Chalillo Dam

Memo from Dr. Guy R. Lanza to Belize Institute of Environmental Law and Policy (BELPO)

Dr. Guy R. Lanza

August 12, 2009


DATE: August 12, 2009
TO:   Ms. Candy Gonzales, President
         Belize Institute of Environmental Law and Policy (BELPO)

FROM: Dr. Guy R. Lanza
           Professor of Microbiology and Director, Environmental Science Program

SUBJECT: Environmental and Human Health Threats from Chalillo Dam Sediment Releases.

SUMMARY:  The recent release of sediments with severe turbidity contaminants from the Chalillo dam is inexcusable and poses immediate risks to human health, livestock health, and the ecology of the Macal, Mopan, and Belize rivers.  Immediate action is required to halt the release of additional sediments from the Chalillo dam, and to quickly respond with appropriate remediation strategies to reduce the threats to humans, livestock, and the Macal, Mopal and Belize river ecosystems. 

The recent release of bottom sediments from the Chalillo dam impoundment presents serious ecological risks, human health risks, and danger to livestock and pets as well.  The extremely high water turbidity clearly evident in the photographs of the sediment contamination are the result of both organic and inorganic sediment material including silts and clays released from the dam gates to the Macal River.  The clay material is of particular concern because it will create colloidal suspensions that will not readily settle out of the water column in the impacted rivers and will remain an environmental problem for an extended period producing negative effects on humans and livestock and harmful ecological effects on the rivers receiving the turbidity contaminants. 

The release is a major concern with regard to use of the water for drinking by humans and livestock and also a major concern to the overall water quality and ecology in both the impoundment and downstream in the Macal, Mopan, and Belize rivers.  The turbidity levels considered safe for drinking water are given in Nephelolometric Turbidity Units (NTU’s).  NTU’s are a standard measure of light transmission through water and the USEPA acceptable level is 1 NTU while the WHO level is 5 NTU’s.  The levels in the photos of the Macal River below Chalillo Dam far exceed acceptable standards and are clearly in the thousands of NTU’s.

The human health concerns about high turbidity in water stem from the fact that turbidity contaminants protect disease causing waterborne microbes (bacteria, viruses, protozoa) by masking their presence and by interfering with the effectiveness of the disinfection chemicals (e.g. chlorine) used to purify the water for drinking purposes.  Also, the dam sediment materials producing the turbidity will overwhelm (clog) the coagulation and filtration systems used to pre-treat drinking water before using chlorine (or other disinfectants) to inactivate pathogens.  Clogging can occur in engineered sand filters at water treatment plants or in the “natural filtration processes” in soil and subsurface rock. It’s not possible to filter and disinfect drinking water with the excessively high levels of turbidity evident in the Macal, Mopan, and Belize rivers.  A good historical example of excess turbidity causing serious human waterborne disease from drinking water was reported in 1993 in Wisconsin (near Milwaukee).  More than 400,000 people became ill with waterborne disease from a protozoan parasite (= cryptosporidium) and more than 100 died.
Toxic elements including heavy metals, pesticides, and generally non-toxic elements such as iron can have their toxicity increased in turbid water because they are often absorbed or adsorbed to fine clay particles where they can easily be concentrated at much higher levels than those in non-turbid water.  The relative longevity of colloidal clay suspensions carrying contaminants in water can extend the exposure period of humans to elevated concentrations of toxic chemicals.  In the case of iron, generally about 2-15 percent is absorbed from the gastrointestinal tract, but, elimination of absorbed iron is only about 0.01 percent of the body burden or amount absorbed.  Excess accumulation of iron can lead to disturbances in liver function, diabetes mellitus, endocrine disturbances and cardiovascular effects.

The very high turbidity will also cause ecological damage by blocking light entering the impoundment and rivers and that will in turn reduce the normal addition of oxygen to the water by photosynthetic plants, algae, and bacteria.  And, some of the dissolved and suspended organic material contributing to the turbidity will simultaneously remove oxygen from the water (BOD/COD) – burning the proverbial candle at both ends. Deficits in oxygen will result in the loss of fish and other important aquatic biota and can prolong the survival of disease causing microorganisms.  Another concern is the abrasive effect of suspended materials on fish and other biota (a sort of wet sandblasting) and the fact that the sediments will clog the bottom habitat essential for the reproduction and survival of many important bottom dwelling organisms.

Dr. Guy R. Lanza

Professor of Microbiology, and Director

Environmental Science Program

University of Massachusetts, Amherst, MA

Categories: Chalillo Dam

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