Source Water and Groundwater
What the exam tests
Source Water and Groundwater tests how wells, aquifers, and surface supplies are protected and how source quality affects treatment. Expect well construction, drawdown, specific capacity, source water assessment, wellhead protection, and common contaminants such as nitrate, iron, hardness, and arsenic.
Core rules and concepts
- A properly constructed well has casing, a sanitary seal, grout to prevent surface water entry, a screen or open borehole in the producing zone, and a pump set above the screen.
- Static water level is measured when the pump is off; pumping water level is measured while pumping; drawdown is the difference. Specific capacity = pumping rate ÷ drawdown.
- Wellhead protection limits contamination near the well and manages activities such as chemical storage, septic systems, and fuel tanks.
- Source water assessments identify susceptibility; groundwater under the direct influence of surface water requires additional treatment and monitoring.
- Common groundwater problems: nitrate from fertilizers/septic, iron and manganese causing color, hardness causing scale, and arsenic requiring special treatment.
Worked example
A well pumps 500 gpm and the water level falls 25 ft after stabilization. Specific capacity = 500 ÷ 25 = 20 gpm/ft. If the pump is later throttled to 300 gpm and drawdown is 20 ft, specific capacity = 15 gpm/ft. The lower value suggests increasing well loss, screen plugging, or pump problems; it is not automatically a reason to lower the pump. Compare with baseline records and inspect the well before changing operation.
Traps that cost marks
- Using static water level instead of pumping level in drawdown calculations.
- Confusing well yield with specific capacity; specific capacity is normalized by drawdown.
- Assuming clear water is safe; nitrate and arsenic are colorless and odorless.
- Forgetting that a sanitary seal and grout protect the annular space, not just the pump.