Source Water, Water Quality and Public Health Protection
Source Water
What you must know
Source water questions test whether you understand where water comes from, how it moves, and what can reach it before treatment begins. Distinguish a watershed (land draining to a surface intake) from a zone of contribution or wellhead protection area (land surface recharging a pumping well). Know porosity (volume of voids - how much water a formation holds) versus permeability / hydraulic conductivity (how easily water moves), plus recharge, the water table, confined versus unconfined aquifers, cone of depression, and time of travel.
New Jersey detail matters. Bedrock wells in the Highlands and Reading Prong can carry radium, uranium and radon. Coastal Plain aquifers commonly produce acidic, low-alkalinity, corrosive water with iron and manganese, and are vulnerable to saltwater intrusion near the shore. Piedmont wells show historic industrial VOC contamination (TCE, PCE). Agricultural areas such as Salem, Cumberland and Warren counties see nitrate. Surface intakes on the Passaic, Raritan, Wanaque and Delaware are influenced by upstream wastewater discharges and by turbidity and TOC spikes after storms.
Traps
- Treating an aquifer as a watershed, or assuming deeper water is always cleaner.
- Assuming a well capture zone is a circle of fixed radius.
- Forgetting that source water quality changes seasonally: reservoir turnover, storm events, intake shutoffs.
Rule of thumb - time of travel
Seepage velocity: v = (K x i) / n_e. With K = 50 ft/day, gradient i = 0.002 and effective porosity n_e = 0.25, v = (50 x 0.002)/0.25 = 0.4 ft/day, so a 1,000-ft journey takes about 2,500 days (roughly 7 years). Verify NJ wellhead protection tier distances in the current rule text before quoting them.
Water Quality and Public Health Protection
What you must know
Regulatory vocabulary drives this domain. An MCL is an enforceable limit; an MCLG is a non-enforceable health goal, often zero; an SMCL is aesthetic (color, odor, corrosivity); a treatment technique is a required process when no feasible MCL exists (turbidity, LT2); an MRDL caps disinfectant residual. Separate acute risks (E. coli, nitrate in infants, Cryptosporidium) from chronic risks (arsenic, radionuclides, disinfection byproducts, lead).
New Jersey is often stricter than federal rules. Learn these: arsenic 5 ug/L (federal 10); PFOA 14 ng/L, PFOS 36 ng/L, PFNA 13 ng/L; nitrate 10 mg/L as N and nitrite 1 mg/L as N; lead action level 0.015 mg/L and copper 1.3 mg/L; TTHM 80 ug/L and HAA5 60 ug/L as locational running annual averages; gross alpha 15 pCi/L. Know the health story behind each: methemoglobinemia (nitrate), neurological and developmental effects (lead), kidney, liver and immune effects (PFAS), cancer risk from DBPs and radionuclides.
Traps
- Calling an MCLG enforceable, or treating a secondary standard as a health limit.
- Forgetting the Lead and Copper Rule uses an action level evaluated at the 90th percentile, not an MCL.
- Forgetting some rules are judged on a running annual average, and others on a treatment technique rather than one sample.
Worked example - 90th percentile
Twenty first-draw lead samples, ranked low to high. 0.9 x 20 = 18, so the 90th percentile is the 18th value. If that value is 0.019 mg/L, the 0.015 mg/L action level is exceeded, triggering corrosion control optimization, public education and, where applicable, lead service line work on the rule's schedule.