The Impact of Stormwater Recharge Practices on Boston Groundwater Levels

Over the past century, the City of Boston has periodically experienced a decline in water table elevations and the associated deterioration of untreated timber piles which support building foundations. To combat declining water tables, Boston has instituted a groundwater conservation overlay district enforced by City zoning boards to require stormwater recharge practices for any new development or redevelopment project that increases impervious area. The primary goal of this research was to determine if such stormwater recharge best management practices (BMPs) have had an impact on groundwater levels in Boston. Recharge to the water table in Boston results from the infiltration of rainfall and snowmelt, leakage from water mains, and recharge from man-made systems (Aldrich and Lambrechts, 1986). As water providers in Massachusetts strive to meet requirements of Massachusetts General Law Chapter 21G, which requires unaccounted-for water (e.g. leaking water pipes) to less than 10 percent (<10%), investigations have been conducted to isolate and remediate leaking water pipes throughout the city. Given the high percentage of impervious cover area of Boston, the remaining sources of recharge are primarily man-made systems, including pump and infiltrate systems and stormwater recharge BMPs. The goal of this study was to determine the extent to which installed stormwater recharge BMPs have led to increased groundwater levels. To address this question, a regional multivariate regression model was developed to determine potential effects of recharge BMPs to observed groundwater elevations. Results indicate that selected recharge BMP explanatory variables have a slight but significant positive increase in observed groundwater elevations. This study reports on some of our initial results; extensive further analyses and testing are planned.