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6.4 COLUMN TESTS
6.4.1 Alachlor
Experimental conditions for the column tests conducted with alachlor are
summarized in Table 6.4. Five foundry sands were used (1, 2, 4, 5, and 12) that
had a broad range of TOC, clay content, and iron content. Tests were also
conducted with Sands 1 and 5 with admixtures of Peerless iron to evaluate how
elevated iron content affects reactivity of the foundry sand. An additional five
comparative tests were conducted using a mixture of Peerless iron and silica
sand. Influent concentrations ranging from 34 mg/L to 53 mg/L were used.
The total iron contents for Sand 1 and Sand 12 were 2.8% and 11.3%,
respectively. However, the zero-valent iron contents for these two sands, as
measured by magnetic separation, are 1.0% and 10%. The zero-valent iron
contents were used to analyze the data for column tests for Sands 1 and 12. For
Sands 2, 4, and 5, the zero-valent iron contents were similar to the total iron
contents. Thus, the total iron contents were used for these sands when analyzing
the data from the column tests.
Dispersion coefficients, dispersivities, partition coefficients, and rate
constants from the column tests are summarized in Table 6.5. The degradation
of alachlor was confirmed by the presence of acetyl alachlor in the effluent. The
mass balances ranged between 97 (Sand 4) and 101% (Sand 2).