Biomethane is a promising alternative fuel to mitigate the climate impacts arising from the natural gas sector. In California, several policies are in place to facilitate the development of biomethane. However, constraints on gas quality and gas properties can limit biomethane introduction into the gas pipeline. In this study, regional biomethane supplies and potential deviations in gas quality were assessed using steady-state simulation of natural gas pipeline networks at the zip-code scale under a variety of biomethane development scenarios and regulatory limits. Three regions of California - San Diego, Hanford, and South San Francisco bay area - were modeled. We explore local impacts to gas quality under various biomethane price scenarios and different levels of regulatory support. Across all regions, we do not find regional or local gas quality deviations to exceed interchangeability guidance with slightly relaxed biomethane heating value standards. Agricultural regions such as Hanford with high concentrations of dairy farms and low natural gas consumption may require pipeline upgrades to act as net exporters of biomethane. Regions with large seasonal variation in natural gas consumption may necessitate more stringent gas quality requirements to ensure safe combustion as gas composition varies across the year. High year-round demand for gas in urban regions will minimize gas quality deviation and could allow for case-by-case relaxation in gas quality requirements. We find that CO2 and biofuel credits under state and federal regulations such as the California Low Carbon Fuel Standard (LCFS) and U.S. Renewable Fuel Standard (RFS) are vital to development of biomethane. With the incorporation of LCFS revenues, the portion of natural gas demands served by biomethane could be 4.3% in San Diego (5.2 bcf/y or 150 million m(3)/y), 54% in Hanford (2.66 bcf/y or 75.3 million m(3)/y), and 2.4% in the South Bay area (3.8 bcf/y or 110 million m(3)/y). Adding in current federal RFS credits, the biomethane supply only rises slightly in San Diego and South Bay Area but exceeds 100% of natural gas demand in Hanford (4.5 bcf/y or 130 million m(3)/y).