Geology and water resources of the Wharton Tract and the Mullica River basin in southern New Jersey

Abstract

The Wharton Tract is an area of 150 square miles located in the Mullica River basin in southern New Jersey's Pine Barrens region. The tract is a relatively flat, low-lying, generally sandy area containing shallowly incised streams. The larger streams are commonly bordered by swamps. The tract was purchased by the State primarily as a water-supply preserve, but also for conservation and recreational purposes. Mean streamflow at three continuous record gaging stations in the Wharton Tract is: Mullica River near Batsto (46.1-square mile drainage area), 6 mgd (million gallons per day); Batsto River at Batsto (70.5-square mile drainage area), 81 mgd; Oswego River at Harrisville (64.0-square mile drainage area), 55 mgd. Thus mean discharge from this 180.6-sq mi (square mile) area is 202 mgd or 1.12 mgd per sq mi. Principal aquifers in the Wharton Tract and Mullic River basin are in the Kirkwood Formation of middle Miocene age, Cohansey Sand of Miocene(?) and Pliocene(?) age, and in overlying hydraulically connected deposits of Quaternary age. The Kirkwood Formation is composed of sand, silt, and clay. Diverse lithologies represent deposition in different environments such as nearshore marine, barrier bar, lagoonal, estuarine, and tidal marsh. Hydraulic characteristics of the Kirkwood in the Mullica River basin are virtually unknown. Most Kirkwood aquifers in the basin are believed to be hydraulically connected with the overlying Cohansey Sand. The Cohansey Sand is dominantly a quartz sand containing minor amounts of pebbly sand, silty sand, and interbedded clay. Almost all of the Wharton Tract and most of the Mullica River basin lie within the sandier area of the Cohansey, which contains approximately 75 percent sand beds and 25 percent silt and clay beds. Data from test drilling show that the upper 100 feet of sediments in the Wharton Tract contain about 93 percent sand beds, 3.5 percent clay beds, and 3.5 percent silt beds. The Cohansey in the Tract ranges in thickness from less than 50 feet to about 180 feet; the average thickness is about 125 feet. The Cohansey Sand is believed to be, in overall aspect, a deltaic deposit. It contains materials that were deposited locally in nearshore-marine, fluvial, estuarine, lagoonal, and beach environments. The hydraulic conductivity of Cohansey aquifer material ranges from about 90 to 250 feet per day (660 to 1,885 gallons per day per square foot) in southern New Jersey. One aquifer test in the Wharton Tract gives an average value of 130 feet per day (1,000 gallons per day per square foot). The transmissivity of the Cohansey Sand aquifer through most of the Wharton Tract is typically between 10,000 and 20,000 square feet per day (75,000 and 150,000 gallons per day per foot). Deposits of Quaternary age form a discontinuous veneer lying unconformably above the Cohansey Sand. The most important hydrologic function of most of these deposits is to absorb precipitation and transmit the water to the underlying Cohansey Sand. Thicker deposits of estuarine sand and clay of the Cape May Formation fill a channel in the underlying Cohansey Sand along the lower reaches of the Mullica River. This channel deposit is 85 feet thick near Batsto. Ground water and surface water in the Mullica River basin are low in dissolved solids, generally less than 50 mg/1 (milligrams per liter). Iron concentrations are generally high, up to 49,000 micrograms per liter (49 mg/1) in ground water and up to 7,100 micrograms per liter (7.1 mg/1) in the streams. The water is acidic as indicated by typical pH values of from 4.5 to 6.5. Color of the surface water is commonly high, ranging from 3 - 150 platinum-cobalt units. After appropriate treatment these waters are acceptable for most uses. The Wharton Tract is well situated to support the growing water needs of nearby New Jersey communities. Maximum development of water can be achieved by conjunctive use of ground and surface water. During most of the year, some water would be withdrawn either directly from streams or from adjacent wells. During periods of low flow during summer or fall water would be pumped from wells farther from the stream~. From analysis of flow-duration curves it is estimated that 70 mgd of water could be developed with minimal effect upon low flows in the half of the tract above the gaging stations on the Mullica and Batsto Rivers. The quantity available in the entire tract is greater, possibly in the order of 150 mgd. With augmentation of streamflow by pumping from ground water, it is likely that considerably more water could be safely used on a perennial basis. A possibility exists for multiple use of the water resources of the Mullica River through construction of an inexpensive tide barrier at the Garden State Parkway. This would create a fresh water lake in a State forest, park, and recreational area, which would also provide a flexible and economical water supply for much of the Atlantic coastal resort development.