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ATTACHMENT B <br /> MODIFICATIONS <br /> Washington Scientific II Site <br /> MPCA Project Number VP 10021 <br /> 1. -The Report presents a conceptual plan for installing one additional deep ground water <br /> monitoring well along the southern WSI property boundary. Rather than one sentinel well, <br /> the MPCA shall require at a minimum two additional sentinel wells. The construction and <br /> location of these wells shall be provided to the MPCA staff for review and approval prior to <br /> installation. <br /> 2. The conceptual plan presented in the Report recommends shutting the ground water pump- <br /> out system off and installation of sentinel well(s). Prior to shutting the ground-water pump- <br /> out system off,the proposed sentinel wells shall be installed, and a revised ground water <br /> monitoring plan shall be submitted to the MPCA for review and approval. The MPCA staff <br /> recommends that this revised ground water monitoring plan include a contingency plan for <br /> response actions to be taken in the event the ground water plume is found to be migrating <br /> beyond an acceptable distance of its current location. <br /> 3. Please note, in advance,that as part of the revised ground water monitoring plan noted above, <br /> the ground water monitoring frequency shall need to be modified to at least quarterly rather <br /> than the current semi-annual frequency,during the year following shutting off the ground <br /> water pump-out system. Recommendations for modifying this monitoring frequency may be <br /> presented as part of the annual ground water monitoring report. <br /> 4. Please note the system should not be dismantled, but only shut off during the proposed initial <br /> monitoring evaluation of the pump-out shut-down. <br /> Page 1 of I <br />