MONITORING WELLS
During the week of September 30, 2009, on behalf of the RP, Riverside Associates installed four monitoring wells at Site A and five at Site B. One of the wells near Site B, was to gather background groundwater samples. The purpose of the monitoring wells was to determine if contaminants of concern were migrating off site through the groundwater. This could occur if there still remained on-site a source of contamination feeding into the groundwater. As noted already, the groundwater is quite high such that the containers were originally found submerged in water. The groundwater fluctuates as at a later visit the groundwater had disappeared from the pit. All wells were drilled to a depth of 20 feet.
Results from monitoring wells do not indicate that contaminants are migrating offsite through groundwater movement.
Site A
The main contaminants of concern at Site A were dimethoate, carbaryl, glyphosate, and AMPA (Amintomethylphosphonic Acid) associated with the pesticides found on site. Dimethoate is an insecticide used to kill mites and insects. Carbaryl (Sevin) is a wide-spectrum carbamate insecticide which controls over 100 species of insects. Glyphosate is an active ingredient in the common pesticide known as Roundup. AMPA is associated with glyphosate as a breakdown product. Arsenic was a contaminant of interest because of historical association with pesticides. However, arsenic is a naturally occurring background contaminant commonly found in well water throughout Washington.
The monitoring well waters for Site A were also analyzed for diesel, lube oil, and BTEX (benzene, toluene, ethylbenzene, and xylene – common constituents found in gasoline) that would be associated with petroleum products.
Arsenic was the only contaminant detected at Site A. Arsenic was measured at concentrations ranging from 11 to 28 micrograms per liter (µg/L). To provide context to these values, the Safe Drinking Water Act Maximum Contaminant Level (MCL) for arsenic in drinking water is 10 µg/L. None were high enough to suspect contamination was due to anything more than background levels.
All other contaminants were non-detect.
Site B
The main contaminants of concern at Site B were diesel, lube oil, and BTEX because oil containers were found as well as oily water in the pits. Lead was of concern because of lead-acid batteries found in the pits. Other metals such as barium cadmium, chromium, mercury, selenium, and silver were other possible contaminants of concern for which the monitoring well waters were analyzed.
The background monitoring well for Site B found arsenic at 6.2 µg/L, barium at 120 µg/L, and lead at 2.6 µg/L (MCL = 15 µg/L). No other contaminants (diesel, lube oil, BTEX, cadmium, chromium, mercury, or silver) were detected.
The results for the four monitoring wells at Site B did not show diesel, lube oil, or BTEX.
Arsenic was found in all four monitoring samples ranging in concentration from 12 to 77 µg/L and all above the MCL of 10 µg/L. None were high enough to suspect contamination was due to anything more than background levels.
The rest of the metals were either non-detect or below MCL. Barium was found in all four wells at concentrations ranging from 74 to 290 µg/L (MCL = 2000 µg/L). Selenium was in three wells at similar concentrations of 6 µg/L (MCL = 50 µg/L). None of the remaining metals (lead, cadmium, chromium, mercury, or silver) were detected in the monitoring wells.
RCRA DISPOSAL
During October 2009, the containers at Site A were placed in a trailer and moved to Site B. The containers were considered hazardous waste and as such needed to be shipped to a hazardous waste landfill (RCRA Subtitle C). Riverside Associates arranged for Waste Management in Arlington, Oregon to receive the shipment.
Riverside Associates encountered a number of delays in shipping off the containers. Questions arose between EPA, Ecology, and the PRP regarding RCRA regulations and policy for proper disposal of containers, totes, and soil. Later concerns arose with disposing of oil containers which Ecology needed for their investigation. Thus the oil containers were separated from the hazardous waste stream. Once these issues were settled, Riverside Associates encountered further delays due to RCRA paperwork requirements, lost paperwork, and finally high workload on the part of Waste Management.
On September 20, 2010, Waste Management removed one roll-off with soil from Site B. On October 1, 2010, Waste Management picked up containers and the tote with liquid waste for shipment to Arlington, Oregon. They followed up on October 4 in removing a roll-off from Site A and Site B each containing soil. The soil was not hazardous, but Riverside Associates decided to send soil to hazardous waste landfill.
The oil containers remained on site.
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