For David J. Powers & Associates and West Coast Aggregates, Inc.
Santa Clara County, California

Questa was retained to peer review and assess hydrologic and water quality impacts associated with the EIR for the expansion of Lexington Quarry, located on the east side of the Santa Cruz Mountain Range. Questa analyzed and described the existing hydrologic and water quality setting, assessed potential impacts associated with the project, and recommended mitigations. Potential hydrology and water quality impacts addressed included:

• Physical hydrologic effects from changing the contributing drainage area of the quarry and associated storm water structures.
• Decreased water quality due to increased sediment input from runoff draining from the expanded mining area into nearby drainages.
• Adverse effects on Limekiln Creek from interruption of creek flow, or diversion of quarry area contributions to base flow.
• Decrease in the life span of Lexington Reservoir due to increased sediment loads.

Work included consultation with the Santa Clara Valley Water District (SCVWD) and Regional Water Quality Control Board.