Classroom activity Grade 12 Engineering & Design

Harrowgill Service Line Inventory and Replacement Sprint

Grade 12 teams classify service line records at four stations, then size the crews, budget, and schedule a fictional district needs to replace lead lines.

Grade: Grade 12
Subject: Engineering & Design
Material: Classroom activity
Time: 55 min
Prep: Moderate prep
Materials: Printed property record cards for four stations, eight cards per station, Calculator for each team, One classification chart per team

Standards

HS-ETS1-2 NGSS

Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

How this material aligns: Students break a district-wide replacement program into four smaller solvable problems, namely material classification, annual replacement rate, crew sizing, and cost per account, exactly as this standard describes.

All materials for HS-ETS1-2 →

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Handout items 1 through 7 carry service line counts through years, crews, dollars per line, and dollars per account per year in one consistent unit chain.

All materials for HSN-Q.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-03.

Objectives

Students will classify service line materials from records into the four inventory categories.
Students will compute the annual replacement rate a ten-year deadline requires.
Students will size crews and annual budget for a lead service line replacement program.

Vocabulary

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.
Action level: A trigger number in lead and copper testing. If too many homes test above this level, the utility must take steps like improving treatment and telling the public.

Also: galvanized requiring replacement, inventory, 90th percentile

Teacher overview

This is a four-station sprint for teams of three, run as one timed rotation followed by a planning block. Teams work as inventory technicians for the fictional Harrowgill Water District, reading property records at each station and sorting service lines into the four categories a materials inventory uses: lead, galvanized requiring replacement, non-lead, and lead status unknown. The planning block then turns the district-wide counts into crews, years, and dollars. A misconception worth correcting at the start is that a service line is a single pipe the utility owns. It has a utility-side portion and a customer-side portion, either of which can be lead, and a line whose material nobody can document counts as unknown rather than as an empty record. Unknown lines carry the same replacement obligation as confirmed lead until a record or a field check proves otherwise.

Activity Directions

Before class, print eight property record cards for each of four stations, thirty-two cards in all. Each card gives one fictional Harrowgill address with a construction year, a permit note, a meter pit description, and, at two stations, a field scratch and magnet test result.
Set up the four stations around the room and label them Records, Permits, Meter Pit, and Field Test. Post the classification chart at each station: lead, galvanized requiring replacement, non-lead, or lead status unknown.
Form teams of three and give each team a classification chart, the student handout, and a calculator. Assign each team a starting station so the four stations fill evenly.
Run four rotations of six minutes each. At every station a team classifies all eight cards and records its four category counts. Teams do not discuss cards with other teams during the rotation.
After the fourth rotation, spend five minutes reconciling. Read the correct classification for any card that teams split on, and require the reasoning, not just the category.
Move to the planning block. Give teams eighteen minutes to complete handout items 1 through 9 using the district-wide inventory totals printed on the handout rather than their own station counts.
End the sprint when every team has an annual budget figure for item 6 and a cost per account for item 7. Post the range of team answers on the board.
Debrief with two specific questions. First, the replacement obligation covers unknown lines as well as confirmed lead, so how much of the fictional district's program cost comes from lines nobody has documented? Second, the district could spend part of the budget on records research instead of pipe, so under what condition would that be the better engineering decision?

Harrowgill Service Line Inventory and Replacement Sprint — Grade 12 Engineering & Design

Name: ____________________________ Date: ______________

Student Handout

The fictional Harrowgill Water District serves 12,400 service lines and bills 12,400 accounts. Its completed materials inventory reports 1,860 lead lines, 620 galvanized lines requiring replacement, 8,060 non-lead lines, and 1,860 lines of unknown material. Lead, galvanized requiring replacement, and unknown lines all must be replaced. Replacement costs $9,500 per line, and one crew completes 210 replacements per year.

The district's most recent round of tap sampling produced ten results, reported in parts per billion: 1.2, 2.0, 3.4, 4.1, 5.6, 6.8, 8.0, 9.5, 12.0, and 21.0 ppb. To find the 90th percentile, sort the results from lowest to highest, multiply the number of samples by 0.9, and read the value at that position.

Harrowgill has 12,400 service lines, of which 1,860 are confirmed lead. Find the percent of all service lines that are confirmed lead.
Lead, galvanized requiring replacement, and unknown lines must all be replaced. Using counts of 1,860 lead, 620 galvanized requiring replacement, and 1,860 unknown, find the total number of lines to be replaced.
Using a replacement total of 4,340 lines and a ten-year deadline, find how many lines must be replaced each year.
One crew completes 210 replacements per year. Using a rate of 434 replacements per year, find the smallest whole number of crews the district needs.
Replacement costs $9,500 per line. Using a replacement total of 4,340 lines, find the total program cost.
Using a total program cost of $41,230,000 spread evenly across ten years, find the average annual program cost.
Harrowgill bills 12,400 accounts. Using an average annual program cost of $4,123,000, find the annual cost per account.
Using the ten tap sample results listed above, find the 90th percentile lead result.
The action level drops to 10 ppb in 2027. Using a 90th percentile of 12.0 ppb, find how many ppb the district's result sits above that action level.

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

Answer Key

Answer: 15.0 percent. In the fictional district, 1,860 divided by 12,400 equals 0.15, and multiplying by 100 gives 15.0 percent.
Answer: 4,340 lines. 1,860 lead plus 620 galvanized requiring replacement plus 1,860 unknown equals 4,340 lines.
Answer: 434 lines per year. 4,340 lines divided by 10 years equals 434 lines per year.
Answer: 3 crews. 434 divided by 210 equals 2.07 crews, and because a partial crew cannot be scheduled, the district needs 3 crews.
Answer: $41,230,000. 4,340 lines times $9,500 per line equals $41,230,000.
Answer: $4,123,000 per year. $41,230,000 divided by 10 years equals $4,123,000 per year.
Answer: $332.50 per account per year. $4,123,000 divided by 12,400 accounts equals $332.50.
Answer: 12.0 ppb. Sorted, the ten results run 1.2, 2.0, 3.4, 4.1, 5.6, 6.8, 8.0, 9.5, 12.0, 21.0. Ten samples times 0.9 gives position 9, and the ninth value is 12.0 ppb.
Answer: 2.0 ppb. 12.0 ppb minus the 10 ppb action level that takes effect in 2027 equals 2.0 ppb above the action level.

Differentiation

Support

Reduce each station to four cards instead of eight so the classification rotation finishes inside the same six minutes without rushing. Provide items 1 and 3 with the division already written, and give a worked model using a different fictional district of 6,000 lines with 900 lead lines before the planning block begins.

Extension

Ask these teams to sequence the fictional district's work rather than average it. Have them argue for replacing the 1,860 unknown lines first, last, or in parallel with confirmed lead, then calculate how the annual budget would change if the district front-loaded 700 replacements in each of the first three years and spread the remainder evenly across the rest.

ELL supports

Provide the classification chart with a photograph-style sketch beside each category, showing a lead line's dull gray surface, a galvanized line's threaded fitting, and a copper line's color. Offer sentence frames for the reconciliation step: "This card shows ___, so the line is classified as ___," and "The record does not show ___, so this line is unknown."

Extensions

Suppose the fictional Harrowgill district can spend $180,000 of its first-year budget either on replacing about 19 more lines or on hiring a records firm to research 4,000 unknown addresses. Ask students to estimate how many unknown lines would have to turn out to be non-lead for the records work to be the better buy, then have them write the assumption their estimate depends on.