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Groundwater Recharge and Groundwater Quality Issues

Groundwater Recharge and Groundwater Quality Issues. Vincent W. Uhl, PH, PG Vincent Uhl Associates, Inc. Lambertville, NJ Slides 11 to 23. Groundwater Recharge as a basis for planning. Geology dependent – Diabase/Lockatong compared to Brunswick and Pre-Cambrian rock aquifers

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Groundwater Recharge and Groundwater Quality Issues

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  1. Groundwater RechargeandGroundwater Quality Issues Vincent W. Uhl, PH, PG Vincent Uhl Associates, Inc. Lambertville, NJ Slides 11 to 23

  2. Groundwater Recharge as a basis for planning • Geology dependent – Diabase/Lockatong compared to Brunswick and Pre-Cambrian rock aquifers • Use Average or extreme recharge events ? • Local experiences in the recent “Drought” ? • Are water use estimates used in developing lot sizes realistic ? • Aquifer Storage as a Drought Buffer • E.g. 1 acre is underlain by 1 million gallons of groundwater in storage at a porosity of 1%. • With that storage, a 3-acre lot could supply a family with water for over 30 years absent any recharge.

  3. Enter Water Quality • Nitrate is the water quality indicator that has been used to date. • The drinking water standard for nitrate is 10 milligrams per liter (mg/l). • Anti-degradation limits for nitrate to protect surface water systems is in the range of 6 mg/l. • Water professionals have been using nitrate-dilution models developed 25 years ago. • Should other chemicals be considered in planning and more importantly in protection measures?

  4. Nitrate Dilution – the Math • Basically a mixing model. • Recharge water is mixed with septic effluent to yield a mix with a nitrate concentration below some criteria (the drinking water standard or anti-degradation limit for nitrate). • Dilution in the aquifer system is not taken into account in the models. • Nitrate renovation in the unsaturated zone is sometimes not taken into account.

  5. Nitrate Dilution – the Equation • A = 640RCeQeP / IC1 • A = Average Area per dwelling unit in acres • R = nitrate renovation factor = 0.80 • Ce = Nitrate input from septic leach field = 40 mg/l • Qe = Per capita input to septic system in gpd/person • P = Number of people per dwelling unit. • I = Natural recharge rate in gallons per day per square mile • C1 = Acceptable nitrate concentration – Drinking water standard at 10 mg/l or anti-degradation limit of say 6 mg/l.

  6. A = 640RCeQeP / IC1 R = 0.80 Ce = 40 mg/l Qe = 80 gpd/person P = 4 C1 = 6 mg/l Using the recharge rates provided above of: 85,000 gpd/mi2 (130 gpd/acre); 225,000 gpd/mi2 (315 gpd/acre); 525,000 gpd/mi2 (820 gpd/acre) This translates to the following lot sizes: For recharge rate of 130 gpd/acre: A = 13 acres For recharge rate of 315 gpd/acre A = 5 acres For recharge rate of 820 gpd/acre A = 2 acres Calculation Example

  7. Should this be the basis for planning? • End result to date has been fairly large lot sizes. • Basis = an equation which might need some field verification. • Field based nitrate studies would be helpful to assess nitrate concentrations: • Immediately beneath/downgradient from a septic leach field. • Over different lot sizes • Over varying geology

  8. Alternatives to Consider • Use recharge estimates on a macro scale – as they should be viewed - to evaluate options such as cluster development with open space. • Use Hydrogeologic professionals in a role to best determine how to configure development and not just for pumping test programs. • In the alternative, hydrogeologists could be used to: • Look at how to configure a development from a water resource perspective. • Assess optimal well and septic field locations • Assess optimal areas for open space (groundwater recharge opportunity). • Protect stream and drainage corridors. • Optimize storm water and paved surfaces runoff management.

  9. Other Alternatives • Community septic systems for clustered development. • Small wastewater treatment plants. • Connect to regional or local sewage treatment plant. • Gray water reuse.

  10. Local Planning Challenges • Storm water management so as to enhance groundwater recharge as well as to maintain stream baseflow and stream corridor protection. • Educational programs in regard to household products with harmful chemicals that end up in septic systems and ultimately in groundwater. • Promotion of groundwater recharge from paved and roofed surfaces: • Roof drains • Vegetated swales • Porous pavement and sidewalks • Etc.

  11. This diagram shows how development and its corresponding increase in impervious cover disrupts the natural water balance. In the post-development setting, the amount of water running off the site is dramatically increased. Center for Watershed Protection “Impacts of Urbanization”

  12. Limitations • Low yielding aquifers in certain areas – Diabase and Lockatong. • Natural groundwater quality constituents – e.g. Arsenic. • Human-induced groundwater quality impacts. • Reduction of baseflow.

  13. Opportunities • Use knowledge of groundwater resources to look at: • Development alternatives. • Optimal areas for open space consideration and to preserve. • Optimal areas for wells and septic systems. • Creative ways to recharge groundwater.

  14. Thank You • Vince Uhl Return to Hunterdon County Smart Growth

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