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Lesson plan Grade 7 Careers & CTE

Marking Tavistock's Water Mains Before the Dig

A grade 7 careers lesson on the utility locator who marks buried pipe, using a fictional town map at one inch to forty feet for scale-drawing practice.

Objectives

  1. Students will describe how a utility locator finds and marks buried water pipe before excavation.
  2. Students will compute actual lengths and areas from a scale drawing of a utility map.
  3. Students will redraw a measured length at a second scale and explain the change.

Vocabulary

Utility locator
A worker who finds and marks buried pipes and cables before anyone digs, so construction crews do not accidentally hit them.
Water main
A big underground pipe that carries drinking water beneath the streets to a neighborhood. Smaller service lines branch off it to reach each building.
Service line
A service line is the small pipe that connects the water main under the street to the plumbing inside one home or building. It is the last leg of the trip water makes to your tap.

Also: scale drawing, excavation

Teacher overview

Before any crew digs in a street, someone comes out and paints the ground to show where the buried pipes and cables run. For water, that person is a utility locator, and the map in the truck is a scale drawing. This lesson introduces the role through the fictional town of Tavistock and turns the locator's map into scale-drawing practice. Students routinely apply a scale in one direction only, multiplying by the scale factor even when they are converting a real length back to a map length, so the modeled example works both directions on purpose.

Procedure

  1. Hook (5 min): Show students a photograph of colored paint marks and small flags on a street, or sketch them on the board. Ask what the marks mean and who put them there. Tell students that blue marks water, and that a water main breaks somewhere in the United States roughly every two minutes even without a shovel involved.

  2. Background (8 min): Describe the job. In the town of Tavistock, anyone planning to dig calls a central number, and the call goes out to every utility with buried lines nearby. Tomas Solberg is the water utility's locator. He arrives with a map, a metal detector tuned to find pipe, and a can of blue paint. Older mains are cast iron and easy to find. Newer plastic mains carry a copper tracer wire so a signal can be sent along them. Some pipe in the oldest part of town appears on no map at all, and he probes for it by hand. Explain the training route, which is on-the-job training after a high school diploma, a state or company certification in locating, and often a distribution operator license later. Note that the same skills lead into leak detection and asset mapping work.

  3. Model the scale (8 min): Write the map scale on the board as one inch to forty feet. Work one example each direction with numbers students will not see again. First, a pipe measuring 5 inches on the map is 5 times 40, which is 200 feet on the ground. Second, a trench 100 feet long is 100 divided by 40, which is 2.5 inches on the map. Say plainly that going from map to ground multiplies and going from ground to map divides, and leave both examples on the board.

  4. Formative check (2 min): Ask one question to the whole class. A driveway is 60 feet wide. Do you multiply by 40 or divide by 40 to find its width on the map? Have students show one finger for multiply and two for divide. If fewer than about four out of five students show two fingers, work another ground-to-map example before moving on.

  5. Handout work (15 min): Distribute the handout and have students work questions 1 through 6 in pairs and question 7 alone. Circulate and check the direction of the conversion on questions 3 and 5, which are the two items that go from a ground distance back to a map length.

  6. Closing discussion (5 min): Ask who pays when a contractor digs without a locate and breaks a main. Collect responses on the board under three headings: the contractor, the water utility, and the households on that street. Push students to name a cost that is not money, such as a day without water or a boil notice.

  7. Exit ticket (2 min): Students write the two rules from step 3 in their own words, one for map to ground and one for ground to map. Collect the tickets and sort them for the next day into correct, reversed, and unclear.

Marking Tavistock's Water Mains Before the Dig — Grade 7 Careers & CTE
Name: ____________________________ Date: ______________

Student Handout

Suppose the town of Tavistock gives its locator a map drawn at a scale of one inch to forty feet. Use that scale unless a question tells you otherwise.

  1. On the map, the water main runs 6.5 inches from the corner of Cranborne Street to the fire hydrant. How many feet is that on the ground?
  2. A service line to a house measures 2.25 inches on the map. What is its actual length in feet?
  3. A crew plans a dig box that is 30 feet long. How many inches long is that box on the map?
  4. A block of pavement measures 4 inches by 3 inches on the map. What is its actual area in square feet?
  5. The locator redraws the map at a scale of one inch to twenty feet. On the new drawing, how many inches long is the 260-foot main from question 1?
  6. Tomas answered 18 of the 24 locate requests on his list before lunch. What percent of the list did he finish?
  7. Explain why a scale drawing is of no use to a digging crew if the scale itself is missing.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: 260 feet. Multiply 6.5 inches by 40 feet per inch.
  2. Answer: 90 feet. Multiply 2.25 inches by 40 feet per inch.
  3. Answer: 0.75 inch. Divide 30 feet by 40 feet per inch. Students who multiply get 1,200 and should be asked whether a box could be that long on a page.
  4. Answer: 19,200 square feet. The sides are 4 times 40, which is 160 feet, and 3 times 40, which is 120 feet. Multiply 160 by 120.
  5. Answer: 13 inches. Divide 260 feet by 20 feet per inch. The line is twice as long on paper because each inch now stands for half as much ground.
  6. Answer: 75 percent. Divide 18 by 24 to get 0.75, then multiply by 100.
  7. Answer: Accept any answer that names the missing link. Sample response: without the scale, a measured distance on paper cannot be turned into a distance on the ground, so the crew would not know how far to dig from the corner.

Differentiation

Support

Give students a printed strip showing the two rules side by side, one for map to ground and one for ground to map, with a small worked example under each. Provide question 4 with the two side lengths already converted, so the remaining work is the area multiplication. On the extension sketch, allow measuring to the nearest quarter inch.

Extension

Ask students to draw their own locate sketch for a corner lot, placing a main, two service lines, and a hydrant at stated distances, then label the drawing with its scale. A partner measures the sketch and works backward to the stated distances. Students compare results and explain any difference larger than a few feet.

ELL supports

Pre-teach "main," "service line," and "excavation" with a labeled street cross-section showing the pipe under the pavement. Provide a sentence frame for question 7, such as "Without the scale, the crew cannot ____ because ____." Allow students to answer question 7 orally before writing.

Extensions

Have students walk the school grounds with clipboards and sketch the visible clues to buried utilities, such as valve covers, meter boxes, hydrants, and manholes. Back in class they place the clues on a scaled sketch of the grounds and mark where they would want a locator to check before any digging. A closing discussion compares which clues turned out to be the most useful.