed and implemented in 1998 to characterize tritium concentrations within tree stands that might be thinned in the future,5 and the results were reported in the Site Environmental Report for 1998. In 1999, a follow-on sampling and analysis plan was prepared and implemented to confirm vegetation tritium levels measured in 1998 and to investigate tritium levels at other locations at Berkeley Lab. Figure 8-1 shows the areas at Berkeley Lab that were sampled in 1998 and 1999. Tree selection and sampling were designed to (a) provide representative samples for characterizing tritium levels within the tree stands, (b) prevent sample cross-contamination, and (c) estimate field sampling variability.

Figure 8-1      Areas Sampled in 1998–1999

In 1999, wood chip, leaf, and duff were collected from several locations within the Laboratory site. See Figure 8-1. Duff consists of tree litter and other decomposing vegetation material that lies on the ground under a tree canopy. Eucalyptus and pine trees were sampled using a systematic and documented procedure. The samples were analyzed at a commercial laboratory for TFWT and OBT.

8.3      III. Results

Tritium results from the vegetation samples collected in 1999 confirm the distribution patterns measured in 1998: concentrations of tritium in vegetation greater than the analytical detection limits occur only within a radius of 200 meters from the NTLF. Figure 8-2 shows all vegetation tritium results from both 1998 and 1999 as a function of distance from the NTLF stack. A detailed listing of tritium results obtained in 1999 is included in Volume II. Background levels for tritium in wood, leaf, and duff were established in 1998 from samples collected at Chabot Regional Park that were all below or near the analytical detection limits.

Figure 8-2      Vegetation Tritium Concentration vs. Distance from NTLF

The maximum tritium concentrations (TFWT and OBT) found in each vegetation media (for both 1998 and 1999 results) and their distance from the NTLF are listed in Table 8-1. All the maximum tritium values occurred in samples located close to the NTLF stack and can be compared with recently published guidance in ANSI/HPS N13.12-1999 (Surface and Volume Radioactivity Standards).6 These standards recommend an unrestricted tritium release limit of 111 Bq/g (3000 pCi/g) of vegetation for derived screening levels. In comparison, the average tritium concentration within a 200-meter radius from the NTLF stack is approximately 3.70 Bq/g (100 pCi/g). Using this average, the total tritium inventory within 200 meters of the NTLF stack is estimated to be less than 0.037 TBq (1 Ci) in the surrounding environment.


Table 8-1      Maximum Tritium Concentration Measured in Wood or Vegetation Materials



Type of vegetation material


Distance from NTLF stack (meters)


Maximum tritium
concentration
measured (Bq/g
*)

Percent of ANSI/HPS N13.12 standard

Duff

20
5

47.4 (OBT)
3.89 (TFWT)

42%
4%

Leaf

4
4

309 (OBT)
21.0 (TFWT)

280%
19%

Wood

4
4

2.44 (OBT)
1.82 (TFWT)

3%
2%

*All values are based on the actual sample weight (wet sample), so the total tritium concentration in a vegetation sample could be found by adding TFWT and OBT concentrations together. 1 Bq = 27 pCi.


The results from the samplings and analyses conducted in 1998 and 1999 confirm what has been previously measured and reported: tritium concentrations in vegetation are elevated above regional background levels near the NTLF main stack and decrease with distance from the stack. At about 200 meters from the NTLF stack, TFWT and OBT levels in vegetation are nearly indistinguishable from regional background levels. This tritium characterization data will be utilized in preparing an application for the authorization of release limits for tritium in vegetation, which will be submitted to DOE for approval.

Routine sampling of vegetation and foodstuffs at Berkeley Lab is not required under any applicable environmental regulations. Berkeley Lab undertakes voluntary sampling efforts to better understand the integrated impact of its operations on all media in the surrounding environment and to verify its overall dose-assessment program. This assessment program, presented in Chapter 9, includes vegetation and foodstuffs as one of the contributing pathways in determining the overall impact of Berkeley Lab’s airborne radionuclides. Dose assessments using very conservative assumptions indicate extremely low impacts.