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6.2 DATA CONTINUITY The monitoring hardware and software components installed at the FSL were selected because they were similar to those used in the Alternative Cover Assessment Program (ACAP)being completed under the direction of the U.S. EPA and therefore have a well demonstrated utility in this application. In spite of this history, technical and operational interference were experienced as a result of new programming codes, computer upgrades and issues of system incompatibility. In addition to these anticipated system idiosyncrasies, electrical disturbance (e.g., lightning strikes), low battery voltages, cloud cover, and/or telecommunications failures (interference with existing networks, such as the gas monitoring system and possible radio signals from the nearby prison) also resulted in interruptions in the continuity of the monitoring data. These types of data interruption are typical of remote soil moisture monitoring installations. The soil moisture monitoring system installed at the Forward Sanitary Landfill was designed to be robust and incorporates significant redundancies to allow for anticipated loss of data. For example,the system incorporates two monitoring stations rather than one. As a result of these redundancies, it is concluded that the monitoring system has yielded sufficient data to effectively characterize the nature of moisture movement within the alternative final cover constructed at the site. 6.3 SOIL MOISTURE 6.3.1 MET STATION The MET station monitoring location is located in the eastern portion of the Stage I closure area and the soil moisture monitoring data from this station is summarized on Figure 8. As expected, soils at this location exhibit variations in moisture content that are broadly associated with periods of precipitation events with only the more severe events (e.g., late February, 2007 and early January, 2008 and the cumulative storms of January 2009 and February 2009) causing distinct soil moisture responses. Contrary to the long-term pattern of dry soils, an increasing soil moisture trend observed in the Summer of 2006 and Summer of 2007, and also observed in 2008. This summer to fall increasing moisture trend when little or no rainfall has been recorded has been observed at other sites and is likely to be the result of the introduction of moisture from the waste. This introduced water is likely to be the results of condensation of vapor phase water in the cover or from the oxidation of methane (i.e., when methane is present in the final cover it oxidizes and creates water as a byproduct of that reaction). The relatively high moisture contents observed during the summer are likely to be exacerbated by the immaturity of the vegetation present at this location. As noted in a letter to the RWQCB—Central Valley Region(dated April 28, 2009) soil moisture ' sensors at the 36 and 24-inch depths malfunctioned in February 2009 and March 2009. A review of the raw data by the manufacturer of the probes (Decagon Devices Inc.) indicates that these are no longer functional. No remedial action has been undertaken to address the loss of these two moisture sensors at the MET Station location. 6 Geologic Associates