BOSC water-balance run — assimilative screen + the new sanitary figures
Run: watermark hydro (live) + the committed buildout scenario, 2026-06-08.
Engine: Tier-0 water balance + 7Q10 low-flow assimilative screen
(watermark.hydrology). Tier-0 is an auditable screen, not a SWMM/HEC-RAS result.
Live streamflow: Ottawa River at Lima, NWIS gage 04187100 (today ~90.5 cfs /
58.5 MGD — ambient flow, well above the regulatory low-flow design condition).
This memo records the run and folds in two newly document-sourced figures from the commissioners’ minutes (sanitary-economics.yaml) that the model did not previously carry.
Headline
All three County receiving streams already FAIL the 7Q10 low-flow dilution screen at their design flows — before any data-center load. The Ottawa River’s regulatory 7Q10 is 0.20 cfs (≈0.13 MGD); the BOSC campus’s consumptive cooling draw alone is modeled at 3.14–10 MGD — i.e. the data center’s evaporative loss is 24–77× the receiving river’s 7Q10 low flow.
The assimilative screen (Tier-0, 7Q10 dilution)
| Discharger | Receiving water | 7Q10 (cfs) | Discharge (cfs) | Dilution | Flag |
|---|---|---|---|---|---|
| Shawnee II WWTP | Ottawa River | 0.20 | 4.64 (3.0 MGD) | 0.04:1 | violation |
| American Bath WWTP | Pike Run | 0.03 | 2.32 (1.5 MGD) | 0.01:1 | violation |
| American II WWTP | Dug Run | 0.78 | 1.86 (1.2 MGD) | 0.42:1 | violation |
Source: NPDES fact sheets (2IG00001 Ottawa/Lima Refining; 2PH00007 American Bath; 2PH00006 American II) [verified]. 3 checks, 3 violations — the receiving waters are effluent-dominated at low flow.
The BOSC cooling load (buildout scenario, sourced)
- IT load 275 MW [document — OEPA Air PTI P0138965, committed
permits/4132514.epa.yaml(final, 2026-05-28); 114 gensets × 2.75 ekW ≈ 313 MW backup (per-engine ekW from the draft public notice — CBI-redacted in the final permit); IT 250–300 MW N+1]. - Makeup demand ≈ 3.92 MGD; consumptive 3.14 MGD (power × WUE 1.8 L/kWh [assumption]) to 10 MGD (FM-2 2.5 MGD blowdown × (CoC−1) [derived]). The two methods disagree ~3× — the consumptive draw is the model’s dominant uncertainty.
- Drawn on Lima’s Ottawa/Auglaize supply (7Q10 0.20 cfs). A 3–10 MGD consumptive loss on a river whose low-flow design condition is 0.13 MGD is the core assimilative concern.
New from the minutes (folded in here)
- Interim BOSC sanitary discharge: 0.13 MGD at 83 °F (sanitary-economics.yaml; minutes 2025-07-29) [document]. Two notes:
- Thermal. 83 °F is a warm return; the model carries flow but not temperature. A warm discharge into a low-flow stream is an additional (unmodeled) assimilative stressor — flagged for a thermal screen.
- Scale coincidence. The interim sanitary flow (0.13 MGD) happens to equal the Ottawa 7Q10 (0.13 MGD) — i.e. even the small early-phase return matches the river’s entire 7-day-10-year low flow.
- The permanent return is the FM-2 2.5 MGD industrial discharge already in the model.
- The Cridersville / Shawnee Oaks reroute loads the worst-violating node. The County is rerouting ~200+ homes + the Shawnee Oaks domestic flow onto Shawnee II (the $1M 0% loan, #137-26) — the same plant that already screens at 0.04:1 on the Ottawa. The reroute adds domestic flow on top of the BOSC industrial return to the most over-allocated receiving water. (Not yet quantified in MGD in the record — followup.)
What the run shows
- The municipal loop’s WWTPs are already effluent-dominated at low flow (2–25× over a 1:1 dilution); BOSC is added on top of a failing baseline, not a clean one.
- BOSC’s consumptive cooling draw (3–10 MGD) is large relative to the Ottawa’s low-flow supply — a withdrawal concern distinct from the discharge concern, and consistent with the residents’ well-drawdown questions in the PAAC minutes.
- The County’s own reroute concentrates more flow on Shawnee II → Ottawa, the worst-screening node.
Caveats
Tier-0 screen only. The 7Q10 is the cited regulatory low-flow (NPDES fact sheets); the live NWIS reading only sanity-checks ambient flow. WUE and cycles-of-concentration are assumptions (low confidence); the 3–10 MGD consumptive range is the headline uncertainty. The 83 °F thermal effect is noted, not modeled. Figures from the minutes are OCR-approximate discussion items — verify against the source PDFs.
Cross-references
- sanitary-economics.yaml — the 0.13 MGD @ 83 °F, the reroute, the fees
- bosc-resolution-ledger.yaml — #469-25/#713-25/#137-26 (PS+FM, CMAR)
data/scenarios/buildout.scenario.yaml— the sourced cooling basis rundata/reference/hydrology/— 7Q10 (low-flow-7q10), TMDL WLAs, sanitary basis- docs/HYDROLOGY.md — the full generated hydrology dossier
data/extracted/regulatory/wastewater-enforcement-history.yaml— Shawnee II capacity history