pH

Chemical symbol/abbreviations:

pH

Units:

Standard unit (s.u.); pH is measured on a logarithmic scale, ranging from 0 to 14 s.u., with 7 s.u. being neutral pH.

Solubility in water:

Constituents influencing pH are soluble in water.

Related constituent:

Alkalinity – the ability to prevent changes in pH due to the presence of carbonate and bicarbonate. Alkalinity acts to buffer a solution in the case that acids are added.

Adverse human impacts:

Both high pH (over 8.5) and low pH (under 6.5) water has an unpleasant taste.[i]  Extremely high or low pH substances can damage human tissue on contact.[ii]  Chronic pH imbalances in the human body can cause effects ranging from muscle weakness to death.[iii]

Adverse impacts on the environment:

Aquatic invertebrates with exoskeletons or shells are particularly sensitive to pH lower than 7[iv] which can impede shell formation.[v]
Adult brook trout can tolerate pH 5.0 – 9.5, while eggs and larvae can only tolerate a narrower pH range around neutral.[vi]
Adult fish may experience non-lethal adverse effects at the high and low ends of this range.[vii]
Low pH within this range may still kill fish if metals are also present in the water, because low pH can bring metals to a more dangerous dissolved state.[viii]

Stormwater Treatment to Affect pH

Background:

pH is a key water quality parameter influencing a wide array of chemical interactions in water.  The solubility of metals, the ionization of ammonium, and boundary layer kinetics are all affected by pH.  pH is a measure of the hydrogen ion concentration in solution indicating the relative presence of acids and bases. Since pH is measured on a logarithmic scale, a shift in pH by 1 unit indicates a ten-fold increase or decrease in the concentration.

The pH of stormwater is slightly higher than that of rainwater due to the alkalinity that stormwater picks up when coming into contact with paved surfaces. Rain water has a pH of 5.6. A common range of pH values for stormwater is 6.5 – 7.2.[vii] Carbon dioxide and sulfur dioxide are prevalent anthropogenic emissions that reduce the pH of surface water. 

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Appendices

[i] U.S. EPA, Secondary Drinking Water Regulations: Guide for Nuisance Chemicals, http://www.epa.gov/safewater/consumer/2ndstandards.html (last visited Aug. 10, 2010).

[ii] See, e.g., Agency for Toxic Substances & Disease Registry, ToxFAQs for Sulfur Trioxide and Sulfuric Acid http://www.atsdr.cdc.gov/tfacts117.html (last visited Aug. 10, 2010); NJ Dept. Health & Human Servs., Hazardous Substances Fact Sheet – Potassium Hydroxide (2010) available at http://www.state.nj.us/health/eoh/rtkweb/documents/fs/1571.pdf.

[iii] Gale Cengage, Acid-Base Balance, Encyclopedia of Nursing & Allied Health (Kristine Krapp, ed. 2002) available at http://www.enotes.com/nursing-encyclopedia/acid-base-balance.

[iv] Penn. Fish & Boat Commission, The Basics of Water Pollution in Pennsylvania, Penn. Angler & Boater 35 available at http://www.fish.state.pa.us/anglerboater/2001/jf2001/wpollbas.htm.

[v] Richard Feely, Ocean Acidification, 17th Annual Endangered Species Act (Jan. 28, 2010) (on file with The Seminar Group).

[vi] Penn. Fish & Boat Commission, supra.

[vii] Penn. Fish & Boat Commission, supra.

[viii] Penn. Fish & Boat Commission, supra.

[ix] Gary Minton, Stormwater Treatment (Resource Planning Associates 2005).

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