← All docs

Hydrology — Tier-0 municipal water-flow findings

Generated by watermark (watermark.hydrology). Tier-0 SCS screening — auditable and fast, not a substitute for SWMM/HEC-RAS. Every figure is tagged [verified] (read from a record or a live gauge) or [inference] (assumption/derived).

1. The municipal loop and its low-flow squeeze

The Lima system is one closed loop on two rivers:

Auglaize/Ottawa → Lima WTP → municipal + data-center demand → WWTPs → Ottawa River

Low-flow assimilative screen (discharge vs the receiving stream’s cited 7Q10):

• ❌ Shawnee II WWTP → Ottawa River: 7Q10 0.2 cfs vs discharge 4.64 cfs → 0.04:1 dilution (violation). [verified] Ohio EPA NPDES fact sheet 2IG00001 (Lima Refining Co.), Stream Flows table — Ottawa River at Lima, USGS gage 04187100, 1989-2021
• ❌ American Bath WWTP → Pike Run: 7Q10 0.03 cfs vs discharge 2.32 cfs → 0.01:1 dilution (violation). [verified] Ohio EPA NPDES fact sheet 2PH00007 (American Bath WWTP), Stream Flows table — USGS Gauge 04186500 adjusted for drainage area
• ❌ American II WWTP → Dug Run: 7Q10 0.78 cfs vs discharge 1.86 cfs → 0.42:1 dilution (violation). [verified] Ohio EPA NPDES fact sheet 2PH00006 (American II WWTP), Stream Flows table — USGS Station 04187500

At design low flow the receiving streams carry less than the effluent they receive — the discharges are effectively undiluted.

A second campus pathway — stormwater to Pike Run. Distinct from the FM-2 process discharge above (routed to Lima’s WWTP), the campus’s stormwater leaves the site via a constructed BOSC Storm Outfall channel that discharges to Pike Run — the loop’s most flow-starved tributary (7Q10 0.03 cfs, already shown undiluted by the American Bath WWTP). Per the roundabout/outfall SWP3 (Ohio EPA eDoc 4091286; operator George J. Igel & Co., engineer WSP USA; prepared 2026-04-16) [verified: document], the site drains east-to-west by subsurface tile and the outfall channel terminates at Pike Run. That SWP3 documents construction disturbance (5.71 ac), not a continuous low-flow discharge, so the pathway is recorded as a receiving-water fact, not added to the routed mass balance below.

The cited 7Q10 is independently reproducible. The denominator above is a single number read off a fact sheet. Computing it ourselves from the raw record — the USGS daily-mean discharge at the same gage the fact sheet names (NWIS 04187100, Ottawa River at Lima OH, 1988-09-30..2024-12-31, 24 complete climatic years) — lands on it. Annual n-day minima by climatic year, fit with log-Pearson III and bracketed by the non-parametric Weibull plotting position [inference: derived]:

The computed 7Q10 is 0.2387 cfs against the cited 0.2 cfs — agreement to within rounding, from an independent method on a longer record than the fact sheet used. The 1-day record is dry in 21% of complete years, so the computed 1Q10 is 0 cfs — the mainstem literally stops, matching the cited 1Q10. So the assimilative screen’s denominator is not an Ohio EPA artifact to be argued with; it is what the river actually carries at design low flow, reproducible by anyone with the public gage record. These computed figures are [inference: derived] and corroborate — they do not replace — the cited regulatory statistic.

The whole loop at design low flow: a routed mass balance

The screen above reads each plant against its own tributary in isolation. Routing the cited headwater 7Q10s, the document-cited WWTP/campus discharges, and the cooling draw through the cited confluence graph (data/reference/hydrology/network.yaml) shows the system picture the per-stream rows miss. At design low flow the loop’s streams carry, in total, only 1.01 cfs of natural low flow (Ottawa 0.2 + Dug Run 0.78 + Pike Run 0.03 [verified: document]). The three county WWTP discharges alone add 8.82 cfs of treated effluent — 8.7x the streams’ entire natural low flow, with no data center in the picture. The river at design low flow is effluent, not stream. The campus then adds its own documented 3.87 cfs FM-2 industrial discharge (routed via Lima’s sewer + WWTP), taking the Ottawa leaving Lima to 93% treated effluent — a conservative floor, since Lima WWTP’s own larger municipal discharge has no cited design flow in the corpus and is not counted.

Under buildout the cooling consumptive draw of 4.85 cfs is 4.8x the loop’s entire natural low flow. It consumes the Ottawa mainstem’s entire design low flow — it runs dry at the intake, leaving a 3.84 cfs shortfall the river cannot supply. The routed balance conserves mass (base + gains - applied loss reconciles to the 13.50 cfs outlet) [inference: derived]. The order-invariant system totals are the robust result; the per-reach values depend on the cited-but-approximate confluence order and are screening-grade.

Industrial toxic dischargers on the same reaches. The municipal screen above covers the three WWTPs; the industrial side is larger. Of the 12 EPA-RSEI facilities that release toxics to water in the county, 3 sit on a near-undiluted reach. Placing each on its receiving stream (ECHO-cited where available, else inferred from the Ottawa River industrial corridor) and reading it against the same cited 7Q10:

* = receiving water inferred from the corridor coordinate cluster, not independently cited. The screen mg/L is a coarse [inference: derived] value (annual reported water pounds, fully mixed at the 7Q10) — an order-of-magnitude screen, not a measured concentration.

The seasonal pinch compounds it: the Ottawa’s 1Q10 is 0 cfs (and summer 30Q10 1.6 cfs [verified: document]) — the mainstem effectively dries at design low flow. That floor falls in the May-Oct window where reference ET exceeds precipitation (§3), so the largest toxic loads meet the smallest assimilative capacity exactly when the river is lowest.

Outfall flood exposure. None of the 3 plant sites sits in the FEMA Special Flood Hazard Area at its ECHO-reported point, but the discharge infrastructure is flood-adjacent on streams already shown to be undiluted at low flow [verified: document]:

ECHO coordinates are the facility location, a proxy for the NPDES outfall; the actual outfall discharges at the receiving stream and is likely closer to the mapped floodplain than the facility centroid. So the mapped exposure understates the outfalls’: the discharge points themselves sit at the receiving water, inside or at the edge of the AE floodplain.

2. The Maumee Nutrient TMDL: the same discharges are capped phosphorus loads

These discharges don’t just strain a local stream. The Ottawa flows to the Auglaize and on to the Maumee — Lake Erie’s largest tributary and the driver of its western-basin harmful algal blooms. The 2023 Maumee Watershed Nutrient TMDL (Ohio EPA, US-EPA-approved) assigns each individually permitted discharger a total-phosphorus wasteload allocation: a spring-season (March-July) cap, also stated as a daily equivalent. The plants the low-flow screen flags as effectively undiluted are the same permits carrying these caps [verified: document]:

Across the whole grouped category of individually permitted dischargers the cap totals 64.1 metric tons (418.8 kg/day) of spring phosphorus. So the local dilution failure compounds a basin-scale constraint: at design low flow these effluents are near-undiluted, and every pound of phosphorus is metered against a Lake Erie nutrient budget.

3. Stormwater: paving the corridor

Climate baseline (NASA POWER). The Lima point averages ~997 mm/yr of precipitation (corrected), peaking in May, at a mean annual temperature of 10.7 °C [reference: NASA POWER climatology]. The satellite climate normal sets the long-run water budget; the design storm below is the NOAA Atlas-14 extreme the corridor must detain — the two are complementary.

Reference ET (FAO-56 Penman-Monteith). Atmospheric water demand runs ~1,085 mm/yr of reference ET0, computed from the same POWER normals (temperature, humidity, wind, solar) [derived: FAO-56 Penman-Monteith]. Net of precipitation that is -88 mm/yr — and ET0 exceeds rainfall across the May-Oct growing season, so summer soil moisture, pond evaporation, and any consumptive cooling draw compete for water in the months the Ottawa is already near its low-flow floor (§4).

A 25-yr 24-hr design storm (4.25 in [inference: assumption]) over the 340-ac footprint [verified]:

• 25-yr 24-hr storm (4.25 in): peak 373 -> 482 cfs (+109, CN 85 -> 94)

• runoff volume 75 -> 100 ac-ft (+25 ac-ft to detain for pre-development control)

The footprint sits just outside the FEMA floodplain — but only just. The recorded campus parcels intersect no FEMA Special Flood Hazard Area, yet Zone AE and AE (FLOODWAY) (1%-annual-chance floodplain and regulatory floodway) reach within ~50 m of them (FEMA DFIRM 39003C_FIS5) [verified: document]. The post-development runoff increase routes toward that corridor; a regulatory floodway tolerates no rise, so added peak discharge there is a permitting constraint, not only a detention-sizing question.

Drainage scope vs the design storm

The roundabout program budgets $1,068,530 of drainage across 6 OPC sub-estimates [verified: document], but the engineering basis is thin. Auditing what the estimates actually quantify against the corridor design rainfall:

Atlas-14 corridor design storm (24-hr) [verified: connector]: 2-yr 2.52 in, 10-yr 3.58 in, 25-yr 4.25 in, 50-yr 4.81 in, 100-yr 5.39 in.

• $1,068,530 of drainage across 6 sub-estimates (7.5% of the $14,233,081 program), but only 1 of 6 carry an extracted line-item breakdown — the rest is a bare section subtotal.

• $100,000 of $120,440 (83%) is lump-sum ‘Drainage improvements’. The only sized conveyance is: 6” shallow pipe underdrains with geotextile fabric, as per plan.

• No estimate cites a design storm or return period. The corridor design rainfall (NOAA Atlas-14): 25-yr 24-hr 4.25 in, 100-yr 24-hr 5.39 in [verified: connector] — the basis the unsized storm-sewer / detention scope must meet.

• Neither the OPC drainage scope nor the 95% SPS grading & storm plan itemizes detention/retention storage (detention_shown=false), echoing the corpus’s own open question on the lump-sum DRAINAGE items.

This is a design-basis / scope-completeness reading, not a sizing of the roundabouts’ hydraulics — the corpus carries no per-roundabout footprint area, so runoff/detention volumes are deliberately not computed.

4. Scenario: data-center cooling vs the Ottawa’s low flow

The cooling demand is sourced, derived from disclosed campus data by two methods:

• top-down: IT load 275.00 MW [verified: document] x WUE 1.80 L/kWh [inference: assumption] → 3.14 MGD consumptive
• bottom-up: FM-2 blowdown x 5 cycles → 10 MGD consumptive (upper bound)

They bracket the consumptive demand at 3.14-10 MGD (FM-2 is not purely cooling blowdown). The conclusion is robust to the range.

Buildout adds 4.85 cfs of net consumptive draw — 24.3x the Ottawa River’s cited 7Q10 (0.2 cfs). At design low flow the Ottawa nearly dries (1Q10 = 0 cfs); a data center’s cooling draw competes for water the river does not have — even the low estimate is tens of times the 7Q10.

The seasonal pinch: the draw lands when the river is lowest

The annual-7Q10 multiple understates the constraint. The growing season (MAY-OCT, where reference ET exceeds precipitation — §3) is exactly when the Ottawa sits at its summer design low flow, with no rainfall buffer. Reading the same consumptive draw against the cited seasonal floor:

In the MAY-OCT window the draw is 3x the cited summer 30Q10 (1.6 cfs) — vs 24.3x the annual 7Q10. And the summer 30Q10 is the generous floor: the Ottawa’s absolute design low flow is 1Q10 = 0 cfs [verified: document], so in the driest growing-season weeks there is no flow to draw against at all. The cooling draw peaks against supply precisely when the atmosphere is also taking the most.

5. Tier-1 escalation (EPA SWMM)

watermark tier1 runs the real EPA SWMM5 engine on the footprint under the design storm for two questions Tier-0 only approximates: the detention volume that holds the post-development peak to the pre-development rate, and the sanitary wet-weather surcharge (dry-weather base + RDII) against each plant’s documented wet-weather headroom. Hydraulic routing parameters (imperviousness, RDII, basin geometry) are assumptions; the footprint, storm, and plant design flows stay document/connector-sourced.

The committed run (pyswmm 2.1.0, 25-yr 4.25-in storm; mass-balance continuity error 0.00%) [inference: derived] sizes the detention the corridor needs. Paving the footprint takes the design-storm peak from 215 cfs (cropland) to 579 cfs (impervious); holding the release back to the pre-development rate (216 cfs) takes a 42 ac-ft basin (13.6 ac, 5.49-ft bottom orifice). The four input decks are committed under data/reference/hydrology/swmm/ so anyone can re-run them in EPA SWMM.

The campus’s storm-driven sanitary peak does not stay on site — it rides the forcemains to the treatment plants. It is judged only against the plants that actually receive it:

Campus sanitary routing: FM-1 → American Bath WWTP + American II WWTP; FM-2 → City of Lima WWTP. Receives campus flow but peak hydraulic capacity not cited (campus share not quantified): American Bath WWTP, City of Lima WWTP. Excluded — no campus routing (FM-3 theorized): Shawnee II.

That 16.9 MGD is the campus’s total wet-weather sanitary peak; it splits across FM-1 (the small American Bath / American II plants) and FM-2 (the City of Lima sewer). The corpus does not quantify the split, so it is not apportioned — but the total alone is several times even American II’s whole wet-weather headroom (2.4 MGD), so the small FM-1 plants cannot absorb their share. The RDII rate is an uncalibrated screening assumption — but the direction is robust, and it lands on the regulatory fact below.

The surcharge lands on a system with no headroom to give. Permitted average / peak design flows are document-cited [verified]: American II 1.2/3.6 MGD (headroom 2.4); Shawnee II 3/12.6 MGD (headroom 9.6). The decisive fact is regulatory: the collection system is already under a 2005 OEPA mandate to eliminate all SSO bypassing by 2015, with $11.8M of storm-water I/I remediation and a 21-inch trunk replaced by 48-inch purely to equalize wet-weather I/I. So each plant’s nominal wet-weather headroom (peak minus permitted average) is already documented as effectively spent before the campus adds load. The campus’s documented dry-weather contribution is the 2.5 MGD FM-2 industrial discharge; the storm RDII multiplier on top remains an assumption.

Detention is the absent control, not a modeled redesign. The campus grading & stormwater plan (1A-C-3104, 95% SPS Design, [verified]) routes runoff via catch basins -> inlets -> storm sewer to headwall outfalls (with rock check dams and overland flood routing) and shows no detention, retention, or infiltration storage across its 207 storm-structure rims (820-829 ft). So the SWMM-sized basin is the on-site control the as-drawn 95% design omits. Pipe connectivity/inverts are drawn as vector geometry with no schedule table, so a routable network is deliberately not transcribed (omission over invention).

Sources: USGS NWIS (streamflow), NOAA Atlas-14 (design rainfall), NASA POWER (climate normals), Ohio EPA NPDES fact sheets 2PH00006 / 2PH00007 / 2IG00001 (receiving-stream 7Q10), Maumee Watershed Nutrient TMDL Appendix 4 (phosphorus WLAs), recorded Bistrozzi parcels (footprint). Regenerate with watermark hydro-report --write.