~ ~ ~ PURPOSE ~ ~ ~ this subroutine calculates pesticides leached through each layer, pesticide transported with lateral subsurface flow, and pesticide transported with surface runoff
units: mm + (m^3/ton)(ton/m^3)mm = mm
compute volume of flow through the layer compute concentration in the flow calculate pesticide lost in surface runoff calculate pesticide lost in tile flow calculate pesticide lost in lateral flow - use surface runoff conc for first layer calculate pesticide leaching