Mill Valley, CA, United States
Mill Valley, CA, United States

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Wright R.H.,AMEC Environment and Infrastructure Inc. | Hall N.T.,107 Denio Drive | Hanson K.L.,AMEC Environment and Infrastructure Inc. | Sharp W.D.,Berkeley Geochronology Center | And 5 more authors.
Environmental and Engineering Geoscience | Year: 2014

A multifaceted investigation of the western portion of the Mesquite Regional Landfill (MRL) site and vicinity (study area), located in the desert of southeastern Imperial County, California, included evaluation of slip geometry and activity of a fault located within the boundaries of the proposed landfill. Municipal waste will be placed on the southwest margin of the Chocolate Mountains on a gently southwest-sloping bajada consisting of seven laterally coalescing Quaternary alluvial fan units capped with variably developed desert pavement surfaces. Q1, the oldest, is estimated to be of early to middle Pleistocene age; Q7, the youngest, consists of historical and Holocene channel and flood deposits. Numerical ages of two intermediate units were calibrated using uranium-series (230Th/U) dating of pedogenic carbonate coatings on gravel clasts. The dates indicate minimum depositional ages of 106.2 ± 3.3 ka for Unit Q3 and 142.9 ± 6.1 ka for Unit Q2. A trench located over a buried step in crystalline basement exposed a near vertical, northwest-trending dextral fault with small (< 1 m) apparent vertical and horizontal separations cutting unit Q2. An extensive varnished desert pavement surface developed across overlying unit Q3 is undeformed across the projected trace of the fault. This observation and the uranium-series ages demonstrate that the minor fault was not active during the Holocene, a regulatory requirement for municipal landfills. The geomorphic expression, pedogenic development and numerical ages indicate that fan deposits and surfaces in the study area resemble alluvial fan sequences found elsewhere in the arid southwestern United States.

Saez J.A.,Loyola Marymount University | Harmon T.C.,University of California at Merced | Doshi S.,Loyola Marymount University | Guerrero F.,County Sanitation Districts of Los Angeles County
Water Science and Technology | Year: 2012

This work examines ammonia volatilization associated with agricultural irrigation employing recycled water. Effluent from a secondary wastewater treatment plant was applied using a center pivot irrigation system on a 12 ha agricultural site in Palmdale, California. Irrigation water was captured in shallow pans and ammonia concentrations were quantified in four seasonal events. The average ammonia loss ranged from 15 to 35% (averaging 22%) over 2-h periods. Temporal mass losses were well-fit using a first-order model. The resulting rate constants correlated primarily with temperature and secondarily with wind speed. The observed application rates and timing were projected over an entire irrigation season using meteorological time series data from the site, which yielded volatilization estimates of 0.03 to 0.09 metric tons NH 3-N/ha per year. These rates are consistent with average rates (0.04 to 0.08 MT NH 3-N/ha per year) based on 10 to 20 mg NH 3-N/L effluent concentrations and a 22% average removal. As less than 10% of the treated effluent in California is currently reused, there is potential for this source to increase, but the increase may be offset by a corresponding reduction in synthetic fertilizers usage. This point is a factor for consideration with respect to nutrient management using recycled water. © IWA Publishing 2012.

Baque R.H.,Ford Motor Company | Gilliam A.O.,Ford Motor Company | Robles L.D.,Ford Motor Company | Robles L.D.,Florida Hospital | And 2 more authors.
Water Research | Year: 2011

Currently, USEPA Method 1623 is the standard assay used for simultaneous detection of Giardia cysts and Cryptosporidium oocysts in various water matrices. However, the method is unable to distinguish between species, genotype, or to assess viability. Therefore, the objective of the present study was to address the shortcomings of USEPA Method 1623 by developing a novel molecular-based method that can assess viability of Giardia cysts in environmental waters and identify genotypes that pose a human health threat (assemblage groups A and B). Primers and TaqMan® probes were designed to target the beta-giardin gene in order to discriminate among species and assemblages. Viability was determined by detection of de-novo mRNA synthesis after heat induction. The beta-giardin primer/probe sets were able to detect and differentiate between Giardia lamblia assemblages A and B, and did not detect Giardia muris (mouse species) or G. lamblia assemblages C, D, E and F (non-human), with the exception of Probe A which did detect G. lamblia assemblage F DNA. Additionally, DNA or cDNA of other waterborne organisms were not detected, suggesting that the method is specific to Giardia assemblages. Assay applicability was demonstrated by detection of viable G. lamblia cysts in spiked (assemblage B) and unspiked (assemblage A and B) reclaimed water samples. © 2011.

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