Evan MaFollow

Department or Program

Environmental Studies

Abstract

Rural areas often use septic systems to treat household wastewater, which may pose a phosphorus (P) loading risk to nearby water bodies if systems fail or if the soil types are unsuitable for P retention. In the Lake Auburn watershed, septic systems may be a source of phosphorus loading to Lake Auburn, an unfiltered drinking water supply. Site evaluations from municipal permits reveal patterns of septic system locations and soil types in septic drain fields. Many septic drain fields have shallow depths to groundwater or a restrictive layer, which may lead to inadequate P retention in the soil. Areas with a high density of septic systems near the two largest inlets to the lake may be P loading hotspots. Near the Basin inlet, shallow soil depths and proximity to the lake suggest that failing systems may be a source of P loading, and that there may not be robust P removal in these drain fields. A high density cluster of systems near Townsend Brook is located on a sand and gravel aquifer, with coarse sands that have less capacity to retain P than finer-textured soils. The creation of a model that simulates 200 years (1900 to 2100) of septic system operation demonstrates that septic systems may create a legacy P issue, because P loading was estimated to increase even after new development ceased. The model shows that policy changes may be able to decrease the septic system P load, but that the impact of such changes on P loading estimates may not be substantial for decades. In Auburn, such policy changes also have land use implications that would increase watershed sources of P loading through additional deforestation, impervious surface, and septic systems from new development. Other studies on Lake Auburn demonstrate that land-based P loading from new development may be higher than the P load reductions from improved wastewater treatment estimated in this study, suggesting that any change to septic system policy that does not also restrict development where it has previously been restricted is likely to lead to a net increase in the cumulative P load.

Level of Access

Open Access

First Advisor

Holly Ewing

Date of Graduation

5-2023

Degree Name

Bachelor of Arts

Number of Pages

143

DOI

https://doi.org/10.26780/2023.002.0001

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