Central Valley Regional Water Quality Control Board
21 June 2022
Joseph D. Angulo
Deputy Director Public Works
City of Merced
678 W 18
th Street
Merced, CA 95340
[email protected]
CONDUCT GROUNDWATER SAMPLING FOR PER AND POLY- FLUORINATED
SUBSTANCES (PFAS) AT CITY OF MERCED MUNICIPAL AIRPORT, MERCED, MERCED
COUNTY, CALIFORNIA
Staff of the California Central Valley Regional Water Quality Control Board (Central Valley Water Board) completed the review of the Merced Regional Hazardous Waste Site, PFOA and PFOS Investigation Report of Findings dated 29 November 2016 (Report). The Report summarizes the results of PFAS groundwater sampling conducted at the Merced Municipal Airport (Airport) in September 2016. This PFAS sampling event was conducted concurrently with the routine groundwater monitoring for chlorinated solvents performed under the Central Valley Water Board Monitoring and Reporting Program (MRP) No. R5-2011-0808. Based on the results presented in the Report (discussed below), the Central Valley Regional Board has determined it is necessary to revise the MRP No. R5-2011-0808 to include PFAS monitoring at the Airport. To facilitate the revision of the MRP, at this time, the Central Valley Regional Board requests that the Airport conduct at least one round of PFAS sampling at all monitoring wells currently present at the Airport and evaluate the present condition of PFAS pollution in groundwater. Please conduct the PFAS groundwater sampling and analysis and include the results as part of the next Semi-annual Groundwater Monitoring Report due 1 November 2022.
The Airport’s September 2016 PFAS Investigation Results and the Central Valley Water Board’s rationale and expectations for the above requested PFAS sampling, analysis and reporting activities are discussed below.
September 2016 Investigation Results and Intended Use of the New Sampling and PFAS Analysis - In the September 2016 event, eight monitoring wells, including two shallow wells, five intermediate-depth wells, and one deep well were analyzed for 12 PFAS compounds with the analytical method available at that time. Multiple PFAS compounds were detected in each shallow and intermediate-depth well, with the concentrations in some wells exceeding the relevant thresholds for PFAS deemed protective of human health. As an example, perfluorooctane sulfuric acids (PFOS) and perfluorooctanoic acids (PFOA) were observed in intermediate-depth well (BZW-5) at concentrations of 79 and 54 nanograms per liter (ng/L),
- 2 - 21 June 2022
Merced Municipal Airport
City of Merced
Merced, CA 95340
respectively, exceeding the current Notification Levels (NLs) for PFOS and PFOA in drinking water (i.e., 6.5 and 5.1 ng/L, respectively).
The September 2016 PFAS sampling was conducted over five years ago and included select monitoring wells and limited numbers of PFAS analytes. Due to analytical method limitations, the September 2016 event did not include fluorotelomer chemicals commonly present in Aqueous Film Forming Foams (AFFF) likely applied historically at the Airport. With the recent development in PFAS analytical method, more PFAS chemicals used in AFFF have become readily analyzable. Results of the new round of sampling and analysis will be used for the following purposes:
1. Evaluate present levels of analyzable PFAS chemicals in the groundwater of the Airport, including evaluating PFAS chemicals not analyzed in 2016 and assessing changes of PFAS concentrations, if available, from those in 2016.
2. Estimate the potential maximum amount of aggregate PFAS concentrations in groundwater to help determine if additional monitoring wells need to be installed to complete PFAS plume delineation at the Airport.
PFAS Sampling and Analysis Expectations – At a minimum, the sampling and analysis activities at the Airport should consist of the following:
1. Field sampling methods should be consistent with the State Water Board’s Per- and Polyfluoroalkyl Substances (PFAS) Sampling Guidelines for Non-Drinking Water
1. 2. All monitoring wells currently present at the Airport, including shallow, intermediate- depth, and deep wells, should be monitored for depth to groundwater (DTW).
3. All monitoring wells currently present at the Airport should be analyzed for the 31 target PFAS analytes contained in Table 1, Adsorbable Organic Fluorine (AOF, Table 2), and the field and general chemistry parameters in Table 3:
a. PFAS analysis should be performed by an analytical laboratory accredited by the California Environmental Laboratory Accreditation Program that is capable to conduct the PFAS analysis compliant with the quality control requirements of Department of Defense Table B-15 of Quality Systems Manual (QSM) 2;
b. AOF analysis should meet the quality control criteria summarized in Table 4 of the draft EPA method 1621
3 and contain reporting limits not greater than 10 ng/L; and c. Analytical methods for the field parameters and general groundwater chemistry parameters in Table 3 should be appropriate for the expected concentrations at the Airport.
1 Available online at Per- and Polyfluoroalkyl Substances (PFAS) Sampling Guidelines for Non-Drinking Water (ca.gov)
2 Available online at http://www.waterboards.ca.gov/pfas/ 3 Available online at Draft Method 1621 Screening Method for the Determination of Adsorbable Organic Fluorine (AOF) in Aqueous Matrices by Combustion Ion Chromatography (CIC) (epa.gov) - 3 - 21 June 2022
Merced Municipal Airport
City of Merced
Merced, CA 95340
PFAS Sampling Results Reporting Expectations – At a minimum, the PFAS sampling results reporting should include the following:
1. A description of the sampling activities performed.
2. A complete list of existing monitoring wells, including the GPS location, well depth, and screen interval information of each well, located within the Airport’s footprint. The Central Valley Water Board staff understands that multiple monitoring wells likely have been destroyed for the re-development of the former Pepsi Bottling Plant area within the Airport. It would be beneficial to have the up to date well list and map of existing monitoring wells to evaluate the available monitoring well network at the Airport.
3. T abular and graphic summary of the DTW, groundwater flow directions and analytical results. QA/QC sample results should also be reported in a tabular format.
4. A survey of sensitive receptors within a one-mile radius from the Airport. Sensitive receptors may include, and not be limited to, surface water bodies and groundwater extraction wells such as domestic, irrigation and municipal supply wells or extraction wells for pump-and-treat purposes. The relevant groundwater extraction well information should include, but not be limited to, well GPS locations, well logs, use purposes of the extracted groundwater, extraction flow rates, and if available, a summary of water quality monitoring activities performed at each well (e.g., schedules and monitoring parameters) and their associated monitoring results. Historical sensitive receptor survey conducted within five years before the date this letter is issued may be submitted to meet this request.
Finally, please include the PFAS sampling results in the next Semi-annual Groundwater Monitoring Report due November 1, 2022. Should you have any questions about the requested sampling and analysis, or sampling result due date, please contact the Project Manager, Xueyuan (Helen) Yu by telephone at (916) 464-4729 or e-mail to [email protected]
.
Sincerely,
Xueyuan Yu
Xueyuan (Helen) Yu
Ph.D., P.E. C74209,
Senior Water Resource Control Engineer, Specialist
cc: (via email)
Chris Flower, Central Valley Water Board, [email protected]
Steven Meeks, Central Valley Water Board, [email protected]
Merced Municipal Airport -4- 21 June 2022 City of Merced
Merced, CA 95340
Table 1. Requested PFAS analytes and the highest acceptable Reporting Limits Chemical Name/ Abbreviation(s) GeoTracker
PARLABEL
Chemical
Abstracts Service
(CAS) No.
Acceptable
Reporting Limit for
Groundwater
(ng/L)
Acceptable
Reporting
Limit for
Stormwater
(ng/L)
Acceptable
Reporting
Limit for Soil
(ng/g)
Perfluorobutanoic acid (PFBA) PFBA, PFBTA 375-22-4 8.0 8.0 1.0 Perfluoropentanoic acid (PFPeA) PFPeA, PFPA 2706-90-3 5.0 5.0 1.0 Perfluorohexanoic acid (PFHxA) PFHxA, PFHA 307-24-4 5.0 5.0 1.0 Perfluoroheptanoic acid (PFHpA) PFHPA 375-85-9 5.0 5.0 1.0 Perfluorooctanoic acid (PFOA) PFOA 335-67-1 5.0 5.0 1.0 Perfluorononanoic acid (PFNA) PFNA 375-95-1 5.0 5.0 1.0 Perfluorodecanoic acid (PFDA) PFDA, PFNDCA 335-76-2 5.0 5.0 1.0 Perfluoroundecanoic acid (PFUnDA) PFUnA, PFUNDCA 2058-94-8 5.0 5.0 1.0 Perfluorododecanoic acid (PFDoA) PFDOA 307-55-1 5.0 5.0 1.0 Perfluorotridecanoic acid (PFTrDA) PFTrDA, PFTRIDA 72629-94-8 5.0 5.0 1.0 Perfluorotetradecanoic acid (PFTA) PFTA, PFTEDA 376-06-7 8.0 8.0 2.0 Perfluorobutane sulfonic acid (PFBS) PFBS, PFBSA 375-73-5 5.0 5.0 1.0 Perfluoropentane sulfonic acid (PFPeS) PFPES 2706-91-4 5.0 5.0 1.0 Perfluorohexane sulfonic acid (PFHxS) PFHXS, PFHXSA 355-46-4 5.0 5.0 1.0 Perfluoroheptane sulfonic acid (PFHpS) PFHpS, PFHPSA 375-92-8 5.0 5.0 1.0 Perfluorooctane sulfonic acid (PFOS) PFOS, PFOS_A 1763-23-1 5.0 5.0 1.0 Perfluorodecane sulfonic acid (PFDS) PFDS, PFDSA 335-77-3 5.0 5.0 1.0 Perfluorooctanesulfonamide (PFOSAm) PFOSA 754-91-6 8.0 8.0 1.0 N-Ethyl perfluorooctane sulfonamido ethanol
(EtFOSE)
ETFOSE 1691-99-2 8.0 8.0 2.0
N-Methyl perfluorooctane sulfonamido ethanol
(MeFOSE) MEFOSE 24448-09-7 8.0 8.0 2.0
N-Ethyl perfluorooctane sulfonamide2 (EtFOSAm) EtFOSAm, ETFOSA 4151-50-2 8.0 8.0 2.0
Merced Municipal Airport -5- 21 June 2022 City of Merced
Merced, CA 95340
Table 1, Continued
Chemical Name/ Abbreviation(s) GeoTracker
PARLABEL
Chemical
Abstracts Service
(CAS) No.
Acceptable
Reporting Limit for
Groundwater
(ng/L)
Acceptable
Reporting
Limit for
Stormwater
(ng/L)
Acceptable
Reporting
Limit for Soil
(ng/g)
N-Methyl perfluorooctane sulfonamide (MeFOSA,
MeFOSAm)
MeFOSAm,
MEFOSA 31506-32-8 8.0 8.0 2.0
N-Methyl perfluorooctane sulfonamidoacetic acid
(NMeFOSAA) NMEFOSAA 2355-31-9 8.0 8.0 2.0
N-Ethyl perfluorooctane sulfonamidoacetic acid
(NEtFOSAA) NETFOSAA 2991-50-6 8.0 8.0 2.0
4:2 Fluorotelomer sulfonic acid (4:2 FTS) 4:2FTS 757124-72-4 8.0 8.0 2.0 6:2 Fluorotelomer sulfonic acid (6:2 FTS) 6:2FTS 27619-97-2 8.0 8.0 2.0 8:2 Fluorotelomer sulfonic acid (8:2 FTS) 8:2FTS 39108-34-4 8.0 8.0 2.0 Hexafluoropropylene Oxide Dimer Acid (HFPO-DA) HFPO-DA, HFPA-DA 13252-13-6 8.0 8.0 5.0 4,8-Dioxa-3H- perfluorononanoic acid (ADONA) ADONA 919005-14-4 8.0 8.0 5.0 9-Chlorohexadecafluoro-3- oxanonane-1-sulfonic
acid (9- Cl-PF3ONS) 9ClPF3ONS 756426-58-1 8.0 8.0 5.0
11-Chloroeicosafluoro-3- oxaundecane-1-sulfonic
acid (11-Cl-PF3OUdS)
11ClPF3OUd S 763051-92-9 8.0 8.0 5.0
Merced Municipal Airport -6- 21 June 2022 City of Merced
Merced, CA 95340
Table 2. Highest Reporting Limit for Adsorbable Organic Fluorine Analysis
Analyte Acceptable Reporting Limit for Groundwater
(ng/L)
Adsorbable Organic Fluorine 10
Table 3. Field and General Chemistry Parameters for Groundwater Samples Field Parameters Units General Chemistry Units
Depth to Groundwater Feet, bgs Total Dissolved Solids mg/L Temperature Degrees C Chloride mg/L
Electrical Conductivity µmhos/cm Carbonate mg/L
pH units Bicarbonate mg/L
Turbidity NTU Nitrate-Nitrogen mg/L
Dissolved Oxygen mg/L Sulfate mg/L
Oxidation/Reduction
Potential
mV Calcium mg/L
Magnesium mg/L
Potassium mg/L
Sodium mg/L
Notes:
bgs – below ground surface C – Celsius
mg/L – milligrams per liter
NTU – nephelometric turbidity units
µmhos/cm – micromhos per centimeter
mV - millivolts