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Environmental Monitoring by Thomas Kwader, Ph.D., P.G. WorldWide Drilling Resource ® Hydrogeologist Considerations for Locating Wells and Septic Tanks on Small Residential Lots Part 2 Note: This is the second of a two-part series on shallow well and septic tank placements on small residential lots. Last month’s article discussed the relative placements of the well in regard to the septic tank. This month’s article will discuss factors regarding location and construction of the septic tank and the minimum hydrogeologic conditions for a drain field. Last month, we decided to locate the domestic well uphill of the house on the 100-foot x 100-foot lot. Now we will discuss the desirable soil and geologic criteria for installing the septic tank downhill from the house. An “ideal” septic tank and drain field would include the following characteristics. A moderately deep water table (at least five or more feet) with moderately aerated soil for the proliferation of aerobic bacteria. A zone of aeration sufficiently thick enough to support a zone of active bacteria that promotes the breakdown organic - biodegradable compounds. A high or shal- low water table may create anaerobic conditions which could slow the biodegradation of septic tank waste. Too much clay content (low permeability layers) may be insufficient to channel the wastewater away from the drain field, causing flooding and stagnant conditions, there- by hindering the aerobic breakdown of organic wastes. On the other hand, highly porous sands, gravels, and/or fractured rock are undesirable because of the difficulty to establish proper filtration and biological processes needed to flourish and cre- ate the conditions conducive to dilute and decompose the wastes. Normally, a percolation test is per- formed on a lot before the actual sale is made to ensure a septic system can be successfully installed. Acceptable per- colation rates are generally considered to be in the range of a drop of the water level in a test hole of 1 to 30 inches per hour. Too slow of a drop could cause flooding of the area. The larger the drain field, the more water can be treated. However, high volumes over short peri- ods of time can be the limiting factor. Too fast of percolation rates are unde- sirable because of the time needed for the biodegradation process to com- pletely treat the waste. Tom Tom Kwader may be contacted via e-mail to michele@ 23 WorldWide Drilling Resource ® SEPTEMBER 2020 ENV November Issue Deadlines! Space Reservation: September 25 th Display & Classified Ad Copy: October 1 st