Project

Project Integral de

Background:

The municipality of Tijuana is located in the north-western state of Baja California, Mexico, comprising an area of 1239.49 Km2, 1.57% of the state. Is situated in extreme geographical coordinates: north 32 º 34 ', south 32 º 04' north latitude east 116 ° 31 'and west 117 ° 07' west longitude. On the north it borders with the United States of America on the east with the municipality of Tecate on the south with Ensenada and Rosarito Beach, on the west by the Pacific Ocean. The state of Baja California and the municipality of Tijuana in particular, are located in a semi-desert area and therefore water is scarce. Streams are few and volumes drained through them are small and very occasional. Annual rainfall is around 204 millimetres, nationalsecond lowest. Most of the Baja California streams and rivers do not exist as such, rather than for short periods in some years.

The supply sources for the City of Tijuana are, in order of importance, the Colorado River aqueduct that supplies the dams: El Carrizo and Abelardo L. Rodriguez; and the wells located along the TijuanaRiver.

The Abelardo L. Rodriguez Dam is usually empty by the lack of significant rainfall and only very occasionally for long periods in years, it gets full and can be exploited. Wells are harvested but the amount extracted is very low for the demand of the city.

Therefore, the best source is the ColoradoRiver, but also very expensive as it is required to bring water to the City of Mexicali with a pipeline of 147 kilometres and because of the pumping that have to go through a height of 1.060 metres on the Rumorosa to finally reach El CarrizoDam, with the resulting costs of electricity.

Water reuse as a strategy to enhance water efficiency

One of the biggest challenges for cities such as Tijuana, developing at a rapid pace among all the cities settled along the border of Mexico and the United States, is to ensure future drinking water supply by rational exploitation of its existing water sources and reuse of treated wastewater for the benefit of its inhabitants.

The fast-paced urban growth in Tijuana and the lack of local fresh water sources has led to the construction of works such as the Colorado River-Tijuana Aqueduct, which has recently increased its capacity by 1.3 m3/s to conduct a total of 5.3 m3/s and the Abelardo L. Rodriguezdam, whose original purpose was to store water for agricultural development in the area currently occupied by the urban sprawl of the city, and today is used exclusively for drinking water.

One of the main strategies for sustainable water management in the region is undoubtedly the reuse of treated wastewater in activities where their nature do not require potable quality, that can reduce significantly the growth trends of first-use water demand without jeopardising social and economic growth of cities or damaging the environment and its capacity for regeneration, but on the contrary, the aim is, through such actions as reuse,the environmental component to be an important factor in the sustainable use of the resource.

With the construction of the treatment plants:“Arturo Herrera”, with capacity of 460 l/s and “La Morita” of 254 l/s, the eastern area of Tijuana, it was plannedto use part of the treated wastewater for irrigation in urban green areas of the Tijuana River and Mesa de Otay, and for the industry. Currently the most important reuse infrastructure to be built is a line of 18 inches in diameter which starts in the “Arturo Herrera” plant and reaches in the first stage the MorelosPark, which is expected to consume over 15 litres second.

There are also some small networks in private properties, such as the Country Club Recreation Centre, with golf course;for irrigation of green area and a nursery in the “San Antonio de los Buenos”treatment plant; 2 systems in Rosarito Beaches, one network of 6.768 metres to irrigate 163.2 hectares of green areas on the toll road Tijuana-Ensenada and another one through a pumping system that takes treated wastewater to the Grand City Park, however, all these works use only a small amount of treated wastewater generated in the city, the rest, which is a significant amount goout the city to eventually reach the sea and therefore, are wasted.

Infiltration Technique for water reuse

In 2007 the State Public Service Commission of Tijuana (CESPT) hired the Mexican Institute of Water Technology (IMTA) to carry out the geohydrological study of the area between Rancho Santa Anita, Abelardo L. Rodriguez dam and Valle de las Palmas, Baja California. IMTA considered that detailed studies should be conducted to specificallyevaluate the indirect reuse potable projects, including a number of necessary studies such as geohydrological characteristics of the area and regional, sites favourable for infiltration. The results of this study identified two areas located on the stream of Valle de las Palmas in "El Dorado"Ranch.

In early 2011 the "Pilot Project on Infiltration with treated wastewater in the aquifer of Valle de las Palmas in Tijuana, BC" was tendered by National Public Announcement, and is currently under development.

The objective of the study is to naturallyinfiltrate 150 m3of treated wastewater into the subsoil and analyse its behaviour and reactions with the porous aquifer and when combined with native water.For this purpose, a structure was built to capture the volume to be infiltrated and several observation and monitoring wells toobservethe variations in the static levels of wells and 82 samples will be taken for physic-chemical characteristics of water.

In order to select the infiltration site, a geological survey was made in an area of ​​approximately 40 km2around the sites selected by the IMTA, and with this information the sites were defined to make 13 electromagnetic transients (EMT) surveys that provided semi-detailed scale information on the aquifer, followed by a detailed ​​9 EMT, with this we were able to determinethe geometry of aquifer, thickness and resistivity of the material and made 3-dimensional sections representing the aquifer and justified the proposed site for the recharge.

Nine open pits were made at the selected site in order to examine the different materials present and correlate them with that observed in geophysical surveys.

Location:

The site of artificial recharge of treated water is located in the municipality of Tijuana in Baja California, in the Valle de las Palmas stream.

Design of infiltration structure and wells drilling

The infiltration system consists of an intake structure or pond of 5x5x1 metres,in which 150m3of treated wastewater will pouredthrough pipes from the effluent of the “Arturo Herrera”treatment plant and the filling will be in such a way that it will always have water and infiltration is continuous. The wells constructed around and downstream of the infiltration structure are spaced strategically and with varying depths to keep record of the groundwater aquifer at different levels to observe the mixing of treated water and native water, several of these wells will be instrumented with precise measuring equipment to define groundwater developments continuously.

During the project, a Design Reference manual on Artificial Recharge System will develop,which will be useful since it will contain the necessary methodology techniques and studies; from site selection to construction of an infiltration system and can be applied elsewhere. It is noteworthy that the study described above is first of its kind, as there have been no similar studiesin the country, in addition to being in accordance with the NOM-014-CNA-2003guidelines, which establishes the requirements for artificial recharge of aquifers with treated wastewater.

Expected results and benefits

The study is achieved through own resources and federal funds that are promotingprojects for water conservation and saving. It is expected that the results are favourable and a greater refinement of treated wastewater is achieved.

The benefits are evident, in the current project small volumesare considered, but subsurface infiltrations may be made with larger volumes of treatedwastewater, being able to be extracted downstream of the infiltration site and used as it is traditionally done in green areas and industry or may be left to increase the volume of the aquifer to be used as first-use water, with the advantage that would reduce discharges of treated water to the sea, preventing pollution and thus benefitingthe population in general.

Hoja 1 de 5