Appendix 6: Procedures for Wetland Surface and Ground Water Monitoring Wells

This set of instructions is written for researchers and environmental consultants in the wetland field. General knowledge of wetland hydrology is assumed

Instructions are divided into 5 parts: Theory, Materials, Installation Procedures, Use and Monitoring of Wells, and Data Analysis. Section V describes methods for installing and using one well plot. To obtain useful data, however, more than one plot must be installed and monitored. Simply repeat these methods for each of the other plots you wish to establish.

In order to be efficient and successful, read these instructions in their entirety, then gather your materials. Just to be safe, bring this document to the site with you in case you need to refer to it.

Wetland hydrology depends on partial or total soil saturation during various parts of the year. This saturation depends on depth to the free water table (surface water). We can measure the surface water level by inserting a slotted PVC pipe into the ground. The reason the pipe is slotted is to allow for free flow of water at this level.

Ground water is normally separated from the surface water by a confining layer of clay. As ground water follows a decreasing slope, confined by the clay layer, water pressure will build (Fig. 1.a). We can provide ourselves with a window to measuring ground water by inserting a solid PVC pipe (acting as a piezometer) through the surface water area, through the confining layer, into the ground water area. As this pressure builds, the water will find an "escape" (the pipe) through the confining layer. As the water is forced up the pipe, it forms a "head". This means that the water inside the pipe is forced, by pressure, to a level above ground surface (Fig. l.b).

Naturally, the free water table parallels the slope of the ground surface of a wetland. The ground water table also parallels this slope, but at a greater depth.

What does all this tell us? If the measured water depths are the same, then the wetland is supported by both ground and surface water. If there is a "head" in the piezometer, then the wetland is mainly supported by ground water. Finally, if water is found in the slotted pipe but not the peizometer, then the wetland is surface water fed.

Figure 1.a and Figure 1.b

This method is designed to be effective as well as inexpensive. All materials can be purchased at the average hardware store. Total cost should not exceed $100 (costs will be much less if you have access to tools such as an auger, pocket knife, bow saw, transit, and stadia rod).

Supplies (single well plot) Tools

1) slotted PVC pipe*
2) solid PVC pipe*
3) 2 PVC caps
4) 10 lb. bag of coarse sand
5) 20 lb. of bentonite clay
6) bucket auger, 2.5" diameter
7) bow saw
8) transit and stadia
9) carpenter’s ruler
10) pocket knife
11) permanent marker

* 2 inches in diameter, 5 ft. in length

V. INSTALLATION PROCEDURES

1. Well plots should be established parallel to the hydrologic gradient (dark circles in Fig. 2). The number of plots depends on the size of the wetland. Spacing of 50 to 100 feet is usually sufficient. If resources allow, more than one transect can be established (lighter circles in Fig. 2).

Figure 2

1. Use the 2.5" auger to dig a hole for each well (one for the slotted well, and one for the piezometer). Well holes should be placed within 2 feet of each other (Fig. 3.a). Keep the soil in a neat pile for later use.

Figure 3.a and Figure 3.b

1. Add about 1 to 2 cups of sand to the bottom of each hole (this prevents the accumulation of soil or clay from clogging the bottoms of the wells) (Fig. 4.a).
2. Insert one well into each hole (if one hole is deeper, use it for the piezometer).
3. Place a mark on the pipe one foot above ground surface (Fig. 4.b).
4. Cut the pipes with the bow saw. Shave the edges of pipes with the pocket knife, until smooth (this helps keep the caps from becoming stuck on the pipes) (Fig. 4.c).

Figure 4.a, Figure 4.b, and Figure 4.c

1. Reinsert the wells.
2. Fill excess space of the solid well with bentonite clay.
3. Fill excess space of the slotted well with sand (the sand allows for easy flow of water from the soil medium through the pipe, Fig. 5)

Figure 5

4. Use soil extracted from digging to form a slight mound around the well to counter settling and avoid flow of excess surface water into the well (Fig. 6)
5. Place one cap lightly on each well to prevent rainwater and debris from entering the well.

Figure 6

1. Take caps off the wells
2. Have person 1 hold the stadia rod on top of the uncapped slotted well (Fig. 7.a). Person 2 can read the elevation through the transit.
3. Have person 1 measure the distance from the top of the well to ground surface. Subtract the distance from the transit reading to obtain the elevation of the ground surface. Do the same for the solid well.

Figure 7.a and Figure 7.b

The monitoring schedule depends on how fine you want your hydrograph to be. Water depths can be measured daily to monthly. Regardless, water depths should be measured throughout the different hydrologic seasons (wet through dry) in order to plot an accurate hydrologic graph.

1. Take the caps off of each well.
2. Using the carpenter’s ruler, measure the distance from the top of the well to the water. (An easy ways to tell when you’ve reached the water is by watching for the reflection of daylight, or a flashlight, to ripple as the ruler touches the water, Fig 8.a).
3. Subtract the distance of the top of the well to ground surface (recorded in step V.E.3) from this distance. This value gives you the distance of the water level to ground surface (Fig 8.b).

Figure 8.a and Figure 8.b

There are many ways to analyze your data. One of the main purposes of installing monitoring wells is to produce a hydrograph. You can do this by hand, or by computer. A simple graph can be set up by labeling "Depth to Water" (calculated in VI.A.3) as the y-axis and your time intervals on your x-axis. Plotting data for both slotted and solid wells on the same graph makes it easy to compare.