R--CASTNET VII

Active

Contract Opportunity

The U.S. Environmental Protection Agency (EPA) Air Quality Assessment Division (AQAD), Office of State Air Partnerships (OSAP) anticipates awarding a single Indefinite-Delivery/Indefinite-Quantity with a one-year base and four one-year option periods. This procurement will be conducted as a full-and-open competition under the Federal Acquisition Regulations (FAR) Part 15: Contracting by Negotiation. The formal solicitation and other related information and items will be posted at this website on or about January 30, 2026. The minimum guarantee for the base year is $750,000.00. All responsible offerors may submit a proposal. Copies of the solicitation will be available on this site. Paper copies of the solicitation will not be provided. An RFI /Sources sought notice was previously posted (68HERH25R0011) to FedConnect on April 25, 2025. It is the responsibility of interested parties to regularly monitor this website for updates to this procurement. Telephone inquiries will not be taken.

The Clean Air Status and Trends Network (CASTNET) is a long-term multipollutant monitoring network that measures spatial and temporal changes in ambient air quality and assesses atmospheric deposition over broad geographic regions of the U.S. (https://www.epa.gov/castnet). Operating since 1987, CASTNET has evolved into a robust regional monitoring program which currently consists of approximately 90 monitoring stations nationwide. The Environmental Protection Agency (EPA) coordinates the operation of the network in cooperation with numerous federal, tribal, state and local partners.
The primary monitoring objectives of CASTNET are to:
•        Provide high quality data on atmospheric concentrations and deposition of ozone (O3), particulate matter (PM), and constituents of PM;
•        Support the primary and secondary ozone National Ambient Air Quality Standards (NAAQS) by providing data that meet the regulatory requirements in 40 Code of Federal Regulations (CFR);
•        Monitor the status and trends in regional air quality and atmospheric deposition;
•        Evaluate changes in air quality as a result of short- and long-term changes in emissions and other environmental impacts;
•        Improve EPA’s understanding of PM and ozone formation and regional transport;
•        Validate and improve air quality and deposition models;
•        Assess the effectiveness of EPA’s emission reduction programs;
•        Act as a platform for air quality and deposition research; and
•        Support science and ecosystem studies.
CASTNET sites measure weekly average concentrations of sulfate (SO42-), nitrate (NO3-), ammonium (NH4+), nitric acid (HNO3), chloride (Cl-) and the base cations (Na+, K+, Mg2+and Ca2+) using a 2-stage filter pack. Between 2022 and 2024, most sites discontinued using a 3-stage filter pack, removing the 3rd filter that was used to capture sulfur dioxide (SO2) concentrations. Certain sites continue to use the 3-stage filter pack and report concentrations of SO2. Starting in 2025, EPA deployed PM2.5 sensors at CASTNET sites. In addition, each site may make ancillary measurements, including hourly ozone (O3), hourly meteorology, ammonia (NH3) gas using passive devices, and trace-level gases. Trace-level gas monitors include reactive oxidized nitrogen (NOy), nitric oxide (NO), sulfur dioxide (SO2) and carbon monoxide (CO). CASTNET O3, meteorological, and trace gas measurements follow the requirements in the CFR and EPA’s Quality Assurance Handbook. A list of the ambient monitoring and meteorological measurement systems currently deployed at CASTNET sites is included as Appendix B.
As a long-term regional monitoring program, CASTNET is critical for characterizing trends in deposition levels and identifying relationships among emissions, atmospheric loadings, ecological effects and human health. The EPA, other government agencies and the scientific community rely on the data and information from CASTNET, used in conjunction with information from other national monitoring networks (e.g., the National Atmospheric Deposition Program/National Trends Network (NADP/NTN), NADP’s Ammonia Monitoring Network (AMoN), NCore, the Chemical Speciation Network (CSN), and Interagency Monitoring of Protected Visual Environments (IMPROVE)), to evaluate the effectiveness of air pollution control strategies for regional areas and assess chemical changes in the atmosphere. Since atmospheric changes occur very slowly and trends are often obscured by the wide variability of measurements and meteorology, numerous years of continuous and consistent data are required to overcome this variability.

The Air Quality Assessment Division (AQAD), Office of State Air Partnerships (OSAP), is the lead in providing support and technical direction for CASTNET. Additional background information, current standard operating procedures (SOPs), and the CASTNET Quality Assurance Project Plan (QAPP) are available at https://www.epa.gov/castnet.

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