Pre-Treatment Systems - Positive effect on groundwater quality?

    A current widespread evolving trend among the regulatory community is to require property
owners to install expensive pre-treatment technologies, allegedly to remove or reduce the
negative health effects of on-site wastewater disposal.

    Many of these systems appear to remove half or more of the easily removable constituents in typical wastewater, which are mainly organic components measured as BOD (Biochemical [biological]  Oxygen Demand) and  -TSS (Total Suspended Solids), and less of the more likely dangerous components such as viruses and pathogens along with other constituents of the heavy metal variety.

    To partly justify the added expense of a costly pre-treatment system, some regulators allow a reduction in the size of the leaching field or a lesser separation to groundwater.  The reduction in required leaching area appears justified since the biological materials required to form a biological film at the wetted perimeter of the leaching system are much reduced, allowing the discharge of increased effluent volumes per unit area.  Thus, the leaching systems are able to function with reduced likelihood of  mechanical failure due to clogging.  Of course, having nearly eliminated the biological slime layer in the leaching fields, most contaminants not removed in the pre-treatment process are easily conveyed down to the underlying aquifers where transport is facilitated to existing water supplies.

    In one Massachusetts study where viruses were introduced into the effluent entering a pre-treatment system and later sampled 24 inches below the infiltration trench, there appeared to be no evidence of any meaningful virus removal.

The separating distance (in some jurisdictions) can be reduced by two feet between the bottom of
the infiltration device and high groundwater for some approved pre-treatment systems.  Again
there is facilitation for more rapid delivery of pollutants.  It appears to be 50/50 logic.  Remove
half the clogging materials and one is rewarded by being able to cut the separating distance by
50%.  This of course would result in financial savings for fill materials etc. but will, most likely, have a negative impact on the aquifers.

Regulators may be wise to evaluate and compare the impact on the groundwater of conventional
infiltration methods vs. the new pre-treatment hype.  The outcome would most likely be
surprising to many.