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DE Water Operator: Source Water and Water Quality

DE Water Operator · Work through your exam, one topic at a time.

All guide sections

Source Water and Water Quality

Delaware's Source Water and Water Quality domain tests where the water comes from and what is in it before and after treatment. About 90% of Delaware's public supply is groundwater drawn from aquifers such as the Magothy, Cheswold, Frederica, Piney Point, and Aquia; the northern county surface supplies come from the Brandywine, White Clay, and Red Clay. The exam expects you to read a water-quality report, convert units correctly, and recognize which standard applies.

Core rules

  • Source water assessments and wellhead protection identify contamination threats and promote local protection.
  • Contaminant groups: microbial, inorganic chemicals, organic chemicals, radionuclides, and disinfection byproducts.
  • Regulatory terms: MCL is enforceable; MCLG is a non-enforceable health goal; an action level triggers treatment; a treatment technique requires a specified process; an MRDL limits disinfectant residual.
  • Nitrate is reported two ways. Nitrate as N has an MCL of 10 mg/L; nitrate as NO3 has an MCL of 45 mg/L. Convert: NO3 = NO3-N × 4.43.
  • Hardness is expressed as CaCO3. Multiply calcium mg/L by 2.5 and magnesium mg/L by 4.12, then add.
  • Know the meaning of pH, alkalinity, turbidity, conductivity, TDS, temperature, iron, manganese, and arsenic in source and finished water.
  • Coastal aquifers face saltwater intrusion; agricultural areas face nitrate; many aquifers carry iron and manganese that cause staining and taste complaints.

Worked example

A well report gives calcium 40 mg/L and magnesium 12 mg/L. Calcium as CaCO3 = 40 × 2.5 = 100 mg/L. Magnesium as CaCO3 = 12 × 4.12 = 49.4 mg/L. Total hardness = 149.4 mg/L as CaCO3, a moderately hard water. If the same report listed nitrate as N at 8 mg/L, nitrate as NO3 would be 8 × 4.43 = 35.4 mg/L, still below the 45 mg/L NO3 MCL.

Traps

Reporting nitrate as N when the limit is written as NO3; treating an MCLG as enforceable; confusing hardness with alkalinity; mixing ppm and mg/L, which are equal in dilute water; ignoring temperature effects on chlorine demand; assuming groundwater is automatically free of microbial risk.