Report on Proposed Improvements on Water Supply and Waste Management on Puerto Ayora, Santa Cruz
I. Past Record
Few of the Galapagos Islands have fresh water, and those that do, get water from rainfall or groundwater. Santa Cruz is unique in that it has sufficient quantity of water to sustain its current human population; however, the water quality is problematic. Santa Cruz's fresh water supply is pumped from 25 m underground by 7 electric pumps each with a capacity of 20 HP. These pumps do not function in coordination with one another, causing inconsistent flow rates. Seawater often mixes in with the water source, so the water's chlorine concentration is too high. 50% of the water is then lost due to leakage in the pipelines.
In the city of Puerto Ayora (Figure 1), the water is contaminated with bacteria because no sewer system exists and most residents dump their waste into two crevices that carry water to the city. There have been several cholera outbreaks in the past as a result.
Each house is equipped with its own small pump with a capacity of 0.5 HP because the pressure in the water grid is not sufficient. Water is only pumped from 6 am to 5 pm. The city has a water purifying factory that produces 800 m3 per day for cooking and drinking, but most of the drinking water is imported.
The other major cities on the Galapagos are located on San Cristobal and Isabela, each having their own set of water issues. For instance, San Cristobal suffers from leakages and from seasonal water shortages and its outdated sewer system needs to be replaced. Isabela has pipe contamination problems. Our team decided to focus on Puerto Ayora because it encompasses all of the problems, and since it has the largest human population, its problems require the most immediate attention.
II. Proposed Improvements
Plan A
a. Install septic tanks in the houses that do not have them. Because a portion of the population already has septic tanks, this plan would go along with what has already been established. Size/Capacity? Number need to be installed? Where on the land? How to pay for them b/c a possible reason that people do not already have them is because of the cost. How often need to be cleaned.
b. Construct Solar Aquatics System (SAS) wastewater treatment plant (Figure 2). SAS ideal for Puerto Ayora because it is not only capable of servicing 20,000 people, double the population, but also is efficient and uses plants instead of chemicals. Sludge from septic tanks periodically would be transported to SAS via trucks. Multiple trucks would operate to cover different blocks, much like garbage trucks. How much land area needed to build SAS? Check whether capacity sufficient? What about toxic wastes from motor oil, car batteries -- these cannot be dumped into SAS.
c. Construct pipe from SAS to farmland for irrigation. Because water required for agriculture comprises roughly 50% of the water consumed (500,000 m3/yr out of 1,334,410 m3/yr), reducing this amount taken from the groundwater would increase the lifetime of the natural water supply. Reducing the amount of water pumped might also reduce the amount of seawater in the water supply because over-pumping can draw in seawater. Because pipe would be running from SAS to farms, the most practical location of the SAS would be between the farms and the city. Must check whether water quality good enough to be safe on crops. Look into drip irrigation -- reduces evaporation considerably so more water for groundwater recharge.
d. Install dry toilets in rural areas. Solid waste separated from liquid and dried using lye and woodchips. Dried solid matter could be burned in desalinization plant, which requires heat to operate.
e. Construct desalinization plant. Construct plant between underground water source and town that employs thermal distillation, which functions at 115°F, to convert saline water. Although desalinization plants are expensive and inefficient, recycling waste to power plant would reduce operation costs and having a plant would reduce the amount of chlorine in the water flowing into houses and prevent corrosion of the pipes.
Plan B
a. Construct sewer system. Most desirable location of sewer is in center of street because convenient to connect to houses on either side of street. House sewers drain to it by gravity. Install at depth of 8 feet if houses have cellars or basements. Other, already existing subsurface installations like water pipelines and electrical wires must be considered. Main pipes should be 8 to 12 in. in diameter to prevent blockage, and pipes from houses should be 4 in. wide. Take advantage of gravity flow to reduce number of pumps required. Storm sewers? Keep sanitary sewer and storm sewer separate.
b. Tighten water pipes and pipe junctions to reduce leakage. Retighten lines to reduce loss of water due to leakage. Examine joints at pipe junctions and make necessary reparations. (Leakage is to be expected, even more so in unstable soil or rock. 15-40 gpcd loss is acceptable.) Install meters on service pipes or in house basements. (PVC pipes that were installed to street mains to house piping are fine because they resist corrosion.)
c. Same as parts b through e in Plan A.
III. Conclusion
A survey would need to be conducted to determine which plan the inhabitants of the Puerto Ayora judge to be more practical and beneficial. Plan A would require less dramatic construction because the roads would not have to be torn up; however, it would require a long-term, inefficient system of truck collection. Plan B would be convenient if the roads already needed to be dug into to repair the water pipes. Perhaps a combination of both plans would be advantageous. A sewer system could be constructed centrally and waste-trucks could operate on the periphery, or if the houses with septic tanks were grouped together, then a sewer system to service houses without tanks.
IV. Bibliography
Hardenbergh, W. A. and Edward B. Rodie. Water Supply and Waste Disposal. Pennsylvania: International Textbook Company, 1963.
Ley, Deborah. An Assessment of Energy and Water in the Galapagos Islands. http://galapagos.solarquest.com/documents/SandiaGalapagosReport200307.pdf
"Puerto Ayora street map." www.TheBestofEcuador.com. http://www.thebestofecuador.com/map_payora.htm
"Solar Aquatics System." OCETA Environmental Technology. http://www.oceta.on.ca/profiles/earthtech/icon.html
