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Work Plan for Additional Subsurface Investigation
<br /> Former Helena Chemical Facility
<br /> July 13,2020
<br /> Page 3
<br /> San Joaquin County Environmental Health Department (EHD) file records documented several incidents
<br /> of improper storage and handling of hazardous chemicals, spills,and the presence of stained soil at the Site.
<br /> Site investigations conducted in 2001 and 2002 found elevated levels of Total Kjeldahl Nitrogen (TKN),
<br /> ammonia, and nitrate as nitrogen (nitrate-N) in soil samples. Soil sample analytical results indicated that
<br /> soil contained nitrate-N concentrations as high as 1,600 milligrams per kilogram (mg/kg), TKN
<br /> concentrations as high as 7,700 mg/kg, and ammonia-N concentrations as high as 2,200 mg/kg. TKN was
<br /> also detected at concentrations as high as 1,000 mg/kg in a boring intended as a background sample (BG),
<br /> which was located approximately 200 feet southeast of the former ASTs. Groundwater samples collected
<br /> near the former AST locations by Kleinfelder contained TKN up to 0.441 milligrams per liter (mg/L);
<br /> ammonia up to 0.34 mg/L; and nitrate-N up to 219 mg/L.
<br /> In 2006, another release incident was reported involving the spill of sulfur and lime to soil near the north
<br /> boundary of the Site. Various drums, sacks, and boxes had been compromised,and various materials were
<br /> reportedly released to the soil. EHD subsequently issued a Notice to Abate to the owner of the property.
<br /> The spilled materials were removed from the Site, and impacted soil was reportedly over-excavated.
<br /> However, EHD contained no records of soil confirmation sampling. A subsurface investigation conducted
<br /> in 2013 also showed that soil and groundwater contained TKN,ammonia,and nitrate-N.EHD subsequently
<br /> placed the Site on their local "Contaminated Site List" and referred the case to the Central Valley Water
<br /> Board for further review and evaluation.
<br /> Between 2016 and 2019, Condor conducted additional soil and groundwater investigations at the Site,
<br /> including the installation,development,and sampling of five groundwater monitoring wells to determine the
<br /> nature and extent of impacts to the Site from past uses and evaluate whether further cleanup activities are
<br /> warranted. The Central Valley Water Board required that additional COCs, including triazines and the
<br /> chlorinated fumigant 1,2,3-TCP,also be evaluated as part of the investigation.Based upon analytical results
<br /> of soil and groundwater samples collected during the investigation, Condor concluded that soil and
<br /> groundwater beneath the Site has been impacted by nitrates and the chlorinated fumigant 1,2,3-TCP.Based
<br /> upon analytical results of groundwater samples collected during the investigation, Condor concluded that
<br /> nitrate-N in shallow groundwater has essentially been defined to the west, south, and southeast. 1,2,3-TCP
<br /> in shallow groundwater occurs primarily in a small area along the northern property boundary and extends
<br /> an unknown distance to the north.Nitrate-N and 1,2,3-TCP concentrations in deeper groundwater("grab"
<br /> samples collected at approximately 30 feet bgs)indicates significant attenuation when compared to shallow
<br /> groundwater samples. The most recent groundwater analytical results from Site monitoring wells (June
<br /> 2020)contained nitrate-N as high as 300 mg/L in well MW-2.None of the Site monitoring wells contained
<br /> detectable 1,2,3-TCP.
<br /> Appendix A of this report contains figures showing the Site vicinity (Figure 1), the Site features and
<br /> locations of historical soil and groundwater samples(Figures 2 and 3),the monitoring well locations(Figure
<br /> 3),and the estimated extent of nitrate-N and 1,2,3-TCP in shallow groundwater beneath the Site(Figures 4
<br /> and 5).Appendix B includes data tables that summarize historical soil and groundwater data.
<br /> 4.0 PROPOSED SCOPE OF WORK SUMMARY AND RATIONALE
<br /> Condor proposes to install and sample three additional groundwater monitoring wells (MW-6, MW-7, and
<br /> MW-8) to further evaluate the extent of COCs in groundwater in the northern and eastern portions of the
<br /> Site. In the following sections, Condor presents the rationale for the proposed scope of work to address the
<br /> data gaps presented by the Central Valley Water Board in their letter dated March 19, 2020. Each "data
<br /> gap"outlined in the letter are summarized below in italicized font,followed by the proposed scope of work
<br /> and rationale.
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<br /> �� CONDOR
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