SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Ms Julie Raining - 2 - . 20 February 2002- Georgia-Pacific Corporation Based on the results of the feasibility study,the Report contains recommendations for: the performance of an air/ozone-pulse sparging pilot study in groundwater in Unit 2; the abandonment of an extraction well(RW-1) and a monitoring well (BC-12), considered potential cross-contamination conduits from Unit 2 to Unit 3; and the installation of an additional up-gradient well to further define the chloroform plume. Our comments on the report are presented below. General Comments 1. The data provided in the report indicate that further investigation activities will be required to define the up-gradient, down-gradient, and lateral extent of the plume. As recommended by the report, a monitoring well, installed south of the basin will provide up-gradient data for Unit 2. Groundwater collected from wells BC-16, and BC-20 contain chloroform concentrations which exceed the current water quality objective (WQO) of 1.1 µg/1 based on the California Environmental Protection Agency(Cal/EPA) cancer potency factor. Therefore,the down- and cross-gradient extent of the plume in Unit 2 have not been adequately defined. Previously, Central Valley Regional Water Quality Board (Board) staff agreed to defer the down-gradient definition of the plume for approximately 2 years following application of a remedial effort. The schedule for future investigations to define the down-gradient and lateral extent of the plume may proceed in accordance with this agreement. 2. The lack of chloroform detections in groundwater samples collected from Unit 3, at the source area, was interpreted as an indication that chloroform contamination to Unit 3 maybe attributable to cross-contamination between Units 2 and 3 at monitoring well BC-12 and potentially at RW-1. Abandonment of these two wells was proposed to mitigate this problem. Elevated concentrations of chloroform are typically detected in BC-12. Therefore, a replacement Unit-2 well, installed in the approximate location and screened at a comparable depth in Unit-2 will be required if BC-12 is abandoned. Installation of the replacement well must be performed within a period of time that will permit regularly scheduled semi-annual sampling to proceed at this location. hi addition, following abandonment of BC-12, monitoring results of BC-13 will be evaluated for two monitoring periods to determine whether abandonment activities eliminated the source of contamination to Unit-3. The data will then be reviewed to determine whether further investigation of the extent of contamination to Unit-3, down-gradient of the source area, is warranted. 3. Of the remedial alternatives presented in the report for the remediation of chloroform in groundwater at this site, pulsed air sparging with ozone injection appears to be the most feasible method. We are concerned however,that the analysis of the in-situ remediation methods presented in the Report did not include a cost evaluation. Therefore,we request that a cost analysis of each method, for treatment from startup to closure,be submitted as an addendum to the Report. In addition,implementation of a selected method will depend on Board approval of a Workplan. Specific Comment 1. Comments provided in Table 1 indicate that the disposition of monitoring well BC-1 is presently unknown. Therefore, the scope of the Workplan should also include provisions for determination of the status of and, if necessary, abandonment of monitoring well BC-1.By 25 March 2002 please submit a letter that explains the status of BC-1 or a Workplan to abandon the well.