Source Water
Core concepts
Know the characteristics of groundwater versus surface water sources: groundwater is typically cooler, more consistent, lower in turbidity and microbes, but higher in dissolved minerals (iron, manganese, hardness, sometimes arsenic or nitrate); surface water is variable, turbidity-prone, and biologically and organically richer. Understand watershed and wellhead protection, source water assessment, intake design, well construction and sanitary seals, and the concepts of safe yield and sustainable withdrawal. Recognize how source quality drives treatment selection and monitoring frequency under the Surface Water Treatment Rules and Ground Water Rules.
Traps to watch
A frequent trap is assuming groundwater is always microbiologically safe-it can be under the direct influence of surface water (GWUDI) and requires surface-water-type treatment. Another is confusing contamination source with treatment: nitrate from fertilizer is a source-protection and blending issue, not something conventional filtration removes well. Distinguish aquifer types (confined vs unconfined) and understand that a confined aquifer is protected from direct surface recharge. Watch questions that ask which parameter indicates a specific problem (e.g., iron/manganese cause staining and taste, not acute health risk).
Worked example / rule of thumb
Safe yield rule of thumb: long-term withdrawal should not exceed long-term recharge; a well pumped beyond safe yield shows declining static water level and increasing drawdown. For blending to meet a limit, use the mass-balance: (Q1·C1 + Q2·C2) ÷ (Q1 + Q2) = blended concentration. Example: 100 gpm at 12 mg/L nitrate blended with 300 gpm at 2 mg/L gives (1200 + 600) ÷ 400 = 4.5 mg/L.
Exam strategy
Match the source characteristic to the treatment or monitoring consequence; do not memorize numbers without the logic behind them.