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DSS33WLD Alluvial Weldona E-32 <br />DSS38BLZ Alluvial Balzac E-33 <br />DSS39BLZ Alluvial Balzac E-34 <br />DSS40JBG Alluvial Julesburg E-35 <br />DSS41JBG Alluvial Julesburg E-36 <br />DSS42JBG Alluvial Julesburg E-37 <br />DSSBR01 Upper Arapahoe Bennett E-38 <br />CO3LTDW Lower Dawson Castle Rock E-39 <br />CO3TKD Denver Castle Rock E-40 <br />CO6KA Arapahoe Castle Rock E-41 <br />CO3KLF Laramie-Fox Hills Castle Rock E-42 <br />2.1 Data Retrieval <br />The data loggers are suspended in each well by a data cable that, at most wells, vents the <br />loggers to atmospheric pressure. At some of the deeper bedrock wells, a sealed data logger that <br />is not vented to atmospheric pressure is used. At these wells, a separate barometric pressure <br />transducer and data logger is used to allow for compensation for barometric pressure changes <br />on tlne water levels. The water level data are downloaded from the data logger by connecting a <br />laptop to tlne data cable or directly to tlnevon-vented data logger using an RS-232 serial port. <br />The downloaded data are saved to tlne laptop and transported back to tlne office for processing. <br />During the field activities for this task, a field book is used to record the manual water level <br />measurements taken with a conductivity meter (described below), the battery and free storage <br />capacity of the data logger, the serial number of the data logger, and tlne interval of data <br />collection by the data logger. <br />Standard data download field protocol includes collecting a manual field measurement before <br />the download of the water level data and comparing it to the instantaneous water level <br />measurement of the data logger. Tlnis is done to verify tlne accuracy of the data logger's <br />measurements since itnitiating the data logging. It is common for the manual and data logger <br />measurements to differ by a couple of tenths of a foot. This difference is commonly referred to <br />as data logger drift. This may be the result of the data logger accuracy limitations, elapsed time <br />since its calibration, cable stretch, subtle changes >ln the data logger's resting lneiglnt and/ or error <br />iln tlne manual measurement. A data logger's drift error can increase from year to year, which <br />may indicate the data logger should be recalibrated. <br />The significance of drift error can be evaluated by comparing the drift error to the magnitude of <br />water level change observed over a given time period. For example, if the drift error is 0.5 foot <br />and the maximum water level change is one foot, then the drift error is a significant portion of <br />the water level change observed. However, if the maximum water level change is ten feet, then <br />the drift error is a small percentage of the overall change. Additionally drift error can be <br />evaluated by review>ing tlne water level data for tlne period of record. If there is a sudden offset <br />iln tlne water level data, the drift error maybe caused by a sudden change in the height of the <br />data logger. This sort of drift error can often be corrected iIn tlne water level data. Each data <br />logger should be evaluated and potentially sent to the manufacturer for recalibration when <br />significant drift error is observed. <br />SPDSS Phase 4 Task 39 Technical Memorandum-Final 11 <br />O~i20%2008 <br />