19970722 Ver 1_More Info Received_19980224

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DIVISION OF WATER QUALITY
February 24, 1998
MEMORANDUM
TO: Boyd Devane
THROUGH: Ruth Swanek"?'
FROM: Jason Doll
SUBJECT: Draft Nutrient Reduction Strategy
Proposed Randleman Reservoir
Piedmont Triad Regional Water Authority (February, 1998)
The Modeling/TMDL Unit has reviewed the Draft Nutrient Reduction Strategy
(NRS) and the associated Support Document for Eutrophication Modeling, both prepared
by Tetra Tech, Inc. for the Piedmont Triad Regional Water Authority in support of the
proposed Randleman Reservoir. We have several concerns with the management
recommendations contained in the document and with the support information utilized to
develop those recommendations. Our concerns are as follows:
Eutrophication Modeling
The most recent efforts to simulate eutrophication conditions in the proposed
reservoir consist primarily of an improved and updated version of the Walker BATHTUB
model previously developed by Black and Veatch for the 1991 EIS. BATHTUB is a
steady state empirical lake model utilized to predict nutrient and chlorophyl a levels in
North American reservoirs. The model allows for spatial segmentation of the reservoir
and predicts mean growing season nutrient and chlorophyl a levels for each segment,
averaged temporally and spatially within the segment. The model also calculates the
percentage of time in the growing season during which each segment is predicted to
sustain nuisance chlorophyl a levels (defined as chlorophyl a greater than 40 µg/l in this
case). In general, the modeling approach is reasonable, and the model options chosen and
the improvements to the model are appropriate.
This most recent and improved version of the model predicts that under existing land
use and wastewater discharge conditions, during an average flow year, mean growing
season chlorophyl a in the upper Deep River (Deep River I) segment of the reservoir will
be 95 µg/l, and that nuisance levels will exist 89% of the time. The model also predicts
that after state-of-the-art phosphorus removal (effluent TP = 0.2 mg/1) is implemented at
the High Point Eastside WWTP (identified as the primary source of phosphorus loading),
with projected future land use conditions, mean chlorophyl a in that arm will still be 67
µg/l for an average flow year, with nuisance conditions existing 73% of the time. It
should be noted that there is a considerable degree of uncertainty associated with these
predictions and that, the higher the predicted chlorophyl a level, the greater the
uncertainty. Previous modeling reports by Tetra Tech indicate that the 95% confidence
interval around the predicted mean chlorophyl a level in Deep River I for existing
conditions would range from about 40 to 150 pg/1. However, given that this is an effort
to simulate a not yet existing impoundment, some degree of uncertainty is inherent in the
evaluation. Regardless of the modeling scenario utilized, it is highly likely that
chlorophyl a levels in violation of water quality standards will be predicted to persist in
this arm of the reservoir for the majority of the growing season.
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The area of uncertainty in the model that may be the largest concern is an overall
potential to under estimate non point source (NPS) nutrient loading. Specifically, the
NPS phosphorus loading function in the model utilizes an attenuation factor based on the
size of each tributary watershed to calculate the portion of the areal load delivered to the
reservoir. The attenuation factor was originally developed specifically for sediment, so
using it in the model assumes that all phosphorus is sediment bound, and does not take
into account the higher delivery rate likely for the dissolved portion of the phosphorus
load. In addition, the land use data utilized to calculate "current" NPS nutrient loads (via
export coefficients) is actually the 1989 land use, data previously assembled by Black &
Veatch. Hence, the data is nearly 10 years old at this point and most likely
underestimates the present levels of development in an area with growth rates as high as
the Triad. The projected land use scenarios used to calculate future NPS loads are also
partly based on an extrapolation from this "current" land use data.
Nutrient Loading and Reduction Efforts
The NRS document gives a phosphorus load estimate for the entire reservoir for
current conditions and average flow of about 77,000 kg/yr, of which 58,000 kg/yr, or75%
is of point source (PS) origin and the other 19,000 kg/yr is NPS. Based on the high
percentage of the PS load and the fact that 99% of that load comes from the High Point
Eastside WWTP discharge, the primary measure presented for the proposed watershed
management plan is a financial incentive to improve the level of phosphorus removal at
the WWTP. The document states that the incentive will cause the facility to maintain an
" operational goal" of less than 0.2 mg/1 effluent concentration of total phosphorus (TP)
as opposed to the 1.0 mg/1 effluent TP limit that would have been imposed by DWQ in
the absence of a reduction strategy. The incentive is estimated to result in an 88%
reduction of the PS phosphorus load to about 7,200 kg/yr.
The dramatic reduction in PS loading is partly offset in the planning period by a near
doubling of NPS phosphorus loading due to projected increased development during the
planning period. Based on the development projections up to the year 2025 from a Triad
Regional Transportation Authority study (not presented in the NRS) and on some
extrapolation from the "current" land use conditions, the plan estimates the future NPS
phosphorus load at 31,600 kg/yr for an average flow year. In the future scenario, after the
load reduction at the WWTP, the NPS proportion of the TP load becomes 81%.
However, the only measures the NRS offers to address NPS loading are: 1) local
watershed protection ordinances as required by the Water Supply Watershed Protection
Act, 2) construction of 6 riparian wetlands which are required as mitigative measures
under the current 401/404 process, and 3) construction of one addition regional
stormwater impoundment already planned by the City of High Point. In short, the plan
offers no measures to address NPS loading to the reservoir other than those already
required by existing programs or permits.
It should be noted that the BATHTUB model results have indicated that phosphorus
loading in Deep River I must be reduced to 1,800 kg/yr in order to prevent predicted
chlorophyl a levels from exceeding 40 µg/l more than 5% of the time. However, even
without the wastewater discharge, current NPS phosphorus loading for that portion of the
watershed is estimated to be in excess of 12,000 kg/yr for an average flow year. After the
reduction in the PS load and implementation of the NPS measures, the total phosphorus
load for future conditions in Deep River I is estimated to be near 28,000 kg/yr for an
average flow year, and, as previously mentioned, this load level is predicted to result in
nuisance algal conditions for 73% of the growing season. While it may not be feasible to
develop a reduction strategy that would completely prevent water quality violations in the
upper Deep River segment, given the magnitude of predicted algal bloom conditions in
that portion of Randleman Reservoir, a much more substantial effort to minimize future
NPS loading should be required in order to protect all uses of the proposed impoundment.
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Consideration of Discharge Bypass
A common perception is that the reservoir would not support the sustained yield of
48 MGD without the hydraulic input from the High Point Eastside WWTP discharge. In
a recent phone conversation with John Sutherland of the Division of Water Resources, he
indicated that the sustained yield was calculated without the input from the discharge.
He further explained that the discharge bypass alternative had been eliminated due to a
prohibitive cost estimate when the option was originally considered. Appendix B of the
1991 Black & Veatch EIS presents the cost of the bypass at $15,000,000 for the least
expensive of the three pipeline alignments considered, as compared to a cost estimate of
upgrading the WWTP at $3,000,000. However, this cost estimate was to upgrade the
WWTP to a treatment level of 1.0 mg/1 effluent TP.
In light of the severity of the eutrophic water quality predictions for the reservoir,
and given the potential current costs to upgrade the WWTP to meet an effluent TP of 0.2
mg/1 for a design flow of 26 MGD, it may be a worthwhile effort to revisit the economic
alternatives analysis for that option at this time.
Evaluation of Forthcoming Toxicant Data
Past assessments of water quality and environmental impacts of the reservoir have
included evaluations of off site migration of toxicants from the Seaboard Chemical and
abandoned High Point Landfill Superfund site(s) near the headwaters of the proposed
reservoir. In Tetra Tech's Phase I report, dated April 1997, it is recommended that
modeling be performed to predict average and peak levels of these contaminants at the
proposed drinking water intake sites in the reservoir. Subsequent reports contained no
further mention of these potential sources of toxicant contamination.
In recent communications, personnel from the Division of Waste Management
(DWM) have indicated that additional groundwater monitoring wells have been
established in the river bed of the Deep River down gradient from these sites. Due to the
legal review process involved in Superfund clean ups, the data from these more critical
well sites has only been available for preliminary review by DWM staff. Review of the
data confirmed their suspicions that higher levels of contamination would be present at
these down gradient sites, and revealed the presence of new organic toxicants in the
groundwater (specifically vinyl chloride).
The data are scheduled to become publicly available any day now, and upon such
availability, an in depth modeling analysis should be performed on these toxicants if any
of the previously evaluated parameters show substantial increases over past levels or if
new parameters of concern are discovered.
Conclusions
While there are some technical improvements that could be made to potentially
reduce the uncertainty in the eutrophication model and improve the estimates for some
key input parameters, such as NPS nutrient loading, it is unlikely that any such
adjustments would alter the fundamental conclusions of the modeling effort. It would be
far more beneficial if the energy and resources of the stakeholders where spent
developing a more deliberate and aggressive set of tangible management efforts to reduce
NPS nutrient loading from existing and future development in the Randleman Watershed.
For the viability of the reservoir as a drinking water supply it is essential, in terms of
both public perception and empirical water quality considerations, that the pending
groundwater contamination data from the Superfund site monitoring wells be given
careful consideration.
W
Thank you again for the opportunity to comment on Draft Nutrient Reduction
Strategy. Please let me know if I can be of any further assistance in this matter.
cc: Preston Howard
Coleen Sullins
Greg Thorpe
Don Safrit
Jimmy Overton
John Dorney
Jay Sauber
Steve Mauney
Judy Garrett