Graduation Year

2025

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

James R. Mihelcic, Ph.D.

Co-Major Professor

Jeffrey Cunningham, Ph.D.

Committee Member

Katherine Alfredo, Ph.D.

Committee Member

Nancy Diaz-Elsayed, Ph.D.

Committee Member

Mahmooda Khaliq Pasha, Ph.D.

Keywords

community health, contamination, groundwater, pit toilet, well protection

Abstract

Latrines are an important sanitation infrastructure that are critical to the United Nations’ effort to end open defecation and achieve the target regarding safely managed sanitation outlined in Sustainable Development Goal #6. This global effort has led to 40,000,000 new users being introduced to improved latrines each year, and this number is expected to increase as the world’s population grows. One of the drawbacks related to these new latrine additions is the potential increase in pollution from hydraulically connected latrine pits to shallow groundwater. This is especially problematic in low- and middle-income countries (LMICs), where communities are more likely to employ principles of self-supply to support their water demands. The overall goal of this dissertation research was to develop quantitative tools to evaluate the potential for pit latrines to contaminate shallow groundwater with chemical or microbial constituents.

Previously, governmental and non-governmental organizations have provided latrine siting guidelines that provide a recommended horizontal distance (“setback distance”) between a latrine and well. In this dissertation, I reviewed over 100 documents giving some sort of recommended distance via field study or previously established literature. I found that the four most commonly used siting documents directly cite a total of four field papers, calling into question previous siting practices used. I also found there was a lack of papers looking at the vertical depth between the bottom of the latrine and the top of the water table, a parameter that can greatly affect the setback distance. Therefore, I recommend that future siting guidelines should focus more on vertical separation, include chemical contamination, and be based on models describing how latrines and wells are hydraulically connected, along with the fate and transport of potentially harmful contaminants. Several modeling papers in fact suggest the safe distance from a latrine to a water source should be 22–75 m, depending on the chemical of concern and whether the pathogen of concern is bacteria or a virus. However, the models used to derive these distances have not been tested outside their respective studies, so there is not a consensus on the model to use moving forward with latrine siting.

One way to protect a well from a nearby latrine is to ensure that there is no hydraulic connection between them. Therefore, I developed equations for determining the conditions under which a downgradient well is not hydraulically connected to an upgradient latrine. Specifically, I considered the case of a single well and a single latrine in steady uniform regional groundwater flow. I determined the minimum “off-center distance” ymin (i.e., distance in the direction perpendicular to regional flow) that ensures the well and the latrine are not connected. I developed two solutions for ymin. For people with computer access and some computing expertise, I present an exact solution (to within the accuracy of a root-finding algorithm). For those without such computing resources or expertise (like in many LMICs), I present a simple pencil-and-paper equation that matches well with the exact method (average error less than 3%). I found that ymin depends on a length parameter (Qw + Qps)/QR, where Qw is the extraction rate of the well, Qps is the injection rate of the latrine, and QR is the regional groundwater flow rate per unit of perpendicular length.

Furthermore, a quantitative model was built to predict the concentration profile of chemical, viral, and bacterial contaminants that enter the vadose zone from the bottom of a pit latrine if the latrine and well are hydraulically connected. For a particular set of conditions, I estimated that a distance of 5 m between the bottom of a latrine pit and the top of the water table would be sufficient to ensure that representative bacterial and viral species (E. coli and Enterovirus, respectively) would be reduced to levels deemed acceptable by the World Health Organization and the U.S. Environmental Protection Agency. However, different site conditions might require deeper vadose zones to protect the underlying groundwater from microbial contamination. There was no distance found for the target chemicals (i.e., ammonia and nitrate, but nitrate especially) at which they reached a concentration deemed acceptable for drinking according to the WHO guideline. Deeper vadose zones do not protect underlying groundwater from nitrate contamination unless the deeper parts of the vadose zone are anaerobic and can promote denitrification. The model then evaluated how different modifications to a latrine (i.e., addition of pour-flush or urine diversion plus placement of a sand liner around the bottom of the pit) would affect the concentration of ammonia, nitrate, E. coli, and Enterovirus. Model output showed that the addition of a urine-diverting component and a sand liner resulted in the best improvements in reducing contaminant concentration out of the four alternative scenarios presented. However, the pour-flush latrine resulted in each contaminant of concern (E. coli, Enterovirus, and nitrate) migrating further down the vadose zone.

This dissertation research will help the world achieve multiple targets under Sustainable Development Goal #6; that is, to achieve access to adequate and equitable sanitation (Target 6.2) and achieve universal and equitable access to safe and affordable drinking water for all (Target 6.1).

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