the remedial alternative selected. This air from the site on a regular basis. This program will be evaluated periodically to ensure it remains and applicable based on the site data. This review will occur at of every five years for a minimum period of thirty years. Institutional controls in the form of deed restrictions on the use bf groundwater beneath the site and limitations on land uses are inclukd. Physical improvements in the form of enhanced fences and posting of the property, vegetation establishment and maintenance, and continugd stormwater/leachate recirculation (as necessary durina storm events) are also included. - - The County must prepare and submit for NYSDOH and NYSDEC acceptance a complete plan for the operational, maintainance and monitoring acti ities, as well as long-term land uses planned for the landfill after const ction. k Time to implement: 6 months Direct Capital Costs: S370,bOO Estimated Annual Costs: $231,$I00 Alternative 2: Containment by Capping - 1 This alternative is the early remedial action currently under contr ct for construction. It includes all the institutional items and post-clo ure monitoring items from alternative 1: No Action. The primary compone ts of this'alternative are a NYSDEC part 360 compliant cap with perimeter leachate and active gas collection systems. The cap design consists of a fle ible geomembrane barrier layer, an active gas collection system, gas fla e system perimeter leachate seeDaae collection. leachate oioina svstems with1 connections to sanitaj sewers on the'mainland and-stormwater manag facilities. The leachate collection svstem will have sufficient st capacity to avoid discharging leachate-to the sanitary sewer systemlduGing periods of high flow to the sewers. - - The selected geomembrane is a forty (40) millimeter very low density. polyethylene membrane (VLDPE) protected by a 24" barrier protectionlayer. Included in the protection layer are location specific drainage layers and a topsoil layor. Steep .lopc- will receive a textured VLDPR t o improve stability. The gas collection system will consist of actjlve gas removal through over 80 fully penetrating wells located within the waste mass and piping to a gas flare system located adjacent to the waste mass in the northeast corner of the property. A landfill gas vent retief system will be constructed as a back-up system and will consist of a g e ~ c ~ m p o s i tgas e collection layer immediately below the VLDPE liner and a sieries of pressure relief valves. L The final elevations of the cap system were designed to fa ilitate stormwater management through a series of swales and drain ge channels to route stormwater runoff offsite in a controlled manner to hree separate discharge points. The final topsoil layer will be planted with various plants and grasses t o promote the Long-term use of the areg for scenic walkways in association with the existing County park facilities on the Croton Point peninsula and t o provide suitable habitat for breeding, migratory and wintering species of birds. Time t o implement: approximately 28 months Direct Ccpital Costs: $28,700,000 Estimated Annual Costs: $304,000 Alternative ZB: Containrent with Pump 6 Treat of leachate This alternative consists of alternative 1:No Action, alteljnative 2:capping, and the additional elements necessary t o actively remove t4e leachate located within the landfill mound. This alternative would include a low permeability barrier around the landfill perimeter, a recodery well system located within the existing leachate mound, and associated 'piping systems. Cost estimates include leachate pretreatment prior to discqarge to sanitary sewers based on the results of samples from well 13 locate4 in the area where the recovery well was modeled. The advantage of actilve leachate mound removal is that the watertable within the landfill would r y c h equilibrium conditions in approximately 2 yeare, based upon model input assumptions. The pumping would be continued for a longer period of time in okder to maintain hydraulic control, but would operate at reduced flows as thp head within the landfill decreases. It is estimated that approximately 1291,000,000 gallons would be recovered at pumping rates ranging from over 58,001D gallons/day at Startup to less than 2500 gallons/day in year 15. The selection of this alternative would result in decreased inorganic loading to the surrounding water bodies at a point in time that is earlier (by several years) then that which is predicted to be achie ed with a cap alone. Using chromium as an example, this alternative wou d reduce loading t o the surrounding areas from an estimated level of 13.7 po nds per year (at a point in time one year after capping is complete and with ut any pumping) to less than 2.4 pounds per year with pumping. Capping alon would achieve a similar 2.4 pounds per year loading in approximately 8 year$ without pumping. The increased capital cost from alternative 2, fo achievement is $26,700,000.