When I worked at the US EPA in the 1970’s there was a sign on the wall of the adjacent office that said, “The Solution to Pollution is Dilution.” There was both truth and cynicism in that sign. At the time we were determining the likely contaminates in a waste stream and the levels of those contaminants that would be acceptable based on the potential impact to life. The guiding principal of toxicology is that there is a relationship between a toxic reaction (the response) and the amount of poison received (the dose). An important assumption in this relationship is that there is almost always a dose below which no response occurs or can be measured. So if the concentration of the contaminant was low enough there would be no toxic reaction.
In addition, there is another factor that has been observed for generations and studied in the recent decades. The planet is able to filter and heal itself from limited amounts of pollution. There have been numerous studies of groundwater and surface water systems that have documented this. In Dutchess County New York and North Carolina studies documented that the most important factor in septic regulation is controlling nitrogen pollution from septic systems was average density. Both studies demonstrated that density of on-site waste disposal should not exceed one unit per 2-3 acres for an average size house (and household) to ensure water quality. Adequate dilution, soil filtration and time are necessary to ensure sustainable water quality. These studies were performed on nitrate concentrations as a proxy to achieve adequate dilution and natural attenuation of all contaminants.
Historically, horizontal and vertical setbacks for septic systems were developed without consideration of the dilution for wastewater components like nitrate, pharmaceutical residue, caffeine and other substances we humans consume, process or produce. The overall regional density of septic systems was examined to ensure that groundwater resources would not be overwhelmed by the total load of contaminants. The density recommendations were developed based on the nitrate concentration in traditional septic wastewater. Nitrate was used as a proxy because all humans produce about 10 pounds of nitrate per year, it does not easily break down and there is a drinking water standard and an inexpensive analytical test. Dilution was really the goal here.
An estuary is a coastal area where freshwater from rivers and streams mix with saltwater from the ocean. Estuaries are protected from the full force of the ocean by mudflats, sandspits and barrier islands. One of the least appreciated functions of estuaries is to help control pollution. Water from upland areas often carries sediment and pollutants. The marshy land and plants in estuaries filter these pollutants out of the water. The plants in estuaries help prevent shoreline erosion. Estuaries also protect inland areas from flooding and storm surges. When a storm hits, estuaries often absorb water from the storm before it can reach upland areas. The Chesapeake Bay is an estuary. Right now we are engaged in a major effort to reduce the nitrogen, phosphorus, and sediment pollution that enters the estuary through its tributaries in an attempt to restore the estuary to some arbitrary historic state.
The Chesapeake Bay and its tidal waters are impaired by the release of excess nitrogen, phosphorus and sediment. These pollutants are released from waste water treatment plants, from agricultural operations, urban and suburban runoff, wastewater facilities, air pollution and other sources, including septic systems that enter the tributaries and Chesapeake Bay. These pollutants cause algae blooms that consume oxygen and create dead zones where fish and shellfish cannot survive, block sunlight that is needed for underwater grasses, and smother aquatic life on the bottom. Over the past quarter century the excess nutrient contamination to the Chesapeake Bay has decreased, primarily because of regulation of wastewater treatment plants and improved farm practices, but the Bay’s waters remain seriously degraded.
The “strict pollution diet” that EPA is imposing on the six Chesapeake Bay Watershed states only addresses nitrogen, phosphorus and sediment it does not address other contaminants that have been noted in the tributary waters by the US Geological Survey. The USGS began looking into skin lesions on bass in the southern branch of the Potomac River. Some fish had bacterial lesions, some fungal lesions, and some fish had parasite. The USGS concluded that there was no specific cause of the lesions and that the fish appeared to be immunosupressed so that any pathogen in the water could attack the fish. A series of studies were performed over a period of years and it was discovered that the bass suffering from lesions were intersexed. This prompted further sampling of the river that identified higher concentrations of wastewater chemicals near the wastewater plants. Pesticides currently used in agriculture were detected at all locations sampled and traces of estrogenic endocrine-disrupting chemicals were found at all locations examined though their source is not yet known. Though they cannot identify a single chemical or group of chemicals responsible, USGS have embarked on further study to gain greater understanding of the implications to the earth’s ecosystem.