The United States Geological Survey computer model Variably Saturated
Two Dimensional Transport (VS2DT) was modified to treat boundary condi
tions imposed by parallel subsurface drain tubes. The modified model w
as used to simulate groundwater flow and aldicarb transport in researc
h plots under conventional drainage, controlled drainage, and subirrig
ation. The reliability of the model was tested by comparing model pred
ictions with field measurements.