ARCHIVED REPORTS XR0009987 - Laserfiche WebLink

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contaminants after excavation work is complete Groundwater samples will be collected from the excavation preceding each dewatering and prior to backfill to ascertain dissolved contaminants presence Representative samples of the known contaminated soil will be collected from stockpile(s) that will be stored at property to east with water holding tanks or at Forward Landfill during characterizations for disposal since space is limited at the site for stockpiling These representative samples will allow contaminant mass removal to be estimated by Wright after the interim remediation work is complete Wright will also obtain additional samples for a bench scale bioremediation feasibility study if required under the RWD and RAP The samples would be provided to (Regenisis ORC) for evaluation As noted above, there are some limitations of using the excavation approach The presence of the aforementioned utility and dwellings will constrain/limit the ultimate size of the excavations and the excavation will likely be phased to address the problems Utilities will have to be temporarily disconnected and relocated, and the excavation will be limited in the near vicinity of the irrigation pipeline The trailers, water service and the irrigation pipeline will be a significant limitation in the area around MW-9 Westside Irrigation District (WSID) indicates the earliest possible time to allow excavation is several days after the pipeline is shut down and allowed to empty The irrigation water supply is to be turned off on or about October 31, 2003 The current schedule and the feasibility of excavation within feet of the pipeline in the summer months when the pipeline is full is not an option Wright believes that the removal of the suspected residual sources in the vicinity of MW- 3 and MW-9, and the area just southwest of MW-3 will remove the residuals that are interpreted to contribute to the long term presence of TPHG observed in these wells Given the requirement of site cleanup, this approach is both timely and cost effective in light of not using the initially selected insitu bioremediation approach Wright anticipates the following field approaches will occur, and be used during excavation • Monitoring wells MW-3 and MW-9 will be closed by pressure grouting prior to starting the excavation The wells will have to be reinstalled upon completion of the excavation as close as practicable in undisturbed soil near the excavations Wright would secure the necessary permits from PHSEHD to close the wells and construct new wells as described Wright would close the wells, perforin the excavation and have the wells reinstalled to meet the February 2004 Quarterly Monitoring for site monitoring Some adjustment may be required depending upon actual starting date of the excavation work after draining the irrigation line and weather in early to mid November 2003 • Excavated soil will be loaded directly into trucks for shipment to the stockpile Iocation off-site or the landfill since there is not room for surface treatment for contaminated soil stockpiling Page 4