Course: BFM 203 Water Treatment and Control

Lecture

Selecting a Water Source

Selecting a Water Source

A sanitary survey is a detailed evaluation and/or inspection of a source of water supply and all conveyances, storage, treatment, and distribution facilities to ensure protection of the water supply from all pollution sources.The sanitary survey should include the location of all potential and existing health hazards and the determination of their present and future importance. The following list notes the essential factors to investigate or consider in conducting a sanitary survey. Not all factors will be applicable to each situation, and other factors may become important based on a given situation. The items listed are essential to identify potential hazards, determine factors that affect water quality, and select treatment requirements. Sanitary surveys are conducted at regular intervals to ensure new and existing pollution sources are evaluated. The table below outlines a series of topics that should be addressed in a sanitary survey.

Groundwater Supplies
a. | Character of local geography; slope (topography) of ground surface.
b. | Nature of soil and underlying porous material, whether clay, sand, gravel, rock (especially porous limestone); coarseness of sand or gravel; thickness of water-bearing stratum; depth of water table; location and GEOLOGICAL LOG of nearby wells.
c. | Slope of water table, preferably as determined from observation wells or as indicated by slope of the ground surface.
d. | Extent of the drainage area likely to contribute water to the supply.
e. | Nature, distance, and direction of local sources of pollution.
f. | Possibility of surface-drainage water entering the supply and of wells becoming flooded.
g. | Methods used for protecting the supply against contamination from wastewater collection and treatment facilities and industrial waste disposal sites.
h. | Well construction: materials, diameter, depth of casing and concrete collar; depth to well screens or perforations; length of well screens or perforations.
i. | Protection of well head at the top and on the sides.
j. | Pumping station construction (floors, drains); capacity of pumps; storage or direct to distribution system.
k. | Drawdown when pumps are in operation; recovery rate when pumps are off.
l. | Presence of an unsafe supply nearly, and the possibility of CROSS CONNECTIONS causing a danger to the public health.
m. | Disinfection: equipment, supervision, test kits, or other types of laboratory control
Surface Water Supplies
a. | Nature of surface geology; character of soils and rocks.
b. | Character of vegetation; forests; cultivated and irrigated land.
c. | Population and wastewater collection, treatment, and disposal on the watershed.
d. | Methods of wastewater disposal, whether by diversion from watershed or by reclamation treatment.
e. | Closeness of sources of fecal pollution to intake of water supply.
f. | Proximity to watershed and character of sources of contamination including industrial wastes, oil field brines, acid waters from mines, sanitary landfills, and agricultural drain waters.
g. | Adequacy of supply as to quantity (safe yield).
h. | For lake or reservoir, supplies, wind direction and velocity data; drift of pollution; and algal growth potential.
i. | Character and quality of raw water: typical coliform counts (MPN or membrane filter), algae, turbidity, color, and objectionable mineral constituents.
j. | Normal period of DETENTION TIME.
k. | Probable minimum time required for water to flow from sources of pollution to reservoir and through the reservoir to the intake tower.
l. | The possible currents of water within the reservoir (induced by wind or reservoir discharge) that could cause SHORT-CIRCUITING to occur.
m. | Protective measures in connection with the use of the watershed to control fishing, boating, landing of airplanes, swimming, wading, ice cutting, and permitting animals on shoreline areas.
n. | Efficiency and consistency of policing activities on the watershed and around the lake.
o. | Treatment of water: kind and adequacy of equipment; duplication of parts for reliable treatment; effectiveness of treatment; numbers and competency of supervising and operating personnel; contact period after disinfection; free chlorine residuals and monitoring of the water supply both during treatment and following treatment.
p. | Pumping facilities: pump station design, pump capacity, and standby unit(s).
q. | Presence of an unsafe supply nearby, and the possibility of cross connections causing a danger to the public health.
Source: Water Treatment Plant Operation: A Field Study Training Program, 6th edition, Office of Water Programs, College of Engineering and Computer Science, California State University, Sacramento, 2009, pp. 26 - 27.