Predicting the Fate of Imidacloprid in a Coastal Plain Setting Using VS2DT

Proceedings of the 1997 Georgia Water Resources Conference, March 20-22, 1997, Athens, Georgia.Imidacloprid has been shown to control pine tip moths (Rhyacionia spp.) in loblolly pine seedlings (Pinus taeda L.). We describe an imidacloprid dissipation study on a small watershed near Downs, Georgia. Field data are utilized to calibrate the computer model VS2DT (Variably Saturated 2- Dimensional Transport) that uses a fmite-difference approximation of the advection-dispersion equation to simulate contaminant transport through variably saturated porous media. The site is simulated in a vertical cross section (X-Z plane) of a treated watershed from the soil surface to the water table (approximately 60 ft) spanning 260 ft horizontally. The cross section is centered on an ephemeral stream which drains the watershed, but for symmetry reasons, only half (130 ft horizontal distance) of the cross section is modeled. Modeling results show that imidacloprid moves more rapidly through sandy soils than sandy clay loam soil material. No imidacloprid concentrations above the detection limit of 0.6 ppb are predicted for the lysimeters in the unsaturated zone or in groundwater.Sponsored and Organized by: U.S. Geological Survey, Georgia Department of Natural Resources, The University of Georgia, Georgia State University, Georgia Institute of TechnologyThis book was published by the Institute of Ecology, The University of Georgia, Athens, Georgia 30602 with partial funding provided by the U.S. Department of Interior, Geological Survey, through the Georgia Water Research Institutes Authorization Act of 1990 (P.L. 101-397). The views and statements advanced in this publication are solely those of the authors and do not represent official views or policies of the University of Georgia or the U.S. Geological Survey or the conference sponsors

Use of Mini-Sprinklers to Strip Trichloroethylene and Tetrachloroethylene from Contaminated Ground Water

Three low-volume mini-sprinklers were tested for their efficacy to strip trichloroethylene (TCE) and tetrachloroethylene (PCE) from water. Deionized water spiked with TCE and PCE as pumped for approximately 1 h at 0.19 to 0.21 MPa (28 to 30 lb in-2) through a mini-sprinkler supported on top of a 1.8-m-tall riser. Water was collected in collection vessels at 0.61 and 1.22 m above the ground on support columns that were spaced at 0.61-m intervals from the riser base, and samples were composited per height and distance from the riser. Overall, air-stripping reduced dissolved concentrations of TCE and PCE by 99.1 to 100 and 96.9 to 100%, respectively, from mean influent dissolved concentrations of 466 to 1675 μg L-1 TCE and 206 to 940 μg L-1, respectively, over a 1-h test period. Mini-sprinklers offer the advantages of (i) easy setup in series that can be used on practically any terrain; (ii) operation over a long period of time that does not threaten aquifer depletion; (iii) use in small or confined aquifers in which the capacity is too low to support large irrigation or purging systems; and (iv) use in forests in which the small, low-impact droplets of the mini-sprinklers do not damage bark and in which tress can help manage (via evapotranspiration) excess water waste