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HomeMy WebLinkAboutGeology & Ground Water Resources of the Town of Southold.Geology and Ground-Water Resources of the Town of [..Southold, Suffolk County New York GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1619-GO Prepared in cooperation with the Suffolk County Board of Supervisors, ttie Suffolk County li~ater ~luthority, and tke New York State Ifrater Resources Commission Geology and Ground-Water Resources of the Town of Southold, Suffolk County New York By H. C. CRANDELL CONTRIBUTIONS TO THE HYDROLOGY OF Tile UNITED STATES GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1619 G~'(' Prepared in cooperation with the Suffolk~" County Board of Supervisors, the Suffolk [e'[~-2 County llfater .quthority, and the New ((~.((~q~ York State l~ater Resources Commission UNITED STATES GOVERNMENT PRINTING OFFICE, W~,SHINGTON : 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director CONTENTS Abstract ............................... Introduction .......................... 1 Purpose and scope of the investigation ........ l Location of the area Previous investigations ............. 4 Methods of investigation ...... 5 Well-numbering system_ Acknowledgments .............. 5 Geography ........................ 6 Topography and drainage ........ 6 Climate_ _ History of development ............. 9 Geology _ Ground water - - .... 11 Hydrology_ ............... 19 Water-level fluctuations Withdrawal__ - - - ....... 24 ........... 24 Sea-watcr encroachinent ......... 28 Chemical quality _ ............. 31 Conclusions References cited _ - ......... 33 ......... 3,5 ILLUSTRATIONS PLATE l. Surficial geologic map. '2. Geohydrologic sections. 3. Water-table mai). FIGURE 1. Map showing location of the towll of Southold GG3 2. Photograph showing stratified drift, thin till cap, and large erratics, north shore 15 CONTENTS TABLES TABLE 1. Precipitation, i~inches, dnring 1958 and 1959 at 1 I stations in tile town of Southold and at 2 nearby stations GG10 2. (]cneralizcd stratigraphic section ill the town of Southold 12 ~ t 3. Logs of selected wells in the town of Southok _ 16 4. Physical characteristics of upper Pleistocene water-bearing deposits in the tow~ of Southold _ 18 5. Chemical analyses, i~ parts per miliio~a, of water from public- supply wells in thc villages of Gree~port and Southold 32 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES GEOLOGY AND GROUND-WATER RESOURCES OF THE TOWN OF $OUTHOLD, SUFFOLK COUNTY, NEW YORK By H. C. Ca.',XVELL PURPOSE AND SCOPE OF THE INVESTIGATION In 193° tile [~.S. Geological Stn",-i,y hog'an :ul orel'al] and conl hming appraisal of ground-water conditions on Lon~z Island. This report GG2 CONTRIBUTIONS TO TI-IE HYDROLOGY OF THE I~ITED STATES presents the results of au investigatiou undertaken as a part of that program in cooperation with the Suffolk Couuty Board of Supervi- sors, the Suffolk ('ouuty Water Autbority. and the New York State Water Resoarces Commissiou (formerly /lie New York State Water Power and Coutrol Commisslou). Fieldwork by the writer begau in September 1957 aud ended in 1)ecember 1959. The present report is based on data available prior 1o ,lanuary 1960. The town of Southold is 1 of 10 major political subdivisions of Suffolk County. In this report the names "towR of Soutbold" and "Southold" are used interchaugeably. Because the town of Southold is almost entirely surrounded by salt water and has a relatively small area for recharde to the ground-water reservoir, development and ys.e of fresh ground water must be such as to prevent or keep to a m~m- mmn the encroachment of sea water into deposits now contaiuing fresh water. Two public water-supply iustallations aud many domestic and crop-irrigation systems are totally dependent on the continued availability of groRud water of good quality. This investigation, therefore, has included study of (1) the areal extent, thickness, and physical properties of the water-bearing deposits: (2) the hydrologic characteristics of the ground-water reservoir; (3) the conditions un- der which sea-water eRcroachmeut may take place; and (4) the estab- lishment of a monitoriug program to observe any futnre sea-water encroachment resulting from depletiou of the ground-water supply. The report includes pertiuent conculsions from previous investiga- tions of the geology and hydrology of Southold as well as data ob- t ained during this investigation. LOCATION OF THE AI%EA The eastern third of Long Island is made up of two narrow penin- sulas septtrated hy Peconic Bay, Gardiners Bay, and contiguous inlets. The town of Southold occupies the easteru 9q0 miles of the northern peninsula and also iucludes Robins, Plum. Great Gull, Little Gull, and Fishers Islands (fig. 1). Robins Island is in Peconic Bay, whereas the other islands form a broken chain in Long Island Sound that is a continuatfon of the Rortheastward-trending peninsula. Plum Island is about 1 nfile from Orient Point, Great Gull aud Little Gull Islands are about 7 miles from Orieut Point, aRd Fishers Islaud is about 13 miles from Orient Point and about 7 miles southeast of New London, Conn. The total area of Southold is about 54 square miles, distributed as showR in the following table: 41° __ 74° NEW JERSE London ~ro~n .' ers Island,' Great Gull I¢Little Gull I , I YORK', AT ANTIC CONTi~IBL*TIONS TO THE HYDROLOGY OF Tk~IE ITNITED STATES 42.90 5.20 Plum Island .03 Gull Islands Fishers Ishtnd .................... 4.22 The whole of Southold lies almost e~tirely between lat 40°57%0'' and 41°17'30'' N. and hmg l l°;m and ~12 ,,o B~. This i~vestigation included the peni~sular part of the town only. The following topographic quadrangle maps of the I:.S. Geological Survey include all parts of Southold: Greenport. . I New York I 1:24, 000 I 1956 Mattituek i New York 1:24, 009 1956 Mat~tituck IIills _ I New York 1:24, 000 ! 1956 3dx tic Conn. ~.Y. lg.I 1:31,680 1951 Soathold I New 5ork i /:24.000 195(5 pI~EVIOUS INVESTIGATIONS P~eferences to parts of Southold apl)ear frequently in early works on the geology of Long lsland. Mather (1843) described in some detail the bluffs and boul(ler strewn beaches of the 1)eni~sula's north shore, as well as the ('lay deposits between the x illages of Greenport and Southold. These deposits were again discussed hy Merrill (1886) and by Ries (U}0o). Veaich (l~)O~;) prepared a detailed report on I,ong ~sland's water resources, which ineluded the logs of eight wells h~ Sonthold. The most comprehensh-e report of Long Island geolo~' was prep:trod by Fuller (1~14). This report contains many specific :~bservari¢nls lnafle ill $outhohl alld evaluates them in their relation , o the geologic history of the Long Island area. An earlier paper by ~uller (1905) deseribes lhe geology of Fishers Island. Very Utile has been written since Fuller's lime dml ntentiol/S Sou~hold. Logs of many wells in Suffolk Comity, imluding some in Southold, were compiled by Leggette (D~3S), Roberts a~d Brashears (1945), and Johnson (1052). Surer, deLaguna, and Perhnutter (19~9) summarized the geology of Long Island and correlated the logs of several deep wells in Somhold with logs of wells elsewhere on ;he island. Data on the temperature and chloride concentration of GEOLOGY AND GROUND WATER, SOUTI~OLD~ NEV, r YORK GG5 water from wells in Soffolk Courtly were presented and interpreted by Hoffman and Spiegel (1958). Mm'e recent work oo Southo]d was done by Hoffman (1961)~ who described tho hydrolo~, of the shallow grou;~d-water re~rvoir, with particular referenre to sea water encroachment, and by Crandell (1962)~ who investigated the geo]o~' and ~romid-water ~:esources of Plum Island. METHODS OF INVESTIGATION In earc:ing ont the purposes of this investigation the author exam- fined outcrops of glacial outwash and tilI ~n Sontho]d and prepared a generalized nmp of tho deposits. Tbil~v-five test holes, ranging in depth from about 50 to 100 feet~ were a~gered to obtab; samples ot outwash for perme,bili~y and si)celtic?icld determinations. ]Veil points and pipe were instal]ed in 32 of the test holes to establish control for a contour map of the water table. Eleven rain ga~es were estab- lished ht different parts of the area to comp, re differences in precipita. tion. I)ata on evaporation uere obtained from the U.S. ]Veather Buremh which operated an eraporation pan at Greenport. Eighty wells were measured momhly to delermine lbe ahitude and trend water levels, and 100 wells and 5 ponds were sampled to determine !he chloride content of the water. On Long Island the Geological Sm'rev uses a well-unmbering sys tern eslablisbed by the New York Water Resources (e mnissio.. ~rells in eaeb eOUllt~, are nmnbered serially as drilling reports are re~ived by the Commission. The well nmnber is prefixed by the initial letter of ~he cmmlv in which it is ]oeated. rl'h.s a well Suffolk County is desitin'ted by the lelter 'S- followed by the signed number (for example, S1036I). The author wishes to acknowledge the aasisl ante of lhe staff mere bern of lhe Long lshmd ofllee of the Xew York State ~Valer Resoui'ees ('omnlission for providing most of 1he ~sell ',. n'ds used in the in,epa- in the compilation of precipitation data. and the author is esl)eeitdlv grateful to Mr. l[Nl'r¥ Monsell, SUl)erh~ endent of Public Works. village of Greenport, f}n' generously lU,ovidinE the Geological Survey with additional manpower and equipmel~ to instnll wells, to measme determhmtions. GG6 CONTRIBUTIONS TO THE t-IYDROLOG¥ OF THE UNITED STATES GEOGRAPHY Much of Southold, particularly the eastern part, may ~ conside~ · s virtually a chain of small islands along an axis trending no~h- e~stward. Even the peninsular part is naturally subdivided by sMt- water ponds, ma~h~, and inlets into six separate morphologic and hydrologic areas~ four of which are desi~ated by the lette~ A, B, C, and D for pur~ses of reference in this repoR (pls. 2 and 3). The other two a~as are Little Hog Neck and Great Hog Neck, which jut south f~m the peninsul~ but are largely detached from it by salt- water mashes and inlets. Plum~ Great Gull, Little Gull, and Fishers Islands are separa~d by o~n salt-water p~ssages and lie in ~ chain extending no~heastward from the peninsula. Robins Island l~ in Peconic Bay between the northern and southex~ peninsulas of I~ng Island. Are~ A (about 7 ~ua~ miles) extends from a sho~ distance west of the weste~x boundaw of the town of Soutbold to Matt~tuck C~ek, is ~bout 3 miles wide, and ~ntains most of the village of Mattituck. Are~ B (abut 25 ~uare miles) ~s bounded on the west by Mattituck Cr~k and on the east by Hashamomuck Pond. This area constitutes the largest p~rt of Southold. It ~nges in width fl~m about 1~/2 to 4 miles. The villages of Cutcho~e, Pecon~c, and Southold are ha this area. Are~ C (a~ut 7 square miles) extends eastward from Hash~- momuck Pond to Dam Pond. It is about I to 1Ve miles wide. Green- port, which is Southold~s largest village~ and East Marion are in this a~a. Are~ D (about 5 squ~ miles) is bounded on the west by Dam Pond and te~inates to the east at Orient Point. The a~a has a width of about I to 1~/~ miles. Little Hog Neck (about 0.75 mile) and Great Hog Neck (about 2.3 square miles) extend ~uthe~t- w~rd from the south shore of area B. The southern shoreline of the peninsula is very irre~lar as it is m~rk~ by numerous salt-water emb~yments ~nd marshes. Attractive beaches~ which are made up of well-sorted clean quartz sand, form the rest of the southe~ shm~llne. In many places they form bayhead beaches and spits. The most prominent spit~ Long Beach (pl. 3) ex- tends southwestward almost 4 miles from Orient Point and is occupied by Orient Beach State Park. The combination of pleasant beaches ~nd embayments, which provide good swimming conditions and boat anchorage, has attracted many summer-home builders. The north shore of peninsular Soutbold is relatively rugged. A prominent ridge lies near the shore except where inlets and ponds m~rk the boundaries between areas A, B~ C~ and D. In the eastern pa~ of area D, however, erosion has removed most of this ridge. The GEOLOGY AND GROUND VgATER, SOUTHOLD, NEW YORK GG7 shoreline is generally regular and smooth, but two small headlands in area B, two in area C, and one in area D extend into Long Island Sound. Most parts of the ridge are more than 50 feet above sea ]eve]. The ridge has a maximum altitude of slightly more than 160 feet in area A. Erosion by storm waves and high tides has removed much of the ridge material and has left steep bluffs which are from about ~0 to more than 50 feet high at the shore, and narrow beaches strewn with cobbles and boulders. Very large boulders are clustered at the headlands and at some places on the southern slope of the ridge. Mather (1543, p. 169) described their size in the following quotation: Some of the erratic blocks of Long Island are of great size. One on Mr. Latham's farm at Oysterpond Point (Orient) was mostly blasted to pieces, and made into a stone fence. He stated that the fragments made eighty rods (one- fourth of a mile) of stone feuce, four feet high. A portion still remains in the ground. The portion used must have weighod more than nine hundred tons. A gently rolling outwash plain with numerous shallow depressions extends from the ridge along the north shore to the south shore. The plain slopes southeastward at about 20 to 30 feet per mile. Great Hog Neck and Little Hog Neck extend southeastward from area B. Little Hog Neck is roughly trlangu]ar, about ~ miles long and about half a mile wide at the base, which is joined to area B by a very narrow sand bar. Much of the ]and surface has an altitude of more than 50 feet and is extremely hilly. Great Hog Neck is almost a rectangle, about 1~ miles wide by 2 miles long. It is joined to area B by a small marshy area about a quarter of a mile wide. l~Iost of the land surface is similar to the gently rolling plain in the central parts of areas A, B, C, and I), although it has somewhat greater relief. Two prominent hills more than 70 feet high lle in the northwestern part o f the neck. :Robins Island has very much the same shape and appearance as Little Hog Neck and is only slightly smaller. It is very hilly; the altitude of most of the land surface.is more than 50 feet and exceeds 80 feet in the north-centra] part. Bluffs that rise 20 to 50 feet above sea level mark the island's western shore]ine. Plum Island also has a triangular outline and ranges in width from about 300 feet near the eastern end to a]most I mile at the southwestern end. The island is about 3 miles long. A lowland in the central part of Plum Island slopes gently to the northeast and thence southeast and separates two low ridges. The northeastern ridge is the more extensive and rises to an altitude of more than 100 feet, whereas the southeastern ridge ranges in a]titude from 40 to 75 feet. Both ridges are marked at the shoreline by steep b]uffs~ and the beaches are strewn with many large boulders. GG8 CONTRIBUTIONS TO THE HYDROLOGY OF TIlE U'NITED STATES Great Gull Island is about one-teuth mile wide by about one half mile long and is only about 30 feet above sea level at its h~gbest point. Little Gull Island is about 400 feet wide by about 800 feet long and is only slightly above sea level. The ontline and topography of Fishers Island are very irregular. The island is ahnost 7 miles long and ranges in width from 500 feet near the northeastern end to 1~/2 miles Dear the southwestern end. The principal ridge of hills, which lies along the south-central shore- line~ bas a maximum altitude of about 70 feet, which is about the average elevation of the many knoblike hills that cover most of the remaining parts of the island. Some individual knobs however, rise to 100 feet above sea level. Shoreline bluffs are m)t well formed and are less than ~0 feet high in most places. Numerous shallow un- drained depressions are scattered over tim ishtnd, and some of these in the central part contain fresh-water ponds. Most of peninsular Soutbold is cropland. Vegatation in the maining parts of Southold consists maiDly of marsh grasses, beach and dune grasses, and wild shrubs and bushes. Stauds of mixed deciduous forest and stone conifers are in the billy areas and where land has not been cleared for farming. None of the islands iu Southnld have streams, and the peninsula has relatively few. Ground water discharge ipso lbese streams is uegligible, and virtually all lhe streams are ephemeral. Surface run- off during and after heavy storms provides the only observable flow in the stream channels. Generally the streams are no more than a mile long and discharge into the marshes aloDg ~ he south shore. Owing to its virtually insnlar nature, its latitude, and the proxin?y of the Atlantic Ocean~ Southo]d has a prednminantly temperate marine climate. Tenq)eratures are moderate, and preeipitation is abundant during the fall, winter, add spring. A brief dry spell commonly occurs during the summer. The following table compiled from infor- mation collectedbv Mordoff (1949) and periodic climatic sumnmries of the U.S. Weathe~~ Bureau sumarizes available temperature and pre- cipitation data. All stations are in Southold except Bridgebampton and New London-Groton (fig. 1 ). GEOLOGY AND GROUND WATER~ SOUTHOLD, NEW YORK GG9 Mean annual temperature and precipitation at stations in and near the ~own of Southold I Distance I (miles and Bridgeharnpton, N.Y _ Cutchogue, N.Y_ _ Greenport, N.Y _ _ . New London-Groton, Conn_ Orient Point, N.Y_ _ Temperature Precipitation 12 SE 44. 85 5 SW 44. 93 4 NW_ __ 37. 80 26 NW_ 44. 36 10 NW. ~ [ 41. 47 The amount of catch in the 8-inch rain gages at Cutcho~m, Green- port, and Orient differs pereeptihly. This difference may be at- tributed to the local topography, the exposm'e aud location of the gage, and the spotty distribution of local storms. In order to obtaiu more accnrate data on precipitation in the mauy parts of Southold, additional 3-inch rain-gaging stations were e~tab]ished as follows: East Marion, Greenport Nm-th, Mattituck Inlet, Mattituek West, village of Orient, Peconic, Southold (pl. 3), aud P/mn Island (fig. 1). Data for 1958 aud 1959 from these statmns toget mr with those for the th~ee earlier long-term stations iu Southold add the two nearby long- term stations are compiled in table 1. ' HISTORY 0~7 DEVELOPMENT Southold was founded in tlhe early ]7th century. Colonists, p~ob- ably EnglisbmeD, settled at Yeuuicott (town of Southold) as early as 1638 (Wood, 1949). Southold was part of a large land graDt nmde by Charles I of Enghmd to Sir William Alexander, Earl f Snrhng. Fishers Island, bowever, was discovered iu 1614 by Adrian Block and grtm(ed in 1640 to Johu Winthrop, in whose family it remained until 1869. The first settlement in Southold was just west of G~eeDport. This was follox~ed by settlements at the village of Southo]d and then hy settlements at other locations; Gresnport was the last village to be founded. Some of the early settlers had come from Southwold, England, and ~l~e Indian name Yemficott, which had beeu apl)lied to the area, was soon changed to Southold. The early inhabitants cleared ]and and established crops, which were mostly ~'aiD, fodder, and pasture. In the early 19th century, shipping and whaling became important aspects of Southold's economy. The need for a fast combined railroad and steamer route from New York to Boston b~'ought about the extension of the Long Island Railroad to Greenport in 1848. Fishing and oyster fanning have always been TAB~m l.--Precipitation, in inches, during 1958 and 1959 at 11 stations in the town of Southold and at 2 nearby station~ IAI1 statioos except for Plum Island, Bridgehampton, and New LonOon-Groton ar~ shown on pL 3] 1958 Area C stations Area I) stations Nearby stations GEOLOGY AND GROUND WATER, $OUTHOLD, NEW YORK GGll important industries, but agriculturs has been the nlain snpport of the area's inhabitants. With the invention of the mechanical potato digger in 1888, potatoes became the most important crop and remain so today. Southold farms a/so produce cauliflower, brussels sprouts~ peas, beans, and other vegetables. In 1948, vegetables were planted in 13,61-I acres, and more than three-quarters of this acreage was used for the cultivation of potatoes (U.S. Depart~nent of Agriculture, 1948). The area under cultivation has renlained relatively constant since 1899 (Itoffman, 1961, p. 5). The following table shows the population trend in the lqllage of Greenport and the town of Southold: Population o! town of Southold and village of Greenport Village of Town of Year O~enport Southold~ 1920 ....................... 3,122 10,147 1930 ........ 1940 ........ ~~~ 3,062 11,669 3,259 12,046 1950 3,028 11, 484 1957_- .................... Jan. l~b; ................... 2, 646 12, 608 .................. 2,653 13,388 GEOLOGY No geologic formatious older than the Pleistocene crop out in Southold; however, older formatlons are present at depth. A gen- eralized stratigraphlc section of the formations in the Southo]d area, together wifl~ their water-bearing characteristics, is shown in table 9. The estlm~ted thickness and ]ithologlc descriptions are based largely on the log of well S189 (Leggette, 1938), drilled in 1935 at Orient Beach State Park, and on the general stratigrapbic studies of Long Island by Suter and others (1949). Logs of the following wells col- lected by Veatch (1906), which penetraie Cretaceous deposits and in places Precambrlan(?) bedrock, also were used to compile the strati- graphic section. S490 (892)~ .................................. Greenport S507 (909)x .................................. Long Beach S5~2 (914): ................................. GreatGull Island S517 (919)~ .................................. Fishers Island Generalized strati#raphic section in the town of Southold · I ] (Ieet/ (Qg) Precambrian (?) Crystalline rocks fresh ground water in Southohl. l,ower part probably contains salt water. GEOLOGY AzN~D GROUND WATER, SOUTI-~OLD, 1VEW YORK GG13 The bedrock basement in the Southo]d arsa is made up of crystalline rocks of probable Precambrian age. On Long Island the basement surface generally slopes to the southeast st about. 80 feet per mile as determined frmn many well logs. Semiconsolidated and tmcensoli- dated deposits of Cretaceous and Quaternary age rest on this surface. The materials coustltuting these deposits were probably eroded from the elevated parts of the bedrock surface north of Southold. The Lloyd sand member of the Raritan formation of Late Creta- ceous age was deposited directly on the Precambrian bedrock. It consists of beds of coarse quartz sand aud gravel, fine sandy clay, clayey sand, and some very thin laye~ of clay. In much of western and central Long Is]~nd, the Lloyd sand member is an excellent aquifer and in most places yields moderate to large supplies of fresh water to wells. In SouthoId at well S490 (No. 89'2 in Veatch, ] 906, p. 331-332), however~ only a small amount of fresh water was found in the Lloyd; and at well S189 (Leggette, 1938, p. 93 97) on Long Beach (Orient Beach State Park) salty water was found. The Lloyd grades upward into the clay member of the Raritan formation. The clay member contains some sandy layers, but it is predominantly gray day and silt:}, clay. Its permeability geuera]ly ]s very low; therefore, it com- monly acts as a confining bed or aquidnde and retards the movement of water between the Lloyd sand member and the overlying beds. An unconformity separates the Raritan formation from the over- lying post-Raritan beds of Late Cretaceous age. These beds consist of fine sand, silt, layers of clay, and scattered beds of coarse sand and gravel. Beds equivalent in age to the Mmgothy formation of New Jersey are preseuj in the post-Raritan depesits of Long Island, but their upper and lower boundaries are not distinct ]n the logs of wells that penetrate tbese deposits (Perhnutter and Crande]l, 1959). Al- though the post-Raritan beds coutain several excellent water-bearing zones that yield large snpp]les of fresh water to wells in most of Long Island, in SouthoId they probebly conta n mostly brackish or salty water. During Tertiary and possibly during early Quaternary time, the post-Raritan deposits were dissected bv streams and po~ib]y by ice into a hilly terraiu of moderate relief.~ Pleistocene glacial deposi(s, eonsistlng largely of saud and gravel but with local ]euses of clay~ were then laid down on this irregular snrface. Southold~s reservoir of fresh ground xvatcr is contained in the upper part of these permeable glacial deposits. Several geologists, including Veatch (1906). Fuller (1905 and 1914), Fleming (1935), MacCliatock and Richards (1936), Thomp- son and others (1937), and Suter and others (1949), have studied the GG14 CONTRIBUTIOXS TO T}IE HYDROLOGY 0r T~{E UNITED STATES comp]ex Pleistocene glacial history of Long Ishmd and vicinity and reeo~ize two or more major glacial advances. This report, however. is concerned with only the most recent, or Wisconsin glaciation of the Pleistocene Epoch. The following discussion is based, iu part., on their findings, and, in part, on tield observations. Much data have been obtained from logs of wells drilled in Sonthold and published in Veatch (1906), Leggette (1938). Ilobems and Brashears (lf)45). and Johnson (1952), as well as from unpublished well logs on file in the Mineola, 5L¥., office of the U.S. Geological Survey, and the Westbnry. N.Y., office of the New York State Water Resources Comndssion. The presen[ topographic features and surficlal deposits of Long Island are rdated largely to the advance of a part of the Huron- Ontario lobe of the great Lam'entide ice sheet during the Wisconsin glaciation (Flint, 1947). The ice in its southward movement accumu- lated rock debris from the brad over which it. passed and shoved addi- tional material ahead of it in the manner of a bulldozer. After pa~ing over most of the northern half of Long Island and the deposits of earlier ice advances, as well as the beds of sand and gravel laid down by its own melt water, the ice was checked by increased melting at its termim~s and by decreased nourishment in its region of accomu- lation. The accumulation of rock debris held in the ice was released by the melting and, together with the material previously pushed ahead, was partly reworked by the melt ~ aler ~o form a ridge of poorly strati- fied sand and gravel r~loeg the ice front. This ridge at the southern terminus of the ice sheet is known on Long Island as the Ronkonkoma tern-final moraine. Continned melting and htck of nonrishment in the region of ice accumulation caused the ice front to recede northward. The Harbor Hill end moraine, part of which is in ~ontho]d, was formed when the ice front readranced to the position shown by the end- moraine deposits on plate 1. The moraine cousists of large coalescing outwash fans of stratified saed and gravel and associa~edt~ll. Tbetill ranges in thickness from about 5 to ahnost 50 feet and is cbara('terized by many large bouhlers (fig. 2). Gaps m' depressions in the ridge formed by the Ilarbor Ilill end moraine are probably the sites of large blocks office that were wholly or partly buried and then melted after the retreat of the main ice front. These gaps provided passageways across the ridge for melt-war er flo~. which, in i)laces, Imrtly refilled the gaps with stratified sand and gravel. However. Ihe marked depres sions now occupied hv Mattituck ('reek. Ilasbamomuck Pond. and Dam Pond, which are ~ide-water inlets separating areas A, B, C, and D. and Plum Gat, which separates area D frnm Plmu Island, were never completely filled. Fuller (191& p. 40) considered Maltiluck Creek. which is now a tidal embaymenl leading to the northwest, to be a GEOLOGY AND GROUND WRATER, SOUTHOLD, NEW YORK GGi5 ket[le valley. Reference to plate :l shows that the creek's tributaries enter it at such an augle as to suggest that its flow was ouee south eastward. Recent deposition of sand [mrs and beaches, largely by longshore currents, bare closed paris of these gaps and thus tied together areas A, B, C, and I) and l,ittle and Great Itog Necks; ali exc~pt for area A, were once separate islands. At several points along the north shore of area l) discontinuous bodies of gray to grayish-brown clay are expend (pl. 1 ) at lhe shore- line. Because of the appearance aud stratigraphic position of this clay, it is teutatively assigned lo the Gardiners clay in this report. although no substantiating fossil evidence has been found. The clay ~curs in irregular~ highly contorted mas~s and was probably moved to its present position by ice-shove. Clay with shnilar characteristics is also found on the western shore (pi. 1} of Robius Island aud on the southeasten~ shore of Plmn Island. Well logs do not iudicate that the clay underlies Soutbo]d except ,t the few localities previously mentioued. Appareutly, it occurs only in isolated masses or dis- contiuuous lenses at ]east m~der the maiu parl of the Southo]d peniusula. Another clay, probably of late Pleistocene age, occurs iu several places along the south shore of peninsular Southold. No exposures have beeu found, but it lies m~der several feet of soil and, in some places, under stratified sand and gravel. This clay underlies most of the south shore, where well logs imlicate that it'rauges in thick- GG16 CONTRIBUTIONS TO THE [IYDROLOGY OF TIlE UNITED STATES l~ess from 5 t. (;0 feet. (~ee l,~s .f wells $4(;77 ,,~nd ~ [7g¢ 5~ table except in tbat part of ar~a (' we~t of Greenport. where it extends nearly to the nm'th shore. Tho clay was once quarried in this area for use in the produetiol~ of brick. On Robbh~ l~land, at l,~tile II.~- Xeck. and at the western end of Great Hog Xeck mm~erous bills flint eonsi<t .f stratified sand and gravel range in :tJlitude fi'om about 30 to T0 feet. The bigbin' bills :~re capped with till, which is generally about 5 feel thick. of the morMne along the north shot'e of the l~eninsubt, as shown by many large lag b(mlders on the botlom of Long Island Sound as far as a quarter of a mile offshore. Also. thin swamI) and marsh deposils have accumub~ted in kettle ponds and depressions, partieuhtr]y around drowned kettle valleys on the south shore (pl. 1). Wave action and tidal cnrrm~ts have constructed several bay-head beaebes and spits. especially along the south slm]'e of the peninsula, lVind-bhm-n beach sand has also accmmdated as dunes on top of the Harbor Hill end moraine in the central part of area B. The physical properties of the uPI>er Pleisio('e~e outwash and strat- ified drift are described in logs in table g. ~t~([ mechanical analyses of samples from ES ob~evvation wells are givet~ in table t. The~e samples are probably representative of the bulk of the upper Pleis tocene deposits underlying Somhold. The deposits consist mainly of angular to subangular quartz grains and rock particles and of sma]]er amounts of biotite, feldspar, ma~'netite, garnet, and hornb]eDde. Particle diameters are commm~lv greater than 0.95 mm (medimn sand) and most are about 0.5 mm ('coarse sand). Sand, rcry eoarsc; ow gr s 17 74 GEOLOGY AND GROUND WATER, SOUTHOLD! NEW YORK (feet) GGI,~ CONTRIBUTIONS TO THE I~YDROLOGY OF T~E L~fglTED STATES TABL~' 4 Physical chara eristics of ~pper Pleislocene water-bear ~ng deposits in ' the town of So~thold 67 72 27-32 87 92 34.5 31.2 Sections ,1 A' through E 5" (pl. '2) show the subsurface geologic relations and the inferred depth to salt water in ea(h of the areas of theSouthohlpeninsula. SectionA A' (pl.2) sbows unstratified drift (till) uot more thau 35 feet thick exposed iu the bluff at the northwest- ern cud of the sect]ou. The log of well S4081 shows about 8 feet of clay at sea level that may be a local body of ice shoved or reworked G~rdiners(?) clay. The logs of the rennduing wells indicate only outwash deposits. Sectiou B-l~' (pl. 2) is very much the same except for a smaller amount of till exposed iu the uorthwestern bluffs. Sec tion C-U' (pl. 2) indicates a till body about 40 feet thick exposed in dm bluff above Long Island Sound aud a ~d (ff clay of htie Pleistocene age about 18 feet thick in well S12151. Section 1) O' (pl. 2) shows till about 35 feet thick exposed in the b nfl, and sectmn ~ ~ (pl. shows about 20 feet of till iu the bluff, whielh according to the log of well S7171, thickens southeastward to almost 35 feet before thbm]ug out or gradiu~ iuto the outwash deposits. Each of these sections indicates that the anmunt of unstratified drift is negligible in com- parison to the great Ihickness of stratified and scm}stratified outwash deposits. Section F-F' (pl. 2) trends approximately alon~ the axis of the peninsula from west to eas~. ttere as in the other seefious~ consider- GEOLOGY AND GROUND x~YATER, SOUTtIOLD, NEW YORK GG19 able thickness of outwas]l deposits are iRdicated at most wells. area (~ the log's of wells 88(;08 and 811748 indicate the presence of abou~ (;0 feet of clay of late Pleistocene age; and in area D the log of well S7171, also shown in section A'-]~" (pl. 2), indicates the pres once of till. GROUND ;VATER HYDROLOGY The following discussion of groined-water hydrology refers only to the Soutbold peninsula (areas A, B, C, and D, Little Itog Neck, and Great Hog Neck). Available ground water data for Robins Island are very meager, but a small body of fresh ground water occurs on the ishmd. Only one family resides on the island at present (1960). (-~round-water conditions on Plmn Ishmd have been described in some detail by Crandell (19{;2). The (}till Islands are nninhabited. Pouded fresh water is the principal soarce for public and domestic supplies on Fishers lshmd, which was not included in this investigation. Precipitation, which averages about 45 inches each year, provides the only natural sour, e of replenishment to the ground-water res- ervoir in $outhold. A part of this precipitation flows overland to tile surrounding bodies of salt water, a paL~ is returned to the atmos- phere by evapm-ation and by transpiration of plants, and a part seeps into the ground. Some of the seepage into the ground eventually reaches the ground-water re.servoir and becomes available for with- drawal by wells. Because of the low moisture-retention capacity of the prevailing silty-loam ~il, the excellent subsoil drainage, thc flatness of most of the terrain, and the ahsence of visible runoff during most storms, Hoffman (1961~ p. 17) suggest that possibly as little as 10 percenf of the annual precipitation iu Soutbold enters the streams as direct runoff. Hoffman's estimate is accepted foL' use in this report. 3,fuch of the precipitation is returned ~o the atmosphere by evapo- ration and by the transpiration of plants, collectively termed "crape- transpiration." Using a ~nethod developed by Meyer (1944, p. 457), Itoffman (1961, p. 16) estitnated evaporation in Southold to be 12 inches for the year of least annual precipitation (1908), 17 inches for the year of greatest, annual precipitation (1948), and 14 inches for the year in which annual precipitation closely approached the long-term average (1949). tloffman's estimates were based on the long-term precipitation records of the Cutchogme gage. However, the U.S. Weather Bureau evaporation pan at the Greenport power house recorded about 23 inches of water evaporated in 1959, a year GG20 CONTRIBUTIONS TO THE HYDROLOGY OF THE L~NITED STATES in which precipitation closely approached the long term average. This ewtporation was measured from a free-water surface without plant growth and open to wind from all directions. The author sng- gests that evaporation may possibly range from Hoffman% low est]- mate of 19 inches to as much as ~0 inches and nmy average about 17 inches. This suggestion is in close agreemen~ with the observations of Spear (1912). Meyer (1944) suggests that the average annmfl rate of transpiration for agricultural crops in the North Central States is from 9 to 10 inches. The nature of the crop and natural vegetative cover in Southold would favor an avera,o'e rate of aboui 10 inches. Thus, the annual evapotranspiration rate for peninsular Southold probably ranges from 2.2 to 30 inches (about 16.000 to million gallons per year). Recharge to the ground-water reservoir iD Southold is the difference between the amount of precipitation and the sum of direct runoff and evapotransplration. This stun may range from abont 75 percent of the annual precipitation in very dry years to about 65 percent in ~ery wet years. Thus, '25 to 35 percent of the total annual precipi- tation would be available for recharging the ground-water reserv.oi[. Recharge in the Southold peninsnla during a year of average precqn ration (assuming 13.5 inches of recharge) would be about 9,400 million gallops. This recharge is summarized for the individual areas as follows: Area i~ million gallo~s A .................................................. 1,500 B ..................................... 5,300 C ............................................. 8~0 ~) ..................................... 1, 10~ IAttle Hog Neck ............................. lO0 Great Flog N'eck ........................ 500 Total ................. 9, 410 The effective recharge a~a of area C was first reduced by about square miles to allow for an area west of Greenport underlain near the surface by clay of late PleistoceDe age and Wisconsin till that would inhibit recharge. The remainder of area C was then rednced by 25 percent because of paving, storm and sanitary sewers, and bnild ings in GreeDport aud vicinity. All other areas were reduced by 10 percent to allow for local near-surface till and clay deposits, paviDg, and built-up areas. Most if not all the fresh ground water available for use in Southold is contained under water-table (unconfined) conditions iD upper PleistoceDe deposits. The fresh water occurs in a series, or chain, GEOLOGY AND GROUND V;rATER, SOUTHOLD, NEW YORK of irreg'ularly shaped lenses that are heralded hath laterally and at (lei)th hy ~la{'ial deposhs saturated with sally gte.nd wate~y (l)]. 2). Areas A, B, (, and D. Little IIo~ Neek. and Great tiaa' Neck are virtually separated from one another by salt-water marshes aud by iulets that also are uuderlah~ by salty grouud water. ('onseqaently, these areas are treated as individual "islands of ~'rouud water," as each has a discrete fresh-water lens. Because the specific gravity of the fresh water is less thau that of the underlying salt water, the fresh water tends to "float" on the salt water within the boundaries of the island ~enerally according- to the Ghyben-Herzberg priuciple. Fig'urc 3 shows the contact betweeR f~,sh water and salt water Well Land ~~~ Wrater table surface Fresh water pl. 8). schematically. Fresh water fills the deposits to the depth at which its head is halanced by the head of the salt water. At equilibrium, the depth of fresh water below sea level at any point on the island is proportional to the fresh-water head above sea level and dependent on the relatiou of the specific gravities of fresh and salt water. This GG'22 CONTi/IBUTIONS TO T[IE HYDI/OLOGY OF THE UNITED STATES relationship is summarized in the following' equation, which is often referred to as the Ghyhen Herzber~ principle: t where ~ depth of fresh water below sea level, ~ beight of fresh water abm'e sea level, and 9--specific gravity of salt water as compared to the assumed specific gravity of 1 e~ fresh water. The specific gravity of sea water x aries somewhat from place to place, bn~ the average of 1.0P5, if used in this equation, sbows lhat ~resh water would extend 40 feet helow sea level for each foot it extends above sea level. The zone of diffusion, or zone of mixed water between nornml fresh ground water and salty greuml water baring' ll~e dens~ty of sea water, is assumed to be of negli~'ible thickness in the general application of the Ghvbe~-Herzberg formula. Also, Hubbe~ (]940) has shown that the ~hyben Herzberg formula is theoretically correct only under conditions of bydrostatic equilibrium. Although neither of these assumptions are e~ntirely valid for the Southold area, a brief study in Greenport (tloffman, 1961, p. ~3) suggests that the 40:1 ratio may be approximately correct in some parts of the area. Therefore. owing to scantiness of data, the 40: 1 relationship is used in this report to define the approximate bottom of the fresh water lenses (pl. ~) under the Sonthold peDinsula. The upper surfaces of the fresh-water lenses in Southold are defined by the water table, whose configuration is shown in plate 8 by contour lines referred to mean sea level. The contours are based on water levd measurements made at the end of July 1~}59 iD 89 obserwtion wells. The upper surfaces of the fresh-water lenses are marked by a chain of ~-ound-water ramrods alined along the axis of the S¢mthold penin sula. These mounds are defined by closed contours on the water lable (pl. 3). Area B apparently contains only one large and eloDgated mound, whose crest is at an altitude of 7 to 8 feet, about a mile north of Cutchogue. Little ttog Neck and Great Hog Neck each centains a monnd with a crest altitmle of slightly more than ] and P feet, respectively. Area C contains three mounds represented hy closed P-foot contours. Also, a shallow cone of depression in the water table is indicated by the 1-foot contour around well S3078 in Green port. Prior to 1950 substantial withdrawals were made from wells in this vicinity, and the cone of depression was deeper. For example, the water table contour map of April 1050 (ttoffman. 1961. pl. 1) GEOLOGY AND GROUND ~VATER, SOUTYIOLD~ NEW YORK GG23 shows the cone of depression extending below an altitude of 0.5 foot. Since I950 the rate of pumping has decreased; consequently, by July ~959, the cone of depression had shrunk to a volume of less than one-third that of 1950. The movement of ground water in each of the areas of the Southold peninsula is radially outward from the crests of the ground-water mounds on the water table, he ~'ound-water dlv de passes through these crests and, in general, follows the northeast trend of the penin- sula. From the vicinity of this divide, ground water moves toward tl~e surrounding salt-water ~)dies along- flow lines whose Qirection is normal to the water-table contours. The local direction of move- ment in the horizontal plane is indicated hy arrows on the contour lines. Section B-B' (pl. 2) shows this movement in the vertical pbme also hy means of arrows indicaling the dh'ection of flow. The direction and rate of flow are largely flmctions of the permeability of the deposits throngh which the water moves and of the hydrauliC. gradient. The net natnral grom~d-warer discharge from the penin sula by lateral ontflow inte lite sea, which lakes 1)lace mostly at or below sea level, and by evapotranspiratlon in nmrshv tracts near the shore is unknown. Ifoffman (19{ 1, p 33) estimates ghat it may range from ~,500 to 6,000 million gallons ammally. No data were collected during this investigation to substantiate/here estimates Saturated upper Pleistocene dcposils, whose volume is estimated to total 126,500 million cubic feet, contain the fresh ground water in storage under Southohl. The estimates for the individual areas are given as follows: IAttle Hog Neck _ Great Hog Neck ................. 2, 9~) ................ 126, 500 The estimate for each area has })cell redllced by 10 ])el'cenf (25 per- cent for area C) to allow for il)e x'o]nme of till and clay, which con- rain {itt]e available water. Not all the water fil]m~ the {nferstices of even the coarse texim-ed deposits is avai{ab{% however. The vohnne of ~vailab]c water is rou~h{y equivalent to the specific yield of thc deposits. Ten determ ~ ttions of ~pecific > iehl made on s}~mi)les from wells in upper Pleistocene deposits on Plum Ishtnd ( ~andelL 1962) ( l'an~e from 18 to Q8 l)ercent and avel'a~e about 22 percent. Mechani- GG24 CONTRIBUTIONS TO T}IE HYDROLOGY OF THE UNITED STATES cai analy~s of samples of upper Pleistocene deposits froni wells on the Southold peninsula (table 4) show tha~ they have v rtn dlv the same physical character as those of Plnm island deposits. For this reason a specific yield of 22 percent was applied in esthnating the volmne of fresh ground water in storage in Southold. This volume in ,July 1959 was computed m be a out 20(~,50(I million gMlons. The volmne eontained in each area is as follows: Owing to lack of data, the zone of diffusion was considered to be of negligible thickness, and the est n ~tes should be therefore regarded as approximate. Seasonal wtriations in precipitation, pumpage for irrigation nsc, and elmnges in the rate of natural discharge are the main fa(ttors affecting fluctuations of the water table in the Southold peninsula. lVater levels have been measured periodically in some observalion wells in Sonthold for 10 years or more. The hydrographs of wells in fignre 4 illustrate the trend and fluctuations of the waler table Sonthold fl'em 1949 to 1959. Below normal precipitation and charge and COhere'rent ~ewy withdrawal for irrigatiou aecount for the low stages of the water table in late 1949, early 1950, and the summer and autamn of 1957. Heavv precipitation and recharge and light withdrawal for irrigation ,~esulted in exceptionally high stages of the ware{' table in the springs of 1953 and 1958. lVithdrawal from Sonlhold's fresh OToHnd-water reservob' in 1957 for public-supply, irrigation, and domestic use was esl imated to be 2~400 million gallons. Of the total withdraw:t] about T percent was used for public supply, 79 l)erce~t for irrigation~ aml 14 percel~t for domestic supply. Withdrawal foc publ SUpl)lV decreased somewha~ in 1958 and 1959~ but Ihe gross withdrawal for all lmrposes was nbout GEOLOGY AND GROUND %~ATER, SOUTI{OLD, NEW YORK GG25 Precipitation, in inches, at LCutchogue,N. y GG26 CONTRIBUTIONS TO THE IIYDROLOGY OF TIlE UNITED STATES Before 1957 there were two public-supply systems in the town of ? O Southold; the privately owned North Fork IR ater C . at the village of Soutbold and the mnnlcipally owned village of Greenport Water Supply. The village of Greenport~ however purchased the ~orth Fork Water Co. in 1957 and now operates both systems. In 1959 the Greenport system, which withdrew water frown two well fields h~ Greenport and one in East Marion, served 1,006 consmners. The North Fork system served 281 consumers from a well field in the village o~ Southold. Both systems supply water for domestic, eom- mercial~ and fire-protection needs. The Greenport system also sup- plied about 5.2 m~lfion gallons in 1957 and about 4.6 million gallons in 1958 for irrigation use. Although pumpage from the Greenport system increased somewhat from 1947 to 1959, the annual withdrawal from year to year has varied markedly, owing largely to seasonal de- mands for irrigation and lawn sprinkling, which are greater in dry than in west summers. Pumpage from the North Fork system im creased steadily from 1950 through 1959. Annual withdrawals from the two systems are shown in the ~ollowing table. The demand on Year 1947 .......................... 1948 ......................... 1949 ........................ 1950 1951 1952 1953 1954 ...................... 1955 1056 ...................... 1957 1958 ........................ 1959 Pumpage (million gallons) Village of North Fork Water Co. Oreenport Water Suppl] 113. 5 131.3 153. 6 114. 2 3. 3 114. 2 4. 1 123. 6 4. 1 148. 5 4. 6 161.4 4. 9 166. 1 5. 0 133. 5 / 17. 0 159. 6 20. 0 130. 0 90. 0 122.7 22. 8 both systems is greatest during the tourist season--June, July, August, and September. The sewer system of the village of Greenport dis- charges directly into Long Island Sound, but elsewhere in Southold the water pumped for public supply and from privately owned domes- tie wells returns to the ground through cesspools and septic tanks. Sprinkler irrigation of crops, particularly potatoes, accounted for a withdrawal of about 1,900 million gallons of ground water in 1957, or about 79 percent of the total ground-water withdrawal in the town of Southhold for that year. Hoffnmn (1961, p. 7) estimates that as much as 4,600 million' gallons may have been withdrawn in 1949, GEOLOGY AND GROUND WATER, SOUTHOLD, NEW YORK GG27 a year of below-normal precipitation. Some farmers irrigate when the soil no longer cakes on being squeezed or supplement precipitation by an amount that will provide I inch of water each week during the growing eeason. Others adjust irrigation to the ]imitations of equip- ment and manpower. Correspondingly, the amount of water used .and the frequency of application varies wlde]y. 5Iost irrigatlon water is withdrawn from wells, 4 to 1'2 inches in diameter. However~ in areas with shallow water tabIes--nearshore in areas A, B~ and C, am] in most of area D--water is pumped from gangs of 4 to 10 shallow small-diameter wells or from artificially excavated ponds. -5{cst oscl]- lating springier heads in use in Southold distribute about 15 gpm (gal- lons per minute), although a few larger ones may distribute as much as 250 gpm. A substantial part of the water distributed by sprinkling systems is transpired by plants or is evaporated, and this represents a net loss from the grouud-water reservoir. Between 9,000 and 10,000 persons are not served by public-supply systems aud use privately owned domestic wells. ]Vithdrawa]s from these wells totaled about 3'25 million gallons in 1957. Ground-water withdrawal in Southold is mostly from driven and drl]led wells, which range from lx~ to 12 inches in diameter. The smaller diameter driven wells are used mainIy for domestic supply, whereas the larger diameter drl]]ed wells are used for irrigation and public supply. The fo]lowing table summarizes well-screen data for Area A ~ ..... Z: iiZiiiZZZiiZZZiZiZiZZZZiZZZZZZ ~l:~f~ii~-:~iii-ZZi'Z:iiZZ_'iZZ :-111'-: .... Great YIog Neck '-- - Approximate depth of bottom of Length ofI screen Median (feet) 3 243 wells. Most htrge-diameter irrigation and public-supply wells are equipped with deep-well turbb~e or snb~nersible pumps, whereas the smaller diameter domestic wells are equipped with jet pumps. Where the depth to water does not exceed suctiou lift, gasoline, diesel, or electrically operated centrifugal pumps are used. Dug wells no longer are constructed in Southold, but many old ones remain in use. Some artifically excavated ponds are used in area D to supply water for irrigation. These are usually constructed where the water table is less than 8 feet below the land surface. GG2$ CONTRIBL'TIONS TO THE I~IYDROLOGY OF TYIE I~ITED STATES In an ideal hydrologic system discharge equals recharge p]us or minus changes in ground-water storage. The system is unbahmced when natural discharge is augmented by artificial di~harge from wells. Balance is reestablished when recharge replaces the water artificially withdrawn from storage. Recharge to the ground-water reservoir in Southold during a year of average precipitation totals about 9,400 million gallons aud avdrages about. '26 mgd (million gallons per day). Ideally', pumpage could be allowed to approach this amount. For practical purposes, however, withdrawal must be kept well bdow Otis amount to minimize demand on storage and thus pre- vent sea-water encroachment. If recharge in 1959 (a year of average precipitation) was about 9,400 milliongallons and pmnpage was ap- proximately ~,400 nfl]lion gallons, then pumpage amounted to about '25 percent of the recharge on the Southold peninsula. On the basis of known geologic and hydrologic conditions, withdrawal generally should not exceed 30 percent of the anmml recharge. Larger with- drawals could be made probably in areas A and B, at least, inter- mittently, where points of withdrawal are widely spaced and the vol- ume of fresh ground-water storage is relatively large. In areas C aud D, however, where the total recharge and the vohmm of fresh- water storage are relatively small and present (1959) heavy with- drawals are concentrated at a few points, continuous pumping in excess of preseut rates may induce sea-water encroachment. SEA-WATEI~ ENCi~OACHM~NT The fresh ground-wa~er supply of the Southold peninsula is po- tentially subject, to sea-water encroachment because the fresh-water lenses that underlie the peninsula are bounded laterally and below by a zone of diffusion and an underlying body of salt water. The fresh water generally has a chloride concentration of less tban 40 ppm (parts per ~nillion). The chloride cmmentration of water in the zone of diffusion increases from abont 40 ppm on the fresh water side to about 18~000 ppm on Ihe salt water side. The thickness of the zone of diffusion varies widely, depending ou such factors as lithology, changes in fresh-wat,er head~ pm tern of movement of fresh water, and tidal fluctuations, which affect heads in the fresh aud salt water. No data on the thickness of the zone of diffusion in Soulhold were col- lected for this report. For the sake of si~nplicity of }malysis and representation~ the zone of diffusion was assumed to be of negligible thickness ou plate 2. The underlying hndy of sahy ground water probably has a eholnride coutent of 16,000 18,000 ppm, as in sea water. J~3ncroachment may occur where wells that are screened close to the boundary between fresh and salt water are pumped heavily and cause GEOLOGY AND GROUND WATER, SOUTttOLD, NEW YORK GG29 an upward or laudward migration of the sal~y water. Where the land surface is low and relatively unprotected, as along the sooth shore, sal't water from high tides or storm waves also may inundate the vi- cinity of wells and coDtaminate the fresh ground water by direct downward seepage. Figure 5 illustrates schematically the manner Well being pumped\ Lan Water level Sand and gravel contain-\ ~, ing fresh water (chloride\ u /Sand and gravel cam- content generallyl~.- r.~/ raining salt water than 4-0 ppm) .~ o ,~ ~,/ ( chloride content ~ ~ ~, ,~?/ 16,000-18,000 ppm) cone o~ salt-water intrusion ~.. ~b¢/ in which a cone of salt water may be drawn up toward a pumping well. Figure 6 shows bow it nmy migrate laterally and vertically loward a pumping well, where the cone of depression has exten(]ed to the shoreline. Available data iudicate that clay and other deposits of low perme- ability m~derlie some parts of the Soutbold peninsula. If these de- posits were extensive, they would provide some degree of protection against the migratioD of salt water toward pumpiag wells. Data from well logs~ bowever~ suggest that these deposits are probably local and diseontinous and, therefore, would have little if any effect in retarding sea-water encroachmeDt. Hoffinan and Spiegel (1958) recorded several instances of salt-water contamination of the fresh ground water of Soutbold. In area B (pl. $) and on Liltle Itog Xeck, four wells (S4091, Sf;059, S547b, add S5476) yielded water having cldoride concentrations ranging from 103 to 1,600 ppm helween 1950 and 1952. Each well was drilled withiD about 500 feet of the souil~ shore and probably penetrated the zone of diffusion or was contaminated by lateral migration of the zone of diffusion. GG30 CONTRIBUTIONS TO TYIE t~YDROLOGY OF TI-rE UNITED STATES Well being pumped /~ surface .Sea. / ,~,,,or tabte__J L~prior t.o .pumping__ ', I'~1 Salt water ~ ~ ~ , Fresh water In area C (pl. 3) several wells (S1678-S1678; S1668~ and S1669) ia the village of Gz~enport yielded water having chloride concen- twfions ranging from 76 to 4'24 ppm between 1949 and 1951. As GEOLOGY AND GROUND WATER, SOUTHOLD, I~rE~r YORK GG3,1 these wells are 0.5 mile from any shoreline, contamination probably took place by migration of the zone of diffusion. In area D (pl. 3) two wells (S7176 and S14597) yielded water hav- ing chloride concentrations ranging from ~96 to 1~000 ppm, and two irrigation ponds near the south shore had water ranging from 100 to 5,810 ppm of chloride. The determinations of chloride concen- trations were made between 1948 and 1952, which was a period when precipitation was generally less than normal, the water table was at below normM stage, and withdrawal of water for irrigation was above normal LaterM migration of the zone of diffusion probably caused the high chloride concentration. In recent years chloride determinations made on water from some of these wells and ponds indicate a substantial decrease in chloride con- centration. For example, in area C, wells S1673-S1678 had chloride coucentratlous averaging about 70 ppm in the summer of 1959 as compared with about 1~5 ppm in May 195~ (table 4). Also chloride concentrations in artificial ponds in area D ranged from 15 to 450 ppm in September 1957 but ranged ~rom 100 to 5~810 ppm in 1948-5~. CI-I~MICAL ~UAL?T¥ The natural chemical quality of most of the fresh ground water of Southold is good to excellent (table 5), except in a few places where sea-water contamination has caused some increase in chloride content (P. GG28-GG31). The fresh water generally meets U.S. Public Health Service limits, which were suggested for interstate carriers in 1946 as follows: (ppm) Iron (Fe) and manganese (/~n) combined ................ 0. 3 Magnesium (Ma) ..................................... 125 Chloride (Cl) ......................................... 250 Sulfate (SO~) ...................... Total solids (desirable) ....... }----22_~222~}2}~-~ 250 50O Total solids (permitted) ........................... 1, 000 Hardness of water from wells of the North ork ~ ater Co. and F from the village of Greenport system (table 4) ranges from 44 to 200 ppm. Although no official classification for hardness of water is available, Lamar (194~) cites the following classification as being generally acceptable: 1-60 ............................... Soft 61-120 ......................... Moderate y hard 121-200 ........................ Hard ~ 20I ........................... Hard to very hard T ^BLr: 5. Chemica anal~/ses, in parts per .lillion, of water,from public-supply wells in the villages of Greenport and Sol~thold manga Calcium na e Sul[~te Oh~o~i ~ (F) GEOLOGY AND GROUND WATER, SOUTHOLD~ NEW YORK GG33 Thus, most of the water sampled can be classed :is moderately hard or hard. The iron conteut of the water is less than 0.3 ppm for all samples, except two ihat contaiu 0.5 ppm and 1.5 ppm. The pH of water sampled ranges from 5.5 to 7.5, but most of the water is aeldic (plI less than 7.0). The chloride content of water from public-supply wells, which were uncontaminated or moderately tout aIninated by sea water, ranged from S6 to 270 ppm. In other wells used for domestic, irrigation, or fire-protection purposes--the chloride content of tbe water ranged as follows: CT~loride concentration of water in private wells screened in upper Pleistocene deposits, %uthold, N.Y., 19,58 1959 CONCLUSIONS Wader-bearing deposits of Late Cretaceous and late Pleistocene age nnder]ie the Southold peninsula. The known £resh ground-water snpply, however, is contained only in the upper Pleistocene deposits under water-table eouditions. The peniDsu]a is naturally divided into six islandlike areas, each having a fresh ground-wrtter lens that is in dynamic balance laterally and at depth with salty ground water in probable accordance with ~l~e Gbyben Herzberg principle. The deposits eoutaining fresh ground-water have relatively uniform hy- draulic characteristics and are moderately to highly permeable. De- posits of Iow perlneability occur only l~cal]y. Fresh water can be drawu from wells or ponds ahnost everywhere ou the peninsula pro- vided that (l) they are not too close to }he shoreline, (~)) the screens of wells are not set too deeply below the water table, or (3) heavy withdrawals are not concentrated in small areas. Sea-water en- croachmeut is likely where these conditions are not fulfilled. Fresh gronnd water iu storag'c probably exceeds 207,000 million gallons, and average recharge is suffi(ient to balance losses due to wilhdrawals from wells and to natural discharge to the sea. IIoffman and Spiegel (1958) reported some salt-water contanfina tion of wells and ponds during the period 1948-52, when precipitation was below normal and withdrawals for irrigation and public supply GG34 CONTmBU~O~'~S TO TYIE I~IYDROLOG¥ OF T}IE I~ITED STATES were high. The current (1960) degree of contain]nation ]s uot critical. With the exception of locally lfigh concentrations of iron and manganese, tbe chemical quality o~ the fresh ground water ]s good and is satisfactory for most uses. A water-level and chloride-monitoring program, which would be intensified during periods of below-normal prec]Ifitatlon and increased withdrawal~ should be mMnta~ned on a continuing basis h, Southo]d. Definite evidence o~ sea-water encroachment or overdevelopment of the grouud-water reservoir can be established only by the accumula- tlon o~ such data over a considerable period of time. Chemical analyses of water ~rom representative wells should be made at periodic intervals to determine changes {n iron content, hard- ness~ and otber constituents important to consumers. Also, water samples fi'mn wells in relatively densely populated areas should ~ analyzed periodically for syuthetic-detergent content. The contact between ~resh and salt water shown on plate 2 is ~heo- retica] and assumes a sharp boundary that does not exist in nature. For simplicity o~ ana]ysis~ the zone o~ diffusion is assmned to be of negligible thickness. In each o~ the hydrologic areas of Southold, the depth and thickness o~ the zone o~ diffusiou and movement of the sMty water need to be determined with nmch more precls~on than available data allow. The construction of "outpost" wells in the central part of each area and at selected poh~ts on the periphery would give the required data. The wells should terminate in or near the top of the zone of diffus]ou between ~resh water and salt water. Periodic deternfinat]ons o~ the chloride concentration of the water from the wells and measurement of water levels would indicate whether salty water is moving upward or inland. "Outpost" wells drilled to a depth of 250-300 {eet below the land surface in the central pat~ of areas A and B and 100~00 ~eet below the land surface in the central part of areas C and D would provide lhe required information. In general, new production wells probably should not be located within 1~000 feet o~ salty surface wa~er or wit]fin 300 feet o~ each other. The~ spacings may be adjusted somewhat for shallow snmll- diameter wel]s that are pumped by suction li~t and that bare a low rato of withdrawal, but large-d~ameter wells used for large with- drawM would require greater spaciug. The hazard of salt-water con- tamination can be markedly reduced by appropriate well spacing and construction. Greater use of field tensiometers to measure soil mois- ture should prove helpful in conserving water pumped for irrigatiou. The amouut of available ground water in Southold is comparatively small, and all reasouable measures should be taken to conserve the GEOLOGY AND GROUND WATER, SOUTHOLD, NEW YORK GG35 supply and to control withdrawal, especially (luring periods of below- p~orma] precipitation. A small increase in withdrawal over the amotmt withdrawn in 1957 59 probably is permissible in areas A and B, provided that withdrawal is not concentrated locally or centered [oo closely to salt-water bodies. Ilydrologic data indicate that the available ground-water supply in areas C and D (pl. 3) has ahnost reached full deve]opmeut; eonsequently~ sustained withdrawal sub stantially exceeding that prevailing in 1957-59 would probably induce sea-water encroachment in these areas. REFERENCES CITED CrandalI, H. C., 1962, Geology and ground-water resources of Plmn Island, Suffolk Co ntv N.Y.: U.S. Geol. Survey Water-Supply Paper 1539-X, 35 p. v. 30, p. 216-238. Flint, R. F., 1947, Glacial geology and the Pleistocene epoch: New York, John Wiley & Sons, 589 p. Fuller, M. L., 1,005. Geology of Fishers Island. New York: Geol. Soc. America Bull., v. 16. no. 6. p. 367~q90. ---, 1914, The geology of Long Island, New York: l!.S. Geoh Survey Prof. Paper 82, 231 p. · tfoffman, J. F. 196I. Hydro ogv cfi lbo shallow ground water reservoir of the GG36 CO~'TRIBUTIONS TO T;rtE YIYDROLOGY OF TIlE UNITED STATES Contributions to the Hydrology of thc United States, 1961 GEOLOGICAL SURVEY WATER-SUPPLy This water-supply paper was printed as separate chapters ~I-GG PAPER 1619 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director CONTENTS (A) Hydrogeology of a spring in a glacial terranc near Ashland. Ohio, by Stanley E. Norris. (B) Ground-water geology and hydrology of Bunker Hill Air Force Basc and vicinity, Peru, Indiana, by F. A. YVatkins and J. S. Rosenshein (C) Subsidence in the Santa Clara Valley California--A progress report. by J. F. Poland and J. H. Green.~ (D) Ground-water resources of thc coastal sand-dune area north of Coos Bay, Oregon, by S. G. Brown and R. C. Newcon~b. (E) Ground-water resources of thc Alma area, Michigan, by t(enneth E. Vanlier. (F) Geology and ground-water features of Point Argucllo Naval Missile F~cility, Santa Barbara County, California, by R. E. Evenson and G. A. Miller. (G) Causes of depletion of the Pecos River in New Mexico, by H. E. Thomas. (H) Reconnaissance of headwater springs in the Gila River drainage basin, Arizona, by d. H. Feth and J. D. Hem. (I) Pumping tests in the Los Alamos Canyon well field near Los Alamos, New Mexico, by C. V. Theis and C. S. Conover. (J) Ground-;vater geology of Edwards County, Texas, by A. T. Long. (K) Hydrogeology of Middle Canyon, Oquirrh Mountains, Tooele County, Utah, by d. S. Gates. (L) Ground water in the alluvium of Kings River Valley, Humboldt County, Nevada, by C. P. Zones. (M) Ground-water resources of Cow Valley, Malheur Countv, Oregon~ by S. G. Brown and R. C. Newcomb. (N) Geology and occurrence of ground water in Lyon County, Minne- sota, by Harry G. Rodis. (0) Problems of utilizing ground water in the west-side business distric~ of Portland, Oregon, by S. G. Brown. (P) Ground water in the Prineville area, Crook County, Oregon, bv J. W. Robinson and Don Price. (Q) Reconnaissance study of the chemical quality of surface watcrs thc Sacramento River basbh California~ by Robert Brennan. (R) Flow of springs and small streams in the Tccolotc Tunnel arca of Santa Barbara County, California, by S. E. Rantz. (S) Geology and ground-water appraisal of the Naval Air Missile Test Center area, Point Mugu, California, by R. W. Page. (T) Beach-area water supplies between Ocean City, Maryland, and Rehoboth Beach, Delaware, by Turbit H. Slaughter. (U) Methods of mcasuring soil moisture in thc field, by A. I. Johnsom CONTENTS tV) Alluvial aquifer in northcast~!rn Louisiana A large source of water, by A. N. Turcan, ,Ir., and R. R Me?r. (W) Chemical quality of surface waters ill Pennsylvania, hy C. N. Durfor and P. W. Anderson. tX) Geology and ground-water resources of Rock County, Wisconsin, by E. F. LeRoux. (5') Geology and hydrology of Valle Grande anti Valle Toledo, Sandoval County, New Mexico, by C. V. Theis, C. S. Conover, and R. L. Griggs. (Z) Water-resources reconnaissance in southeastern part of ltoney Lake Va ley, Lasse Connt~, California, by George S. Hilton. (AA) Ground-wat(r conditions in the Fernley-Wadsworth area, Churchill, Lyon, Storey, and Washoe Counties, Nevada, hy W. C. ~4inclair and O. J. Loeltz. (BB) (iround-watcr exploration and test pumping in the Halma-Lakc Bronson area, Kittson County, Mimmsota, by G. R. Schiner. (CC) Ground-water in the P, aft River basin, Idaho, with special reference to irrigation use, 1956 1960, hy M. J. Mundorff and H. G. Sisco. (DI)) Analysis and evahmtion of availat)le hydrologic data for San Simon basin, Cochise and Graham Counties, Arizona, by Natalie D. White. tEE) Sedimentation of Lake Pillsbury, Lake County, California, hy G. Porterfield and C. A. I)unnam. (FF) Geology and ground-water resources of Barrow County, Georgia, by M. G. Croft. (GG) Geology and ground~water resources of thc town of Southold, Suffolk County, N.'i'., by H. C. Crandell. UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY A / 0 N G Duck Pond Qhm Qhm L N D ,Qsh HE TE SL AND SOUND F' Osh G HAr~ 0 U N D E T Qsl WATER-SUPPLy ~APER PLAT£ 1 1619-GG LONG BEA C BAY Qsh Qhm Qsh Qsh G R E A T P E C O N / C EXPLANATION Qsh Y Qo LITTLE PECONIC BAY ARDINERS BAY boulde~ gravel deposited by Oo Outwash Gardlners(?) clay Marsh deposits Harbor Hill end moraine deposits ROSINS ISLAND Qsh Base from U,S Ge0loglcal Survey topograph}c maps A A' SURFICIAL GEOLOGIC MAP OF THE TOWN OF SOUTHOLD, LONG ISLAND, NEW YORK I 2 3 Geology largely adapted from M · Fuller (1914) -50 EXPLANATION SECTION A-A' FROM LONG ISLAND SOUND TO GREAT PECONIC BAY (AREA A) SECTION B-B' FROM LONG It;LAND SOUND TO LITTLE PECONIC BAY (AREA B) 75 50 -25 Chloride 20 ppm SECTION C-C' FROM LONG ISLAND SOUND TO SHELTER ISLAND SOUND (AREA B) 25 25 -25 depth ~ -85 x / M ' I ..,,-.X SECTION D-D' FROM LONG ISLAND SOUND TO FIREENPORT HARBOR (AREA C) 25 5O -5O -300 -350 --400 AREA A I I I / / / ?/ / SECTION F-F* FROM HERRICKS LANE TO PLUM GUT C-EOHYDROLOG[C SECTIONS IN TI-II~, 'I'OW~ OF 5;O[TT~IOLD, SUFFOLI~ COUNTY, ~EW 5O UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY WATER-SUPPLY PAPER PLATE [ 5 REA 8 AREA C ~REA A- 1676E E OSt 1619-GG 016 756 8,52 5.27 H E L 'T E /? HA~ ISLAND SOUND L BEACH BAY O ri G R E A T EXPLANATION Ob~rvation well E C 0 N / C B A Y /LITTLE HOG 6 LITTLE PEGONIC BAY ARDINERS BAY Well for which hydrograph is given in figure ~5475 Well which yielded water of high chlorldeconeentration Well for which log is given in table 3, or log is shown graphically on geohydrologie + Preelpitation station [3 Approximate center of populated MAP OF THE TOWN OF SOUTHOLD, LONG ISLAND, NEW YORK, SHOWING LOCATION OF WELLS .~ ,/AND POSITIONal - - ~- = ~' ,,~OF o THE WATERi, TABI,E21 IN~i MiLEsJULY~ 1959 / A A' Line of geohydrologie section See report for description of hydrologic areas A-D tY by H C Crandell, 1959