Trellis Point Aquifer Storage: A Research Brief Project

Driving question

Should Trellis Point store treated surplus water underground in the Hollis Sand aquifer, or build the proposed Vantry Creek reservoir?

Scenario and client

Trellis Point, the Hollis Sand aquifer, the Vantry Creek reservoir proposal, and every person and organization named in the packet are fictional, and every document in the packet was written for this project. Trellis Point is a town of about eleven thousand people. It has enough water in most years and not enough in one year out of six. The town council's water committee has asked for recommendations before it votes, and your team will deliver one.

Aquifer storage and recovery means injecting treated drinking water into an aquifer during wet months and pumping it back out during dry ones. The aquifer acts as the tank. A surface reservoir does the same job in the open air, behind a dam, where the water can be seen and used for recreation and where some of it evaporates.

One acre-foot equals 325,851 gallons, a standard conversion used in water accounting.

Constraints

• The brief runs 1,200 to 1,500 words. Briefs outside that range lose credit on the rubric.
• The brief uses at least five of the seven packet documents, plus at least one source your team locates from the approved public agency list your teacher provides.
• The brief includes at least one quantitative comparison that converts acre-feet to gallons using the standard conversion above, and at least one comparison the table in Document 2 does not state directly.
• The brief states a recommendation in its first paragraph and answers the single strongest objection to it before the close.
• The team submits an annotated source list. Each entry gives one or two sentences on what the source contributed and one sentence on what it cannot settle.
• The presentation runs six minutes, followed by three minutes of questions from the committee panel.

Deliverables and audience

Each team submits the written brief and the annotated source list, and presents to a panel of three students acting as the Trellis Point water committee, with the teacher as chair. The panel scores the presentation criteria on the rubric and asks at least one question that presses on a source the team relied on.

Source packet

The seven documents below make up the packet. Read all of them before you decide which ones your brief will rely on.

Document 1. Hydrogeologist's report on the Hollis Sand aquifer (summary section)

Prepared for the Town of Trellis Point by R. Delacroix, licensed geologist, Corwell Groundwater Consulting.

The Hollis Sand is a confined aquifer of fine to medium sand that lies 340 to 520 feet below the town. A layer of clay 60 to 90 feet thick sits above it and keeps injected water from rising toward the surface. Water already in the Hollis Sand carries about 1,100 milligrams per liter of dissolved minerals. The treated water the town would inject carries about 220 milligrams per liter, and the town's own delivery target is 450 milligrams per liter.

Injected water pushes the native water outward and forms a zone of fresh water around each well. At the edges of that zone, the fresh water and the mineralized water mix. When the town pumps stored water back out, the recovered water grows more mineralized over time, and pumping has to stop once it reaches the 450 milligram target. The water left behind in the mixed zone is the main reason recovery is incomplete.

In our pilot test last winter, we injected 60 acre-feet into a test well, stored it for 90 days, and recovered 41 acre-feet before the target was reached. That is a recovery efficiency of 68 percent. At other sites, recovery has usually improved over the first several cycles, because each cycle leaves behind a buffer of fresher water. On that basis we project a recovery efficiency of about 78 percent by the third or fourth cycle. This projection cannot be confirmed until those cycles have been run.

The proposed system has three wells that both inject and recover water, with a combined capacity of 2.0 million gallons per day. Total storage is limited to 1,900 acre-feet so that injection pressure stays well below the level that could crack the clay layer. At the full rate over a 180-day wet season, the wells can store about 1,100 acre-feet, so filling the aquifer completely would take two wet seasons.

Two uncertainties remain. First, the Fenwick Farms irrigation wells, about two miles east, pump from the same sand, and heavier pumping there could draw stored water away from the town's wells and lower recovery. Second, oxygen in injected water can react with some minerals in the sand and release arsenic. Recovered water in the pilot test showed no arsenic above the laboratory's detection limit, but only one cycle has been tested.

Document 2. Engineer's cost estimate for both options (summary page and notes)

Prepared by Halvorsen Civil Engineering for the Trellis Point water committee.

Item	Aquifer storage and recovery	Vantry Creek reservoir
Capital cost	$12,700,000	$41,000,000
Annual operating cost	$860,000	$240,000
Storage available	1,900 acre-feet	5,400 acre-feet
Water lost to evaporation each year	None	About 310 acre-feet
Share of stored water recoverable	About 78 percent	About 94 percent
Land required	6 acres	220 acres
Years to permit and build	4	11

Notes on the estimate:

• All costs are in 2026 dollars and include a 25 percent allowance for unexpected costs.
• The aquifer capital cost covers three wells, 2.4 miles of pipeline, land, and equipment to disinfect recovered water and remove iron before delivery. The operating cost covers electricity to pump water down and back up, water-quality monitoring, and regular cleaning of the well screens, which slowly clog with fine particles.
• The reservoir capital cost covers the dam and spillway, purchase of 220 acres, relocation of 1.3 miles of Vantry Creek Road, and a pipeline to the treatment plant. The operating cost covers dam safety inspections, one full-time staff position, and maintenance.
• For the aquifer, the recoverable share is the hydrogeologist's projection for later cycles (Document 1). For the reservoir, it is the share of stored water that sits above the lowest outlet, after seepage. Evaporation is listed separately because it depends on how long water is held and how hot the summer is. In normal years, creek inflow replaces it; in dry years, it does not.
• The schedule assumes that no party objects to the reservoir's storage water right.
• The estimate does not include water released downstream for other users, any state grant, or the cost of borrowing.

For context, the town uses about 1,850 acre-feet of water in a normal year. The town's supply plan estimates a shortfall of about 650 acre-feet in a single dry year and about 1,400 acre-feet over two dry years in a row.

Document 3. Minutes of the Trellis Point water committee, March 4 (public comment)

Committee chair Deborah Ames opened public comment on the two water storage options. Three residents spoke.

Mr. Lyle Kowalczyk of Ridge Road spoke in favor of the reservoir. He said his family has fished Vantry Creek for three generations and that a lake would bring families to the town. He said water put into the ground "never comes back the way it went in" and that a town in his wife's home state had lost most of what it stored underground. He did not name the town.

Ms. Teresa Odum of Mill Street, a retired civil engineer, spoke in favor of the reservoir. She said the reservoir would store almost three times as much water as the aquifer option and that the town should plan for droughts longer than two years. She said a dam is a proven technology that staff can inspect directly, while water underground cannot be seen. She asked whether the engineer's estimate included water that would have to be released downstream.

Mr. Ray Pruitt of Pruitt Orchards spoke against the reservoir. He said 64 of the 220 acres in the reservoir footprint are his family's orchard and that the family will not sell willingly. He said a lake in a valley with hot summers will lose water to the air every year, and that eleven years is too long to wait when a dry year is likely to arrive before then.

Chair Ames thanked the speakers and asked staff to report on downstream releases, borrowing, and permit timelines at the next meeting. The committee took no action.

Document 4. Letter from the Lower Vantry Irrigation District

Dear members of the water committee,

The Lower Vantry Irrigation District delivers water from Vantry Creek to 48 farms covering about 6,800 acres below the proposed dam site. Our right to divert water from the creek is older than the town's, and in dry summers the creek already falls short of what our members need.

A dam would capture winter and spring flow that now reaches our diversion. Part of that flow soaks into the creek bed and seeps back into the channel later, which keeps the creek running in late summer. The engineer's estimate (Document 2) appears to assume that the town may keep all of the water that reaches the reservoir.

We ask that any storage permit require the town to release at least 600 acre-feet to the creek each summer. If the town applies for a storage water right without that condition, our board has voted to object at the state hearing.

The district takes no position on aquifer storage, provided the town injects only water it already has the right to use.

Sincerely,
Anita Brandt, General Manager

Document 5. Memo from the town finance director

To: Water committee. From: Gordon Phiri, Finance Director. Subject: Borrowing capacity and rate effects of the two storage options.

The town can borrow up to $20 million for water projects through the state revolving loan fund, at 2.0 percent interest over 30 years. Borrowing above that amount would require a general obligation bond approved by voters, which I estimate at 4.0 percent over 30 years. The town has never put a bond of this size before its voters.

The figures below assume the full capital cost of each option is borrowed. I have spread the yearly loan payments and operating costs across the town's 4,300 water accounts.

Item	Aquifer storage and recovery	Vantry Creek reservoir
Amount borrowed	$12.7 million state loan	$20 million state loan and $21 million voter-approved bond
Yearly loan payments	About $567,000	About $2,107,000
Yearly operating cost	$860,000	$240,000
Total yearly cost	About $1,427,000	About $2,347,000
Added to the average monthly bill	About $27.70	About $45.50

The average monthly water bill is now $54, so the aquifer option would raise it by about 51 percent and the reservoir by about 84 percent. The state's drought-resilience grant program could lower either figure, yet awards are competitive and the town has not applied before. These figures do not allow for operating costs rising over 30 years.

Document 6. State permit checklist for local water storage projects (summary for local governments)

Aquifer storage and recovery

• State aquifer storage permit, which requires a completed pilot test and at least one year of monitoring data
• Authorization for the injection wells under the federal Underground Injection Control program, which the state administers
• A well construction permit for each well
• Local land-use approval for the well sites

Since 2008 the state has approved five aquifer storage projects. The time from application to first recovery ranged from 3 to 6 years, with a median of 4 years.

Surface reservoir

• A new water right for storage, decided at a public hearing if any party objects
• Dam safety approval of the design and of construction
• A federal permit for placing fill in a stream channel and in wetlands
• State environmental impact review
• A streambed alteration agreement with the state fish and wildlife agency

The last three dams of similar size in the state took 9, 13, and 16 years from application to first storage. No one objected to the water right for the 9-year project. The other two went through contested hearings.

Document 7. Letter from the Vantry Valley Paddle and Trail Association

Dear committee members,

Our association has 210 members who paddle, fish, and hike in the Vantry Valley, and we write in support of the reservoir. A lake of this size would allow boating, shoreline fishing, a swimming beach, and a loop trail. The aquifer option would offer none of these.

Kessel Lake in the next county draws about 70,000 visits a year. Kessel Lake is about twice the size of the proposed reservoir, so we estimate the Vantry Creek reservoir could draw about 35,000 visits a year and support new businesses such as a boat rental and a bait shop.

Our members would volunteer to build and maintain the trail. We ask the committee to count recreation as a benefit when it compares the two options, because the engineer's estimate (Document 2) leaves it out.

Sincerely,
Marcus Webb, President

1. Session 1, scope the question. After reading the packet, each team submits a one-paragraph research memo naming which option it will examine first, three sub-questions its sources might settle, and one question it expects the packet cannot answer. The memo must name the sub-question the team thinks will decide the recommendation.
2. Session 2, triage the sources. Each team submits an annotated list of at least five of the seven packet documents plus the one located source, with a single sentence for each stating what it can settle and a single sentence stating what it cannot. Any packet document the team plans to leave out must be named with a reason.
3. Session 3, build the quantitative comparison. Each team submits a one-page comparison that converts both storage figures in Document 2's table to gallons using 325,851 gallons per acre-foot, applies the recoverable share to each, and states at least two derived comparisons the table does not give directly. Derived comparisons may also draw on figures in Documents 1, 4, 5, and 6. The page must end with one sentence saying what the numbers do not decide.
4. Session 4, draft the brief. Each team submits a complete draft of 1,200 to 1,500 words with the recommendation in the first paragraph, evidence from at least six sources, and a paragraph stating and answering the strongest objection. Drafts are exchanged with another team for a written response naming the weakest piece of support.
5. Session 5, revise and present. Each team submits the final brief and annotated source list, then presents for six minutes and takes three minutes of questions from the committee panel. Every team member speaks, and the team must answer at least one question about a source's limits.