HomeMy WebLinkAboutAppendix L - Groundwater Modeling Report.pdf STRONG'S YACHT CENTER
GROUNDWATER ANALYSIS
GROUNDWATER MODELING REPORT
Submitted to:
Town of Southold Planning Board,As Lead Agency
Prepared For:
Strong's Yacht Center
5780 West Mill Road
Mattituck, New York 11952
Prepared By:
P.W.Grosser Consulting,Inc.
630 Johnson Avenue,Suite 7
do Bohemia,New York 11716
Phone:631-589-6353
Fax:631-589-8705
PWGC Project Number:STR2001
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GROUNDWATER ANALYSIS
GROUNDWATER MODELING REPORT
STRONG'S YACHT CENTER, &1ATT|TUCK, NY
TABLE OF CONTENTS PAGE
1.8 INTRODUCTION............................................................................................................1
1.1 Background ..............................................................................................................1
1'2 Objectives.................................................................................................................2
2.0 MODEL CONSTRUCTION ...............................................................................................G
2.1 Model Extents/Limits................................................................................................5
2.2 Background Map.......................................................................................................7
2.3 Layers----'-.-------'-.-----------.---------.---.-------.---.-------7
2.3.1 Layer Geometry....................................................................................................... 8
2/4 Boundary Conditions ................................................................................................Q
2.5 Aquifer Parameters...................................................................................................B
2.6 Preliminary Model Runs..........................................................................................1O
3.0 MODEL CALIBRATION.................................................................................................11
3.1 Calibration Target...................................................................................................11
3.2 Automated Sensitivity Analysis...............................................................................12
4.0 MODEL SIMULATIONS................................................................................................16
4.1 Local Domestic Supply Well Identification...............................................................15
4.2 On Site Groundwater Analysis................................................................................2O
4~3 Aquifer Evaluation..................................................................................................21
4.4 Groundwater Travel Determination........................................................................22
4L5 Depth and Elevation Estimation..............................................................................23
4.6 Proposed Excavation Evaluation—Saltwater Intrusion into the Aquifer..................25
4.7 Proposed Excavation Evaluation—Upcmning...........................................................25
4.8 Potable Freshwater Elevation Estimate...................................................................27
4.9 Sea Level Rise....,..,.............,..,............,..,.............,..,............,..,.2Q
5.0 CONCLUSION..............................................................................................................2g
8.0 REFERENCES...............................................................................................................32
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TABLES
Table 1 Initial Boundary Conditions
Table 2 Groundwater Model - Initial Input Parameter Values
Table 3 Groundwater Model -Calibrated Parameter Values
Table 4 Uncalibrated versus Calibrated Boundary Conditions
Table 5 Existing Conditions Saltwater Interface Elevation and Freshwater Lens Thickness
Table 6 Ghyben-Herzberg Predicted Saltwater Interface Elevations and Freshwater Lens
Thicknesses
Table 7 Sea Level Rise Boundary Condition Adjustments
FIGURES
Figure 1 Site Location Map
Figure 2 Site Area Map
Figure 3 Strong's Yacht Center Groundwater Model—Model Extents
Figure 4 Strong's Yacht Center Groundwater Model—Cross Section View
Figure 5 Strong's Yacht Center Groundwater Model—Boundary Conditions
Figure 6 Strong's Yacht Center Groundwater Model—Calibrated Model
Figure 7 Strong's Yacht Center Groundwater Model—Grid Refinement
Figure 8 Strong's Yacht Center Groundwater Model—Cross Sectional View—Sub-Layering
Figure 9 Strong's Yacht Center Groundwater Model—Surrounding Domestic Well Locations
Figure 10 Strong's Yacht Center Groundwater Model—Surface Elevations—Unexcavated Site
Figure 11 Strong's Yacht Center Groundwater Model — Groundwater Conditions —
Unexcavated Site—Surface Elevations
Figure 11a Strong's Yacht Center Groundwater Model — Groundwater Conditions —
Unexcavated Site
Figure 12 Strong's Yacht Center Groundwater Model—Surface Elevations—Excavated Site
Figure 13 Strong's Yacht Center Groundwater Model — Groundwater Conditions - Excavated
Site—Surface Elevations
Figure 13a Strong's Yacht Center Groundwater Model — Groundwater Conditions — Excavated
Site
Figure 14 Strong's Yacht Center Groundwater Model—Surface Elevations— Unexcavated Site
with Particle Tracks
Figure 14a Strong's Yacht Center Groundwater Model—Unexcavated Site with Particle Tracks
Figure 15 Strong's Yacht Center Groundwater Model—Surface Elevations—Excavated Site with
Particle Tracks
Figure 15a Strong's Yacht Center Groundwater Model—Excavated Site with Particle Tracks
Figure 16 Strong's Yacht Center Groundwater Model — Excavated Site with Particle Tracks
Tracked Forward
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Figure 16a Strong's Yacht Center Groundwater Model — Unexcavated Site with Particle Tracks
Tracked Forward
Figure 17 Strong's Yacht Center Groundwater Model — Unexcavated Site with Particle Tracks
Tracked Forward and Time Posting
Figure 17a Strong's Yacht Center Groundwater Model — Excavated Site with Particle Tracks
Tracked Forward and Time Posting
Figure 18 Strong's Yacht Center Groundwater Model — Cross Section View — Saltwater
Interface-Chloride Concentration in lb/ft3—Unexcavated Site
Figure 18a Strong's Yacht Center Groundwater Model — Unexcavated Site Chloride
Concentrations—Layer
Figure 18b Strong's Yacht Center Groundwater Model — Unexcavated Site Chloride
Concentrations—Layer
Figure 18c Strong's Yacht Center Groundwater Model — Unexcavated Site Chloride
Concentrations—Layer 3
Figure 18d Strong's Yacht Center Groundwater Model — Unexcavated Site Chloride
Concentrations—Layer 4
Figure 19 Strong's Yacht Center Groundwater Model — Cross Section View — Saltwater
Interface-Chloride Concentration in Ib/ft3—Excavated Site
Figure 19a Strong's Yacht Center Groundwater Model—Excavated Site Chloride Concentrations
—Layer 1
Figure 19b Strong's Yacht Center Groundwater Model—Excavated Site Chloride Concentrations
—Layer 2
Figure 19c Strong's Yacht Center Groundwater Model—Excavated Site Chloride Concentrations
—Layer 3
Figure 19d Strong's Yacht Center Groundwater Model—Excavated Site Chloride Concentrations
—Layer 4
Figure 20 Strong's Yacht Center Groundwater Model—Excavated Site—16" Sea Level Rise
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1.0 INTRODUCTION
Strong's Yacht Center(a.k.a.The"Yacht Center" ) is located on Mattituck Creek in Mattituck, New
York which is on the north fork of Long Island (see Figure 1 for the approximate site location and
Figure 2 for site area map). The Yacht Center is proposing to undergo renovations and site
improvements that includes the construction of two boat storage buildings. The boat storage
buildings will require significant excavation work that will approach 40 feet of cut in some areas
to achieve a similar elevation to the existing buildings and infrastructure at the Yacht Center. All
of the proposed excavation work for the boat storage buildings will take place above the water
table. However, due to the site's proximity to Mattituck Creek and the reliance of nearby
residences on private water supply wells, the potential effects that the excavation may have on
local water quality,quantity and possible saltwater intrusion is required for evaluation in the Draft
Environmental Impact Statement(DEIS). Accordingly, a detailed analysis has been undertaken to
evaluate what, if any, effects or impacts the proposed excavation and site improvements may
have on the local aquifer system. The analysis has been accomplished through the use of a three-
dimensional (3-D) sub-regional numerical groundwater model.
1.1 Background
The Yacht Center includes an existing marina,boat repair/maintenance,sales,and storage
facility that is situated on the west side of Mattituck Creek, within the hamlet of in
Mattituck, New York (see Figures 1 and 2). The Yacht Center is proposing to construct
two new boat storage facilities near its southern end and associated appurtenances
including an evergreen concrete retaining wall, upgrades to the sanitary disposal system,
and connection to the public water supply. The proposed construction will necessitate
the partial excavation of a hillside which will entail cuts at a maximum of 40 feet.
Groundwater conditions in the area indicate typical watertable elevations range between
1 to 2 feet above mean sea level(NAVD88)with a flow direction towards Mattituck Creek.
The site is situated amongst numerous residential properties that rely on the local aquifer
system for their water supply via on-site domestic water supply wells. The proposed
excavation, though deep, will not intersect the water table beneath the site, but due to
the close proximity of residential properties that utilize the local aquifer system for
drinking water purposes, concerns have been raised over the possible effects such an
excavation may have on local groundwater conditions and an evaluation and analysis has
been requested to be performed. The evaluation and analysis have been accomplished
through the use of 3-D numerical groundwater model that was specifically constructed
for the site and surrounding area.
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A groundwater model was employed rather than taking monthly water level observations
over the course of a year because it has several advantages. A carefully constructed and
calibrated model can reliably predict groundwater levels and aquifer responses under
numerous different conditions and scenarios. Multiple years of groundwater level data
were used to construct and calibrate the model (in this particular case some of the local
monitoring wells used to construct the model had monthly data going back as far as 1975)
as opposed to a single 12 month period. This allows for more long term averages to be
used and also provides for the identification of anomaly years such as when drier or
wetter conditions may prevail. Longer term groundwater trends (rising or falling water
levels and potential causes) can be observed as well when looking back over many years
as opposed to a single year.
The numerical model constructed for Strong's Yacht Center was created by utilizing the
Suffolk County North Fork groundwater model as a starting point and refining the regional
scale model down to a sub-regional one. The County accepted model was thus reviewed
and used to facilitate construction and calibration of the current groundwater model
which in turn greatly aided in the overall conceptualization, layout, development and
simulations that were performed.
The groundwater model developed for Strong's Yacht Center is able to predict
groundwater levels under a variety of conditions, predict groundwater travel times, flow
paths, estimate wellhead capture zones or zones of influence and can also be used to
model the saltwater interface and thickness of the freshwater lens under different
stresses such as changing recharge patterns or excavated site conditions(model potential
saltwater intrusion or upconing effects). Again, the model developed for Strong's Yacht
Center relied upon many years worth of USGS local groundwater level data for its
construction and as is explained later on in this report to a high degree of calibration. A
single year of monthly groundwater level observations would not provide anywhere near
the same ability of a properly prepared groundwater model to carry out the desired
analyses that have been requested.
1.2 Objectives
The objectives of the groundwater modeling effort were as follows:
1. Construct and calibrate an accurate three-dimensional, sub-regional, numerical
groundwater flow model that could reliably be used to simulate local aquifer
conditions in the Mattituck area,
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2. Identify nearby local domestic supply wells and determine if the proposed
excavation will adversely impact any wellhead zone of influence or the quantity
or quality of water in the aquifer system for residential water supply,
3. Provide an analysis of the groundwater on site and its contribution to the aquifer
serving the nearby wells under existing conditions and the potential adverse
effects, if any, to the aquifer system serving nearby wells following the
excavation,
4. Evaluate the nature of the aquifer that supplies the nearby wells and the
relationship of the subject property as a contributing source and that the
proposed excavation will not affect the quantity of water available to the nearby
wells,
S. Determine the direction of groundwater travel on site and travel times and
whether the proposed excavation would disrupt or interrupt groundwater travel
or timeframes to reach surface waters,
6. Estimate the depth of the freshwater lens and elevation of the saltwater
interface,
7. Evaluate whether the proposed excavation would alter the saltwater interface in
a way that may cause saltwater intrusion into the aquifer or nearby wellhead
zones of influence,
8. Evaluate whether the proposed excavation would cause upconing and saltwater
intrusion by reducing the amount of fresh water entering the aquifer used by the
nearby wells, and
9. Estimate at what elevations does potable freshwater begin and end (at the
expected saltwater interface) on site pre and post excavation.
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Figure 1—Site Location Map
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SHELTERISL.i\-i7
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(model location/extents represented by magenta square)
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2.0 MODEL CONSTRUCTION
A finite difference method (FDM) model was utilized to predict aquifer responses under steady
state and transient conditions that result from the proposed excavation to take place at the
existing Yacht Center site on Mattituck Creek in Mattituck, NY. The modeling platform was run
using the USGS program MODFLOW (MODFLOW 2005). The software package used to run the
model code was Groundwater Vistas Version 8.16 (GV8) Build 15 by Environmental Simulations,
Inc.
A three-dimensional, sub-regional, numerical groundwater flow model was constructed to
represent a portion of the North Fork of Long Island, centered around the Mattituck area. The
model extents encompass an area that ranges from the Long Island Sound on the north,the Great
Peconic Bay to the south,approximately Aldrich Lane to the west,and approximately Alvah's Lane
to the east (see Figure 3). The model was constructed using standard modeling methodology
which consisted of:
• Identify model areal extents based on critical features and boundary conditions
• Formulate mesh or grid, import background maps, etc.
• Establish layers and zones based on area hydrogeology
• Adjust model geometry to approximate known conditions
• Input model properties such as aquifer parameters, boundary conditions, recharge, etc.
• Conduct initial model test runs
• Input calibration targets such as groundwater heads at known locations (targets)
• Calibrate the model using sensitivity analyses and calibration methods
• Refine model grid/mesh in areas of interest, recalibrate model as necessary
• Input pumping and recharge wells
• Conduct groundwater flow scenarios using calibrated model
• Analyze and review modeling run results to predict aquifer responses to various pumping
schemes or aquifer conditions
2.1 Model Extents/Limits
The model was built using a 3-d framework by creating a grid or mesh of evenly spaced
nodes in both the directions of the horizontal plane(x and y). Mattituck Creek was chosen
to be roughly near the center of the mesh and the mesh was extended outward 9,000 ft
in the east and west direction and 9,500 ft in the north and south direction producing a
rectangular area that measures 18,000 ft by 19,000 ft (see Figure 3). These distances
were selected because they capture key features of the area such as major surface water
bodies and is believed to extend far enough away from the area of focus (the Yacht
Center) to reasonably establish sub-regional boundary conditions such as constant and
general head boundaries that would be far enough away from the focus area within the
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model boundaries to not drastically influence it. A 100 by 100 grid with nodes spaced 100
feet apart was selected and as mentioned above centered around Mattituck Creek.
2.2 Background
A scaled GIS background map was imported into the groundwater model software from
AutoCAD as a DXF file to visually depict the outline of the model study area (a portion of
the north fork of Long Island in Mattituck), prevalent water bodies in the model area, as
well as to represent where the site and the other important features such as major
roadways, streets and property boundaries are positioned (see Figure 3).
.3 Layers
The model was initially constructed with four (4) layers to represent the four major
hydrogeological units on Long Island,the Upper Glacial Aquifer,the Magothy Aquifer,the
Raritan Clay and the Lloyd Aquifer. The base of the model is the surface of the bedrock,
which for the purposes of the modeling exercise is assumed to be an impermeable surface
(no flow boundary).
The Upper Glacial layer was then revised into four separate layers that included,from top
to bottom,the Harbor Hill Outwash,the Ronkonkoma Drift,the Lower Clay and the Lower
Drift. These stratigraphic representations are consistent with the Suffolk County
groundwater model and work done by the United States Geological Survey (USGS) to
delineate the various North Fork hydrogeologic units. The Magothy Aquifer layer was
divided into two separate layers to represent the Middle and Basal Magothy units, again
consistent with the Suffolk County North Fork groundwater model. The top two layers of
the model were modeled as unconfined aquifers and every layer below the third layer
(the Lower Clay) was modeled as confined aquifers.
The Harbor Hill Outwash and Middle Magothy layers were subsequently further divided
in multiple sub-layers. The Harbor Hill Outwash layer or the upper most layer of the
model was sub-divided into four layers and the Middle Magothy was also sub-divided into
an additional four layers. These two layers of the model, the Harbor Hill Outwash layer
and the Middle Magothy layer,were sub-layered to provide greater definition in the area
of main focus of the model,i.e.,the shallow portion of the aquifer system where the Yacht
Center excavation is to take place, as well as where the residential supply wells are
screened. The Middle Magothy layer was sub-divided for better definition with regards
to saltwater interface modeling. In total, the groundwater model ended up with 14
separate layers.
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2.3.1 Layer Geometry
Once the layers were created, the model then basically resembled a cube shape.
The model geometry was then adjusted so that layers had shapes, sizes,
thicknesses and orientations that approximated actual known or inferred
hydrogeological conditions. Layer top and bottom elevations were sloped and
pitched to produce varying thicknesses and inclines or declines that reflected
more realistic aquifer conditions. All geometry adjustments were made using
available published USGS information. Figure 4 is a typical cross-sectional
depiction of the model layering.
2.4 Boundary Conditions
Boundary conditions were then assigned to the areas of the model to represent as close
as possible the natural conditions of the study area. Boundary conditions are typically
located at the edges of the model and are used to control heads and allow/compute the
flux of water into and out of the model. Boundary conditions were assigned in layer 1 of
model (the upper most layer of the model or the top layer of the Harbor Hill Outwash). A
total of four constant head boundaries were established and each represented a surface
water body. These included: the northern boundary as the Long Island Sound (inclusive
of Mattituck Creek); and the southern boundary as the Great Peconic Bay (inclusive of
several south shore creeks) and Marratooka and Laurel Lakes. Figure 5 presents the
boundary conditions as they relate the Yacht Center site. The eastern and western edges
of the model were left as simple groundwater flow boundaries with no conditions
assigned to them. The initially assigned boundary conditions are presented below in
Table 1.
Table 1—Initial Boundary Conditions
Long Island Sound Constant Head 0.00
Great Peconic Bay Constant Head 0.00
Laurel Lake Constant Head 6.00
Marratooka Lake Constant Head 5.00
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2.5 Aquifer Parameters
With the model framework roughed out,the next step was to input numerical values for
key parameters and establish a set of consistent units for the inputs that included:
• Horizontal hydraulic conductivity- Kx,y(ft/day)
• Vertical hydraulic conductivity- K,(ft/day)
• Specific storage—S,(1/ft)
• Specific yield—Sy(unitless)
• Porosity—n (unitless)
• Recharge—R (ft/day)
Every zone of all the layers of the model had each of the above parameters assigned to it
based on published USGS values or values used in the regional Suffolk County model,with
the exception of recharge. Recharge was only applied to layer one of the model where it
is introduced (the uppermost layer or top of the model). Table 2 below is a summary of
the model inputs based upon available published USGS values or values that were used
in the regional Suffolk County model for the study area.
Table 2-Groundwater Model - Initial Input Parameter Values
Harbor Hill
Outwash
300 30 0.000001 0.15 0.24 0.005
Ronkonkoma
400 40 0.000001 0.15 0.24 ---
Drift
Lower Clay 30 3 0.000001 0.15 0.24 ---
Lower Drift 250 25 0.000001 0.15 0.24 ---
Middle Magothy 50 5 0.000001 0.15 0.24 ---
Basal Magothy 100 10 0.000001 0.15 0.24 ---
Raritan Clay 0.3 0.001 0.000001 0.15 0.24 ---
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Lloyd 35 3.5 0.000001 0.15 0.24 ---
*Recharge was only applied to Layer 1 of the model.
2.6 Preli i t e! Runs
Initial test runs to generate graphical output were run once the model framework was
constructed, the aquifer parameters and model inputs were entered, and the boundary
conditions established. This was done to identify problems such as significantly incorrect
model geometry, input values, or boundary conditions. These initial uncalibrated model
runs often generate groundwater head contours that are far from the actual or observed
conditions but at least allow the modeler to determine if the model is headed in the right
direction as far as its initial development and where to look for major problems. Model
simulation criteria such as selection of which solver package to use and when
convergence is reached between consecutive iterations are selected at this point as well.
The initial test runs for the sub-regional model fared reasonably well. The model was able
to converge and generate groundwater head contours that at least appeared to represent
the general shape and orientation of the contours depicted on historical USGS maps for
the study area (USGS Groundwater Conditions on Long Island, 2016). Though not
completely 100%accurate, but off by only about a few feet or so in portions of the upper
layers of the model, the model was able to produce output that, from a starting point,
was usable and allowed for progression to the calibration phase of the model
development.
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3.0 MODEL CALIBRATION
The calibration process is often the most complex portion of groundwater modeling. The vast
array of inputs,geometry and boundary conditions that can be adjusted to manipulate the model
output can be significant and daunting. Additionally, the number of combinations of any of the
above-mentioned variables can quickly become overwhelming even for experienced modelers.
Groundwater Vistas has several means to simplify the process such as automated sensitivity
analyses and calibration procedures like PEST (automated Parameter Estimation and
optimization.
3.1 Calibration Target
The calibration process was begun by identifying known points of groundwater elevation
within the model framework. Due to the size or extents of the model (18,000 ft x 19,000
ft), several known USGS groundwater monitoring wells were able to be located or
identified that coincided with the model grid. A total of four (4) active USGS monitoring
wells were located and included four (4) wells installed in the Harbor Hill Outwash. The
monitoring wells were subsequently used as calibration targets in order to adjust model
parameters to get a best match or fit between actual water level values and modeled or
predicted ones.
The purpose of calibration targets is to use them to assess model adjustments. The closer
target residuals (the difference between the target value and model predicted
groundwater heads) get to zero, the better the model is considered calibrated. The raw
uncalibrated model was run with the initial inputs all unadjusted and the residual sum of
squares was approaching 7.6 (model is calibrated to April 2016 USGS water level data).
The residual sum of squares is a summation of the squared value of all the calibration
target residuals. The squared value is used because a residual can be positive or negative,
thus by squaring, all values become positive. The squared residuals when summed
produce a positive value that is the starting point in the calibration process. The idea is
to adjust model parameters to result in a lower residual sum of squares value. The lower
this number is driven the better the calibration of the model is considered. Other values
or calibration goals that are looked at closely in terms of an acceptable degree of
calibration include the residual mean divided by the range of target values should be less
than 0.05,the residual standard deviation divided by the range of target values should be
less than 0.10 and the absolute residual mean divided by the range of target values should
be less than 0.10.
A model with 4 calibration targets and a starting value of 7.57 for the residual sum of
squares is reasonable based on past modeling experience. This indicates that the average
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initial uncalibrated residual was just under 1.38 ft. The target residuals were all positive
meaning that the model simulated values overpredicted the actual or observed water
level values. The other three key calibration values were well off the above stated goals,
and thus, indicated the model needed a decent degree of calibration before it could be
considered acceptable.
• residual mean divided by the range of target values = 1.23 / 2.56 = 0.48
(acceptable value should be<0.05)
• residual standard deviation divided by the range of target values = 0.62 / 2.56 =
0.24 (acceptable value should be<0.10)
• absolute residual mean divided by the range of target values = 1.23/2.56 = 0.48
( acceptable value should be<0.10)
The below image shows the model calibration statistics for the raw uncalibrated model.
Target Re.iduaI Name.
1.95 1.11 S 53325
2.76 1.56 S 39269
4.43 0.28 S 6558
4.51 1.95 S 53333
Residual Mean =1.23 Close
Residual Standard Dev. =0.62
Absolute Residual Mean =1.23
Residual Sum of Squares 7.57e+00
RMS Error =1.38
Minimum Residual =0.20
Maximum Residual =1.95
Range of Observations =2.56
Scaled Res.S td.D ev. =0.244
Scaled Abs. Mean =0.479
Scaled RMS =0.537
Number of Observations =4
3,2 Automatednsi i i alysis
Automated sensitivity analyses were performed to determine which model inputs would
have the greatest influence on model results. Using the built-in auto-sensitivity analysis
features of GV8, it became obvious fairly quickly that the most sensitive model
parameters were the horizontal and vertical hydraulic conductivities of the upper and
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middle layers of the model (Harbor Hill Outwash , Lower Drift and Middle Magothy) and
recharge. By using the automated features such as PEST (parameter estimation) the
modeling software does a numerical analysis to derive optimum parameter values to
calibrate the model. The starting input values produced a fairly reasonable model and
the auto-calibration process yielded results that did not vary by much and were within
acceptable ranges for the various aquifers. Table 3 below highlights the aquifer
parameters that were adjusted following the calibration process.
Table 3-Groundwater Model-Calibrated Parameter Values
W W .
Harbor Hill
Outwash
150 18.34 0.000001 0.15 0.24 0.0085'
Ronkonkoma
400 40 0.000001 0.15 0.24 ---
Drift
Lower Clay 30 3 0.000001 0.15 0.24 ---
Lower Drift 150 25 0.000001 0.15 0.24 ---
Middle Magothy 25 7.5 0.000001 0.15 0.24 ---
Basal Magothy 100 10 0.000001 0.15 0.24 ---
Raritan Clay 0.3 0.001 0.000001 0.15 0.24 ---
Lloyd 35 3.5 0.000001 0.15 0.24 ---
• *Recharge was only applied to Layer 1 of the model.
• Highlighted values represent parameters that were modified from initial input following calibration.
Assuming reasonable aquifer parameters were identified and input the next set of
variables considered were the boundary conditions. These were the four constant head
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boundaries that represented the surface water bodies. Each of these were evaluated
using auto sensitivity analyses. The analyses indicated that by adjusting the boundary
condition values even greater improvement could be achieved with regards to the
calibration goals. Table 4 below compares the uncalibrated boundary conditions to the
calibrated ones.
Table 4—Uncalibrated versus Calibrated Boundary Conditions
ENMENIMMEMINSEW
Long Island Sound Constant Head 0.00 1.19
Great Peconic Bay Constant Head 0.00 1.01
Laurel Lake Constant Head 6.00 5.40
Marratooka Lake Constant Head 5.00 6.89
Once the various inputs and boundary conditions were calibrated, a new residual sum of
squares value was calculated to be 0.413 equating roughly to an average absolute residual
of around 0.321 ft,which represented an improvement over the uncalibrated model. The
additional three calibration goals were also reevaluated and all showed acceptable
values.
• residual mean divided by the range of target values = 0.01 / 2.56 = 0.0039
(acceptable value should be <0.05)
• residual standard deviation divided by the range of target values = 0.32 / 2.56 =
0.126 (acceptable value should be <0.10)
• absolute residual mean divided by the range of target values=0.29/2.56=0.112
(acceptable value should be <0.10)
The below image shows the calibration statistics for the calibrated model. Though not
quite below the goal of 0.10 for the latter two of three calibration goals, still a very good
degree of accuracy and calibration. Additional calibration to further adjust the two latter
calibration goals below 0.10 required adjusting model inputs to values that were
considered outside acceptable ranges, and thus,the model was considered calibrated.
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Target Statistics
Target Resi&J Name
1.95 -0.30 S 53325
2.76 0.12 S 39269
4.43 -0.10 S 6558
4.51 0.47 S 53333
Residual Mean =0.01 Close
Residual Standard Deis. _ .32
Absolute Residual Mean =0.29
Residual Sum of Squares =4.13e.01
RMS Error =032
Minimum Residual =-0.38
Maximum Residual =0.47
Range of Observations =2.56
Scaled Res.Std. Dev. _0 120
Scaled Abs. Mean =0.112
Scaled RMS =0.126
Number of Observations =4
zz
Figure 6 depicts the calibrated model showing the water table contours in layer 1, or the Harbor
Hill Outwash.
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4.0 MODEL SIMULATIONS
Once the model was calibrated, some refinements were made to enhance the resolution of the
graphical output in the vicinity of interest (at and around the site). The model grid spacings for
both the rows and columns were reduced from 100 ft to 50 ft to produce a refined grid right
around the Yacht Center location on Mattituck Creek (see Figure 7). Additionally, two layers of
the model were sub-divided to provide enhanced vertical precision as well. The Harbor Hill
Outwash or layer 1 was sub-divided into 4 layers (now layers 1 thru 4) and the Middle Magothy
layer was also sub-divided into 4 separate layers (now layers 8 thru 11). Figure 8 is a cross
sectional view of the model depicting the various layers/sub-layers. The model calibration was
rechecked to confirm that the refinements did not negatively impact the model accuracy.
4.1 Local Domestic Supply ell Identification
(Identify nearby local domestic supply wells and determine if the proposed
excavation will adversely impact any wellhead zone of influence or the quantity
or quality of water in the aquifer system for residential water supply)
A conservative approach was taken with regards to analyzing whether or not the
proposed excavation would have an adverse impact on nearby domestic supply wells
with regards to water quantity and quality. This was accomplished through steady state
modeling where conditions are held constant and are independent of time. First, local
surrounding properties that do not have a public water service were identified. Second,
vacant properties without a private water supply well were also identified. Figure 9
shows the location of surrounding properties with private domestic water supply wells.
All of the domestic wells were assumed to be shallow wells due to assumed low flow
rates and the suspected shallow depth to saltwater in the area, and thus, they were all
entered into the second layer of the model to meet the Suffolk County Department of
Health Services (SCDHS) requirement of the well screen being set at least 40 feet into
groundwater. Each domestic supply well was assigned a pumping rate of 325 gallons per
day (gpd) which is consistent with the SCDHS design flow rates for single family
residences(sanitary system flow rates of 300 gpd). Wells were located at approximately
the centroid of each lot as exact locations are unknown as they are not mapped.
Two separate model runs were performed under this case. The first entails the
unexcavated site and the second involves the site following excavation. The site
excavation only takes place in the upper most layer of the model, which is layer 1 and is
part of the Harbor Hill Outwash. Figure 10 indicates the location of the proposed site
excavation and also indicates the model elevations at that area of the site.
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The sub-regional model was constructed using roughly 25-foot contour intervals for the
model surface elevations,thus,the portion of the site where the proposed excavation is
to take place. The unexcavated surface elevations range between 25 to 50 feet AMSL.
The model was run under steady state conditions and targets were installed at the
proposed excavation site and at the surrounding properties with private domestic supply
wells. The targets were set to display the groundwater elevation at that location.
Figures 11 and 11a depict the existing conditions with the site unexcavated. Figure 11
is presented with the surface elevations and Figure 11a is the same image but without
the surface contours for better clarity of the groundwater target residual values. The
target values are displayed as negative values as a result of the model output but actually
represent positive values. For instance, in the middle of the proposed excavation area
at the Yacht Center site, the target residual is posted as -1.73 ft. This is a result of the
target value being entered as zero and the model predicted head elevation at that
location being subtracted from the target value to produce a residual which is being used
to identify the groundwater surface at that location, thus zero minus any positive
number will yield a negative result. The actual resulting or predicted head value is then
1.73 ft, meaning the model is predicting a groundwater surface elevation of 1.73 ft AMSL
NAVD 88.
The site surface elevations were then altered in the area of the proposed excavation.
The elevations were adjusted from 25 to 50 ft AMSL to a uniform 5 ft AMSL elevation.
The other adjustment that was made was the recharge in the excavated area,which was
increased from 0.0085 ft/day to 0.0101 ft/day. This increase results post-construction
due to the installation of on-site drainage which will accommodate and recharge
stormwater to the aquifer. This results in less surface runoff losses and less
evapotranspiration as well. Figure 12 depicts the proposed site excavation elevation.
The model was then re-run to determine if any changes in groundwater elevations would
occur as a result of the site excavation. Figures 13 and 13a depict the proposed site
excavation and the resulting groundwater elevations. Figure 13 is presented with the
surface elevations and Figure 13a is the same image but without the surface contours
for better clarity of the groundwater target residual values.
Comparing Figures 13 and 13a to Figures 12 and 12a,there is only a single change that
occurs right at the site where the target is located at the centroid of the proposed
excavation. The groundwater elevation rises by 0.01 ft. The surrounding domestic well
locations remain unaffected. Thus, even though the excavation is deep, over 40 feet in
some spots, it is still above the water table (water table elevation in centroid of
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excavation area predicted at 1.72 ft AMSL(NAVD 88)), and thus, is predicted to have no
effects on groundwater quantity at the surrounding domestic well locations.
Wellhead zone of influence is evaluated using particle tracking. Under this scenario,
particles are either released at the well screen zone and reversed tracked back to their
respective points of origin or, released upgradient of the well and tracked forward until
they are subsequently captured at the well screen. Again,two separate model runs were
performed for comparison purposes. The first run was under the unexcavated
conditions and the second run was performed post excavation.
MODPATH Version 5 was employed to analyze and visualize the particle tracks.
MODPATH is a particle-tracking post-processing model that computes three-
dimensional flow paths using output from groundwater-flow simulations based on
MODLFOW,the U.S.Geological Survey(USGS)finite-difference groundwater flow model.
The program uses a semi-analytical particle-tracking scheme that allows an analytical
expression of a particle's flow path to be obtained within each finite-difference grid cell.
A particle's path is computed by tracking the particle from one cell to the next until it
reaches a boundary, an internal sink/source, or satisfies another termination criterion
(i.e., a certain time in the future or the past). Under the unexcavated case a ring or
cluster of particles were installed around each of the well screens that were identified
for lots that surround the Strong's Marina site that are not serviced by the SCWA. The
particles were set to reverse track back to their respective points of origin. The predicted
particle tracks or paths depict the wellhead zones of influence or capture.
The particle tracking analysis indicates the domestic supply wells having relatively low
pumping rates (325 gpd) have as expected very narrow zones of influence. Figure 14
depicts the predicted wellhead zones of influence under unexcavated conditions and
again also shows the surface contours. A line of particles was placed in the middle of
layer 2 diagonally across the proposed limits of the site excavation in addition to the
particle clusters installed around each well at about the midpoint of the well screens
which are also located in layer 2 of the model. Figure 14a is the same image as Figure
14 with the exception of surface contours being turned off for better clarity of the
particle tracks.
The model was then run under excavated conditions to determine if excavating the site
would have any influence on surrounding well head zones of influence. Figure 15
presents the model output for this condition where nothing changes except for the
ground surface elevation within the limits of excavation at the Yacht Center and the
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amount of recharge occurring within those limits (the recharge increases from 0.0085
ft/day to 0.0101 ft/day). Figure 15a again is the same information presented in Figure
15 but with the surface contours turned off for better particle track clarity.
Comparing Figures 14 and 14a to Figures 15 and 15a, there are no noticeable changes
in particle track trajectories between the pre- and post-excavated site conditions. This
again is attributable to the fact the site excavation is proposed to take place entirely
above the water table and the proposed site modifications are only slightly adding more
water to the local aquifer system due to the increased recharge post construction. Thus,
the proposed site excavation is not predicted to have any impact hydraulically on the
nearby surrounding domestic supply wellhead zones of influence. Another condition to
note is that a few of the on site wells at Strong's Yacht Center will be abandoned post
construction. Comparing Figure 14a to Figure 15a two wells are removed. Observing
Figure 14a the two wells to be removed are called out. The significance of this is that by
removing two wells from service the Yacht Center is thus withdrawing less water from
the aquifer post construction. Less water withdrawal has multiple benefits with regards
to the site having even less influence on neighboring wells, and what will be addressed
later on in this report, saltwater intrusion and upconing.
The water quality of the aquifer system with respect to the nearby surrounding domestic
supply wells is also not expected to be impacted by the site excavation. This was
investigated by tracking the particles released diagonally across the excavation in the
middle of layer 2 in a forward fashion as opposed to the reverse fashion as explained
above. Under this scenario, the particles are released at their origin point and tracked
forward until they reach a termination point like an active pumping well or boundary
condition. Groundwater flow at the Yacht Center is towards Mattituck Creek. Thus,the
model predicts groundwater beneath the proposed site excavation will head in an
easterly direction until it reaches the creek. Figure 16 presents the forward tracked
particles released beneath the site excavation location. The significance of this is that
groundwater beneath the site excavation does not flow towards or is intercepted by any
of the nearby surrounding domestic supply wells, meaning groundwater quality at the
domestic supply wells is not predicted to be impacted by the Yacht Center.
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4.2 n Site Groundwater Analysis
(Provide an analysis of the groundwater on site and its contribution to the aquifer
serving the nearby wells under existing conditions and the potential adverse
effects, if any, to the aquifer system serving nearby wells following the
excavation)
Shallow groundwater beneath the Yacht Center site, as stated in Section 4.1 above,flows
eastward towards Mattituck Creek. USGS data supports this flow direction as do the
groundwater model flow simulations (see Figure 16). The overall site is approximately
16.5 acres in land area and the proposed site excavation area is around 4.6 acres in total.
Groundwater recharge varies annually but has been estimated to be anywhere between
50 to 75% of the annual precipitation. Precipitation records going back over the past 70
years show an average annual total precipitation off 49 inches per year. The groundwater
model calibrated to a recharge rate of 0.0085 ft/day or 37.23 inch/year, which based on
the annual average precipitation rate of 49 inches/year equates to a recharge rate of 76%,
the extreme upper end of the recharge range. Assuming the unexcavated site recharges
in its entirety at 76% of the annual precipitation amount the site then recharges to the
aquifer system the following amount on average each year
R= 16.5 acres x(43,560 ft2/acre)x(0.76 x 49 in/yr) x(1 ft/12 in) = 2,230,489.80 ft3/yr
or, on a daily basis-
R= 2,230,489.80 ft3/yr x 1 yr/365 day= 6,110.93 ft3/day
The excavated site following construction is going have an additional 2.4 acres as either
paved or have buildings occupying it. The entire excavated area is planned to be
constructed with a drainage and sub-surface recharge system that will collect and
recharge nearly 100% of the precipitation that lands upon it. The actual drainage plan
accommodates 7.77 acres of land area, which includes the project area and contributing
off-site area. Such a system will greatly reduce runoff and evapotranspiration effects and
thus have a net increase with regards to groundwater recharge. Drainage systems are
rarely 100% effective at capturing all precipitation so a 10% reduction is used for the
amount of precipitation being recharged to the sub-surface or shallow aquifer system.
The post excavated site is predicted to have the following recharge—
R1 = (16.5 acres - 4.6 acres) x (43,560 ft2/acre) x (0.76 x 49 in/yr) x (1 ft/12 in) _
1,608,656.28 ft3/yr
R2=4.6 acres x(43,560 ft2/acre)x (0.9 x 49 in/yr) x(1 ft/12 in) =736,381.80 ft3/yr
RT= R1+ R2= 1,608,656.28 ft3/yr+736,381.80 ft3/yr= 2,345,038.08 ft3/yr
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This equates to 114,548.28 ft3/yr of additional recharge reaching the aquifer system.
Under both flow conditions, the unexcavated and the post excavated site, groundwater
flows towards Mattituck Creek from beneath the limits of the proposed excavation
location. Figures 16 and 16a depict these cases. Though under the post excavated
conditions a slight increase in the water table is predicted immediately beneath the
excavation area, no particle deflections or trajectory changes are observed and thus no
effects upon nearby wells are anticipated.
4.3 Aquifer Evaluation
(Evaluate the nature of the aquifer that supplies the nearby wells and the
relationship of the subject property as a contributing source and that the
proposed excavation will not affect the quantity of water available to the nearby
wells)
The aquifer system beneath the site is comprised of multiple hydrogeologic units. The
upper or most shallow unit where the neighboring domestic supply wells are screened is
commonly referred to as the Harbor Hill Outwash. Directly beneath that is a thin, highly
permeable layer that is known as the Ronkonkoma Drift. Immediately below that is a
confining clay layer. Figure 4 depicts a typical cross section through the groundwater
model with all the layers and hydrogeologic units numbered and identified. The upper
two hydrogeologic units are considered and modeled as unconfined aquifers while the
units below them are treated as confined aquifers or layers. Thus, the shallow aquifer
where the domestic supply wells are screened, being unconfined can be directly
susceptible to surface related activities. However,as explained above in Sections 4.1 and
4.2, though the site is being excavated, the excavation takes place entirely above the
water table and does not affect the quantity or quality of the groundwater as it relates to
the nearby domestic supply wells. A slight increase in groundwater recharge is expected
to take place post excavation once the site is developed. This increase in quantity is
relatively minimal and is not predicted to affect the nearby wells. Figures 16 and 16a
show no significant or noticeable differences in particle tracks or trajectories between the
excavated and unexcavated site conditions.
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4.4 Gr er Travel Determination
(Determine the direction of groundwater travel on site and travel times and whether
the proposed excavation would disrupt or interrupt groundwater travel or timeframes
to reach surface waters)
Groundwater flow direction across the Yacht Center site is in an easterly direction
towards Mattituck Creek. A line of particles has been installed along the western
boundary of the proposed site excavation and released at the mid-point of layer 2 which
is approximately 40 feet below the water table at that location and is consistent with
SCDHS domestic supply well screen depths. The particles are tracked forward and head
eastward again towards the creek. They start with a downward trajectory and then
eventually begin to flow upwards towards the creek bed. Under the existing site or
unexcavated conditions, the groundwater travel time from the location of the western
boundary of the proposed excavation area the particles are predicted to take between 4
and 4.5 years to reach Mattituck Creek with a starting depth of 40 feet below the water
table. Figure 17 is a depiction of the model output under steady state conditions and with
the site unexcavated. The numbers posted along the particle tracks are times in years
since release and coincide with the arrowhead locations along the tracks. The predicted
travel times are consistent with the Suffolk County Subwatershed maps which show the
site water table travel time to be primarily within two travel time categories, the 0 to 2
years and 2 to 10 years categories. The Suffolk County travel times are based on water
table travel to the surface water body. The model predicted travel time of 4 to 4.5 years
is based on a deeper starting point than the water table for the particles. As mentioned
above,the particles do not travel in a straight line but rather follow a curvilinear trajectory
where they start out headed downward and then curve back upward towards the creek
bottom, thus following a longer flow path rather than a relatively straight path directly
across the surface of the water table to the creek.
Figures 17a depicts the same information as Figure 17 except now the model is run under
post excavation conditions where the soil is removed from the proposed excavation area
down to an elevation of 5 ft AMSL and the recharge over that same area is increased
slightly to account for subsurface recharge via roofs and paved surfaces. The buildings
are proposed to have a finished first floor elevation of 10 ft AMSL,the modeled elevation
of 5 ft AMSL accounts for the excavation required to construct and install the building
foundation elements. Under the scenario depicted in Figure 17a, the post excavation
case,no noticeable changes in particle tracks or trajectories are observed when compared
to Figure 17 which presents the unexcavated conditions. Additionally, the travel times
are posted in half year increments along the tracks and these again are identical to the
unexcavated scenario showing travel times of between 4 and 4.5 years to travel from
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roughly 40 feet below the water table at the western excavation boundary to the bottom
of Mattituck Creek. Thus, the groundwater model predicts that the proposed site
excavation will not disrupt groundwater flow directions or travel times to reach the
nearby surface water body.
4.5 Depthn levi Estimation
(Estimate the depth of the freshwater lens and elevation of the saltwater interface)
Estimation of the saltwater interface was accomplished using the 3-d numerical
groundwater model and checked using analytical methods. The USGS program SEAWAT
Version 4 was employed to model and simulate saltwater. The SEAWAT program is a
coupled version of MODFLOW and MT3DMS designed to simulate three-dimensional,
variable density, saturated groundwater flow and multi-species transport. The variable
density flow(VDF) process in SEAWAT is based on the constant density groundwater flow
process of MODFLOW-2000. The VDF process uses the familiar and well established
MODFFOW methodology (finite difference method) to solve the variable density
groundwater flow equation. The MT3DMS part of SEAWAT, referred to as the Integrated
MT3DMS Transport(IMT) process solves the solute transport equation.
The analytical method used to check the modeling results is the Ghyben-Herzberg
relation. This relation states that for every foot above sea level in water table elevation
that exists, the saltwater interface will be 40 times that below sea level. In most real
situations, the Ghyben-Herzberg relation underestimates the depth to the saltwater
interface (Freeze and Cherry, 1979), thus, it can be used for conservative preliminary
estimates.
The existing unexcavated site had two test holes conducted in September of 2018. The
water table elevations in these test holes were observed to be at 1.2 and 1.4 ft AMSL
(NAVD 88). PWGC also performed 13 soil borings in June 2021—groundwater was found
at 1.0 to 2.5 ft AMSL across the site at that time. The groundwater model under steady
state conditions and calibrated to USGS April 2016 groundwater conditions predicted
groundwater elevations at the two 2018 test hole locations of 1.48 and 1.45 ft AMSL.
Under the same conditions, the model predicted the water table elevation beneath the
middle of the proposed excavation limits for the unexcavated case to be 1.73 ft AMSL
(NAVD 88), see Figure 11a. Based on the Ghyben-Herzberg relation, the saltwater
interface would then be expected to least be at an elevation as calculated below:
SWint=—(40 x WTelev) _-(40 x 1.73 ft) _-69.2 ft AMSL(NAVD 88)
The thickness of the freshwater lens is calculated as such:
FWlens=WTelev+40WTel,v= 1.73 ft+(40 x 1.73 ft) =70.93 ft
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The groundwater model was run utilizing the SEAWAT program to estimate the saltwater
interface elevation and freshwater lens thickness beneath the proposed excavation area
at the Yacht Center site. The model graphical output used to represent the chloride
concentrations is a color flood. Here, different colors represent varying concentrations
of chlorides. The model units for chlorides are in lb/ft', typically chloride concentrations
are expressed in mg/l. The model uses lb/ft'due to the rest of the model being designed
around units of feet. The USGS considers the saltwater interface to be located where the
groundwater concentration meets and begins to exceed the drinking water concentration
for chlorides which is 250 mg/I or 0.0156 Ib/ft3. Chloride concentrations in seawater can
vary but typically range on the order of 14,000 to 19,000 mg/I or 0.874 to 1.19 Ib/ft3. The
groundwater model calibrated to a seawater concentration of 16,500 mg/l or 1.03 Ib/ft3.
The lower end of the color scale was set to terminate at 250 mg/I or 0.0156 Ib/ft3
(rounded to 0.02 on the legend—model display only allows two decimal places).
Figure 18 depicts a cross section through the model showing the predicted saltwater
extents based on chloride concentrations. The saltwater interface is predicted to be
contained in layer 4 of the model beneath the site excavation limits. The elevations of
the top and bottom of layer 4 beneath the proposed site excavation area are -75 and -
87.88 ft AMSL (NAVD 88). Using the most shallow elevation of layer 4 as a conservative
position for the saltwater interface,the elevation would then be -75 ft AMSL which is 5.8
feet deeper than estimated by the Ghyben-Herzberg relation. As referenced above, the
Ghyben-Herzberg relation tends to underestimate the interface depth as it was calculated
to be -69.2 ft AMSL, a minimum difference of 5.8 ft. The model predicts a freshwater
lens thickness of 76.73 ft. Figures 18a through 18d show plan views through the upper
four layers of the model and depict the horizontal extents of the saltwater under the
unexcavated site conditions. The figures depict a landward migration of the interface
with depth as would be expected. Layer 4 directly beneath the proposed site excavation
limits shows near complete saltwater conditions, indicating that the interface would be
between -75 and -87.88 ft AMSL. Table 5 below is a comparison of the analytical
expression to the numerical groundwater model results.
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Table 5—Existing Conditions Saltwater Interface Elevation and Freshwater Lens Thickness
EMESEMEE=
Ghyben-Herzberg -69.2 70.93
Groundwater Model -75 76.73
4.6 Proposed Excavation Evaluation—Saltwater Intrusion into the Aquifer
(Evaluate whether the proposed excavation would alter the saltwater interface in a way
that may cause saltwater intrusion into the aquifer or nearby wellhead zones of
influence)
The groundwater model was run under the excavated site conditions to evaluate
potential saltwater interface effects that maybe caused as a result of the excavation. The
difference between the excavated and unexcavated site conditions being that the surface
elevations at the location of the proposed excavation are decreased from between 25 to
50 ft AMSL to 5 ft AMSL and the recharge occurring within the limits of the proposed
excavation is increased from 0.0085 ft/day to 0.0101 ft/day. Figures 18 and 18a through
18d depict the existing saltwater conditions prior to the site being excavated. Slightly
increasing the recharge across the area of the proposed site excavation increases the
amount of freshwater being received by the aquifer and in turn would have the effect of
causing the saltwater interface to migrate seaward and downward. Under the excavated
site conditions, the water table is expected to rise 0.01 ft due to the increased recharge
(see Figures 11a and 13a for unexcavated and excavated site groundwater conditions).
Applying the Ghyben-Herzberg relation to the slightly higher water table elevation yields
the following with regards to the saltwater interface elevation and freshwater lens
thickness:
SWint=—(40 x WTeiev) =-(40 x 1.73 ft) =-69.2ft AMSL(NAVD 88)
FWIens=WTelev+40WTelev= 1.73 ft+(40 x 1.73 ft) =70.93 ft
This equates to a saltwater interface that is estimated to be 0.40 ft deeper and a
freshwater lens that is 0.41 ft thicker,thus saltwater intrusion is not expected to occur as
a result of the site excavation, but just the opposite is predicted.
Figure 19 is a cross sectional view through the model output depicting the excavated site
conditions and the chloride concentrations. Layer 4 where the saltwater interface is
expected to occur beneath the site excavation is 12.88 ft thick. Based on the Ghyben-
Herzberg relation, a deepening of at least 0.40 ft is expected. The layer being over 12 ft
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thick, the groundwater model, as constructed, is unable to differentiate this increase
graphically. However, comparing Figures 18 and 19 a difference in layer 3 is noticed.
Under the unexcavated case, Figure 18, in layer 3 just to the north of the site excavation
area,the saltwater interface is present. Reviewing Figure 19 for the excavated case, the
chloride concentrations that were observed in Figure 18 are no longer present. Similar
observations can be made by comparing the plan views shown in Figures 18a through
18d for the unexcavated case to Figures 19a through 19d for the excavated case. Here
again, the chlorides concentrations are predicted to be pushed towards Mattituck Creek
away from the site and the surrounding or neighboring domestic supply wells. This is as
stated above the opposite effect of saltwater intrusion. The neighboring domestic supply
wells were all shown to have zones of influence that track in land away from Mattituck
Creek (see Figure 14a), so by locally moving the chloride concentrations towards
Mattituck Creek,wells in proximity to the site will experience a subtle improvement with
regards to saltwater intrusion.
Also to be considered in regard to the saltwater interface, and as mentioned above in
section 4.1, two existing water supply wells are going to be removed from service, the
entire site will be connected to the SCWA for domestic water supply and the two
remaining on site wells will be converted to irrigation wells that will have overall less
water consumption then their combined previous water supply usages. The net effect is
again less water withdrawal from the aquifer and a benefit with regards to the saltwater
interface position beneath the site. The difficulty with modeling this at the sub-regional
scale is that the wells are withdrawing on the order of for potable usage under the
unexcavated site conditions and the two remaining wells under the post excavated site
conditions get reduced to an annualized flow rate of 218 gpd for irrigation purposes, not
a large or even very noticeable amount of water so the effect though positive is difficult
for the model to distinguish.
4.7 Proposed Excavation Evaluation®Upconing
(Evaluate whether the proposed excavation would cause upconing and saltwater
intrusion by reducing the amount of fresh water entering the aquifer used by the nearby
wells)
Sections 4.2 through 4.6 above explain how there is an increase in recharge to the aquifer
post excavation. The previously unexcavated site area becomes developed with two
roofed structures and the remainder of the area is paved with an impermeable surface.
Runoff from these areas is collected and discharged to the subsurface via below ground
drainage structures. Thus, an increase in recharge is experienced in this area of the
Strong's Marina site. The result is a slight increase of the water table elevation which
results in a deepening of the saltwater interface. Upconing occurs when there is a
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decrease in the water table elevation which would be the opposite of what is predicted
to occur under the post excavated site conditions. The Ghyben-Herzberg calculations
performed and presented in sections 4.5 and 4.6 clearly support this and are summarized
below in Table 6 for a side by side comparison.
Table 6— hyben-Herzberg Predicted Saltwater Interface Elevations and
Freshwater lens Thicknesses
SIMENEESEIRM
Unexcavated Site -68.8 70.52
Post Excavated Site -69.2 70.93
4.8 Potable Freshwater Elevation Estimate
(Estimate at what elevations does potable freshwater begin and end (at the expected
saltwater interface) on site pre and post excavation)
Under existing or unexcavated site conditions the water table beneath the proposed site
excavation area is predicted to be 1.72 ft AMSL NAVD 88 (see Figure 11a). The saltwater
interface under the unexcavated site conditions is estimated to be at an elevation of-68.8
AMSL NAVD 88 based on the Ghyben-Herzberg relation. The groundwater model
estimates the saltwater interface under the existing conditions to be contained within
layer 4 of the model. Layer 4 at the location of the proposed site excavation has a top
elevation of-75 ft AMSL NAVD 88 and a bottom elevation of-87.88 ft AMSL NAVD 88.
See Figure 18 for a cross sectional view through the groundwater model output for the
unexcavated site conditions showing chloride concentrations. As previously stated, the
Ghyben-Herzberg relation tends to under predict the depth of the saltwater interface and
the groundwater model output supports this statement.
The post excavated site groundwater conditions are predicted by the groundwater model
to show a slight increase in groundwater elevation right at the center of the proposed
excavation limits. The groundwater elevation is predicted to increase by 0.01 ft, or to an
elevation of 1.73 ft AMSL NAVD 88 under the post excavated site conditions (see Figure
13a). The Ghyben-Herzberg relation then estimates the saltwater interface to deepen by
0.40 ft,or to an elevation of-69.2 ft AMSL NAVD 88. The groundwater model still predicts
the saltwater interface to remain in layer 4 of the model (see Figure 19) and as the layer
is over 12 feet thick it is unable to distinguish a more precise elevation under post
excavated site conditions. Assuming the worst case conditions that the top elevation of
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layer 4 previously saw chloride concentrations of at least 250 mg/I under the unexcavated
scenario, then under the post excavated site conditions the interface elevation is
expected to be deeper than -75 AMSL NAVD 88.
4.9 Sea Level Rise
A sea level rise of 16" (1.33 ft) is predicted to occur over the next few decades. The
groundwater model was used to simulate a 16" increase in sea level and predict what the
groundwater conditions would look like on site should that occur. The way sea level rise
is accounted for in the model is by adjusting the boundary conditions that include the
Long Island Sound, Mattituck Creek, the Great Peconic Bay and James Creek. Table 7
below presents the model modifications that were made to account for a rise in sea level
of 16".
Table 7—Sea Level Rise Boundary Condition Adjustments
EMEMEMMIM
Long Island Sound Constant Head 1.19 2.52
Mattituck Creek Constant Head 1.19 2.52
Great Peconic Bay Constant Head 1.01 2.34
James Creek Constant Head 1.01 2.34
The model was re-run under the excavated site conditions to predict a groundwater level
right at the site excavation that could be expected with a 16" sea level rise. Figure 20 is
the model output showing this condition. The model predicts the groundwater beneath
the site to rise to an elevation of 3.05 ft AMSL NAVD 88, or a rise of 1.31 ft (model
predicted the post excavated site groundwater elevation to be 1.74 ft AMSL NAVD 88
without any sea level rise—see Figure 19a)
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5.0 CONCLUSION
Numerical groundwater modeling was performed to evaluate the potential effects a proposed
excavation at the Yacht Center site in Mattituck, NY would have on neighboring domestic supply
wells and the local shallow aquifer system. The excavation will entail cuts on the order of 40+
feet in depth and cover an area of approximately 4.6 acres. The entire excavation will take place
above the water table and as such is predicted to have no noticeable effects or impacts on the
neighboring domestic water supply wells.
Numerous cases and possible conditions were evaluated using the groundwater model to predict
what effects if any the proposed site excavation would have with regards to local groundwater
quantity, quality, flow paths, travel times, well capture zones and the position of the saltwater
interface.
Groundwater quantity is expected to increase slightly as a result of the proposed site excavation.
This is due to an increase in recharge resulting from the area where the excavation will take place
being developed with two roofed structures and impermeable paving with all runoff (from the
project area and off-site contributing areas) being collected and discharged to subsurface
drainage structures. This will reduce the effects of the existing site runoff and evapotranspiration
currently occurring and allow more of the precipitation being received by the area to be recharged
to the shallow aquifer system. The groundwater model predicts a slight increase in the water
table elevation right at the center of the proposed excavation area. See Figures 11a and 13a for
a comparison of the local groundwater conditions both pre and post excavation.
The groundwater model was used to investigate potential groundwater quality effects on the
surrounding nearby domestic supply wells that might occur as a result of the proposed site
excavation using particle tracking. Under this case, particles were released from beneath the site
excavation and tracked forward until they reached a termination point. Groundwater recharging
beneath the proposed site excavation was predicted to flow towards Mattituck Creek(see Figure
16)and was not intercepted by any of the domestic supply wells that are in proximity to the Yacht
Center site. Thus,the model predicts that the neighboring wells will not be impacted with respect
to groundwater quality as a result of the proposed site excavation. Saltwater conditions were
addressed separately from general water quality effects.
Groundwater flow paths or directions on site at the Yacht Center were predicted also using
particle tracks. Figures 17 and 17a present predicted flow directions from beneath the proposed
excavation site. The particles were tracked in a forward direction and under both the unexcavated
and excavated site conditions all particles migrate towards Mattituck Creek. No noticeable
differences such as particle deflections or changes in trajectories were observed between the two
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conditions even with a slight increase in the water table elevation under the unexcavated case.
The travel times were also predicted for the two cases and again the time postings presented in
Figures 17 and 17a show no noticeable differences. Thus,groundwater flow directions and travel
times are not expected to be disrupted by the proposed site excavation.
The potential impacts of the proposed site excavation on the position of the saltwater interface
and effects of possible saltwater intrusion as it relates to the neighboring domestic supply wells
were evaluated and analyzed using the numerical groundwater model and an analytical
expression. The model predicted the groundwater surface elevation beneath the site to be 1.72
ft AMSL NAVD 88 for the unexcavated site conditions (see Figure 11a). Employing the Ghyben-
Herzberg relation, the saltwater interface was estimated to be at an elevation of-68.8 ft AMSL
NAVD 88. The model predicted chloride concentrations to exceed 250 mg/1 at an elevation
between-75 to-87.88 ft AMSL NAVD 88,which is lower or deeper than estimated by the analytical
expression. The top elevation of layer 4 of-75 ft AMSL NAVD 88 was selected as the elevation of
the interface under existing conditions scenario for a worst case approach. The Ghyben-Herzberg
relation has been stated to underestimate the depth to the interface (Freeze and Cherry, 1979)
and the model output supports this statement. Figure 18 presents the predicted chloride
concentrations beneath the proposed excavation site for the unexcavated site conditions. The
model predicts the freshwater lens beneath the location of the proposed site excavation for the
unexcavated conditions to be 76.72 ft thick while the Ghyben-Herzberg relation estimates it to be
70.52 ft thick.
The proposed site conditions post excavation are expected to slightly increase the amount of
freshwater being recharged to the shallow aquifer system. The addition of more freshwater to
the aquifer system produces the opposite effects of saltwater intrusion and upconing. A
downward and seaward migration of chloride concentrations would be expected and is
substantiated by the groundwater model and the analytical expression. The water table elevation
is predicted to increase by 0.01 ft under the post excavated site conditions. The Ghyben-Herzberg
relation then estimates a deepening of the interface by 0.40 ft. The groundwater model still
predicts the interface to be located within layer 4 of the model, but now it can be assumed to be
deeper than-75 ft AMSL NAVD 88. Comparing Figures 18 and 18a through 18d (the unexcavated
site conditions) to Figures 19 and 19a through 19d (the post excavation site conditions) the
seaward movement of the interface can be seen. Thus, the post excavated site is predicted to
improve the local aquifer conditions with respect to location of the saltwater interface, which is
a direct result of increasing the subsurface recharge on site at the Yacht Center.
Related to the site excavation/construction,two of the four existing on site water supply wells are
going to be removed from service and the site connected to the SCWA for public water supply.
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The remaining two domestic supply wells are going to be converted to irrigation wells with lower
annualized daily pumping rates of 218 gpd as opposed to the average domestic supply pumping
rate of 0.225 gallons per minute (GPM). The overall reduction in water withdrawal from beneath
the site will be beneficial with regards to the position of the saltwater interface and also further
reduce the potential for the site to have any influence on neighboring or nearby domestic supply
wells.
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6.0 REFERENCES
1 Brookhaven National Laboratory,
https://www.bnl.gov/weather/4cast/Month1.Precip.htm, Monthly Precipitation Records
Since 1949,April 2021.
2 Camp Dresser McKee, Comprehensive Water Resources Management Plan for Suffolk
County, Task 4.2 Hydrogeologic Framework,January 12, 2006.
3 CDM Smith, Subwatersheds Wastewater Plan Executive Summary, Suffolk County
Department of Health Services,August 2019.
4 Freeze, R.A., Cherry, J.A., Groundwater, Prentice Hall, Inc., Upper Saddle River, New
Jersey, 1979.
5 National Oceanographic and Atmospheric Administration,
https://tidesandcurrents.noaa.gov/noaatidepredictions.htmI?id=8512668&units=standa
rd&bdate=20160401&edate=20160430&timezone=LST/LDT&clock=12hour&datum=ML
LW&interval=kilo&action=monthlychart
6 New State Department of Environmental Conservation,
https://www.dec.ny.gov/docs/fish marine pdf/marralkmap.pdf,
https://www.dec.ny.gov/docs/fish marine pdf/laurlkmap.pdf
7 Suffolk County Water Authority, Well Completion Reports and Monthly Pumpage Data
(2010 to 2020)for Well Fields at Inlet Drive, Laurel Lake Drive, Sunset Drive— Mattituck,
NY.
8 Suffolk County Water Authority, correspondence regarding water availability and
connection status for private lots surrounding Strong's Yacht Center site, October 21,
2020.
9 United States Geological Survey, Delineation of Areas Contributing Groundwater and
Travel Times to Receiving Waters in Kings, Queens, Nassau and Suffolk Counties, New
York, Scientific Investigations Report 2021-5047, Reston,Virginia, 2021.
10 United States Geological Survey, https://ny.water.usjzs.jzov/maps/, Groundwater
Conditions on Long Island.
11 United States Geological Survey, https://nwis.waterdata.usgs.gov/ny/nwislgwIeveIs,
Groundwater Levels for New York, Monitoring Wells Used — S53325 3/4/1975 to
4/19/2021, S39269 3/30/1093 to 4/19/2021, S6558 6/21/2000 to 4/19/2021, S53333
3/4/1975 to 4/19/2021.
12 United States Geological Survey, Hydrogeologic Framework of Long Island, New York,
Hydrologic Investigations Atlas HA-709, 1989.
13 United States Geological Survey, Hydrogeologic Framework of the North Fork and
Surrounding Areas, Long island, New York, Water Resources Investigations Report 02-
4284, U.S. Department of Interior, U.S. Geological Survey, Coram, New York, 2004.
•• a ®® -®®
P.W. GROSSER bSULTI NG ENGINEER& �iYDRO EOLOG€ T„ P.C, PWGROSSER,COM BOHEMIA, NY 11716
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14 United States Geological Survey, Hydrogeology and Hydrologic Conditions of the
Northern Atlantic Coastal Plain Aquifer System From Long Island, New York to North
Carolina, Scientific Investigations Report 2013-5133, U.S. Geological Survey, Reston,
Virginia, 2013.
15 United States Geological Survey, Simulated Effects of Pumping and Drought on Ground-
Water Levels and the Freshwater-Saltwater Interface on the North Fork, Long Island, New
York, Water Resources Investigations Report 03-4184, U.S. Department of Interior, U.S.
Geological Survey, Reston,Virginia, 2004.
16 United States Geological Survey,Simulation of Groundwater Flow in the Regional Aquifer
System on Long Island, New York, for Pumping and Recharge Conditions in 2005-2015,
Scientific Investigations Report 2020-5091, Simulation of groundwater flow in the
regional aquifer system on Long Island, New York, for pumping and recharge conditions
in 2005-15 (usgs.gov), U.S. Department of Interior, U.S. Geological Survey, Reston,
Virginia, 2020.
RW. GROSSER CONSULTING, INC. PHONE� 631,589.6353 630 JOHNSON AVENUE,STE 7
P.W. GROSSER CONSULTING ray HYDROGEOLOGIST, RC. PWGROSSER.COM BOHEMIA, NY 117-16
LONG ISLAND - M NHATT N ' - SARATOGA SPRINGS m SYRACU SE - S ATTL - SHELT N
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FIGURES
•• e s ® ® o sa- -®®
. GROSSER CONSULTING, SHONE. 63 569,E - 0 JOHN ON AVENUE,STE
P.W. GROSSER CONSULTING ENGINEER& HYDROGEOLOGIS'T, RC. PWGROSSER,,COM BOHEMIA, NY 11716
LONG ISLAND * MANH TTAN ¢ SARATOGA SPRINGS - SYRACUSE - SEATTLE - SHELTON
Ma ck Inlet _
ES
Long Island Sound - REF�Re��s�
1.. Brook.tia',ren,Natianal Laaorator,"',
Month hi Predprtetion Records Since 1949,.April 2021.
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' r Health Sere ce_o.Ru a st2G1�.
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5 Ne•�.�� State Deparrrnerrt o� S.a���6iconrr-senral Oonserw"at=,.rn;.
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7 Suf o k Count Meter �.uthor ,=n '�" pietion Reports and Nlonthl •_ Well n P .. ' 13at ,2010 to
2e52D'for�a e I Fields.at Inlet Drivr� Laurel Lake Dr�.�re Sunset Drive-Mattltuck,NK
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3 Sufffo,k Daun T 4�atvrAut-.horiti,corre_,por,dence reaardingvru•ate eve Iab,%ity and connection status
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� for prig,°:�Iot_�srar:raa�ndin._Strang"s to .nt a�°enter Site,Cctober 21,2a32D.�
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� . �} 20 United States Se�l�wcal Surrey ��tt�_. r`ra��_crsates�::�a��s�o�y"�' a °`. Sroundwavar Dond`tions on
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12, United.States Geological Survey,� H dry eoifo, is o=o't5a�'Fewor`k of L:ng lsldar�J New t'o r,k H` a�rzlogd`
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ATrFasw !arid aszro,nu, erw'r��,aP�,'vN'ater Resources In°v�es`a,�,a�;o�ns??eport r32-sF2 Department of
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M�rratooka Lake ,� � �
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14 United States Geolceical Saurvaq .. drn 'eoio and,H droho i Uo�to",�°leons of the Northern Ataahti
Coasrm'R,ralr;A. u!"farS step �rrx cn Is:lara New York t.� "os* Casa°a iertrfic
'ate r _
-aurel Lake Dr --
,� , In:rrestipbons Report"2t113-5133, U.S_Caedogzel Survey,Reston,`�"irginia,2023.
r 15 Unlit States SIe:�I,c%wca1 S P ey,5,iv�ri.2ted Effects cf Fumphng dar,d Draug�7t oa urc.Ljnd-1,,Vorer
,.{ 1 i .a•' �, % Lleve6 an a`,E Frss"�h'�t1are,•-5a,1lr�"Gte'.r Int"�'f",��u�'?��a!t"s,"�,d�s nth Fork,.. "Long fsiand�e..,e etv York,�k��°at;er
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Reference list shown above applies to all groundwater model output figures.
4
w
,
Great Peconic Bay
5000 feet
Figure 3 - Strong's Yacht Center Groundwater Model - Model Extents
Mattituck, New York RAW
Scale:As Shown
CLIENT DRIVEN SULU"r"iUII S
P.W.Grosser Project No.STR2001 -09/10/2021
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Mattituck,New York
Scale:As Shown
taatN DRIVEN
SOLUTIONS
tN
P.W.Grosser Consulting Project No.STR2001 -09/10/2021
Mat' ck Inlet
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Mattituck, New York pv4W
Scale:As Shown
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT DRIVEN SOLUTIONS
t'� t e jnlet
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Mattituck,New York
Scale:As Shown PAW
CLIENT DRIVEN
P.W.Grosser Project No.STR2001 -09/10/2021 SOLUTIONS
Original grid Refined grid
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Mattituck, New York
Scale:As Shown
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT DRIVEN SOLUTIONS
1
2 Harbor'Hill Outwash
3
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6
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7
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8
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Figure 8 - r 's Yacht Center Groundwater Model - Cross Sectional View - Sub-Layering
Mattituck,New York PVVW
Scale:As Shown
CLIENT DRIVEN SOLUTIONS
P.W.Grosser Consulting Project No.STR2001 -09/10/2021
SCWA Well Field
Inlet or
----------- - — ------- ..........
LEGEND
----------------------------- ...........................................
.......... --------
4.0
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Mattituck,New York
Scale:As Shown Pvv jC
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT DRIVEN SOLUTIONS
,
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Mattituck,New York
Scale:As Shown 41V
P.W.Grosser Project No.STR2001 -09/10/2021 �✓ CLIENT DRIVEN SOLUTIONS
ZGne Database Information
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Mattituck,New York
Scale:As Shown - 41V
P.W.Grosser Project No.STR2001 -09/10/2021 V CLIENT DRIVEN SOLUTIONS N
11� 11 Fuld
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Mattituck,New York � /
Scale:As Shown -
P.W.Grosser Project No.STR2001 -09/1012021 V CLIENT DRIVEN SOLUTIONS
Zane Database Information
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GEND
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Figure 12 - Groundwater l - Surface Elevations - Excavated Site
Mattituck,New York PVVW
Scale:As Shown - -
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT DRIVEN SOLUTIONS
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Domestic VVell Public Supply Well
Lot Not Served by SCWA
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Mattituck,New York
Scale:As Shown Al�v
P.W.Grosser Project No.STR2001 -09/10/2021 V CLIENT DRIVEN SOLUTIONS
V .00
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LEGEND
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Figure 13a - Strong's Yacht Center Groundwater Model - Groundwater Conditions - Excavated Site
Mattituck,New York
Scale:As Shown —�� PVW
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENTDRIVEN SOLUTIONS
Zone Database Information }
Zone Database
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Mattituck,New York
Scale:As Shown Al�v
P.W.Grosser Project No.STR2001 -09/10/2021 \✓ to DRIVEN SOLUTIONS
LEGEND
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Figure 14a - Strong's Yacht Center Groundwater Model - Unexcavated Site with Particle Tracks
Mattituck,New York
Scale:As Shown A11V
P.W.Grosser Project No.STR2001 -09/10/2021 V CLIENT DRIVEN SOLUTIONS
w
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LEGEND
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Domestic Well € Public Supply Well'
Lot Not Served by SCWA
10
igure 15 - Strong"s Yacht Center Groundwater Model - Surface Elevations - Excavated Site with Particle Tracks
Mattituck,New York z
Scale:As Shown - /1 1,V// PVM
P.W.Grosser Project No.STR2001 -09/10/2021 `✓ CLIENT DRIVEN SOLUTIONS
CWA Well Field
LEGEND
/ Inlet Dr. 4.0
Groundwater nt ur in ft AMSL NAND 88
Domestic Well Public Supply Well
_ Lot Not Served by SCWA
�.
...
/
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1,
J
,
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r
e
-1.7 Limits of Site
i
excavation Well converted to
irrigation well post
- excavation with
' reduced
pumping
rate
2 1 mpi
i.
a
i
Figure - Excavated SiteiParticle Tracks
Mattituck,New York
Scale:As Shown 41V
P.W.Grosser Project No.STR2001 -09/10/2021 �✓ CLIENT
DRIVEN SOLUTIONS
50
In or
i
LEGEND
r.
v \ ' 4.0
Groundwater Contour in ft AMSL NAVD 88
r �
�.. �
E Domestic Well 6 Pubiic Supply Well �
._
Irl
SCWA
.........., ' �V Lit t Served by
.. 1 P C\4
w
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71
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Figure 16 - Strong's Yacht Center Groundwater Model - Excavated Site with Particle Tracks Tracked Forward
Mattituck,New York
Scale:As Shown -�/ PV4W
P.W.Grosser Project No.STR2001 -09/10/2021 \✓ CLIENT DRIVEN SOLUTIONS
LEGEND?
t
T -
4.0
t
In�LDr
Domestic Well l Public Supply Well
IV
Let Not Served by SCWA
000
.. I
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i
C 7
a R%
...
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.,
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Stron s Yacht Center �
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a
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tat � Ea
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Site
excavation - .73 .
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Figure 16a - Strong's Yacht Center Groundwater Model - Unexcavated Site with Particle Tracks Tracked Forward P%&CC
Mattituck,New York j7 /
Scale:As Shown
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT DRIVEN SOLUTIONS
- � V -
El
ry
(V
41
" Zone Database Information X
I
Zone Database
r
Recharge Property lone Values
stress Pe>7ad Plumber I (Recharge.+ETGnty)
T )dz 9 3 plumber of Zones 1I} 1
rr Strong' Yacht Center I ✓ r ".,.._ ;,
. r,.
i
T 1 0.0085 0 0 0
4) 0.010 0 0 0
w
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0 0 0 0
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Q;5 1 � " 2.
.f? .;.
Limits of Sits �� �����: , Z.,0 4.�
,GP ,t I, ?_-: �„ " 4 t3 JK Cancel met HeIP
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7
1
'yt LEGEND
l
`= �� ✓ �_ - / .0Groundwater Contour in ft AMSL NAVD 88
i f
r
Domestic WeH Public Supply Well
1 f e Lot Not Served by SCWA
1
t y 1 4 J t
Figure 17 - Strong's Yacht Center Groundwater Model - Unexcavated Site with Particle Tracks Tracked Forward and Time postings
Mattituck,New York JGC
Scale:As Shown 4-�P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT DRIVEN SOLUTIONS
N
K 1
tN1
d
} = i Zone Database Information X
-1. ', Zone Database
Recharge Property Zone Values
Stress Period Number 1 (Recharge/ET Only)
3,�
Strong's acht Center Irr hlumberofZones 11} ,ia-
j
i
71
1
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0.010 t 0 0 0
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�} Limits C3fGlt �1: � a� �' x.� ✓Q 10 10 o � .
40
;
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IS
w� �
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Lot Not Served by SCWA
tl
Figure 17a - Strong's Yacht Center Groundwater Model - Excavated Site with Particle Tracks Tracked Forward and Time Postings
Mattituck,New York
Scale:As Shown - /I�
P%&AX
P.W.Grosser Project No.STR2001 -09/10/2021 �✓ CLIENT DRIVEN SOLUT11ONS
attituck C� k nc ntr�,i Lang iii �,a l
1
�ir�iti cif Sits excavation
113
Harbor Hill Outwash }�yvvvv�
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Lloyd'',
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Figure 18 - Strong's Yacht Center Groundwater Model Cross Section View - Saltwater Interface - Chloride Concentrations in Ib/ft3 - Unxcavated Site
Mattituck,New York
Scale:As Shown PVM
CLIENT DRIVEN Lt.1MN
P.W.Grosser Consulting Project No.STR2001 -09/15/2021
LEGEND ✓ ��3t
y tf�it{
s „1
4.0 Groundwater Contour in ft AMSL NAVD 88
Domestic Well l Public Supply Well G.
92
Lot Not Served by �3
,
f
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Limits of Site
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Figure 18a - Strong"s Yacht Center Groundwater Model - Unexcavated Site Chloride Concentrations - Layer 1
Mattituck,New York
Scale:As Shown -
P.W.Grosser Project No.STR2001 -09/10/2021 \✓ CLIENT DRIVEN SOLUTIONS
ti _
--------
-----------------
LEGENC
Ja,t yg 5 � •� ,„ � -
4.O Groundwater ContourIn ft ASS NAVD 8
Cu centratii
i
1
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Lot Not Served by SCWA
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/
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........... I�ti
Figure 18b - Strong's Yacht Center Groundwater Model - Unexcavated Site Chloride Concentrations - Layer 2
Mattituck,New York
Scale:As Shown 41V P%&CC
LI N�DRIVEN SOLUTIONS
P.W.Grosser Project No.STR2001 -09/10t2021 �✓
LEGEND
Yt
Cu centratin
x .
03
Domestic Well I Public Supply Well
Lot Not Served by SCWACV
tx `
t;t tt j
5
i
u
,
el' Stro tg's Yacht Center
I
-
Limits of site
excavation
--------
1 .35
t
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1
Figure 18c - Strong's Yacht Center Groundwater Model - Unexcavated Site Chloride Concentrations - Layer 3
Mattituck,New York /
Scale:As Shown z/�v Pvvrjc
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT
DRIVEN SOLUTIONS
}3tt I r✓ _
M3�b•
LEGEND lti{ ttl F
tS is,>;{ „£zi�✓�,�` �r £t£��✓✓S� a1 s� 4 �. 11�t t �ed.._ � .:- _._
4.0 Groundwater Centaur in ft AMSL_ NAVD 8 � �, 4s✓£4`t1 t t
Cucen
✓eta ,✓ �.>,t,
tratj
Domestic Well l Public Sully Utilel'I
Lot Not Served by SCWA t ���✓✓` �' �✓ t �
i
/ t3 _ _
t � F
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MINSt r ng's Yacht Center (rr
r, £ ✓✓
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Figure 18d - Strong's Yacht Center Groundwater Model - Unexcavated Site Chloride Concentrations - Layer 4
Mattituck,New York
Scale:As Shown 41V PVVW
P.W.Grosser Project No.STR2001 -09/10/2021 V CLIENT DRIVEN SOLUTIONS
Mlattituck Lirr�itS �f Sits �eCav�tit r� Long Island Sound
_ 1 Conc ntratiG7
U
Harbor Hill Outwash 2
t
: Lower Clay
t
1
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Figure - i i - Saltwater Interface - Chloride Concentrations i / 3 - Excavated Site
Mattituck,New York
Scale:As Shown PVW
CLIENT DRIVEN SOLUTIONS
P.W.Grosser Consulting Project No.STR2001 -09/15/2021
LEGEND
... ................
CGn centratiai
4 i / 1 .
rt�r�d�vr Contour in tt�tL � L� � ����}rsz � _
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Domestic WeH 1 P biic Supply Well
.
132
Lot Not Barged by SCWA1 1
.Sol
J
L.
Strong's acht Center
Irr
\ ,
GAT
Limits of Si
excavation
t1 '35
-1.74
1113
Figure " - Excavated Siteide Concentrations - Layer I
Mattituck,New York
Scale:As Shown P%NW
P.W.Grosser Project No.STR2001 -09/10/2021 CLIENT DRIVEN SOLUTIONS
- - - -
LEGEND qM
Ciancentratiai,
�: #5z
4.0
Groundwater Contour Its tt AMSL NAVD 88
js
i � 1
/ 2 ESL
Domestic Well I Public Supply Well
.
92
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t�
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Figure 19b - Strong's Yacht Center Groundwater Model - Excavated Site Chloride Concentrations - Layer 2
Mattituck,New York PVM
Scale:As Shown -
P.W.Grosser Project No.STR2001 -09/1012021 �✓ CLIENT DRIVEN SOLUTIONS
r
am
-----------
LEGEND [ ��'
}
clancentratial
4.0 Groundwater Contour in ft AMSL I` AVD 88 GO
f
Domestic WelJ/ Public Supply Well
i
Lot Not Barged by SCWA
ss}e d
` I G.
Stro g's Yacht Center
kit a Asa j
G.
2
r
s
s
- _
Limits of site
0 35
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sir �
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Figure 19c - Strong's Yacht Center Groundwater Model - Excavated Site Chloride Concentrations - Layer 3
Mattituck,New York /
Scale:As Shown -
PVVW
P.W.Grosser Project No.STR2001 -09/10/2021 \✓ CLIENT DRIVEN S TU N
t
Y
r t
f ; }
3 a
LEGEND
.� --------- ..........................._ -.
4.0 Groundwater Contour in ft AM L C AVD 88
C
Domestic Well d Pu llc Supply Well
Lot Not Served by SCWA l;,tz s,
l
0.32
i �s sit
........
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t7 J
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t
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excavation r mow&
t
LM
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Figure 19d - Strong's Yacht Center Groundwater Model - Excavated Site Chloride Concentrations - Layer 4
Mattituck,New York
Scale:As Shown -
PWW
CLIENT DRIVENTtN P.W.Grosser Project No.STR2001 -09/10/2021 \✓
LEGEND
D
4.4 Groundwater Contour 1n fit AMSL NAVD 88
Inlet Dr
1010
f) \ Domestic Well Pubhc Supply Well
1
✓� Let Not Served by SCWA
V —
CWA Well FIel
\ ✓
a
✓" /' Strong's Yacht Can rT Irr
Limits of Site � ✓ cl�
excavation
-10
r
100 - -
r
' -
v
Figure 20 - Strong"s Yacht Center Groundwater Model - Excavated Site - 16" Sea Level Rise Z4 PVM
Mattituck,New York
Scale:As Shown
P.W.Grosser Project No.STR2001 -09/10/2021 \✓ CLIENT DRIVEN SOLUTIONS