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Debate kit Grade 9 Science

Where Ivenden's Concentrate Goes: River or Injection Well

A grade 9 science debate kit on whether a fictional brackish water plant should send its salty reverse osmosis concentrate to a river or into a deep injection well.

Objectives

  1. Students will explain what reverse osmosis concentrate is and why it must be disposed of somewhere.
  2. Students will evaluate two disposal designs against cost, reliability, and environmental criteria.
  3. Students will deliver a rebuttal that cites a specific point from the evidence file.

Vocabulary

Reverse osmosis
Reverse osmosis cleans water by pushing it through a membrane with holes so tiny that salt and most other dissolved things cannot fit through. It can even turn seawater into fresh water.

Also: concentrate, brackish, dilution, injection well, chloride

Teacher overview

This kit runs as a two-team structured debate across two class periods, with the first period used for evidence study and preparation and the second for the rounds themselves. Reverse osmosis produces clean water and a leftover salty stream called concentrate, and every plant that uses the process must send that concentrate somewhere. The choice in this fictional case is genuinely contested, because the cheaper route puts salt into a river while the injection route keeps salt out of the river but costs far more and depends on a well that has to hold for decades.

Where Ivenden's Concentrate Goes: River or Injection Well — Grade 9 Science
Name: ____________________________ Date: ______________

Resolution & Background

Resolution: "The Ivenden Water District should discharge its reverse osmosis concentrate to the Slipford River through a diffuser, rather than build and operate a deep injection well."

Background: Ivenden is a fictional town whose groundwater is brackish, meaning it is salty enough to taste but far less salty than seawater. To make it drinkable, the district built a reverse osmosis plant. In reverse osmosis, pumps push water at high pressure against a membrane. Clean water passes through, and the salts stay behind in a smaller, saltier stream called concentrate.

The fictional Ivenden plant produces 3 MGD of drinking water and about 0.6 MGD of concentrate. The concentrate is roughly six times as salty as the water entering the plant. Salt does not break down, so treatment cannot destroy it the way disinfection kills bacteria or oxidation breaks down organic matter. The district must choose where the salt ends up.

Two options are on the table. The first is a pipe to the Slipford River, ending in a diffuser, which is a length of pipe with many small ports that spreads the discharge across the channel and speeds up mixing. The second is a deep injection well that would place the concentrate in a salty rock layer far below any aquifer people drink from.

Roles. Form two teams of equal size. The affirmative team argues for the river diffuser. The negative team argues for the injection well. Each team assigns one speaker for the opening case, two for evidence questions, and one for the closing rebuttal. Choose two students as judges who score with the rubric below, and one as a timekeeper. Suggested rounds are four minutes for each opening, three minutes for each cross-examination, and three minutes for each closing.

Evidence File

Case for the river diffuser:

  1. Cost is the clearest difference. A fictional engineering study prepared for this debate puts the diffuser pipeline at about $6 million to build, against about $24 million for the injection well and its monitoring wells. Ivenden has roughly 9,000 customers, so the difference lands on a small number of households. (Illustrative estimate created for this debate.)
  2. Dilution is real and measurable. In the same fictional study, the Slipford River carries far more water than the plant discharges, so a diffuser spreads the concentrate across the channel and mixes it within a short distance downstream. Engineers design the mixing zone and the permit sets its limits. (Illustrative engineering description created for this debate.)
  3. A discharge permit can be written with conditions. A fictional state permit writer testifies for this debate that the district could be required to monitor chloride continuously, and to hold the concentrate in a lined basin whenever river flow drops below a stated level. That makes the risk manageable rather than permanent. (Illustrative testimony created for this debate.)
  4. An injection well is not risk-free. Its casing must stay sealed for decades, it needs constant pumping energy, and if it fails the district still has to find another route for the concentrate. (Illustrative engineering description created for this debate.)

Case for the deep injection well:

  1. Dilution spreads salt but does not remove it. Chloride stays dissolved and travels downstream, and a fictional downstream irrigation district testifies for this debate that several of its crops are sensitive to rising chloride in irrigation water. (Illustrative testimony created for this debate.)
  2. Dilution is weakest in late summer, when the river is lowest. A fictional river study prepared for this debate shows Slipford River flow dropping sharply in late summer, which is also when water temperatures peak and aquatic life is already stressed. Less river flow means less dilution on the worst days. (Illustrative study created for this debate.)
  3. Concentrate is not only salty. Because reverse osmosis leaves everything the membrane rejects in a smaller volume, naturally occurring elements in the source groundwater are also concentrated. A fictional laboratory report for this debate found the concentrate carried elevated levels of several such elements. (Illustrative laboratory report created for this debate.)
  4. Injection places the salt below the aquifers people use, in rock that is already salty. A fictional hydrogeologist testifies for this debate that this is the only option of the two that keeps the salt out of the river permanently, rather than moving it downstream. (Illustrative testimony created for this debate.)

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

Rubric
Criterion Emerging Developing Proficient Advanced
Use of evidence States a position without citing the evidence file Cites one point but does not explain why it matters Cites at least two points and explains how each supports the team's position Cites several points, explains them, and distinguishes illustrative material created for this debate from technical description
Reasoning about trade-offs Names only one criterion, usually cost Names two criteria but does not weigh them against each other Weighs cost, reliability, and environmental impact and states which the team ranks highest Weighs all three criteria, states a priority order, and defends that order against the other team's ranking
Rebuttal quality Does not respond to the opposing case Responds in general terms without evidence Answers a specific opposing point using a named piece of evidence Answers several opposing points and explains why its own evidence carries more weight
Delivery and organization Hard to follow, no clear structure Structure present but transitions unclear Clear claim, evidence, and conclusion within the time limit Clear structure, controlled timing, and direct engagement with the other team's strongest point

Differentiation

Support

Give these students a one-page version of the evidence file with the strongest two points for their side, each reduced to a single sentence, and a rebuttal frame: "The other team says ___, but our evidence shows ___." Let them deliver from written notes and reduce their speaking time to two minutes.

Extension

Ask these students to prepare a third option that neither side has argued, such as evaporation ponds or a shared regional pipeline, and to explain in a short written brief which of the two debated options it most resembles on cost and on permanence. They should identify what additional data the fictional district would need before choosing it.

ELL supports

Pre-teach "concentrate," "brackish," "dilution," "diffuser," and "injection well" with a simple labeled drawing of a membrane, two outgoing pipes, and a river. Provide a glossary card at each seat and allow students to write their opening in their first language before translating the key claim.

Extensions

After the debate, have students write a one-paragraph recommendation to the fictional Ivenden board that names the option they would choose, the criterion they ranked highest, and the one piece of evidence that would change their mind. Collect these and sort them by choice, then discuss whether students who chose differently ranked the criteria differently rather than reading the evidence differently.