Presentation to PlymouthCarver Aquifer Advisory Committee by David JP Foss, CPG

1
Presentation toPlymouth-Carver Aquifer Advisory
Committeeby David JP Foss, CPG

• CT-ENV-12210600000000002210

February 8, 2006
2
Glacial Geology

• Glacial Deposits
• Till
• Fluvial - Outwash
• Lacustrine - Lake
• Post Glacial
• Eolian - Wind
• Organic sediments - bogs
• Alluvial River
• Human Transported

Dr. Sharon Johnson, Alaska, 1996
Hansen, 1992
3
Glacial Soil

• Typical Soil Cross-Section
• Organic Material
• Eolian Mantle
• Outwash Sand
• Outwash Gravel

Pete Fletcher, Matunuck, RI
4
Hydrogeology of Glacial Outwash

• Groundwater Moves Quickly in Outwash Deposits.
• Hydraulic Conductivity
• Fine Sand Gravel 40 to 100 ft / day
• Fine Gravel 150 to 200 ft / day
• Coarse Gravel 300 to 700 ft / day
• Contaminants movequickly, too!

5
Hydrogeology of Glacial Outwash

• Typical Yields for Water Supply Wells
• 45 gpm - Low transmissivity sand gravel
• 1,100 gpm - High transmissivity gravel
• 325 gpm Average Public Water Supply wells
• 1 to 50 gpm - Other aquifer conditions beyond PCA

6
Earthwork Effects on Water Quality

• Gravel Pit / Earthwork often Intercept the
  Saturated Zone
• Removal of rich topsoil a natural filter and
  vegetation
• Removal of gravel to the water table
• Pumping / handling water for operation, washing
  silt and impurities from gravel into wash pond
• Introducing industrial chemicals to aquifer
• Excavations become Injection Points
• Increasing Risk for
• Release of OHM
• Migration of OHM
• Impacts to nearby wells

Joseph Kelly, Tracey Corner, Maine
7
Dewatering Effects on Stream Flow

• Excavation dewatering is equivalent to pumping
  well.

8
Earthwork Effect on Water Quantity

• Earthwork / Gravel Pit
• Locally lowers water table
• Discharges water to stream / storm system -
  water leaves aquifer
• Decreases total recharge
• Alters local stream flow
• Increases evaporation
• Man-made ponds decreasetotal recharge