Semester of Graduation

Summer 2026

Degree

Master of Science in Civil Engineering (MSCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

On-site wastewater treatment systems (OWTS) serve roughly 25% of U.S. households and are a key component of decentralized sanitation. Most OWTS are septic systems; however, aerobic treatment units (ATUs) are increasingly utilized in areas unsuitable for conventional septic systems and often discharge into surface waters, creating potential contamination and exposure risks. We analyzed 76 water samples from roadside stormwater ditches across four Louisiana parishes to compare water quality in OWTS and centrally sewered areas. Water in OWTS-impacted ditches exhibited significantly elevated concentrations of ammonia nitrogen (7.58 ± 13.9 mg/L, p < 0.0001), orthophosphate phosphorus (9.96 ± 5.57 mg/L, p = 0.004), total organic carbon (22.94 ± 10.05 mg/L, p < 0.0001), chemical oxygen demand (86.06 ± 53.81 mg/L, p < 0.0001), Escherichia coli (2,390 ± 4,223 MPN/100 mL, p = 0.0199), and Enterococci (25,753 ± 68,487 MPN/100 mL, p = 0.0115) compared to ditches in areas served by centralized sewerage. The human-associated fecal marker HF183/BacR287 was significantly higher (up to 6.8 log10 gene copies/100mL) in OWTS ditches (p = 0.0218), in some instances reaching levels comparable to untreated sewage. HF183 concentrations in over 60% of OWTS ditch samples exceeded gastrointestinal illness risk thresholds (30 illnesses/1000) for both marine-water and stormwater exposure scenarios. Additionally, the 5-day biochemical oxygen demand to chemical oxygen demand ratios imply that roughly 40% of OWTS ditch samples were primarily raw or untreated wastewater. These findings show that OWTS-impacted ditches can act as near-source reservoirs of human sewage, highlighting the need for improved public health, environmental monitoring, and infrastructure management. 

Date

7-27-2026

Committee Chair

Bivins, Aaron

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

Download

Available for download on Thursday, June 21, 2029

Share

COinS