Reports
Simulation of future water-level conditions and saltwater encroachment in the Ocean City-Manokin aquifer system at Ocean City, Maryland, using water-use projections through 2025
2012, Achmad, G.J and Bolton, D.W.
Open-File Report 12-02-18
Abstract
A three-dimensional ground-water flow model (Visual MODFLOW) and three two-dimensional solutetransport
models (SUTRA, version 2D3D.1) were constructed to represent the aquifer system beneath Ocean City,
Maryland. The models were populated with hydrogeologic information and historical water-level and chloride
data collected through 2005. The flow model and cross-sectional models were used to simulate water levels and
chloride concentrations at Ocean City’s well fields through 2025, using Ocean City’s future development plan of
maximum pumpages of 6 million gallons per day from the 15th Street well field, 4 million gallons per day from
the 44th Street well field, and 8 million gallons per day from the Gorman Avenue well field by 2025. The key
results of this study are as follows:
At the 15th Street well field, the simulated water level in the Ocean City aquifer in August 2025 was about
115 feet below sea level. The model indicates about 75 feet of remaining available drawdown (the height
of the water column above the 80-percent management level). Simulated chloride concentrations in the
15th Street wells range from about 55 to 60 milligrams per liter in 2025, representing an average simulated
increase of about 5 milligrams per liter over 2005 levels.
At the 44th Street well field, the simulated water level in August, 2025 in the Ocean City aquifer was
about 81 feet below sea level (about 50 feet deeper than in 2005), with about 119 feet of available
drawdown. The 2025 simulated average chloride concentrations ranged from about 150 to 250 milligrams
per liter, compared with about 125 to 215 milligrams per liter chloride in 2005.
At the Gorman Avenue well field, the deepest average water level in the Manokin aquifer simulated in
August, 2025 was about 34 feet below sea level (about 15 feet deeper than the 2005 simulated water
level), with approximately 306 feet of available drawdown. The highest simulated average chloride
concentration in the Gorman Avenue well field was about 150 milligrams per liter in 2025, compared
with about 130 milligrams per liter in 2005
An exploratory well (WO Bh 102), drilled in 2004 to a depth of 580 feet at the corner of 14th Street and
St. Louis Avenue, indicated that the ground water at the basal part of the Manokin aquifer tested 889
milligrams per liter chloride. Brackish water at the basal part of the Manokin aquifer encroached the
farthest inland beneath Ocean City at 44th Street, less at 15th Street, and the least at Gorman Avenue.
The model suggests that the water levels at the 15th Street well field, which prior to 2003 had returned to
above sea level during the winter, only recover to about 80 feet below sea level in winter, 2025. Winter
2025 water levels at the 44th Street and Gorman Avenue well fields (about 23 feet and 8 feet below sea
level, respectively) also do not recover to above sea level, but the water levels are closer to sea level than
at the 15th Street well field.
