Treating Emerging Contaminants in Drinking Water: LADWP’s Planning and Design

Authors:

  • Nicole Blute - Hazen and Sawyer

Historically, up to a quarter of the Los Angeles water supply has been provided by groundwater. This has decreased due to contamination mainly from industrial practices of the past. The Mayor’s city sustainability plan targets 50% locally sourced water by 2035.

LADWP has plans to expand basin groundwater pumping by ~70 mgd over the next 30 years.

Significant industrial pollution, as shown by the example here of the TCE and PCE plumes, is impacting the San Fernando production wells. The City's groundwater supply goals require treatment upgrades in multiple wellfields.

The majority of treatment upgrades are anticipated within 5 years.

North Hollywood West will be the first treatment facility to be updated. Both 1,4-Dioxane and VOC plumes were found.

Remedial Action Objectives are goals that protect human health and the environment. RAOs were developed to address the groundwater entering the NHW groundwater production wells, the potential contaminants in the groundwater, the use of the groundwater for domestic purposes, and the potential exposure routes including ingestion, inhalation and dermal contact with groundwater containing contaminant concentrations exceeding numerical or risk-based cleanup goals.

After an analysis of potential solutions, groundwater pump and treat was selected as preferred alternative.

Regional groundwater flow modelling with the San Fernando Basin model (MODFLOW model) with particle tracking was used to evaluate 1,4-dioxane plume capture and identify the remediation wells that would require treatment, and secondary wells that could potentially require treatment.

Selective pumping is predicted to concentrate the plume within 3 wells over 15 years.

The results of the engineering evaluation has been the design of an innovative UV advanced oxidation treatment facility with granular activated carbon for peroxide quenching that will treat the primary contaminant of concern (i.e., 1,4-dioxane), as well as VOCs.

The City of Los Angeles encompasses an area of 465 square miles with a population of nearly 4 million residents. Local groundwater provides approximately 11% of the City’s total water supply and the City has a goal of achieving 50% of the water sources supply from the San Fernando Basin by 2035.

Many Los Angeles Department of Water and Power (LADWP) groundwater production wells in the San Fernando Basin are impacted by contamination caused by various commercial and industrial activities. Without comprehensive containment and groundwater basin remediation, the City will significantly lose the ability to use this valuable local resource within the next decade. To improve groundwater clean-up and increase the supply of high quality renewable water resources for the City, LADWP is undertaking a program to evaluate and implement groundwater treatment throughout the SFB. This 10 year program of up to $600M will greatly improve local renewable water supplies for the City.

Design of treatment for the first wellfield is underway and illustrates the complexity of trying to implement treatment of the various contamination plumes given the extensive pumping activity within the basin. Challenges have included evaluation of contaminants of concern, treatment alternatives, and facility sizing given project uncertainties. Extensive modeling and bench-scale testing have been completed to reduce the potential uncertainties and improve the treatment design criteria. The results of the engineering evaluation has been the design of an innovative UV advanced oxidation treatment facility with granular activated carbon for peroxide quenching that will treat the primary contaminant of concern (i.e., 1,4-dioxane), as well as VOCs.

For more information, please contact the author at nblute@hazenandsawyer.com.

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