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Home My WebLink AboutNC0025879_Fact sheet v2- 26Aug2022_20220906FACT SHEET EXPEDITED - PERMIT RENEWAL NC0025879 – WPCS Grade III Basic Information for Expedited Permit Renewals Permit Writer/Date Joe R. Corporon, P.G. / NPDES / 26Aug2022 Permit Number - Class NC0025879 – WPCS Grade III Flow Phased – [existing] 0.630 MGD, and [proposed] 0.850 MGD Owner Town of Robbinsville, Graham County Facility Name Town of Robbinsville Sewer Plant Permittee Contacts Shaun Adams, Mayor PO Box 126, Robbinsville 28771-0126 Consultant MJ Chen, PhD, P.A. / 828-412-4597 Mcgill & Associates, PA, 55 Broad Street, Asheville, NC 28801/ 828-252-0575 [mj.chen@mcgillassociates.com] Type of Waste 100 % domestic Basin / Sub-basin Santeetlah Lake / Little Tennessee River Basin Receiving Stream(s) / Segment(s) Phase 1 flow => Long Creek [Tributary to Cheoah River] Phase 2 flow => Cheoah River [segment 2-190-4-(5)] Hydrological Unit / [12-digit HUC] 04-04-04 / 060102040106 Stream Classifications in Permit C; Trout / C; Trout Does permit need Daily Max NH3 limits? No (both phases have both Summer and Winter limits) Does permit need TRC limits/language? No (language included Does permit have toxicity testing? No Does permit have Special Conditions? Yes – Mercury sample once (1) during the last permitted year, results to be submitted with the permit APP to Renew. Does permit have instream monitoring? No Is the stream impaired (on 303(d) list)? No Any obvious compliance concerns? No Any permit MODS since last permit? No Requests for Renewal Received July 15, 2022 New expiration date November 30, 2027 Changes to current permit? Updated map, text, eDMR language; reformatted table; added instream monitoring (see below - Note to Cover Letter). The Town of Robbinsville (Robbinsville) is a 100%-domestic WWTP (WPCS Grade III) currently discharging under Phase 1 flow (0.630 MGD) averaging 0.462 MGD. They estimate their inflow/Infiltration at 0.069 MGD. The treatment facility disinfects by Ultra Violate (UV) using chlorine as backup only [see A. (1.) and A. (2.)]. Robbinsville services a population of ~ 2,079 (2020). They monitor Ammonia (NH3 as N), complying with both Summer and Winter permit limits; they do not currently monitor for Whole Effluent Toxicity (WET) – no changes recommended. Summary of Changes for Renewal: 1) updated Site Map and permit text for Electronic Reporting [section A. (4.)] 2) added parameter codes to Effluent Characteristics [Tables A. (1.) and A. (2.)] 3) resorted effluent tables according to monitoring frequency (most frequent to least frequent) 4) added pH to the monitoring tables instead of a previous footnote reference. Stream Monitoring - Note to Cover Letter “This draft permit includes significant changes from your existing permit. DWR requires these changes because your facility discharges to a receiving stream classified C; Trout [see permit sections A. (1.) and A. (2.)]. Instream monitoring includes: ➢ Monitoring for Turbidity has been added to determine compliance with 15A NCAC 02B.0211 (21). ➢ Monitoring for Dissolved Oxygen has been added to determine compliance with 15A NCAC 02B.0211 (6). ➢ Instream monitoring for Temperature and a footnote regarding temperature increases was added to determine compliance with 15A NCAC 02B.0211 (18).” Violation Summary (BIMS Jan2019-Aug2022) – during the previous permit cycle, only three (3) violations proceeded to NOV: • Flow - MA exceeded (Feb2020) • BOD 5-day - WA exceeded (Jan2021) • pH - minimum not reached (Mar2021). See attached Violations Data Review. No changes recommended. Proposed Schedule of Issuance Draft Permit to Public Notice: 06Sep2022 (est.) Permit Scheduled to Issue: 14Oct2022 (est.) Effective Date 01Dec2022 (est.) NPDES Division Contact If you have questions about any of the above information, or on the attached permit, please email Joe R. Corporon, P.G. [joe.corporon@ncdenr.gov]. NAME: DATE: 26AUG2022 NPDES Implementation of Instream Dissolved Metals Standards – Freshwater Standards The NC 2007-2015 Water Quality Standard (WQS) Triennial Review was approved by the NC Environmental Management Commission (EMC) on November 13, 2014. The US EPA subsequently approved the WQS revisions on April 6, 2016, with some exceptions. Therefore, metal limits in draft permits out to public notice after April 6, 2016 must be calculated to protect the new standards - as approved. Table 2. NC Dissolved Metals Water Quality Standards/Aquatic Life Protection Parameter Acute FW, µg/l (Dissolved) Chronic FW, µg/l (Dissolved) Acute SW, µg/l (Dissolved) Chronic SW, µg/l (Dissolved) Arsenic 340 150 69 36 Beryllium 65 6.5 --- --- Cadmium Calculation Calculation 40 8.8 Chromium III Calculation Calculation --- --- Chromium VI 16 11 1100 50 Copper Calculation Calculation 4.8 3.1 Lead Calculation Calculation 210 8.1 Nickel Calculation Calculation 74 8.2 Silver Calculation 0.06 1.9 0.1 Zinc Calculation Calculation 90 81 Table 2 Notes: 1. FW= Freshwater, SW= Saltwater 2. Calculation = Hardness dependent standard 3. Only the aquatic life standards listed above are expressed in dissolved form. Aquatic life standards for Mercury and selenium are still expressed as Total Recoverable Metals due to bioaccumulative concerns (as are all human health standards for all metals). It is still necessary to evaluate total recoverable aquatic life and human health standards listed in 15A NCAC 2B.0200 (e.g., arsenic at 10 µg/l for human health protection; cyanide at 5 µg/L and fluoride at 1.8 mg/L for aquatic life protection). Table 3. Dissolved Freshwater Standards for Hardness-Dependent Metals The Water Effects Ratio (WER) is equal to one unless determined otherwise under 15A NCAC 02B .0211 Subparagraph (11)(d) Metal NC Dissolved Standard, µg/l Cadmium, Acute WER*{1.136672-[ln hardness](0.041838)} ∙ e^{0.9151 [ln hardness]- 3.1485} Cadmium, Acute Trout waters WER*{1.136672-[ln hardness](0.041838)} ∙ e^{0.9151[ln hardness]- 3.6236} Cadmium, Chronic WER*{1.101672-[ln hardness](0.041838)} ∙ e^{0.7998[ln hardness]- 4.4451} Chromium III, Acute WER*0.316 ∙ e^{0.8190[ln hardness]+3.7256} Chromium III, Chronic WER*0.860 ∙ e^{0.8190[ln hardness]+0.6848} Copper, Acute WER*0.960 ∙ e^{0.9422[ln hardness]-1.700} Copper, Chronic WER*0.960 ∙ e^{0.8545[ln hardness]-1.702} Lead, Acute WER*{1.46203-[ln hardness](0.145712)} ∙ e^{1.273[ln hardness]-1.460} Lead, Chronic WER*{1.46203-[ln hardness](0.145712)} ∙ e^{1.273[ln hardness]-4.705} Nickel, Acute WER*0.998 ∙ e^{0.8460[ln hardness]+2.255} Nickel, Chronic WER*0.997 ∙ e^{0.8460[ln hardness]+0.0584} Silver, Acute WER*0.85 ∙ e^{1.72[ln hardness]-6.59} Silver, Chronic Not applicable Zinc, Acute WER*0.978 ∙ e^{0.8473[ln hardness]+0.884} Zinc, Chronic WER*0.986 ∙ e^{0.8473[ln hardness]+0.884} General Information on the Reasonable Potential Analysis (RPA) The RPA process itself did not change as the result of the new metals standards. However, application of the dissolved and hardness-dependent standards requires additional consideration in order to establish the numeric standard for each metal of concern of each individual discharge. The hardness-based standards require some knowledge of the effluent and instream (upstream) hardness and so must be calculated case-by-case for each discharge. Metals limits must be expressed as ‘total recoverable’ metals in accordance with 40 CFR 122.45(c). The discharge-specific standards must be converted to the equivalent total values for use in the RPA calculations. We will generally rely on default translator values developed for each metal (more on that below), but it is also possible to consider case-specific translators developed in accordance with established methodology. RPA Permitting Guidance/WQBELs for Hardness-Dependent Metals - Freshwater The RPA is designed to predict the maximum likely effluent concentrations for each metal of concern, based on recent effluent data, and calculate the allowable effluent concentrations, based on applicable standards and the critical low-flow values for the receiving stream. If the maximum predicted value is greater than the maximum allowed value (chronic or acute), the discharge has reasonable potential to exceed the standard, which warrants a permit limit in most cases. If monitoring for a particular pollutant indicates that the pollutant is not present (i.e. consistently below detection level), then the Division may remove the monitoring requirement in the reissued permit. 1. To perform a RPA on the Freshwater hardness-dependent metals the Permit Writer compiles the following information: • Critical low flow of the receiving stream, 7Q10 (the spreadsheet automatically calculates the 1Q10 using the formula 1Q10 = 0.843 (s7Q10, cfs) 0.993 • Effluent hardness and upstream hardness, site-specific data is preferred • Permitted flow • Receiving stream classification 2. In order to establish the numeric standard for each hardness-dependent metal of concern and for each individual discharge, the Permit Writer must first determine what effluent and instream (upstream) hardness values to use in the equations. The permit writer reviews DMR’s, Effluent Pollutant Scans, and Toxicity Test results for any hardness data and contacts the Permittee to see if any additional data is available for instream hardness values, upstream of the discharge. If no hardness data is available, the permit writer may choose to do an initial evaluation using a default hardness of 25 mg/L (CaCO3 or (Ca + Mg)). Minimum and maximum limits on the hardness value used for water quality calculations are 25 mg/L and 400 mg/L, respectively. If the use of a default hardness value results in a hardness-dependent metal showing reasonable potential, the permit writer contacts the Permittee and requests 5 site-specific effluent and upstream hardness samples over a period of one week. The RPA is rerun using the new data. The overall hardness value used in the water quality calculations is calculated as follows: Combined Hardness (chronic) = (Permitted Flow, cfs *Avg. Effluent Hardness, mg/L) x (s7Q10, cfs *Avg. Upstream Hardness, mg/L) (Permitted Flow, cfs + s7Q10, cfs) The Combined Hardness for acute is the same but the calculation uses the 1Q10 flow. 3. The permit writer converts the numeric standard for each metal of concern to a total recoverable metal, using the EPA Default Partition Coefficients (DPCs) or site-specific translators, if any have been developed using federally approved methodology. 4. The numeric standard for each metal of concern is divided by the default partition coefficient (or site-specific translator) to obtain a Total Recoverable Metal at ambient conditions. In some cases, where an EPA default partition coefficient translator does not exist (ie. silver), the dissolved numeric standard for each metal of concern is divided by the EPA conversion factor to obtain a Total Recoverable Metal at ambient conditions. This method presumes that the metal is dissolved to the same extent as it was during EPA’s criteria development for metals. For more information on conversion factors see the June, 1996 EPA Translator Guidance Document. 5. The RPA spreadsheet uses a mass balance equation to determine the total allowable concentration (permit limits) for each pollutant using the following equation: Ca = (s7Q10 + Qw) (Cwqs) – (s7Q10) (Cb) Qw Where: Ca = allowable effluent concentration (µg/L or mg/L) Cwqs = NC Water Quality Standard or federal criteria (µg/L or mg/L) Cb = background concentration: assume zero for all toxicants except NH3* (µg/L or mg/L) Qw = permitted effluent flow (cfs, match s7Q10) EPA default partition coefficients or the “Fraction Dissolved” converts the value for dissolved metal at laboratory conditions to total recoverable metal at in-stream ambient conditions. This factor is calculated using the linear partition coefficients found in The Metals Translator: Guidance for Calculating a Total Recoverable Permit Limit from a Dissolved Criterion (EPA 823-B-96-007, June 1996) and the equation: _Cdiss__ = _______1_______________ Ctotal 1 + { [Kpo] [ss(1+a)] [10-6] } Where: ss = in-stream suspended solids concentration [mg/l], minimum of 10 mg/L used, and Kpo and a = constants that express the equilibrium relationship between dissolved and adsorbed forms of metals. A list of constants used for each hardness-dependent metal can also be found in the RPA program under a sheet labeled DPCs. s7Q10 = summer low flow used to protect aquatic life from chronic toxicity and human health through the consumption of water, fish, and shellfish from noncarcinogens (cfs) * Discussions are on-going with EPA on how best to address background concentrations Flows other than s7Q10 may be incorporated as applicable: 1Q10 = used in the equation to protect aquatic life from acute toxicity QA = used in the equation to protect human health through the consumption of water, fish, and shellfish from carcinogens 30Q2 = used in the equation to protect aesthetic quality 6. The permit writer enters the most recent 2-3 years of effluent data for each pollutant of concern. Data entered must have been taken within four and one-half years prior to the date of the permit application (40 CFR 122.21). The RPA spreadsheet estimates the 95th percentile upper concentration of each pollutant. The Predicted Max concentrations are compared to the Total allowable concentrations to determine if a permit limit is necessary. If the predicted max exceeds the acute or chronic Total allowable concentrations, the discharge is considered to show reasonable potential to violate the water quality standard, and a permit limit (Total allowable concentration) is included in the permit in accordance with the U.S. EPA Technical Support Document for Water Quality-Based Toxics Control published in 1991. 7. When appropriate, permit writers develop facility specific compliance schedules in accordance with the EPA Headquarters Memo dated May 10, 2007 from James Hanlon to Alexis Strauss on 40 CFR 122.47 Compliance Schedule Requirements. 8. The Total Chromium NC WQS was removed and replaced with trivalent chromium and hexavalent chromium Water Quality Standards. As a cost savings measure, total chromium data results may be used as a conservative surrogate in cases where there are no analytical results based on chromium III or VI. In these cases, the projected maximum concentration (95th %) for total chromium will be compared against water quality standards for chromium III and chromium VI. 9. Effluent hardness sampling and instream hardness sampling, upstream of the discharge, are inserted into all permits with facilities monitoring for hardness-dependent metals to ensure the accuracy of the permit limits and to build a more robust hardness dataset. 10. Hardness and flow values used in the Reasonable Potential Analysis for this permit included: Table 4 Parameter Value Comments (Data Source) Average Effluent Hardness (mg/L) [Total as, CaCO3 or (Ca+Mg)] N/A No metals monitored Average Upstream Hardness (mg/L) [Total as, CaCO3 or (Ca+Mg)] N/A 7Q10 summer (cfs) N/A 1Q10 (cfs) N/A Permitted Flow (MGD) N/A Phased: 0.630 and 0.850