Tid tech comments re sed

Page 1

March 15, 2017

MEMORANDUM To:

Art Godwin, Turlock Irrigation District

From:

Gus Yates, Senior Hydrologist

Re:

San Joaquin River Flows and South Delta Water Quality Substitute Environmental Document—Comments on Groundwater Impact Analysis for the Turlock Subbasin

The Substitute Environmental Document (SED) for the Lower San Joaquin River (LSJR) flow program greatly underestimates the impact of reduced water deliveries to Turlock Irrigation District (TID) on groundwater levels. This was the result of inappropriate averaging of impacts over a large area and unrealistic assumptions regarding future increases in groundwater pumping in response to decreased surface water deliveries. In addition, the SED summarily dismisses concerns regarding the economic impacts of groundwater declines by asserting that issues related to groundwater imbalance will be solved at a future date by the Sustainable Groundwater Management Act (SGMA). However, even a cursory analysis of local water resources conditions indicates that SGMA would not be able to offset future increases in groundwater pumping with increased recharge because nearly all potential sources of water for replenishment are themselves tributary to the Tuolumne, Merced and San Joaquin Rivers. Those sources could not be developed for supplemental groundwater recharge without decreasing river flows and exacerbating the very problem the LSJR flow program is attempting to solve. The inevitable result of reduced water deliveries to TID at the magnitudes contemplated in the LSJR flow program is fallowing of substantial amounts of cropland with significant associated economic impacts. These major comments are substantiated below, followed by a section containing additional comments on specific technical and interpretive deficiencies of the SED.

COMMENT 1: THE SED UNDERESTIMATES GROUNDWATER IMPACTS BY AVERAGING THEM OVER TOO LARGE AN AREA. The SED incorrectly asserts that evaluation of impacts at a geographic scale smaller than whole subbasins is infeasible: “The impacts of the LSJR alternatives on groundwater elevations, aquifer storage, and risk of subsidence cannot be determined with certainty because groundwater conditions vary within each aquifer subbasin and water users would have varied responses to reduced surface water deliveries.” (page 9-2)


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