Attenuation Rates for PRD-1 and MS2 During Recharge with Artificial Recharge with Recycled Water at a Research Basin in Los Angeles County

By Robert Anders¹, William A. Yanko², Roy A. Schroeder¹, and James L. Jackson^2
1U.S. Geological Survey, 5735 Kearny Villa Road, Suite O, San Diego, CA 92123
²County Sanitation Districts of Los Angeles County, 1965 Workman Mill Road, Whittier, CA 90601

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Abstract

Recharge experiments with recycled water conducted at a small research basin constructed adjacent to a large recharge facility in the Montebello Forebay of Los Angeles County, California indicated that bacteria can move through the soil with the percolating recycled water. These conclusions formed the basis for two field-scale tracer experiments using bacterial viruses (bacteriophage) PRD-1 and MS2 as surrogates for human viruses and bromide as a conservative tracer, to estimate virus attenuation rates under actual recharge conditions.  Extensive data on the ratios of bacteriophage to bromide during the second experiment were obtained for samples collected from the research basin itself and from depths of 1, 2, 3, 5, and 10 ft below the floor of the research basin. Regression analysis of the ratios collected during the 9-day experiment indicated an attenuation rate for MS2 of approximately 1.1 log units over 10 ft, and an attenuation rate for PRD-1 of approximately 1.7 log units over 10 ft.  Using the observed attenuation rates, extrapolation suggests that a 7-log removal of bacteriophage should occur within less than 100 ft of travel through the subsurface.

In George R. Aiken and Eve L. Kuniansky, editors, 2002, U.S. Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2-4, 2002: USGS Open-File Report 02-89

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