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HomeMy WebLinkAboutGround Water Supply Analysis 1983E~H-l~orth~-~zst REC£i¥2D JUL 6 1983 JUly ? ANALYSIS OF AVAILABLE GROUND WATER SUPPLY TOWN OF SOUTHOLD Prepared for Town of Southold Planning Board May 1983 Prepared by ERM-Northeast 88 Sunnyside Blvd. Plainview, New York 11803 Korth t INTRODUCTION The Southold Town Planning Board is currently updating its Master Plan. ERM-Northeast was retained by the Planning Board to estimate the quantity of ground water available throughout the Town. The availability of ground water in the central portion of the Southold peninsula (water budget areas) was estimated during the preparation of the North Fork Water Supply Plan (ERM-Northeast, April 1983). The focus of this investiga- tion is, therefore, to estimate the available ground water yield in coastal areas of the Town. BACKGROUND Five ground water supply zones were delineated in the North Fork Water Supply Plan (NFWSP). Three of these zones (3, 4 and 5) are wholly within Southold Town. Zone 3 extends from the Mattituck Inlet to Hashamomuck Pond; Zone 4 extends from Hasha- momuck Pond to Dam Pond; Zone 5 starts at Dam Pond and ends at Orient Point. These three zones function as independent aqui- fers. Zone 2 is partially within Southold; it extends from Doctor's Path in the Town of Riverhead to the Mattituck Inlet in Southold. Approximately 25 percent of Zone 2 is located within Southold Town. In each ground water supply zone, a water budget area was delineated. In these areas, sufficient ground water exists to 1 permit the development of public supply wells. In Zones 3, 4 and 5, the available ground water supply is rather limited. The water budget areas in these zones were defined by the two foot (above sea level) ground water contour. Areas within those zones have a minimum of 80 feet of fresh ground water(1). In Zone 2, the available supply is less limited and the water budget area was defined by the five-foot ground water contour. The budget area is, therefore, underlain by a minimum of 200 feet of fresh ground water. The permissive sustained yield(2) for the water budget area in each zone was estimated in the NFWSP using unit yield factors (million gallons per day per square mile of area).obtained from the Suffolk County Comprehensive Water Supply Plan (CPWS-24). These factors vary from zone to zone depending on the thickness of fresh water and aquifer parameters. It was estimated that a permissive sustained yield of 6.4 mgd can be derived from the water budget areas in Zones 2 (Southold portion) 3, 4 and 5. No estimates were made in the North Fork Water Supply Study of the available ground water yield outside of the water budget areas. ~l)The Ghyben-Herzberg principal states that the depth ~f fresh water below sea level is 40 times the height of fresh water above sea level. The validity of this principal on the North Fork, was confirmed in the North Fork Water Supply Plan. (2)The permissive sustained yield is the maximum rate at which water may be withdrawn from the aquifers perennially without bringing about the undesirable effects of saltwater intrusion. 2 EP,~;-North~st METHODOLOGY During this analysis, the quantity of water available out- side of the water budget areas was estimated as follows: a.) The area was divided into two sub-areas: (1) between the coastline and the one-foot ground water contour, and (2) between the one-foot contour and the water budget area. - --- b.) Unit yield factors were then determined for these areas by extrapolating the yield factors (for the water budget areas) contained in CPWS-24. c.) The unit yield factors were then applied to the areas delineated in Step (a) and total permissive sustained yields obtained. The location of mated based upon: one-foot ground water contours was esti- o the Suffolk County Department of Health Services ground water monitoring network o the United States Geological Survey's ground water monitoring network (SCDHS) o data on home wells obtained from the files of the SCDHS o the topography of the area o the geological cross-section prepared in the North Fork O Water Supply Study proximity with respect tidal bays, inlets and to saline water bodies (including streams). 3 E P, t-1 - Table 1 SUMMARY OF AVAILABLE WATER SUPPLY (Ail Figures Rounded) PERMISSIVE UNIT YIELD SUSTAINED AREA FACTOR YIELD ZONE LOCATION (sq. miles) (mgd/sq. mile) (mgd) 2 Water Budget Area 0.60 0.4 0.2 (Southold Portion) Between 1' & 5' _ Contour 5,0 0.35 1.8 Between Coastline and 1' Contour 1.0 0.15 0.2 Total .... 2.2 3 Water Budget Area 14 0.35 4.9 Between 1' & 2' Contour 6.2 0.20 1.2 Between Coastline and 1' Contour 4.9 0.15 1.1 Total .... 7.2 4 Water Budget Area 3.4 0.25 0.9 Between 1' & 2' Contour 1.5 0.20 0.3 Between Coastline and 1' Contour 2.1 0.15 0.3 Total .... 1.5 5 Water Budget Area 1.6 0.25 0.4 Between 1' & 2' Contour 2.2 0.20 0.4 Between Coastline and 1' Contour 1.2 0.15 0.2 Total .... 1.0 EP.H- i o,-th st Creek. Along end of Orient, inland. To further It was found that the one-foot ground water contour was in close proximity to the coastline along the north shore (except the eastern end of Orient) and the banks of Mattitock the south shore and the north shore of the east the one-foot ground water contour was further assist in the development of the Master Plan, the yields in Zones 3 and 4 were subdivided into a number of discrete geographic sub-areas. Zone 3 was subdivided into eight sub-areas including Nassau Point, Bayview and New Suffolk. These areas are underlain by aquifer systems which function in- dependently from each other and the main aquifer beneath Zone 3. The remaining area in Zone 3 was divided (east/west) based upon major physical features (water bodies) in the zone. The Long Island Railroad tracks were used as the dividing line between the north and south shore boundary between sub-areas. Table 2 provides the permissive yields for these areas. Zone 4 was subdivided into two sub-areas utilizing the east boundary of the Greenport Water District as the line of demarcation. This line was used to delineate the sub-areas because new development within the Greenport Service District should utilize public supply from the Village of Greenport (consistent with the capacity of the Greenport system). The 5 CPWS-24 provides unit yield factors for water budget areas throughout the County including the North Fork. CPWS-24, how- ever, does not provide these factors for locations outside of the water budget areas. To obtain these, the factors provided in CPWS-24 were extrapolated dox~ward. The unit yield factor for areas between the coastline and the one-foot contour was estimated to be 150,000 gallons per day per square mile; a yield of 200,000 gallons per day per square mile was estimated for the area between the one and two foot contours. A yield of 350,000 was estimated for the area in Zone 2 between the one and five foot ground water contours. For comparison, the unit factors in the water budget area in Zone 5 (Orient Point)~ is 250,000 gallons per day per square mile. RESULTS The results of this analysi's indicate that the total per- missive sustained yield in Southold Town is 11.9 mgd. Of this total, 6.4 mgd (54 percent) can be obtained from within the water budget areas, and 5.5 mgd (46 percent) between the coast- line and the budget areas. Table 1 provides a summary of the results organize~ by water supply zone. As indicated in Table 1, 60% of the total yield can be obtained from Zone 3, with lower percentages from Zones 2, 4 and 5 (listed in order of decreasing available yield). Table 2 AVAILABLE WATER SUPPLY ZONE 3 PE~,~ISSIVE TOTAL UNIT SUSTAINED AREA YIELD YIELD SUB-AREA _ (Sq. Miles) (mgJ/Sq~ Hile) (mgd) North Shore - West of Goldsmith Inlet Water Budget Area 5.4 0.35 1.9 Between 1' and 2' Contour 1.3 0.20 0,26 Between Coastline and 1' Contour 0.6 0.15 0.09 Total Area 7.3 -- 2.25 North Shore Between Goldsmith Inlet and Hashamomack Pond Water Budget Area 2.4 0.35 0.84 Between 1' and 2' Contour 1.3 0.2 0.26 Between Coastline and 1' Contour 0.9 0.15 0.14 Total Area 4.6 -- 1.24 South Shore - Between Matt. Creek and East Creek (Contiguous Areas Water Budget Area 3.2 0.35 1.1 Between 1' and 2' Contour 0.65 0.20 0.13 Between Coastline and 1' Contour 2.15 0.15 0.32 Total Area 6.0 -- 1.55 7 ERH- [~orth~-~st Table 2 (cont'd) AVAILABLE WATER SUPPLY ZONE 3 PE~,IISSIVE TOTAL UNIT SUSTAINED AREA YIELD YIELD SUB-AREA (Sq ~__Miles) __(m~d/Sq. Hile) (mgd) South Shore - Between East Creek and Jockey Creek Water Budget Area 2.2 0.35 0.77 Between 1' and 2' Contour 1.5 0.20 0.30 Between Coastline and 1' Contour 1.8 0.15 0.27 Total Area 5.5 -- 1.34 South Shore - Between Jockey Creek and Hasha- momack Pond Water Budget Area 0.4 0.35 0.14 Between 1' and 2' Contour 0.3 0.20 0.06 Between Coastline and 1' Contour 0.4 0.15 0.06 Total Area 1.3 -- 0.26 New Suffolk Water Budget Area 0.0 N/A 0.0 Between 1' and 2' Contour 0.18 0.20 0.04 Between Coastline and 1' Contour 0.19 0.15 0.03 Total Area 0.37 -- 0.07 8 E~F~- North~-~st Table 2 (cont'd) AVAILABLE WATER SUPPLY ZONE 3 PErmISSIVE TOTAL UNIT SUSTAINED AREA YIELD YIELD SUB-AREA __ (Sq. Miles) _(mgd/Sq. Mile) (mgd) Nassau Point Water Budget Area 0.0 N/A 0.0 Between 1' and 2' Contour 0.38 0.20 0.08 Between Coastline and 1' Contour 0.37 0.15 0.06 Total Area 0.75 -- 0.14' Bayview Water Budget Area 0.40 0.35 0.14 Between 1' and 2' Contour 0.40 0.20 0.08 Between Coastline and 1' Contour 1.0 0.15 0.15 Total Area 2.3 -- 0.37 9 area east (0.39 mgd) Site of the Greenport service area has only 25 percent of the total yield of Zone 4 (see Table 3). specific investigations and field measurements are required to accurately determine the availability of the area. The yields obtained in this analyses however, are judged to be conservative estimates suitable for general planning put- poses. 10 ERFi-i~:~rth~st Table 3 AVAILABLE WATER SUPPLY ZONE 4 PErmISSIVE TOTAL UNIT SUSTAINED AREA YIELD YIELD SUB-AREA (Sq_. Mi]es) (mgd/~. Mi]e) (mgd) West of Greenport Water ~rvice Area Water Budget Area 2.6 0.25 0.65 Between 1' and 2' Contour 1.3 0.20 0.26 Between Coastline and 1' Contour 1.1 0.15 0.17 Total Area 5.0 -- 1.08 East of Greenport Water Service Area Water Budget Area 0.8 0.25 0.2 Between 1' and 2' Contour 0.2 0.20 0.04 Between Coastline and 1' Contour 1.0 0.15 0.15 Total Area 2.0 -- 0.39 11