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11 <br />ii <br />r <br />11 <br />1. SCOPE <br />This report describes the calibration of ECHO water content probes for soil used to <br />construct a final cover at the Forward Landfill. <br />The calibration was conducted following the method described in Benson and Wang <br />(2006) in a calibration cell constructed of polyvinyl chloride (PVC). The cell had inside <br />dimensions of 330 x 152 x 127 mm. <br />Soil was compacted in the cell in three lifts of equal thickness. An ECHO probe was <br />inserted in the middle of the second lift, with the soil compacted directly on top of the <br />probe to ensure good soil -probe contact. A thermocouple was also placed in the center <br />of the cell when the second lift of soil was placed. A compaction hammer was used to <br />compact the soil, with the number of tamps adjusted to achieve the target density (90% <br />of maximum dry unit weight for modified Proctor, as specified by the requestor). <br />Calibrations were conducted at four volumetric water contents (8 = 0.036, 0.13, 0.18, <br />and 0.39) and at five temperatures (T = 5, 10, 20, 25, and 30 °C). All calibrations were <br />conducted in a temperature -controlled chamber. Echo probe output was recorded for <br />each volumetric water content and soil temperature using a data logger. <br />3. RESULTS <br />Calibration curves for the ECHO probes in Forward soil are shown in Fig. 1. The data <br />are tabulated in Table 1. Each curve in Fig. 1 was fit with the second -order polynomial: <br />8=a+bR+cR2 (1) <br />Where R is the response (mV) of he ECHO probe and a, b, and c are calibration <br />coefficients. A summary of the coefficients is in Table 2. <br />The calibration coefficients are temperature dependent, as shown in Fig. 2. The <br />temperature dependency of these coefficients can also be described by a second -order <br />polynomial: <br />Zi = (Xi + RiT + XIr (2) <br />where zi is the ith coefficient in Eq. 1 (i.e., a, b, or c for I = 1, 2, or 3) and al, Di, and xi are <br />the thermal coefficients corresponding to the ith calibration coefficient in Eq. 1. The <br />thermal coefficients are summarized in Table 3. <br />4. APPLICATION <br />The calibration described in Section 3 is implemented as follows: <br />1 <br />