Hydrogeology of the South Fork of Long Island, New York: Discussion and reply

Discussion

M. P. ANDERSON Department of Geology and Geophysics, University of Wisconsin - Madison, Madison, Wisconsin 53706 C. ALAN BERKEBILE Geology Department, Southampton College of Long Island University, Southampton, New York 11968

The concept of safe yield used by Fetter (1976) is an elusive one. not object to simplifying reality for modeling purposes. However, Although several definitions have been suggested, none is com- we are concerned that a numerical value for safe yield based on an pletely acceptable and most are vague. Todd's (1959, p. 200) idealistic arrangement of wells and a narrow definition of "unde- definition, probably the most often quoted, refers to thè amount of sired result" may be misused. Taken out of context, without a re- water that can be withdrawn from a ground-water basin without alization of the very special circumstances in which the value for producing an "undesired result." One is immediately led to ask safe yield was estimated, it could be interpreted to imply that the what constitutes an undesired result. The answer, of course, will South Fork's ground-water resource can support a substantially in- vary with the respondent. Thomas (1951, p. 261) called safe yield creased population. Such an interpretation would be unfortunate an "Alice-in-Wonderland term which means whatever its user because some of the population is already experiencing water- chooses," and Kazmann (1956) called upon hydrogeologists to supply difficulties due to salt-water intrusion. eliminate the concept of safe yield as an object of ground-water In addition to water quality and ecological considerations, there studies. are several factors related to economics and engineering that In light of this, it is disconcerting that Fetter (1976) used the term should be included in any reasonable estimate of safe yield. Because and proposed a numerical value for the safe yield of the aquifers of the many factors involved in a safe-yield determination and the underlying the South Fork of Long Island, New York. Fetter as- necessarily subjective nature of some of these factors, we agree with sumed a value equal to 20% of the average annual recharge. Then Kazmann that it is best to avoid the concept altogether. Perhaps the he demonstrated that the undesired result — namely, intrusion of concept of maximum stable basin yield (Freeze, 1971) is a step water-supply wells by saline water — will not occur if consumptive toward formulating a more rational approach. use of water does not exceed this safe yield and if water-supply The Thornthwaite method of calculating évapotranspiration has wells are evenly spaced and located farther than 914 m from the been recognized by many soil physicists to give questionable results shoreline. Fetter recognized that impacts of ground-water with- (C. B. Tanner, 1976, personal commun.). In general, it is true that drawal on coastal ecology should be considered, and he suggested évapotranspiration exceeds ground-water recharge. Therefore, that his value for safe yield be modified after these impacts have when ground-water recharge is computed by differences, errors in been assessed. However, he then implied that this determination évapotranspiration will produce a larger percentage error in need not be made prior to the implementation of a long-range ground-water recharge. Fetter estimated recharge to be 40% of an- water-supply management plan based on ihe unmodified safe-yield nual precipitation. Lower estimates have been given by Spiegel value. (1974), who suggested that recharge to the water table is only 30% The proposed arrangement of supply wells is unrealistic. Public of precipitation in the North Haven area of the South Fork, and by and private water-supply wells are already located less than 914 m Jacob (1968), who estimated ground-water recharge to be 17% of from the shoreline, and salt-water intrusion is already occurring in precipitation in the village of Southampton. some parts of the South Fork (Fetter, 1974; Spiegel, 1974; Berk- We also point out that the Gardners (sic) clay is the Gardiners ebile and Anderson, 1975; Anderson and Berkebile, 1976). We do clay.

The article discussed was published in the Bulletin, v. 87, p. 401-406.

Geological Society of America Bulletin, v. 88, p. 895-896, June 1977, Doc. no. 70618.

895

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C. W. FETTER, JR. Department of Geology, University of Wisconsin - Osbkosh, Oshkosh, Wisconsin 54901

Anderson and Berkebile share with many others a disdain for the COMBINED REFERENCES CITED term "safe yield." However, I think that if it is properly used it conveys a useful concept. Ground-water management programs Anderson, M. P., and Berkebile, C. A., 1976, Evidence of salt-water intru- must be based upon the concept that some of the water can be sion in southeastern Long Island: Ground Water, v. 14, p. 315-319. withdrawn from the aquifers for human use; otherwise, ground Berkebile, C. A., and Anderson, M. P., 1975, Town of Southampton, water would be an unusable resource. The question, then, is exactly 1974-75 Ground-Water Resources Monitoring Program: South- ampton, N. Y., Southampton College, Geology Department, Report to how much water can be withdrawn. Although relatively large the Town of Southampton. 110 p. amounts of water could be pumped initially from an aquifer, it is Cohen, P., Franke, O. L., and Foxworthy, B. L., 1968, An atlas of Long possible to overpump the aquifer so the initial rate could not be Island's water resources: New York Water Resources Comm. Bull. 62, sustained. There are many reasons why the amount of water that 111 p. can be removed is limited. Often these are related to falling water Fetter, C. W., Jr., 1972, The concept of safe ground water yield in coastal tables and water-quality problems. A generally accepted definition aquifers: Water Resources Bull., v. 8, p. 1173-1176. of safe yield is the amount of water that can practicably be with- 1974, Water quality and pollution — South Fork of Long Island, New drawn perennially without an undesired result (Todd, 1959). The York: Water Resources Bull. v. 10, p. 779-788. undesired results have traditionally been related to the cost of de- 1976, Hydrogeology of the South Fork of Long Island, New York: velopment, maintaining water of acceptable quality, and legal re- G eoi. Soc. America Bull., v. 87, p. 401-406. Franke, O. L., and McClymonds, N. E., 1972, Summary of the hydrologie quirements. I have suggested (Fetter, 1972) that environmental im- situation on Long Island, New York, as a guide to water management pacts should also be evaluated. In the broadest sense, environmen- alternatives: U.S. Geol. Survey Prof. Paper 627-F, 58 p. tal impacts include ecological, economic, social, cultural, and polit- Freeze, R. Allen, 1971, Three-dimensional transient saturated-unsaturated ical values. The safe yield of an aquifer system is not a physical flow in a groundwater basin: Water Resources Research, v. 7, phenomena but is, rather, a subjective phenomena based upon p. 347-366. human values. Jacob, C. E., 1968, Subsurface hydrology and future water supply of Determination of safe yield can only be made by an interdiscipli- Southampton, New York: Report to the Southampton Town Board: Northridge, Calif., C. E. Jacob & Associates, 26 p. nary team using optimization techniques and evaluating all impacts Kazmann, R. G., 1956, "Safe yield" in ground-water development, reality of the various ground-water management schemes considered. or illusion?: Am. Soc. Civil Engineers Proc., Jour. Irrigation and The numerical value I gave in the section on safe yield (Fetter, Drainage Div., v. 82, no. IR 3, p. 1103-1-1103-12. 1976) is only a first approximation of the value of the safe yield. It Pluhowski, E. J., and Kantrowitz, I. H., 1964, Hydrology of the Babylon- is based solely on the steady-state position of the saline water inter- Islip area, Suffolk County, Long Island, New York: U.S. Geol. Survey face with wells evenly spaced. As I wrote, "Environmental impacts Water-Supply Paper 1768, 119 p. should be established and then the safe yield taking them into ac- Spiegel, Zane, 1974, Geohydrology of the Village of North Haven and count should be determined." A more refined model based on the nearby portions of the Town of Southampton, Suffolk County, New location of existing well fields and transmission lines would be de- York: Report to the Incorporated Village of North Haven: Sante Fe, N. M., Zane Spiegel, 52 p. sirable, but it was not feasible for me to determine these. Thomas, H. E., 1951, Conservation of ground water: New York I feel there is sufficient time to make a thorough determination of McGraw-Hill Book Co., 327 p. the safe yield. However, as Anderson and Berkebile point out, local Todd, D. K., 1959, Ground water hydrology: New York, John Wiley & salt-water intrusion in shoreline areas is occurring, and extreme Sons, 336 p. care must be used in well location in those areas. Warren, M. A., de Laguna, Wallace, and Lusczynski, N. J., 1968, Hydrol- I agree that in determining ground-water recharge by use of the ogy of Brookhaven National Laboratory and vicinity, Suffolk County, water-balance equation, the results are dependent upon computa- Long Island, New York: U.S. Geol. Survey Bull. 1156-C, 125 p. tion of evapotranspiration. The Thornthwaite method is often used because only standard climatological records and Thornthwaite's tables are needed. Estimates of recharge that I made using this method are similar to those made for other areas of Long Island by

the U.S. Geological Survey (for example, Cohen, and others 1968; MANUSCRIPT RECEIVED (DISCUSSION) BY THE SOCIETY MAY 24, 1976 Franke andMcClymonds, 1972; Pluhowski and Kantrowitz, 1964; MANUSCRIPT RECEIVED (REPLY) BY THE SOCIETY JULY 26, 1976 Warren and others, 1968). MANUSCRIPTS ACCEPTED OCTOBER 4, 1976

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