Laserfiche WebLink
bottom of the slab, regardless of the soil type or transmissivity. If the depth to the water table <br />is less than the value from Plot 1, further evaluation is necessary. <br />3. If the soil type of the aquifer, below the water table, is mostly clay OR if the aquifer is <br />perched (a continuous clay layer is less than 5 feet below the water table), Plot 2 must be <br />used. The appropriate pond level increase (2, 4, or 6 feet) for flood conditions must be used <br />in Plot 2 to find the minimum permissible depth to the water table. If the depth to the water <br />table from Plot 2 is less than the actual depth to the water table, the proposed floor elevation <br />is too low and must be raised to equal the value from Plot 2. <br />4. If the soil type of the aquifer is mostly silt AND the pond bottom is 3 feet or less above the <br />water table, Plot 3 should be used. <br />5. If the soil type of the aquifer is mostly sand or gravel AND the pond bottom is 3 feet or less <br />above the water table, Plot 4 should be used. <br />6. If the soil type of the aquifer is mostly silt AND the pond bottom is 3 feet or more above the <br />water table, Plot 5 should be used. <br />7. If the soil type of the aquifer is mostly sand or gravel AND the pond bottom is 3 feet or more <br />above the water table, Plot 5 should be used. <br />The values from the plots are guidelines, based on typical conditions. If the plots indicate the <br />proposed floor elevation is too low, additional analyses and data collection could be pursued by the <br />applicant. These additional analyses could include additional soil borings, long-term monitoring of <br />piezometers, or more sophisticated modeling. <br />Determining Depth to the Water Table <br />If a variance to a lowest floor elevation ordinance is to be considered, the depth to the water table at <br />the location in question must be known. Without this knowledge, there cannot be a technical basis for <br />approving a variance. Furthermore, the applicant should demonstrate that the measured water -table <br />elevation is both representative of conditions over the entire floor area and is representative of values <br />typical for seasonally high conditions (e.g. spring conditions). A suggested requirement for <br />collecting this information is the following: <br />1) A minimum of two soil borings shall be installed at or near the perimeter of the lowest floor. <br />At least one of these borings shall be where the floor is closest to the nearest pond. <br />1 <br />