2022-07-22_REVISION - M2010071

• Permit No: M2010071
• IBM Index Class Name: Revision
• Doc Date: 7/22/2022
• Doc Name Note: Cover Letter
• Doc Name: Adequacy Review Response
• From: City of Lafayette
• To: DRMS
• Type & Sequence: TR1
• Media Type: D
• Archive: No

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 C 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 C Pre-Mine Plan Map and the drill logs are given in Exhibit G Attachment A.
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;

Piezometer
Winter Baseline
December 31

Water Elevation

Spring Baseline
March 31

Water Elevation

Summer Baseline
June 30

Water Elevation
Fall Baseline
September 31

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