Constructability Challenges With Structural BMPs – Goldentop Rd. Water Quality Project
The purpose of this presentation is to discuss site constraints for construction of structural BMP’s and solutions for alleviating construction challenges to ensure successful implementation. The presentation will discuss important considerations of existing site conditions, design development and measures for reducing owner liability during construction. The presentation will take a detailed look at one of the County of San Diego’s water quality projects located in the community of 4S Ranch in San Diego, California and describe how it overcame utility conflicts, geotechnical challenges and environmental constraints.
Approximately 120-acres of local drainage from residential, commercial, and industrial uses near Goldentop Road 4S Ranch Business Park is collected in a County-maintained storm drain system and discharged into Artesian Creek, a tributary to the San Dieguito River. Water sampling result from this location indicate elevated levels of fecal indicator bacteria, nutrients and visual detection of trash, all of which can negatively impact waterbodies. The primary goal of Goldentop Road 4S Ranch Business Park Water Quality Project is to capture trash and bacteria found in runoff before it discharges to Artesian Creek. The project consists of modifying the existing storm drain system to include a water treatment facility with a debris-separating baffle box (DSBB) and modular wetland system (MWS) to remove trash, bacteria, and other pollutants found in low-flow conditions.
The project encountered many challenges during the design phase that would ultimately impact the construction schedule and methodologies. Overhead and underground utility conflicts were explored and identified early on. Feedback from utility agencies was received and the necessary standby and avoidance measures were incorporated into the construction drawings. It wasn’t until geotechnical borings were performed that an unknown fiber optic utility conflict was identified that would result in a major re-design of the project. Additionally, geotechnical results indicated high groundwater near the Goldentop Road outfall, large components of gravel and cobble that would result in heavy ripping and complicated excavation methodologies and clay soils not suitable for backfilling.
Prior to re-designing the new water treatment facility, a concept analysis was performed to investigate feasible project alternatives and construction costs. The project team investigated options for moving the treatment facility upstream and modifying the storm drain alignment to connect back into the existing storm drain system instead of creating an additional outfall. The project team worked closely with DPW Roads, Flood Control and Environmental Services sections to discuss maintenance requirements, access, environmental limitations and flood control capacity impacts. Upon selecting a preferred alternative, additional utility potholing was performed to collect more information on known and unknown utilities. The revised design resulted in minor utility conflicts, reduced environmental impacts, a smaller project impact area, lower construction costs and reduced owner risk as a result of investigating subsurface conditions. Although the project schedule was delayed due to the re-design effort, the team’s ability to thoroughly investigate existing site conditions and navigate around those challenges proved to be an essential step in design to ensure construction success. If these constraints were determined during construction, the project would have encountered expensive change order fees, potential contracting constraints and delayed coordination with utility agencies.
Constructability challenges will be presented by Project Manager, Amanda Parra via PowerPoint and aligns with conference track, Construction and Post-Fire Response. The project manager will engage the audience with interactive visuals and photos.