NEBRAMail learned at the end of November that Pima County (Tuscon area) Arizona has reinstated its Class B biosolids land-application program following a moratorium imposed by the Pima County Board of Supervisors effective December 31, 2019. Following a concern raised to the Board regarding the potential to contaminate ground water with per- and polyfluoualky substances (PFAS) in the biosolids, the Board instituted the moratorium on agricultural land application of biosolids “pending obtaining a better understanding of how PFAS present in biosolids may disperse through soils into groundwater or fugitive dust” according to a memo obtained by NEBRAMail.

Pima County Administrator C.H. Huckelberry, in a memo dated October 29th, provided the Board of Supervisors with a copy of a report on a comprehensive study by the University of Arizona, Jacobs Engineering, and the National Science Foundation titled “PFAS in Biosolids – A Southern Arizona Case Study.” The study was initiated in March 2020 and the results presented by Dr. Ian Pepper of the University of Arizona at a PFAS-related webinar on October 28th. To read the full report, go to: https://casaweb.org/wp-content/uploads/2020/11/PFAS-in-Biosolids_A-Southern-Arizona-Case-Study.pdf

Pima County was one of the case studies in the recent report “Cost Analysis of the Impacts on Municipal Utilities and Biosolids Management to Address PFAS” – a collaboration of the Water Environment Federation, the National Association of Clean Water Agencies, NEBRA, and CDM Smith. According to the report, Pima County Wastewater Reclamation had been successfully using its biosolids as a soil amendment/fertilizer on agricultural land since 1984. Prior to the moratorium, Pima County recycled 100% of its solids to the land using a single service provider. On January 1st 2020, as a result of the moratorium, Pima County began landfilling their biosolids. The cost impacts were severe (see Table 3-2 from the CDM Smith report).

The costs do not reflect the loss of benefits which were cited by Administrator Huckelberry in the recommendation to reinstate the land application program, because the “beneficial use of biosolids will improve soil health, minimize topsoil erosion, reduce biosolids transportation emissions, reduce landfill loading and improve fiscal responsibility.”

In addition to the research team, led by Dr. Pepper from the University of Arizona, farmers were a key collaborator – they wanted answers too. This study is believed to be the largest study on PFAS ever conducted. It was performed on lands where biosolids had been applied for over 20 years with detailed records of biosolids land application rates. There was also a control field where the soils were undisturbed meaning no agriculture, no irrigation, no biosolids applications, no PFAS contamination. In order words, the only known influences were from wind and rain.

The researchers found very low PFAS concentrations in the agricultural soils. They found typical concentrations in the biosolids – 14 to 36 parts per billion (ppb) of PFOS. Surprisingly PFOA concentrations were very low, non-detect in most samples. A total of 18 PFAS were selected for the study.

The study concluded that there is minimal transport of PFAS through the top soil and negligible concern for groundwater. Of course, the Tuscon area is very arid and the depth to groundwater can exceed 150 feet. However, the agricultural lands received a lot of irrigation water – which equates to rainfall in heavy precipitation areas of the country. PFAS in soils where biosolids had been mixed in were slightly higher than agricultural soils without biosolids. Nonetheless, they observed minimal transport through the soils – PFAS concentrations rapidly decreased with depth. The researchers found 90% to 97% attenuation and minimal migration below 6 feet. They concluded that the potential for groundwater contamination is minimal. The study results gave Pima County what it needed to reinstate its biosolids land application program. The County Administrator plans to negotiate a new master agreement for the program right away.