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

Home

AECOM Mr. Jankowski December 8, 2008 Response action plans for R-Area 1 (R-Area 1 RAP) and for R-Area 2 (R-Area 2 RAP) were prepared by BNSF and submitted to the MPCA for review. Both plans received approval from the MPCA with modifications. As part of the approved plans, arsenic-impacted soil present within R-Area 1 and R-Area 2 will be excavated and transported off-site for disposal at a licensed landfill facility. The approximate excavation areas are illustrated on Figure 2 and will result in the removal. of approximately 5,700 cubic yards of arsenic-impacted materials (i.e., source area removal). As indicated on Figure 2, the base of a storm water retention pond on Dolphin property (pond base) is included in the source area removal program. No specialized permits have been obtained to excavate the pond base as it is our understanding that this storm water retention pond is not considered a designated wetland. The R-Area 2 RAP includes plans to restore the pond base for continued use as a storm. water retention pond. To facilitate implementation of the RAPs, certain water management controls need to be established at the Site. The following sections discuss the water. management activities proposed to support response actions at the Site. Water Management Water from three potential sources will require management during response actions to address arsenic-impacted pond base materials. The three potential sources are: • Pond Water -Approximately 1 to 3 feet of standing surface water (Pond Water) has been observed in the pond since it was constructed in 1999, which equates to approximately 100,000 to 300,000 gallons of standing water. • Storm Water Runoff- Paved parking areas on the Dolphin property and a paved parking area on the Anoka West Pet Hospital property drain into the pond at three inlets. During excavatian activities, storm water runoff will need to be intercepted and managed before it enters the pond. • Excavated Soil Dewatering -Some of the pond base materials may need to be dewatered before transport for off-site disposal. Arsenic-impacted water resulting from these activities may require management. Pond Water Laboratory analytical results for Pond Water samples collected annually indicate the Pond Water contains arsenic at very low concentrations. Table 1 presents the arsenic concentrations detected in the Pond Water over time. The Pond Water will be removed from the pond prior to initiating excavation activities to facilitate soil removal, loading, and transport activities. The water will be removed in a manner that minimizes disturbance of sediments and minimizes the concentration of suspended solids in the discharge. Figure 3 provides a generalized depiction of the facilities that will be used to support the Pond Water management activities at the Site. The Pond Water will be removed from the pond using electric powered pumps, or equivalent pumping methods, and discharged to a discharge area on BNSF R.O.W. north of the railroad tracks (see Figure 3). BNSF proposes to remove the Pond Water through implementation of the following steps: • Excavate a shallow sump (i.e., less than two feet deep) in the western portion of the pond, at the deepest point, and install a pump with protective screening to keep debris and suspended solids from fouling pumping operations. N:ProjectW/BNSF/2000/2983 Ramsey/Correspondence/Other/09 Dec City Ltr