Fig. 7. Effects of chemical amendments on 1 M HCl extractable Fe(II)/Fe(III) (Day 48) and soluble S(–II)/SO₄ ratios (Day 56) for all Hanford and Imperial soil suspensions. Method detection limit (MDL) for S(–II)/SO₄^2– ratio is 0.05. Note missing values for Imperial Valley, MnO₂ amendment, Day 48.