Groundwater Recharge and Groundwater Quality Issues Vincent W. Uhl, PH, PG Vincent Uhl Associates, Inc. Lambertville, NJ Slides 1 to 10

Presentation Summary Assess Groundwater Resources from a Growth – Management Perspective Look at Limitations and Opportunities Local Planning to Protect Water Resources Tools needed to accomplish this planning

Hunterdon Aquifers Piedmont (Brunswick, Lockatong, Stockton) Highlands (PreCambrian and Limestone) Sourlands and Cushetunk Mountain (diabase)

Water Budget Overview P = R + I + ET P = Precipitation R = Runoff I = Infiltration (Recharge) ET = Evapo- transpiration Annual Averages usually used

Infiltration ≈ Baseflow Recharge to ground water eventually flows to streams unless taken out through wells

GW Recharge Soils, precipitation, land cover Part moves “quickly” to streams Part moves to aquifers and then “slowly” to streams or wells

Groundwater Recharge – Ways to Estimate Sophisticated Water Balance (See Van Abs Slide 4) NJGS Method Recharge as a fixed percentage of precipitation Baseflow Analysis  Very Conservative – e.g. 7day 10 year low flow  Average Baseflow  DRBC Approach in SE PA Watersheds which is 75% of the 25-year recurrence baseflow.

Recharge Estimates – The Math Recharge is often expressed as gallons per day per square mile (gpd/mi 2 ) Examples for the Highlands Precambrian Rock aquifers:  7 day 10 year low flow – 85,000gpd/mi 2  Average annual base flow – 525,000 gpd/mi 2  75% of 25-year baseflow recurrence interval – 225,000 gpd/mi 2

Translating Recharge to: Gallons per day per acre 640 acres in a square mile. 85,000 gpd/mi 2 525,000 gpd/mi 2 225,000 gpd/mi gpd/acre 820 gpd/acre 350 gpd/acre

Translating Gallons per day per acre of recharge to lot sizes Using 400 gpd/household 130 gpd/acre 820 gpd/acre 315 gpd/acre 3 acre lots 0.5 acre lots 1.25 acre lots Go to Slides 11 to 23