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(Lccf---77)
<br /> CIVII RFsIOuRCES
<br /> locations upgradient of the Site. Furthermore, groundwater rise at the locations in the Town of Gilcrest was minimized to
<br /> 0.2 feet of rise or less.
<br /> Table 1: Base Model Com ared to Cell 2B S urry Wall with Miti ation
<br /> Well Base Modell Difference Cell IJK
<br /> PZ-01 4,712.3 4,709.9 -2.4 146,111,1
<br /> PZ-04 4,712.4 4,712.1 -0.3 136,119,1
<br /> PZ-09 4,725.4 1 4,723.7 -1.7 142,136,1
<br /> PZ-15 4,724.4 4,722.0 -2.4 153,136,1
<br /> PZ-20 4,737.8 4,738.8 1.0 162,133,1
<br /> PZ-25 4,733.1 4,733.3 0.2 162,115,1
<br /> PZ-27 4,741.2 4,742.7 1.5 148,122,1
<br /> BBA-MW4 4,740.3 4,740.5 0.2 148,122,1
<br /> BBA-MW11 4,736.9 4,736.9 0.0 148,122,1
<br /> BBA-MW17 4,734.4 4,734.4 0.0 166,164,1
<br /> BBA-MW18 4,737.3 4,737.4 0.1 148,122,1
<br /> Table 2 (below)compares the previous mitigated model run described in section 6.3.4.3 of the Groundwater Model
<br /> Report(Model 1)to the fully constructed Site with Cell 2B slurry wall and underdrain (Model 2). The groundwater at the
<br /> upgradient monitoring well locations rise slightly from the Model 1 run, on the order of 0.5 feet or less. PZ-15,
<br /> downgradient of Cell 2B, does see a drop in groundwater elevation from Model 1 of approximately 0.7 feet, 2.4 feet
<br /> below the Base Model run. Since the unnamed slough and the South Platte River are downgradient of the Cell 2B slurry
<br /> wall and there are no wells or structures between the river and the slurry wall,the additional drop in groundwater
<br /> elevation was not identified as needing mitigation.
<br /> Table 2: Original Mitigated Model Compared to Cell 2B Slurry Wall with Mitigation
<br /> Well Modell Model Difference Cell IJK
<br /> PZ-01 4,709.8 4,709.9 0.1 146,111,1
<br /> PZ-04 4,712.1 4,712.1 0.0 136,119,1
<br /> PZ-09 4,723.6 4,723.7 0.1 142,136,1
<br /> PZ-15 4,722.7 4,722.0 1 -0.7 153,136,1
<br /> PZ-20 4,738.5 4,738.8 0.3 162,133,1
<br /> PZ-25 4,732.9 4,733.3 0.4 162,115,1
<br /> PZ-27 4,742.7 4,742.7 0.0 148,122,1
<br /> BBA-MW4 4,740.5 4,740.5 0.0 148,122,1
<br /> BBA-MW11 4,736.9 4,736.9 0.0 148,122,1
<br /> BBA-MW17 4,734.4 4,734.4 0.0 166,164,1
<br /> BBA-MW18 4,737.3 4,737.4 0.1 148,122,1
<br /> In conclusion,the construction of the Cell 2B slurry wall will reduce the groundwater flow area between Cells 2 and 3
<br /> causing groundwater mounding in excess of the previously approved mitigation cutoff. The model demonstrated that the
<br /> addition of 960 feet of 12-inch slotted pipe to the southeast corner of Cell 2B can successfully mitigate this mounding.
<br /> The Cell 2B underdrain will be designed in conjunction with the Cell 2B slurry wall and will be constructed concurrently.
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