Human Health Risk Assessment - Raytheon

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Human Health Risk Assessment
DRAFT
area that as of the time of the inventory continued to emit this constituent in amounts up to 7.87
tons per year.
TCE was detected at low levels (1.2 µg/m 3 ) in two samples collected on-Site northeast and
northwest of Building M on November 20, 2007 with winds out of the northeast. TCE was also
detected in six of six ambient air samples collected off-Site to the south and southeast of the
facility on December 4, 2007 when winds were blowing steadily out of the north at 3 to 6 miles
per hour. Concentrations ranged from 9 to16 µg/m 3 . However no TCE was detected in followup
samples collected from the same area on January 14, 2008 when winds were blowing out of
the north, and no TCE was detected in ambient air samples collected on-Site over three days of
sampling in April, 2008 when winds were blowing out of the north and east. TCE was detected
in only one other sample, which was collected near the Azalea Park Recreation Center.
TCE concentrations detected in Azalea Park over the past three years (2005, 2006 and 2007)
ranged from non-detect to 0.16 µg/m 3 (see Table 8). These data reflect 24-hour average
concentrations recorded every 6 days over the past three years (from 2005 to 2007) and
provide a more representative indication of average conditions in the park near the tennis
courts.
For comparison, the maximum concentration of TCE estimated in outdoor air on-Site is 0.14
µg/m 3 . This value was used as the average exposure point concentration for estimating
potential long-term exposures to on-Site maintenance workers, on-Site trespassers and users of
the Pinellas Trail. Similarly, the estimated outdoor air concentration generated during lawn
irrigation with groundwater containing 0.046 mg/L TCE 15 is 0.7 µg/m 3 . When converted to a 24hour
average basis, this estimated value falls within the range of values detected in Azalea Park
by Pinellas County.
Cone Penetrometer Samples May Overestimate Well Concentrations. Groundwater
concentrations in samples collected using Cone Penetrometer Technology (CPT) may
overestimate irrigation and monitoring well concentrations because CPT samples are collected
from narrow, discrete zones in the aquifer (immediately surrounding the probe tip) whereas
wells are typically screened over a much wider zone (five to ten feet, or open borehole) that
allows for dilution with cleaner water. Use of these data may result in an overestimation of
potential risks to on-Site workers from exposure to groundwater.
7.2 Exposure Assessment
Under the standard approach to exposure assessment recommended by the USEPA, if a
constituent is found to be present at a site, it is generally assumed that exposure to that
substance will occur. The human health risk assessment attempts to make use of Site-specific
exposure information where available. Uncertainties associated with the exposure assessment
include calculation of exposure point concentrations and selection of exposure parameters.
15 The highest concentration of TCE detected in off-Site groundwater as of May 23, 2008 is 0.065 mg/L.