Doesn't that come out to 1/4-acre lots? That's not very small.

How are these "detached 4-plexes" contaminating groundwater more than traditional 4-plexes or triplexes or duplexes or townhomes or apartment buildings? The fact that each has its own septic system means each handles less waste than if one system handled multiple units, doesn't it?

The article should explain this issue.