Lecture 39

Sampling in the Saturated and Vadose

Zones and Methods of Analysis

Fetter 11

One of the most important components of any contaminant study is the installation

of wells and/or soil-monitoring equipment.

A monitoring well(s) is required under RCRA

1. Subtitle C (Hazardous Waste Sites)
2. Subtitle D (Landfills)
3. Subtitle I (Underground Storage Tanks)

Also required at most Superfund sites, environmental site assessments

A useful standard has been developed by ASTM Subcommittee D-18.21 (Ground-water

and vadose zone investigations), ASTM Standard D5092

	Standard practice for design and installation of ground-water monitoring wells in aquifers.
	Promotes durable and reliable monitoring well construction and acquisition of representative ground-water data.

Location map of the Pilot Wells and Science Trench Boreholes in relation to the RWMS

with geologic cross-section interpreted from core and drill-cuttings at Nevada Test Site.

Figure 1. Basic principle of rotasonic drilling.

Figure 2. Rotasonic drilling rig.

Truck mounted cable tool rig.

Mud-rotary drill rig.

Installing and completing a well in a hollow-stem auger.

Water-table well and piezometer.

Typical design of a very deep water well.

Purpose of aquifer/vadose zone monitoring

1. To collect representative samples of ground water or soil water
2. To collect accurate information about ground-water flow and soil-water flow

It is important to have a knowledge base before designing a monitoring

network and leaving the possibility open for modifying the network

design during installation.

Hydrogeological data needed

1. Geology (stratigraphy/sedimentology/ structure)
2. Primary porosity/secondary porosity
3. Units (depths) of interest
4. Long-term hydraulic behavior of the aquifer

Biogeochemical information needed

1. Background water chemistry
2. Types and concentrations of contaminants
3. Microbiology

Important to minimize sources of chemical interference in well/lysimeter design by

1. Drilling method - fluids, equipment
2. Monitoring well materials - casing, screen

Well casing

1. Types of materials - PFTE, metal, PVC
2. Properties of materials - mechanical and chemical
3. Joints
4. Dimensions - ID, OD, thickness

Well screens

1. Select appropriate slot size - based on grain size data
2. Type of screens

   	Hand slotted
   	Factory slotted
   	Continuous-slot wire-wound

3. Screen length
4. Filter pack materials - natural/artificial

Annular seals - a seal of the annular space above the filter pack

1. Annular seal materials

   	Bentonite - dry/wet
   	Neat cement
   	Permeability contrast

2. Chemical considerations

Surface completion

1. Flush to ground surface
2. Above-ground surface

   	protective casing
   	Lock
   	bumper guards

Well development

Ground-water sampling

1. Bailor
2. Syringe sampler
3. Bladder pump
4. Gas-drive piston pump
5. Submersible centrifugal pump
6. Peristaltic pump (suction)
7. Gas-driven pump

ASTM standards have been/are being developed for Vadose zone monitoring

Soil-water sampling

1. Soil-water extraction
2. Lysimeters

   	porous ceramic/Teflon/stainless cup
   	pan

Soil-water sampling

1. Direct-push samplers

Soil-moisture measurement

1. Time-domain reflectometry
2. Neutron probe
3. Gamma probe

Soil-pressure measurement

1. Tensiometer
2. Quick draw

Analytical methods

Organic chemicals

1. Gas chromatography
2. High performance liquid chromatography
3. Enzyme-linked immunoadsorbant

Inorganic chemicals

1. Atomic adsorption
2. Ion chromatography
3. Colormetric techniques
4. Many others

Field parameters

1. Electrodes
2. Titration

Microbiological

1. Enumeration
2. Scans

ENV 302 - Lectures