State of Oregon

Department of Environmental Quality       Memorandum

_____________________________________________________________________________________

Date:    September 28, 2006

To:    Audrey O’Brien, Manager, Solid Waste Program

From:    Bob Schwarz, Cleanup Program

Subject:  Santosh Landfill, ECSI # 1383; Recommendations for next steps

This memo provides recommendations for next steps in addressing contamination at the Santosh Landfill. Based on substantial sampling conducted between September 2004 and May 2006, we draw two key conclusions. One, contamination from the landfill does not extend far from the landfill boundary. Two, during periods of heavy precipitation, there are significant leachate seeps that appear throughout the landfill. Steps should be taken to prevent generation of these seeps.

To prevent leachate seeps, we recommend that the landfill be regraded to promote drainage of precipitation and thereby minimize infiltration of clean water into the waste. Regrading would involve eliminating depressions on top of the landfill where water can collect and would also involve reducing the steepness of the landfill side slopes so that water that does enter the landfill will not be discharged above the ground surface as seeps. Portions of the landfill surface where vegetation is covered or damaged would then be revegetated. Clean fill would be placed over areas where waste has been exposed.

The approximate cost of regrading the landfill is $1.3 million. The remainder of this memo provides site information related to these recommendations.

Project status. Site investigation activities have included the following:

-  Groundwater monitoring. Groundwater at the landfill has been sampled five times between April 2005 and May 2006. Nine wells were installed along the landfill perimeter. An additional five wells were installed between 200 feet and 500 feet to the south and west to assess groundwater impacts away from the landfill. In addition, 21 residential drinking water wells were sampled in the summer of 2004, and residential wells closest to the landfill have been sampled a number of times since then.

-  Other sampling. Surface water and sediment were sampled twice in 2005. Samples were collected in Scappoose Creek, Santosh Slough, and in the wetlands near the landfill. Soil was also sampled on the surface of the landfill. Landfill gas was measured on and off the landfill eight times between May 2005 and March 2006. Leachate seeps were sampled in January 2006.

Seep quantity and quality. Public concern was primarily focused on leachate seeps along the south side of the landfill. DEQ had considered measures to address these areas by themselves. However, when leachate seeps appeared at several other locations throughout the landfill, we postponed a decision regarding the south end of the site until we had analytical data on the other seeps.

The following table shows the maximum concentrations of those contaminants found above risk screening levels. The table also shows human health risk screening levels (USEPA Region 9’s preliminary remediation goals, or PRGs) and DEQ’s ecological screening level values (SLVs). Most of the contaminants in this table are metals, many of which occur naturally. However, as shown in this table, concentrations in the seeps are much higher than in the nearby creek and slough. This indicates that these contaminants are from the waste in the landfill.

The seeps results shown in this table are from four samples collected on the east and west sides of the landfill. Unfortunately, no samples were collected from the seeps on the south end of the landfill, which are the most persistent, and where we have observed discolored soil and foul odor. We recently attempted to collect a sample there but could not because of dry conditions. It is possible that the seep concentrations shown below therefore do not represent the worst case.

Contaminants in leachate seeps found above risk screening levels, ug/l ¹

Notes:

1.  ug/l = micrograms per liter

2.  PRG = preliminary remediation goals (USEPA Region 9, 2004)

3.  SLV = ecological screening level values (DEQ, 2001)

4.  NL = not listed

5.  NT = not tested

Next steps. Given the exceedance of risk screening levels, Cleanup Program rules and guidance suggest one of two approaches. The first would be to proceed with a risk assessment, to quantify risk to human and ecological receptors. If risk exceeds acceptable levels, as defined in OAR 340-122-115(1), the risk assessment would be followed by a feasibility study to determine the most appropriate way to reduce risk to acceptable levels.

The second approach is to proceed directly with a removal action, without conducting a risk assessment or feasibility study. Removal actions are sometimes performed if DEQ determines that certain measures should be taken before a risk assessment or feasibility study is completed.

We recommend that DEQ proceed with regrading of the landfill, as a removal action. Reasons for this are:

•  Leachate seeps have been observed throughout the landfill during periods of heavy precipitation. Contaminants have been found in these seeps at concentrations above risk screening levels.

•  Site regrading is the most cost-effective way to reduce or eliminate leachate seeps.

•  Given limited funds for work at this site, proceeding with site regrading would enable us to reduce or eliminate leachate seeps without first spending additional time and money conducting a risk assessment.