Source: Federal Reserve Bank of St. Louis  

Release: St. Louis Bi-Weekly Reserves and Monetary Base  

Units:  Ratio, Seasonally Adjusted

Frequency:  Biweekly, Ending Wednesday

Updates of this series will be ceased on December 19, 2019. There is no direct replacement to this seasonally adjusted series. Interested users can construct a proxy of the series as the ratio of M1 from the H.6 release and the monetary base from the H.3 release. The discontinued series plotted on the same graph with the calculated data can be accessed for comparison here.
For more details, see the FRED Announcement.