Which of these is an environmental concern associated with failing septic systems?

Failing septic systems pose significant environmental risks, primarily through the contamination of groundwater. When a septic system malfunctions, untreated or partially treated sewage can leach into the surrounding soil and eventually reach the groundwater. This can lead to serious health risks for nearby residents, as groundwater is often a source of drinking water. Contaminants such as pathogens, nitrates, and other harmful substances can compromise water quality, leading to pollution that affects not only human health but also local ecosystems.

The other options do not reflect the environmental impact of failing septic systems accurately. While local fish populations might decline due to pollution from different sources, the direct consequence of a failing septic system primarily involves groundwater contamination rather than immediate effects on fish. Increased property values would not be a concern linked to failing systems; in fact, such failures typically decrease property values due to health and safety risks. Improved soil fertility is also misleading, as the nutrients from septic systems can lead to eutrophication and ecological imbalances rather than a healthy increase in soil fertility.