09-22-1986 Council Packet - Laserfiche WebLink

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Page 2 of 6 saturation zone at the east end of the primary site, and no reported evidence at the midpoint of the site, the code standards would allow trenches to be up to 1.5 feet deep into original soil at the east end and deeper, up co 36" deep into the original soil (24" maximum cover, 12" of rock) at the midpoint of the system, with the interceptor drain being optional and not required by code. 3. Based on the above, and based on the actual 2' of cover we find now at the west end of the trench system, and with the elevation of the ground surface over th - drainfield at the west end being level with or just slightly below the surrounding original ground elevation, and with the obviously elevated ground over the east end of the system, it is my considered opinion that the drainfield was installed essentially according to the plan approved by the City based on the soils information reported. 4. Although an actual determination of elevations of the rock in the trenches has not been made, we did find water at the top of the rock in the boring over the west end of the drainfield, which appeared to correspond with the water level at the top of the distribution box. This generally -ou'd indicate that the trenches do not run uphill and are in pact '_ing loaded from the distribution box with no blockage, and are being used to their entire extent. You may wish to survey the trench rock and distribution box elevations in _-der to verify that the trenches do not run uphill. 5. We also found in the boring I made on 4/9/86, located about 15-20' from the west end of the drainfield, that the soil is currently saturated as shallow as 18" be' - v the surface, and we observed mottling at a depth of about 30" in that boring. This was not reported in the boring logs submitted by Percor, Inc.; however I would expect to find similar mottling at the 30" depth throughout the existing drainfield site based on the topography of the site. 6. The currently occurring high water table to the immediate west of the drainfield site is likely not caused by the drainfield, but probably does have a major effect on the drainfield, perhaps even extending into the drainfield and causing a flooding effect. The trenches appear to be within or just above a saturated zone during wet periods of the year, and during those periods the trenches cannot adequately treat and dispose of the effli•ent flow from the household. This seasonal saturation also will likely have a long term limiting effect on the life of the system, because the "biomat" in the trench will not decay as fast as it builds up, as would normally happen in a trench in dry ground.