Subsection -613-70.2 requires collecting influent samples as well as effluent samples for General Approval testing and evaluation. For some technologies, it is not feasible to obtain a representative “influent” sample. Thus, the requirement is likely to encourage invalid and unscientific conclusions and comparisons between technologies.

The proposed regulations should be revised to clearly define what is meant by “influent sample,” and at what point in the treatment train the “influent sample” is to be collected. For technologies for which it is not feasible (for reasons explained below) to collect a representative influent sample, the requirement for influent sampling should be waived. In such cases, for performance evaluation purposes the VDH should assume that the influent composition was typical of domestic quality septic tank effluent, and use appropriate values from the published literature.

When testing is conducted at a controlled research facility (for example, when testing is according to NSF/ANSI Standard protocols), influent sampling is feasible because the influent consists of primary-treated wastewater delivered to the treatment unit through a controlled pipeline.

But influent sampling is not necessarily feasible for field-testing at actual residences such as the General Approval testing described in the proposed regulations at Section -613-70. Raw domestic sewage enters the treatment train as a non-homogeneous mixture. Its composition depends on the last household activity, what was last flushed down the drainpipe, and how long ago it entered the treatment train. It is only feasible to obtain a meaningful “influent sample” if it is possible to sample from the back end of a primary treatment tank or primary compartment that precedes, and is hydraulically isolated from, the contents of the secondary treatment unit.

In contrast, it is not possible to obtain a representative influent sample from a multiple-pass recirculating technology (such as a media filter) where the treatment unit pump is in a compartment hydraulically connected to the compartment where primary treatment occurs.

I note that the current policy (GMP 147) for performance testing and technology evaluation, does not require influent sampling. That evidently reflects acknowledgment that for some technologies it is impossible to obtain representative “influent” samples when samples are collected in the field at actual residences. The same acknowledgment should likewise be reflected in the proposed regulations.