Los Angeles Regional Water Quality Control Board
January 31, 2024
Mr. Akbar Farokhi
City Manager & Director Public Works
City of Hawthorne
4455 West 126th Street
Hawthorne, CA 90250
SUBJECT: CONDITIONAL APPROVAL OF CONFIRMATION SAMPLING WORK PLAN
SITE: FORMER NEW LIFE CLEANERS, 12601 HAWTHORNE BLVD.,
HAWTHORNE, CALIFORNIA (SCP NO. 1425, SITE ID NO. 4040003, GLOBAL ID NO. T10000011548)
Dear Mr. Farokhi:
The California Regional Water Quality Control Board, Los Angeles Region (Los Angeles Water Board) has reviewed the Confirmation Sampling Work Plan (Workplan) dated October 27, 2023, prepared by L. Everett & Associates (LEA) for the above-referenced site (Site).
A summary of the Workplan, followed by Los Angeles Water Board comments are included below.
SUMMARY OF WORKPLAN
The Workplan was prepared in response to the Los Angeles Water Board letter dated September 15, 2023, which requested confirmation sampling data to be collected from the Site following the soil vapor extraction (SVE) rebound test completed in the first half of 2023. Results from the SVE rebound test were included in the Soil Vapor Rebound Test Report dated June 15, 2023.
The following scope of work is proposed; proposed locations are depicted on the attached Figure 2 – Confirmation Sampling Proposed Locations:
1. Seven borings will be advanced in an approximate grid-like pattern across the Site. Borings CS-01, CS-02, CS-03, CS-04, and CS-05 will be advanced in areas where elevated tetrachloroethylene (PCE) was detected in preremediation samples. Two borings, CS-06 and CS-07, will be advanced along Mr. Akbar Farokhi - 2 - February 2, 2024
Former New Life Cleaners
the southern property boundary to evaluate potential vapor intrusion at the southern adjacent property.
a. Soil samples will be collected from all seven borings at 10-foot intervals from 10 feet below ground surface (ft bgs) to 60 ft bgs or first encountered groundwater (reported at 64 ft bgs). Soil samples will be analyzed for volatile organic compounds (VOCs).
b. Groundwater samples will be collected from borings CS-01, CS-02, CS03, and CS-07 by using a bailer lowered to groundwater through the hollow stem auger; samples will be analyzed for VOCs. Groundwater is encountered at approximately 64 ft bgs at the Site.
c. Soil vapor probes will be installed at all seven borings at 10, 25, and 55 ft bgs. Probes will be installed in accordance with the Department of Toxic Substances Control (DTSC) Final – Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air (Vapor Instruction Guidance) (2011), and the DTSC Advisory: Active Soil Gas Investigations (2015). Probes will be secured, capped, and completed. At least fortyeight hours after installation, probes will be sampled and the soil vapor will be analyzed for VOCs.
The soil, soil vapor, and groundwater sampling results will be summarized in a report and submitted to the Los Angeles Water Board. The report will include field activities, sampling protocols and lab results, including tables and figures, and an evaluation of the potential risk from vapor intrusion.
LOS ANGELES WATER BOARD COMMENTS
The Los Angeles Water Board approves the scope of work in the Workplan, with the following comments:
1. Soil vapor probe depths should be adjusted to 5, 15, 25, and 55 ft bgs, and should be installed as permanent probes. In the event that confirmation sample results are reported at concentrations that exceed screening levels, additional monitoring may be warranted at the Site.
2. In addition to the borings proposed, the following additional borings should be advanced; soil matrix samples should be collected at 10-foot intervals to 50 ft bgs, and soil vapor probes should be installed at 5, 15, 25, and 55 ft bgs:
Mr. Akbar Farokhi - 3 - February 2, 2024
Former New Life Cleaners
a. One boring should be advanced in the northeast corner of the Site in the vicinity of SV-05, which reported PCE up to 5,700 micrograms per cubic meter (µg/m3) at 48.5 ft bgs when sampled in 20181.
b. One boring should be advanced in the southwest corner of the Site in the vicinity of SG-21, which reported PCE up to 3,100 µg/m3 at 60 ft bgs when sampled in 20171.
3. Grab groundwater samples should be collected from all the onsite borings, including the seven proposed locations and the two additional locations requested by the Los Angeles Water Board.
4. Submit the confirmation sampling report by April 30, 2024. The report should include plume maps with concentrations by depth, figures and a discussion comparing pre-remediation and post-remediation results, and a recommendation for future activities at the Site, if warranted.
If you have any questions regarding this letter, please contact the undersigned at (213) 576-6732 or via email at [email protected], or Dr. Angelica Castaneda, Site Cleanup Unit IV Supervisor, at (213) 576-6737 or via email at [email protected].
Sincerely,
___________________
Devin DiNapoli
Engineering Geologist
Attachment:
Figure 2 – Confirmation Sampling Proposed Locations
cc:
Ms. Selena Acuna, City of Hawthorne
Mr. James Wells, LEA
1 Soil vapor concentrations reported in the Remedial Action Plan dated July 31, 2018.
Devin
DiNapoli
Digitally signed by Devin
DiNapoli
Date: 2024.01.31 10:35:02
-08'00'
C:\Users\jmatos\LEA Environmental, Inc\LEA Environmental, Inc. Team Site - Share\Projects\080_City_of_Hawthorne\GIS\Hawthorne\Hawthorne.aprx FORMER NEW LIFE CLEANERS12601 HAWTHORNE BOULEVARDHAWTHORNE, CALIFORNIA SCALE: AS SHOWN
0 30 15
Feet
LEGEND
Proposed location (soil, soil vapor and groundwater)Proposed location (soil, soil vapor)Groundwater monitoring wellSoil vapor extraction wellSite parcel boundary and former site features FIGURE 2
CONFIRMATION SAMPLINGPROPOSED LOCATIONS
W 126th St
Hawthorne Blvd
Boiler room
Dry cleaner suite
Hotel building
Former commercial building now demolished
VE-1
VE-2
VE-3
VE-4
MW-01
MW-02
MW-03
CS-01 CS-02
CS-03
CS-04 CS-05
CS-06 CS-07
Maxar