Grantee Research Project Results

Final Report: Modeling Straight Pipe Prevalence in Rural Alabama

EPA Grant Number: SV840024
Title: Modeling Straight Pipe Prevalence in Rural Alabama
Investigators: Elliott, Mark , Cohen, Sagy , Greer, Ashton
Institution: The University of Alabama , Oregon Institute of Technology
EPA Project Officer: Aja, Hayley
Phase: II
Project Period: July 1, 2020 through June 30, 2022 (Extended to June 30, 2023)
Project Amount: $75,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2020) Recipients Lists
Research Category: P3 Awards

Objective:

This project is part of a long-term initiative to characterize and address onsite wastewater failures, including building partnerships and raising funds to facilitate installation of appropriate, affordable and sustainable wastewater management in the Black Belt region of rural Alabama. This effort involves quantification of straight pipes (raw sewage discharges from homes directly to the surface) in rural Alabama through the development, validation, and application of a model to predict the scope and location of straight pipe use in the study area.

Straight pipes are illegal and there is no database of their presence; therefore, data needed to validate the model must be acquired through our project. We hoped that initial model validation could be performed using a survey of homes in Wilcox and Hale counties in 2017. However, these surveys included a small fraction of the county population and area; we found that they were inadequate for model validation. As described in the proposal, we surveyed licensed septic system pumpers and installers, local experts who know the onsite wastewater status in the areas where they work. Because all Alabama pumpers and installers are licensed through the Alabama Onsite Wastewater Association (AOWA), we conducted surveys at AOWA meetings. We developed an online survey that can be run from an iPad, Android tablet, laptop or smart phone. The initial draft of the survey was trialed at the AOWA continuing education event in March and September 2022. The trial helped identify both the advantages of an online hosted survey as well as potentially unforeseen challenges. We consulted with the university’s Institute for Social Science Research (ISSR) to refine the survey for best practices and to ensure the survey methods were rigorous. The updated online survey was deployed at the AOWA event in March 2023. Variable weights for the model were extracted from the survey data using the Analytical Hierarchy Process (AHP) as described by Marinoni (Marinoni, 2004).

This is the first attempt to model straight pipe system location in the world, so unique equations have been developed based on the factors that are reported to lead to straight pipes in unsewered homes in the rural Black Belt (soil/geology conditions and rural poverty) (Maxcy-Brown et al., 2021). This model uses publicly available secondary data on saturated soil hydraulic conductivity, depth to seasonal high-water table, depth to bedrock, and property data records in county tax assessor parcel data. The knowledge of local experts (e.g., septic system installers and pumpers) was used to validate model results. Our goal was to build the first predictive model of straight pipes using publicly available data with model validation based on expert knowledge.

Conclusions:

The model has been built and applied using publicly available secondary data. Illustrative outputs using the model have demonstrated that the model is able to produce a diverse array of outputs, including a map with estimates of the number of straight pipes in US Census Block of a study county, and the volumetric accumulation of wastewater in the surface water bodies of a county given a large precipitation event following a dry period of a given number of days. Model validation has been accomplished by conducting surveys for expert knowledge. Volunteer response to the surveys was low, but we still obtained feedback from more than ten experts as stated in our phase 2 goals. While the survey response rate and validation weren’t as robust as desired, the functionality of the survey and Analytical Hierarchy Process (AHP) model to quantify expert knowledge has been borne out. The model and the tools developed to support it can be deployed anywhere that the requisite secondary data are available, and it can be adjusted to include new variables for use in different geographic regions. The model has been applied to several Alabama counties. Not all of the counties named in the proposal have been run due to difficulties obtaining some of the necessary data or time constraints.

Representative model outputs (using Wilcox County) have also been generated to demonstrate outputs and data visualization products that are possible using the model. These include a map with estimates of the probability of straight pipe usage in a study county (Figure 1), and the volumetric accumulation of wastewater in the surface water bodies of a county given a large precipitation event following a dry period of a given number of days (Figure 2).

Figure 1: Model output mapped. The validated model yields a county map of estimated probability of straight pipes throughout the county.

 

Figure 2: A map of sewage accumulation throughout the county from a precipitation event that flushes the sewage accumulated during a dry period of a given number of days.

 

This project is directly relevant to EPA priorities nonpoint source pollution prevention and the Clean Water Act, in addition to environmental health and environmental justice for low income, underserved, racial minority, rural communities. As stated in EPA’s 2018-2022 Strategic Plan “Water quality programs face challenges such as increases in nutrient loadings, nonpoint source and stormwater runoff, and aging infrastructure. EPA is carefully examining the potential impacts of and solutions to these issues.” Defining the scope of nonpoint source pollution from onsite wastewater failures is essential to determining impacts and solutions.

Partnership activities have raised the profile of this issue in Alabama and enabled us to raise additional funding for decentralized wastewater system design and installation (Columbia World Projects, 2020; Pillion, 2020, 2021). The most important of these partnership activities has been the formation of the “Consortium for Rural Alabama Water and Wastewater Management” founded and organized by Dr. Elliott and his colleagues at the University of South Alabama, Drs. Kevin White and Lynne Chronister.  Partnership activities through the Consortium for Rural Alabama Water and Wastewater Management (the Consortium) have continued to move forward. Consortium meetings have continued at their previous twice per year frequency but were fully remote (Zoom meetings) from March 2020 through March 2023; in April 2023 we switched to a hybrid model with in-person in Montgomery, AL supplemented with an online (Zoom) option.

References:

Columbia World Projects. (2020). Columbia World Projects to Pilot New Approach to Wastewater Treatment in Rural Alabama. https://worldprojects.columbia.edu/news-media/columbia-world-projects-pilot-new-approach-wastewater-treatment-rural-alabama

Marinoni, O. (2004). Implementation of the analytical hierarchy process with VBA in ArcGIS. Computers and Geosciences, 30(6), 637–646. https://doi.org/10.1016/J.CAGEO.2004.03.010

Maxcy-Brown, J., Elliott, M. A., Krometis, L. A., White, K. D., Brown, J., & Lall, U. (2021). Making Waves: Right in Our Backyard- Surface Discharge of Untreated Wastewater from Homes in the United States. Water Research, 190, 116647. https://doi.org/10.1016/j.watres.2020.116647

Pillion, D. (2020, November 19). Potential solution emerges for Alabama’s Black Belt sewage woes. AL.Com, 2. https://www.al.com/news/2020/11/potential-solution-emerges-for-alabamas-black-belt-sewage-woes.html#

Pillion, D. (2021, March 14). Black Belt sewage woes: Feds give $4.9M for rural wastewater project. AL.Com, 2. https://www.al.com/news/2021/03/black-belt-sewage-woes-feds-give-49m-for-rural-wastewater-project.html

 

Journal Articles:

No journal articles submitted with this report: View all 8 publications for this project

Supplemental Keywords:

safely managed sanitation, poverty, high-income countries

Relevant Websites:

Dr. Elliot's Research Group Website Exit

Consortium for Alabama Rural Water and Wastewater Management  Exit

Progress and Final Reports:

Original Abstract

2021 Progress Report

2022 Progress Report

P3 Phase I:

Modeling Straight Pipe Prevalence in Rural Alabama  | Final Report