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Permanent benchmark definition install#
Permanent benchmark definition plus#

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Send him questions about septic system maintenance and operation by sending an email to. Subsequent elevations will be determined using the new H.I.Ībout the author: Jim Anderson is connected with the University of Minnesota onsite wastewater treatment program and is an emeritus professor in the university’s Department of Soil, Water and Climate. If the rod reading is 10.50 at the turning point and the instrument is moved so the rod reading is 3.88 at the B.S., the elevations are as follows: Turning point (T.P.) = 102.95 (H.I.) – 10.50 = 92.45 and the new H.I.

The rod would be set at the turning point and a reading taken (this is called the foresight, or F.S.). When this occurs, a turning point elevation and new H.I. If the elevation change across the site is more than the length of rod available, the instrument will need to be moved. The elevation specified on the plans for the bottom of the tank should be 102.95 - 11.85 = 91.10. If aggregate is needed to properly set the tank according to specifications, the excavation will need to be deeper than the desired bottom of the tank elevation. Similarly, if the installer knows that the dimension of the septic tank below the inlet invert is 5.35 feet, then the bottom of the tank excavation or the top of the aggregate material beneath the tank needs to be 5.35 feet (tank dimension) + 6.50 feet (depth to the invert) = 11.85 feet for a rod reading. During installation of the septic tank, the invert of the pipe needs to be at a rod reading of 6.50 when the tank is set. Let’s say the plans call for the invert (bottom) of the pipe into the septic tank to be at an elevation of 96.45 the rod reading should be 102.95 (H.I.) - 96.45 (desired elevation) = 6.50.

Permanent benchmark definition plus#

The height of the instrument is the rod reading plus 100.00 (the benchmark).

This reading is called the backsight, or B.S., as indicated earlier in the definition of terms. The first rod reading is taken by placing the rod on the benchmark. The instrument (transit or level) should be set up to see all parts of the system if possible. This is arbitrary and only for the convenience of not having to deal with negative numbers. When a benchmark is set on site, it is usually given an elevation of 100.00 feet.

Permanent benchmark definition install#

Obviously, we do not need to know how high above sea level we are to install a septic system. In my part of the world, it means an elevation of approximately 1,100 feet above sea level. Geological Survey, you would be working off a benchmark where the elevation is given in terms of elevation above sea level.

If you were to work off a surveying post established by the U.S. Get Onsite Systems articles, news and videos right in your inbox! Sign up now.Ī benchmark should be relatively permanent, which is why one is often set at a corner of a building, large boulder or some other location that will be there for a long time.