2007-12-19_REVISION - M1988112 (12)

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G.2 Irrigation Pipeline and Pond Design Implementation of this revised water management program will require construction of two irrigation water storage ponds in the West Pit, modification of the existing water supply pipeline to enable the transfer by gravity flow of irrigation water between the West Pit and the ranch, and modification to the center pivot irrigation system. The design and operation of these constructed facilities are described in detail in the following sections. Detailed construction drawings will be prepared prior to construction, and upon completion of construction, an as-built report documenting the constructed facilities will be submitted to DRMS. This report will consist of record drawings, a summary of construction quality control and quality assurance testing, and photographs of construction progress. G.2.1 Pond Sizing - Water Balance Calculations The primary design objective for the irrigation ponds is to ensure adequate storage for West Pit area water management during the non-irrigation period. Water balance calculations were completed to provide an estimate of storage requirements. The water balance calculations were completed using existing augmentation flow records, monthly discharge monitoring reports, water management system operational logs, and crop irrigation requirements. The analyses include the seasonally variable records of pumping rates from West Pit ground water wells (1317-5R, BF-4, and BF-3) and alluvial capture wells (M-32 and M-33) (Figure G.2-1). Inflow sources in the water balance model included the West Pit ground water, the alluvial ground water, and direct precipitation. Flows from the ground water wells in the West Pit and alluvial aquifer were calculated using available historical pumping records. The pumping records for the analyses cover the period from 2002 through 2005. The average annual flow from West Pit and alluvial well pumping during this period was 390 acre-feet. Precipitation inputs for the water balance model were calculated as direct precipitation to the irrigation ponds. All upland runoff will be routed around the irrigation ponds. An average annual precipitation of 15 inches was taken from climatic data for San Luis (Western Regional Climate Center; Battle Mountain Resources, Inc. 23 P:\Pmjmts\212-New i(SenLWs)\SmL=\Pe tAmendm t - West Pit Mnm®emeot\V5 Report @PDFAText\P-tAoeodmem_v5c.doo December 2007