PERMFILE138823

• Permit No: M2006003
• IBM Index Class Name: Permit File
• Doc Date: 4/28/2006
• Doc Name: Groundwater Reports
• From: Civil Resources
• To: DMG
• Media Type: D
• Archive: No

Mining activities are presently ongoing ai the Site directly between the Parker Property and Dersham Property and at the
Brighton Pit directly east of the Site as seen in Figure 7. An active settling pond is located as shown and a perimeter
bentonite-soil slurry wall has been constructed around the Brighton Pit. The aggregate has been removed from the
Brighton Pit and activities in the middle of the Site consist of dewatering and mining. To the south of the Site, Aggregate
Industries' Tucson Pit has installed a perimeter slurry wall and this site is now moving towards reclamation as observed
during a site visit. Another gravel mine to the west of Tucson Road just south of WCR 2 is actively dewatering (no slurry
wall has been constructed) and through this dewatering, mitigation of a Sakata Farms irrigation well is occurring. The
mitigation consists of the dewatering water being conveyed to the north side of WCR 2 through a pipe to a small 2-3 foot
deep holding pond where water percolates back to the ground to create a mounded groundwater table. These Site
conditions and surrounding conditions were all observed during a Site visit and through discussions with the Brighton Pit
manager. The existing conditions discussed above are reflected in the model in order to calibrate to the most current
and accurate Site conditions.
Figure 7 shows the modeled groundwater contours. Table 7 below reports the steady-state modeled water levels and
the measured water levels ai the Site. Figure 6a shows a graph of the location versus site groundwater level. Overall,
the model matched the existing groundwater gradient to a good degree of accuracy.
Table 7
Measured and Modeled Site Groundwater Levels

Well
Observed
Modeled Difference
fl
MW01 4929. 32 4928. 61 0.71
MW02 4933. 35 4933. 56 -0.21
MW03 4933. 85 4933. 71 0.14
MW04 4935. 81 4935. 36 0.45
MW05 4933. 38 4933. 86 -0.48
MW06 4938. 05 4938 .01 -0.56
Notes:
1.Observed values are average measured water levels from the
2005 and January -March 2006.
4.1.1 Baseline Conditions
A modeling run was performed considering a "Baseline Condition" in order to compare the changed groundwater levels
to a more representative case than the existing conditions. The existing conditions case was modeled in order to
calibrate the model to known water levels as described above in Section 4.1. The baseline condition was run using the
same parameters as the existing conditions and removing the active dewatering occurring on the parcel between the
Parker Site and Dersham Site and removing the ongoing dewatering and recharge ai the gravel pit to the southwest.
The Brighton Pit slurry wall remained as well as the Tucson Pit slurry wall. The water levels during the baseline
simulations were used to compare mining phases and most importantly are a more representative comparison to the
reclamation water levels because the existing condition takes into account too many stresses on the system.
4.2 Mining Simulation
Mining conditions were modeled to show the potential impacts that dewatering could have on surrounding wells. The
mining conditions model was run to match the proposed mining phases as presented in Table 8 and Figure 8. A model
run was done for each phase of mining to evaluate the effects of dewatering. Constant head nodes approximately equal
to the bedrock elevation within the mined area were applied to each phase to reflect dewatering. Surrounding ponds and
Groundwater Model Report -Hall-Irvin Parker-Dersham Site - 7 • April 2006