A Microsoft Excel spreadsheet-based design tool has been developed to assist remediation professionals in the design of injection systems for distributing soluble substrate (SS) to enhance in situ anaerobic bioremediation. The user provides site data, design parameters, and unit-cost information to generate estimates of remediation-system cost and steady-state contact efficiency (CESS) for various designs. CESS is estimated from a nonlinear regression equation that includes terms for the SS injection concentration (CI), minimum substrate concentration (CMIN), groundwater travel time between rows of injection wells (TT), SS half-life (TH), substrate reinjection time interval (TR), and pore volumes of substrate solution injected (PV). With this tool, users can quickly compare the relative costs and performance of different injection alternatives and identify the best design for their specific site conditions. The design process embodied in the tool includes: (1) entering injection-well configuration and unit costs for well installation, injection, and substrate; (2) determining treatment-zone dimension; (3) selecting trial injection-well spacing, time period between substrate reinjection, and injection pore volume; and (4) estimating contact efficiency and capital and life-cycle costs. This process is then repeated until a final design is selected. In most cases, injection costs increase with increasing CESS. However, the best (highest) ratio of CESS to injection cost typically occurs for CESS in the range of 70 to 80 percent. © 2013 Wiley Periodicals, Inc.