ISG presents water system master plan to Eldridge utility board; recommends new well, clear‑well fix and long‑term plant options

Lenny Larson of ISG presented a master‑plan review of Eldridge City’s water system at the April 7 meeting of the Eldridge Electric and Water Utility Board, laying out current demand, identified deficiencies and a phased list of improvements. "For existing water demand, for example, the average is 580,000 gallons per day with a peak of 1.34 million gallons per day," Larson said, citing the study’s baseline numbers.

Larson told the board the system’s per‑capita use is about 86 gallons per day and that growth projections for 2045 range from roughly 9,040 to about 9,990 residents. Using the higher projection, ISG recommended planning on an average day demand of roughly 810,000 gpd and peak demand up to about 1.86 million gpd.

At the top of ISG’s recommended immediate work is correcting clear‑well short‑circuiting and fixing the chlorine feed configuration. "That water mixing in the clear well is a safety and disinfection issue," Larson said, and he estimated the exterior re‑piping work and associated changes at about $200,000. Larson also recommended adding an isolation valve between the plant’s two clear‑well tanks so each half can be serviced independently.

Near‑term projects in the report include constructing a new production well (and abandoning Well No.2) with an estimated cost of about $1.6 million, rehabilitation of a detention tank and aerator (estimated $400,000–$450,000), and replacement or upsizing of a 6‑inch distribution main leaving the treatment plant to improve system pressure and feed capacity. Larson said replacing the filter media in filter cells 1–4 was recommended but not immediately urgent; recent vendor pricing provided to the board came in at about $180,000–$190,000, below ISG’s initial $300,000 estimate.

Larson described options for long‑term capacity increases. Expanding the existing plant with reverse‑osmosis (RO) softening or additional filtration could roughly double capacity; ISG gave a working range of $15–25 million for an expansion and said building a new plant with different treatment technology could cost more. "With the RO, would that push that to the $25,000,000 range?" a board member asked. Larson replied, "Yeah," and explained the board would see a wide cost band depending on technology and siting.

ISG recommended the city consider partnering with Iowa American Water to serve a southern industrial area rather than building a large new plant immediately. Larson said that build‑out for the industrial site could require 6–7 million gpd and might mean a $40–$70 million facility depending on aquifer depth and treatment; partnering could provide a quicker, lower‑cost supply for heavy industrial demand while preserving an emergency interconnection to Eldridge’s system.

Larson also outlined rate and financing implications. Using a 20‑year SRF loan scenario, ISG presented an illustrative annual debt service of about $257,536 for a $3.5 million first loan package (projects 1–5), and a separate scenario for a $25 million plant expansion showed a potential per‑user increase in the ballpark of $55 per year at a 4% interest assumption. Larson cautioned that interest rate assumptions and the number of active connections affect per‑customer numbers and said grant opportunities exist (for example, a DNR grant up to $500,000 with a 50% match for eligible health‑and‑safety projects tied to nitrates/nitrites).

Board members asked about water age and distribution‑system nitrification in the eastern parts of town. Larson said water age there can be 7–10 days under current operation and that operating towers differently or installing a control valve could reduce age toward the 5‑day target; he noted any change would be modeled and phased so pressures in older northwestern neighborhoods remain adequate. "We can operate the towers differently where we actually set it where the tower would run lower on the East side of town," Larson said, but he cautioned the change might reduce pressure in some locations and should be tested incrementally.

Larson closed by offering to provide more detailed cost breakdowns and to coordinate site tours and operator exchanges if the board pursues specific treatment technologies. The utility board did not take an immediate policy vote on the master plan itself; members asked staff to factor the report into upcoming rate and capital planning work and to return with additional financial detail as requested.