From 1994, the City of Los Angeles applied Class B biosolids from the Hyperion Treatment Plant (HTP) at its Green Acres Farm in Kern County, California. In response to local regulations, since October 2002 HTP has produced Exceptional Quality (EQ) biosolids by thermophilic anaerobic
digestion. EQ biosolids comply with the most stringent limits in the U.S. EPA 40 CFR Part 503 Rule for pollutants (503.13), pathogen reduction (503.32) and vector attraction reduction (503.33) and are considered to be as safe as any other fertilizer. In a further effort to protect the public
and the environment, the City of Los Angeles conducted an evaluation of the potential impact of biosolids land application on the groundwater quality. A literature review of the fate and mobility in soil of biosolids constituents indicated a potential for the leaching of nitrate from biosolids.
However, this potential is minimal because of the Part 503 Biosolids Rule requirement of land application of biosolids at nitrogen-based agronomic rates. Leaching of other biosolids constituents to groundwater is relatively insignificant because of immobilization in soil (phosphorus, heavy
metals, some organic pollutants), biodegradation or volatilization to the atmosphere (some organic pollutants), or inactivation (pathogens). This was confirmed by a review of groundwater monitoring data from several land application sites in the USA with over 10 years of biosolids application.
Elevated nitrate concentrations in groundwater were sometimes observed, however, an unequivocal correlation between nitrate in groundwater and the land application of biosolids could not be established. The presence of other biosolids constituents in groundwater has never been reported. Groundwater
monitoring at the Green Acres Farm in Kern County over 1990-2002 did not indicate any effect of biosolids land application on the groundwater quality. This can possibly be attributed to a combination of two factors: a) low concentrations of pollutants in HTP biosolids; b) limitation of the
biosolids application rate to the agronomic rate as calculated from the nitrogen needs of the crops cultured on the Green Acres Farm. Overall, this study confirms the findings of the 2002 reviews of the Part 503 Biosolids Rule by the National Research Council that there is no scientific evidence
that the Part 503 Biosolids Rule has failed to protect public health. However, additional scientific work has been recommended.
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