We conducted soil evaluations with the DEP, installed 8 borings and monitoring wells with a well driller, and conducted hydraulic conductivity (slug) tests in each monitoring well using our transducers and slug test equipment. We read groundwater levels in all monitoring wells and calculated a seasonal high adjustment to the water table using the Frimpter Method. We then contoured the estimated seasonal high water table. We also used the borings and hydraulic conductivity tests results across the site to create a bedrock surface (bottom of aquifer) contour map, and a hydraulic conductivity distribution contour map.

Next, we created a MODFLOW hydrogeologic model of the site.  Bedrock contours were imported into the model at two-foot elevation intervals using SURFER software by Golden Software, Inc.  This process creates discretized grid files from the bedrock contour data at a five-foot grid spacing across the project site.  The grid spacing used in ModelCAD and MODFLOW was also five feet. Constant head boundary cell elevations corresponding to the existing seasonal high groundwater elevations in the easterly and westerly wetlands were assigned. No-flow cells were assigned essentially along the northerly and southerly cross-gradient property boundaries of the model.  The cross-gradient sides represent the lateral extent of the model in the direction perpendicular to the groundwater flow direction.  The upgradient and downgradient constant head cells represent the wetland hydraulic boundaries of the model. 

The model was calibrated so that the model produced the estimated seasonal high groundwater contours. Then, using the calibrated model, we determined the mounding effects to the water table elevation due to the recharge of the treated effluent, and contoured the proposed mounded groundwater table using the MODFLOW model. We engineered and designed two equal treated effluent soil absorption systems (SAS) consisting of plastic open-bottom "Infiltrator" chambers in a leach trench configuration. Leaching trenches were used with reserve trenches between the primary trenches primarily to spread out the SAS footprint so that the groundwater mounding effects could be minimized. Each leach trench chamber was fed by an outlet from a total of three distribution boxes, which were fed from a force main from the wastewater treatment plant (WWTP). The WWTP was designed by Linden Associates contracted by the owner. 

We successfully filed for and secured a Groundwater Discharge Permit (GWDP) by MA DEP for discharge of treated effluent, including the approval the construct the WWTP and treated effluent SAS.  The owner maintains the permit and is planning for the commencement of construction of the project in the near future.