New construction is managed closely, as the addition of new impervious surface can increase the water flowing into sewer systems. La Grange has very restrictive drainage and stormwater management requirements that go above and beyond what is required by the MWRD for all municipalities within their jurisdiction. Residential site development standards require grading improvements and below ground, on-site retention facilities (dissipation systems) for new single-family homes.
As a result of these requirements, new construction sites improve stormwater management as compared to properties developed without these requirements. Once constructed, these properties provide storage equivalent to one inch of rainfall over 45% of lot coverage and groundwater displaced by building foundations.