1.2 Watershed Contamination & Source Protection

Why This Topic Matters for the Exam

Protecting the source water is the first and most cost-effective barrier in the multi-barrier approach to safe drinking water. In exam questions, operators are frequently tested on identifying types of watershed contamination, conducting sanitary surveys, implementing source protection plans, and managing reservoir water quality. Specifically, you must master the chemistry and math behind algae control using copper sulfate, understanding how environmental factors like water temperature and alkalinity affect chemical effectiveness and fish toxicity.

Point vs. Non-Point Source Pollution

Contaminants entering a watershed are classified into two primary categories:

1. Point Source Pollution: Contamination that originates from a single, identifiable source. Examples include municipal wastewater treatment plant discharges, industrial sewer pipes, or accidental chemical spills from a factory. Because point sources are localized, they are relatively easy to identify, monitor, and regulate under federal permits like the National Pollutant Discharge Elimination System (NPDES).
2. Non-Point Source Pollution: Contamination that comes from diffuse, scattered sources across a wide area. This occurs when rainfall or snowmelt moves over and through the ground, picking up pollutants and depositing them into water bodies. Common examples include agricultural runoff (containing fertilizers, pesticides, and animal wastes), urban runoff (carrying oil, grease, road salt, and heavy metals), and sediment from construction sites. Non-point source pollution is much harder to control and represents the leading cause of water quality impairment in reservoirs.

Agricultural Contamination and Sanitary Surveys

Agricultural runoff introduces high levels of nitrogen and phosphorus (nutrients) into watersheds. This nutrient enrichment leads to eutrophication, which stimulates rapid algae blooms. Runoff also introduces pesticides, herbicides, and pathogens like E. coli from livestock.

A sanitary survey is an on-site review of the water source, facilities, equipment, operation, and maintenance of a public water system to evaluate its adequacy for producing safe drinking water. Under federal regulations, sanitary surveys must be conducted at least every 3 years for community water systems and every 5 years for non-community systems. The survey evaluates key components: source, treatment, distribution, storage, pumps, monitoring, management, and operator compliance.

Source Water Protection and Reservoir Management

To safeguard raw water, utilities implement a Source Water Protection Plan (SWPP). This plan involves mapping the watershed boundary, identifying potential contamination sources, prioritizing risks, and implementing management strategies (such as zoning laws, land acquisition, and agricultural best management practices).

Within reservoirs, operators manage water quality by controlling algae, weeds, and invasive species. Planktonic algae can clog filters, produce taste and odor compounds (like geosmin and 2-methylisoborneol or MIB), and form harmful algal toxins. The most common method of control is applying copper sulfate ($CuSO_4 \cdot 5H_2O$).

Copper Sulfate Algae Dosing Math and Alkalinity Limits

When dosing copper sulfate, operators must perform calculations based on reservoir volume. Reservoir volume is calculated in gallons, million gallons (MG), or acre-feet (one acre-foot is 325,851 gallons).

The formula to calculate the required amount of copper sulfate is: $\text{Chemical Required (lbs)} = \text{Volume (MG)} \times \text{Dosage (mg/L)} \times 8.34\text{ lbs/gal}$ If the dosage is specified as copper ($Cu$) rather than copper sulfate ($CuSO_4 \cdot 5H_2O$), operators must account for the fact that copper sulfate is only about 25% copper by weight. Thus, the required copper sulfate is: $\text{Copper Sulfate Required (lbs)} = \frac{\text{Copper Required (lbs)}}{0.25}$

Alkalinity Constraints: The effectiveness and environmental impact of copper sulfate are highly dependent on the water's alkalinity (its capacity to neutralize acid).

• If the alkalinity is less than 50 mg/L, copper sulfate is extremely toxic to fish, particularly trout. In low-alkalinity water, copper ions remain dissolved and active, which increases fish mortality. Operators must reduce the dosage (typically to a maximum of 0.9 lbs of copper sulfate per acre-foot or 0.1 mg/L of copper) or avoid treatment.
• If the alkalinity is greater than 150 mg/L, copper reacts rapidly with carbonate ions and precipitates out of solution as copper carbonate. This renders the chemical ineffective for algae control, requiring higher doses or chelated copper formulations that prevent rapid precipitation.

Realistic Exam Scenarios

Scenario A: An operator is preparing to treat a 12-million-gallon reservoir with copper sulfate to control a blue-green algae bloom. The target dosage is 0.2 mg/L. The water's alkalinity is measured at 85 mg/L, which is within the safe range (50 to 150 mg/L) where standard doses can be applied without extreme fish toxicity or rapid chemical precipitation. The operator calculates: $\text{Copper Sulfate Required} = 12\text{ MG} \times 0.2\text{ mg/L} \times 8.34 = 20.016\text{ lbs}$ Scenario B: A sanitary survey reveals manure runoff entering a reservoir. The operator notices spikes in nitrate levels and low dissolved oxygen. This indicates non-point pollution, requiring agricultural buffer strips to protect the reservoir.