Gitxaala Nation’s community at Kitkatla sits on a remote, barge-access site on the north coast of British Columbia. Its treated-water storage reservoir - the community’s only treated-water supply - needed replacing. I was the sole structural author of the feasibility study supporting an Indigenous Services Canada funding submission: three-option analysis, reservoir sizing, seismic and foundation basis, Class D cost estimates, and the recommendation, all against a tight end-of-March deadline.

My Role

Sole structural author. Authored the Options 1-3 structural descriptions, viability screening, advantages and disadvantages, recommendation, and limitations.

Sizing

  • Sized to the 20-year (2045) design horizon: 685 m³ governing design storage against 700 m³ provided as two 350 m³ tanks - a 2% margin
  • Built the underlying population projections (343 in 2025 rising to 824 in 2045) and water-demand tables at 670 L per capita per day, with a 2045 maximum day demand of 15.99 L/s

Value Engineering Under a Site Constraint

The original 2 x 420 m³ configuration did not fit between the two existing reservoirs. Resolving the footprint constraint meant revisiting the governing fire-flow basis:

  • Re-sized the tanks to 2 x 350 m³
  • Shifted the governing fire-flow case from community-building (60 L/s x 1.5 h = 324 m³) to multi-family residential (45 L/s x 1.25 h = 203 m³)
  • Cut 20-year design storage from 837 m³ to 685 m³, and roughly $0.53M from the recommended option
  • Community-building fire protection reassigned to alternative means for review by the Nation, ISC, and the fire authority

Cost Basis Calibrated to Local Evidence

Generic remote-location multipliers do not survive scrutiny on a barge-access site. I calibrated one against hard local data:

  • Prior Kitkatla flocculation-tank bid history - engineer’s estimate $821K against winning bids of $1.46M to $2.88M, a 2.91x average bid ratio
  • Cross-validated against comparable BC-coast First Nations water projects: Hartley Bay (~$16M) and Ts’uubaa-asatx ($6.2M)
  • Settled on a 2.50x remote-location factor, with 30% contingency, 20% engineering and PM, and 6% escalation to mid-construction

Class D opinions of probable cost: Option 1 at $5.34M, Option 2 at $4.73M, Option 3 at $6.42M.

Specification Correction

Option 1 had been specified as stainless steel. I corrected it to AWWA D103-19 factory-coated bolted carbon steel (glass-fused-to-steel), avoiding a 60-80% tank-supply cost premium that NSF 61 potable service does not require.

Top Water Level as the Governing Criterion

The cheapest option was not the right one. Top water level turned out to be the controlling criterion - both the partially and fully buried concrete options (2 and 3) cannot achieve the required system pressure regardless of cost. The recommendation went to the above-ground bolted-steel configuration.

Site and Seismic Basis

Established from a desktop geotechnical assessment: preliminary NBCC 2020 Site Class C on shallow bedrock in a moderate-to-high seismic zone of the BC north coast. Specified a raft-slab-on-bedrock foundation with seismic anchorage, and flagged the mandatory pre-design geotechnical field investigation as a limitation on the assessment.

Outcome

The feasibility report cleared senior technical review, with reviewer markup on version 1.4 resolved through revision and brought to issue - delivered on a tight deadline while a subdivision-elevation data blocker gated the top water level determination.

Codes and Standards

NBCC 2020, BCBC, ACI 350, AWWA D103-19, NSF 61, CAN/CSA A23.3, CAN/CSA S16.