Geology topics
Publications and source records attributed to Henry C. Barksdale.
The water supply drought in the Northeast began in the autumn of 1961 and marked the beginning of a severe water shortage that continued with little relief through the summer of 1966. During this time, throughout much of the Northeast, water supplies remained below normal.
The purpose of this report is to appraise and evaluate the groundwater resources of a tri-state region adjacent to the lower Delaware River that is centered around Philadelphia, Pa., and Camden, N. J., and includes Wilmington, Del., and Trenton, N.J. Specifically, the region includes New Castle County, Del.; Burlington, Camden, Gloucester, Mercer, and Salem Counties in New Jersey; and Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties in Pennsylvania. The peculiar advantages of ground water, such as its availability in many places without the necessity for expensive pipelines and its relatively uniform temperature and quality, make it an especially valuable resource in an industrial area. Large, readily available supplies of good, fresh water have contributed substantially to the recent rapid industrial growth of the lower Delaware River basin and will be vital to its continued prosperity. The major part of these supplies is drawn from the streams passing through the region, but very large quantities of ground water also are used. The region is divided almost equally by the Fall Line, which extends in a southwesterly direction along the general course of the Delaware River from Trenton, N.J., to Wilmington, Del., and beyond. Northwest of the Fall Line is a region of consolidated rocks in which ground water occurs mainly in cracks, crevices, and openings created or enlarged by weathering. The capacity of the various geologic formations to yield water depends largely upon the degree to which they have been fractured and weathered. The yield of individual wells in this part of the region is generally small to moderate and not readily predictable. Ground water in this part of the region is generally low in dissolved minerals and suitable for many uses without treatment. Southeast of the Fall Line lie the unconsolidated rocks of the Coastal Plain. Ground water occurs in these rocks largely in the pore spaces between the individual mineral grains. The major formations and the principal aquifers are rather uniform in their water-bearing characteristics over large areas. The yield of individual wells is moderate to very large and may be predicted with a reasonable degree of assurance. Sufficient quantities of ground water are available in most places for all ordinary purposes. The chemical quality of the ground water from the Coastal Plain aquifers is generally acceptable for most uses, but objectionable quantities of iron or other minerals are found in some places, and some waters have a low pH and are corrosive. More than 40 distinct geologic formations occur in the region. They range in age from Precambrian to Recent. Nearly all will yield some water to wells. However, only about a dozen yield water freely enough to be considered major aquifers. Of these, the sands of the Raritan and Magothy formations have been developed most intensively, and the Cohansey sand appears to have the greatest capacity for additional development. The present withdrawal of ground water in the region is estimated to average more than 200 mgd, of which more than half is drawn from the aquifers in the Raritan and Magothy formations. It is estimated that additional supplies of ground water, aggregating more than 1 billion gallons a day, can be developed within the region. Furthermore, substantial additional quantities can be developed outside the region for use within it if the need should ever arise. Induced recharge from the Delaware River supplies a substantial portion of the total water drawn from the Raritan and Magothy formations. In some areas, the quality of the water from these aquifers is approaching that of the river. Increased withdrawals of water from wells along the river will tend to increase induced recharge. Thus, the maintenance of a good quality of water in the river, which is desirable for many other reasons, is imperative if the quality of the ground-water supply is to be maintained. The proposed deepening of the Delaware River channel from Philadelphia to Trenton will greatly increase the opportunity for the interchange of water between the river and the adjacent aquifers. Whether this will be beneficial or detrimental to the ground-water supplies will depend upon the quality of the water in that reach of the river. If an acceptable quality of river water is maintained, the groundwater resources of the region will be augmented. If salt water from the ocean or excessive contamination from other sources should render the river water undesirable as a source of recharge, actual and potential ground-water supplies aggregating about 250 mgd would be endangered. The danger of salt-water encroachment into the aquifers normally yielding fresh water may limit the optimum yield of some of the most important aquifers in the region. Encroachment may come either from salt water in the surface-water bodies of the region or from parts of the aquifers, normally containing salt water. The protection of ground-water supplies against salt-water encroachment can be maintained only by constant vigilance, careful distribution of the pumping from the aquifers, regular sampling of outpost wells in exposed localities, and adjustment of rates of pumping in the light of changing conditions. The maximum beneficial utilization of the ground-water resources cannot be accomplished in haphazard fashion. It must be planned and controlled on the basis of sound, current information about the hydrology of the various aquifers. Continued and, in some areas, intensified investigations of the ground-water resources of the region should form the basis for such planning and control.
In the Newark area, ground water is used chiefly for industrial cooling, air-conditioning, general processing, and for sanitary purposes. A small amount is used in the manufacture of beverages. Total ground-water pumpage in Newark is estimated at not less than 20,000,000 gallons daily. The Newark area is underlain by formations of Recent, Pleistocene and Triassic age, and the geology and hydrologic properties of these formations are discussed. Attention is called to the important influence of a buried valley in the rock floor beneath the Newark area on the yield of wells located within it. Data on the fluctuation of the water levels and the variation in pumpage are presented, and their significance discussed. The results of a pumping test made during the investigation were inconclusive. The beneficial results of artificially recharging the aquifers in one part of the area are described. The intrusion of salt water into certain parts of the ground-water body is described and graphically portrayed by a map showing the chloride concentration of the ground water in various parts of the City. Insofar as available data permit, the chemical quality of the ground water is discussed and records are given of the ground-water temperatures in various parts of the City. There has been marked lowering of the water table in the eastern part of the area, accompanied by salt water intrusion, indicating that the safe yield of the formations in this part of Newark has probably been exceeded. It is recommended that the study of the ground-water resources of this area be continued, and that artificial recharging of the aquifers be increased over as wide an area as possible.
This report is the second progress report on the ground-water investigations in the Atlantic City region. Many important problems still remain to be solved, however, and it is in no sense a final report. The report covers the area immediately surrounding Atlantic City, extending from Brigantine to Sea Isle City along the coast and from Absecon to Somers Point on the mainland. In addition to this, a few data are presented bearing on the area along the coast as far south as Wildwood. The area lies in the southern part of the New Jersey Coastal Plain, and the water-bearing formations considered are all unconsolidated and of Miocene or more recent age. The major formations in the region dip gently toward the ocean and possibly extend out under the ocean to the edge of the Continental Shelf, about 100 miles from Atlantic City. The principal ground-water supplies in the area are derived from the so-called "800-foot sand," a member of the Kirkwood formation, and from the overlying Cohansey sands. The 800-foot sand is of wide extent and apparently fairly uniform. The Cohansey sands, on the other hand, cover a wide area but are by no means uniform. At the Atlantic City Water Works two Cohansey sands are recognized-the so-called "100-foot" and "200-foot" sands. Neither of these sands can be differentiated from the other sands of the Cohansey formation over a distance greater than 4 or 5 miles in any direction. In addition to the supplies derived from ground water, some surface water is used at present by two of the public water supplies. The quality of the water from all the sources of supply now used is satisfactory. The total consumption of water in the region has increased gradually over the entire period of record, except for a moderate decline from 1929 to 1934. Additional water supplies can be obtained from either of two fairly large streams near the region, and possibly also from a more widespread development of the Cohansey sands. The 800-foot sand should not be counted upon as a source of additional water supply, in view of its liability to salt-water contamination. The same danger also exists in the Cohansey sands on the mainland near the shore, but farther inland it is not a serious menace to the supply from these sands The 100-foot sand at the Atlantic City Water Work has been overdeveloped since 1930, with the result that the head of the water in it has been lowered materially and salt water has been drawn into it through holes in the overlying clay beneath the nearby salt marshes. Three of the five new large-capacity wells drilled to this sand in 1930 have been temporarily or permanently abandoned on account of salt-water intrusion, and the two others will probably have to be abandoned also, unless suitable remedial measures are promptly adopted. It is recommended that the wells to the 100-foot sand be used only when needed to supply the seasonal peak demand and that consideration be given to a project to transform the tidal marshes into a fresh-water pond by means of a suitable dam in order to protect the formation from further contamination. If detailed study proves that the dam and fresh-water pond would not be economically justified, a smaller pond and an embankment and tide gates on the main stream to keep the salt water from flooding the marshes are recommended as less effective but less expensive remedial measures. In view of the experience with the 100-foot sand at the Atlantic City Water Works, it is further recommended that any additional development of the Cohansey sands be preceded by a comprehensive test-well program that will indicate not only the capacity of the sands, but the location of salt water in them and the possibility of its being drawn into existing wells or the proposed new wells. The salt-water intrusion into the 100-foot sand was effectively studied by means of driven-well points, which, it was found, could easily be driven to a depth of about 100 feet. The fact that the screen of these wells was driven with the casing and that no water was used in the drilling process made it possible to collect true samples of water from every sand encountered in them. This, in turn, made it possible to study the vertical distribution of salt water in each well. The interpretation of the vertical distribution of salt water in these wells was very helpful in arriving at a final decision as to the source of the salt water. The 200-foot sand at the Atlantic City Water Works has also been subjected to a considerably increased draft since 1930. Although there is no evidence at present that this sand has been overdeveloped, a study of its characteristics suggests that it may not be capable of yielding permanently the capacity of the present wells that tap it. Three test wells have been installed between the well field and the source from which this sand might derive salt water, and they should be sampled regularly to determine the danger of salt-water intrusion into the sand. In a landward direction this sand merges into the other Cohansey sands. It is therefore advisable that any additional development of the Cohansey sands should be undertaken so far inland that the pumping from it will not affect the present wells to the 200-foot sand and thereby increase the danger of salt-water contamination in them. At present more potable water is taken from the Atlantic City 800-foot sand than from any other source of supply for the region. This sand is the sole source for some of the smaller communities on the barrier beaches. The original static head of the water in it at Atlantic City was between 20 and 25 feet above sea level. The head has been lowered more than 50 feet over much of the region, and in parts of Atlantic City it has been lowered considerably more than 100 feet. A consideration of the principles governing the relation between salt water and fresh water in water-bearing sands indicates that the 800-foot sand probably contained salt water at a distance of 5 or 10 miles out from Atlantic City before any water was pumped from it. The evidence collected in this investigation indicates that the cone of depression created by the pumping from this sand in the Atlantic City region has probably extended inland to the intake area of the sand, the nearest part of which is probably about 40 miles from Atlantic City. If this is so, the conclusion is almost inescapable that it has also extended oceanward for a distance considerably greater than the 5 or 10 miles to the original zone of contact between the fresh and salt waters, and that salt water is probably being drawn toward the Atlantic City region through this sand. The time of its arrival will depend primarily upon the rate of pumping in the region and upon how much of the fresh water that originally lay between the region and the zone of contact must be removed before the salt water can reach the region. It may arrive in the near future if it advances in the form of a narrow tongue. On the other hand, if it advances along a broader front; so that more of the intervening fresh water must be pumped out of the formation, its arrival may be delayed for some time.