I-DEV0362: 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 28 February 2007 – 19 October 2007 only one measurement of methane content was carried out in
29 September 2007. The monitoring frequency does thus not comply with requirement to have quarterly
analysis as outlined in the monitoring plan and the methodology, as only one measurement was 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 and two measurements made in the subsequent monitoring period on 23 December 2008 and
19 January 2009. 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 GCM19 CH4_95%Cl_3samples.xls).
The project participants propose to apply the lower value (68.23%) of the 95% confidence interval 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.