Asphalt Plant

The Public Works Department reviewed the proposed asphalt plant at 18825 SE Renton Maple Valley Road during the environmental review process and responded to concerns raised in 2019 and 2022. Based on some recent on-line post making assertions about the impacts to the city’s water aquifers, we have provided some background information based upon staff’s experience and expertise.

The proposed site is located outside of the city’s Wellhead Protection Areas. The proposed development is located approximately 1.75 mile outside of the city’s Maplewood Wellhead Protection Area and approximately 3.7 miles outside of the city’s Downtown Wellhead Protection Area. The Maplewood Wellfield is a supplementary supply that provides 20% of Renton’s water during peak summer demand conditions. The assertion that the city will need to buy majority of our water from City of Seattle at a cost of $10 million per year is not correct.

While it has been stated that the proposed development is within Renton’s aquifer area, there is an important distinction between Renton’s Wellhead Protection Area and EPA’s Sole Source Aquifer. The proposed development is located within the EPA’s Cedar Valley Aquifer Area that was designated a Sole Source Aquifer (SSA) by the EPA in 1988, however the SSA designation does not govern the city’s critical areas regulation for aquifer protection. The SSA program is specifically applied by EPA to review proposed projects located within SSA areas that receive federal financial assistance. The proposed development does not include federal funding and will not be subject to EPA review.

As part of the internal environmental review, the Public Works Department evaluated the potential contamination risk to the city’s drinking water sources by the proposed site activities and determined the risk to be relatively low for the following reasons:

• The city’s Maplewood Wells do not pump from the shallow Cedar Valley Aquifer. The Maplewood Wellfield is drilled into the deep production aquifer from approximately 135 to 345 feet below ground surface. The Maplewood Wells are located approximately 3.2 miles from the proposed Asphalt Plant (see the Renton Wells and Asphalt Plant Map).
• The city’s Downtown Wells are located approximately 5 miles away from the proposed Asphalt Plant an even lower risk due to the length of time it would take to travel the 5 miles underground. The sampling wells between the plant and our wells would provide ample notice of a change.
• The Maplewood Aquifer has a low contamination susceptibility rating based on the depth of the wells and the confined layer of clay which acts as a barrier that prevents the downward migration of hazardous chemical spills or other releases of contaminants on the surface.
• The risk to our aquifer is low because of the natural rock and layers of clay that buffers our deep water sources, and the monitoring wells that will provide ample warning to address any issues that could impact them in the future, whether from the asphalt plant or other contamination from vehicles, gas stations, septic systems, etc.

Stormwater Runoff is Not Injected Directly into the Aquifer

The contamination risk is further lessened by on-site requirements of the asphalt plant.

1. Primary and secondary containment for on-site, above ground, hazardous material storage facilities (one 10,000-gallon diesel tank and one 10,000-gallon emulsified asphalt tank). Any spills from those tanks would be confined to the containment areas to allow for cleanup.
2. A spill prevention and response plan are required.
3. Monitoring of secondary containment areas.
4. The proposed Asphalt Plant project will reduce the amount of ground that does not allow rain to be absorbed that currently exists on the site. The stormwater from the impervious areas on the site will be collected in a storm water collection system. Stormwater quality treatment will be provided using an oil/water separator, lined biofilter swales, a settling vault, and a large sand filter before being discharged into an infiltration gallery to infiltrate the runoff into the ground. These facilities are required in accordance with the current King County Surface Water Design Manual, which are the same standards as the City of Renton Surface Water Design Standards. This is treated stormwater that will be infiltrated into the ground.
5. Since the proposed Asphalt Plant’s storm water system infiltrates the onsite storm water runoff, any spill of hazardous materials on the site will be contained onsite making it easier to clean-up and prevents the stormwater runoff from reaching the Cedar River.
6. If a spill of hazardous material were to occur, it would result in an emergency response with King County, federal and state agencies enforcing clean-up and long-term groundwater monitoring to confirm the spill has been cleaned-up and there are no impacts to ground water, surface waters or neighboring areas.

The King County’s Shoreline Management Substantial Development Report and Decision for the shoreline permit required for the Asphalt Plant construction was Affirmed by the State’s Shoreline Hearings Board when it was appealed by opponents of the Asphalt Plant. The Shoreline Hearings Board considered extensive testimony regarding many environmental concerns including impacts to ground water and surface water that could result from the project (SHB No. 22-007 – Findings of Fact, Conclusions of Law and Order – Citizens to Stop the SR-169 Asphalt Plant v. King County and Lakeside Industries Inc.)

Water District 90 did pass Resolution No. 1041 in April 2018 opposing the proposed Lakeside Industries Asphalt Plant as the plant location was within the 10-year recharge area of one of the district’s wellfield. The attached resolution and letter (in the additional documents section) explain the district’s position. As to the wells being shut down, It is our understanding that the well facilities of KC Water District 90 are currently not in use because of quality of the water. They must build a treatment plant in order to utilize the water, and at this time it is likely cheaper for them to purchase water from Seattle than to build the treatment plant. We do not know the depth of their well and so cannot comment on the quality of the source of the water. However, it is not surprising given that the city must treat the water from our Maplewood Wells before putting it into our water system.