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N.C. Department of Environment and Natural Resources

NC Department of Environment and Natural Resources
Water Quality - Hard/D-Metals

Water Quality

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FACILITY INFORMATION

    

8-DIGIT HUC HARDNESS 

 

   

 

 

 

 

 

 


 

Dissolved Metals & Hardness Determination

v. 5/27/2010

I. How to Determine Hardness for use with Dissolved Freshwater Standards for    Permitting Purposes

HARDNESS - Use 25 mg/L, expressed as CaCO3 or Ca+Mg, as the default Hardness
OR
To determine a Hardness value for permit limit development, use the following equation:

  Hardness        =   (Hardness instream(a), mg/L * 7Q10, MGD)+(Hardness effluent(b), mg/L* Plant flow, MGD)
(mass balance)                                                           (7Q10, MGD + Plant flow, MGD)

(a)    Use the median instream Hardness value of the ambient 8-digit HUC data collected by the Division of Water Quality.  To find the 8-digit HUC hardness value for your facility, Click Here.
(b)    For the purpose of this estimation, use the facility's median effluent Hardness value, if available.  The Division will request the permittee to sample effluent hardness once/month and submit one to two years of data with the permit renewal application. If no effluent hardness data is submitted, a default of 25 mg/L will be applied.

II. To Develop Dissolved Metal concentrations for permitting purposes use the Freshwater Standards for Hardness Dependent Metals listed in Table A below.
  

Table A: Dissolved Freshwater Standards for Hardness Dependent Metals
Metal µg/L
Cadmium, Acute {1.136672-[ln hardness](0.041838)} · e^{0.9151 [ln hardness]-3.1485} 
Cadmium, Acute (Trout Waters) {1.136672-[ln hardness](0.041838)} · e^{0.9151[ln hardness]-3.6236}
Cadmium, Chronic {1.101672-[ln hardness](0.041838)} · e^{0.7998[ln hardness]-4.4451}
Chromium III, Acute 0.316 · e^{0.8190[ln hardness]+3.7256}
Chromium III, Chronic 0.860 · e^{0.8190[ln hardness]+0.6848}
Copper, Acute 0.960 · e^{0.9422[ln hardness]-1.700}
Copper, Chronic 0.960 · e^{0.8545[ln hardness]-1.702}
Lead, Acute {1.46203-[ln hardness](0.145712)} · e^{1.273[ln hardness]-1.460}
Lead, Chronic {1.46203-[ln hardness](0.145712)} · e^{1.273[ln hardness]-4.705}
Nickel, Acute 0.998 · e^{0.8460[ln hardness]+2.255}
Nickel, Chronic 0.997 · e^{0.8460[ln hardness]+0.0584}
Silver, Acute 0.85 · e^{1.72[ln hardness]-6.59}
Silver, Chronic Not applicable
Zinc, Acute 0.978 · e^{0.8473[ln hardness]+0.884}
Zinc, Chronic 0.986 · e^{0.8473[ln hardness]+0.884}

Complete information on all the proposed Surface Water Quality Standards can be viewed at: http://h2o.enr.state.nc.us/csu/trirev_SW.html.

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