The U.S. Army Environmental Center (USAEC) directed ABB Environmental Services, Inc. (ABB-ES), under Contract No. DAAA15-91-D-0008, to collect environmental samples at Fort Devens, Massachusetts to fill data gaps identified during initiation of the Feasibility Study (FS) for Group 1A sites. The Group 1A sites include the Shepley's Hill Landfill and Cold Spring Brook Landfill at Fort Devens. This Remedial Investigation (RI) Addendum report summarizes the supplemental field investigations, presents the data obtained, and updates the baseline risk assessment prepared for the RI report. Field investigation programs were conducted between September 1992 and July 1993 and included collecting and analyzing of sediment core samples from Plow Shop and Cold Spring Brook ponds, collecting and analyzing fish tissue samples from these two ponds, and conducting a macroinvertebrate study of the two ponds. In addition, several new monitoring wells were installed and groundwater samples were collected for analysis from 27 monitoring wells at Shepley's Hill Landfill and from 10 monitoring wells at Cold Spring Brook Landfill. Soil, sediment, and groundwater samples were also collected from several other areas, including Nonacoicus Brook Wetland and Grove Pond adjacent to Shepley's Hill Landfill, and the Magazine Area adjacent to Cold Spring Brook Landfill.