SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

EPA Comments Draft Remedial Action Documents, SWMU 6, 20, and 27 Small Excavations and SWMU 4 Wet Season Controls DDJC-Tracy, February 1999 Remedial Action Work Plan 1. Section 1.3.4, SWMU 4 - Wet Season Controls, page 1-5 and 1-6 This section explains that DDJC-Tracy is planning to submit an Explanation of Significant Differences (ESD) to document why SWMU 4 sediments do not pose an ecological threat and why excavation of these sediments is unnecessary. This section further explains that a sediment trap at the northern inlet (required in the ROD) may not be necessary based on the anticipated effectiveness of the planned outlet structure. If DDJC-Tracy believes that a sediment trap in unnecessary, this will also need to be addressed and explained in an ESD. The text of Section 1.3.4 should be revised to reflect this understanding. 2. Section 4.1, SWMU 6 Remedial Activities, page 4-1 To maintain consistency with Section 4.3.1.5 of the previous Remedial Design Work Plan (describing the data collection plan for SWMU 6) , Section 4.1 of the Remedial Action Work Plan should explain why data gaps will not be filled prior to construction and what impact this may have on achieving Data Quality Objectives. 3. Section 4.9, Excavation, page 4-5 As discussed during the March 3, 1999 technical meeting at Radian's Sacramento office, there was a stated concern that excavation may occur when the groundwater table is relatively high. This would increase the potential for leaving behind a greater volume of soil at the bottom of each excavation pit which is above the cleanup levels. DDJC-Tracy should evaluate the feasibility of dewatering each excavation area and/or excavating the last few feet "in the wet" in order to maximize the volume of contaminated soil removed from the small excavation sites. The results of this feasibility analysis and DDJC-Tracy's intended approach for dealing with a high water table should be included in Section 4.9. 1