added to each sample. The samples were again

Field studies

shaken for 20 minutes, then returned to the dark.

Isotope ratios across the contaminated plume at LAAP

The samples selected for analysis were centri-

Four transects were drawn across the LAAP site

fuged for 45 minutes at 2000 rpm. The aqueous

(Fig. 1) between wells in the source region of the

TNT plume and wells along the leading edge of

phase was poured off, weighed, then transferred

the plume. Table 1 describes the specifics of each

to a brown glass jar. The aqueous phase was ana-

transect. Six 1-L samples were collected from each

lyzed by HPLC as described above to determine

of the six wells selected in April 1998 and then

the concentration of TNT and the 2-amino- and 4-

again in September 1998.

amino-dinitrotoluene reduction products. Three