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Rockland County’s Water Resources-Selected Findings from the USGS Study-
Paul M. Heisig, HydrologistNew York USGS Water Science Center
Troy, NY
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Water SourcesRockland County, NY
Subject to Permits
Subject to Permits
Streamflow gage site
Lake DeForest
-Lake DeForestReservoir
-Alluvial AquifersRamapo and Mahwah Valleys
-Bedrock AquiferNewark Basin
Sedimentary rock
-LetchworthReservoirs(since 2006)
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Residential 62.8 percent
Commercial, industrial,
governmental, and institutional 10.2
percent
Summertime increase in residential, and
commercial, industrial,
governmental, and institutional use
18 percent
Industrial cooling water 5.6 percent
Golf courses 3.1 percent
Nurseries, orchards, farms 0.3 percent
2005 Water UseRockland County
12.9 Billion Gallons
Water Use
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Water-Resource Concerns in Rockland County (2004)
• Is Pumpage from the Bedrock Aquifer Sustainable?
• What are the shape and size of Wellfield Capture zones?
• How much Recharge does the Aquifer Receive?• What are effects of:
– Impervious Surfaces– Sanitary Sewering
• Additional Sources of Water?
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Evapotranspiration(ET)
Storm Runoff
Recharge
Precipitation
Stream Baseflow(GW Discharge)
Aquifer
Lake, Stream, or Wetland
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Evapotranspiration(ET)
Storm Runoff
Recharge
Precipitation
Stream Baseflow(GW Discharge)
Well
Aquifer
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The Bedrock Aquifer
1. Physical Framework / Water-bearing properties
2. Hydrology – use groundwater-level data and framework to delineate:
– Groundwater flow-system– Production Well Capture Zones
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Sedimentary Bedrock of theNewark Basin Aquifer
East
West
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Surface of Water-BearingFracture (saturated)
Fracture Surface(unsaturated)
Water-Bearing Fractures
Regional GW Flow Direction
Recharge
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Spring 2007 Ground Water Levels,Bedrock Framework,GW Divides,GW Flow
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Groundwater flow model results from R. Yager, USGS
Production Well Capture Zones(250 ft below bedrock surface)
From Numerical GW Flow Model
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Aspects of Aquifer Health
• Aquifer Responses to Groundwater Withdrawals• Streamflow• Recharge
– Natural Variability – Effects of Impervious Surfaces
• Sanitary Sewering – Water Loss from Aquifer
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UWNY Well
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Seasonality of Bedrock Aquifer Withdrawals
2005
Jan Mar Jun Sep Dec
With
draw
al R
ate
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Seasonal Groundwater-Level Changes
Observation Well and Pumping Wellfield are 0.7 miles apart.
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Example Annual Pumping Rate and Groundwater-Level Data from Production Well
Growing Season
UWNY Well 69
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If pumped continuously, about 1/3 of UWNY Supply wellswould reach the bottom of airline prior to the end of the growing season.
Most wells are not pumped continuously, so this is a worst-case assumption. However, it also assumes constant drawdown rates, which is a best-case assumption:
•Drawdown rates can increase as water-bearing fractures become dewatered. •Air entrainment may reduce pumping rates prior to water levels nearing the pump.
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Areas of Dry Streams over the Aquifer, Sept. 2005 (brown shaded areas)
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Factors that AffectRecharge Totals:
•Precipitation Amount
•Overburden Thickness
•Wetland / Surface WaterArea
•Impervious Surface Area
58 in.
48 in.
52 in.
24.8 in.
15.1 in.
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How much of recharge to the bedrock aquifer is pumped out for water supply?
(2006 data)
Estimates from watersheds with streamflow gages:• Mahwah River 12%
• Saddle River 24%
• Pascack Brook 21%
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Impervious Surface Effects
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Effects --Loss of Recharge (less base flow), Streambed Erosion, Turbidity, and Temperature Fluctuations
12%
17%
3 %
Stormflow Hydrographs and Impervious Surfaces
Est. Annual incr. in Storm Runoff with % impervious surface:Pascack Br. ~400 Mgal.
Saddle R. ~150 Mgal.
Mahwah R. ~ 20 Mgal.
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Sanitary Sewer SystemSewer Mains are a SubsurfaceDrainage Network, Much Like Streams
Total Outflow to Hudson River was 14.1 Billion Gallons in 2005
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2005
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Potential Sources of Water-• Sedimentary Bedrock Aquifer
• Ambrey Pond Reservoir
• Stormwater Retention / Use
• Stony Brook Watershed (Ramapo River)
• Desalinization of Hudson River Water
• Indirect Use of Recycled Water (Example, with possible increased use of Lake Deforest)
Each with it’s own set of issues and caveats
A purely hydrologic perspective
High volume, year-round sources
Summer season sources
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Recycled water– indirect re-use
(hypothetical example)
14 Billion GallonsLost to Hudson R.in 2005
Higher Level of Treatment at WWTP and transfer water to Hackensack River Valley
Discharge of Water to wetland area for additional biological treatment prior to joining Hackensack River
1
2
Augmentation of Flow in Hackensack R.
4
3
Potentially more water available for Rockland water-use needs
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Conclusions
• Long-term, progressive declines in groundwater levels across the aquifer are not indicated by available data or by computer modeling with historic pumpage data.
• Of Greatest Concern are Seasonal Groundwater-Level Declines at Supply Wells caused by increased Water Use During Prolonged Dry, Hot Spring and Summer Periods.
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Summary and Conclusions (continued)
•Sustainability of Current Water Resources inRockland County is Largely Dependent on:
(1) the ability to curtail water-use duringduring summer peak-demand periods, and
(2) to avoid loss of supply from groundwater contamination
•Recharge in Rockland County is SignificantlyHigher than Previous Estimates, but is HighlyVariable in Space and Time.
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Summary and Conclusions (continued)
•Impervious Surfaces Increase Storm Runoff in Pascack Br. by nearly 400 Mgal./yr and Probably Decrease Recharge by about 200 Mgal./yr.
•The Sanitary Sewer System behaves like a River - it transports wastewater, but also receives Stormwater Inflows and Infiltration of Groundwater.
•Potential Additional Water Sources:1. Additional pumpage from Bedrock Aquifer2. Ambrey Pond3. Retention/Use of Stormwater4. Augmentation of Ramapo River flow from the Stony
Brook Watershed.5. Desalinization of Hudson River Water6. Indirect Reuse of Recycled Water
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End