Stewart Air National Guard Base PFOS AND PFOA MITIGATION PLAN Final PFOS/PFOA Interim Mitigation Stewart Air National Guard Base, New York Contract No. W9128F-14-D-0009 Delivery Order: W9128F19F0079 September 2019 Prepared by: US Army Corps of Engineers Omaha District Special Projects Program Management Office With Support From: Bristol Environmental Remediation Services, LLC 720 Corporate Circle, Suite D Golden, CO 80401
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Stewart Air National Guard Base
PFOS AND PFOA MITIGATION PLAN
Final
PFOS/PFOA Interim Mitigation Stewart Air National Guard Base, New York
PFOS/PFOA Mitigation Plan Stewart Air National Guard Base Contract No. W9128F-14-D-0009, DO W9128F19F0079 Bristol Project No. 34190046
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ACRONYMS AND ABBREVIATIONS
AFFF Aqueous Film Forming Foam APP Accident Prevention Plan BWS BERS-Weston Services JVA, LLC CAD Computer Aided Design CFR Code of Federal Regulations CWA Clean Water Act DMR discharge monitoring records EPP Environmental Protection Plan FAA Federal Aviation Administration FAR Federal Acquisition Regulations ft feet GAC granular activated carbon gpm gallons per minute HDPE high density polyethylene kW kilowatt LHA Lifetime Health Advisory MCLs Maximum Contaminate Levels mg/L milligrams per liter NY New York NYDOT New York Department of Transportation NYNJPA New York and New Jersey Port Authority OEC Onion Equipment Company OSHA Occupational Safety & Health Administration PDT Project Delivery Team PFAS per-and polyfluoroalkyl substances PFOA perfluorooctanoic acid PFOS perfluorooctanesulfonic acid PLC programmable logic controller ppt parts per trillion psi pounds per square inch PSIG Pounds per Square Inch Gauge QA/QC Quality Assurance/Quality Control
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QC Quality Control SANGB Stewart Air National Guard Base SSHP Site-Specific Safety and Health Plan SPDES State Pollutant Discharge Elimination System TAA Tennant Alteration Application TWTS Temporary Water Treatment System UPS uninterrupted power supply USACE United States Army Corps of Engineers VFD variable frequency drive
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1.0 INTRODUCTION
1.1 SITE LOCATION AND PROJECT BACKGROUND
BERS-Weston Services JVA, LLC (BWS), under Contract W9128F-14-D-0009 with the
United States Army Corps of Engineers (USACE), is required to provide time-sensitive
response actions for Stewart Air National Guard Base (SANGB), Newburgh, New York (NY)
whose stormwater discharge is contaminated with perfluorooctanesulfonic acid (PFOS) and
perfluorooctanoic acid (PFOA). PFOS and PFOA are two constituents of aqueous film
forming foam (AFFF), that have been detected above the U.S. Environmental Protection
Agency (EPA) drinking water lifetime health advisory (LHA) standard of 70 parts per trillion
(ppt) (individually or combined) in the off-base stormwater discharge into the Recreational
Pond. Flow out of the Recreational Pond is through a weir outfall, which then flows into
Silver Stream, which flows into Moodna Creek and eventually the Hudson River. A
diversionary channel could also direct Silver Stream to Lake Washington, which is the
drinking water reservoir for the City of Newburgh, NY. This diversionary channel was
closed in 2016 when per- and polyfluoroalkyl substances (PFAS) contamination was
detected. This action is being undertaken by SANGB to protect drinking water under the
Clean Water Act (CWA). A site location map is included as Attachment 1.
As part of the response actions under this Contract, BWS is required to develop and
implement interim mitigation measures for the treatment of stormwater runoff by reducing
PFOS/PFOA concentrations to acceptable levels. A Temporary Water Treatment System
(TWTS) will be mobilized to withdraw waters from the Recreational Pond, reduce
PFOS/PFOA, and discharge treated water to the existing pond outfall location.
The TWTS described in this mitigation plan is just one of several initiatives being undertaken by
the Air National Guard (ANG) to mitigate PFAS from being discharged to the Recreational
Pond. Other ANG activities not part of this current project include stormwater drainage
monitoring, sampling and modeling of PFAS contributions into the pond, and collection of data
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that will allow for evaluating long term strategies to mitigate or remediate PFAS from
stormwater discharges.
Stormwater runoff from the SANGB is diverted to the Recreational Pond, located at the
south side of the base via four main storm drains commonly referred to as Outfall’s A, 002,
003, and the 17K outfall. The existing detention pond is approximately 2.5 acres and the
pond depth to the top of sediment is believed to range between 3 to 8.3 feet deep with an
average pond depth of approximately 5.5 feet deep. The Recreational Pond has an average of
approximately 1.8 feet of sediment in the bottom based on 2017 soundings completed by
Aqua Survey, Inc. The detention pond outfall consists of an overflow structure equipped
with a 15’-6” crest width concrete trapezoidal weir that is approximately 7-feet high
measured from the water surface.
Interim mitigation shall include drawing down the dry weather pond level in order to
provide storage in the pond for rain events that exceed a determined runoff quantity. The
stored volume will then be treated and discharged at the existing overflow weir via a new
outfall structure. This Mitigation Plan clarifies proposed implementation methods for the
interim response actions.
Services required to successfully execute this task order will include but are not limited to:
development and installation of the approved PFOA & PFOS mitigation system, including an
interim TWTS; complete with needed ancillary infrastructure required for start-up,
operation, maintenance, and monitoring of the system.
Mitigation measures shall result in the discharge of treated water that is below the 70 ppt
lifetime health advisory (LHA) standard, in drinking water, for PFOS and PFOA
(individually or combined). Discharge water shall also meet local and state standards and be
in accordance with the CWA, and the conditions set forth in the existing State Pollutant
Discharge Elimination System (SPDES) Permit as it relates to the water quality requirements.
Concurrently with implementation of this interim mitigation, the State of New York is
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working on establishing more stringent Maximum Contaminant Levels (MCLs) for PFOS and
PFOA compounds at 10 ppt respectively. Although the current system has not been
Contracted or designed for these future standards, the TWTS should have the ability to
comply with the proposed lower state standards for PFOS and PFOA.
1.2 STORMWATER QUALITY AND FLOW DATA
Available discharge monitoring records (DMRs) including historical flow and water quality
data for stormwater overflowing the outfall structure are included in Attachment 2. This
outfall location is referred to as Outfall 010. There is limited water quality data available for
PFAS at Outfall 010. However the available data confirms the presence of PFAS compounds
at the outfall between 300 and 700 ppt, which exceed the 70 ppt LHA. BWS collected
additional stormwater quality samples in early April 2019 for PFAS, along with SPDES water
quality parameters and other wet chemistry parameters that will help confirm the interim
TWTS design requirements. These samples were collected at the existing Outfall 010 weir
structure as well as Outfall 002 entering the pond. These locations were selected to provide
additional water quality data that can be used for TWTS design purposes and verify the
limited available data set. The BWS sample results are included and summarized in
Attachment 3. As part of other concurrent initiatives being undertaken by SANGB,
additional sampling and monitoring is being performed by SANGB to further define the
concentrations and sources of PFAS contamination throughout the overall drainage system
including the Recreational Pond and outfall 010.
1.3 PROJECT PLANNING AND REPORTS
In addition to this Mitigation Plan, the following plans and planning activities have been or
are planned to be performed:
• Right of Entry (ROE) access agreements will be obtained for access to the Recreational Pond for both planning and construction purposes.
• BWS has prepared and submitted the following plans prior to mobilization: Uniform Federal Policy Quality Assurance Project Plan (UFP-QAPP), Contractor Quality
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Control Plan (CQCP), Accident Prevention Plan (APP)/Site-Specific Health and Safety Plan (SSHP), Environmental Protection Plan (EPP), Waste Handling/Management Plan, Community Involvement Plan, and a Restoration Advisory Committee Development Plan prior to mobilization.
• The TWTS and existing outfall structure are located on land owned by the New York Department of Transportation (NYDOT) and leased to New York and New Jersey Port Authority (NYNJPA). BWS and the Project Delivery Team (PDT) will coordinate the project activities with the NYNJPA and SANGB as the property tenant. The BWS team has submitted a Tenant Alteration Application (TAA) for implementation of the TWTS to the NYNJPA for review and approval. This TAA was prepared by a licensed engineer in the State of New York, referred to as the Engineer of Record (EOR) and submitted to the NYNJPA for approval. It is anticipated that TAA approval by NYNJPA will be provided in advance of mobilization.
• BWS has prepared and submitted a Work Plan for this project. The Work Plan further describes the procedures and work required to implement construction and operation of the TWTS.
• A project schedule will be submitted and updated weekly during planning and construction.
• Prior to TWTS operation, the following additional plans will be prepared and submitted for approval: Weatherization Plan, Startup and Maintenance Plan, Operations and Maintenance (O&M) Manual and a Transition Plan,
• BWS is procuring required site supplies and subcontractor services needed to implement this project.
• A submittal register and project submittals are on-going and being prepared and approved for all materials incorporated into the work.
• BWS will, set-up a field office, and conduct a Project Kickoff meeting with all PDT members.
• BWS will monitor the effectiveness of the stormwater interception and treatment measures to determine if additional mitigation measures are needed.
• A completion report will be prepared at the end of the project.
1.4 PROCUREMENT
Procurement of the following equipment and subcontractors will be necessary to implement
this project:
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• Site facilities (trailer, restroom, hand wash station, site security, and temporary power);
• Private underground utility locating survey services for all areas to be disturbed;
• Civil works services including; erosion and sediment controls installation, gravel pad construction, access road improvements, utility trenching/backfill, TWTS equipment rigging and installation/testing of interconnecting piping.;
• Pre-manufactured TWTS treatment system;
• Temporary outfall structure installed at the existing Recreation Pond overflow weir;
• Site power connection to the SANGB electrical system;
• Electrical services including 3-phase transformer, electrical distribution, and interconnecting communications and
• Operations subcontractor services during operations and maintenance (O&M).
All procurement activities are performed and administered in accordance with the Service
Contract Act, Federal Acquisition Regulations (FAR), and the Defense Federal Acquisition
Regulations Supplement (DFARS).
1.5 MOBILIZATION ACTIVITIES
Mobilization will commence after Prior to initiating any subsurface work on any site, Dig
Safely of NY will be contacted to mark-out utilities for each applicable work area. BWS will
also retain an independent underground utility locating firm utilizing ground penetrating
radar equipment to locate on-site utilities in disturbed areas. Mobilization/setup includes set-
up of a temporary job trailer; sanitary facilities and a portable generator for temporary power
to job trailer.
Placement of the TWTS enclosures will require use of a crane. BWS has received a Federal
operation of a temporary 120 ton crane with a maximum height of 100 feet above ground
level at the Recreation pond area. BWS and the Crane operator will perform the required
notifications prior to mobilization and when the crane is dismantled in accordance with the
determination.
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1.6 HEALTH AND SAFETY
An SSHP and APP has been prepared and approved for this project. The SSHP and APP
contains health and safety criteria, procedures, and work practices sufficient to protect on-
site personnel and the environment.
BWS will utilize qualified personnel, including a field dedicated Site Safety and Health
Officer (SSHO) to oversee the development and implementation of required safety and
health documents and all activities will comply with the following:
• Federal Acquisition Regulation, F.A.R. Clause 52.236 13: Accident Prevention.
• U.S. Army Corps of Engineers (USACE), Safety and Health Requirements Manual, EM 385 1 1 (Nov 2014).
• Occupational Safety & Health Administration (OSHA) Construction Industry Standards, Title 29 Code of Federal Regulations Chapter 1926 (29 CFR 1926), and General Industry Standards, 29 CFR 1910.
• Other applicable Federal, State, and local safety and health requirements.
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2.0 PROPOSED REDEVELOPMENT
2.1 TEMPORARY WATER TREATMENT SYSTEM
BWS has procured and will install, test, and make fully operational Pre-manufactured
containerized mitigation systems for temporary treatment of stormwater for PFOS/PFOA
prior to discharge from the Recreational Pond to include pretreatment (screening/filtration),
granular activated carbon (GAC), followed by PFAS adsorption using ion exchange media.
The TWTS will be located in the open area south east of the existing overflow structure at
the approximate location shown on Figure 1.
The TWTS will be pre-engineered to treat water up to 500 gallons per minute (gpm). The
TWTS is to be housed in three (3) Conex enclosures to provide protection from weather and
freezing temperatures. The first Conex will enclose the pretreatment filtration system and
controls. The other two enclosures will house parallel trains of one Pre-treatment GAC
vessel and two primary treatment of ion exchange media vessels arranged in a lead/lag series
configuration. The treatment system conceptual design is shown on Figure 2. The TWTS
shall be engineered and constructed by Onion Equipment Company (OEC) who
manufactures pre-engineered (modular) treatment equipment and experienced with PFAS
water treatment for surface water. OEC will engineer and manufacture the system and
support start-up and commissioning of the installed treatment system.
The TWTS Conex enclosures will be installed behind the Recreational Pond berm and
southeast of the weir structure outfall as depicted in Figure 1. To protect against syphoning
of Recreational Pond, a vented high point will be provided in the effluent discharge line
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Figure 1 TWTS System Location
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Figure 2 TWTS Conceptual Diagram
2.1.1 Recreational Pond Water Intake and TWTS Feed Pump
Water will be drawn from the Recreational Pond via a submerged suction pump, which will
be mounted to a floating or temporary dock in a portion of the pond selected to maximize
usable volume and minimize exposure to damage and erosion. The intake will be submerged
and screened to prevent entry of floating debris, but off the bottom to minimize entrainment
of sediments. The screen will be sized to have a low intake velocity to reduce the likelihood
of collecting debris and adequately protect the pump. The screen will be accessible from the
floating or fixed dock for maintenance and cleaning if necessary. Water will be transferred
from the pump via flexible suction hose and high density polyethylene (HDPE) pipe to the
TWTS. The above ground line between the pond and the enclosure will be protected from
freezing. The pump will supply up to five-hundred (500) gpm to the TWTS. The pump will
be driven by a variable frequency drive (VFD) to maintain a flow processing rate under
variable TWTS back pressure. The pump will be controlled on/off by maintaining a target
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level in the pond that is below the overflow level. A level transducer will be installed in the
pond to monitor and document the water level during system operation and control the
TWTS.
2.1.2 Pre-Treatment Enclosure
The first Conex enclosure will house the pre-treatment system. Pre-treatment is required to
remove solids that may enter the TWTS and prematurely foul the treatment media. The pre-
treatment system will consist of 1 centrifugal separator and bag filtration. The centrifugal
separator will be a carbon steel separator manufactured by Rosedale as shown in Figure 3.
The separator shall be designed for 500 gpm with less than 15 pounds per square inch (psi)
pressure drop. The separator shall remove solids contained in the pond water via centrifugal
action. The separation systems have a timed solenoid valve that opens and flushes out the
accumulated solids automatically. Flush water will be returned to the Recreational Pond.
Figure 3 Pretreatment Separator
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Following the separator, the water will enter a second filtration system. The filtration system
consists of Rosedale multi-bag, two stage, No. 2 size bag filtration system constructed of
carbon steel. Each stage will have 6 filters in order to process 500 gallons per minute. The
first stage will have coarse bag filters (approximately 25 micron). The second stage will have
fine bag filters (approximately 10 micron). Figure 4 shows a Rosedale multiple bag filter
housing that could serve as either the coarse or fine filtration. The bag filter housings will
have pressure gauges and pressure transmitters located on the inlets and outlets, to
continuously monitor operating pressure during system operation. The pressure transmitter
will continuously document differential pressure at the control system and notify operations
staff when high differential pressure occurs indicating the bags will require change out.
Figure 4 Multi Bag Filter Skid
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2.1.3 Treatment System Enclosures
After pre-treatment, process water will be divided into two streams and process forward flow
will be sent to two identical and independent treatment system enclosures installed in
parallel. Each independent treatment system will be configured with two (2) total treatment
trains housed in a single Conex enclosure for a total of four (4) treatment trains running in
parallel within two (2) Conex enclosures.
Each treatment train shall contain GAC pretreatment, primary ion exchange and polishing
ion exchange. The GAC pretreatment system will be comprised of two (2) GAC vessels,
running in parallel, for the removal of organic compounds that could impact the long term
performance of the ion exchange media for PFOS/PFOA removal. Each GAC vessel will be
approximately five (5) foot diameter, and contain approximately 2,500 lbs. of carbon.
Between the two (2) Conex enclosures there will be a total of four (4) GAC treatment vessels,
each containing approximately 2,500 pounds of GAC media. The GAC vessels will initially be
filled with 8x30 Calgon Filtrasorb 300 granular activated carbon media. When GAC is
exhausted and requires to be replaced during system operation, it will be profiled and
properly disposed at a landfill following incineration. Each GAC vessel will have an air vent,
drain and inlet/outlet valves, sample ports and pressure gauges in order to monitor their
performance and control their operation. Provisions will be made to allow for manually
backwashing the vessels if premature fouling occurs. If backwashing is performed backwash
water would be returned to the Recreational Pond away from the pump intake and in a
manner that does not disturb the pond or cause erosion.
In each enclosure after passing through the two GAC pretreatment vessels, the flow will
then be directed into the primary ion-exchange resin treatment vessels (two located within
each Conex enclosure) followed by the polishing ion exchange resin treatment vessels (two
located within each Conex enclosure) for the removal of PFOS/PFOA from the water. Each
vessel will contain approximately 70 cubic feet of Purolite® PFA694 ion-exchange media (or
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equal). The eight ion exchange vessels will contain a total media volume of 560 cubic feet.
Four (4) ion-exchange treatment vessels will be installed in each parallel Conex enclosure.
Each vessel will be approximately five (5) foot diameter and have six (6) foot sidewalls. With
this configuration, there will be four (4) total treatment trains running in parallel (two
within each Conex enclosure). A manifold or flexible hoses with quick disconnects will be
provided to allow bypass of the primary vessels when they are exhausted and swapping the
primary and polishing vessels when media is replaced. The manifold will be equipped with
pressure gauges and sample ports to allow for monitoring the performance of each skid. Each
individual ion exchange vessel will have isolation valves to be able to service each unit
independently. Each ion exchange vessel will have an air vent, drain and inlet/outlet valves,
sample ports and pressure gauges in order to monitor their performance and control their
operation. During system operation when ion exchange media becomes exhausted and
requires to be replaced, it will be profiled and properly disposed at a landfill following
incineration.
The treated water will be combined and will exit both Conex treatment enclosures via a
single effluent line. The two effluent lines (one from each enclosure) will then be combined
and a single effluent flow meter will be installed to monitor the overall flow rate (gpm) and
total gallons treated. Discharge control valves are installed downstream of the flow meter
that will divert treated effluent either back to the Recreational pond (e.g. recycle) or direct
treated water adjacent to the outfall structure located adjacent to the overflow weir. Each
gravity discharge line will have a constructed high point and be vented.
2.1.4 General TWTS System Requirements and Controls
The treatment systems will contain sample ports on the influent (raw water), after each
pretreatment stage, and after each GAC and each ion exchange media stage as well as the
combined treated effluent. Intra-process monitoring is important to evaluate each process
stage and confirm breakthrough of PFOS/PFOA on the primary ion exchange media. Once
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breakthrough of PFOS/PFOA are detected on the primary ion exchange at concentrations
exceeding one-half the HAL (35 ppt) the resin in the primary vessels will be replaced.
Following media replacement, the polishing vessels will then become the primary vessels and
the newly serviced primary vessels will become the polishing vessels. Water samples will be
collected approximately on a weekly basis during the first month and monthly thereafter.
More frequent sampling will be performed if raw water quality changes or observed or if
treatment system performance warrants more frequent monitoring. The sampling schedule
will be adjusted appropriately to ensure that ion exchange media change outs are conducted
in advance of PFAS breakthrough in the polishing effluent to ensure that the systems are
serviced in a timely manner to meet treatment objectives.
Pressure gauges and pressure transducers will be installed on the influent and effluent of
each treatment stage to monitor for pressure differentials, which could indicate the need for
system servicing or backwashing. The treatment system will have automated controls that
will allow local monitoring of system performance from a single location.
The controls will include a programmable logic controller (PLC) with a touch screen panel,
similar to one shown in Figure 5. A cellular modem with a static IP address will be installed
to allow for remote access and monitoring of the system on computers and smart phones.
Access will be password protected and secure. The control system will monitor; equipment
run status, system flows, system pressures, pond level, and alarms. If an alarm occurs the
system will be equipped with an alarm dialer or alarm management system that can be
custom configured to notify operations personnel of an alarm. Operations personnel will be
available to address any operations and maintenance concerns, 24 hours/day, 7 days a week.
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Figure 5 Typical Control Panel
2.1.5 Conex Enclosures
Each Conex enclosure will be approximately eight (8) feet wide by forty (40) feet long by
nine (9) feet high. The enclosure will be insulated and will have electric heaters to protect
the systems from freezing. The enclosures will be constructed with interior lighting,
ventilation, personnel doors, fire extinguishers and double doors to allow for access to the
systems for servicing. These containers are not considered “confined space” under OSHA.
The systems and controls will come pre-fabricated within each Conex enclosure, minimizing
on-site time required for the erection of the systems and start-up.
The Conex enclosures will be installed on a level, gravel laydown pad that will be
constructed prior to delivery to the site. The Conex enclosure will arrive at the site via
flatbed truck and will be offloaded at the site using a crane. Interconnecting piping and
electrical for the treatment systems will then be constructed once the Conex enclosures are
situated on the laydown pad. A Conex enclosure similar to the enclosures envisioned at
SANGB is shown in Figure 6.
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Figure 6 Typical Conex Enclosed TWTS
2.1.6 TWTS Electrical Service
Because of the remote location of the Recreational Pond and TWTS, no local, secondary
electrical power is readily available. Site reconnaissance has confirmed that high voltage
power (13,200 volts) is available at a nearby substation operated by SANGB. A temporary
high voltage electrical service will be installed through a combination of new and existing
spare underground raceways between the substation and the TWTS. At the TWTS area a
300 kVA, 3 phase, 460 volt, pad mounted transformer will be installed. The electrical service
will have a main fused service switch, a manual transfer switch, and all necessary secondary
distribution equipment and low voltage transformers to power the supply pump, equipment,
heat tracing, heaters, lighting, instrumentation and system controls needed to operate and
maintain the TWTS. The manual transfer switch will allow for connection of a temporary
generator to power the TWTS if an extended power outage occurs.
2.1.7 Interconnecting Process Piping
As discussed herein the TWTS will be mobilized as pre-engineered fabricated skids to reduce
construction field effort. Field fabrication and assembly of interconnecting process piping
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will be required. Interconnecting piping will be comprised of PVC Pipe, HDPE Pipe, and
Suction Rated Flexible Hose. All exterior piping not subject to submergence or fully
drainable will also be insulated and heat traced for freeze protection.
2.1.8 TWTS Effluent Outfall The TWTS will be able to discharge treated water to both the existing outfall and recirculate
treated effluent back to the Recreational Pond via a central return line. The treated effluent
will normally be diverted to the existing overflow weir. The 8-inch HDPE line will be a
gravity return. It will discharge treated effluent to a temporary outfall structure situated
directly upstream of the existing overflow weir. Dam Safety flow curves were prepared by
BWS and submitted to NYSDEC to document estimated hydraulic impacts to the existing
overflow weir as a result of the temporarily outfall structure. These calculations are included
in Attachment 4. NYSDEC reviewed the temporary outfall drawings and calculations and
confirmed that the proposed outfall structure hydraulic impact is within acceptable limits
and no dam safety permit would be required. The temporary outfall structure will be a pre-
cast concrete chamber, equipped with an overflow installed at the same elevation as the
existing weir. The outfall structure will dissipate energy before flowing over the existing
weir. A 3-foot wide overflow spill way will be used to convey treated water to the existing
outfall weir. The temporary structure will be designed to resist buoyant forces.
2.1.9 Weather Protection Plan
A separate Weather Protection Plan will be submitted prior to mobilization. In general the
treatment systems will be housed in an insulated/heated enclosure, designed to protect the
system from freezing. Process piping (e.g., influent suction line, effluent piping and,
interconnecting Conex enclosure process lines) that are external from the enclosures shall be
placed on ground surface, insulated and heat traced to protect against freezing. The gravity
effluent lines will be sloped to fully drain so they do not require freeze protection. If a loss
of power occurs, the PLC based control system shall be provided with an uninterruptable
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power supply (UPS) and configured to notify operations staff of a loss of power condition. In
addition, each enclosure should be equipped with a temperature transmitter and
automatically notify staff of a potential freezing condition. If an extended power outage
occurs during cold weather operations staff will need to either drain the system, provide
temporary heat and power to protect the system from freezing or mobilize a generator to
temporarily power the system. Additional specific weather protection details will be
submitted in a follow-up submittal.
2.1.10 TWTS System Commissioning and Start-up
After the TWTS is constructed, the treatment system be commissioned and started up in
accordance with the individual equipment O&M manuals, and the TWTS system supplier
O&M manual.
Following system commissioning, initial samples will be collected from the influent, GAC
pretreatment effluent, primary ion exchange media effluent, and overall effluent and sent to
the approved analytical laboratory for analysis of PFOS/PFOA and other applicable SPDES
parameters. After confirmation that effluent quality is acceptable, effluent will be diverted to
its normal discharge at the new outfall structure and over the existing overflow weir.
Following startup, sampling will be performed as needed to monitor system performance.
2.2 RECREATIONAL POND STORAGE
In order to reduce discharge of untreated stormwater off site, the existing Recreational Pond
will be lowered approximately 2-feet to create approximately 1.86 million gallons of storage
capacity. This stored water will allow treatment and eventual discharge as described in
Section 2.1. As previously indicated the existing Recreational Pond is approximately 2.5 acres
and the pond depth to the top of sediment is believed to range between 3 to 8.3 feet deep
with an average pond depth of approximately 5.5 feet deep. The Recreational Pond has an
average of approximately 1.8 feet of sediment in the bottom based on 2017 soundings
completed by Aqua Survey, Inc.
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Stormwater storage will be created by operating the TWTS and lowering the water level in
the pond. See the Stormwater Review Technical Memorandum issued 17 June 2019 included
as Attachment 5 for additional information. This storage approach does not require
modifications to the existing Recreational Pond outfall structure, which would take
significant time to evaluate and implement modifications that allow for raising the pond
level and increasing storage.
If the volume created by lowering the pond water level were determined to be insufficient or
if the estimated volumes are impacted by either increased groundwater infiltration or
sediments in the bottom of the pond, modifications to the outfall structure may be required
to increase storage by increasing the weir elevation. The modifications to the pond outfall
structure (if required) would raise the wet weather pool elevation while maintaining the dry
weather pool elevation through pumping of stored water to the TWTS. In order to evaluate
the optimal storage capacity and ensure stability of the stormwater system, a complete
geotechnical investigation and modeling of the facility-wide and of site stormwater
conveyance system would be necessary. This effort would be completed as part of the
CERCLA process and implemented, if necessary, as part of the final selected remedy. All
future modifications to the outfall structure will be coordinated by the NGB with the NY
DOT and NYNJPA, the lessee and owner of the outfall, and the NYDEC who regulates the
outfall structure.
2.2.1 Stormwater Condition Assessment
Limited stormwater condition assessments have been performed based on the minimal
stormwater flow dataset and information available for the existing stormwater system to
determine statistical returns and anticipated performance metrics for the proposed TWTS.
Since the weir outfall structure is not being substantially modified as part of the interim
mitigation a more robust analysis is not necessary at this time to support TWTS
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September 2019 21 Final
implementation. However, data collection is on-going and a more in depth analysis will be
prepared as part of the CERCLA process to determine the appropriate final remedy.
The stormwater condition assessment will be a critical component to determining the final
remedy and will determine the feasibility of temporarily retaining stormwater in the
Recreational Pond above the existing dry water elevation by constraining flow through the
existing outlet structure. Weir stability, earthen embankment stability, and pond area
stability all depend on the results and findings of the stormwater condition, and require
supporting information from a geotechnical investigation, structural investigation, and
engineering assessment to fully quantify the ability to control the system utilizing structural
modifications to the outlet structure.
The stormwater condition assessment will additionally determine up to what storm event, or
series of events, will be able to be retained in the pond without overflow of the outlet
structure. It will consider continuous withdraw from the pond to the TWTS to a specified
maximum drawdown elevation, as well as event based stormwater runoff in determining
inflow into the pond and staged elevations if modifications to the weir are determined to be
necessary.
2.2.2 Outlet Structure
The existing outlet structure consists of a trapezoidal shaped broad crested weir built into an
earthen berm with wing walls on both the upstream and downstream sides. Dry weather
flow through the weir is continuous due to suspected groundwater influence and the
combined flow from the four outfalls previously described. It is reported that these water
sources provide a near constant flow depth of less than one inch to flow over the structure as
shown in Figure 7. A rock lined channel is downstream of the outlet structure as shown in
Figure 8. As discussed, BWS will install a temporary outfall structure just upstream of the
weir. The proposed temporary outfall structure will be a pre-cast concrete chamber,
equipped with an overflow installed at the same elevation as the existing weir. The outfall
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structure will dissipate energy before flowing over the existing weir. A 3-foot wide overflow
spill way will be used to convey treated water to the existing outfall weir.
Figure 7 Existing Outlet Structure (Upstream)
Figure 8 Downstream of Outlet Structure
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September 2019 23 Final
2.2.3 Other Activities
As previously discussed, the TWTS is just one of several initiatives being undertaken by the Air
National Guard (ANG) to mitigate PFAS from being discharged to the Recreational Pond. Other
ANG activities not part of this current project include stormwater drainage monitoring, sampling
and modeling of PFAS contributions into the pond, and collection of data that will allow for
evaluating long term strategies to mitigate or remediate PFAS from stormwater discharges.
The results of these studies will likely be completed prior to considering potential, modifications
such as drainage infrastructure modifications, or outfall structure modifications that could
be considered to increase storage volume by raising the water level. Any further
modifications would be evaluating through the CERCLA process.
This TWTS is being installed as an interim mitigation system, in order to reduce the
contamination level in the recreational pond outfall, while the site proceeds through the
CERCLA process. The site is currently at the Site Investigation (SI) phase within the
CERCLA process. The next phase in the CERCLA process is the remedial investigation phase.
During that phase a complete CSM and risk assessment are completed. Following the
CERLCA process a feasibility study, in which remedy alternative are evaluated for
consideration, will be undertaken. After remedy evaluation, a final remedy is chosen and
will be implemented as, required under the CERCLA process, to achieve New York state
and/or federal cleanup standards once those standards are properly promulgated.
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3.0 AREAS OF ENVIRONMENTAL CONCERN
The only known or suspected contamination with the work area is the PFOS and PFOA
contaminants contained in the stormwater and groundwater. The presence of this
contamination is not expected to impact construction activities.
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4.0 PERMITS
The proposed work will include electrical construction, installation of TWTS, modifications
to the existing Recreational Pond outlet structure, and earth disturbance activities associated
with establishing site access and construction of the proposed features.
The NYNJPA TAA process will require design and application submittal from SANGB and a
licensed engineer in the State of New York.
4.1 ELECTRICAL
All work associated with the electrical interconnection will follow all applicable codes and
regulations, however, no permits are expected to be obtained to complete the electrical
connection. Work will be performed by licensed electricians familiar with the type of work.
4.2 SPDES PERMIT
The ANG currently holds an expired discharge permit and is coordinating the continued use
of this SPDES Permit, with the New York State Department of Environmental Conservation
(NYSDEC). The system will be operated in and monitored in accordance with the
requirements set forth in the permit. In addition to the existing SPDES permit, PFAS
compounds will be monitored as discussed in Section 2.1 of this Plan.
4.3 STORMWATER AND EARTH DISTURBANCE
Prior to excavation or earth disturbance work Dig Safely New York will be contacted to
acquire state required utility clearances. Additionally, it is expected SANGB and NYNJPA
will require dig permitting to perform all earth disturbance activities.
Although a separate Stormwater Pollution Prevention Plan and SPDES permit for discharges
related to construction activities are not required for construction sites disturbing less than
one acre, an Environmental Protection Plan (EPP) will be prepared to depict the locations
and purpose of erosion and sediment control devices as well as depict the construction
activities and site development plan.
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5.0 SITE MANAGEMENT ACTIVITIES
5.1 ENVIRONMENTAL PROTECTION PLAN
The EPP will be implemented by BWS personnel and involve the installation of a stabilized
construction entrance, silt fence, and disturbance area mulch and seed. Inspection of the site
will be completed monthly and after every significant rain event. A log of site inspections,
findings, and corrective actions will be kept on site.
5.2 SPILL CONTINGENCY PLAN
The nature of the work includes the potential for the spilling of small quantities of
construction equipment related fluids and TWTS operational fluids. BWS on site personnel
and contractors will be trained in the response for construction and TWTS operation related
spills and maintain adequate spill kits containing booms, absorbent pads, and containment on
site at all times. Spills will be recorded and reported in accordance with Federal, State, and
Local requirements. A detailed spill control plan is provided in the EPP.
5.3 MANAGEMENT OF EXCAVATED SOILS
Soils will only be excavated while installing the electrical conduit to the TWTS. No
contaminated soils are expected to be encountered and no off-site disposal of soils will be
performed. Any excess soils will be placed below the TWTS gravel pad in support of leveling
off that area.
Electrical Service raceways will be bedded in sand. No trenching is anticipated to be greater
than 4-feet deep. However, if deeper trenching was required, workers will not enter an
unsupported trench deeper than 4 feet and all other applicable OSHA and HASP
requirements will be maintained.
5.4 DEWATERING
Due to the shallow groundwater condition expected at the site, dewatering of the trench
excavations is anticipated. Excavation dewatering fluids will be directed to the Recreational
PFOS/PFOA Mitigation Plan Stewart Air National Guard Base Contract No. W9128F-14-D-0009, DO W9128F19F0079 Bristol Project No. 34190046
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Pond after passing through a sedimentation device such as a filter bag or settling tank to
remove any fines or silts and discharged to the Recreational Pond in a manner that will not
cause erosion or disturb the pond sediments.
5.5 DUST CONTROL
Dust will be policed on site by maintaining stable, dust free work surfaces such as gravel pads
and adding erosion controls to areas as soon as earth disturbances are complete.
5.6 AIR MONITORING
No air monitoring is required for this mitigation activity.
5.7 SECURITY
The TWTS location is installed in a secure area but in a remote location. Access to the job
site will be controlled with locked perimeter entry gates. All TWTS Conex enclosures are
lockable and secure. No additional local security fencing or security measures are anticipated.
However, additional temporary fencing or video surveillance around the TWTS enclosures
could be provided if deemed necessary following construction.
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6.0 TRAINING PROCEDURES
The TWTS Equipment Supplier (Onion Equipment Company, Inc.) is responsible for
leadings commissioning, start-up and training of the Pre-engineered TWTS. BWS personnel
will assist with commissioning, start-up and have hands-on training on system operations
and provide initial operation of the system. BWS will also perform all required system
monitoring as part of the Start-up and operations.
Hazard communication and documentation will be provided in accordance with Federal,
State, and Local requirements. All personnel entering the work areas will be provided with
site specific training and hazard communication.
Upon turnover of the TWTS, BWS will provide training to the future TWTS operator.
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7.0 DOCUMENTATION AND REPORTING
A Completion Report will be prepared for the facility following completion of the final
maintenance period at that facility. The final Completion Report will contain: an executive
summary, a summary for completed work, schedule, a signed or certified statement by the
contractor that the system complied with all relevant standards during the project execution,
as-builts, warranties, certifications, testing, samples and analyses results, validation, and
points of contact for completed work.
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September 2019 35 Final
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ATTACHMENT 1
Site Location Map
ATTACHMENT 2
Outfall 010 – Stormwater Quality and Flow Data from DMR Records
Attachment 2 - Outfall 010 Storm water Quality and Flow Data
1 of 1
Month 2016 2017 2018January No Data 3,570,320 4,865,070 February 1,898,560 No Data No DataMarch 1,769,890 1,481,170 10,659,100 April 1,808,240 6,001,870 9,587,740 May 6,906,790 5,405,350 No DataJune No Data 5,580,890 4,696,920 July 303,598 1,411,670 3,801,720 August No Data No Data No DataSeptember 616,100 No Data 6,553,550 October 46,115 3,538,927 No DataNovember 2,191,550 No Data 4,348,690 December 1,151,190 No Data 6,139,710 Minimum 46,115 1,411,670 3,801,720 Average 1,854,670 3,855,742 6,331,563 Maximum 6,906,790 6,001,870 10,659,100 1Flow Data source - Flow Data & Outfall 010 DMR Records in PWS Attachment G
3Sample result source - Wood Environment & Infrastructure Services, Inc. Abbreviationsppt - Parts per Trillion mg/L - milligrams per liter SU - standard unit
TSS 1.79 J mg/LT. Alkalinity 164 mg/L Note: Current Health Advisory is 70 parts per trillion for PFOA/PFOS Bicarbonate Alk. 164 mg/L Individually or Combined.Carbonate Alk. 4.0 U mg/LBOD 3.05 mg/LO/G HEM 4.0 U mg/LBTEX No Detections NASVOCS No Detections NAGlycols No Detections NAN as No3 0.090 U mg/LP as PO4 0.30 U mg/LTOC 2.9 mg/L
BOD - Biochemical Oxygen DemandBTEX - Benzene, toluene, ethylebenzene and xylenes mg/L - milligrams per liter or parts per millionng/L - nanograms per liter or parts per trillionNO3 - NitratePO4 - PhospateSVOC - Semi-volatile Organic CompoundsTOC - Total Organic CarbonTSS - total suspended solidsA full list of SVOCs and glyclols is available on request
SANG-EFF010-04042019
Stewart ANG Sample Results
Sample Date 04/04/2019
SANG-RPOND-04042019
ATTACHMENT 4
Recreation Pond Outfall Stage Discharge Curves
23 August 2019
CALCULATION COVER SHEET
PROJECT: Stewart ANGB
WORK ORDER NO. 15254.002.037.0003
CALC NO. 1
SHEET 1 of_7__
SUBJECT: Recreation Pond – Stage Discharge Curves
DISCIPLINE (Civil, Mech. Process, Elect.): Civil
PREPARED BY: H. Nathanson DATE:08/20/2019
CALCULATION STATUS ISSUED FOR REVIEW
FINAL
CONFIRMED
SUPERCEDED
VOIDED
COMPUTER PROGRAMS USED:
Yes No DESCRIPTION/VERSION: Microsoft Excel 2013
REFERENCE SPECIFICATIONS:
REFERENCE DRAWINGS:
SOURCES OF DATA: 1. HydroCAD Software Solutions LLC. HydroCAD Stormwater Modeling System: Owner’s Manual Version 10. HydroCAD
Software Solutions LLC, 2011. 2. Weston Solutions, Inc. (August 12, 2019). Temporary Water Treatment System (TWTS) Outfall Alternatives.
SUMMARY OF RESULTS: Weston Solutions, Inc. (WESTON) performed an analysis to determine the hydraulic impacts associated with placement of a precast outfall structure against the existing weir in Recreation Pond, to facilitate a Temporary Water Treatment System (TWTS). The precast outfall would behave as a six inch (6”) tall, five foot (5’) wide obstruction on the weir crest. WESTON’S analysis of the hydraulic impacts associated with partially obstructing the existing weir in Recreation Pond indicated that the restriction will increase the stage height to achieve the same discharge flowrate as that over the unrestricted weir. WESTON estimates that the restricted weir will have an increased stage height (head) over the unrestricted weir of approximately three to four inches (3 to 4”), dependent on actual flow. For example, at a discharge rate of 500 CFS, the TWTS restricted weir indicates an increased stage height (head) over the weir of approximately three-and-a-half inches (3.5”). Based on limited available flow data, weir flows have peaked at approximately 400 CFS in response to a 1.69" rain event, with a peak precipitation rate of 1.1 in/hr. WESTON’S calculations estimate the unrestricted weir capacity is in excess of 900 CFS with a maximum height of six feet (6’) with one foot (1’) of freeboard. Based on the calculated capacity compared to the available storm response data, the increase in stage height (e.g. approximately 4”) is expected to have de minimus impacts on the performance and safety of the existing weir structure. Please note that WESTON has not been provided design data for the existing weir, and it should it be made available, WESTON may utilize this data to further evaluate the findings.
RECORD OF REVISIONS NO. REASON FOR REVISION TOTAL NO.
OF SHEETS LAST SHEET
NO. BY CHECKED APPROVED/
ACCEPTED DATE
0 Issued for Review 7 HN CS AB 8/20/19 1 Response to Comments 7 HN CS AB 8/23/19
SHEET 2 OF 7 _
CLIENT/SUBJECT Stewart ANGB W.O. NO 15254.002.037 .
PREPARED BY H. Nathanson DEPT 2118 DATE 8/19/2019 . APPROVED BY
MATH CHECK BY C. Sembera DEPT 2118 DATE 8/19/2019 .
METHOD REV. BY A. Brown DEPT 2118 DATE 8/20/2019 .DEPT_ DATE_
File Name: 2-Stewart_ANGB_Rec_Pond_Stage Discharge Curve.docx Print date: 08/23/19 11:19 AM
For the unrestricted weir, total flow is calculated using:
𝑄𝑄𝑉𝑉1 =12
(0.593) �8
15tan
1.572 � (𝐻𝐻5 2⁄ )�2(32.3)
𝑄𝑄𝑅𝑅1 = (2.95)(15.5′)𝐻𝐻32�
𝑄𝑄𝑇𝑇 = 2𝑄𝑄𝑉𝑉1 + 𝑄𝑄𝑅𝑅1
For the TWTS restricted weir, total flow is calculated using:
𝑄𝑄𝑉𝑉1 =12
(0.593) �8
15tan
1.572 � (𝐻𝐻5 2⁄ )�2(32.3)
𝑄𝑄𝑅𝑅1 = (2.95)(15.5′ − 5′)𝐻𝐻32�
𝑄𝑄𝑉𝑉2 = 12
(0.593) � 815
tan 1.572� (𝐻𝐻 − 0.5)5 2⁄ �2(32.3) for values of H above six inches (6”)1
𝑄𝑄𝑅𝑅2 = (2.95)(5′)(𝐻𝐻 − 0.5)3 2� for values of H above six inches (6”)1
𝑄𝑄𝑇𝑇 = 𝑄𝑄𝑉𝑉1 + 𝑄𝑄𝑅𝑅1 + 𝑄𝑄𝑅𝑅2 + 𝑄𝑄𝑉𝑉2
The resultant stage discharge curves for both scenarios are depicted in Figure 2.
1 Flow is obstructed in this portion of the weir until the stage height exceeds six inches (6”). Therefore the stage height above these potions of the weir is equivalent to the original stage height less six inches (6”).
SHEET 6 OF 7 _
CLIENT/SUBJECT Stewart ANGB W.O. NO 15254.002.037 .
INSTALLATION NOTES: : 1. DIVERT FLOW TO WEST SIDE OF EXISTING WEIR DIVERT FLOW TO WEST SIDE OF EXISTING WEIR WITH SAND BAGS IN ORDER TO SET TEMPORARY PRE-CAST STRUCTURE. 2. SET TEMPORARY OUTFALL STRUCTURE AT EAST SET TEMPORARY OUTFALL STRUCTURE AT EAST END OF HORIZONTAL TRAPEZOID WEIR. 3. RELOCATE 8"-12" RIPRAP AS REQUIRED TO SET RELOCATE 8"-12" RIPRAP AS REQUIRED TO SET PRECAST STRUCTURE AND INSTALL TEMPORARY EFFLUENT LINE AT REQUIRED ELEVATIONS. 4. SET STRUCTURE OVERFLOW TO MATCH EXISTING SET STRUCTURE OVERFLOW TO MATCH EXISTING OUTFALL ELEVATION. SET STRUCTURE ON COMPACTED LEVEL STONE BASE (NYSDOT OPEN GRADED SUBBASE 2) OR APPROVED EQUAL. 5. ANCHOR 8" DROP TO OUTFALL STRUCTURE WALL. ANCHOR 8" DROP TO OUTFALL STRUCTURE WALL. ARMOR SUBMERGED RUN WITH EXCESS RIPRAP.
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APPROX. 4'x6'x2' I.D. PRE-CAST STRUCTURE
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±12" ROCKSIN CHANNEL (LEVEL W/WEIR)
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±12" ROCKSIN CHANNEL (LEVEL W/WEIR)
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STAIR
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WEIR
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8" FROM TWTS
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EXISTING FLOW METER
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APPROXIMATE BOTTOM OF CHANNEL
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UNKNOWN BELOW GRADE
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SPILLWAY
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PRECAST STRUCTURE
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SPILLWAY
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RECREATIONAL POND
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STREAM FLOW
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PIPE SUPPORT
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8" TREATED EFFLUENT AS LOW AS POSSIBLE
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FABRICATED SPILLWAY LEVEL W/WEIR
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6" ABOVE EXISTING WEIR (MAX.)
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FABRICATED SPILLWAY LEVEL W/WEIR
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FLANGE/LIP AND BOLTED WATER TIGHT SEAL TO INSIDE FACE ON THREE SIDES
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KOR-N-SEAL BOOT (TYP)
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OUTFALL WEIR
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PRECAST CONCRETE STRUCTURE IN ACCORDANCE WITH ASTM C913
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FABRICATED SPILLWAY NOT SHOWN
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MATCH TOP OF EXISTING WEIR
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APPR.
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USACE OMAHA DISTRICT
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PFOS/PFOA INTERIM MITIGATION
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STEWART AIR NATIONAL GUARD BASE
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NEW YORK
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G:\ACADPROJ\15254002037 USACE Stewart ANG\
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15254.002.037.0003
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AS SHOWN
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D.ZIEGLER
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7/19/19
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NOT VALID UNLESS SIGNED AND DATED
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Information shown on this plan is not necessarily complete or correct.
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Date:
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LIMITATIONS NOTE: : THESE DRAWINGS ARE PART OF A LARGER DESIGN PACKAGE AND MAY NOT BE USED WITHOUT REVIEWING THE DOCUMENT IN ITS ENTIRETY. THESE DRAWINGS HAVE BEEN PREPARED TO CONVEY THE INTENDED SITE DEVELOPMENT AND INTERACTIONS WITH EXISTING INFRASTRUCTURE ONLY. SITE CONDITIONS HAVE NOT BEEN CONFIRMED AND MAY DIFFER FROM THOSE DEPICTED HERE. ALL CHANGES TO THE PLANS AND SYSTEMS DEPICTED IN THIS DRAWING PACKAGE MUST BE CONVEYED TO THE ENGINEER FOR REVIEW AND CONCURRENCE
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& SECTIONS
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ATTACHMENT 5
Stormwater Review Technical Memorandum 17 June 2019
Technical Memo - Stormwater Review and Analysis - Final - Stormwater Review and
Analysis Page 1 of 4
June 17, 2019
TECHNICAL MEMORANDUM
TO: Michelle Lordemann, Project Manager, USACE
Cc: PFOS/PFOA Interim Mitigation Project Delivery Team Members
From: Adam Brown, P.E Date: June 17, 2019
NY License No. 097396
RE: PFOS/PFOA Interim Mitigation Project
Stormwater Review and Analysis
INTRODUCTION
Weston Solutions, Inc. (WESTON) has reviewed and analyzed available stormwater and survey data for
the Recreation Pond, including draft and progress datasets provided by the John Wood Group (Wood), to
better characterize the Pond’s response to storm events and determine its ability to be utilized for storing
stormwater runoff for treatment prior to discharge. The project Performance Work Statement defines the
objective of these analyses stating, “Measures are to be implemented to limit overflow during storm events,”
which can be achieved by, “…raising the height of the outfall weir structure, approximately three feet.”
This Technical Memorandum is supported by two calculation packages that analyze both the stormwater
flows experienced by Recreation Pond and the Pond’s storage capacity, and are and included as the
following attachments:
Attachment A - Recreation Pond Water Retention Analysis
Attachment B - Pond Storage Volume Analysis
BOTTOM LINE UP FRONT
WESTON recommends artificially reducing the pond elevation by two feet, and maintaining this elevation
between storm events through artificial drawdown via pumping stormwater to the treatment plant for
discharge. WESTON does not recommend making modifications to the weir at this time. WESTON
considered the following facts, either determined by our analysis or presentation by others, in our review:
SUBJECT: Recreation Pond – Precipitation vs. Volume Analysis
DISCIPLINE (Civil, Mech. Process, Elect.): Civil
PREPARED BY: M. Mardenov DATE:06/17/19
CALCULATION STATUS ISSUED FOR REVIEW
FINAL
CONFIRMED
SUPERCEDED
VOIDED
COMPUTER PROGRAMS USED:
Yes No DESCRIPTION/VERSION: PCSWMM 7.2
REFERENCE SPECIFICATIONS:
REFERENCE DRAWINGS:
SOURCES OF DATA:
1. HDR, Inc. (November 17, 2017). Melissa E. LaMacchia to Tony Palumbo. New York Air National Guard Base, Stewart International Airport, Newburgh, Orange County, New York, Recreation Pond Pre-Design Investigation [Letter].
2. John Wood Group, PLC (October 29, 2018). Preliminary Estimate of Rec Pond Base Flow and Storm Flow Treatment Stewart Air National Guard Base, Newburgh, Orange County, New York [Draft Memorandum].
3. John Wood Group, PLC (May 21, 2019). Rich Niles to Adam Brown. Rec Pond Flow Data [Email]. 4. New York State Department of Environmental Conservation (January 2015). New York State Stormwater
Management Design Manual. Albany, NY. Retrieved from https://www.dec.ny.gov/docs/water_pdf/swdm2015entire.pdf 5. PCSWMM Professional 2D, Version 7.2.
SUMMARY OF RESULTS:
Weston evaluated the data collected by HDR, developed a linear relationship and yielded a storm depth of 0.44 inches that can be retained within a 3.0 million gallon storage volume. WESTON also determined a water quality volume for Outfalls 02, 03, 14 per the requirements of the New York State Stormwater Manual. This water quality volume was compared to the observed flow and precipitation data collected by HDR on August 2nd, 2017, to determine an estimate for discharge associated with the unknown watershed contributing to Outfall 17K.
Weston’s analysis of the previously collected data yielded a linear relationship (Equation 1) that predicts
storm depth given a discharge volume. An example calculation for a 3.0 MG discharge volume yields a
0.44 inch precipitation event.
Limitations:
Conclusions stated or referenced in this analysis are limited to the precipitation and flow metering data
provided by HDR, Inc. (HDR, 2017). The dataset was concise, but not complete with many data gaps and
interpretation was necessary to create complete storm responses. This interpretation can affect the total
runoff volumes calculated. For instance, the HDR report interpreted the duration of discharge over a
shorter period than interpreted by WESTON using the same dataset. Interpretations can vary for a number
of reasons depending on the analysis goals.
Additionally, the metered flow data and precipitation measurements occurred over a limited time spanning
from July 20, 2017 to September 11, 2017. Therefore, the data collection does not account for seasonal
variations or statistical normalization from data collection spanning multiple years. Variability in storm
duration and intensities also cause variation in final runoff volumes as compared to those describe herein.
An analysis relying on a small number of storm events (seven (7) storm events were utilized for this
analysis) inhibits the accuracy of the trends generated.
Lastly, the WQv calculation relies solely on precipitation and impervious area acreage, and does not
account for all watershed characteristics (e.g. conveyance routing, soil types, etc.). These characteristics
would normally be captured in a site wide conceptual model that, when calibrated, would allow more
accurate discharge predictions.
OUTFALL 010DISCHARGE POINT
OUTFALL 002
OUTFALL A
WEIR
RECREATIONPOND
17K OUTFALL
OUTFALL 003
0
OUTFALL A
OUTFALL 002
OUTFALL 003
17K OUTFALL
RECREATION POND
LEGEND
SCALE (ft)
400 ft
Recreation PondStewart International Airport - Air National Guard Base
Newburgh, NY
Site Layout
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Text Box
OUTFALL 002
borgerd
Text Box
Outfall A = Outfall 14
PCSWMM Professional 2D Version 7.2 – Drainage Area Measurements for Outfalls 02, 03, and 14
mardenom
Text Box
Area = 509.4 acres Percent Impervious = 70.2%
ATTACHMENT B
CALCULATION COVER SHEET
PROJECT: Stewart ANGB
WORK ORDER NO. 15254.002.037.0003
CALC NO.
1 SHEET 1 of_12__
SUBJECT: Pond Storage Volume
DISCIPLINE (Civil, Mech. Process, Elect.): Civil
PREPARED BY: A. Brown DATE:06/06/19
CALCULATION STATUS ISSUED FOR REVIEW
FINAL
CONFIRMED
SUPERCEDED
VOIDED
COMPUTER PROGRAMS USED:
Yes No DESCRIPTION/VERSION:
REFERENCE SPECIFICATIONS:
REFERENCE DRAWINGS:
SOURCES OF DATA: 1. HDR, Inc. (November 17, 2017). Melissa E. LaMacchia to Tony Palumbo. New York Air National Guard Base, Stewart
International Airport, Newburgh, Orange County, New York, Recreation Pond Pre-Design Investigation [Letter]. 2. John Wood Group, PLC (October 29, 2018). Preliminary Estimate of Rec Pond Base Flow and Storm Flow Treatment
Stewart Air National Guard Base, Newburgh, Orange County, New York [Draft Memorandum]. SUMMARY OF RESULTS:
Weston evaluated the bathymetry data available for the Recreation Pond and determined a relationship of storage volume versus depth of artificial drawdown and/or raising the weird overflow elevation. One foot of drawdown or weir elevation increase results in roughly one million gallons of additional storage capacity. After three feet of drawdown, significant portions of the Pond will start to dry up, thereby reducing the increase in storage for every foot of additional drawdown.
RECORD OF REVISIONS
NO. REASON FOR REVISION TOTAL NO. OF SHEETS
LAST SHEET NO.
BY CHECKED APPROVED/ ACCEPTED
DATE
0 Issued for Review 12 AB HN/CS AB 6/6/2019
1 Final 12 AB HN AB 6/17/2019
SHEET 2 OF 12
CLIENT/SUBJECT Stewart ANGB W.O. NO 15254.002.037 .
TASK DESCRIPTION Pond Storage Volume TASK NO 0003 .
PREPARED BY A. Brown DEPT 2118 DATE 6/6/2019 . APPROVED BY
MATH CHECK BY C. Sembera DEPT 2118 DATE 6/6/2019 .
METHOD REV. BY H. Nathanson DEPT 2118 DATE 6/6/2019 .DEPT_ DATE_
File Name: Stewart ANG Pond Volume Analysis - Final Print date: 06/17/19 11:42 PM
Objective:
Determine the potential storage volume within the Recreation Pond at Stewart Air National Guard Base
(ANGB). Calculate the amount of artificially increased storage volume of the Pond via drawn down for
various drawdown depths as well as increase in dry weather storage by modifying the weir outlet
structure.
References:
Attachment A – Site Layout
Attachment B – Stewart Airport Pond Depth 1, July 2017, Sheet 1 of 1, ASI Project #: 37-133
Attachment C – Stewart Airport Pond Depth 2, July 2017, Sheet 1 of 1, ASI Project #: 37-133
HDR, Inc. (November 17, 2017). Melissa E. LaMacchia to Tony Palumbo. New York Air National
Guard Base, Stewart International Airport, Newburgh, Orange County, New York, Recreation
Pond Pre-Design Investigation [Letter].
John Wood Group, PLC (October 29, 2018). Preliminary Estimate of Rec Pond Base Flow and
Storm Flow Treatment Stewart Air National Guard Base, Newburgh, Orange County, New
York [Memorandum to Kerry Tull, from Rich Niles, James Barbis, and Sarah Dickert] (Not
attached)
Assumptions:
Elevation datum for all referenced reports (Wood Memorandum and Aqua Survey, Inc. (ASI)) is
NAD 88.
The Recreation Pond weir elevation is 376.24 feet NAD 88.
Recreation Pond can be divided into 39 equal areas (sectors) that comprise the total area of the
Pond.
The bathymetry elevations, shot by Aqua Survey, Inc. (ASI), represent an average depth within the
area of the corresponding sector.
SHEET 3 OF 12
CLIENT/SUBJECT Stewart ANGB W.O. NO 15254.002.037 .
TASK DESCRIPTION Pond Storage Volume TASK NO 0003 .
PREPARED BY A. Brown DEPT 2118 DATE 6/6/2019 . APPROVED BY
MATH CHECK BY C. Sembera DEPT 2118 DATE 6/6/2019 .
METHOD REV. BY H. Nathanson DEPT 2118 DATE 6/6/2019 .DEPT_ DATE_
File Name: Stewart ANG Pond Volume Analysis - Final Print date: 06/17/19 11:42 PM
Discussion:
The existing Recreation Pond (Pond), located at the southern edge of the Stewart Air National Guard Base
(ANGB), receives stormwater drainage from four (4) outfalls (Outfalls 02, 03, 14, and 17K) and local
overland flow. A trapezoidal weir, located at Outlet 10, controls outflow from the Pond. A site layout
indicating the locations of these items is included in Attachment A.
The following volumes will be calculated to determine the amount of storage the Recreation Pond can
provide, prior to discharging via Outfall 10 to the receiving watercourse:
1. Free Water Volume – the volume of water below the weir elevation;
2. Dredge Volume – the additional volume below the weir elevation that could be gained if soft
sediments at the bottom of the Pond were removed or dredged;
3. Gate Volume – volume of storage available if the discharge weir elevation was raised from its
current elevation, by modifying the weir using permanent or temporary structures, such as a sluice
gate or stop logs; and,
4. Additional Storage Volume – the volume of additional storage that could be obtained by
artificially drawing down water levels in the Pond to make room for additional flows.
To calculate the Free Water Volume and Dredge Volume, the total area of the pond was subdivided into
39 equal sectors. The depth of each sector was then determined via a bathymetry survey, completed by
ASI (HDR, Inc., 2017), by subtracting measured values from a reference elevation. In the case of the Free
Water Volume, depth was calculated by subtracting the elevation of the sediment (Pond bottom) at each
sector (shown in Attachment A) from the weir crest elevation. The Dredge Volume depth was calculated
SHEET 4 OF 12
CLIENT/SUBJECT Stewart ANGB W.O. NO 15254.002.037 .
TASK DESCRIPTION Pond Storage Volume TASK NO 0003 .
PREPARED BY A. Brown DEPT 2118 DATE 6/6/2019 . APPROVED BY
MATH CHECK BY C. Sembera DEPT 2118 DATE 6/6/2019 .
METHOD REV. BY H. Nathanson DEPT 2118 DATE 6/6/2019 .DEPT_ DATE_
File Name: Stewart ANG Pond Volume Analysis - Final Print date: 06/17/19 11:42 PM
by subtracting the elevation of the bottom of the soft sediment at each sector (Attachment B) from the
corresponding sector’s top of soft sediment, or Pond bottom (Attachment A).
To calculate the Gate Volume, the total Pond area was measured using aerial imagery, as exhibited in
Figure 1 below. The total Pond area (approximately 124,000 square feet) was then multiplied by an
increase in elevation that could be generated by weir modifications.
Figure 1 - Recreation Pond Area
To artificially increase the storage volume of Recreation Pond, one proposed method is to create a volume
of water could be drawn down to create airspace for new stormwater flows to enter the Pond. This would
be an intermediate measure, similar to the Free Water Volume, that would prevent the need to fully drain
the Pond. To calculate this Additional Storage Volume available, the height of the weir is “adjusted” by a
drawdown depth, and calculated in the same manner as the Free Water Volume at the reduced elevation.
SHEET 5 OF 12
CLIENT/SUBJECT Stewart ANGB W.O. NO 15254.002.037 .
TASK DESCRIPTION Pond Storage Volume TASK NO 0003 .
PREPARED BY A. Brown DEPT 2118 DATE 6/6/2019 . APPROVED BY
MATH CHECK BY C. Sembera DEPT 2118 DATE 6/6/2019 .
METHOD REV. BY H. Nathanson DEPT 2118 DATE 6/6/2019 .DEPT_ DATE_
File Name: Stewart ANG Pond Volume Analysis - Final Print date: 06/17/19 11:42 PM
The difference between the original Free Water Volume and the adjusted Free Water Volume represents
the Additional Storage Volume. This volume generally follows the trend of the Gate Volume until sectors
of the Pond no longer have water available, which are reflected as zero or negative volumes as the
artificial weir elevation exceeds the water depth.