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HomeMy WebLinkAboutWritten Comments from Donna McGuire// BOTTOM LINE Our original complaint was that the Housing Element EIR under -analyzed sewer capacity and needed an independent look. The produced data confirms that --- and sharpens it. The EIR's numbers lean optimistic on both sides of the equation at once: it understates the load (Old Ranch counted residential -only, --2x low) and the City's model overstates the capacity (pipes drawn 3-8 inches larger than the City's own as-builts). Correct just the pipe sizes, using the study's own flows, and 18 stretches the City's consultant called adequate cross the deficiency line — roughly tripling the deficient footage. The case got stronger and more specific; a couple of our weaker talking points fall away. What changed, at a glance ♦ STRONGER NOW • The §65589.7 case. The City now has hard, measured grounds for written findings of "sewer service limitations." • The independence argument. The diameter error is exactly what an inside consultant inherits and an outside reviewer catches. • The load undercount. No longer a lone gripe — it stacks with the capacity error, same direction. • AKM's deficiency list. Now a floor, not the answer. // THE ONE TEST THAT SETTLES IT ♦ WEAKER I RETIRE IT • "They rely on stale 2005 data." Drop it — the file spans 2000- 2026. The real issue is data integrity, not age. • "The force -main bid is fake." It now looks real and rational — but that reads for us: it corroborates a known -bad gravity trunk. One checkable question settles it: are the trunk pipes the model's 15-18", or the 8--12" the as- builts, meters, and geometry all show? A CCTV pass or a few manhole pops answers it — and we should be first to ask. ♦ NEW QUESTIONS • Which City record is right — the model or the as-builts? (Settled by a field check.) • Why has no one reconciled them, when every study inherits the model? • If the developer force -mains around the trunk, where does it discharge — and can that system take it? // THE HONEST COMPLICATION The same evidence hands the developer a workaround: a force main that reroutes off the deficient reaches. So the case is strongest for conditioning the gravity path; against a force main the fight moves to the discharge point ---- still open. i; L'F—.',iL l �; 01 The reframe: three optimistic inputs, all leaning the same way Whether a sewer passes is a ratio — how much flow is coming versus how much the pipe can carry. The EIR's "less than significant" conclusion depended on that ratio looking comfortable. The produced data shows three separate inputs that each pushed the ratio in the reassuring direction: Load (Old Ranch) Capacity (pipe size) Review (independence) --26,720 gpd — residential units only (167 du) Trunk modeled at 12- 1811 Consultants tied to the projects and the model 51,626 gpd --- same units plus flow understated a 150-room hotel, medical --2x office, and clubhouse As -built GIS shows 8-12" on capacity the same reaches overstated 3-8" of diameter No outside party ever checked the error went the model against the as-builts uncaught The first two matter most because they compound. Understate the numerator and oversize the denominator and a strained system reports as healthy — not because of one masking error, but two, multiplying. That's the single most important thing the FOIA data changed: our complaints stopped being a list and became one coherent mechanism. // DETAIL • 2 OF i 02 The marquee finding: the model and the as-builts disagree The City keeps two records of the same pipes. The 2018 InfoSewer hydraulic model — the model AKM's Lampson study runs on — and the 2025 as -built GIS, the City's official asset map. On the College Park East trunk they don't match, and the model is always the larger of the two: Elder Ave (lower) 12" 8" +4- 0.38 0.77 flips Ironwood Ave 15" 10" +5" 0.36 0.67 flips Candleberry Ave 18" 10" +8" 0.26 0.82 flips Aster St 15" 12" +3" 0.40 0.57 flips Basswood St 18" 12" +6" 0.34 0.64 flips Lampson Ave 18" 15" +3- 0.36 0.47 holds Reading the table. "d1D" is depth -of -flow - pipe diameter — how full the pipe runs. The City's design limit is 0.50 for pipes 15" and smaller. A pipe drawn too large in the model reports a comfortable d/D; shrink it to the as - built size and the same flow has to climb higher, so d/D jumps. "Flips" means a reach the study rated adequate crosses the 0.50 limit once you use the real pipe. How the flip was computed •— no new assumptions This isn't a competing model. I took AKM's own future peak -flow and slope for each reach — their numbers, unchanged — and solved the standard open -channel flow equation (Manning's, n=0.013) for depth at the as - built diameter instead of the modeled one. Only one variable moves: the pipe size. That's what isolates the effect and keeps it apples -to -apples. Across the trunk, 18 reaches the study rated adequate come back over the limit, adding -4,000 ft of deficient pipe to the study's 2,748 ft. // DETAIL - 3 OF 6 03 Why we trust the smaller pipe — three records agree, only the model doesn't The whole finding rests on believing the as -built size over the model. It isn't one document against another — it's three independent City records landing on the same answer: The 2025 as -built GIS — the City's official map — puts Elder at 8 , Ironwood and Candleberry at 10", Aster and Basswood at 12". • The 2002 flow monitoring -- back -calculating pipe size directly from the City's own meters (flow velocity gives the flow area, which gives the diameter) returns 8-12" That's measured field data, not a drawing. • The manhole geometry — reading rim and invert elevations at the chokepoint manholes returns the same 10" and 12" pipes. The model is the lone outlier at 15-18" And it isn't quietly modeling a second relief pipe alongside a small one — the model's own "parallel pipe" flag is blank on every one of these reaches, so it's a single pipe of the assumed size. The most economical explanation is an optimistic diameter carried forward from an older master plan and never verified against the ground. // DETAIL • 4 OF 6 04 How each original suspicion moved The EIR punted the The City has a model and 26 years of data — so the stronger real sewer analysis to a issue isn't absence of analysis, it's that the analysis runs later study on inputs that contradict the City's own as-builts, and still shows exceedances The cumulative load Unchanged on its own, but now the load half of a stronger (Old Ranch) was stacked, same -direction error — more consequential undercounted -2x than in isolation No independent review Now demonstrable: the diameter error is the textbook stronger — conflicted thing an inside consultant inherits and an outside consultants reviewer catches §65589.7 "sewer Best gain: measured exceedances (Edinger surcharged much stronger service limitations" at 1.10 in 2002; 4 of 5 reaches over capacity) plus a findings continuous, understated deficiency give the City a real factual basis for written findings The City is relying on Retire it — the record spans 2000-2026. The stronger retire stale (2005) data replacement: the problem is data integrity (model vs. as -built), not age The $3.54M force- It now looks real and rational — a bypass of a genuinely reframed main bid might be fake deficient trunk. That corroborates us, but it also gives the developer a rerouting workaround AKM's -2,748 ft It's a floor. At as -built sizes the deficiency runs stronger deficiency is the continuously Elder->Basswood,-4,000 ft more; the number 57/43 fair -share split likely shifts too // DETAIL • 5 OF 6 05 The risk we created, and the strategic complication We made a falsifiable claim — on purpose. If the City pops those five manholes and the pipes really are 15- 18', the marquee finding collapses and the consultant is vindicated. Three independent records say otherwise, so I judge the risk low — but it is a real, checkable claim, and that cuts both ways. Better that we call for the field check and stand on it than have the other side spring it. Being first to ask for verification is the credible posture. The force main is double-edged. If the gravity trunk is deficient, a force -main -and -lift -station bypass is a logical fix — which is why the bid reads as real. But a bypass that routes flow off the deficient reaches is also the developer's answer to §65589.7: "we're not loading your bad trunk, so there's no limitation." 5o the capacity case is strongest for conditioning or stopping the gravity path. Against the force -main path it becomes a different question — where does the force main discharge, and does that receiving system have capacity? The pump -round data helps (the downstream stations show headroom), but the discharge point itself is the open item to press next. // DETAIL • 6 OF 6 06 What to do with it • Ask for the field check. A short records/CCTV request to field -verify diameter at Elder, Ironwood, Candleberry, Aster, and Basswood — cheap, fast, and it settles the one open variable. • Put the reconciliation on the record. The model -vs -as -built conflict is the City's to reconcile before any capacity conclusion is certified; surfacing it now is the point of maximum leverage. • Support written §65589.7 findings. The measured exceedances give the Commission a defensible basis, independent of the modeling dispute. • Pin the discharge point. If a force main is the developer's path, the next question is where it lands and whether that system can take it. // SOURCES City 2018 InfoSewer model (pipe geometry and results); City 2025 sewer GIS (line and manhole layers); City 2002 15-minute flow monitoring; AKM "4665 Lampson Ave Sewer Study," May 28 2026, Table 6. All produced under CPRA #26-274. Method: Manning partial -flow (n=0.013) solved for depth at AKM's stated flows; d/D criterion 0.50 (ng15") / 0.64 (�!13") per the City's 2018 SMP §3-5.2. College Park East / Lampson sewershed — briefing on the CPRA #26-274 findings • Aug 19, 2026 • internal working document, not a stamped engineering opinion // THE ONE -PARAGRAPH VERSION The model and the as-builts disagree — always in the direction that hides the problem Put the City's two records side by side on the same reaches and they don't match. The 2018 InfoSewer hydraulic model — the model AKM's May-2026 Lampson study runs on — carries pipe diameters 3 to 8 inches larger than the City's own 2025 as -built GIS across the College Park East trunk. A bigger pipe in the model means a lower computed d/D, so the model shows headroom the ground may not have. When I re -run AKM's own future flows through the as - built diameters, 18 reaches that AKM called adequate cross the City's 0.50 depth -to -diameter limit — Elder, Ironwood, Candleberry, Aster, Basswood — adding roughly 4,000 feet of deficient trunk on top of AKM's 2,748 feet. And this isn't a lone typo: the City's 2002 flow -meter data, back -calculated independently, lands on the same 8-12 inch pipes the GIS shows, not the 15-18 inch pipes the model assumes. // THE CAVEAT, UP FRONT This turns on which City record is right — the hydraulic model or the as -built GIS. I'm not asserting AKM did anything improper; AKM inherited the diameters from the City's model. What I'm showing is that two City datasets conflict, the conflict is large, it runs one way, and nobody has reconciled it. That's exactly the reconciliation an independent reviewer should force before the EIR leans on the capacity conclusion. // EXHIBIT A - THE MARQUEE Model vs. as -built diameter, reach by reach Same manhole IDs, same streets, same trunk. Left column is what the 2018 InfoSewer model (and therefore AKM) .....-.-. _:..I..I I.. :.. 41-.. r,:L. .I- rl nl .... L_.:ii -i� TI- 1.......-- ___ AI/R AI - _A X.-,._- -1 if - aL- — -J-I diameter versus the future d/D I get when I feed AKM's identical future PDWF and slope through the smaller as -built pipe. B12-A32 4 Elder Ave 12- 8" +4" 0.38 0.77 flips B08-A25 (lower) B08-A24 Ironwood Ave 15" 10" +5" 0.36 0.67 flips B07-A23 B06-A22 Candleberry 18" 10" +8" 0.26 0.82 flips B06-A21 Ave B05-A20 Aster St 15" 12' +3" 0.40 0.57 flips B03-A17 B03-A16 Basswood St 181, 12' +6" 0.34 0.64 flips B03-A15 1303-A14 Lampson Ave 18" 15" +3" 0.36 0.47 holds Criterion is 0.50 at peak dry -weather flow for pipes s15" (all as -built diameters here are s15" so 0.50 governs). d/D above 1.0 means the pipe is running full and surcharging. The same thing, as a picture ■ AKM future d/D (at model diameter) ■ future d/D at as -built diameter the black line is the 0.50 limit Elder Ave 12"->8" Ironwood Ave Candleberry Ave 18"410rr Aster St 15" 412'r s Basswood St 18"->12" Lampson Ave I 18"--)15" 18 -4,000 ft reaches AKM called adequate that cross 0.50 at the of added over -criterion trunk — on top of AKM's as -built diameter 2,748 ft, roughly tripling the deficient footage // WHY I BFLZEVE THE SMALLER PIPE Three independent records land on 8--12 inch — only the model says 15— • The 2025 as -built GIS — the City's official asset map — carries Elder at 8" Ironwood and Candleberry at 10", Aster and Basswood at 12" • The City's 2002 flow monitoring — back -calculating diameter straight from the meters (area = flow velocity) at these reaches returns 8-12" matching the GIS. That's field data, not a drawing. • The freeboard pull — reading rim and invert at the chokepoint manholes returns the same 10" and 12" pipes. The model is the outlier. And it isn't modeling a hidden relief line: the InfoSewer PARALLEL flag is blank on every one of these reaches, so it's a single pipe of that assumed size, not a small pipe twinned with a big one. The most economical explanation is that the model carries an optimistic diameter inherited from an older master plan and never field -verified — while the GIS, the 2002 meters, and the manhole geometry all describe the pipe that's actually in the ground. // WHAT IT MEAN The reconciliation makes the §65589.7 question sharper, not softer The whole fight has narrowed to one statutory hinge: under Gov. Code §65589.7 the City must give priority sewer service to qualifying housing unless it makes written findings of specific "sewer service limitations." AKM's study already documents localized deficiencies. This reconciliation says those deficiencies are likely understated — that at the diameters the City's own as-builts and meters describe, the constrained trunk runs continuously from Elder through Basswood, not in three isolated segments. Either reading supports written findings; the as -built reading makes them close to unavoidable. The clean ask for an independent reviewer is narrow and cheap: field -verify the pipe diameter at Elder, Ironwood, Candleberry, Aster, and Basswood — a handful of manhole pops or a CCTV pass — and reconcile the model to whatever's actually there before any capacity conclusion is certified. // EXHIBIT B - SUPPORTING What the whole collection system looks like Parsed from the 2025 GIS (733 reaches) and the 2018 model. Context for why a mid -trunk constraint is plausible here rather than surprising. Total gravity mains 31m4 733 reaches,165,957 ft mapped Mains 8" or smaller 82% a small -diameter collector network - little spare barrel to absorb added load Reaches flatter than 38 ° % 260 of 676 sloped reaches - flat pipe means low capacity 0.2% grade and weak self -cleansing velocity Predominant material ~76 o vitrified clay (625 of 828 modeled) - the older, joint -leak / VCP root -intrusion -prone material Diameter neck -downs 7 / 0 7 step-downs system -wide, 0 in CPE - the CPE constraint is undersized -for -cumulative -flow, not a pinch Model install -year n/a InfoSewer YR-INST is a 2004-05 import date, not true age - field real pipe age needs as -built records (open item) // EXHIBIT C - SUPPORTING The pumps are not the constraint - the gravity mains are Daily operator rounds, 202242026, average run -hours per day by station. Every station sits well inside its firm capacity; even the workhorse (Station 35) has multiple pumps in reserve. Rising demand shows up as gravity depth on the trunk, not as pumps running out of room. 1st St. 0.3 0.6 0.6 0.5 0.5 well within capacity 8th St. 1.6 1.8 1.7 1.4 1.5 well within capacity Aquatic Park 3.7 2.0 2.9 2.0 1.8 within; declining Boeing 1.3 1.4 1.7 1.5 1.7 within capacity Yard 2.8 4.3 4.7 4.0 3.8 within capacity Station 35 7.6 8.4 8.4 7.9 9.6 workhorse - rising, still within 3-pump capacity This matters because it rules out the easy rebuttal. The problem can't be pumped away - a lift -station or force -main fix (see the separate bid review) reroutes flow off the deficient gravity reaches; it doesn't add capacity to them. // EXHIBIT D - SUPPORTING Why d/D — not "will it overflow" — is the right test here The chokepoint manholes are deep: rim sits about 9 feet above the pipe crown at Ironwood, Candleberry, Aster, and Basswood. So these reaches can surcharge a long way before anything reaches the street — you won't necessarily see a manhole geyser. That's precisely why the City wrote its standard as a depth -to -diameter design limit rather than a "does it flood" limit: the failure mode is lost freeboard, backed -up laterals, and reduced conveyance, not an obvious overflow. Judging this system by whether it's visibly spilling would let a genuinely over -criterion trunk pass. The d/D check is the honest one, and it's the check the as -built diameters fail. // METHOD & HONEST LIMITS How this was built, and where it could be wrong • Sources. City 2018 InfoSewer model (PIPEHYD. DBF diameters/inverts, PIPEOUT. DBF d/D); City 2025 sewer GIS (sewerline2025, sewermanhole2025); City 2002 15-minute flow monitoring; AKM "4665 Lampson Ave Sewer Study," May 28 2026, Table 6. All produced under CPRA #26-274. • d/D math. Manning partial -flow, n=0.013, solving depth for AKM's stated future PDWF and slope on each reach; criterion 0.50 (s15") 10.64 (z18") per the City's 2018 SMP §3-5.2. • The load -bearing assumption. Everything in Exhibit A assumes the as -built GIS diameter is the real pipe. If the model diameter turns out to be correct, the flips disappear — which is why the recommendation is to field -verify, not to litigate the model. • What this is not. A working analysis for decision -makers, not a stamped engineering opinion. It isolates one variable — diameter — cleanly, using AKM's own flows, so the comparison is apples to apples. College Park East / Lampson sewershed — Supplemental Technical Analyses, Part 2 • built from CPRA #26-274 primary data • Aug 19, 2026 • internal working document Five things the records establish 1. The system already runs over its own limit. The City's 2002 flow monitoring, measured against the City's own capacity standard, shows 3 of 5 College Park East reaches over the design criterion — and one (Edinger Ave) running completely full — in ordinary dry weather, before any new development. 2. Four of five reaches exceed what the pipes can carry by gravity when peak flows hit. That's the definition of a system with no headroom. 3. The model can't be trusted to say "no impact." The 2018 — — ---- - -- computer model the EIR relies on has an empty pump -station The 10" chokepoint (reef) along Ironwood/CandIeberry, table — it doesn't simulate the six pumps or the force mains at on City manhole locations from the City's own GIS. The all. reach that runs full — "Edinger" — isn't shown because 4. The bottleneck has an address. The line necks down to 10 it isn't in the City's map at all. inches along Ironwood/Candleberry (City manholes B08-A24 B06-A22) before it widens downstream — the classic spot for backups. 5. The data to check this always existed. The City has had daily flow meters and pump logs since 2000. The claim that only "dated 2005 numbers" were available doesn't hold. // WHY IT MATTERS State law (Gov. Code §65589.7) can require the City to prioritize sewer service to affordable housing -- unless the City makes written findings of real "sewer service limitations." Measured, dry -weather, over -capacity flow at multiple College Park East reaches, from the City's own monitoring, is exactly the kind of concrete evidence those findings require. It also directly undercuts the EIR's conclusion that the collection system has "no significant impact," which rested on undocumented "personal conversations" rather than data. WHAT TO ASK FOR • An independent engineer's review of the collection -system capacity — not the incumbent's or the developer's numbers — focused on the College Park East reaches and the 10" chokepoint. • The missing records: where the "Edinger" meter was and whose pipe it is; any CCTV/condition and overflow (SSO) history for the Ironwood/Candleberry/Aster trunk; and the April 30, 2025 "personal communication" behind the EIR's wastewater conclusion. • That any finding on sewer service rest on this measured record, so the City's position under §65589.7 is defensible. Backup: capacity analysis (CPE_dD_Capacity_Check), chokepoint trace +aerial (CPE_Edinger_and_Chokepoint, CPE_Chokepoint_Aerial), the full records catalogue (FOIA-26- 274-Catalogue_and_Analysis), and the Bates -stamped production (FOIA_26-274_Bates-Production). All figures trace to the City's own PRA #26-274 production. // Briefing - College Park East sewer capacity Summary of public records (PRA #26-274). Working analysis, not a stamped engineering opinion. INTERNAL - FIELD REFERENCE • CONFIDENTIAL The College Park East sewer chokepoint, on the ground The 10-inch reach where the trunk necks down — Ironwood Ave & Candleberry Ave, Seal Beach // CITY MANHOLES • CITY GIS • REAL COORDINATES Area College Park East, Seal Beach Reach mh B08-A24 � B07-A23 4 B06-A22 Prepared Aug 2026 I� - r w .� �.�.. r a �,.w�rrr..�rr�.._i•--�"`-� - -- ------__ ,-may Aerial: Esri World Imagery. Sewer alignment and manhole IDs from the City of Seai Beach 2025 sewer GIS, converted to IatJlong (CA State Plane VI). Old Ranch Country Club is upper -left; the 1-405 runs along the bottom; College Park East is the neighborhood at right. � 10" chokepoint reach (atlover capacity) - - -- downstream trunk (12" 4 15-18") toward OC San •. City sewer manhole (ID labeled) 2002 monitor result at the reach // WHAT YOU'RE LOOKING AT The red line is the constriction: the College Park East trunk runs 10-inch along Ironwood Avenue and around onto Candleberry Avenue (manholes 1308-A24 1307-A23 B06-A22) before it finally widens to 12" at Aster Street and then 15-18" on the way to the Orange County Sanitation District connection. That 10" segment is where the City's own 2002 flow meters recorded depths at and over the capacity criterion — a pipe already running near full a generation before the Lampson and Old Ranch loads. • It's a specific, walkable location — the block along Ironwood/Candleberry on the western edge of College Park East, backing onto the Old Ranch greenbelt — not a vague "somewhere in the system." • Flow runs from 1308-A24 (upper right) downhill to the southwest, toward the 405 and the OC San connection near Lampson. • The measured peaks here already meet or exceed the 10" pipe's gravity capacity (--0.60 mgd) — see the d/D and capacity exhibits. // MANHOLE COORDINATES (FOR THE RECORD) B08-A24 Ironwood Ave 33.779215 -118.058778 10" chokepoint B07--A23 Ironwood Ave 33.778811 -118.059466 10" chokepoint B06-A22 Candleberry Ave 33.778395 -118.060186 10" chokepoint 1305-A20A Aster St 33.777930 -118.059681 12" (widens) 1305-A20 Aster St 33.777557 -118.060326 downstream 1303-A19 Aster St 33.777150 -118.061005 downstream B03-A16 Basswood St 33.775780 -118.062025 18" (AKM) trunk Manhole IDs are the City's own and match the B-series used in AKM's Lampson study, so they cross-reference directly. // AND WHERE'S EDINGER? The reach that runs completely full — "Edinger" — is deliberately not on this map, because it isn't in the City's GIS. There's no pipe or manhole to plot. Its full -pipe, low -velocity signature points to a downstream backwater, most likely on an OC San regional trunk the City doesn't own. That's the open question to put to the City and OC San: where was that meter, and whose pipe is it? // SOURCES & LIMITS Basemap: Esri World Imagery. Sewer geometry: City of Seal Beach 2026 GIS (sewerline2025, sewermanhole2025), projected from NAD83 California State Plane Zone VI (US ft) to WGS84. Alignment shown is the traced downstream trunk; marker positions are the GIS manhole coordinates (one manhole, B06- A21A, carried null coordinates and is omitted). Downstream sizes past Aster St are from AKM's Lampson study. Working reference, not a survey. // END — CHOKEPOINT AERIAL Internal field reference • City GIS on Esri imagery • Not a survey. h INTERNAL — TNDEPENDENT ANALYSIS • CONFIDENTIAL Pinning "Edinger" Minding the College Park East chokepoint Tracing the City's own GIS from the surcharged meters to the OC San connection // GIS NETWORK • MEASURED FLOW vs CAPACITY • WHERE IT NECKS DOWN Source 2025 sewer GIS + FOIA #26-274 Exhibits 3-7 Prepared Aug 2026 // THE SHORT VERSION Two things fell out of tracing the network. First: "Edinger" — the reach that runs full -- is not in the City's 2025 sewer GIS at all. No pipe, no manhole, anywhere. A monitored, surcharging location that isn't in the City's own asset map is a question worth asking out loud. Second: the reaches that are mapped tell a clean story — the College Park East trunk necks down to 10" through Ironwood and Candleberryr and four of the five monitored reaches carry measured peak flows that exceed what those pipes can pass by gravity. The 10" Ironwood/Candleberry segment is the chokepoint — undersized for the flow it already carries, before the line finally widens downstream toward OC San. // WHERE IS "EDINGER"? We searched every field of the City's 2025 sewer -line and manhole GIS (733 pipes, 778 manholes) for "Edinger." Nothing. The other four 2002 monitors map cleanly to College Park East streets and to the same B-series manholes AKM used in its Lampson study — but Edinger has no home in the current inventory. Its measured signature is distinctive: a 10" pipe running full (d/D 1.10), deep, and slow (-0.8 fps) for three straight weeks. That is the fingerprint of a downstream backwater point — the kind of place you'd find near a regional trunk or a connection structure. The most likely explanations, in order: • It sits on an OC San regional trunk, which wouldn't appear in the City's GIS because the City doesn't own it — and a regional trunk running full near the connection would explain the deep, slow, surcharged profile. • The asset was renamed or retired between 2002 and the 2025 GIS. • The meter label is a location shorthand (a cross -street or landmark) rather than a City street name. Question to put to the City/ OC San: where physically was the "Edinger" flow meter, is that pipe in the current GIS, and does it sit on a City main or an OC San trunk? If a City reach that runs full is missing from the asset map, that gap matters on its own. // THE DOWNSTREAM TRUNK - WHERE IT NECKS DOWN Following the GIS from the Ironwood/Candleberry monitor downhill (steepest -descent, City manhole IDs shown), the trunk runs 10" for four reaches before widening to 12" at Aster St, then — per AKM's own Lampson study — 15-18" along Basswood and Lampson to the OC San connection. Ironwood Ave Candleberry Ave Aster St Basswood St Lampson Ave B08-A24 • cap -0.60 B06-A22 - cap --0.60 B05-A20A - cap -0.81 (AKM) trunk (AKM) to OC San flow �4� toward OC San connection (1301 manholes) Box height - pipe diameter; capacity in mgd (Manning, full -flow, from GIS geometry). Red = the 10" chokepoint. Downstream diameters (Basswood/Lampson) are from AKM's Lampson study Table 6, past where the GIS trace was cleanly walkable. // MEASURED FLOW VS. PIPE CAPACITY (A SECOND, INDEPENDENT CHECK) The d/D check already showed these reaches running deep. Here's the same conclusion from a different angle — measured peak flow against what the pipe can carry full by gravity. Over 100% means the pipe can't pass the peak without surcharging. Ironwood @ Candleberry 8" 0.35 0.59 169 a Aster St NE of Basswood 10" 0.57 0.86 151% Ironwood Ave @ Elder 8" 0.33 0.37 111% Edinger Ave (est. slope) 10" 0.55 0.59 108% Aster @ Birchwood 12" 1.03 0.81 79% Capacity and peak in mgd. Capacity uses the median GIS slope for each street, so it's an estimate that moves with slope — but four reaches clearing 100% lines up with the depth -based d/D result, and the two reaches that agree across both methods (Ironwood@Candleberry, Edinger) are the robust ones. // THE CHOKEPOINT The 10-inch Ironwood/Candleberry reach is the constriction. It's the narrowest part of the downstream trunk, its --0.60 mgd gravity capacity is already met or exceeded by measured 2002 peaks, and it sits upstream of where the line finally widens to 12" and then 15-18". Flow backs up behind a neck — so a 10" segment carrying accumulated College Park East flow, feeding into larger pipe below, is exactly where you'd expect the surcharging the meters recorded. • It's a specific, nameable target —City manholes B08--A24 / B07-A23 (Ironwood) and B06-A22 (Candleberry), the same IDs in AKM's study — not a vague "the system is old." • It predates the new load. This is 2002 flow in a reach that's still 10" in the 2025 GIS. Add Lampson and Old Ranch on top and the neck only tightens. • It sharpens the §65589.7 record — a mapped, City -owned reach at or over gravity capacity under baseline is concrete "sewer service limitation" evidence, tied to specific manholes. // CAVEATS • Depth beats capacity for certainty. The d/D result is a direct depth measurement; the utilization percentages depend on the pipe slope (we used each street's median GIS slope), so treat those as corroborating, not exact. • Edinger's slope is estimated (it isn't in the GIS), so its 108% is the softest number here; its measured full -pipe depth is the harder fact. • The GIS trace was walked cleanly to Aster St; the Basswood/Lampson continuation and their 15= 18" sizes are from AKM's Lampson study, not re -derived here. • 2002 data — confirm none of these reaches were re -lined or upsized since; any change (more flow, smaller effective bore from age) favors the finding. Built from the City's 2025 sewer GIS (sewerline2025, sewe nnanhole2025) and FOIA #26-274 Exhibits 3-7. Method +figures stored in seal-beach_sewer.db (cpe_capacity). Independent working analysis, not a stamped engineering opinion. // END - EDINGER & CHOKEPOINT Internal working analysis - Built from the City's CPRA production + GIS • Not a stamped engineering opinion. 4 INTERNAL - INDEPENDENT ANALYSIS • CONFIDENTIAL College Park East r-- Does the sewer already run over capacity? The City's own 2002 flow meters, measured against the City's own d/D criterion // MEASURED DEPTH • BACK -CALCULATED DIAMETER • CITY'S OWN STANDARD Source FOIA #26-274, Exhibits 3-7 Data 15-min,-1,900 readings/site, May -Jun 2002 Prepared Aug 2026 // THE SHORT VERSION We ran the City's own 2002 flow -monitoring data at five College Park East manholes against the City's own capacity criterion. The result: in dry -weather baseline conditions — with zero new development load — three of the five reaches already run over the 0.50 depth -to -diameter design criterion, and one (Edinger Ave) runs completely full. Two reaches exceed even the City's lenient 0.64 "existing -pipe" upsizing threshold, and Edinger exceeds it 100% of the time. This is the City's data, the City's meters, and the City's standard — and it says parts of College Park East were capacity- limited a generation before anyone added the Lampson or Old Ranch flows. // THE RESULT Ironwood Ave @ Elder (8") I 0.50 Aster St NE of Basswood - - I (10) 0.54 Aster @ Birchwood (12") 0.69 ironwood @ Candleberry (8") 0.85 Edinger Ave (10") 1.10 Bars = peak measured d/D (scale 0-1.15). Gold line = 0.50 design criterion (pipes s1511); orange line = 0.64 existing - pipe upsizing threshold. A bar past 1.0 means the pipe ran full / surcharged. Ironwood Ave @ 8- 0.50 0.27 0. 1% 0 % at design limit at peak Elder Aster St NE of 10- 0.54 0.31 0.7 % 0 % just over 0.50 at peak ; Basswood - --- Aster @ Birchwood 12" 0.69 0.48 47 % 20 over 0.50 --half the time Ironwood @ 8" 0.85 0.55 68 0 26 a 0 over both thresholds Candleberry routinely Edinger Ave 10" 1.10 0.81 100% 100% runs full J surcharged // HOW WE GOT THE DIAMETER (SO THE D/D IS DEFENSIBLE) d/D needs two things: the flow depth and the pipe diameter. The depth is measured directly — it's the "Level (in)" the meter recorded every 15 minutes. For the diameter, we didn't guess: an area -velocity meter records depth, velocity, and flow, and flow = velocity x cross -sectional area, so the area (flow velocity) plus the depth uniquely implies the pipe size the meter was set to. We back -calculated it from each of-r1,900 readings per site and took the median. Those back -calculated sizes — 8", 10', 12"? 8", 10" — match the City's 2025 sewer G15 diameters for those same streets (Elder 8"; Ironwood 8-10"; Aster 12"; Candleberry 8-10"). Two independent sources agree, so the d/D values rest on the record, not an assumption. The data spans three dry - weather weeks in late May -June 2002; different reaches peak on different days (a diurnal pattern, not a storm), so these are dry -weather peaks — the right comparison for the criterion. // WHAT IT MEANS • The "no significant impact" story gets harder. The EIR concluded the collection system was fine on the strength of "personal conversations with the City." The City's own meters say otherwise: reaches of College Park East were running at, over, or past full in 2002, before a single new unit. • This is the record for a §65589.7 finding. A city can lawfully condition or refuse sewer service to affordable housing only if it makes written findings of real "sewer service limitations." Measured, dry -weather, over -criterion flow at multiple reaches — from the City's own monitoring — is exactly that kind of substantial evidence. • It's conservative. This is 2002. Twenty -plus years of infill have been added since, and the Lampson + Old Ranch loads come on top of that. If the baseline already exceeds the criterion, the added load only makes the case stronger. • Edinger is the flag. A pipe running full continuously, at very low velocity, is the signature of a downstream constriction or backwater — worth pinpointing, because it may be the real chokepoint. // HONEST CAVEATS • These are 8-12" local collector mains at the meter sites —not the 15-18" downstream trunk reaches AKM's Lampson study modeled. So this doesn't say AKM's specific trunk numbers are wrong; it says the broader College Park East system already runs at/over capacity in places, which the program -level EIR did not capture. • Two thresholds. 0.50 is the City's design criterion for new pipes; for existing built -out pipes the 2018 Master Plan only flags upsizing above 0.64. We report both — and two reaches (Ironwood@Candleberry, Edinger) clear even the lenient 0.64 bar. • Meter accuracy. Area -velocity meters lose precision at very low velocity, which affects Edinger's absolute number most (mean -0.8 fps). But the consistently deep levels across three weeks are hard to explain except as a full/backwatered pipe. • 2002 vintage. Confirm nothing was re -lined or resized on these reaches since; the direction of any change (more flow) favors the finding. Underlying data: FOIA #26-274 Exhibits 3-7 (Bates SB-26274 series), diameters cross-checked against sewerline2025 GIS. Method and per -site figures stored in seal beach-sewer.db (table dD_analysis). Independent working analysis, not a stamped engineering opinion. // END - CPE d/D CHECK Internal working analysis • Built from the City's CPRA production • Not a stamped engineering opinion.