Source Water and Preliminary Treatment
Source water
Know the difference between true groundwater, groundwater under the direct influence of surface water, and surface supplies, because the category drives treatment and monitoring requirements. Be able to describe aquifers, well construction, wellhead protection, cone of depression, and sanitary survey findings. Surface sources vary in turbidity, color, algae, and natural organic matter; those variations drive coagulant dose and disinfection byproduct risk. Intakes should be screened and located to avoid stagnation and debris.
Preliminary treatment
For wastewater, preliminary treatment means screening and grit removal ahead of primary clarification. Coarse bar screens protect pumps; fine screens remove smaller solids; grit channels remove sand and eggshells that would abrade equipment. For drinking water, preliminary steps may include raw water pumping, coarse screening, presedimentation, pre-aeration to strip gases or oxidize iron and manganese, and flow measurement.
Traps
Questions often swap screening and grit removal, or ask what happens when grit-channel velocity is wrong. Too fast and grit passes on; too slow and organic solids settle with the grit, causing odors. Watch units, and do not confuse preliminary treatment with primary treatment.
Worked example
A grit channel carries 2 ft3/s with a water cross-section 2 ft wide by 1 ft deep. Area = 2 ft2, so velocity = Q/A = 2/2 = 1 ft/s, a good target. If flow doubles and depth is unchanged, velocity doubles and grit removal suffers unless the channel is flow-controlled.