MATERIAL PHYSICAL HARM ANALYSIS FOR A GROUNDWATER AUGMENTATION PROJECT, SOUTHERN LOS ANGELES COUNTY, CALIFORNIA

The Water Replenishment District of Southern California (WRD) manages groundwater for nearly four million residents in 43 cities of southern Los Angeles County. The 420 square mile service area uses about 220,000 acre-feet per year (AFY) of groundwater, which equates to over 40 percent of the total demand for water. WRD ensures that a reliable supply of high quality groundwater is available through its clean water projects, water supply programs, and effective management principles.

A Material Physical Harm Analysis (MPH) was performed for a groundwater augmentation project where advanced treated recycled water would be injected into local groundwater aquifers and later removed with the installation of at least two large water supply wellfields in southern Los Angeles County, California. The groundwater basin is adjudicated and as condition of the legal judgement the parties proposing a project must evaluate the potential for MPH. The criteria that must be considered include (1) degradation of water quality, (2) liquefaction, and (3) land subsidence. The talk will describe the modeling and groundwater quality analysis conducted for the MPH assessment. A recently updated groundwater model developed by the USGS was used to assess risk of liquefaction and subsidence due to excessive drawups/drawdowns. Readily available data from EPA, DTSC, and RWQCB was used to evaluate water quality impacts. The talk will also discuss how uncertainties and data-gaps were addressed to support resilient decision-making for the project.