Photo: FLOW sponsored a Septic Summit on November 6, 2019, at Northwestern Michigan College’s Hagerty Center. Read about the Summit here. Photo by Rick Kane.
Most Michiganders don’t know that September 14-18 is Septic Smart Week — and that an estimated 130,000 septic systems in our state are failing. In many cases that means sewage and associated microorganisms are reaching groundwater, lakes and streams.
As FLOW described in our fall 2018 report on groundwater contamination in Michigan, our state is the only of the 50 states that lacks a statewide sanitary code requiring regular inspection and maintenance of small, mainly domestic septic systems. Some counties, townships, cities and villages are enacting local ordinances in place of statewide requirements.
Septic systems are small-scale wastewater treatment options, used when a home or complex cannot easily be connected to a municipal sewer system. Raw sewage and wastewater (e.g., bath water and dishwater) are first pumped from the home into the septic tank. This is an underground, sealed, concrete tank where the household waste is treated. Here, solid waste sinks to the bottom of the tank and materials such as oil form a layer of scum on top. Bacteria in the tank break down the solid waste, while the wastewater migrates out of the septic tank and into the drain field. Perforated pipes distribute the liquid wastewater throughout the drain field. Once out of the pipes, the wastewater effluent seeps through a gravel layer, then through the soil. Both filter the wastewater before it flows into the groundwater or nearby surface water.
Leaking or malfunctioning septic systems allow organic wastewater compounds like nitrate and E. coli to percolate through the soil and enter the groundwater. Leakage and effluent runoff are also major contributors to E. coli levels in surface water. The Michigan Department of Environmental Quality (MDEQ, now EGLE) has identified 196 rivers, lakes, and beaches with E. coli levels over the EPA limit. Between 2013 and 2014, an estimated 5.7 billion gallons of untreated sewage were pumped into surface water in Michigan. A 2015 study headed by Dr. Joan Rose, co-director of Michigan State University’s Center for Advancing Microbial Risk Assessment and Center for Water Sciences, sampled 64 river systems that drain approximately 84 percent of the Lower Peninsula, for E. coli and the human-specific source tracking marker bacteria called B-theta. The more septic systems in the watershed, the more human fecal source tracking bacteria were found in the water.
Human wastes are not the only pollutants that failing septic tanks are releasing to groundwater and surface water. So-called emerging contaminants like pharmaceutical residues and endocrine disruptors are found in household wastes whether they discharge to publicly-owned sewage systems or septic tanks. Little groundwater monitoring is done to identify these substances in groundwater.
In a 2017 journal article in Environmental Science and Technology, researchers conducted a meta-analysis of 20 different studies on septic systems, identifying 45 contaminants, including pharmaceuticals, personal care product ingredients, chemicals in cleaning products, flame retardants, hormones (both natural and synthetic), and other common substances such as caffeine. The analysis found that septic systems are somewhat effective at removing chemicals such as acetaminophen, caffeine, and alkyphenols, a common group of ingredients used in cleaning products. But some chemicals remain largely untreated, including TCEP, a carcinogenic flame retardant, an anti-epilepsy drug called carbamazepine, and the antibiotic sulfamethoxazole. “In high density areas where you have a large number of homes with their own septic systems, these systems are likely the primary source of emerging contaminants in the groundwater,” said Laurel Schaider, the study’s lead author.
Eleven Michigan counties have ordinances that require septic tank inspection at the time property is sold. Within the first six years of implementing their ordinances, two Michigan counties found 1,000 failed septic tanks and 300 homes without any septic system.
Dave Dempsey is FLOW’s senior policy adviser.