ATCH 13 - 2020 Addendum — Napa City Council, April 2, 2024 (part 8 of 9)

ATTACHMENT 13

6.0 CONCLUSIONS AND RECOMMENDATIONS

6.1 SOIL GAS CONDITIONS
VOCs in Soil Gas
PCE and TCE were the only VOCs detected in the soil gas samples. PCE and TCE were detected above the screening level (Tier 1 ESL) in the sample (SG -1) located in the yard of the residence addressed 711 1st Street (on the northeastern corner of the Property ) and in the sample (SG -2) located in the driveway to the east of the commercial building. PCE was also detected above the screening level (Tier 1 ESL) in the two samples (SG -3 and SG -4) located to the south of the commercial building. PCE was detected below the screening level (Tier 1 ESL) in the sample (SG -5) located to the west of the commercial building. The commercial building reported housed dry-cleaning tenants in the past.

Out of a total of eight sample locations, the f uel constituent VOC benzene was not detected, but at an elevated laboratory RL. The detections of benzene could be as high as 100 µg/m3, which would exceed the Tier 1 ESL value of 48 µg/m3, the most conservative value and is based upon a residential use scenario. However, these detections would be below the respective commercial/industrial land use ESL of 420 µg/m3.

A cursory Risk Assessment using the modified Johnson and Ettinger (J&E) soil vapor screening model estimate for human health risks from subsurface vapor intrusion was conducted as detailed in Section

5.3. A portion of the Property is used for residential and the results of the residential scenario analysis indicate the maximum soil vapor concentrations for PCE and TCE produce a calculated carcinogenic risk from vapor intrusion approximately one order of magnitude above the risk threshold of 1E -6 and a non - cancer hazard quotient from vapor intrusion approximately twice the risk threshold 1.0 at a depth of 5 feet. Based on the evaluation presented herein, there is a potential risk of vapor intrusion resulting in an incremental lifetime carcinogenic risk exceeding 1.0E -06 which is a threshold level typically considered acceptable for an unrestricted residential use. It should be noted that the governing risk values are driven under the residential use scenario , since the current use of the Property includes both residential and commercial.

A portion of the Property is also used fo r commercial purposes , and as such, ODIC calculated an incremental lifetime carcinogenic risk (ILCR) as well as a non -cancer hazard quotient (HQ) in a commercial scenario . ILCR and HQ from an inhalation exposure to the maximum detected soil vapor concentrations of PCE and TCE are lower than the threshold level of 1.0E-5 and 1.0, respectively, at depth of 5 feet, indicating a low risk of vapor intrusion into the commercial building or health hazard to the indoor occupants in a commercial use scenario. A one-in-one hundred thousand (1.0E-05) excess cancer risk is typically recognized by Federal and State agencies as acceptable in commercial/industrial scenarios.

Summary

ODIC therefore concludes that the detections of PCE and TCE indicate a release in the area, likely from the former dry-cleaning tenant, and there is a potential risk of vapor intrusion resulting in an incremental lifetime carcinogenic risk exceeding 1.0E-06 and hazard quotient higher than 1.0 in a residential scenario.

Additionally, for future assessments, lower laboratory detection limits should be used to further assess benzene levels in soil gas.

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6.2 SOIL CONDITIONS
TPH as GRO, DRO and ORO in Soil
Two samples from two borings SB6 and SB8 located at the vacant lot at the western portion of the Property had detections of TPH-DRO and TPH-ORO at relatively low concentrations, significantly below the Tier 1 ESL values. TPH-GRO was not detected in the two soil samples at concentrations at or above the laboratory RLs, with none of the laboratory RLs exceeding the Tier 1 ESL value of 100 mg/kg .

Summary
ODIC therefore concludes that TPH in soil in the areas investigated do not represent a significant environmental risk or hazard based on site observations and analytical data.

VOCs in Soil
PCE was the only VOC detected in the soil samples analyzed and was detected in two samples at low concentrations, significantly below the Tier 1 ESL value . The Tier 1 ESL value represents the potential for the contaminant to migrate downward and negatively impact the groundwater quality. The PCE was found in the eastern portion of the Property.

The fuel constituent VOC benzene was not detected in the two soil samples at concentrations at or above the laboratory reporting limit.

Summary
ODIC therefore concludes that the detections of PCE in soil indicate a likely release from the former dry- cleaning tenant.

Title 22 Metals in Soil
Detected concentrations of Title 22 metals in the soil samples analyzed were below regulatory screening levels except for arsenic , which showed a detected concentration of 5.9 mg/kg, and lead, which showed detected concentrations of 6.9 mg/kg and 170 mg/kg.

In regard to the arsenic detections, a n independent study conducted at 14 Air Force installations across California (Hunter, et al, “Inorganic Chemicals in Ground Water and Soil: Background Con centrations at California Air Force Bases”, March 10, 2005) determined that the 95th percentile of arsenic in the upper 3 feet of soil (considered a good representation of background concentrations) is 12.7 mg/kg

This independent study resulted in similar conclusions regarding arsenic in natural soil as compared to anthropogenic sources. Using the criteria presented in t hese studies, 12 mg/kg is a defensible background level for arsenic in soil. As such, 12 mg/kg has been widely accepted by regulatory agencies as the cleanup goal concentration for anthropogenic and naturally occurring levels of arsenic in soil in California. The detected concentration of arsenic in one soil sample is significantly below what is typically accepted as a natural background soil concentration.

The soil samples analyzed for arsenic had concentrations and laboratory RLs well below the 12 mg/kg background level for arsenic in soil. The highest concentration of arsenic was 5.9 mg/kg, significantly below what is typically accepted as a natural bac kground soil concentration. Based on the foregoing, detected arsenic concentration is not likely an indicator of significant environmental risk. Based on prior experience with elevated arsenic at similar sites, ODIC opines that the detected arsenic concen trations ATTACHMENT 13
are representative of background conditions and are not resultant from past use of the Site. It is therefore concluded that detected concentrations of arsenic in soil in the areas investigated do not represent a significant environmental risk or hazard.

The detected lead concentration (6.9 mg/kg) in the sample (SB -6-5) from the northwestern corner of the vacant lot (western portion of the Property) was well below regulatory screening levels but the lead concentration (170 mg/kg) in the sample (SB -8-5) from the southwestern corner of the vacant lot was above the Tier 1 ESL which represents the health risk of direct exposure to the contaminant in a residential land use scenario but below the commercial/industrial land use ESL of 320 mg/kg and the RSL of 800 mg/kg.

Summary
Lead was the only metal of potential concern based upon a single detection at a location in a vacant lot on the western p ortion of the Property, which is designated for commercial use . This detected lead appears to be isolated and does not exceed the commercial screening levels. The absence of pavement/hardcover at the surface means that there are complete exposure pathways of ingestion, inhalation or dermal contact. However, with the lead detections below the ESLs, there is low risk to human health and environment as long as the use and configuration of the vacant lot remain unchanged.

It should be noted that in a residentia l-use scenario of the lot, there would be a risk to human health and the environment.

ODIC therefore concludes that metals in soil in the areas investigated do not represent a significant environmental risk or hazard based on site observations and analytical data , as long as the use and configuration remain unchanged.

6.3 CONCLUSIONS AND RECOMMENDATIONS
Based on the results and findings presented in this report , there is evidence of impacts in the areas investigated around the on-site commercial building. The presence of PCE and/or TCE in soil gas and soil around the commercial building would be consistent with a release from dry -cleaning operations by past site tenants. The levels of PCE and/or TCE reported in four of the soil gas samples to the east and south of the commercial building are above the Tier 1 ESLs, the most conservative screening values, and t he levels of PCE reported in the two soil gas samples to the east of the commercial building are al so above the respective commercial/industrial land use ESL.

There is a potential risk of vapor intrusion resulting in an incremental lifetime carcinogenic risk and non - cancer hazard exceeding threshold levels typically considered acceptable for an unrestricted residential use.

Groundwater was expected to be encountered at depth of approximately 10 feet, but during this investigation groundwater was not encountered at the maximum exploratory depth of 15 feet. It is unlikely that contamination found in t he shallow samples has impacted the groundwater, but the vertical extent of chlorinated organic solvents, particularly PCE, in soil gas and soil matrix has not been defined.

The source for the single soil sample with the elevated concentration of lead in soil matrix sampled on the commercial vacant lot is unknown but could potentially be related to lead -based paint on former structures on this portion of the Property. Lead in soil was detected at a concentration of 170 mg/kg in the sample (SB-8-5) from the southwestern corner of the vacant lot , which is above the Tier 1 ESL for direct exposure to the contaminant in a residential land use scenario but below the commercial/industrial land ATTACHMENT 13
use ESL of 320 mg/kg and the EPA Region 9 Screening Level of 800 mg/kg. Background concentrations of lead could vary significantly across the area and should be evaluated against regulatory standards applicable to planned future use (residential versus commercial/industrial).

There is no pavement or hardscape surface cover in the area where the elevated concentration of lead was detected, thereby a direct exposure pathway to human receptors can be complete. Although the lead detections are below the commercial land use screening criteria, given the unhindered access to the contaminated soil by children and other human receptors , the Client is advised to consider removing the impacted soils in order for the exposure pathways of lead impacted soils to become incomplete.

This report is to be submitted to the NCDPBES in accordance with the drilling permit requirements.

6.4 FUTURE CONSTRUCTION AND RISK MITIGATION
ODIC was made aware that the entire Property w ould be redeveloped into a commercial complex consisting of retail buildings overlying subterranean parking structures. Since the Project is currently in a conceptual design stage, detailed use and configuration of the future improvements have yet to be finalized. However, the future development is designed to feature at least one level of underground parking beneath at least the entire footprint of the current commercial building, where the final depth of excavation for the entire Property area is expected to be approximately 15' below ground surface (bgs).

The basement parking level is to be open to ambient air, thus a potential risk of vapor intrusion from detected concentrations of PCE and TCE in the subsurface beneath the former dry -cleaning area to degrade indoor air quality of the future commercial occupants on the ground level is mitigated, as typical subterranean parking structures are designed to accommodate sufficient air volumes to be exchanged, and more than 12 feet of vertical clearance will be provided between the base of the underground parking level and the ground floor of the retail commercial building.

The final grading plan or excavation plan has not yet been developed. However, based on the preliminary site development plans, it appears that project grading and excavation will occur on the majority of the Property to a depth of approximate 15' bgs. Planned development site plans are attached to this Report in Appendix E.

Therefore, the areas impacted with lead at 5' bgs will be subjected to excavation and removal, posing no potential risk or hazard to the future occupants.

In the unlikely event that the current design plan changes, areas where carcinogenic risks and non - carcinogenic hazards exceed the levels typically recognized by Federal and State agencies as acceptable for unrestricted land use should be subject to environmental covenant or institutional controls.

Prior to commencing grading and soil excavation activi ties, a Soil Management Plan, a Health and Safety Plan and a Human Health Risk Assessment to Construction Workers should be prepared to ensure that contaminants of concern discussed in this Report do not pose an adverse carcinogenic risks and health hazards to future construction and utility workers, and also to comply with the requirements of the regulatory oversight authorities.

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FIGURE 1

SITE LOCATION MAP
ATTACHMENT 13
FIGURE 1
No Scale
N
S
EW
Site Location Map
ODIC Environmental
3255 Wilshire Blvd. #1510, Los Angeles, CA 90010
Tel: 213-380-0090 Fax: 213-380-0505
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FIGURE 2

SOIL BORING LOCATION MAP
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FIGURE 2
N
S
EW
Boring Map
SITE ADDRESS: 711-831 1st Street and 718-730 Water Street, Napa, CA 94559
No Scale
ODIC Environmental
3255 Wilshire Blvd. #1510
Los Angeles, CA 90010
Tel: 213-380-0090
Fax: 213-380-0505
Water Street
McKinstry Street
1st Street
Soscol Avenue
Railroad
Soil/soil vapor boring location
Soil/soil vapor boring location
Property boundary
Previous 2014 BSK Phase II investigation boring location 731
730 718
7115'
5'
5'
5'
15'
15'
5' 5'
SG-1/
SB-1
SG-2/
SB-2
SG-3/
SB-3
SG-4/
SB-4
SG-5/
SB-5
SG-7/
SB-7
SG-6/
SB-6
SG-8/
SB-8
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TABLE 1

SOIL GAS ANALYTICAL RESULTS FOR VOCS
ATTACHMENT 13
Table 1

SOIL GAS ANALYTICAL RESULTS FOR VOCS
Commercial and Residential Property
711 - 825 1st Street and 718 - 730 Water Street
Napa, CA 94559
Sample ID PCE TCE cis-1,2-DCE trans-1,2-
DCE
Vinyl
Chloride Benzene Ethyl
benzene Toluene Xylenes Other VOCs
Units µg/m3 µg/m3 µg/m3 µg/m3 µg/m3 µg/m3 µg/m3 µg/m3 µg/m3 µg/m3 U.S. EPA Method 8260B 8260B 8260B 8260B 8260B 8260B 8260B 8260B 8260B 8260B SG-1 @ 5' 5 12/26/2018 6,800 1,600 <100 <100 <100 <100 <100 <200 <200 <RL SG-2 @ 5' 5 12/26/2018 14,000 2,900 <100 <100 <100 <100 <100 <200 <200 <RL SG-3 @ 5' 5 12/26/2018 1,600 <100 <100 <100 <100 <100 <100 <200 <200 <RL SG-4 @ 5' 5 12/26/2018 790 <100 <100 <100 <100 <100 <100 <200 <200 <RL SG-5 @ 5' 5 12/26/2018 210 <100 <100 <100 <100 <100 <100 <200 <200 <RL SG-6 @ 5' 5 12/26/2018 <100 <100 <100 <100 <100 <100 <100 <200 <200 <RL SG-7 @ 5' 5 12/26/2018 <100 <100 <100 <100 <100 <100 <100 <200 <200 <RL SG-8 @ 5' 5 12/26/2018 <100 <100 <100 <100 <100 <100 <100 <200 <200 <RL 240 240 4,200 42,000 4.7 48 560 160,000 52,000 Varies
Notes:
ft bgs = Feet below ground surface
TPH = Total petroleum hydrocarbons
VOCs = Volatile organic compounds
PCE = Tetrachloroethene
TCE = Trichloroethene
cis-1,2-DCE = cis-1,2-dichloroethene
trans-1,2-DCE = trans-1,2-dichloroethene
µg/m3 = Microgram per cubic meter
< = Analyte not detected at or above the stated laboratory reporting limit BOLD = Detected above stated laboratory reporting limit <RL = Analyte not detected above respective laboratory reporting limit Orange highlight = Analytical result above applicable screening level Tier 1 ESLs - Environmental Screening Levels, San Francisco Bay Regional Water Quality Control Board, February 2016 (Rev. 3) Source: http://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/ESL/Tier%201%20and%20Summary%20ESLs_22Feb16.pdf Depth
(ft bgs) Date
Tier 1 ESLs - Soil Gas
ODIC Environmental
Phase II Environmental Site Assessment Report
January 2019
ATTACHMENT 13
TABLE 2

SOIL ANALYTICAL RESULTS FOR TPH AND VOCS
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Table 2

SOIL ANALYTICAL RESULTS FOR TPH AND VOCS
Commercial and Residential Property
711 - 825 1st Street and 718 - 730 Water Street
Napa, CA 94559

TPH-GRO
(C7 to C12)

TPH-DRO
(C10 to C28)

TPH-ORO
(C28+) PCE TCE cis-1,2-
DCE
trans-1,2-
DCE
Vinyl
Chloride Benzene Ethyl
benzene Toluene Xylenes Other VOCs
Units mg/kg mg/kg mg/kg µg/kg µg/kg µg/kg µg/kg µg/kg µg/kg µg/kg µg/kg µg/kg µg/kg U.S. EPA Method 8015B 8015B 8015B 8260B 8260B 8260B 8260B 8260B 8260B 8260B 8260B 8260B 8260B SB-1 @ 5' 4.5 - 5 12/26/2018 NA NA NA <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <9.9 NA SB-2 @ 5' 4.5 - 5 12/26/2018 NA NA NA 10 <5 <5 <5 <5 <5 <5 <5 <10 <RL SB-3 @ 5' 4.5 - 5 12/26/2018 NA NA NA 25 <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <9.9 <RL SB-4 @ 5' 4.5 - 5 12/26/2018 NA NA NA <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <4.9 <9.9 <RL SB-5 @ 5' 4.5 - 5 12/26/2018 NA NA NA <5 <5 <5 <5 <5 <5 <5 <5 <10 <RL SB-6 @ 5' 4.5 - 5 12/26/2018 <0.5 19 200 <5 <5 <5 <5 <5 <5 <5 <5 <10 <RL SB-7 @ 5' 4.5 - 5 12/26/2018 NA NA NA <5 <5 <5 <5 <5 <5 <5 <5 <9.9 <RL SB-8 @ 5' 4.5 - 5 12/26/2018 <0.49 21 240 <5 <5 <5 <5 <5 <5 <5 <5 <9.9 <RL 100 230 5,100 420 460 190 670 8 44 1,400 2,900 2,300 Varies NE NE NE 390,000 19,000 2,300,000 23,000,000 370,000 420,000 20,000,000 47,000,000 2,500,000 Varies Notes:
ft bgs = Feet below ground surface
TPH = Total petroleum hydrocarbons
VOCs = Volatile organic compounds
GRO = Gasoline range organics
DRO = Diesel range organics
ORO = Oil range organics
TBA = Tert-butyl alcohol
MTBE = Methyl tert-butyl ether
mg/kg = Milligram per kilogram
µg/kg = Microgram per kilogram
Y = Sample exhibits chromatographic pattern which does not resemble standard < = Analyte not detected at or above the stated laboratory reporting limit BOLD = Detected above stated laboratory reporting limit NA = Not analyzed for noted compound
<RL = Analyte not detected above respective laboratory Reporting Limit Orange highlight = Analytical result above applicable screening level Tier 1 ESLs - Environmental Screening Levels, San Francisco Bay Regional Water Quality Control Board, February 2016 (Rev. 3) Volatile Organic Compounds (VOCs)
USEPA RSLs - Industrial
Tier 1 ESLs - Soils
Sample ID
TPH
Depth
(ft bgs) Date
ODIC Environmental
Phase II Environmental Site Assessment Report
January 2019
ATTACHMENT 13
TABLE 3

SOIL ANALYTICAL RESULTS FOR METALS
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Table 3

SOIL ANALYTICAL RESULTS FOR METALS
Commercial and Residential Property
711 - 825 1st Street and 718 - 730 Water Street
Napa, CA 94559
Sample ID
Antimony Arsenic Barium Beryllium Cadmium Chromium Cobalt Copper Lead Mercury Molybdenum Nickel Selenium Silver Thallium Vanadium Zinc Units mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg U.S. EPA
Method 6010B 6010B 6010B 6010B 6010B 6010B 6010B 6010B 6010B 7471A 6010B 6010B 6010B 6010B 6010B 6010B 6010B SB-6 @ 5' 4.5 - 5 12/26/2018 <3 <5 86 <1 <2 17 5.5 5.8 6.9 <0.1 <5 15 <5 <2 <2 27 68 SB-8 @ 5' 4.5 - 5 12/26/2018 <3 5.9 270 <1 <2 46 15 34 170 0.49 <5 70 <5 <2 <2 40 210 31 0.067 3,000 42 39 see below 23 3,100 80 13 390 86 390 390 0.78 390 23,000 470 480 220,000 2,300 980 see below 350 47,000 800 46 5,800 8,100 5,800 5,800 230 5,800 350,000 California Background Concentrations (1) 0.6 12 (2) 509 1.28 0.36 122 14.9 28.7 23.9 0.26 1.3 57 0.058 0.8 0.56 112 149 Notes:
bgs = Below ground surface
mg/kg = Milligram per kilogram
< = Not detected at or above laboratory reporting limit BOLD = Detected above listed reporting limit
Orange highlight = Analytical result above applicable screening level Tier 1 ESLs - Environmental Screening Levels, San Francisco Bay Regional Water Quality Control Board, February 2016 (Rev. 3) Source: https://www.waterboards.ca.gov/sanfranciscobay/water_issues/programs/ESL/ESL%20Workbook_ESLs_Interim%20Final_22Feb16_Rev3_PDF.pdf RSLs = USEPA Region IX Regional Screening Levels Composite Worker Soil Table Noncancer Hazard Index and Noncarcinogenic Hazard Index=1 (U.S. EPA November 2018), http://www.epa.gov/region09/superfund/prg Chromium III ESL = 120,000 mg/kg; Chromium III RSL = 1,800,000 mg/kg Chromium VI ESL = 0.3 mg/kg; Chromium VI RSL = 3,500 mg/kg Depth
(feet bgs) Date
Tier 1 ESL - Soil
USEPA RSLs - Industrial
ODIC Environmental
Phase II Environmental Assessment Report
January 2019
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APPENDIX A

SITE PHOTOGRAPHS
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APPENDIX A

SITE PHOTOGRAPHS

Sample location SG-1/SB-1. Drilling rig set up on sample location SG-2/SB-2.

Drilling rig set up on sample location SG-4/SB-4. Drilling rig set up on boring SB-5.

Drilling rig set up on sample location SG-6/SB-6. Placing liner in probe at boring SB-7.

ATTACHMENT 13
Sampling at SB-8. Constructed soil gas sampling point at SG-4.

Collecting soil gas sample at SG-4. Soil gas sampling equipment.

Backfilled probe and borehole at SG-2/SB-2. Backfilled probes and boreholes at SG-3/SB-3.

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APPENDIX B

SOIL BORING LOGS
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ODIC Environmental
Field Boring Log Sheet 1 of 1
Location of Boring: Project: 1st St & Water St Boring No. SB-1 1st St Napa, CA 94559 Total Depth: 5 ft bgs
731 Job No. 6366822 Logged by: Lita Freeman
711 Drilling Contractor: TEG
Drill Rig Type: Not Applicable
Drillers Name: Craig
730 Sampling Methods: Hand sampling equipment
Hammer WT. NA Drop NA
Start Time: 10:45 AM Date
Water St Completed Time: 10:50 AM Date
NTS Boring Depth: 5 ft bgs
Casing Depth: