Project Grade 8 Engineering & Design

Tarnholt Lagoon Aeration: Model, Test, and Refine a Retrofit

A five-session grade 8 project where teams build tabletop lagoon models, test three air-delivery layouts for dead zones, and recommend a retrofit to a village board.

Grade: Grade 8
Subject: Engineering & Design
Material: Project
Time: 5 sessions, ~250 min total
Prep: Moderate prep
Materials: Shallow plastic tray or storage bin, one per team, about 40 cm by 25 cm, Water and a bucket for emptying and refilling the trays between trials, Aquarium air pump with a T-splitter, one per team, Flexible airline tubing, 2 m per team, Air stones or short lengths of tubing pierced with pin holes, Food coloring and droppers, Stopwatch, ruler, and masking tape, Graph paper and a grid overlay printed on transparency or drawn on the tray bottom

Standards

MS-ETS1-4 NGSS

Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

How this material aligns: Teams build a tabletop lagoon model and run repeated dye-tracer trials on three air-delivery layouts, generating the data for iterative modification that this standard describes.

All materials for MS-ETS1-4 →

MS-ETS1-3 NGSS

Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.

How this material aligns: In session four teams compare trial data across all three layouts, identify the best feature of each, and merge those features into a fourth layout they test again.

All materials for MS-ETS1-3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-23.

Objectives

Students will model a treatment lagoon and measure how completely each air layout mixes it.
Students will use dye-tracer data to locate dead zones in a tested layout.
Students will combine the strongest features of tested layouts into a refined design and retest it.
Students will recommend one retrofit to a village board and justify it with their own trial data.

Vocabulary

Aeration: Aeration means mixing air into water. At a wastewater plant, blowers bubble huge amounts of air through tanks so the helpful microbes have the oxygen they need to eat the waste.
Dissolved oxygen: Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.
Biochemical oxygen demand (BOD): Biochemical oxygen demand, or BOD, measures how much oxygen tiny microbes will use up as they eat the waste in water. Dirtier water has a higher BOD.

Also: lagoon, diffuser, dead zone, tracer

Teacher overview

Many small communities treat wastewater in shallow lagoons, where bacteria break down waste using oxygen that enters at the surface or through added air. Secondary treatment standards set a monthly-average effluent limit of 30 mg/L for BOD (biochemical oxygen demand) and TSS (total suspended solids), and a lagoon that mixes poorly can miss that limit in late summer even when the average air supply looks adequate. Teams build a tabletop lagoon model, test three air-delivery layouts for dead zones using dye tracers, then combine the best features into a fourth layout and retest it. The deliverable is a design report with a scale sketch, trial data, and a recommendation presented to a panel acting as a village board.

Tarnholt Lagoon Aeration: Model, Test, and Refine a Retrofit — Grade 8 Engineering & Design

Name: ____________________________ Date: ______________

Project Brief

The client. The fictional village of Tarnholt treats its wastewater in one shallow lagoon. Each August the lagoon smells and the treated water leaving it carries more waste than the village's permit allows. The village board suspects the problem is not the total amount of air but where the air goes.

The driving question. Where should air be delivered in a lagoon so that the whole basin is treated, not just the part nearest the pipe?

The model. Your tray is the lagoon, seen from above. The air pump is the village's blower, and the tubing is the air piping. A drop of food coloring released in a corner is a tracer: if the dye reaches every part of the tray quickly, that part of the lagoon is being mixed, and if a patch of dye sits still, you have found a dead zone.

The three layouts to test.

Layout 1, single diffuser. One air stone near the inlet end.
Layout 2, two diffusers in a line. Two air stones spaced evenly along the long axis.
Layout 3, perimeter loop. Tubing pierced with pin holes running around the edge of the tray.

Your criteria. Your recommendation must be judged on these, and your team decides how to measure each one.

Coverage. How much of the tray shows dye movement within 60 seconds.
Speed. How long the dye takes to reach the far corner.
Simplicity. How many pieces the layout needs and how easy it would be to clean.

Your constraints. These come from the village and cannot be changed.

The blower cannot be replaced, so every layout must run on one pump at the same setting.
The lagoon keeps its current shape. No new berms or walls.
The village can afford no more than 30 m of new air piping, which your model represents at a scale you state in your report.
Any diffuser must be reachable from the bank for cleaning.

The deliverable. A design report of three to five pages containing a scale sketch of the recommended layout, a data table from every trial, a grid map marking the dead zones you found, and a written recommendation. Teams present for six minutes to a panel acting as the Tarnholt village board.

Milestones

Session 1, build and calibrate (50 minutes). Teams assemble the tray, draw or overlay a grid, set a fixed water depth, and run one practice trial to agree on how dye release and timing will be done identically each time. Keep each air pump and its plug on a dry surface above the water line, and wipe up spills right away. Output: a written test protocol the whole team signs.
Session 2, test layouts 1 and 2 (50 minutes). Three trials each, recording coverage by grid square at 30 and 60 seconds and the time for dye to reach the far corner. Output: a completed data table for two layouts.
Session 3, test layout 3 and map dead zones (50 minutes). Three trials of the perimeter loop, then a grid map for each layout shading squares where dye did not move. Output: three labeled dead-zone maps.
Session 4, combine and retest (50 minutes). Teams identify the best feature of each layout, build a fourth layout from those features, and run three trials on it. Output: a sketch of the combined layout plus its data table, with a sentence naming which feature came from which trial.
Session 5, report and board review (50 minutes). Teams finish the report and present. The panel asks each team to explain one dead zone it could not eliminate. Output: the report and the six-minute presentation.

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

Rubric

Criterion	4, exceeds	3, meets	2, approaching	1, beginning
Test protocol and fairness	Dye volume, release point, water depth, and timing are held constant across every trial, and the report says how	The protocol is stated and mostly followed	Some variables drift between trials without comment	Trials are not comparable and no protocol is recorded
Data quality	Three trials per layout with coverage and time recorded, plus a note on how repeatable the results were	Three trials per layout with complete data	Fewer than three trials, or gaps in the table	Data are missing or were not recorded during testing
Use of data to refine	The combined layout takes a named feature from each tested layout, each justified by a specific data column, and the retest is reported honestly even if it did worse	The combined layout is justified by data from the earlier trials	The combined layout is asserted without pointing to data	No combined layout was built
Meeting the constraints	Every constraint is met, the piping scale is stated, and the report shows where a constraint changed the design	Every constraint is met	One constraint is violated, such as changing the pump setting between layouts	Two or more constraints are violated
Report and presentation	The sketch is to scale and labeled, dead-zone maps are readable, and the recommendation answers the panel directly	The report contains all required parts and the presentation is clear	A required part is missing or the sketch is unlabeled	The report is incomplete

Differentiation

Support

Give these teams a printed grid overlay and a prepared data table with the column headings and trial numbers already filled in, so recording is a matter of shading squares and writing times. Assign fixed roles of dye releaser, timer, recorder, and grid marker, and rotate them once per session.

Extension

Ask the team to add a fourth criterion for energy, estimating which layout would need the pump running longest to reach the same coverage, and to explain how that criterion would change the recommendation. Teams may also test whether water depth changes the dead-zone pattern, holding everything else constant.

ELL supports

Supply a labeled top-view diagram of a lagoon with inlet, outlet, berm, and diffuser marked, and pair each vocabulary term with a picture on the team's table tent. Offer sentence frames such as "In trial ___ the dye did not reach ___, so that area is a dead zone" and "We kept ___ from Layout ___ because ___."

Extensions

Ask teams to write a short maintenance note for the operator who would clean the recommended diffusers, naming how often and from where. Comparing maintenance notes across teams usually reveals that the layout with the best coverage is not always the one an operator can service, which is a trade-off worth a full class discussion.