Lorelay is an environmental engineering PhD candidate working in the Tarpeh lab at Stanford University. Her research is centered around recovering valuable resources from wastewater and other pollution streams. She earned her undergraduate degree at San Diego State University, where her research focused on detecting river water contamination during storm events.

Education & Certifications

  • M.S., Stanford University, Civil and Environmental Engineering
  • B.S., San Diego State University, Civil, Construction, and Environmental Engineering

All Publications

  • Diurnal Variability of SARS-CoV-2 RNA Concentrations in Hourly Grab Samples of Wastewater Influent during Low COVID-19 Incidence. ACS ES&T water Mendoza Grijalva, L., Brown, B., Cauble, A., Tarpeh, W. A. 2022; 2 (11): 2125-33


    Wastewater-based epidemiology (WBE) has been widely deployed during the COVID-19 pandemic, but with limited evaluation of the utility of discrete sampling for large sewersheds and low COVID-19 incidence. In this study, SARS-CoV-2 RNA was measured in 72 consecutive hourly influent grab samples collected at a wastewater treatment plant serving nearly 500 000 residents when incidence was low (approximately 20 cases per 100 000). We characterized diurnal variability and relationships between SARS-CoV-2 RNA detection and physicochemical covariates [flow rate, total ammonia nitrogen (TAN), and total solids (TS)]. The highest detection rate observed was 82% during the first peak flow, which occurred in the early afternoon (14:00). Higher detection rates were also observed when sampling above median TAN concentrations (71%; p < 0.01; median = 40.26 mg of NH4/L). SARS-CoV-2 RNA concentrations were weakly correlated with flow rate (Kendall's τ = 0.16; p < 0.01), TAN (τ = 0.19; p < 0.05), and TS (τ = 0.18; p < 0.01), suggesting generally low RNA sewer discharges as expected at low incidence. Our results elucidated sensible adjustments to maximize detection rates, including using multiple gene targets, collecting duplicate samples, and sampling during higher flow and TAN discharges. Optimizing the lower-incidence bounds of WBE can help assess its suitability for verifying COVID-19 reemergence or eradication.

    View details for DOI 10.1021/acsestwater.2c00061

    View details for PubMedID 37552729

    View details for PubMedCentralID PMC9063989

  • Standardizing data reporting in the research community to enhance the utility of open data for SARS-CoV-2 wastewater surveillance ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY McClary-Gutierrez, J. S., Aanderud, Z. T., Al-faliti, M., Duvallet, C., Gonzalez, R., Guzman, J., Holm, R. H., Jahne, M. A., Kantor, R. S., Katsivelis, P., Kuhn, K., Langan, L. M., Mansfeldt, C., McLellan, S. L., Grijalva, L., Murnane, K. S., Naughton, C. C., Packman, A., Paraskevopoulos, S., Radniecki, T. S., Roman, F., Shrestha, A., Stadler, L. B., Steele, J. A., Swalla, B. M., Vikesland, P., Wartell, B., Wilusz, C. J., Wong, J., Boehm, A. B., Halden, R. U., Bibby, K., Vela, J. 2021

    View details for DOI 10.1039/d1ew00235j

    View details for Web of Science ID 000672875100001

  • SARS-CoV-2 RNA in Wastewater Settled Solids Is Associated with COVID-19 Cases in a Large Urban Sewershed. Environmental science & technology Graham, K. E., Loeb, S. K., Wolfe, M. K., Catoe, D., Sinnott-Armstrong, N., Kim, S., Yamahara, K. M., Sassoubre, L. M., Mendoza Grijalva, L. M., Roldan-Hernandez, L., Langenfeld, K., Wigginton, K. R., Boehm, A. B. 2020


    Wastewater-based epidemiology may be useful for informing public health response to viral diseases like COVID-19 caused by SARS-CoV-2. We quantified SARS-CoV-2 RNA in wastewater influent and primary settled solids in two wastewater treatment plants to inform the preanalytical and analytical approaches and to assess whether influent or solids harbored more viral targets. The primary settled solids samples resulted in higher SARS-CoV-2 detection frequencies than the corresponding influent samples. Likewise, SARS-CoV-2 RNA was more readily detected in solids using one-step digital droplet (dd)RT-PCR than with two-step RT-QPCR and two-step ddRT-PCR, likely owing to reduced inhibition with the one-step ddRT-PCR assay. We subsequently analyzed a longitudinal time series of 89 settled solids samples from a single plant for SARS-CoV-2 RNA as well as coronavirus recovery (bovine coronavirus) and fecal strength (pepper mild mottle virus) controls. SARS-CoV-2 RNA targets N1 and N2 concentrations correlated positively and significantly with COVID-19 clinically confirmed case counts in the sewershed. Together, the results demonstrate that measuring SARS-CoV-2 RNA concentrations in settled solids may be a more sensitive approach than measuring SARS-CoV-2 in influent.

    View details for DOI 10.1021/acs.est.0c06191

    View details for PubMedID 33283515

  • Fluorescence-based monitoring of anthropogenic pollutant inputs to an urban stream in Southern California, USA. The Science of the total environment Mendoza, L. M., Mladenov, N., Kinoshita, A. M., Pinongcos, F., Verbyla, M. E., Gersberg, R. 2020; 718: 137206


    Fluorescence spectroscopy has been increasingly used to detect sewage and other anthropogenic contaminants in surface waters. Despite progress in successfully detecting bacterial and sewage inputs to rivers over diverse spatial scales, the use of fluorescence-based in-situ sensors to track contaminant inputs during storm events and to discern bacterial contamination from background natural organic matter (NOM) fluorescence have received less attention. A portable, submersible fluorometer equipped with tryptophan (TRP)-like and humic-like fluorescence sensors was used to track inputs of untreated wastewater added to natural creek water in a laboratory sewage spill simulation. Significant, positive correlations were observed between TRP fluorescence, the TRP:humic ratio, percent wastewater, and Escherichia coli concentrations, indicating that both the TRP sensor and the TRP:humic ratio tracked wastewater inputs against the background creek water DOM fluorescence. The portable fluorometer was subsequently deployed in an urban creek during a storm in 2018. The peak in TRP fluorescence was found to increase with the rising limb of the hydrograph and followed similar temporal dynamics to that of caffeine and fecal indicator bacteria, which are chemical and biological markers of potential fecal pollution. Results from this study demonstrate that tracking of TRP fluorescence intensity and TRP:humic ratios, with turbidity correction of sensor outputs, may be an appropriate warning tool for rapid monitoring of sewage or other bacterial inputs to aquatic environments.

    View details for DOI 10.1016/j.scitotenv.2020.137206

    View details for PubMedID 32325614