DOE/ORO/2327 Oak Ridge Reservation Annual Site Environmental ...

4.4.2.1 Mercury
Annual Site Environmental Report
The Y-12 Complex ambient air monitoring program for mercury was established in 1986 as a best
management practice. The objectives of the program have been to maintain a database of mercury
concentrations in ambient air, to track long-term spatial and temporal trends in ambient mercury vapor,
and to demonstrate protection of the environment and human health from releases of mercury to the
atmosphere at Y-12. Originally, four monitoring stations were operated at Y-12, including two within the
former mercury-use area near the west end of Y-12. The two atmospheric mercury monitoring stations
currently operating at Y-12, Ambient Air Station No. 2 (AAS2) and Ambient Air Station No. 8 (AAS8),
are located near the east and west boundaries of Y-12, respectively (Fig. 4.21). Since their establishment
in 1986, AAS2 and AAS8 have monitored mercury in ambient air continuously with the exception of
short intervals of downtime because of electrical or equipment outages. In addition to the monitoring
stations located at Y-12, a control or reference site (Rain Gauge No. 2) was operated on Chestnut Ridge in
the Walker Branch Watershed for a 20-month period in 1988 and 1989 to establish a reference
concentration.
Fig. 4.21. Locations of ambient air monitoring stations at the Y-12 Complex.
In order to determine mercury concentrations in ambient air, airborne mercury vapor is collected by
pulling ambient air through a sampling train consisting of a Teflon filter and an iodated-charcoal
sampling trap. A flow-limiting orifice upstream of the sampling trap restricts airflow through the
sampling train to ~1 L/min. Actual flows are measured weekly with a calibrated Gilmont flowmeter in
conjunction with the weekly change-out of the sampling trap. The charcoal in each trap is analyzed for
total mercury using cold vapor atomic fluorescence spectrometry after acid digestion. The average
concentration of mercury vapor in ambient air for each 7-day sampling period is calculated by dividing
the total mercury per trap by the volume of air pulled through the charcoal trap during the corresponding
sampling period.
The Y-12 National Security Complex 4-41