Septic System Impacts on Source Water: Two Novel Field Tracer Experiments in Fractured Sedimentary Bedrock

Rachael Marshall,Jana Levison,Edward Mcbean,Beth Parker

doi:10.3390/su14041959

Abstract

Septic systems are a common contributor of contaminants to groundwater that have implications for source water protection, particularly in fractured sedimentary bedrock environments. Two 24-h tracer experiments were performed that applied (1) the dye Lissamine Flavine FF and (2) three artificial sweeteners (acesulfame, sucralose, and cyclamate) in the leaching bed to examine solute transport from a single-family septic bed to a multilevel monitoring well installed in fractured sedimentary bedrock on a First Nation reserve in Southern Ontario, Canada. Tracer was first observed 3 h and 20 min after deployment, and breakthrough curves showed that multiple pathways likely exist between the septic bed and the monitoring well. Cyclamate concentrations were more elevated than expected compared to other studies that examined cyclamate’s attenuation in the laboratory and in porous media aquifers. Solute transport through the septic bed was analyzed with the numerical modeling software Hydrus 1D, which indicated that the septic bed may be too thin, located directly on bedrock, underlain by fractured soils, or bypassed through a short-circuit. The rapid transport of septic leachate to fractured sedimentary aquifers is problematic for First Nation and rural communities. More stringent regulations are needed for the design and use of septic systems in these environments.

Highlights

Source water protection is a complex process that must consider a number of sociopolitical and technical factors, including jurisdictional considerations, flow and transport of water and contaminants in the natural environment, and built infrastructure [1]
The purpose of this study was to examine the impact to groundwater of an aging single-family septic bed of typical design located above a fractured sedimentary bedrock aquifer on a First Nations reserve in Southern Ontario, Canada using two infiltration tracer experiments
Tracer Breakthrough Curves hydraulic gradient was calculated from hydraulic head data from four ports with similar Lissamine tracer first(aobserved at approximately h and min after tracer applidepths in CMT1 andwas

Summary

Introduction

Source water protection is a complex process that must consider a number of sociopolitical and technical factors, including jurisdictional considerations, flow and transport of water and contaminants in the natural environment, and built infrastructure [1]. While many advances have been made towards protecting drinking water sources around the world in recent years [2,3,4,5,6,7], issues persist in many environments, including vulnerable hydrogeology, aging or inappropriate infrastructure, and where socio-economic and other factors have made it difficult to implement adequate source water protection measures, as is the case in many rural and Indigenous communities [3,5,6] It is well-known that septic systems are a common contributor of contamination to groundwater, streams, and lakes [8,9,10,11,12,13,14,15,16]. They are often approved for use in vulnerable fractured rock aquifer

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