Town of Philipstown Groundwater Report and Planning Resource
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Groundwater Report Town of Philipstown Groundwater Report and Planning Resource Town of Philipstown Putnam County, New York June 2007 Prepared for: Town of Philipstown 238 Main Street P.O. Box 155 Cold Spring, NY 10516 ©2007 The Chazen Companies Groundwater Report Town of Philipstown Groundwater Report and Planning Resource Town of Philipstown Putnam County, New York June 2007 Prepared by: The Dutchess County Office The Chazen Companies 21 Fox Street Poughkeepsie, New York 12601 (845) 454-3980 Orange County Capital District North Country (845) 567-1133 (518) 273-0055 (518) 812-0513 Philipstown Groundwater Report TABLE OF CONTENTS EXECUTIVE SUMMARY ............................................................................................. 1 1.0 INTRODUCTION .............................................................................................. 4 2.0 PHILIPSTOWN HYDRO-GEOGRAPHY.......................................................... 5 2.1 Setting, Population, Water & Sewer Service................................................... 5 2.2 Topography......................................................................................................... 5 2.3 Geology ............................................................................................................... 6 2.4 Land Uses......................................................................................................... 10 2.5 Water Requirements, Consumption, and Wastewater Generation ............... 11 2.6 Climate, Vegetation and Imprevious Surfaces............................................... 12 3.0 PHILIPSTOWN GROUNDWATER RESOURCES........................................... 14 3.1 Bedrock Aquifers.............................................................................................. 14 3.2 Surficial Aquifers............................................................................................. 15 3.3 Soils and Aquifer Recharge ............................................................................. 16 3.4 Groundwater Flow ........................................................................................... 19 3.5 Groundwater Quality....................................................................................... 19 3.5.1 Natural Groundwater Quality .................................................................. 20 3.5.2 Introduced Contaminants.......................................................................... 22 3.6 Future Water Supplies .................................................................................... 26 4.0 GROUNDWATER RESOURCE MANAGEMENT............................................ 28 4.1 Groundwater Summary................................................................................ 28 The Chazen Companies June 2007 Philipstown Groundwater Report Page ii 4.2 Minimum Parcel Sizes..................................................................................... 28 4.3 Aquifer Protection............................................................................................ 33 4.4 Pumping Test Protocols................................................................................... 35 4.5 Road De-Icing................................................................................................... 35 4.6 Wastewater Management................................................................................ 36 5.0 REFERENCES.................................................................................................... 37 TABLES Table 1 –Depth & Yield Statistics for Bedrock Formations Table 2 – Well Depth Trends Table 3 - Natural Groundwater Quality in Aquifer Formations FIGURES Figure 1 – Hillshade Site Reference Map Figure 2 – Bedrock Geologic Map Figure 3 – Linear Features (Fracture) Map Figure 4 – Soil Survey and NYS Museum Surficial Geology Maps Figure 5– Hydrologic Soil Groups Figure 6 - TMA and State Aquifer Maps Figure 7 – Septic System Density Analysis Figure 8 – Groundwater Sampling Locations PLATES Plate 1 – Aquifer Map Plate 2 – Draft Zoning Overlay Map APPENDICES Appendix A - Groundwater Quality Data Appendix B - Wastewater Treatment Options Analysis Appendix C - Model Aquifer Protection Ordinance The Chazen Companies June 2007 Philipstown Groundwater Report Page 1 EXECUTIVE SUMMARY The Town Board of the Town of Philipstown retained The Chazen Companies (TCC) to review groundwater relationships in the Town. The work scope for this study was defined during meetings held in early 2006 by a project team consisting of community residents and Town Board liaisons. Development of aquifer planning recommendations was a recommendation of the Town’s Comprehensive Plan, and justified since a majority of Philipstown residents and many businesses use groundwater as their primary water source. Only residents in Cold Spring and residents in parts of Nelsonville and Continental Village use water from surface water reservoirs. Various reference groundwater maps are provided in this report. Plate 1 shows aquifer boundaries, watershed boundaries, estimated watertable contours, and groundwater flow arrows identifying directions of groundwater migration. Plate 1 is designed to help visualize aquifer conditions throughout the town. Figure 5 shows areas with different aquifer recharge rates throughout the Town. Over 90 percent of the town has either silty soil which allows annual infiltration of 7.6 inches of aquifer recharge or sandy soils which allow 14.7 inches of annual aquifer recharge. Plate 2 is a draft aquifer boundary map showing the extent of the bedrock aquifer under all of Philipstown, Cold Spring and Nelsonville. Plate 2 also identifies the boundaries of a sand and gravel aquifer near the Clove Creek. Plate 2 may be used as an overlay layer map in town zoning. Minimum lot size recommendations are provided for areas where individual septic systems and individual wells will continue to be used. For 90 percent of the Town, the recommended minimum average parcel sizes are between 1.6 and 3.0 acres. Figure 7 identifies areas where existing parcels may already be undersized. Conceptual approaches for improving wastewater treatment in such areas or in other areas with high concentrations of septic systems are reviewed in Appendix B. The report includes recommended levels of aquifer protection for different aquifer areas in Philipstown. These are generally consistent with groundwater management recommendations provided in Putnam County’s 2004 groundwater planning study, also prepared by the Chazen Companies. Hydrogeologic factors governing groundwater availability in Philipstown are summarized here: • Aquifers underlie all parts of Philipstown. These include a sand and gravel aquifer extending under the northern portion of Route 9 near the Clove Creek, and a bedrock aquifer underlying the entire town. These aquifers offer the only ready source of water to many residents and so warrant protection and/or planning management. The Chazen Companies June 2007 Philipstown Groundwater Report Page 2 • In general, adequate groundwater is available in Philipstown to support most present and future water requirements. However, groundwater resources can be locally overtapped, either by over-extraction from wells, or by overloading local aquifer areas with septic system discharges or road salt residues. • The varied topography in Philipstown isolates segments of the bedrock aquifer into discrete subwatershed areas, such as those around the Indian Brook, Philipse Brook, Arden Brook, Clove Creek and Canopus Creek. Although a generally common bedrock aquifer extends across the entire Town, groundwater in these separate watersheds does not mix and cannot be readily moved from one watershed to another, allowing the possibility of local over use or local contamination which cannot be relieved by, or will not cross-contaminate, groundwater in adjacent watersheds. • Expanded future water demand can be readily accommodated in Philipstown, but wells may need to be spread over wider areas to ensure that sufficient aquifer recharge areas are available to support each new well. Site specific well testing is warranted for higher water use wells. • Groundwater quality degradation from septic systems is a form of groundwater over-use if waste constituent concentrations impair drinking water quality. • Philipstown has higher density areas, including commercial and residential centers, and both moderate and low-density areas. Where groundwater is the principal source of water supply, different groundwater management strategies are recommended for the high and the lower density areas. • Federal and State environmental regulations passed since the 1970s, as well as growing availability of improved remediation techniques, have significantly reduced groundwater threats from point sources such as gas stations, dry cleaners, and heavy industry activities. Although the enforcement of groundwater protection regulations applicable to such uses continue to be a concern, outright prohibition of such land uses may be warranted only in highest-risk aquifer areas. Such highest-risk areas could be defined on the basis of aquifer capacity, highly settled areas, or in recharge areas for central water supply wells. • Septic systems represent a wide-spread and potentially-significant source of non- point aquifer contamination. Contaminants from septic systems include not only compounds with existing regulatory standards such as for nitrate or e-coli, but also include more recently recognized constituents such as