Prepared for:
Westchester County Department of Transportation

Prepared by:
FIRST ENVIRONMENT, INC.
90 Riverdale Road
Riverdale, New Jersey 07457
February 14, 2001
Project No. WESTC001

CONTENTS

Overview    1
LOCALIZED AREAS WARRANTING ADDITIONAL INVESTIGATION   3
Former Air National Guard Septic Area #3 – Area # 34  3
Aircraft Rescue and Firefighting (ARFF) Burn Pit - NYSDEC Spill #9911702 – Area #25  3
Fuel Tank Farm Area - NYSDEC Spill #s 9309928, 9811558, 98006992, 9108093, 9811676 - 
Areas #12 through #16  4
Building 10 - NYSDEC Spill #0000994 – Area #36  5
Former Air National Guard Area - NYSDEC Spill #9011175 – Area #19  5
Building 1 - NYSDEC Spill #9713222 – Area #22  6
Hanger B - NYSDEC Spills #9809015 & #9811689 - Areas #26 & #27  6
NYSDOT Landfill Off-Site Location – Area #31  7
Hangar B - Septic 1 – Area #32  7
Weights and Measures Building - NYSDEC Spill #0008724 – Area #38  8
T-1 Former Airfield Blockhouse - NYSDEC Spill #0009172  8
Hanger D-1, Bay 2 – Area #8  8
Hanger D-1 Bay 1 - NYSDEC Spill #9813569 – Area #9  9
Groundwater Monitoring Program   10
Conclusion   14

TABLES
TABLE 1      Areas of Completed Investigation Requiring No Further Action

FIGURES Are in Portable Document Format (PDF)
FIGURE 1            Monitoring Well and Sample Location
FIGURE 2            Groundwater Monitoring Program Locations
NOTE: You will need Adobe® Acrobat® Reader, available (FREE) for download from Adobe Systems Incorporated, in order to view PDFs.
Overview
First Environment, Inc. (First Environment) on behalf of the Westchester County Department of Transportation (WCDOT) has completed the groundwater site investigation and remediation activities at the Westchester County Airport (Airport) in accordance with the approved Investigation Work Plan dated June 2000 (the Work Plan).  As the investigation progressed, the scope expanded beyond that initially proposed in the Work Plan to ensure any additional potential concerns were investigated as they were identified.  This investigation has confirmed that there is no pervasive groundwater plume or groundwater pollution threat to Rye Lake or the surrounding environment.  Specific localized areas of environmental concern have been identified; many of these have been addressed and the others are currently in the process of being addressed.   In addition, a groundwater monitoring program has been developed and will be implemented to monitor these localized areas on site where chemical constituents have been detected in groundwater above regulatory guidelines (regulatory control wells) as well as to monitor the perimeter of the site to ensure that there is no adverse impact to Rye Lake or the surrounding environment (sentinel wells).  This program will ensure the County’s ability to identify and respond to any potential contamination threat from the Airport to the waters of Rye Lake or the surrounding environment on an ongoing basis.

The Work Plan was designed voluntarily to serve as a compilation of action items in
response to concerns raised by First Environment and interested parties after completion of the Airport’s proactive hydrogeologic study, originally initiated in August 1999.  In addition, the Work Plan was designed to develop a complete set of data necessary to determine if the operations at the Airport are or are not adversely impacting Rye Lake or the surrounding environment.    

All action items in the Work Plan have been performed and the objectives of the Work Plan have been met.  Additional hydrogeologic investigations have been conducted and have more thoroughly defined groundwater flow patterns and the groundwater divide present at the Airport.  The groundwater divide, as illustrated on Figures 1 and 2, identifies the boundary between the two watersheds on site, with groundwater to the northwest of the divide flowing towards the Rye Lake watershed and groundwater to the southeast of the groundwater divide flowing towards the Blind Brook watershed.  The findings of this investigation were consistent with First Environment’s previous investigation; specifically, that the groundwater in the upper water-bearing zone flows from the northern and southwestern portions of the Project Area in a westerly direction towards Rye Lake.  Groundwater in the upper water-bearing zone on the rest of the Project Area flows towards the east and southeast away from Rye Lake.  Additional delineation of the groundwater divide indicates that the divide actually trends in a more southwesterly direction from the center of the site than had previously been reported.  As such, a smaller portion of the Project Area actually discharges to Rye Lake, as opposed to the Blind Brook, than previously reported.  

During the investigation, possible contaminant sources on-site were identified and investigated to determine their potential impact.  The investigations included a thorough review of available documentation, interviews with Airport personnel and Air National Guard (ANG) personnel in Latham, NY, as well as intrusive investigations consisting of soil and/or groundwater sampling. 

The additional site investigation activities began in June 2000 and over six months approximately 125 soil samples, upwards of 30 post excavation soil samples, and 130 groundwater samples from temporary and permanent monitoring wells have been collected, submitted for lab analysis and evaluated.  The soil and groundwater sampling locations are presented on Figure 1.  Based on the additional information, First Environment has concluded that there are no on-site sources that are adversely impacting Rye Lake.  Table 1 provides a list of the areas that were thoroughly characterized and for which no further action is warranted.  There are several areas, discussed below, where the need for additional investigation or monitoring has been identified and is now ongoing.  Top

LOCALIZED AREAS WARRANTING ADDITIONAL INVESTIGATION
Former Air National Guard Septic Area #3 – Area # 34
The groundwater in the former Air National Guard septic system area, south of Hangar 6 (Area #34 – Septic #3) has been impacted.  The groundwater in this area flows towards Blind Brook and will not have an adverse impact on Rye Lake.  The approximate location of Area # 34 is presented on Figure 1.  The soil and groundwater investigation in this area included the collection of approximately 50 samples.  The investigation identified volatile organic compounds (VOCs) in the groundwater in both the shallow (overburden) and deeper (bedrock) aquifers at concentrations above regulatory guidelines.  Tetrachloroethene, trichloroethene, ethylbenzene and xylems were identified in the shallow aquifer at concentrations above regulatory guidelines and tetrachloroethene was identified in the bedrock aquifer at concentrations above regulatory guidelines. 

The extent of the contamination in the shallow aquifer has been delineated, however additional investigation of the bedrock aquifer is warranted.  Two additional bedrock monitoring wells should be installed and sampled to delineate the extent of VOCs in the bedrock aquifer.  Based on the results of this additional investigation, these wells may or may not be included in the groundwater monitoring program, discussed below.

The area should also be investigated through a geophysical survey, specifically ground penetrating radar, to determine if a septic tank remains.  If a septic tank is identified, it, along with any contaminated soil, should be removed to prevent the possibility of future discharges of VOCs to the area.  Top

Aircraft Rescue and Firefighting (ARFF) Burn Pit - NYSDEC Spill #9911702 – Area #25
Historic aircraft rescue and firefighting operations conducted in this localized area impacted the surrounding soil and groundwater.  The approximate location of the ARFF Burn Pit, Area #25, is presented on Figure 1.  A total of 2,803 tons of soil was excavated from the ARFF Burn Pit area and post-excavation soil sampling verified that all contaminated soil has been removed.  The excavation has been backfilled to grade. 

The shallow groundwater in this area generally flows to the north, but based on available information, this area is believed to be part of the Rye Lake watershed.  A trace amount of trichloroethene, well below the regulatory guideline, was identified in one of the three shallow monitoring wells in the area.  Three shallow monitoring wells down gradient of the former ARFF burn pit, FMW-6, FMW-7 and FMW-15 are included in the groundwater monitoring program discussed below.

In this area, groundwater in the deeper bedrock aquifer flows to the south away from Rye Lake.  Vinyl chloride at a concentration above the regulatory guidelines and tetrachoroethene and trichloroethene at concentrations below regulatory guidelines were identified in the bedrock monitoring well in this area (FMW-23). The installation of two additional bedrock monitoring wells is warranted in the area of FMW-23 in order to determine the extent of vinyl chloride in the bedrock aquifer.  Based on the results of the additional proposed investigation, a request to close this spill case may be made to the NYSDEC or further investigation may be warranted.  In addition, depending on the results of the additional investigation, these bedrock wells may be included in the groundwater monitoring program, discussed below.    Top

Fuel Tank Farm Area - NYSDEC Spill #s 9309928, 9811558, 98006992, 9108093, 9811676 - Areas #12 through #16
The Fuel Tank Farm Area has been the site of past investigation and remediation activities, including the removal of approximately 8,000 tons of contaminated soil and the installation of a series of groundwater monitoring wells.  It should be noted that this area is at the east end of the site, east of the groundwater divide, and therefore does not have the potential to impact Rye Lake.  The approximate location of Areas #12-16 is presented on Figure 1. 

The groundwater in the fuel tank farm area is currently being monitored on a quarterly basis by the Airport’s consultant, HDR.  The initial report produced by HDR identified free phase gasoline floating in one well (MW-G), and an unidentified free-phase product floating in another monitoring well.  The first quarterly groundwater monitoring report for this area again identified free-phase floating gasoline in monitoring well MW-G, but no free-phase gasoline in any other wells.  Subsequent groundwater monitoring reports should be reviewed to verify the localized groundwater flow in this area and to evaluate the need for further action.  If free phase product continues to be identified and/or if groundwater with concentrations above regulatory guidelines is identified, additional investigation and or remediation may be warranted.  Future remediation of this area may include the active or passive recovery of free phase product from the groundwater.  Monitoring well FMW-38, located in the general proximity of this area will be included in the groundwater monitoring program to continue to evaluate impacts to groundwater in the Fuel Tank Farm Area. Top

Building 10 - NYSDEC Spill #0000994 – Area #36
The investigation and remediation of Area #36 was completed in order to address past releases associated with a 5,000-gallon diesel underground storage tank (UST), a 3,000-gallon gasoline UST and an associated pump island, previously removed.  The approximate location of Area #36 is presented on Figure 1.  Post excavation soil sampling results confirmed that soil removal activities were complete, however down gradient (to the north) groundwater samples (from FMW-17 and FMW-27) identified the presence of VOCs above regulatory guidelines, indicating that the groundwater has been slightly impacted by the former tank operations. 

Contaminants from this area are not migrating off site and the extent of VOCs in the groundwater in this area is limited.  There are no VOC concentrations above regulatory guidelines in groundwater samples collected down gradient of FMW-27.  Specifically, groundwater samples from monitoring wells FMW-15 and FMW-16 and temporary monitoring wells GB-25, GB-26 and GB-27, located approximately 400 feet down gradient (north) of FMW-27, had no concentrations of VOCs above regulatory guidelines. 

Based on the VOCs detected at FMW-17 and FMW-27, the continued monitoring of these locations is warranted to document the natural attenuation of VOCs in groundwater and to allow for closure of this NYSDEC spill case.  These wells will be monitored as part of the groundwater monitoring program, discussed below.   Top

Former Air National Guard Area - NYSDEC Spill #9011175 – Area #19
The past removal of a 2,500-gallon UST in this area resulted in the installation of three monitoring wells (DPW-1 through DPW-3) to evaluate the effectiveness of the remediation and groundwater quality in the area.  The approximate location of Area #19 is presented on Figure 1.  Based on the location of the groundwater divide, Area #19 is located primarily in the Blind Brook watershed however, due to possible seasonal variations in groundwater elevations, groundwater in this area may flow into either the Blind Brook or Rye Lake watersheds.  Monitoring wells are present in nearby areas down gradient of Area #19 in both watersheds to monitor groundwater quality as part of the groundwater monitoring program.  During this and previous investigations, the VOCs, ethyl benzene, xylems and 1,2,4-trimethylbenzene, and two SVOCs, chrysene and benzo(b)fluoranthene, were identified at concentrations slightly above regulatory guidelines in one of the three monitoring wells, DPW-2.  Groundwater quality in monitoring wells DPW-1 and DPW-3, located on either side of DPW-2, is below regulatory guidelines, demonstrating the detections identified at DPW-2 are localized.  Although this spill case has been previously closed by the NYSDEC, continued groundwater monitoring is recommended to verify that natural attenuation is continuing to effectively reducing VOC and SVOC concentrations to levels below regulatory guidelines.  Monitoring well DPW-2 is included in the groundwater monitoring program, discussed below.   Top

Building 1 - NYSDEC Spill #9713222 – Area #22
The past removal of a 3,000-gallon UST was investigated by the collection of a groundwater sample at the former UST location.  Groundwater in this area flows away from Rye Lake.  The location of Area #22, the site of a spill case previously closed by NYSDEC, is presented on Figure 1.  During the investigation, petroleum staining was observed and VOCs and SVOCs were detected in groundwater above regulatory guidelines.  The impact to groundwater to the north, down gradient, has not been fully defined. 

Although the spill case has been closed, additional investigation of this area is warranted and should include the installation of three soil borings to evaluate the extent of petroleum impacted soil present and the installation of three permanent monitoring wells, one at the former UST area and two hydraulically down gradient to evaluate groundwater quality.  The results of this additional investigation would be used to determine the need for additional action, including monitoring and/or possible remediation.  Top

Hanger B - NYSDEC Spills #9809015 & #9811689 - Areas #26 & #27
These areas were investigated to determine the potential impact to the area resulting from USTs, either removed or abandoned in place.  The approximate location of Areas #26 and #27 is presented on Figure 1.  Based on the results of this and previous investigations, soil and groundwater in the vicinity of the USTs near Hanger B have been impacted with VOCs.  While groundwater in this vicinity does flow in the direction of Rye Lake, wells down gradient of this area demonstrate no exceedances of regulatory guidelines. 

The Airport will be demolishing Hanger B as part of the construction of a new taxiway.  This area will be remediated at that time.  The remediation should include post-excavation sampling and groundwater monitoring as dictated by NYSDEC requirements to ensure appropriate closure of the associated Spill Case #9811689.  Spill #9809015 was previously closed by the NYSDEC.   Top

NYSDOT Landfill Off-Site Location – Area #31
The Harrison Subresidency Area, also referred to as the NYSDOT Landfill, located off site between the Airport and Rye Lake has two separate areas that have been investigated by others under the direction of NYSDOT, a landfill, and a groundwater contamination plume associated with three USTs removed in 1994.  The approximate location of Area # 31 is presented on Figure 1.  The landfill closure has been approved by the NYSDEC and is now in the groundwater monitoring stage.  The groundwater contamination plume associated with the former USTs is being treated by an air spurge/soil vapor extraction system that commenced operation in October 2000. 

Based on a preliminary review of available documentation, the extent of groundwater contamination present has not been fully delineated vertically and the installation of additional deep monitoring wells by NYSDOT may be warranted.  Well construction information should be provided and reviewed to determine the specific hydrologic units being monitoring (shallow versus deep) and to evaluate groundwater flow direction both horizontally and vertically in order to optimize the locations and construction of additional monitoring wells, as necessary.  Future quarterly groundwater monitoring reports should be reviewed as they become available to determine if past and ongoing remedial activities are sufficient to prevent detrimental impacts to Rye Lake.  Monitoring wells DEPMW-1 and DEPMW-2, located off-site near the shore of Rye Lake, are included as sentinel wells in the groundwater monitoring program discussed below to further evaluate potential future impacts from the Harrison Subresidency Area.   Top

Hangar B - Septic 1 – Area #32
The investigation of the septic system for Hanger B identified the VOC (1,4-dichlorobenzene) at a concentration slightly above the regulatory guideline, 3.14 ppb versus a guideline of 3 ppb, in one groundwater sample from a temporary monitoring well.  However, the VOC concentration of 3.14 ppb was below the laboratory method detection limit of 5 ppb and is therefore an estimated value.  In order to verify if the VOC detected is representative of site conditions and is in fact above the regulatory guideline, the groundwater at this location should be resampled for VOCs.  Further MW-1, the nearby sentinel well will be included in the groundwater monitoring program.  The approximate location of Area #32 is presented on Figure 1.  Top

Weights and Measures Building - NYSDEC Spill #0008724 – Area #38
The investigation of the Weights and Measures Building, adjacent to the former Air National Guard UST tank farm area, identified VOCs and SVOCs in groundwater above regulatory guidelines.  This area is southeast of the groundwater divide, therefore groundwater in this area flows away from Rye Lake.  The approximate location of the Weights and Measures Building is presented on Figure 1. 

In order to investigate the extent of VOCs and SVOCs above regulatory guidelines the installation and sampling of three additional monitoring wells is proposed.  One monitoring well is proposed in the area of the previous groundwater sample at GB-40, the other two additional monitoring wells are proposed down gradient of GB-40 to evaluate the extent of VOCs and SVOCs in the groundwater in this area.  Upon receipt of the results a determination will be made as to further action required to close this spill case.  Top

T-1 Former Airfield Blockhouse - NYSDEC Spill #0009172
The investigation of a former diesel UST at this location identified VOCs and SVOCs in the soil and groundwater above regulatory guidelines.  The approximate location of T-1 is presented on Figure 1.  This area is southeast of the groundwater divide, therefore groundwater in this area flows away from Rye Lake.  Although the free phase floating petroleum product identified at this location was fingerprinted to closely resemble #2 fuel oil, it is suspected that this material is in fact diesel fuel as diesel fuel and #2 fuel oil are nearly identical.  The extent of petroleum-impacted soil in this area should be investigated and remediated, as necessary.  After remediation, the groundwater in this area should be monitored including the installation of additional monitoring wells as necessary.  These wells would then be included in the groundwater monitoring program.  Top

Hanger D-1, Bay 2 – Area #8
The presence of chlorinated solvents in the groundwater in this area is being investigated by independent consultants working on behalf of Exxon Mobil.  The groundwater in this area flows to the southeast, away from Rye Lake.  The approximate location of Hangar D-1, Bay 2 is presented on Figure 1.  The results of the latest and each successive round of groundwater sampling should be reviewed as they become available to determine the need for additional investigation and/or remediation.  Several monitoring wells in this area are also included in the groundwater program discussed below.  Top

Hanger D-1 Bay 1 - NYSDEC Spill #9813569 – Area #9
This area of petroleum-contaminated soil was recently remediated under the supervision of Malcolm Pirnie.  They are currently preparing the closure report.  Groundwater flow in the area of Hanger D-1 flows to the east, away from Rye Lake.  The closure report for this remedial action should be reviewed to evaluate if any further action is warranted.  The approximate location of Hangar D-1 Bay 1 is presented on Figure 1.   Top