Agenda - Council - 02/09/2010 - Laserfiche WebLink

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AECOM Mr, Jankowski December 8, 2008 depending on where excavation activities are occurring. A removable cover, or gate, will be installed at each outlet to direct flow. • Excavate shallow sumps in the East Swale and West inlet to intercept storm water flow. Water that accumulates in the sumps will be pumped to and discharged on BNSF property using the piping system estabEished for Pond Water management activities. Excavated Sail Dewatering Some of the pond base soils will likely be saturated after the Pond Water has been removed and wi{I require dewatering before transport to the landfill. Saturated soils will be stockpiled adjacent to the areas being excavated to allow water to .drain from the soil. Water draining from the excavated soil will be contained or managed to minimize the potential for further impacts at the site. The excavated soil dewatering activities will be conducted within the pond and in areas where arsenic impacted materials have yet to be addressed. Depending on the actual soil conditions encountered and the precipitation events that occur during pond excavation activities, it is possible that little or no drainage water will require treatment at the end of the pond excavation program. For planning purposes, it is assumed that all drainage water accumulated throughout the excavation program will be managed on-Site. Based on this assumption, the following generalized plan will be implemented to manage excavation drainage water: • Begin Pond Water removal activities approximately two weeks before excavating pond base materials. Use sumps and shallow trenches to dewater the materials in-place to the extent practical • After the Pond Water has been removed, utilize storm water runoff collection points and berms constructed in the pond to limit re-introduction of water info pond base materials. • Stockpile pond base soil on impacted soil that will be excavated later and use temporary berms to control and prevent drainage water from flowing into areas where excavation is complete. Managing drainage water in this manner will allow dewatering fluids to evaporate or infiltrate into non-saturated materials that will be excavated later. • Some saturated pond base materials may need to be addressed when excavation activities are nearly complete. The saturated pond base materials that cannot be managed in the. pond will be temporarily staged on BNSF R.O.W. (i.e., R-Area 1) for drying until saturation levels are reduced to acceptable levels. Only areas on BNSF property adjacent to the pond and where arsenic- impacted soil is planned for removal will be used for drying pond base materials. In the event that all accumulated drainage water cannot be managed during the excavation program, residual water would be discharged to the publicly owned treatment works (POTW) utilizing the sanitary sewer manhole located south of the BNSF R.O.W. and west of Ramsey Boulevard (see Figure 3), contingent. upon receiving the necessary City approval. Decontamination water generated during implementation of the response action would also be managed in this manner. All collected water requiring treatment at the POTW will be sampled prior to discharge for comparison to the POTW acceptance criteria. Temporary storage may be required during certain phases of the water management plan discussed in this letter, depending on actual conditions encountered in the field. Temporary storage options that will be available, should they be needed, include polyvinyl chloride (PVC) holding tanks up to 1,500 gallons, or larger frac tanks that can be delivered to the Site. It is the intent of the RAPs to conduct water management activities at the Site without the need for temporary containment. N:ProjectW/BNSF/2000/2983 Ramsey/Correspondence/Other/09 Dec City Ltr