Environmental Engineering Reference
In-Depth Information
AgDRIFT ® contains the Tier I levels for ground and orchard air blast spraying, and
the Tier I, II and III levels for aerial spraying. Tier II and III ground and orchard air
blast spraying screens have not been developed. The Tier I predictions for this
assessment were used for all application methods.
The 2005 version of the Soil and Water Assessment Tool (SWAT) model was cho-
sen to link and route CPY transport in the three focus watersheds. SWAT is a semi-
distributed model developed by the U.S. Department of Agriculture to predict effects
of land management practices on water, sediment and agricultural chemical yields in
large complex watersheds that have varying soils, land use, and management condi-
tions over long periods of time (Neitsch et al. 2010 ). Model components include
weather, surface runoff, return flow, percolation, evapo-transpiration (ET), transmis-
sion losses, pond and reservoir storage, crop growth and irrigation, groundwater flow,
reach routing, nutrient and pesticide loading, and water transfer. PRZM was used to
simulate CPY in runoff and erosion, because SWAT is unable to simulate losses of
CPY due to volatilization and runoff from furrow/flood irrigation tail-waters.
The Risk Assessment Tool to Evaluate Duration and Recovery (RADAR) was
used to evaluate SWAT model output. RADAR is a software program commissioned
by the Ecological Committee for FIFRA Risk Assessment Methods (ECOFRAM)
in the late 1990s to conduct evaluations of exposure events from time-series data
(ECOFRAM 1999 ) and to assess pulse-dose study designs. RADAR relies on the
concept of defining a threshold value (or trigger value) for the water column con-
centration believed by the user to be of some interest in interpreting exposure. The
software identifies each occurrence, in which CPY residues exceed this threshold
and defines such occasion as an “event.” Once an event has been triggered, the pro-
gram calculates the duration that residues continue to be above this level (event
duration) and then how long before the concentration again exceeds this threshold
value (post-event interval).
3.2
Chemical Input Parameter Values, Source, and Rationale
The chemical properties used in models used in this assessment are summarized in
Table 5 . Selection of chemical properties began by evaluating the properties used by
the U.S. Environmental Protection Agency for a dietary exposure assessment con-
ducted in 2011 (USEPA 2011 ). USEPA's assessment was designed to be a conserva-
tive screening evaluation of pesticide fate and transport. However, this USEPA
assessment did not adequately represent the behavior of CPY at the level of resolu-
tion and accuracy needed for the present assessment. Therefore, an expanded data-
base on environmental fate properties was assembled and reviewed to better
characterize relevant fate and transport processes.
Physicochemical properties . Available molecular weight, water solubility, and
vapor pressure values were used for other elements of this risk assessment as
needed (Mackay et al. 2014 ). PRZM simulates volatilization by using a dimension-
less expression of Henry's law constant. The value provided in Table 5 was obtained
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