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To whom it may concern,

Regarding your request for comment on how to appropriately quantify
the carbon intensity of a mixed feedstock digester, Bluesource has
a proposal on how to achieve this. We believe the following
approach is conservative, reduce risk of overestimating credits,
avoid crediting ineligible feedstock, do not overburdening digester
owner/operators with testing or metering requirements, and lower
risk of credit invalidation. The approach is as follows;
Approach:
Assuming there is one feedstock that makes up the majority of the
feedstock, and any other feedstocks fall into an eligible category
under the LCFS
1. Calculate the CI of the main feedstock (>75% of total feedstock
by mass) using conventional methods (i.e. using simplified
calculator)
2. Perform biomethane potential (BMP) test on one or both
feedstocks to determine the quantity of gas produced by each
feedstock. Tests can be performed once or twice annually.
3. Assume the temporary carbon intensity for the secondary  carbon
intensity (i.e. 45 g/MJ for WWTP sludge, -150 g/MJ for dairy manure

4. Apply for fuel pathway validation under a tier 2 pathway

Requiring a digester operator to meter volatile solids for each
feedstock, fossil fuels for each feedstock's handing and processing
is extraordinarily onerous. This would undoubtedly would deter
facilities and individuals from developing digester projects, thus
slowing California's progress towards reaching its 2030 GHG
reductions targets. 

Regards,
Justin Friesen