Creekside Park is proposed residential subdivision located in southeastern Hillsborough County.  The original plans called for a 30-foot deep stormwater retention pond that was located within close proximity to a seepage wetland system.  Based on review of the original application, the SWFWMD was requiring the installation of a clay barrier wall along most of the perimeter of the retention pond.  The clay barrier wall was to tie in to the clay confining layer beneath the surficial aquifer, at a depth of 30-feet.  In response to SWFWMD’s request, HEA was retained by King Engineering, Inc. and Faulkner Engineering, Inc. to evaluate the impacts of the proposed retention pond and optimize design of the barrier wall.

HEA developed a groundwater flow model of the area based upon the SWFWMD’s DWRM II regional model to evaluate the drawdown impacts from the proposed stormwater pond.  The model was used to predict the impacts of the proposed pond on the surficial aquifer and nearby wetland system.  The barrier wall package of MODFLOW was used to optimize the design of the clay barrier wall.  Groundwater flow modeling was conducted using both average annual water levels conditions and seasonal high water level conditions.

The results of the groundwater flow modeling proved that the barrier wall could be reduced in depth by 20 feet and in length by about 100 feet, and still provide adequate protection to the wetland system from drawdowns due to the proposed stormwater retention pond.  As a result of the groundwater flow modeling, the Environmental Resource Permit was successfully obtained without monitoring requirements.