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B21D Using Numerical Models to Assess a Rapid Infiltration Basin System (RIBS), Cape Henlopen State Park, Delaware

B21D Using Numerical Models to Assess a Rapid Infiltration Basin System (Ribs), Cape Henlopen State Park, Delaware
Publication Type:
Bulletin
Publication Date:
Dec 2015
Authors:
He, C., Andres, A.S.
Abstract:

The long-term performance of rapid infiltration basin systems (RIBS) and their potential impacts on the receiving environment have been previously unknown for Delaware. A variety of field experiments were conducted to characterize the geology and hydrogeology of a RIBS facility that has been in operation for more than 20 years at Cape Henlopen State Park. Pairs of standard monitoring wells and short-screened multi-level wells were used to evaluate the significance of small-scale vertical variability in water quality. A three-dimensional transient groundwater flow and contaminant transport model was constructed to simulate the groundwater mounding and the movements of nitrate-nitrogen (NO3--N) and orthophosphorus (OP) in the groundwater. In the numerical model, NO3--N was treated as a reactive species and denitrification was simulated with a first-order degradation rate constant. The major mechanism affecting OP transport in groundwater is sorption/desorption, which was simulated using a linear sorption isotherm. Simulated concentrations reasonably fit observed concentrations of NO3--N and OP in both standard wells and multi-level wells. The calibrated model predicts that with a denitrification rate of 0.006/day and a distribution coefficient of 4×10-7 L/mg, 63 percent of the reduction in the mass of NO3--N is attributable to denitrification, and more than 99 percent of OP is detained in the aquifer due to sorption on subsurface solids. However, the long-term operation of RIBS has led to a reduction of the sorption capacity of subsurface solids for phosphorous, resulting in significant concentrations of OP in groundwater adjacent to RIBS.

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Please give proper credit to the Delaware Geological Survey.

He, C. and Andres, A.S. , 2015, D Using Numerical Models to Assess a Rapid Infiltration Basin System (RIBS), Cape Henlopen State Park, Delaware: Delaware Geological Survey Bulletin 21 , 14 pp.

Contact Info

Delaware Geological Survey
Phone: (302)-831-2833
Fax: (302)-831-3579
delgeosurvey@udel.edu

University of Delaware
Delaware Geological Survey Building
Newark, DE 19716
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