Agenda - 01-04-1988 - Laserfiche WebLink

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7 deep trenche r' ��(1 s with a greater depth of rock below the distribution pipe ....,;. to increase the sidewall area is more suitable. : Reserve Area: When planning and locating the absorption system, consid- erat on s ou d be given to reserving a suitable area for construction of a second system. The second system would be added if the first were or if the system required expansion due to a to �� flows. Care must be used in constructing the second increased wastewater original system is not damaged by the construction equipnent.so that the 4,, _The reserve area should be located to facilitate simultaneous or alter- ' nating loading of both systems. If the reserve area is used because system has failed, the failing system should not be "' se the abandoned. With time, the initial system will be naturally rejuvenated and can be used alternately with the reserve system. be provided very easily with trench systems by reserving can ,:. between the initial trenches as shown in Figure 7-4. S;�y' sufficient area +Mr . Dimensions: The absorption system should be dimensioned of a maintaining separation distances and-avoiding excessive the of excavation. Commonly used dimensions are given a depths :� _ g en in Table 7.3. _ The depth of excavation is determined by the location able soil horizon and flow restricting layers or the high most r pe table elevation. Unless a deep, more permeable horizon exists,g thblr bed bottom elevation should be maintained at about 18 to 24ein trench to or 61 cm) below the natural ground surface. To prevent (46 cold r: climates, 6 to 12 in. (15 to 30 cm) of cover should b freezing it in over the aggregate (11). be backfilled over • mow: If the water table or a very slowly permeable layer is too near the ground surface to construct the system at this depth, the system can be .. _ raised. Very shallow trenches 6 to 12 in. (15 to 30 cm) deep can stalled and the area backfilled with additional soil (see F n be i). x: Adequate separation distance must be provided between the trench e bottom t). and the seasonally high groundwater level we , contamination. prevent groundwater The length of the trench or bed system depends on the _ tics. The length of the distribution laterals is commonly erestricted it 100 ft (30 m). This is based on the fears of root penetration, to settling, or pipe breakage which could disrupt the flow down tthe� ipevto render the remaining downstream length useless. p fe to are unwarranted because the aggregate transmits the astewaterse fears (17). 7o assure adequate transmission and distribution of)(the the 219