NC0083909_Fact Sheet_20030409

DENR/DWQ
FACT SHEET FOR NPDES PERMIT DEVELOPMENT
NPDES No.NCO083909
Facility Information
Applicant/Facility Name: Dare Coun /Rodanthe,Waves,Salvo R.O. WTP
Applicant Address: P.O. Box 500; Rodanthe,North Carolina 27968
Facility Address: Off NCSR 12; Rodanthe,North Carolina 27968
Permitted Flow 0.3 MGD
Type of Waste: 100%reject water from reverse osmosisplant)
Facility/Permit Status: Class I/Active; Renewal
Count Dare Count
Miscellaneous
Receiving Stream: Blackmar Gut Regional Office: Washington
Stream Classification: SA-HQW State Grid/USGS Quad: E36SE
303 d Listed? no Permit Writer: Natalie V. Sierra
Subbasin: 03-01-55 Date: 4/9/03
Drainage Area(mi2): NA
Summer 7Q10 cfs NA tidal
Winter 7Q10(cfs): NA(tidal)
30Q2 cfs NA tidal
Average Flow cfs : NA tidal
IWC (%): TIDAL
Lat. 35°35'43"N Lon 75°28' 12"W
BACKGROUND
Dare County's Rodanthe, Waves, Salvo Reverse Osmosis Water Treatment Plant is a Class I
Physical/Chemical plant with a permitted flow of 0.3 MGD. The plant discharges reject water
from a reverse osmosis water treatment plant serving the communities of Rodanthe, Waves and
Salvo, all on Hatteras Island. The WTP produces 1.0 MGD of potable water by treating
groundwater from two wells on the Yorktown Aquifer.
The only chemicals added during the water treatment process (and thus expected to be in the
reject water) are a scale inhibitor and sulfuric acid. From concentration of the source water, the
discharge contains detectable levels of barium, boron, calcium, iron, magnesium, potassium,
sodium, tin, ammonia nitrogen,bromide, chloride, sulfate and fluoride.
The permit was last issued on December 22, 2000 and expired March 31, 2003. The Permittee
applied for renewal of the NPDES permit by submitting Standard Form C-RO on October 7,
2002.
Instream Monitoring and Verification of Existing Conditions and DMR Data Review
This facility discharges to Blackmar Gut (classified SA-HQW), located within sub-basin 03-01-
55 of the Pasquotank River Basin. In the May 2002 Pasquotank Basinwide Water Quality Plan,
most of the waters in this subbasin were rated as fully supporting their designated uses.
Blackmar Gut is considered a primary shellfishing (for market purposes) area with water quality
higher than North Carolina's standards for such waters (High Quality Waters (HQW)).
The facility is not required to monitor instream water quality, so no instream data were reviewed.
Effluent data from February 2001 (the first full effective month of the permit) through February
2003 were compiled from Discharge Monitoring Reports (DMRs) for conventional parameters,
metals and toxicants. Flow, conductivity, salinity, total suspended solids (TSS), settleable solids
and turbidity values are presented in Table 1 below. The remaining monitored parameters were
analyzed using a reasonable potential analysis. This analysis is presented in a later section of
this fact sheet.
Flow Conductivity '
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(MGD) iSolids
Average 0.069 18216 13.31 1 NC I NC NC
Maximum 0.150 9750 14.34 1 1.0 10.1 14.7
Minimum 0.020 5500 12.77 1 <1 I <0.1 I <1
Table 1 Summary of effluent DMR data. NC=not calculated,because most of the values were below detection level.
It is difficult to assess the conductivity and salinity values with no knowledge of the instream
values. TSS, settleable solids and turbidity were extremely low and most of the data points were
below detection level. Flow was well within the permit limit of 0.3 MGD.
Correspondence
The Washington Regional Office (WaRO) conducted one site visit to this facility in February
2001. The facility received a compliant rating at that time. The Aquatic Toxicology Unit (ATU)
conducted a toxicity test in March 2002 that resulted in an LC50 of 76.8%, which is less than the
90% acute limit in most permits.
PERMITTING STRATEGY
Waste Load Allocation (WLA)
The permit was last issued in December 2000. The permit contains limits for flow, TSS,
settleable solids, pH, turbidity, arsenic, cadmium, cyanide, lead, mercury, nickel, and selenium.
Due to the tidal nature of the receiving waterbody, no Instream Waste Concentration (IWC) can
be established for this discharge without proper modeling. Limits for toxicants were therefore
implemented as acute limits at 1/2 the water quality standard (since Blackmar Gut is classified
HQW). The facility is also required to monitor for conductivity, chloride, chromium, copper,
salinity, silver, zinc, fluoride, iron, and acute toxicity.
Reasonable Potential Analysis (RPA)
The Division conducted EPA-recommended analyses to determine the reasonable potential for
toxicants to be discharged by this facility, based on DMR data from February 2001 through
February 2003. Calculations included: arsenic, cadmium, chloride, chromium, copper, cyanide,
lead, mercury, nickel, selenium, silver, zinc, fluoride and iron.
Results suggest no reasonable potential for the facility to discharge arsenic, cadmium, chloride,
fluoride, iron, lead, mercury, silver and nickel. These parameters will be monitored on a
quarterly basis.
Chromium, copper, cyanide, selenium and zinc all showed reasonable potential to exceed water
quality standards. Copper and zinc will be monitored but not limited, as they are action level
parameters. As per North Carolina's current action level policy, copper and zinc should only be
limited if a facility shows recurrent toxicity problems that can be linked to copper and zinc.
Chromium, cyanide and selenium will all be limited at the standard. Monitoring for copper and
zinc will be monthly, while monitoring for chromium, cyanide and selenium will be twice per
month.
Water Treatment Plant Permitting Strategy
As per the findings of the interagency Water Treatment Plant Workgroup (as summarized in
Assessment and Recommendations for Water Treatment Plant Permitting), the following will
also be incorporated into the draft permit:
• Temperature and dissolved oxygen monitoring - monthly
Elimination of settleable solids and turbidity monitoring (scarcely detected during
entire permit period). The intent of these monitoring requirements will now be met
with monthly total dissolved solids monitoring.
Ammonia nitrogen, total nitrogen and total phosphorus monitoring—monthly
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Instream monitoring for pH, dissolved oxygen, salinity, conductivity, and
temperature- monthly
• Total residual chlorine limit—with footnote indicating that this limit is only
required if chlorine or a chlorine derivative is used in the treatment process
Other Changes
It is recommended that the total suspended solids monitoring be reduced to quarterly given that it
was so rarely detected in the past two years. Moreover, this type of discharge is more likely to
include high levels of dissolved solids, not suspended solids. At the next renewal, the permit
writer may wish to consider elimination of the total suspended solids monitoring requirement.
SUMMARY OF PROPOSED CHANGES
In keeping with Division policies and the updated policy for permitting reverse osmosis water
treatment plants, the following will be incorporated into the permit:
Addition of monthly temperature and dissolved oxygen monitoring
Elimination of settleable solids and turbidity monitoring
Addition of monthly total dissolved solids monitoring.
Addition of monthly ammonia nitrogen, total nitrogen and total phosphorus
monitoring
Addition of monthly instream monitoring for pH, dissolved oxygen, salinity,
conductivity, and temperature
Addition of total residual chlorine limit (with footnote)
• Removal of limits for arsenic, cadmium, mercury, lead, and nickel (with
monitoring reduced to quarterly).
Reduction of monitoring frequency for silver, fluoride and iron from monthly to
quarterly.
Addition of limit for chromium, monitoring frequency increased to twice
monthly.
• Increase of monitoring frequency for cyanide and selenium to twice monthly.
Reduction of TSS monitoring to quarterly.
New Weekly Average and Daily Maximum limits are derived from the latest NC/EPA policies
considering t/2 FAVs and allowable concentrations based on reasonable potential.
Requirements for flow, effluent pH, chloride, copper, zinc, salinity and toxicity will remain the same.
PROPOSED SCHEDULE FOR PERMIT ISSUANCE
Draft Permit to Public Notice: April 23,2003
Permit Scheduled to Issue: June 16,2003
Attachments: Conventional effluent data summary, toxicant effluent data summary, reasonable potential
analysis, toxicity report, relevant pages of WTP permitting recommendations report.
NPDES DIVISION CONTACT
If you have questions regarding any of the above information or on the attached permit, please contact
Natalie Sierra at(919) 733-5083 ext. 551.
NAME: DATE:
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REGIONAL OFFICE COMMENTS
NAME: DATE:
SUPERVISOR: DATE:
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