Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
route of water infiltration into soil, to a large extent, determine pesticide concentrations and
losses in surface runoff. The timing of the rainfall after application also would have an effect.
Rainfall interacts with pesticides at a shallow soil depth (¼ to ½ inch), which is called the mixing
zone (Baker and Miller 1999). The pesticide/water mixture in the mixing zone would tend to
leach down into the soil or runoff depending upon how quickly the soil surface becomes
saturated and how rapidly water can infiltrate into the soil. Leaching would decrease the amount
of pesticide available near the soil surface (mixing zone) to runoff during the initial rainfall event
following application and subsequent rainfall events.
• Terrain slope would affect the potential for surface runoff and the intensity of runoff. Steeper
slopes would have greater potential for runoff following a rainfall event. In contrast, soils that
are relatively flat would have little potential for runoff, except during intense rainfall events. In
addition, soils in lower areas would be more susceptible to leaching as a result of receiving
excessive water from surrounding higher elevations.
• Depth to groundwater would be an important factor affecting the potential for pesticides to leach
into groundwater. If the distance from the soil surface to the top of the water table is shallow,
pesticides would have less distance to travel to reach groundwater. Shallower water tables that
persist for longer periods would be more likely to experience groundwater contamination. Soil
survey reports are available for individual counties. These reports provide data in tabular format
regarding the water table depths and the months during which it is persists. In some situations, a
hard pan exists above the water table that would prevent pesticide contamination from leaching.
7.5 Determining Effects to Air Quality
Pesticides may volatilize from soil and plant surfaces and move from the treated area into the
atmosphere. The potential for a pesticide to volatilize is determined by the pesticide’s vapor pressure
which would be affected by temperature, sorption, soil moisture, and the pesticide’s water solubility.
Vapor pressure is often expressed in mm Hg. To make these numbers easier to compare, vapor
pressure may be expressed in exponent form (I x 10 -7 ), where I represents a vapor pressure index. In
general, pesticides with I1,000 would have a high potential to volatilize (Oregon State University 1996). Vapor pressure
values for pesticides are usually available in the pesticide product MSDS or the USDA Agricultural
Research Service (ARS) pesticide database.
7.6 Preparing a Chemical Profile
The following instructions would be used by Service personnel to complete Chemical Profiles for
pesticides. Specifically, profiles would be prepared for pesticide active ingredients (e.g., glyphosate,
imazapic) that would be contained in one or more trade name products that are registered and labeled
with USEPA. All information fields under each category (e.g., Toxicological Endpoints,
Environmental Fate) would be completed for a Chemical Profile. If no information is available for a
specific field, then “No data is available in references” would be recorded in the profile. Available
scientific information would be used to complete Chemical Profiles. Each entry of scientific
information would be shown with applicable references.
Completed Chemical Profiles would provide a structured decision-making process utilizing
quantitative assessment/screening tools with threshold values (where appropriate) that would be used
to evaluate potential biological and other environmental effects to refuge resources. For ecological
risk assessments presented in these profiles, the “worst-case scenario” would be evaluated to
G-34 Appendix G. Integrated Pest Management