Premium
Wastewater Flow and Pathogen Transport from At‐Grade Line Sources to Shallow Groundwater
Author(s) -
Weldeyohannes Amanuel Oqbit,
Kachanoski Gary,
Dyck Miles
Publication year - 2018
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2017.12.0486
Subject(s) - vadose zone , water table , wastewater , groundwater , hydrology (agriculture) , environmental science , subsurface flow , groundwater flow , surface water , water well , environmental engineering , geology , aquifer , geotechnical engineering
On‐site wastewater treatment systems are commonly used in sparsely populated areas where capital‐intensive centralized wastewater treatment facilities are not feasible. The primary objective of this work was to investigate vadose zone and groundwater transport of a bromide (Br) tracer and naturally occurring Escherichia coli applied to the soil surface in secondarily treated wastewater at a public rest stop in central Alberta, Canada, with seasonally fluctuating water table (between 0.2 and 1.5 m) over a 1‐yr period. A transect within the wastewater application field was instrumented with 10 nests of three monitoring wells ( N = 30). We found that travel times for Br and E. coli were most likely related to vadose zone thickness under wastewater application lines, with Br and E. coli initially detected in monitoring wells within 4 d at locations where the vadose zone was 0.2 to 0.4 m thick. When the vadose zone thickness increased to ≥0.9 m, however, E. coli levels in the monitoring wells decreased dramatically despite continued high surface application of E. coli . The observed travel times were consistent with those calculated assuming piston flow. Therefore, the risk of groundwater contamination from wastewater at this site is greatest during times when high wastewater applications (high facility use) and shallow water table conditions coincide. We recommend that detailed knowledge of vadose zone and groundwater hydrology be used to guide the design of on‐site wastewater treatment systems and also to assess the probability of human exposure to E. coli and other pathogens that are transported to groundwater. Core Ideas Transport under temporally variable boundary (surface flux and water table elevation) was studied. Optimum vadose zone thickness for effective mitigation of E. coli transport was identified. Requirements for assessing risks of on‐site wastewater treatment systems were investigated.