GSI worked with the City of Portland to develop an innovative regional risk-based decision making tool to aid in conducting a groundwater protectiveness demonstration for its 9,000 underground injection control (UIC) facilities.


The City of Portland uses about 9,000 UIC facilities to manage a portion of the stormwater that comes from public rights-of-way. UICs are well-like structures that collect stormwater and allow it to seep into the ground.  The UICs are beneficial because they provide a recharge mechanism for surrounding streams and aquifers.  However, pollutants in stormwater have the potential to adversely affect groundwater beneath the UICs.

Since groundwater is a drinking water source in Oregon, the City was issued the first state permit to operate its UICs. This permit required the City to show that groundwater was being protected at its UICs.  Since, the City operates many UICs; it needed a process to help meet this requirement in a timely and cost efficient manner. Without a precedent from earlier permits, the process had to be developed from scratch.

GSI’s Solution

GSI worked with the City to develop a regional risk-based decision making framework for groundwater protectiveness demonstrations for UICs. This framework used the results of simple pollutant fate and transport models developed by GSI to provide a consistent, streamlined evaluation and decision-making process.

Results of individual demonstrations were applied to groups of UICs with common characteristics to determine if they were protective of groundwater quality and met state and federal water quality requirements. This approach was accepted by the Oregon Department of Environmental Quality and resulted in no further action determinations for more than 300 of the City’s UICs, which in turn led to significant cost savings for the City because costly retrofits did not have to be performed at these UICs.