• I saw this note on the SWMM List Server which maybe answers your question

    When the ability to route underdrain flow to separate locations was added to EPA SWMM 5.1.008 a lot of internal re-wiring had to be done to the LID routines to make this happen. As a result, it appears that a bug was introduced --  the LID infiltration was not being added on to the total subcatchment infiltration passed on to the groundwater routine like it was in earlier releases. If the LID infiltration was contributing to groundwater in your PCSWMM runs I assume it was because you were using the 5.1.007 (or earlier) engine in PCSWMM. Thanks for discovering this bug. I will work with Michael Tryby to try and get it fixed as soon as possible.

    Lew Rossman
    US EPA (Emeritus)

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