The quality of the surface and groundwater in Puerto Rico varies from excellent to highly contaminate, depending mainly on the geographical location of the water resources and the time of the year. Even so, most of the waters meet the standards set by the Environmental Quality Board (EQB) and the Environmental Protection Agency (EPA) as sources for the production of drinking water.
The Quality of Surface Waters
Studies carried out by the EQB (Reports 303(d) and 305(b)) and the US Geological Survey (USGS) show that the principal problems of surface water quality in Puerto Rico are the presence of bacteria of fecal origin, nutrients and suspended sediments. The concentrations of these contaminants- for the most part from the segments of rivers, streams and reservoirs that have been studied- exceed the local and federal standards for human contact.
The data from 2002 on concentrations of bacteria of fecal origin in the network of USGS stations in Puerto Rico are summarized in Figure 1. The concentrations of nutrients in the network of USGS stations in Puerto Rico are presented in Table 1. Only in isolated areas of the mountains, or in protected forest reserves, does the quality of surface waters remain unaffected by such contaminants. During periods of intense runoff in the rainy season in Puerto Rico the concentration of bacteria and nutrients tends first to increase in the early stages of such events (washout), then decrease as the runoff dilutes the matter. On the other hand, this process increases the concentration of suspended sediment significantly.
|Description: Concentration of fecal-origin bacteria in the rivers, reservoirs, and lagoon of Puerto Rico.(USGS)|
|Description: Average concentration of total nitrogen and phosphorous in major rivers of Puerto Rico.(USGS,DRNPR)|
The federal Safe Drinking Water Act (SDWA 1974, as amended) does not set quality norms for sources to be used for supply of drinking water. However, it does delegate to the Health Department (HD) the adoption of additional requirements to guarantee the quality of drinking water at the local level.
The Health Department requires the Autoridad de Acueductos y Alcantarillados (AAA, Aqueducts and Sewer Authority) and other entities that propose the development of new water distribution systems to comply with the following norms:
To complete a sanitary survey in the drainage basin or aquifer that is to be the source of the water to be treated to serve as drinking water.
To comply with the regulations set out in the SWDA, including the Filtration Rule, Disinfection Products Rule, Total Coliforms Rule from the Safe Drinking Water Act, among others.
To cooperate with the HD and the EQB in evaluating the design of new drinking water treatment plants to assure that the physical and chemical processes provide appropriate treatment to comply with the SDWA.
The EQB has established, as part of the norms for water quality, the maximum concentrations for certain permitted parameters in waters for different human activities (Article 3 of the Regulations on Water Quality Standards, Regulation No. 6616 of May 14, 2003). These regulations set the norms and requirements for maintaining the bodies of water in Puerto Rico so that they will be adequate for the different uses for which they may be designated. The standards established control the water quality to protect the health of the population and to facilitate the economic growth of Puerto Rico.
The EQB norms are the guidelines used by the HD in its review of new drinking water production systems. These norms for water resources should not be confused with the federal drinking water standards, which include another series of water compliance parameters for water already purified for human consumption. In the case of raw waters, the EQB and the EPA require that the water source comply with Regulation No. 6616. These norms were set taking into account the chemical and physical techniques and processes used generally in modern treatment plants water to make water safe to drink. It is possible that if the concentration of a chemical or biological component of the raw waters exceeds a certain limit, the available treatment processes will not be adequate to guarantee that the water will meet the federal standards for drinking water. In such cases, the HD may refuse to issue a permit to use the water as a source of public supply.
In contrast to the case of surface waters, the quality of water in the aquifers of Puerto Rico is generally excellent, with the exception of areas near the coast that are affected by the entry of seawater, or isolated places where the waters are contaminated by chemicals and nutrients. In the coastal portions of the northern and southern regions, the entry of seawater, naturally or induced by excessive extraction of water from the aquifers, affects these substantially, making it impossible to use the water for consumption or irrigation. In several areas of aquifers in coastal and central valleys, underground waters have been contaminated with synthetic chemical compounds and nutrients, which exceed the standards for sources of drinking water (Figure 2). These compounds come from industrial and agricultural activities, accidental spills and leaching from waste in both active and inactive dumps. These conditions limit the potential of some areas where there are aquifers as sources for the production of drinking water in Puerto Rico.
|Description: Puerto Rico major aquifer zones affected by synthetic, iron, and magnesium pollutants.(USGS 1998, JCA 2000)|
The quality norms issued by the EQB apply to underground waters that are proposed as sources of supply for drinking water, particularly when there is the possibility that volatile organic compounds may be present (EQB Regulation No. 6616, Article 3, 2003). These are synthetic compounds, usually solvents, which are used in a great many industrial, commercial and domestic products. The principal families of such products include tri- and tetra-chlorethylene (TCE and PCE), as well as derivatives from carbon tetrachloride (CCl4). These compounds and their derivatives are recognized as agents that may cause cancer. The water in areas with the presence of these substances cannot be used as a source of drinking water unless systems and reserve tanks for the removal of such volatile compounds are installed prior to the disinfection treatment required for making water safe to drink. However, this does not prevent the use of such waters for irrigation, since the compounds quickly volatilize once exposed to the atmosphere and the heat at the surface of the ground.
The HD and the EPA also regulate the maximum salinity of drinking water, particularly the concentration of the chlorine ion as a secondary parameter. This means it is a suggested, not obligatory concentration in drinking water. This limits the use of underground waters as a source of drinking water unless it is treated in several coastal areas from aquifers in the northern and southern regions. The aquifers in both coastal regions are affected by saline intrusion caused by excessive pumping of water and by the natural characteristics of the rock in which they are formed. Dozens of wells operated by the AAA and by farmers have been closed in coastal valleys due to saline intrusion. Through treatment to remove part of the salts, so that the concentration meets the norms of the HD and the EPA, these waters can be used for human consumption after the salts (dissolved sediment) have been removed effectively.
At present, saline intrusion affects the agricultural use of groundwater from the Upper Aquifer in the northern region and the coastal alluvial aquifers of the southern region (Figure 3). The guidelines of the US Department of Agriculture and the Agricultural Extension Service recommend that waters containing concentrations of sodium chloride (common salt, NaCl) in excess of 250 mgl not be used in order to avoid damage to crops and soils. The accumulation of sodium chloride and other salts eventually affects the chemical equilibrium of the ground, as part of the sodium is absorbed, which limits its fertility. Soils in various areas of Puerto Rico, principally in the Caño Tiburones area of Arecibo and the Lajas Valley in the southwestern region, are contaminated with sea salts due to irrigation with briny water, which limits their utility for agriculture.
|Description: Saline intrusion zones in the coastal valleys of Puerto Rico. (USGS 2003, DRNA, 2004)|
Saline intrusion also affects the groundwater resources of the islands of Vieques and Culebra. The problems of contamination of the aquifers in fractured rock and alluvial matter in Culebra and Vieques are typical of aquifers on small islands surrounded by the sea. The 1975 closing of wells in the Esperanza-Colonia-Luján aquifer area of Vieques was due to saline intrusion caused by excessive pumping at the many coastal wells. The effect of septic tanks on these aquifers is not notable, given that the development of housing units in the southern portion of Vieques has been limited to the strip along the coast. The salinity of the coastal aquifers of Esperanza-Colonia-Luján in Vieques has now returned to levels recorded prior to the development of the wells.
Puerto Rico generates approximately 300 million gallons of wastewater each day, mainly from sewage. Although the industrial sector generates approximately 77 mgd of wastewater, most of that is reused, with only minimal discharge into the environment. By comparison, the AAA generates on average some 223 mgd of wastewater, of which only the effluent of the Guayama Treatment Plant is reused directly (up to 4 mgd). Indirectly, up to 35 mgd of the wastewater generated by the AAA, principally from the Río Grande de Loíza, Río Grande de La Plata, and Río Grande de Arecibo basins, is reused. The discharges from treatment plants operated by the AAA in several municipalities in these basins are reused in the Carraízo, La Plata and Caonillas-Dos Bocas reservoirs.
The quality of the wastewater generated by the AAA depends on the level of treatment provided by the AAA plants, which provide primary, secondary and tertiary treatment levels (Figure 4). The network of wastewater treatment plants operated by the AAA in Puerto Rico is summarized in Figure 5, in which the level of treatment provided is indicated. The combined volumes of each level of treatment for the whole of the island are summed up in Table 2, and the final disposal of the effluent is indicated. These data reveal that approximately 67 percent of the wastewaters generated by the AAA plants (2003) receive only primary treatment (149 mgd); 63 mgd receive secondary treatment (28 percent of the total); and the remainder of 11 mgd receives tertiary treatment (5 percent of the total).
|Description: Used-Water treatment levels.(DRNA, 2004)|
|Description: Network of water-treatment plants operated by AAA in Puerto Rico.(DRNA 2004)|
|Description: Generation and disposition of used water in Puerto Rico in 2003.(AAA, 2003)|
The largest part of the liquid waste discharged (effluents), including water treated at the primary and secondary levels, is discharged directly into the sea through underwater outlets. Discharges into the sea from all sources come to approximately 185 mgd. Discharges into the sea of effluents treated at the primary level are made with permits under Section 301 (h) of the federal Clean Water Act of 1970 (CWA). The EPA permits these discharges subject to periodic revision and frequent monitoring, which shows that the waters discharged by the primary plants have no significant adverse effect on the marine life environment.
Author: Sigfredo Torres González
Published: September 05, 2014.
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