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City Ditch piping project: trenchless boring finds high-iron groundwater; staff presents up-to-$375,939 change order for dewatering and treatment
Summary
Project manager Stephanie Ellis told the board that trenchless boring under Slaughterhouse Gulch found groundwater iron at about 21,000 micrograms per liter (regulatory standard 1,000 μg/L); remediation requires a CDPHE permit and staff presented a maximum change order of $375,939 within existing staff-managed contingency.
Project manager Stephanie Ellis updated the Water and Sewer Board on construction progress for Reaches 3 and 4 of the City Ditch piping project and informed the board of an unanticipated groundwater issue requiring remediation.
Ellis reported that the contractor (HEI Civil) has installed pipeline in Reach 4 and the majority of Reach 3; work included rerouting stormwater, adding access manholes, and restoring disturbed areas. In Reach 3 the team will use trenchless boring to pass under Slaughterhouse Gulch and a wetland. As part of permit requirements for dewatering, staff collected water-quality samples. The first sample showed elevated iron levels and a second test taken Oct. 29 returned 21,000 micrograms per liter for iron; Ellis noted the CDPHE water-quality standard for iron is 1,000 micrograms per liter.
Because the groundwater exceeds the standard, the discharge requires remediation and a different CDPHE permit than originally scoped. Staff presented a maximum change order of $375,939 to cover a dewatering and iron-treatment system (baseline four weeks with potential week-to-week extensions), required effluent sampling, and potential media replacement in the treatment system. Staff told the board this amount is within the project’s staff-managed contingency but emphasized the size of the change order and explained the breakdown of costs.
No formal vote on the change order was recorded at this meeting; staff presented the change order for board awareness and flagged next steps: secure required CDPHE permits, adjust construction sequencing as needed, and track actual treatment duration week-to-week to manage costs. Staff also said piping the city ditch will reduce hard urban-runoff influences on source water and that pH is managed in the treatment process rather than by the piping work itself.
This update included technical sampling results and a staff-requested change-order authorization that will be acted on through the city’s procurement and permitting procedures.
