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3.3.2 Alachlor and Metolachlor
3.3.2.1 Serial Batch Kinetic Tests
Serial batch sorption tests for alachlor and metolachlor were conducted to
determine an adequate mixing time to achieve equilibrium, and to obtain rate
data regarding reduction of alachlor and metolachlor. The foundry sands were
selected to provide a broad range of TOC (0.8% to 4.0%) and clay contents (0%
to 13%). Bottles containing identical contents (5g) were tumbled for various times
and concentration was measured at a designated sampling time.
Concentrations for alachlor and metolachlor during the serial batch kinetic
tests are shown in Fig. 3.4. The data are analyzed in Section 3.4.2.2. The rate of
sorption is highest at the beginning of the test, and decreases as the test
continues. The alachlor concentrations became stable at about 5 hr, whereas
approximately 24 hrs was required to reach equilibrium for metolachlor. Based on
the results of these tests, a mixing time of 24 hrs was used to ensure equilibrium
for alachlor and metolachlor.
3.3.2.2 Batch Sorption Tests
Batch sorption tests conducted with foundry sand and alachlor or
metolachlor were performed using 2-7 g of sorbent (i.e., foundry sand). The
concentration of sorbate (i.e., alachlor or metolachlor) was held constant. Other
aspects of the tests were the same as those used for TOE (see Sec. 3.3.1.1 ).