I-DEV0371: Deviation from monitoring plan regarding the quarterly measurement of methane content in the biogas of the biodigester

According to monitoring plan described in the registered PDD and the methodology AMS-III.D (version 09)
the “amount of methane recovered and used as fuel or combusted shall be monitored, using flow meter and
analysing the methane content of the combusted gases either online, or with samples at least quarterly, and
more frequently if the results show significant deviations from previous values.” However, in the monitoring
period from 20 October 2007 – 09 February 2009 only two measurement of methane content were carried out
in 23 December 2008 and 19 January 2009. The monitoring frequency does thus not comply with requirement
to have quarterly analysis as outlined in the monitoring plan and the methodology, as only two measurements
were made in the monitoring period, a request of deviation is required.
A statistical analysis of the methane content analyses was performed, including the measurements made on 29
September 2007 in the previous monitoring period and the two measurements made on 23 December 2008 and
19 January 2009 in this monitoring period. Using the monitored data available (3 measurement points) and in
compliance with the Guidelines to calculate the fraction of methane in the landfill gas from periodical
measurements used as reference for the similarity of the calculation presented in this deviation, a standard
deviation was calculated with a 95% of confidence interval (refer to spreadsheet GCM21
CH4_95%Cl_3samples.xls)
The lower bound value (67.59%) of the 95% confidence interval was for this site found to be higher than the
lowest measurement (67.53%). Hence, the project participants proposed to apply the lowest measurement
(67.53%) as the methane content for the whole monitoring period. Using this value results in a conservative
determination of the project’s emission reductions.

Since December 2008, the project participant complies with the requirement to have quarterly methane content
measurement. The deviation is thus only applicable to the monitoring period in question, and the deviation
does not require a revision of the monitoring plan and any amendment of the methodology AMS-III.D.

The methane content applied to the whole monitoring period is the lowest methane content measured during
the monitoring period in question. Hence, the deviation is expected to rather result in an underestimation of the
emission reductions.