SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

rewritten to correct inconsistencies with EPA guidance and to make better distinction between "no action, " "institutional controls" and "remedial alternatives. " The "no action" alternative means exactly that, i.e. , no action. The FS should not include the IRM in this alternative. Institutional controls are a type of action (albeit not a remedial action) and should therefore also not be included in the "no action" alternative. However, costs for monitoring the plume can be included under "no action. " "Institutional controls" currently included under "no action" should be a separate non-remedial-action alternative. Neither the 120 gpm IRM nor the 340 gpm IRM will address the OU-1 plume and therefore it is not clear why the FS is considering these as remedial alternatives (Alternatives 1 and 2) in the first phase. (It is understood that the current IRM will be incorporated into the alternatives which do address the entire plume. ) Text should be added to the alternatives which address all of OU-1 to explain how the IRM will be incorporated. • DDRW-Tracy might consider the following restructuring of alternatives: 1 No Action 2 Institutional Controls 3 930 gpm, air stripping, IRM, injection 4 930 gpm, carbon, IRM, injection 5 930 gpm, UV/Ox, IRM-wells, injection 6 930 gpm, air stripping, IRM, injection, bio- remediation 7 930 gpm, bioreactor, injection Note in the text that the flow rates for all the alternatives are estimates and that exact rates will be set during design. 43 . Section 3 . 2 . 1. 1, Page 3-4 Why is the maximum influent concentration limited to 500 µg/L? See comment 12 . 44 . Section 3 . 2 . 3 . 0, Page 3-10 Treatment of air by vapor-phase groundwater-activated carbon (GAC) is not described as part of the first alternative. However, both Table 3 . 3-1 and Section 3 . 2 . 3 .4 include vapor- phase GAC as part of the alternative. 11