into the Hudson River at Croton-on-Hudson, New York. The park was partially built on two (2) closed landfills; Croton Landfill and Railroad I Landfill. Collectively they are referred to as the Croton Sanitary Landfill. 2.1 RAILROAD I LANDFILL Site Description The Railroad I Landfill is located southwest of the Village of Croton-on-Hudson as shown on Figure 1 and Figure 2. The Railroad I Landfill is a separate landfill located north of the main landfill adjacent to the Metro North Croton-Harmon Rail Yard. Railroad I is a lined landfill with a combination synthetic cap and clay-side liner, a leachate collection system and the landfill gas collection and control system. Railroad I Landfill operated from 1980 until 1982 and received only municipal solid waste (MSW), as reported in the Post Closure Care and Operation Manual for the Railroad I Landfill, dated April 2004. Based on liquid level elevations observed at landfill gas extraction wells and around the landfill, preferential groundwater flow in the water table (unconfined) system is primarily from the northwest flowing toward Haverstraw Bay. Basic information as well as O&M requirements for these landfills are contained in the Railroad I Landfill O&M Manual dated April 2004. Apart from the landfill areas, much of the land use on Croton Point is recreational. There are camping areas to the southwest of the Railroad I Landfill, a beach and picnic area further to the southwest. 2.2 CROTON POINT LANDFILL Site Description The Croton Point Landfill is located southwest of the Village of Croton-on-Hudson as shown on Figure 1 and Figure 2. The Croton Point Landfill is classified as a Class II inactive waste disposal site under the NYSDEC regulations pertaining to inactive hazardous waste disposal sites, 6 NYCRR Part 375. The Croton Point Landfill is divided in two (2) distinct disposal facilities as shown on Figure 2. The largest of these facilities is the “Original Landfill”, an unlined area used from 1927 until 1986 as reported in the Operation Manual for the Croton Point Landfill, dated X:\PROJECTS\WCDEF\190446 - Croton LF Periodic Review Report\2019 PPR Report\2019 PRR rpt 2019-06-14.docx 8 July 1996. The other area, known as the “Ballfield Landfill,” is an immediately adjacent lined landfill operated from 1982 until 1986, as reported in the Operation Manual for the Croton Point Landfill, dated July 1996, which was the last landfill cell of the Croton Landfill. The Ballfield Landfill was designed with a bottom liner and leachate collection system. The “Original Landfill” has no synthetic liner, however, it is underlain by an organic clay/peat deposit. This deposit inhibits vertical flow of groundwater and would be expected to promote a predominately lateral flow of groundwater out of the landfill. Based on liquid level elevations observed at landfill gas extraction wells and around the landfill, preferential groundwater flow in the water table (unconfined) system is from the northwest flowing toward Haverstraw Bay and southeast flowing toward the tidal shallows off the Croton Marsh. A deeper groundwater system exists under confined conditions beneath the organic clay/peat deposit. Although flow in this confined system is more complicated by tidal influence than flow in the unconfined system, deep well liquid levels reveal a general direction of flow from the mainland toward Croton Bay. The organic clay/peat layer impedes the flow of groundwater between the shallow unconfined system and the deeper confined system. Apart from the landfill areas, much of the land use on Croton Point is recreational. There are camping areas to the north and south of the Original Landfill, picnic area to the west, and a beach area along Haverstraw Bay to the northwest. X:\PROJECTS\WCDEF\190446 - Croton LF Periodic Review Report\2019 PPR Report\2019 PRR rpt 2019-06-14.docx 9 3 PERIODIC REVIEW REPORT 3.1 INTRODUCTION The purpose of this PRR is to evaluate the institutional and engineering controls (IC/EC) at the Site and to summarize monitoring results and evaluate O&M activities to document the following: • IC/EC are in place, performing properly and remain effective; • The SM plan is being implemented; and • Operation and maintenance activities are being conducted, as needed, to maintain the engineering controls. The PRR documentation is as follows (relevant DER-10 citations shown in parentheses): • Performance and Effectiveness (6.3(b)2.i.) ▪ • New Conclusions or Observations (6.3(b)2.ii.) ▪ • CD-ROM Sampling and Well Locations (6.3(b)5.i.) ▪ • Section 3.4; Appendix B Field Data (6.3(b)4.viii.) ▪ • CD – 1; CD-3 Optimization and Performance Problem Resolution (6.3(b)4.vi. and vii.) ▪ • Sections 3.4 through 3.9 Performance Monitoring (6.3(b)4.v.) ▪ • Section 3.8 Routine Maintenance and Inspection (6.3(b)4.iii and iv.) ▪ • Section 3.6 Contaminant Removal (6.3(b)4.ii.) ▪ • Section 3.10 Recommendations for Change (6.3(b)2.iii.) ▪ • Sections 3.2, 3.3, 3.5, 3.6, and 3.8 Figure 2 Change of Use Documentation (6.3(b)6.) X:\PROJECTS\WCDEF\190446 - Croton LF Periodic Review Report\2019 PPR Report\2019 PRR rpt 2019-06-14.docx 10 ▪ • Recommendations for