El Dorado Disposal had acquired the property now located at 4100 Throwita Way, Placerville, and needed to convert it to support their operations.  Over the years 1991, 1993, 1994, and 1997, Youngdahl performed additional studies supporting various improvements on the property.  In 1997 the Union Mine Landfill located near the town of El Dorado stopped receiving most solid waste; the former Dimetrics facility had by then been fully converted to the Western El Dorado Recovery Systems, Inc., El Dorado Materials Recovery Facility which focuses on recycling as much material as is practical.  Western El Dorado Recovery Systems, Inc. was acquired by Waste Connections, Inc. and the facility was renamed the Western El Dorado Material Recovery Facility, also referred to as the Material Recycling Facility or MRF.

The MRF had been built on property that was once part of a lime kiln facility.  The grading work to support the various construction projects (including the original Dimetrics facility) had to take into account the presence of lime sludge. In January of 2012, surface water with a reported pH of 12.8 was identified in a shallow pond on the north side of the El Dorado Trail. The pond lies within an unnamed seasonal drainage that is a tributary to Weber Creek. Further testing of surface water pH during storm events identified areas with elevated pH in ditches and storm drains within and around the properties created from the former lime plant property.

Investigations by the California Department of Fish and Wildlife (Fish and Wildlife) identified residual lime materials with a high pH on the portion of the former lime plant property owned by a Mr. Lindeman; this property adjoins the north side of the MRF.  Fish and Wildlife concluded that the source of the high pH surface water found in the pond mentioned above was this residual lime material. Fish and Wildlife subsequently approved a corrective action plan that included grading and which was designed to isolate and contain the residual lime materials. The property owner proceeded with grading without obtaining the required permits.  Fish and Wildlife notified the property owner of violations.

In the spring of 2016, Youngdahl advanced several geotechnical borings to obtain additional information on subsurface conditions in preparation for a significant remodeling of the MRF.  Some of these borings penetrated and collected samples of the residual lime.   The Central Valley Regional Water Quality Control Board (Water Board) requested data on the soil pH values identified by Youngdahl in the various investigations.  Some of the pH values exceeded 12 so the Water Board requested that an investigation be performed to identify the extent of the residual lime and to see if groundwater had been impacted.

Youngdahl advanced 60 borings by direct push technology and 16 hand auger borings in areas of difficult access to collect soil samples, to determine the thickness of the residual lime materials, and to develop an understanding of groundwater conditions. Gasch Geophysical Services, Inc. (Gasch) used several seismic refraction lines to “connect the dots” between some of the boring locations.  The direct push borings and hand auger boring locations were surveyed by CTA Engineering and Surveying, Inc.  (CTA) allowing them to use the boring data and seismic lines to establish a map of the bedrock topography beneath the facility, confirming earlier concepts that the facility was built on top of two former ponds containing lime sludge.

Youngdahl installed 12 monitoring wells at the site; five of which were installed using direct push methods in the residual lime materials.  Youngdahl had developed a working conceptual model that there might be two water bearing zones; 1) a shallow zone within the residual lime materials, and 2) a deeper zone in the fractured bedrock underlying the site.  Five monitoring wells were installed through the residual lime materials and into the underlying bedrock by advancing hollow stem augers into the top of the bedrock, installing a string of intermediate casing, and then using air rotary drilling to advance the borings into water bearing fractures where a well could then be installed to characterize the deeper groundwater conditions.  The combination of shallow and deep monitoring wells confirmed that there are two, partially isolated zones of groundwater.

Water Board staff requested that Waste Connections prepare a remedial alternatives evaluation report, suggesting that they look at, 1) source removal, 2) source isolation; 3) in-place treatment, and 4) excavation and treatment.  Youngdahl has presently prepared a draft alternatives analysis currently under revision.  In the early stages of the analysis all four alternatives were evaluated, but it quickly became evident that in-place treatment, excavation and treatment, and complete source isolation were impractical.  The current preferred alternative is to remove the entire source of residual lime that may come into contact with groundwater, place clean engineered fill back into the potentially saturated zone, place a mixture of lime and soil above that zone as engineered fill in the dry zone, and to then place an impermeable cap over the entire site.  Horizontal drainage controls would be installed as necessary to intercept lateral groundwater flow that might impact shallow materials.

Once the remedial alternatives analysis report is complete and accepted by the Water Board, a removal action workplan (RAW) will be required.  Once this is approved, then remediation work can begin.  Once the earthwork is complete and the impermeable cap (foundations, pavement) has been installed, a closure report will be required.  Groundwater monitoring may be required to continue until it can be shown that all impacts to groundwater have been mitigated.