The Challenge
With increasing annual precipitation, groundwater is rising and has the potential to affect new areas impacting basements, septic systems, roads and other ground-level or shallow below ground infrastructure as well as the natural environment as wetlands take over previously dry areas.
Project Scope
The goal of this project is to enable engineers, planners and policy makers to consider the impact of projected increases in groundwater elevation across the state. For example, septic systems and stormwater recharge infrastructure require a certain separation from the groundwater table. Therefore, these systems may need to be altered or sited in alternate locations to accommodate rising groundwater elevations. On the policy side, new areas may become wetlands which could be considered under MassDEP’s jurisdiction for the Wetlands Protection Act.
This project identified areas of the state that are currently vulnerable to groundwater flooding based on recent historical average annual groundwater elevation data (2003-2010), average annual groundwater elevation modeling and the proximity of the modeled elevations of the groundwater table to the near-surface (2-11 feet) and surface (<2 feet). In addition, based on projected precipitation increases from ResilientMass, recharge rates were scaled by the same percent increase to create future low and high increase in recharge scenarios for which potential rise in historical groundwater elevation was determined. These historical and projected maps are the primary products of the project. Currently, sea level rise based on MC-FRM projections are being modeled and the projected coastal groundwater elevations in the statewide model will be updated. In addition, work is underway on three case studies that will be higher resolution than the statewide model and will use a transient groundwater model. Transient models allow the modeling of time series rather than a static snapshot. This allows for the estimation of annual maximum groundwater elevations rather than average annual elevations. These case studies are taking place in environmental justice communities that also have groundwater contamination with concerns over the movement of such contamination with groundwater elevation changes. In addition to benefiting the three areas selected for the case studies, these high-resolution case studies will provide additional quantification of uncertainty in the statewide model by comparing results.
Ancillary products that were develop during this project include statewide maps of shallow unconfined aquifers, surficial hydraulic conductivity, and specific yield. These products are available on MassGIS as the new Hydrogeologic Atlas of Massachusetts. The first, public report is forthcoming in the Fall of 2024 which details the methods, results and limitations of the analyses and maps, provides guidance for the proper use of the maps and provides guidance for considering the effects of groundwater flooding in the Frimpter method for siting septic systems and design of stormwater recharge systems. Multiple webinars have been hosted for interested entities such as the Water Resources Commission, MassDEP and the U.S. Geological Survey. Once the report and map products are available on ResilientMass, additional webinars will be hosted including for Boards of Health who regulate septic systems, stormwater community, watersheds group, state staff implementing SHMCAP actions and other planning and engineering communities.
Once these initial, public products are released, the next phase will work on transforming the statewide model into a transient model, pending the utility of this activity based on the high-resolution case studies. Additional sensitivity and uncertainty analyses will be conducted to continue to quantify the magnitude of error in modeled values for potential users of the detailed data such as engineers. Finally, a GIS-based interface will be built to accommodate planners exploring the data online and engineers who may need to download detailed data. This viewer will be integrated in ResilientMass.
Metrics
Process metrics include 1) data acquisition, compilation and cleaning (completed) 2) creation of the first public model (almost complete) 3) public release of maps and data through MassGIS (completed) and ResilientMass (Fall 2024) and 4) additional webinars delivery (Fall 2024).
Outcome metrics can be measured by the delivery of the ResilientMass and MassGIS products and the success of webinars to encourage the use of the products including in grant applications for resilience projects that mitigate groundwater flooding. In addition, a special layer will be delivered for MassDEP Wetlands with just acres that are within 2’ of ground surface. Finally, the report will detail the number of acres that are estimated to become vulnerable under future conditions, identifying EJ and contaminant hotspots.
Results
MassGIS products can be found compiled as the Hydrogeologic Atlas for Massachusetts
Report and results (maps and tables) are forthcoming in Fall of 2024.
Best Practices and Lessons Learned
Given state staff’s science and policy expertise on this project, we found it important to meet with UMass Amherst on a bi-weekly basis. This allowed state staff to review and advise on decisions made during modeling and post-processing of results so that the final products reflect not only the best scientific understanding but are most relevant for a wide audience of potential users ranging from engineers and policy makers to the public and that associated products such as the report serve the needs of this wide range of stakeholders with transparency and reproducibility of the results.
Project Alignment with ResilientMass Plan Priority Actions
This project helped with the update of the 2023 ResilientMass Plan. Groundwater flooding was included in the plan for the first time. For the next update, project results will provide quantitative estimates for and an assessment of the State’s vulnerability to this hazard. This project informed an EOEEA priority action under 2018 SHMCAP of using climate change projections to develop stormwater management actions and projects; and identify areas where stormwater design, especially those with recharge, will need to consider rising groundwater, based on results of vulnerability assessment for EOEEA properties and vulnerability assessments from other agencies.
Further Action
The model will be refined under Phase 3 by transforming the model developed under Phase1 and 2 into a transient rather than static model. This will enable the estimation of future maximum groundwater elevations rather than average annual elevation. Additional sensitivity and uncertainty analyses will be conducted to more accurately quantify model error. These results will provide important additional information for designers and engineers. Finally, a viewer will be developed for exploring the maps in detail and for data downloads.