WRS Masters Defense

Chemicals of Emerging Concern in Minnesota Subsurface Sewage Treatment Systems

Subsurface Sewage Treatment Systems (SSTS) are effective at treating traditional wastewater contaminants like nitrogen and phosphorous. However, they are not designed to treat contaminants of emerging concern (CEC). As the scientific community has discovered, CEC are prevalent in our environment. This paper includes two studies aiming to quantify concentrations of CEC in and coming from SSTS.

The first study includes in-field data of CEC in septage, septic tank effluent, groundwater, and soil around three MNDOT rest area SSTS and one septage field application site. The second study is a complimentary laboratory soil column study which quantified CEC concentrations throughout the soil column and in wheat samples following a known septage application. Both studies used mass spectrometry to quantify CEC in collected samples.

The field study revealed that SSTS effluent and septage field application contribute to CEC concentrations found in the environment. SSTS do offer partial treatment of CEC, but many CEC escape secondary treatment and are found in the shallow groundwater near soil treatment areas. The Secondary Treatment Unit at the Rum River rest area significantly decreased several CEC concentrations but did not fully degrade any of the target compounds. SSTS primary treatment—solids removal—also decreases the concentration of many CEC. However, the septage generated from solids removal is often land applied in Minnesota. This reintroduces removed CEC back into the environment.

The soil column study showed detects of target CEC in groundwater, soil, and plant samples. However, poor recoveries in lab analysis resulted in high uncertainty in CEC concentrations. Because of the poor recoveries, a fate and transport analysis was not possible.