NC0089915_Responses to SELC Comments_20200918

Responses to SELC Comments
1). Review of the Engineering Report and Addendum to the Report indicates that the effluent
concentrations of the two indicator PFAS compounds (PFMOAA and HFPO-DA) is highly variable
depending on the type of the GAC used and other factors. PFMOAA concentration varies anywhere from
<10.6 ng/L to 31,059 ng/L and HFPO-DA varies anywhere from <11.7 ng/L to 4,622 ng/L. Such a
significant variation shows that even under a tightly controlled laboratory conditions the treatment
technology must be optimized for the facility to meet the permit limits, which are much closer to the
lower end of the identified range of the effluent concentrations (60 ng/L for HFPO-DA and 850 ng/L for
PFMOAA).
2). The study performed by the consultants was conducted under a predictable and controlled
laboratory conditions on a small scale during a short time period. When this technology is implemented
in the field, there will be additional complications that will have a negative impact on the performance,
including: variation in temperature (daily and seasonal); variations in the influent pH, volume, TSS,
oxidation-reduction potential, additional chemical compounds impacting GAC, etc. Additional difficulties
might be encountered during scaling -up the technology from the lab to the field.
3). In addition, the facility will encounter substantial treatment difficulties as the influent concentration
of the PFAS compounds decreases. Consistent removal of 99% compounds in the influent is jeopardized
as the wastewater coming to the treatment system becomes less polluted. The DEQ has observed these
difficulties with numerous facilities and parameters.
4). When EPA develops Effluent Guidelines, they rely on the data obtained from the implemented and
successfully operating technologies. For example, the latest update for the 40 CFR 423 (Power Plants)
was based on the multiyear data collection from Duke facilities and facilities in other states and
countries. In this case we don't have a reliable field data from other similar facility, which significantly
increases uncertainty in our ability to predict the PFAS effluent concentrations.
5). When the high uncertainty exists in the effluent concentrations, the EPA recommends using the 99%
for establishing Daily Maximum limits and 95% for Monthly Average limits. The DEQ proposed limits are
even tighter since both limits are based on the 99% removal rate.
6). The DEQ proposes to re-evaluate the data after 3 years of the GAC treatment system operations. The
DEQ will reduce the limits if the facility demonstrates ability to consistently achieve levels that are lower
than the proposed limits. It is necessary to emphasize that the wastewater treatment operations need
time to optimize their performance. It is especially important for a new technology with a very limited
application history.