Metals and Dissolved Ions

Dissolved ions are commonly measured by conductivity, pH, and hardness. These parameters are vital to stream ecosystem conditions, such as bioavailability of nutrients, heavy metals toxicity, and metabolic processes of aquatic communities. pH can be naturally lower because of soils and watersheds with coniferous forests, but also can be affected by industrial, commercial, and other land uses. Levels can be affected by other imbalances such as nutrients or discharges with extreme temperatures or low DO concentration. Metals in an aquatic environment may be in suspended, colloidal, or soluble/ dissolved form. Metals criteria in Georgia are expressed as dissolved metals. Dissolved metals exclude those bound to materials in the water, such as clay and organic matter, and are most available for

bioaccumulation. Hardness is a measure of certain metal ions, and as hardness increases, the toxicity of

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metals decreases. Because of this relationship, the State’s criteria for cadmium, copper, lead, and zinc vary and are calculated based on the hardness of each particular water body. Potential sources of metal pollutants are commonly particulates from roadways and runoff from commercial and industrial areas from components such as gasoline, tires, brake pads, corroded metals, paint, and motor oil.

Key findings related to metals, hardness, conductivity, and pH are summarized below.

x pH (Figure A-3)

 During this reporting period, pH measured at all bacteria and water quality sampling stations was within the state standard of 6.0 and 8.5 standard units.

 The pH in Carr Creek at Bailey Street (Site 12) was consistently low relative to other sampling sites, although levels are still within state standards.

 During the November 2016 wet-weather event, Tanyard Creek (Site 14) recorded its lowest pH value (6.52) since sampling began at this location in 2011.

 During the January 2017 dry-weather event, Turkey Creek (Site 15) recorded its second lowest pH value (6.52) since sampling began at this location in 2011.

x Conductivity (Figure A-5)

 There are no State standards for conductivity. EPA has indicated that conductivity of most rivers in the United States is between 50 and 1,500 microSiemens per centimeter (ʅ^ͬĐŵ) and

ƐƵŐŐĞƐƚƐƚŚĂƚůĞǀĞůƐŽĨĐŽŶĚƵĐƚŝǀŝƚLJďĞƚǁĞĞŶϭϱϬĂŶĚϱϬϬʅ^ͬĐŵĐĂŶƐƵƉƉŽƌƚŚĞĂůƚŚLJĨƌĞƐŚǁĂƚĞƌ

fish and macroinvertebrate communities (EPA, 1997). Conductivity in ACC streams is generally ůŽǁĞƌƚŚĂŶϮϬϬʅ^ͬĐŵ͕ǁŝƚŚƚŚĞĞdžĐĞƉƚŝŽŶŽĨĂƌƌ and Tanyard Creeks, although Tanyard Creek was below 200 ʅ^ͬĐŵ during all sampling events for this reporting period.

 Conductivity in Tanyard Creek was high, relative to stations other than Carr Creek, since sampling began. During this reporting period, conductivity levels in Tanyard Creek were lower than the previous reporting period; however, levels are still high relative to other ACC streams.

 Conductivity was consistently high relative to other sampling sites in Carr Creek, with levels ranging from 256 to 620 ʅ^ͬĐŵ during the reporting period. These patterns may be related to other water quality parameters and are discussed further in the summary of results.

 Conductivity was slightly elevated in North Oconee River (Site 4) compared to the previous reporting period and historical averages.

x Hardness (Figures A-21 and A-22) Dissolved Metals (Table 3-8)

 On average, the hardness of ACC streams is lower than the 50-mg/L as calcium carbonate (CaCO3) value used to develop water quality criteria for many metals. However, the hardness in Carr Creek is significantly higher during dry weather than the hardness in other ACC streams.

 During the October 2016 dry-weather event, North Oconee River (Site 4) recorded a hardness value of 94 mg/L as CaCO3, the highest value recorded outside of Carr Creek (Site 12).

 The toxicity of metals, and therefore the State water quality criteria for metals, is dependent on the hardness of the waterbody. Because the toxicity of metals increases as the hardness of a water body decreases, the metals criteria for ACC streams generally are more stringent than those established for streams with the value of 50 mg/L as CaCO3.

x Dissolved Metals (Table 3-8)

 Dissolved metals were measured during both wet and dry events for the second consecutive reporting period.

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 All dissolved metals were below the reporting limits (5 micrograms per liter [ʅg/L] cadmium, 25 ʅg/L copper, 10 ʅg/L lead, 50 ʅg/L zinc), with the exception of dissolved zinc at Carr Creek (Site 12). Hardness and Zinc concentrations at Carr Creek are summarized in Table 3-7.

 During the October 5 dry-weather event and November 29 wet-weather event, the acute and chronic dissolved zinc criteria were not exceeded at Carr Creek.

 During January 31 wet-weather event, the acute and chronic dissolved zinc criteria were exceeded at Carr Creek.

TTable 3--77. Dissolved Zinc CConcentrations at Carr Creek

Date Event Type

Hardness (mg/L as CaCO3)

Dissolved Zinc (μg/L)

Dissolved Zinc Standard - Acute

(μg/L)^a

Dissolved Zinc Standard - Chronic (μg/L)^b

Criteria Exceeded

October 5, 2016 Dry-weather 304 90 301 303 No

November 29, 2016 Wet-weather 96 91 113 114 No

January 31, 2017 Dry-weather 30 111 42 43 Yes

aAcute standards are the highest concentration of a pollutant to which aquatic life can be exposed to for a short period of time (1 hour average) without deleterious effects.

bChronic standards are the highest concentration of a pollutant to which aquatic life can be exposed to for an extended period of time (4 days) without deleterious effects.

3.2.5 Sediment

Excessive sediment loading in streams can decrease water clarity; provide a transport mechanism for other pollutants (such as nutrients and fecal coliform, which can adhere to sediment particles); and can lead to flow and habitat impairments because of aggradation on large point bars. Turbidity may be caused by a wide variety of suspended materials, such as clay, silt, fine organic and inorganic matter, some soluble organic compounds, plankton and other microscopic organisms, and similar substances.

Total suspended solids (TSS) is a measure of particles found in water that can be removed by filtration.

The suspended material is often from natural sources (e.g., silt captured in runoff), but may result from other human sources including construction sites and urban and agricultural land uses. Key findings related to sediment are summarized below:

x Total Suspended Solids (Figures A-23 and A-24)

 During the November 2016 wet-weather event, levels of TSS were elevated at Turkey Creek (160 mg/L), and all other measurements were less than or equal to 75 mg/L.

 TSS levels at all locations during the dry-weather monitoring events were less than or equal to 15 mg/L.

x Turbidity (Figure A-6)

 Similar to weather TSS patterns, turbidity was elevated during the November 2016 wet-weather event at Turkey Creek (124.3 nephelometric turbidity units [NTU]).

SECTION 4

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Assessment of Stream Health and Potential