In general the problem in certain areas of town may be summed up as follows:
Density of Development
Older septic systems that do not meet the current Health Code
Areas with high groundwater, ledge, and/or poor soils
proximity to water bodies.
The public health code addresses lot-by-lot requirements of on-site septic systems. It does not directly address densely developed residential areas with septic systems and the potential for impacts to groundwater from the increased nitrogen load (see DPH Circular Letter 2000-01)
The presentation by the DEEP in 2012 explains the problem best.