Sea level rise poses a threat for waste disposal infrastructure. In houses with septic systems, rising wastewater can cause unhygienic overflows and system failures. More funding and community involvement can help address this expensive, growing problem.
One serious manifestation of global climate change, in terms of its insidious destruction of prevailing infrastructure and natural systems, is sea level rise. Average global sea levels have increased by about eight or nine inches since 1880, and scientists expect the rise to continue—and even accelerate in some locations—through the end of the century. Along the contiguous US coastline, sea levels are expected to rise, on average, as much over the next three decades—between 10 and 12 inches—as they have over the last century. With 40 percent of the US population living in coastal counties, sea level rise has potential impacts on a large number of people.
Sea level rise causes myriad problems. It exacerbates tidal flooding and the storm surge flooding associated with hurricanes, disrupting daily life and damaging property and infrastructure. It also leads to saltwater intrusion into soils, which causes problems for drinking-water aquifers and agriculture. It alters land-cover types: beaches, dunes, salt marshes, and wetlands gradually turn to open water, and neighboring lands may convert from forests or farmland to wetlands. And the rising water table creates problems for the functioning of infrastructure.
One particular type of essential infrastructure that is affected by sea level rise is onsite waste disposal, or septic, systems. Many rural communities are not served by public sewer, and households in those communities must rely on individual, or sometimes community-based, septic systems for waste disposal. According to the US Environmental Protection Agency, more than one in five households in the United States depend on septic systems. That’s about 25 million septic systems across the country. A rising water table can make it hard for septic systems in coastal areas to properly drain and filter wastewater, leading to backups of waste into homes and contamination of soils and waterways. In some regions of the country, including the mid-Atlantic states of Maryland and Virginia, the problem is a growing concern.
Maryland is expecting higher-than-average relative sea level rise, in part due to lands that simultaneously are sinking. More than 260,000 homes have septic systems in the 16 Maryland counties (and Baltimore City) that border the Chesapeake Bay, its major tributaries, and the Atlantic Ocean, making up 24 percent of all properties in the region. In some of these counties, 70 to 90 percent of all homes rely on septic systems. More alarmingly, these septic systems are prevalent in areas that have a high risk of coastal flooding.
Working with an interdisciplinary team of researchers from the University of Maryland and George Mason University, and with a community-based partner, the Southeast Rural Community Assistance Project, we are investigating the extent of the septic problem in coastal areas of Maryland and evaluating solutions through the lenses of environmental justice, infrastructure, public health, and economics. Our research so far shows that, under current conditions, properties with septic systems make up 46 percent of all properties in Maryland that are exposed to a 100-year coastal flood event. And by 2050, the number of properties that are exposed to flooding will increase by 30 percent because of sea level rise, even without the building of more homes. As our research partners investigate the flood issues more carefully through more detailed flood modeling, we may find these numbers change slightly; but the results so far clearly highlight the challenge that state and local governments face. The problem is getting worse, and without attention to it now, it will only become harder to solve.
One important consideration is for justice, equity, and deep community involvement to be centered in the solutions.
Three potential solutions are available to address failing septic systems in areas that are subject to persistent flooding and sea level rise: (1) replacing and upgrading to more advanced septic systems, (2) connecting homes to public sewers, or (3) relocating households to less flood-prone areas. The first option is likely to be the least expensive of the three but is a short-term fix in the areas that are most susceptible to sea level rise. While advanced systems do a better job of reducing nitrogen and phosphorous and are less affected by rising waters, the water table will rise enough in some locations so that no septic system there will work properly in the future. Extending sewer lines to new areas is costly, so unless a home is located in an area that’s already served by a sewer system, option (2) may be out of reach for many communities. Option (3), relocation, is extremely costly and politically fraught.
One important consideration is for justice, equity, and deep community involvement to be centered in the solutions. Poorer households in marginalized communities are more likely to have older and/or failing septic systems, experience health effects when those systems fail, and have less money to pay for upgrades and sewer connections. These households need help addressing the problems.
In our research, we mapped the location of septic systems that are at risk of coastal flooding in 2050 due to sea level rise, in conjunction with a measure of social vulnerability at the level of census tracts, which are subdivided areas that the US Census Bureau designates for statistical purposes. The Social Vulnerability Index (SVI), constructed by the Centers for Disease Control and Prevention, is created from a combination of 16 variables, including household income, poverty rates, education, race and ethnicity, housing types and costs, and English-language proficiency. The index measures a tract’s national rank from least vulnerable (numbers near zero) to most vulnerable (numbers near one). In the map at the right (Figure 1), darker colors represent more vulnerable tracts, and the dots show the location of flood-exposed septic properties, based on our analysis of data from Maryland’s MdProperty View database and information on the location of sewer service areas.
Figure 1 highlights a few notable features about septic systems and flooding in Maryland. First, flood-prone septic properties are located all along the Chesapeake Bay and the Atlantic Ocean, as well as inland along some of Maryland’s tidal rivers. Second, the east side of the Chesapeake Bay, Maryland’s so-called “Eastern Shore,” is home to the most septic-dependent properties that also are subject to flood risks. Many of the lands on the Eastern Shore are low lying and flood prone, particularly in the southern portion of the region, which is home to Dorchester and Somerset Counties. Third, septicdependent and flood-exposed properties show up in both low- and high-vulnerability communities, but more than 30 percent of the high-risk properties are in tracts that fall within the 75th percentile or above for social vulnerability.
One area where social vulnerability and flood risks loom large is Somerset County, the southernmost county on Maryland’s Eastern Shore. Figure 2 zooms in on the seven census tracts in this county. All the tracts qualify as above the median for social vulnerability, and three are above the 80th percentile. Almost two-thirds of the residential properties in the county rely on septic systems, and of these, 60 percent—more than 2,500 properties, according to our analysis—are at risk of flooding in 2050.
Median household income in Somerset County in 2019 was only $37,800—less than half the median household income for the state as a whole ($84,500). In Somerset County, 22 percent of the population lives below the poverty line. Installation of a new conventional septic system can cost $10,000 or more, depending on its size and the site conditions; advanced systems are significantly more expensive, often twice as much as a conventional system. Connecting homes to the sewer system in Somerset County is difficult because of the limited coverage of existing sewer lines. However, according to our analysis, approximately 20 percent of the flood-exposed septic properties are in areas that already are served by a sewer system. Prioritizing these homes for sewer connections, to the extent possible, is paramount.
Who should pay for these connections, however, remains an open question, and many households are reluctant to take on the monthly costs associated with sewer. The state of Maryland provides grants for septic-system replacements and sewer connections from its Bay Restoration Fund. Since the program began in 2004, almost 15,000 septic-system upgrades and 1,242 sewer connections have been financed across the state by the fund. Spending priorities are based on a strict set of criteria, set by the state, that revolve around whether a septic system is failing and whether the property with the septic system is located within 1,000 feet of the mean highwater line of tidal waters or the landward edge of tidal wetlands in the Chesapeake Bay and its tributaries. Neither household income, nor any measure of social vulnerability, is on the state’s official list of criteria.
By all accounts, the funding from the Bay Restoration Fund is not enough. County governments, which award the grants, carefully manage the money they get from the state over the course of each year, stretching it out to pay for what they can. But additional financial resources are needed, especially in coastal areas that face the growing threat of sea level rise. As our project continues, we and our research partners will investigate these problems more carefully by identifying the factors that lead to septic failure, the links to public health outcomes, and other aspects of this complex problem. All along the way, we’ll be looking for creative new approaches that prioritize cost-effectiveness, equity, and community involvement in finding solutions.