EnvironmentalAssessment

of the Cerro Prieto Geothermal Field

Phase IV

Final Report ReviewMexicali, January, 2018

Dr. Ronald AmundsonDr. Charlotte Smith

Dr. Michael Bates

Ronald Amundson, Ph.D.Professor

Department of Environmental Science, Policy, & Management

Research Interests / Specializationso Pedology isotope biogeochemistryo Impact of climate and life on earth processeso Soils in biogeochemical cycleso Human impacts on soils and ecosystems

• Collaboration with Dr. Abel Ibáñez (Soil Working Group)• Field visits, meetings in person and by teleconference• The type and chemical makeup of the soils that have been studied in this

report are consistent with the local geography and with soils in theUnited States immediately across the International Border

• The accumulation of total salt (salinization) and sodium (sodification) has occurred through a long term geological processes, and likely as a resultof the addition of surface water from the Colorado River and fromshallow groundwater

• The S and O isotope data provide very clear and strong support for thisinterpretation, as oppossed to salinization and sodification beingderived from the Cerro Prieto deep wells

• The future productivity of the soils requires a special and challengingmanagement

• The maintenance of soluble salt below levels that impede cropproduction requires the addition and leaching of the soil with irrigationwater of low salt content

• The standard method for the removal and lowering of sodium in the soilrequires both low sodium irrigation water and the addition of a calciumsource

• This strategy in turn, however, will impact the shallow ground water level, possibly decreasing its depth and adding additional salt to this reservoir

• While unrelated to Cerro Prieto and geothermal energy, the question of ground and surface water irrigation management will be a key to the longterm suitability of the soils for agricultural production

• The chemistry analyses revealed a relatively high concentration of theanion nitrate (NO3

-) in the soil extracts (up to several thousand mg/L), thus:

• Nitrate in shallow ground waters may exceed drinking standards• The high nitrate concentrations in the soils (the exact source is not

known) may lead to a significant production of the greenhouse gas nitrous oxide (N2O)

• It would be useful to examine the nitrate in ground and surface water, conduct N and O isotope measurements on the soil nitrate, and conductsome systematic measurements of N2O in soil and its flux to theatmosphere

• Again, this health and environmental concern is apparently unrelated to activity at the Cerro Prieto plant (since nitrate is unlikely to be associatedwith thermal waters), but is one that is part of the hydrological and agricultural management of the area

“In summary, the report suggests that the activities of theCerro Prieto geothermal plant do not appear to havemeasureable impacts on the local soils, or on the shallowwell and canal waters… For the soil work specifically, thedeliverables matched the goals and objectives that wereidentified at the beginning of the project. Independent ofthe geothermal plant, if agriculture is to remain a majorindustry and activity, water and soil management will berequired to facilitate the future of farming.”

Charlotte Smith, Ph.D.Lecturer

School of Public Health

Research Interests / Specializationso Microbial ecology of waterborne pathogenso Bacterial endosymbionts of free-living protozoao Drinking water quality regulationso Geospatial-geostatistical analysiso Mobile-GIS data collection

• Collaboration with Dr. Aurora Armienta and Dr. Patricia Bonilla (Water WorkingGroup)

• Field visits, meetings in person and by teleconference

• A group of chemical analyses was performed on water bodies in proximity to theCerro Prieto Geothermal Field

• The water quality constituents were selected based on prior observation of chemical contaminants in this environment, and/or chemicals with significantimpact on public health

• Only one microbe was analyzed, Naeglaria. Naeglaria was chosen due to itssignificant impact on those who are infected, and that this organism had beenidentified in prior studies near Mexicali

• Sample collection and analysis was conducted according to Standard Methods for theExamination of Water and Wastewater (APHA-AWWA 2005)

• The protocols used by the UNAM microbiology team were based on their many years of experience and allowed for the identification of Naeglaria in some waters that weretested in the study

• The results from the chemical and protozoan samplings were sent to Berkeley forreview and comment

• The conclusions reached by the UNAM teams were consistent with the data producedfrom both the chemical and microbial sampling campaigns

• The focus of the chemical sampling was on wells and canals related to irrigation

• Water in the Ever16 agricultural zone is not suitable for irrigation due to highsalinity

• Only one drinking water well was surveyed for chemical contamination. The waterin that well met water quality standards related to human consumption

• According to the results of our analyzes and previous studies carried out in the area, there is no communication between the CGCP and the irrigation channels of the Mexicali Valley, so it can be affirmed that the amoebas of the genus Naegleria found in the irrigation channels they do not come from the Geothermal Field.

“Future water quality sampling should take place withthe input from a hydrogeologist to assist in predictingflows in the sub-surface. Future sampling locationscould consider those predictions… Additional samplingfor Naeglaria at the well field does not appear to bewarranted. However, CFE should consider testing thecooling towers for Legionella.”

Michael Bates, Ph.D.Adjunct Professor of Epidemiology

School of Public Health

Research Interests / Specializationso Environmental and occupational epidemiologyo Health risks of long-term, low-level exposure to

hydrogen sulfideo Health effects of exposure to household air

pollution in developing countrieso Neurologic and reproductive risks of solvent

exposureso Cancer risks in firefighterso Safety of dental amalgamsHealth effects of

arsenic in drinking water

• Collaboration with Dr. Óscar Peralta (Atmosphere Working Group) and Dr. Jorge Salmerón (Health Working Group)

• Field visits, meetings in person and by teleconference• Appropriate attempt to identify levels of hydrogen sulfide (H2S), sulfur

dioxide (SO2) and various others metals to which the residents aroundthe Cerro Prieto geothermal field have been exposed

• A survey was carried out to estimate the prevalences of varioussymptoms and health conditions experienced by the residents of thesecommunities

• Ambient atmospheric concentrations of H2S and SO2 are well belowlevels thought to be potentially of harm

• As are most of the blood and urinary concentrations of metals in thefield workers

• Some of the urinary lead levels were higher than desirable, but bloodlead levels were within the normal range

• Spirometry values are difficult to interpret, as it was not possible to relate them to

• H2S or SO2 exposures at the individual person level• Most FVC and FEV1.0 measures were within the normal ranges

“In general, the results show nothing of particular concernto human health that is likely to be attributed to the CerroPrieto plant or its emissions… The conclusions of the reportare appropriately cautious, given the limitations of thestudy, and I support the recommendations for ongoing work.”

Gracias