Addendum to the 1991 Environmental Impact Report: Water from the Owens Valley to Supply the Second Los Angeles Aqueduct 1970 to 1990, 1990 Onward

Addendum to the 1991 Environmental Impact Report: Water from the Owens Valley to Supply the Second Los Angeles Aqueduct 1970 to 1990, 1990 Onward

[Continued Project Title]: …Pursuant to a Long-Term Groundwater Management Plan for Replacement Wells 247 and 379 The City of Los Angeles Department of Water and Power (LADWP) and Inyo County reached a preliminary agreement on a joint long term groundwater management plan for the Owens Valley on August 1, 1989. Signed in October of 1991, the goal of the final Agreement between the County of Inyo and the City of Los Angeles and Its Department of Water and Power on a Long Term Groundwater Management Plan for the Owens Valley (Agreement) is to manage water resources within Inyo County to avoid certain described decreases and changes in vegetation and to cause no significant effect on the environment which cannot be acceptably mitigated while providing a reliable supply of water for export to Los Angeles and for use in Inyo County. The approved project, Water from the Owens Valley to Supply the Second Los Angeles Aqueduct 1970 to 1990, 1990 Onward, Pursuant to a Long-Term Groundwater Management Plan (1991 EIR, project), analyzed in the 1991 EIR consists of all water management practices and facilities that were implemented or constructed in Owens Valley to supply water to the second Los Angeles Aqueduct, together with the projects and water management practices contained in the Agreement for Owens Valley and Inyo County. LADWP is refining the 1991 EIR to include the replacement of two existing wells, well W247 with W247R and well W379 with W379R. Both replacement wells were described and analyzed in the 1991 EIR. The replacement wells are located in the immediate vicinity of and will have the same purpose and capacity the wells they are replacing. Well W247 was constructed in 1928 in the laws Wellfield to a depth of 495 feet below ground surface (bgs) to supply water for in-valley uses and the Los Angeles Aqueduct. The well casing is perforated from 28 to 470 feet-bgs. In recent years, W247 has been used primarily to supply water to the McNally Pasture Enhancement/Mitigation Project in the summer months if the vegetation monitoring Site L1 is in ON status. The capacity of W247 is 5.3 cubic feet per second (cfs), which has been unchanged as of recent operation in the summer of 2020. An exploratory borehole for W247R will be drilled to approximately 700 feet-bgs. The preliminary design of W247R with a screen interval from 350 to 700 feet-bgs. The final depth and screen zone of the replacement well will be determined after reviewing the lithologic and geophysical logs of the borehole. Model simulations of W247R operations result in less drawdown in the shallow aquifer than the existing W247, which minimizes any potential for impacts to vegetation. Production well W379 is among the three production wells located north of Big Pine. All three wells discharge water to Big Pine Canal for enhancement and mitigation (E&M) irrigation uses. Well W379 was constructed in 1986 to a depth of 410 feet below the ground surface (feet-bgs) and is screened from 200 to 400 feet-bgs. In recent years, W379 has been out of commission because of excessive sanding and damage to the screen. To minimize potential effects of operating the replacement well on vegetation depending on water from the shallow aquifer, W379R will be screened below the semi-confinement separating shallow and deep aquifers in the Big Pine area. An exploratory borehole for W379R will be drilled to approximately 700 feet-bgs. The preliminary design of W379R includes a screen interval from 350 to 700 feet-bgs. However, the final depth and screen zone of the replacement well will be determined after reviewing the lithologic and geophysical logs of the borehole. An Addendum has been prepared pursuant to the state CEQA Guidelines to provide additional detail concerning the project description for the Agreement since approval of the project and its associated EIR in October 1991. Based upon the analysis prepared for the refined project, as presented in Chapter 3 of the addendum, implementation of the refined project would not result in substantial changes requiring major revisions to the previously certified EIR. Further, the refined project would not result in any significant environmental impacts that have not already been addressed in the EIR, and no new mitigation measures are required. Since only minor changes are required to the EIR, and none of the conditions described in Public Resources Code Section 21166 or CEQA Guidelines Section 15162 requiring preparation of a subsequent EIR or ND have occurred, LADWP has determined that the preparation of an addendum to the 1991 EIR is the appropriate level of CEQA documentation.

Unincorporated area

Inyo

Unincorporated

Inyo