Abstract
The original design of the pretreatment works for the Sacramento Filtration Plant provided a double-decked, reinforced concrete structure with aeration field and raw water storage above and sedimentation basins below. The aeration field comprised 420 aeration nozzles of the Sacramento Type, mounted over a gravity type primary sand sedimentation basin which was about twenty feet deep. From this point the water flowed into the upper raw water storage basin 7 feet deep by 191 by 270 feet in plan with a capacity of about 2.3 million gallons. From this basin raw water was admitted to four circular mixing tanks 44 feet in diameter by 22 feet deep, into which alum was introduced and floe produced by the mixing action of long paddle arms and plate paddles revolved at a maximum speed of about 2 r.p.m., these paddles being rotated by hydraulic ram type engines operated by water power from the force mains. Water then flowed to three sedimentation basins in series, each of these basins being located directly under the raw water storage basin and being about 12 feet deep below invert of inlet gates. The total depth of each of these sedimentation basins was about 21 feet and the first basin was of approximately 0.95, the second of 1.9 and the third of 3.8 million gallons capacity. The water traveled in each basin an approximate distance of 350 feet between inlet and outlet gates, the velocity in each basin being progressively reduced in the inverse ratio to the basin capacities. From the third basin the settled water passed to the rapid sand filters ready for final clarification. Experience with these basins which were designed for a load of 32 to 35 million gallon daily rates indicated that they functioned satisfactorily at these rates and up to 40 m.g.d. rate, at which rate the pretreatment works were overloaded. The original filter installation consisted of 8 rapid sand filters of 4 m.g.d. rating each, and this was soon proved to be inadequate after the commencement of the plant operation in 1924. In 1927 a bond
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