vt VX X + vt 1.) Co C= 2 C=(erre + experfect) erfc (276) )( 2VDt 2VDt where C is the concentration at location x and time t Co is the influent concentration v is the velocity of the ground water D is the dispersion coefficient erfc() is the complementary error function Chloride was injected as a continuous step function source into a 1-D column 100 cm long at an average linear velocity of 10-3 cm/sec. The concentration in the effluent after 1800 seconds from the beginning of the test was 0.3 of the initial concentration. Use Goal Seek in Excel to find the dispersion coefficient D