2021-07-22_REVISION - M2010071 (6)

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6.4.7 Exhibit G - Water Information (1) The operation will affect groundwater systems, however through execution of the temporary substitute water supply plan, there will not be a net change to tributary groundwater flow to Boulder Creek. (2) (a) Surface water structures are shown in Exhibit C1, Pre-Mining Plan Map (b) The sand and gravel deposit to be mined is an alluvial aquifer tributary to Boulder Creek. (c) Water from dewatering operations is routed to sediment pond to allow for settling of suspended sediment. A stormwater management plan has been prepared for the site which identifies BMP's to prevent pollution to surface waters due to stormwater runoff. (3) Under full operation, the project will consume approximately 20 acre-ft/ year due to evaporative loss of exposed groundwater in dewatering trenches, water lost within the mined product and water consumed for dust control. (4) The replacement source for all depletions to Boulder Creek is fully consumable water rights owned by the City of Lafayette. (5) The applicant has applied for and received a NPDES Stormwater Discharge Permit. The permit number is COG501535 The groundwater Monitoring and Mitigation plan has been revised as follows, Step 1 - Establish Monitoring Well Grid and Baseline Ground Water Elevations CTL Thompson, Inc. had supervised the installation of 7 piezometers (4 up gradient and 3 down gradient from the proposed mining operations) within the City of Lafayette property surrounding the proposed mining operations. Piezometers 1 through 3 have been in service for several years and piezometers 4 through 7 were installed on July 1,9 and 16, 2009. The piezometers are at the locations shown on Exhibit F. Water level measurements were made at the time of drilling and several days after drilling. Since that time the City of Lafayette has continued monitoring of the piezometers. The measurements are attached as an appendix. From these measurements, we have established the following seasonal baseline ground water elevations, Winter Baseline Spring Baseline Summer Baseline Fall Baseline December 31 March 31 June 30 September 31 Piezometer Water Elevation Water Elevation Water Elevation Water Elevation 1 5037.9 5036.4 5039.3 5038.8 2 5036.2 5035.9 5036.7 5036.3 3 5030.4 5030.3 5033.7 5031.7 4 5062.6 5062.6 5064.8 5064.1 5 5060.7 5060.7 5061.9 5061.3 6 5044.2 5043.3 5045.9 5045.8 7 5039.1 5039.0 5041.5 5041.4