Water Department
The Monitor 1998
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Owens Lake Groundwater Evaluation Robert Harrington, Assistant Hydrologist In July 1998, the Los Angeles Department of Water and Power and the Great Basin Unified Air Pollution Control District signed a Memorandum of Agreement specifying a time-table for implementing dust abatement measures on the Owens Lake playa. The MOA requires that LADWP have 10 square miles of dust abatement measures in place by 2001, with incremental implementation after that. By 2006, LADWP must have attained federal air quality standards. The dust abatement measures identified as being feasible are seasonal shallow flooding, cultivation of salt grass, and spreading of gravel on the playa surface. The first two of these methods require large volumes of water, and LADWP has proposed using groundwater from beneath the Owens Lake to meet part of the water need. Because the Inyo/Los Angeles water agreement applies to any LADWP groundwater extraction in Inyo County, the Inyo County Water Department must evaluate the proposal and determine whether it complies with the agreement.
To conduct the evaluation, Inyo County and LADWP agreed to retain, at LADWP's expense, an independent consultant. The first phase of the evaluation comprises three tasks: (1) solicit input from the public regarding the environmental criteria by which groundwater pumping impacts should be judged, (2) evaluate LADWP's proposed near-term (1999-2001) groundwater pumping at Owens Lake, and (3) prepare a workplan for technical work to be done on the lake for a long-term evaluation of the resource. The execution of the work described in the workplan will be undertaken during a second phase of the evaluation. In September 1998, Camp Dresser & McKee was awarded the contract for the first phase of the evaluation. ICWD is administering the contract. CDM has sought public input by conducting a series of meetings and interviews, and has worked with ICWD, LADWP, and the public to develop standards and objectives for groundwater pumping. The standards and objectives recommended by the public include protection of non-LADWP wells; protection of springs, seeps, and other water-dependent habitat; and prevention of subsidence near buildings and other infrastructure. CDM will compile the public's recommended standards and objectives, and convey them to the Inyo/Los Angeles Standing Committee in summer 1999. CDM's work also includes evaluating LADWP's proposal for using water from APCD's wells for a one square mile dust mitigation prototype to be implemented in 1999-2001. Under LADWP's proposal, they will use about 1,400 acre-feet during 1999 and 2,700 acre-feet during 2000 and 2001. Monthly average groundwater production rates would peak at approximately 470 acre-feet per month during late summer. To evaluate the impacts of this initial pumping, CDM is revising an existing groundwater model that was developed by a team of scientists working for APCD. Modifications to the groundwater model include improving the representation of the hydrostratigraphy of the Owens Lake groundwater system, increasing the spatial resolution of the model, and improving the representation of evapotranspiration and spring flow. These modifications will improve the model's ability to predict the effect of the proposed pumping. ICWD, APCD, and LADWP have acted in an advisory and review capacity for the technical aspects of the evaluation. The evaluation will be completed in summer 1999. The long-term work plan will include recommendations for further work needed at Owens Lake to evaluate the groundwater resources available for LADWP's use in dust mitigation. Components of this work plan will include recommendations for further data collection and groundwater modeling necessary to evaluate the long-term availability of groundwater. The long-term workplan is scheduled to be finalized in late 1999. |
