1977-08-31 Septic System Design Report

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77-423 George Jackson $ Associates -2- August 31, 1977 Percolation tests were run in 6-inch diameter holes, drilled to a depth of 36 inches, in accordance with procedures normally used on lots that will be developed residentially. In accordance with standard procedures, the holes were permitted to soak overnight before conducting the tests. Each of the borings were probed immediately after completion to check for the presence of groundwater. RESULTS: The log of soils encountered in the borings and the water level observations are shown on the attached Log of Boring sheets. Boring B-1 encountered a sandy clay glacial till from the surface to the 11-foot depth, underlain by coarse alluvium sands and silty sands to the 20-foot termination depth in this boring. Boring B-2 encountered a silty clayey sand glacial till from the surface to the 4-foot depth, which was immediately underlain by a clayey silt lacustrine deposit fruw the 4 to the 13-foot depth. Sandy clay glacial till was then encoun- tered to the 20-foot termination depth in this boring. The balance of the borings, B-3 through B-8, all encountered glacial tills consisting of silty clayey sands in the upper portions of the borings to sandy clays at depth. In probing the borings immediately after completion, it was noted that cave-ins had occurred in all of the borings between the 13 and 18�-foot depths, the exception being boring B-1, where groundwater was encountered at the 16-foot depth. Approximately 24 hours later, a recheck of each of the bore hole borin s B- - Water 7 eet in orin B-5, eet in boring B-1, 15 feet in boring in o ings B-3 and B-4, and at the 17-foot depth in boring B-6. Water level readings vary considerably, ranging from elevation 936, as indicated by boring B-6, taken in the far southeastern corner of the site in what appears to be the lowest area on the site, to elevation 988, indicated by boring b-1 and taken in the upland area in the southwestern portion of the site. These water level variations can be attributed to several factors. 1) The undulating topographic features of the site indicate that water levels are following the contours and subsequent drainage patterns d^veloped in this area. 2) Because of the cohesive nature of the soils encountered, considerable time is required in order for the groundwater to stabilize in the borings. It does not appear BRAun* ENGINEERING TESTING