Agenda - 01-04-1988 - Laserfiche WebLink

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4 17 e• 2 . hydraulic gradient across the infiltrative surface. In some instances, -,- deep systems can be used to reach more permeable soil horizons when the proximity of groundwater tables do not preclude their use. ik . i Freezing of shallow absorption systems is not a .problem if kept in con- tinuous operation (4)(11). Carefully constructed systems with 6 to 12 in. (15 to 30 cm) of soil cover, which are in continuous operation, will ie not freeze even in areas where frost penetration may be as great as 5 ft (1.5 m) if the distribution pipe is gravel packed and header pipes:4- lated where it is necessary for them to pass under driveways or other ' areas usually cleared of snow. , r• Alternating Systems: Dividing the soil absorption system into more than y,.. one field to. allow alternate use of the individual fields over extended periods of time can extend the life of the absorption system. Alterna- ,=;., ting operation of the fields permits part of the system to "rest" a .: pert- •:- odically so that the infiltrative surface can be rejuvenated naturally 4i through biodegradation of the clogging mat (4) (11) (12)(13) (15) (16). ?.•° The t : "resting" field also acts as a standby unit that can be put into immedi- .• ate service if a failure occurs in the other part of the system. This `7 provides a during` p period of time Burin which the failed field can 'be rehabili- tated or rebuilt without an unwanted discharge. 4=. • Alternating systems commonly consist of two fields. Each field contains 50 to 100% of the total required area for a single field. Common prac- tice is to switch fields on a semiannual or annual - schedule by means of a diversion valve (see Figure 7-3 and Chapter 8). Though it has not yet 73. been proven, such operation may permit a reduction in the total system 'Y: size. In sandy soils with a shallow water table, the use of alternating . beds may increase the chance of groundwater contamination because of the il - . loss of treatment efficiency when the clogging mat is decomposed after resting. • c. Layout of the System itl: 15� Location: Locating the area for the soil absorption system should be _ done with care. On undeveloped lots, the site should be located prior -_:'to locating the house, well, drives, etc., to ensure the best area is- :: reserved. The following recommendations should be considered when -: locating the soil absorption system: - 1. Locate the system where the surface drainage is good. - Avoid depressions and bases of slopes and areas in the path of runoff from roofs, patios, driveways, or other paved areas unless sur- face drainage is provided. 217 .,