Water Lecture 4

Mineral particles

Suspended sediment/particles.

Dissolved substances

Ca, Mg, K, Na, Cl, SO4, HCO3.

Microscopic solids & organic matter

Includes pathogenic microorganisms (cholera, typhoid, dysentery).

Industrial contamination

Heavy metals (lead), synthetic chemicals (DDT, PCBs, PFAS), nuclear waste.

Water with >500 ppm dissolved solids

Unsuitable for human consumption.

US EPA regulation

Over 100 organic & inorganic contaminants must be tested 4 times per year.

Point source contamination

Identifiable, localized (e.g., leaking storage tank, landfill).

Non-point source contamination

Diffuse contamination (e.g., pesticides, road salt).

Trace metals

Lead, mercury.

Nutrients

Phosphorus, nitrogen compounds.

Microbes

Bacteria, viruses.

Organic compounds

Carbon-based pollutants.

Radioactive waste

Uranium, plutonium.

Safely Managed Drinking Water Services (SMDWS)

Criteria for improved water delivery (e.g., tap water, boreholes, protected wells).

4.4 billion people in LMICs

Lack SMDWS.

Sub-Saharan Africa SMDWS

Has the lowest rates of SMDWS (<10% of the population in 12 countries).

EPA regulates ~100 contaminants

But many more exist, including ~700 disinfection by-products and ~1,200 chemicals from fracking.

Key Contaminants

Arsenic, linked to skin, bladder, and lung cancers.

EPA MCL for Arsenic

10 µg/L, but no safe level (MCLG = 0 µg/L).

Disinfection Byproducts (DBPs)

Formed from chlorine interacting with organic matter, linked to bladder cancer and pregnancy complications.

Fracking-Related Substances

~150,000 active wells in the US with toxic, radioactive, endocrine-disrupting, and carcinogenic chemicals.

Lead

Highly toxic, affecting the nervous, cardiovascular, kidney, and immune systems.

Nitrates

From fertilizers, manure, wastewater, septic systems; MCL: 10 mg/L.

PFAS ('Forever Chemicals')

Linked to cancer, immune suppression, and hormone disruption; 98% of Americans have detectable PFAS in their blood.

EPA's 2022 advisory level for PFAS

0.004 ng/L (extremely low tolerance).

Maximum Contaminant Level (MCL)

Highest allowed concentration.

Maximum Contaminant Level Goal (MCLG)

No known health risk threshold.

Treatment Technique (TT)

Required process to reduce contaminants.

Units

mg/L = ppm (parts per million).