Underground Heterogeneity 9/5/2017. Groundwater Monitoring Well Construction. Groundwater Sampling. Groundwater Movement and Related Terms.

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1 Groundwater Monitoring Well Construction Groundwater Sampling Groundwater Movement and Related Terms Stormwater overland flow = rate of precipitation - rate of infiltration Infiltration rate affected by soil composition and other factors Movement Fate of groundwater downward flow and lateral flow Slow, even if obstructions are minimal Interaction of surface and groundwater Underground Heterogeneity Surface soil infiltration Not all layers contain water Some layers are not very permeable Some layers very permeable Not all layers will contain contaminants Heterogeneity is three dimensional Lens creates perched water Bedrock Soil Origin Terms: Alluvial water related sediments Fluvial river sediments Lacustrine lake sediments Palustrine wetland sediments Glacial sediments deposited by glaciers Karst dissolution of limestone 1

2 Subsurface Zones Vadose Constructing Wells Driven wells Direct push Limitations and benefits Jetted wells Augured wells Drill rig Method used for wells on CCC campus Dug wells old style farm-type watertable wells Others Monitoring Wells Construction Above grade casing riser or at grade screen annular space annular seal bentonite Portland cement filter pack or sand pack around well screen well cap or expanding plug Protector cap 2

3 Borehole construction and sampling to identify water bearing strata Placing the well casing Packing the annular space Sealing the annular space Constructing the manway Developing the well Borehole construction and sampling the strata Hollow stem flight auger, additional sections Center plug and drill rod Drill bit with changeable teeth Split spoon sampler Hammer Blow count Sampled Placing the well casing PVC or other depending on likely contaminants Inner diameter variable Base plug Risers Screens Annular space 3

4 Packing the annular space Filter pack Sealing the annular space Grout Bentonite Portland cement structure concrete Constructing the manway Above grade or at grade Vault contains top of casing and well plug Locking expanding plug Bolted metal cover Developing the well Eliminate the effects of smear get water flowing Clears the filter pack of fines and gets the groundwater flowing through the strata Manage developed water as waste? Why sample groundwater? Assessment and protection of drinking water Monitor groundwater point of compliance under RCRA Subtitle C Monitor MSWLFs under RCRA Subtitle D Identify and monitor clean up of contaminated sites under CERCLA RCRA Subtitle I UST regulations Others? 4

5 Prepare site to protect surface soil from contamination with well contents Opening and Closing Note condition of well opening and manway Check for critters Check for vapors Note need for repairs Listen for pressure release when opening plug Evidence of VOCs in groundwater Makes notes as appropriate Well development (mentioned previously) and/or purge before sampling Purge ARBITRARILY three well volumes removed Compute well volume using depth to surface, depth to bottom, and diameter Bail out volume x 3 slowly, no cascading! Or use some other parameter to determine well is in equilibrium with aquifer - C, ph, conductivity Collect purge water for management as waste Sample Well Purge Record Well Water Quality Stabilization Record Date: Sheet of Signature: Well Number Print name and title then sign Total Volume Parameter Measurements Withdrawn DO Bore EC Time gal ph C (mg Turbidity volume (µmho/cm) O2/L) Casing Diameter Gallons/Linear Foot 2 inch inch inch inch inch inch Table 1. Number of gallons per linear foot of water Calculation of Well Purge Volume Total depth of well casing ft Casing Depth to Water - ft Linear Feet of Water = ft Diameter in Gallons/linear foot X See Table 1. Amount of water in casing = X3 = Amount of water to be purged gal Condition of well 5

6 Measuring depth to water, depth to free product, depth to bottom using depth meter/interface meter Choose reference point on top of casing north side sounds good Prepare meter or interface probe before heading into the field Lower probe/device Watch/listen for top of liquid and interface (beeps not splashes!), if any, then continue to bottom Wipe clean while you remove, decon as necessary Collecting samples Powered pumps available for deeper and large-volume wells Bailer Do something to keep it from falling in! Bail slowly protect your VOCs Dispose of, dedicate, or decontaminate 6