Groundwater Recharge and Groundwater Quality Issues

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

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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?

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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.

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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.

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Calculation Example

• 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

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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

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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.

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Other Alternatives

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

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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.

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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
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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.

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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.

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Thank You

• Vince Uhl

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