Evaluation of Wastewater inputs into the Presa …...1 Evaluation of Wastewater Inputs into the Presa Allende Janna Owens, Ph.D.; Terry Griffith, P.E. INTRODUCTION In 2012, the Chaac

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EvaluationofWastewaterInputsintothePresa

Allende

Janna Owens, Ph.D.; Terry Griffith, P.E.

INTRODUCTION

In 2012, the Chaac Water Group released their Las Cachinches Sanitary Survey Phase 1 Report for civic

and governmental groups to use as a resource for improving local water quality (Griffith and Owens, 2012). The

present Phase 2 Report is a continuation of that work which expands upon recommendations made for

evaluating the ‘health’ of the Presa Allende. Specifically, the focus of this research was to ‘characterize’ the

water quality of the Presa and its tributaries for untreated wastewater inputs. To that end, we evaluated the

quality of water in relation to public health risks by testing for concentrations of Escheria coli (E.coli) bacteria.

It is an indicator of the microscopic pathogens present in wastewater since it is found in the gut of warm-

blooded animals and is far more feasible for analysis than all the other pathogens. Research has well established

to what extent other pathogens (viruses, bacteria, protozoa, helminth eggs) are present in wastewater by the

number of E.coli bacteria found in a water sample (Jimenez and Asano, 2008). The quantity of wastewater not

processed by the municipal wastewater treatment plant was calculated using systematic flow measurements

made in key locations within the San Miguel area. Flow patterns and the quantity of untreated wastewater inputs

into the streams could then be established.

The Presa Allende serves many purposes to the surrounding community and those that benefit from its

waters. Agricultural lands above and below the dam are watered in a yearly cycle by its rising waters, allowing

recreational opportunities including boating and kayaking, while local people collect fish from it regularly. It is

also a habitat for birds of many species that only add to the beautiful views of the large expanse of water. But

what is the true ‘health’ of the Presa waters? A reservoir is similar to a large mixing bowl, and its characteristics

reflect not only the quantity of the waters that feed it, but the quality as well. There are four primary

contributors to the Presa Allende that must be considered in where and how its waters are generated, as well as

its associated health risks:

Stormwater System: Stormwater is the flow of rainwater across surfaces, where it either soaks into the ground

or becomes surface runoff in the case of hard surfaces like pavement. San Miguel does have a type of

stormwater runoff system. It is composed of storm grates, pipes, and channels that lead to the arroyo, or the

informal path of runoff that finds its way down the streets or hills to enter the stream. In some cases, stormwater

can become sewer inflow through direct entry to the pipe, such as a misguided storm drain, and would become

‘sewer water’ through mixing. Sewer infiltration during the rainy season is also possible, with stormwater

soaking into cracks or breaks in the sewer line. Both of these add to the amount of wastewater to be treated at

the wastewater treatment plant. During rain events, stormwater combined with sewage can result in overflows

from the sewer system into the arroyos. Sewer line breaks or stoppages can also cause overflows into the

arroyos, however this is not related to stormwater events.

Wastewater Treatment Plants: There are three existing wastewater treatment plants that are capable of

discharging into the Arroyo Las Cachinches:

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1. Currently the treatment plant at Presa de Las Colonias is not operating, so wastewater in the Landeta

area is pumped up and over the hill to enter the main sewer collection system of San Miguel. This

treatment plant was designed to handle approximately 5 liters per second (L/sec) of domestic-strength

wastewater through a simple, low maintenance process. Instead, the community wastewater is now sent

into the primary sewer system for treatment at the SAPASMA’s main plant some distance away. When

the small plant located near Jardin Botanico was operational, the treated discharges into Presa de Las

Colonias provided clean water for the aquatic ecosystem and became part of the Las Cachinches flow.

2. An industrial treatment plant operates at the Esmarelda cheese factory. This plant handles high-strength

organic waste with few pathogens, and discharges into Las Cachinches several kilometers upstream

from the Presa Allende.

3. The main wastewater treatment plant of SAPASMA is located farther downstream on the Las

Cachinches and serves the majority of the San Miguel area. The plant was designed to handle mostly

domestic-strength wastewater. It provides re-use of treated wastewater for the irrigation of public areas

and local golf courses. A portion of the treated wastewater is discharged to the Arroyo Las Cachinches

not far upstream of it entering the Presa Allende. The measured discharge rate of treated effluent into the

stream during the study period was consistently around 107 liters per second (L/sec). Despite requests

for information to SAPASMA, it is unknown at this time what amount of treated water is provided for

other uses within San Miguel, such as public works and golf courses.

The two largest tributaries to the Presa Allende are the Rio Laja and the Arroyo Las Cachinches, both of which

differ dramatically in flow regimes and water quality.

Rio Laja: The Rio Laja has a very large watershed, and flows with wide variation in quantity and quality year

round. It is commonly used for recreational purposes by kayakers during higher flows and swimmers who take

advantage of its many sandy beaches. Before entering the Presa, the stream passes through several communities,

the largest of which are Dolores Hidalgo and Atotonilco. These communities lack wastewater treatment plants,

and so sewage is discharged into the Rio Laja untreated or managed by local septic systems. The river also

picks up sediment and pollution all along its channel from commercial and agricultural activities. Since the Rio

Laja flow is higher during the wet season, these waters have a diluting and cleansing effect over the long

distance it travels, but during the dry season, the self-cleansing is less effective for water quality. Ultimately,

much of this sediment ends up in the Presa, which shortens its years of usefulness by silting up.

Arroyo Las Cachinches: Despite springs located between the Presa las Colonias and Presa del Obraje, this

stream is a dry channel most of the year other than the rainy season. It is downstream of the Obraje Bridge that

significant amounts of wastewater inputs begin on the Las Cachinches. At the Guadalupe Bridge, the Arroyo del

Atascadero joins the stream and contributes a wastewater flow collected from multiple outfalls along the way.

Occasionally, a portion of this flow could be a break in the municipal sewer system, as noted on more than one

occasion. Farther downstream on the Las Cachinches, a primary source of untreated wastewater is a sewer

system ‘diversion box’ located below the Libramiento a Dolores Hidalgo bridge. During the dry season, the Las

Cachinches at this location becomes all wastewater flow (Figure 1).

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A particular emphasis in evaluating water quality for the

San Miguel region has been the wastewater inputs from point

(pipe) and non-point (other) sources. As tributaries empty into

the Presa Allende, they contain the pollutants and pathogens

that are inherent in wastewater from both types of sources. For

example, part of the sewer diversion box flow (Fig. 1) goes

directly into the Las Cachinches through a pipe (Fig. 2). The

remaining portion from diversion box is channelized to an area

known as Bypass 2 (Fig. 3), where it continues on through

canals to irrigate crops in the area. When this wastewater is

not required for irrigation or has an excessive flow, it simply

spills over into the Las Cachinches.

From the streamside location of Bypass 2, extensive

irrigation canals spread the wastewater into approximately 80-

100 hectares of surrounding land. Here there are orchards and

crop lands that receive the water via a system of trenches, with

stones and sandbags serving as dams to control the flow. Just

before SAPASMA’s wastewater treatment plant, there is an

aqueduct that carries a portion of the wastewater flow across

the Las Cachinches and into the surrounding fields. The crops

grown in these fields include corn, green beans, squash,

chamomile, alfalfa, grasses for grazing, and field corn for

livestock. Eventually, the irrigation channel system flows into

the Presa or is absorbed by soil and crops (Fig. 4).

The use of untreated wastewater for irrigation has been

identified globally as a problem of serious concern and yet is a

very common practice in Mexico. The Mezquital Valley (Tula

Valley) is recognized as the largest area of crop land using raw

wastewater for irrigation in the world, with tens of thousands

of hectares under cultivation (Jimenez and Asano, 2008).

Mexico also accounts for nearly half of the hectares using this

practice in Latin America (Scott, et al., 2004) and yet does not

have an effective community outreach policy to reduce public

health risks from exposures. Even basic measures, such as

public education focusing on increased hygiene for personal

health or the handling of produce can reduce health risks in a

population (WHO, 2006).

The practice of using wastewater for irrigation is a

paradox, in which the water and its nutrients benefit the

production of crops. It can enable a community’s subsistence

or commerce when other options are simply not available. Re-

Figure 1. A municipal sewer system ‘diversion box’

located just downstream of Libramiento a Dolores

Hidalgo Bridge. Its untreated wastewater flow

branches into a) an irrigation canal, and b) the

remainder enters the arroyo through an outfall pipe

called Bypass 1.

Figure 2. The Bypass 1 outfall pipe as it empties into

the stream channel. This is untreated wastewater from

the SAPASMA ‘diversion box’ located meters away.

Figure 3. The Bypass 2 area beside the Las Cachinches.

Irrigation canals from this point divert the wastewater

to crops.

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use of wastewater under certain conditions is actually considered an effective method of land treatment for

reducing pathogens. Yet there is an inherent ripple-effect in public health risks of infection and degradation to

natural resources associated with this practice. Research has shown that with time, dissolved salts and minerals

can accumulate in the soils causing crop productions to decline. For example, the above-mentioned Mezquital

Valley soils are beginning to experience the effects of long-term usage of wastewater after decades of this

practice (Scott, et al, 2004). Salts, and heavy metals, such as lead, cadmium, or copper accumulate in the soil

and its produce, before eventually leaching into the ground water (Bahri, 2009). Freshwater resources become

polluted from the irrigation by runoff from fields into the streams or with bypasses of the water not utilized

(WHO 2006).

Pathogenic organisms are the greatest concern in the agricultural reuse

of wastewater, as it is full of viruses, bacteria, protozoa and most

significantly, helminth eggs. These parasites are a highly infectious group of

pathogens that includes flat worms and roundworms, of which Ascaris is the

most common. Helminthiasis is a parasitic infection of humans and animals

that includes its most common form in Latin America, Ascariasis. In

regions with a poor economy and reduced hygiene practices, this syndrome

can affect up to 90% of the local population. Although it has a low mortality

rate, Helminthiasis has a long list of symptoms and is particularly difficult

for those under 15 years of age (Drechsel, et al, 2010). It appears that with

continuous exposure, immune systems of those infected can become weaker

and open the doors to other diseases. Helminthiasis is transmitted through:

1) ingestion of polluted crops, 2) contact with polluted soils, sludge or

wastewater, and 3) ingestion of infected meat. In the ‘farm to fork’ cycle of

agriculture, the infectious eggs of helminths can spread from the irrigation water to farmers, their families,

harvesters, vendors that sell produce or prepare it and into the homes of those that purchase the food product

(Jimenez-Cisneros, 2007; Jimenez-Cisneros & Maya-Rendon, 2007).

In summary, the ‘health’ of the Presa Allende is best characterized by the associated public health risks that

are present in untreated wastewater inputs into the freshwater system. This affects those that come into direct

contact with the water through recreational and agricultural activities. It continues to have an indirect effect by

way of the handling and consumption of the product that results from irrigating with wastewater. This holds true

for the status of natural resources and any wildlife that depend upon the waters from the rivers and the Presa.

METHODS

Water quality sampling and flow measurements of streams or wastewater input sources began in late August

through October 2013 to characterize the end of the annual rainy season. Samples and flow measurements were

collected within 12-24 hours after rain events (wet weather), or at least 72 hours after rain events (dry weather).

E. coli Sampling

Water samples were collected for E.coli analysis throughout the area from the Presa Allende, Arroyo Las

Cachinches and the Rio Laja. In addition, samples were collected directly from the wastewater Bypass 1, its

diverted irrigation canal and the wastewater treatment plant’s outfall pipe prior to it mixing with the Las

Cachinches (Figure 4 in appendix). The collected samples were stored in sterile containers and kept on ice until

inoculated into a Micrology Lab Coliscan Easygel medium within a 1-4 hour timeframe. This gel produces

Figure 5. Fertilized Ascaris lumbricoides

egg at 400x magnification. The egg is

what infects humans or animals, and

ultimately hatches a worm within its

host body.

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results by reacting to specific enzymes in coliforms and highlighting the bacteria colonies by a color code. A

standard serial dilution method was used to accommodate significant wastewater concentrations within samples

according to best professional judgment. The incubation temperature of the gels was approximately 22o Celsius

(+/- 2o) for over 48 hours, as per the manufacturer’s instructions. The E.coli colony forming units were then

counted and calculated for a 100 milliliters sample size (CFU/100ml), which is the standard measurement for

comparison in water quality analysis (Micrology Lab, 2013). Replicates of individual samples and blanks of

sterile water are not included in the results table, but were part of the quality assurance/quality control protocol.

Samples were labeled ‘TNTC’ (too numerous to count) if an excessive amount of E. coli colonies were present

and counting them all was not feasible (Table 1).

Flow Measurements

Thirty two flow measurements were collected from various points in the drainage system, such as the

irrigation canals and streams. The in-channel flow measurement process involved a series of ten, semi-floating

small objects timed over a course of five to twelve meters in length within a fairly consistent channel. The

average channel cross-sectional dimensions were measured to calculate the average velocity and flow, with

some rough stream channel correction factors. The accuracy and precision with this method are estimated to be

within +/- 20%. The wastewater treatment plant outfall flow was calculated from measurements at the lip of the

outfall pipe using the Van Leer equation of the California Pipe Method and a small correction factor since the

pipe appeared to be slightly off level (Dodge, 2001). The estimate for the outfall pipe is also believed to be

within +/- 20% of the actual flow, and correlated well with observations of measured flow inside the wastewater

treatment plant.

Flow measurements were made weekly during the rainy season of 2013. Half of the measurements were

made within 24 hours of a rain event, and the remainder was taken more than 3 days after a rain event. None of

the measurements were performed during a rain event and were normally made around the noon hour. The

treatment plant operated at a surprisingly consistent rate of approximately 107 liters per second (L/sec) of

treated effluent into the stream throughout the two months of measurements. Table 2 documents the flow

measurements for: within the Las Cachinches channel, the irrigation canal, and the wastewater treatment plant

effluent of treated water into the stream. The total wastewater flow from the sewer ‘diversion box’ that goes

untreated is further highlighted in Table 3 with wet and dry weather calculations such as minimum, maximum,

average flow and daily volume. The daily volume calculation includes estimates of diurnal flow, which is 50%

of high flow for 8 hours per day, while high flow is considered ‘as measured’ for 16 hours per day.

DISCUSSION

The following discussion characterizes water quality by its concentration of the bacteria, E. coli, which is

an indicator of fecal contamination that is usually wastewater in origin. General standards that have been

established for public health risk and exposure are:

• 250 CFU/100 ml for primary contact where water can be ingested, such as swimming, kayaking

• 1000 CFU/100 ml for secondary contact such as fishing, or limited exposure to the water

E. coli concentrations do not represent other water quality factors, such as nutrients, sediment, biological

oxygen demand (BOD), total suspended solids (TSS), but is indicative of public health risk to pathogens. For

example, processes within the wastewater treatment plant may reduce BOD in the stream, and yet may have

little impact on concentrations of E. coli before it enters the Presa. This research focuses on the risk of

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pathogenic contamination, whether it is through recreational contact, or through the use of raw wastewater for

irrigation.

Rio Laja

A preliminary survey was conducted on the Rio Laja from the community of La Pateca downstream to

the Presa Allende. The waters of the stream were very turbid, whether or not there had been recent rain activity.

Cultivated fields line the top of the river channel and show signs of sediment runoff into the river. There were

visible scars all along the channel from the excavation of sand and gravel used locally for construction. The

combination of these activities not only introduces excess sediment into the river during rains or heavy flows,

but has created large sandbars in the channel. These sandbars will keep the sediment circulating in the river

continuously and can eventually flow on into the Presa.

The E. coli testing basically revealed two areas in which the lower Rio Laja shows evidence of

wastewater inputs. The E. coli concentration at La Pateca was well above suggested levels for human contact,

and yet many locals were observed swimming in the stream at the time the samples were collected. Farther

downstream at Atotonilco, there is a wastewater outfall pipe that severely impaired the Rio Laja at this point.

The E. coli concentrations several meters downstream from it were either ‘too numerous to count’ or 800,000

CFU (Table 1). Local residents stated that during weekends or festivals, thousands of people visit the Sanctuary

of Jesús Nazareno de Atotonilco, and the flow of wastewater from their pipe is greatly increased. It is unknown

at this time how far downstream the effects of this outfall are impairing the Rio Laja and ultimately, the Presa.

Arroyo Las Cachinches

WATER QUALITY

The E. coli testing basically revealed two areas in which the lower Rio Laja shows evidence of

wastewater inputs. The E. coli concentration at La Pateca was well above suggested levels for human contact,

and yet many locals were observed swimming in the stream at the time the samples were collected. Farther

downstream at Atotonilco, there is a wastewater outfall pipe that severely impaired the Rio Laja at this point.

The E. coli concentrations several meters downstream from it were either ‘too numerous to count’ The

stewardship and protection of the natural areas surrounding them, such as the Jardin Botanico, act as buffers and

filters to improve water quality. There are concerns about the impacts of surrounding agriculture and livestock

grazing with rain runoff, but E. coli concentrations were within the suggested range for recreational contact. It

should be noted that the upper part of the stream is informally known as Arroyo Las Cachinches, but actually

joins the ‘official’ Arroyo Cachinches just upstream of the Guadalupe Bridge in the urban center.

It is just upstream of the Guadalupe bridge that untreated wastewater

inputs become evident in the Las Cachinches, both with visual observation of

sources and with E. coli sampling (Table 1). Beyond this point downstream, the

flow is impaired by wastewater, and cannot achieve an acceptable quality again

as it flows into the Presa Allende. The significant contributions of the Arroyo

Atascadero, an outfall pipe at the bus station, Bypass 1 and Bypass 2 altogether

are not dilute much by the treated water outfall of the wastewater treatment

plant. In fact, when the Las Cachinches’ urban area flow is dry, wastewater

inputs below the Dolores a Hidalgo bridge are the stream’s only water source

with the exception of the wastewater plant effluent and the Esmeralda factory Figure 6. Livestock and wildlife

drink from the Las Cachinches

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outfall. Direct human exposure on this portion of the Las Cachinches is minimal, however local wildlife and

livestock were often observed drinking from the channel.

The sewer diversion box located below the Dolores a Hidalgo bridge provides the wastewater used for

irrigation in the surrounding hectares of fields and orchards. The approximate size of this area is 100 hectares

and extends all the way to the banks of the Presa Allende. E. coli sampling of the liquid that exits the sewer

diversion box creating the irrigation channel flow confirmed it is untreated wastewater with an approximate 7.2

million CFU/100 ml of sample (Table 1). This is within the average concentration expected in municipal

wastewater. A portion of the diversion box wastewater stream is piped out into the nearby Las Cachinches as

the Bypass 1 outfall (Figure 2). The wastewater flow for irrigation continues in a canal along the stream channel

to Bypass 2 below the railroad crossing before it branches off into the fields (Figure 3).

The wastewater treatment plant itself is

surrounded by fields that are irrigated with the untreated

wastewater that began from the diversion box. The World

Health Organization (WHO) recommends a restriction of

crops that can be consumed when grown in untreated

wastewater to reduce public health risks. Generally, it is

orchards, pastures, fodder, industrial and cereal crops that

should be grown under these conditions (WHO, 2006).

However, it has been personally observed by the authors

that besides alfalfa, pasture grass and feed corn, there are

crops grown here for consumption. These include

chamomile for tea (also known as manzanilla), squash,

corn and green beans. It can be argued that these are subjected to some type of cooking to decontaminate, but

that ignores the exposure to pathogens through casual contact with the produce, and the contamination of the

cooking area itself.

At issue here in the usage of wastewater is the

cycle of health risks from exposure to its pathogens. The

farmers that maintain the channels and dikes for the

wastewater were never observed to be wearing protective

gear, such as gloves. Many locals, including children,

were observed in this area with no obvious means of self-

protection. The soils are also inundated with pathogens, so

its dust coats the fur of animals and the clothes and shoes

of humans. This begins the transport of pathogens to the

home from the fields, and then on to the merchants or

food-preparers that handle the produce. Ultimately, the

consumer will be included in this loop, without knowledge

of where the produce was grown. In addition, animals that

consume plants irrigated with wastewater, or drink the

contaminated water, develop many health problems that

shorten their lives (Blanca, 2006).

Figure 7. Fields of green bean plants irrigated by

wastewater, as viewed from inside the WWTP

Figure 8. Cornfield adjacent to the local WWTP that uses

wastewater for irrigation. All surrounding fields were the

same.

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In summary, the wastewater treatment plant effluent of 107 L/sec does little to achieve a reduction of

health risks in the Las Cachinches or waters of the Presa, particularly in the bay which includes the mouth of the

stream. For example, E. coli is measured on a geometric scale (orders of magnitude, described by N x 10n).

Dilution does very little to achieve health risk standards, since untreated wastewater is so high in E. coli

concentration, typically 6 to 7 million CFU/100ml (6 x 106 to 7 x 10

6). Since health risk standards are typically

250 and 1000 CFU/100ml for full body contact and limited exposure contact respectively, untreated wastewater

in the stream would require a dilution factor of 6000 to 7000 times to achieve limited exposure contact, such as

fishing.

WATER QUANTITY (FLOW)

Flow measurements were taken during the months of August, September, and October of the 2013 rainy

season, which was fairly typical in its average seasonal precipitation. Consistent flow measurements made

possible an estimation of the total pollutant load (kilograms/day) in the stream and irrigation canals. While the

wastewater pollutant load coming from the city remained relatively unchanging within the sewer system, the

fate of this load changed with rain events, the diversions for irrigation usage, and any accidental or intentional

sewer discharges. There was great variation in the untreated wastewater flows which were bypassed to the

stream or sent to the fields for irrigation (Table 2). During our observations, very little if any of the untreated

wastewater sent through the irrigation canals was returned to the stream or reached the shoreline of the Presa.

Stormwater runoff and wastewater flows are an issue of variability that effect water quality as well as

water quantity. During the measurement period, rainfalls varied dramatically, often causing relatively high

runoff flows to enter the Las Cachinches and the sewer system. Within the urban area, the stream receives sewer

overflows, the most notable of which was the Arroyo Atascadero. To illustrate the contribution of stormwater

flows, during the first few weeks of flow measurements, there was no channel flow in the Las Cachinches from

upstream of the urban area. However, with increased rains, an unpolluted stream flow originating above the

urban area was quite high for many weeks. Still, during these rain events, the wastewater flows at the diversion

box remained relatively consistent, at least when a flow measurement was taken. It is possible that much higher

wastewater flows can occur at night during storm events.

The flow data indicates the treatment plant’s collection of wastewater was relatively consistent during

the period of measurement. The treatment plant’s effluent into the Las Cachinches was maintained at a regular

107 L/sec rate throughout the study period. Although, there was at least one treatment plant upset for a few days

caused by a rain event and observed on a tour of the plant. During the first week of flow measurements, a large

sewer stoppage caused a sewer overflow (labeled CSO in Table 2) of about 120 L/sec. This was during a period

of no rain and with very little flow in the Las Cachinches upstream of the sewer overflow. Yet, wastewater

continued to be diverted from the diversion box to the irrigation canals at a low rate of 37 L/sec, and the treated

effluent exited the plant at 107 L/sec.

The calculated projected daily flows of wastewater going untreated from the sewer collection system

varied between 121 L/sec and 215 L/sec during our study period (Table 3). The portion of the wastewater flow

leaving the diversion box varied widely between Bypass 1, Bypass 2, the irrigation canal and the Las

Cachinches itself. It should be noted the sewer diversion box manages all of this wastewater and the flow to the

treatment plant through manual controls located at the box.

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Table 3. Wastewater flows that go untreated by the wastewater treatment plant in San Miguel.

Calculations are for the “rainy season”: minimum, maximum, average flow for both wet and dry

weather, and the overall average flow in liters per second (L/sec). The daily volume is in cubic meters

per day (M3/day). The SAPASMA plant’s treated effluent flow into the Las Cachinches averaged 107

L/sec during the end of the rainy season 2013.

PRECIPITATION UNTREATED WASTEWATER

FLOW (L/SEC)

DAILY VOLUME

(M3/DAY)

Minimum wet weather flow 200 12,859

Maximum wet weather flow 215 13,939

AVERAGE WET WEATHER FLOW 206 13,291

Minimum dry weather flow 121 7,171

Maximum dry weather flow 157 9,763

AVERAGE DRY WEATHER FLOW 144 8,851

RAINY SEASON OVERALL AVERAGE FLOW 175 11,071

The average daily volumes of untreated wastewater ranged between 8,850 M3/day and 13,300 M

3/day,

depending on the dry or wet weather conditions within the rainy season variability. During the dry season,

which is the majority of the year, untreated wastewater flows would be similar to the low end of the calculated

average daily volume in Table 3. However, occasional storms of high intensity and duration occur during the

dry season, causing the untreated wastewater daily volumes to increase. All of the untreated wastewater either

ends up in the Las Cachinches or the fields for irrigation, depending mainly on the needs and actions of those in

control of the irrigation canals or SAPASMA.

Presa Allende

The ultimate receptor of the significant wastewater inputs to the Las Cachinches is the Presa Allende.

The mouth of the river and the subsequent mixing zone in the lake reflect this continuous source of impaired

water with mud and muck that smells foul. The sludge-like bottom of the Presa at this point has turned

anaerobic due to the quantity of solids settling out from the wastewater and then decomposing.

To mimic the recreational activities of kayaking and rowing activities here, sampling was performed in

the Presa directly outwards from the Las Cachinches input up through the middle of that inlet area in front of

the community of Las Frailes. The E. coli concentrations a few meters upstream in the Las Cachinches were

well above acceptable contact limits, and decreased with distance from the stream source (Table 1). As

expected, there is a dilution effect when the waters mix, but the reservoir water shows significant impairment

far out into the inlet area near the entrance of the arroyo. It is not until the metal pole marker in the Presa,

approximately 200 yards out from the Las Cachinches mouth, that E. coli concentrations were even within

contact limits for pathogen exposure during one sample, and but not on another. All of this characterization of

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the inlet area is complicated by two factors that are difficult to quantify or predict: 1) Presa water levels were

experiencing a seasonal rise of freshwater from all over its watershed, and 2) the volume of wastewater inputs

from the Las Cachinches would vary dramatically at any given time because of rainfall events or alteration in

the wastewater inputs. Overall, logic dictates that this region of the Presa has significant public health risks by

pathogen exposure that is variable in time and distance, and should be avoided. Consider what the E. coli

concentrations could be in a very dry time of year, with the Presa level lowering, and wastewater inputs within

the Las Cachinches not diluted with rainfall.

Most other sampling areas of the Presa had acceptable to zero E. coli concentrations detected, and do not

appear to be a health risk at this time. However, in the area of the reservoir near the submerged church, there is

an inlet that is actively used by the fishermen that should be analyzed further. Multiple samples of the area from

the church spire to the inlet shore have grown an excessive amount of colonies that were not indicative of E.

coli, and yet were a bit of a mystery. Nowhere else in the Presa yielded those results during our study. Upon

further review, it is found that the pathogen, Aeromonas sp., which is a component of wastewater, can react in

this fashion with the gel protocol. Further study is indicated.

In evaluating the health of the Presa through the indicator bacteria E. coli, the overall water quality

should not be forgotten. Since the lower Las Cachinches’ only beneficial use is irrigation, the pollutants of

BOD, TSS, are not really very important in the stream. However, as the stream empties into Presa, BOD and

TSS become more important, as they impact the dissolved oxygen levels in the waters, affecting aquatic life.

The effectiveness of the wastewater treatment plant in removing BOD, TSS and nitrogen will have some

beneficial impact on the stream and could reduce the concentrations significantly at times of low stream flows.

This is especially true when most of the in-stream flow is untreated wastewater from the bypasses upstream. At

other times of high rainwater runoff, BOD and TSS from untreated wastewater bypasses will already be diluted

somewhat and the plant effluent will dilute it further. What this means to the waters of the Presa is for the

wastewater treatment plant to operate at its current full capacity is beneficial.

The Mexican goals of wastewater management at all levels include efficiently utilizing wastewater in a

beneficial manner whenever possible while meeting established discharge standards. While these goals are not

achieved at any time in the current operations in San Miguel de Allende, this report includes data and

information necessary and valuable to move forward with a plan to sustainably achieve them.

RECOMMENDATIONS

• Raise discussion of hygiene information with communities and workers using the wastewater

• Investigate alternative irrigation practices that can lower the pathogen contamination on produce

• Perform a more in-depth screening of the bay area’s water where Las Cachinches enters the Presa

• Sample in the Presa for other indicator organisms associated with wastewater, such as Pseudomonas

• Evaluate effectiveness of the wastewater treatment plant further

• Implement alternatives for treatment of wastewater that is bypassed

Acknowledgments: Ina Lepore, (EWB-UK), Susan Broadfoot, Jeffrey Schreiber, Rebecca Pedrick-Case

REFERENCES

Bahri, A. 2009. Managing the other side of the water cycle: Making wastewater an asset. GWP TEC

Background Paper No 13, January 2009, 66 p., ISBN: 978-91-85321-74-2.

11

Dodge, R., Water Measurement Manual: A Guide to Effective Water Measurement Practices For Better

Water Management., Interior Department, Bureau of Reclamation, ISBN 0-16-061763-4, 2001

Griffith, Terry R., and Owens, Janna. (2012). Rio Las Cachinches Sanitary Survey Phase 1 Report.

Drechsel, P., C.A. Scott, L. Raschid-Sally, M. Redwood, and A. Bahri. 2010. Wastewater Irrigation

and Health: Assessing and Mitigating Risks in Low-income Countries. London: Earthscan.

Griffith.T., and Owens, J., (2012), http://chaacwater.org/the-las-cachinches-sanitary-survey-phase-1-report/

Jimenez, B., (2006). Irrigation in Developing Countries Using Wastewater, International Review for

Environmental Strategies Vol. 6, No. 2, pp. 229 – 250.

Jimenez-Cisneros, Blanca, (2007), Helminth Ova Control in Wastewater and Sludge For Agricultural

Reuse., [Ed.W.O.K. Grabow], in Encyclopedia of Life Support Systems (EOLSS), Developed under the

Auspices of the UNESCO, Eolss Publishers, Oxford, UK.

Jimenez-Cisneros*and C. Maya-Rendon, (2007), Helminths and Sanitation, in Communicating Current

Research and Educational Topics and Trends in Applied Microbiology ,A. Méndez-Vilas (Ed.)2007.

Jiménez, B. & Asano, T. (eds) in Water Reuse: An International Survey of Current Practice, Issues and

Needs, 3–26, IWA, 2008.

Micrology Labs, http://www.micrologylabs.com/page/93/Coliscan-Easygel,

Scott, C.A., N.I. Faruqui, and L. Raschid-Sally, eds. Wastewater Use in Irrigated Agriculture: Confronting

the Livelihood and Environmental Realities. CABI/IWMI/IDRC, 2004

WHO, Guidelines for the Safe Use of Wastewater, Excreta and Greywater., World Health Press, Geneva

Switzerland, 2006

12

PPPPRESA RESA RESA RESA DDDDE LAS E LAS E LAS E LAS

CCCCOLONIASOLONIASOLONIASOLONIAS

AAAARROYO LAS RROYO LAS RROYO LAS RROYO LAS

CCCCACHINCHESACHINCHESACHINCHESACHINCHES

RRRRIO IO IO IO LLLLAJAAJAAJAAJA

WWTP

SEWER DIVERSION BOX

LC-1

LC-2

LC-5

LC-7

LC-9

LC-8

LC-6

PA-1

PA-2

PA-3

PA-4

PA-5

RL-1

RL-2

RL-3

RL-4

RL-5

La PataLa PataLa PataLa Patacacacaca

AtotonilcoAtotonilcoAtotonilcoAtotonilco

San MiguelSan MiguelSan MiguelSan Miguel

Arroyo Arroyo Arroyo Arroyo

AtascaderoAtascaderoAtascaderoAtascadero

LC-3

LC-4

PPPPRESA RESA RESA RESA AAAALLENDELLENDELLENDELLENDE

Bypass 2 and Irrigation canals

Bypass 1

Figure 4. E. coli sample locations: LC = Las Cachinches, RL = Rio Laja, and PA = Presa Allende

13

Table 1. Results for E. coli analysis is given in colony forming units per 100 milliliters of sample water

(CFU/100 ml). Suggested primary and secondary contact levels are 250 and 1000 CFU/100ml respectively.

Of special note, the average, untreated wastewater contains approximately 6,000,000 CFU/100ml.

Note: LC = Las Cachinches, RL = Rio Laja, and PA = Presa Allende

SAMPLE ID LOCATION DATE CFU/100 ml

LC-1 Presa de Las Colonias 09/04/13 200

LC-2 Obraje Bridge 10/02/13 100

LC-3 Upstream 100 meters of Guadalupe Bridge 10/15/13 1,000

LC-4 Upstream 30 meters of Guadalupe Mercado

Bridge 10/15/13 33,000

LC-5 Upstream of Bypass 1 outfall pipe into Las

Cachinches 10/10/13 TNTC*

LC-6 Bypass 1 irrigation canal, 10 meters down

from source 09/06/13 7,200,000

LC-7 Upstream Las Cachinches before WWTP

treated outfall 10/10/13 3,500,000

LC-8 Sampled within WWTP outfall pipe before it

enters arroyo 09/13/13 9,400

LC-9 40 meters upstream of Las Cachinches

entering Presa Allende 10/10/13 1,400,000

PA-1 30 meters out from mouth of Lac Cachinches 09/13/13 400,000

PA-1 30 meters out from mouth of Las Cachinches 10/05/13 200,000

PA-2 Metal pole out from arroyo mouth 09/13/13 220,000

PA-2 Metal pole out from arroyo mouth 10/05/13 3,000

PA-3 Mid-Presa 10/05/13 1,000

PA-4 Cortina (dam) 10/05/13 200

PA-5 Submerged church 10/05/13 0

PA-5 Submerged church and screen of surrounding

area 10/16/13 0

PA-5a Submerged church and screen of surrounding

area 10/16/13 0

PA-5b Submerged church and screen of surrounding

area 10/16/13 0

PA-5c Submerged church and screen of surrounding

area 10/16/13 0

RL-1 La Pateca, upstream of bridge 10/06/13 10,000

RL-2 Ranchito Casabel, downstream of chicken

farm 10/06/13 0

RL-3 Atotonilco, upstream of bridge crossing 10/13/13 0

RL-4 30 meters below outfall of Atotonilco sewage

pipe 09/13/13 TNTC*

RL-4 30 meters below outfall of Atotonilco sewage

pipe 10/13/13 800,000

RL-5 Tributary stream from a hot spring

(Cieneguita) 08/31/13 1,320

14

Table 2. Flow measurement sites along the Arroyo Las Cachinches and the wastewater irrigation canals in liters per second (L/sec).

POINT NAME LATTITUDE LONGITUDE DATE TIME FLOW NOTE

1 Las Cachinches Lib. a Dolores H. bridge 20 54 50.23 100 45 56.76 29/8/13 10:30 122 CSO in Cuevitas

4 Sewage canal upstream railroad crossing 20 54 45.29 100 46 4.06 29/8/13 11:04 37 No rain previous 72 hours

6 Las Cachinches upstream WWTP outfall 20 54 26.17 100 46 35.56 29/8/13 12:24 88 No discharge at Bypass 2

7 WWTP outfall pipe 20 54 26.34 100 46 37.11 29/8/13 12:15 107

8 Las Cachinches at old slaughterhouse 20 54 49 100 45 23 30/8/13 17:00 122 No rain previous 72 hours

5 Sewage canal below railroad crossing 20 54 34.04 100 46 14.39 5/9/13 1:04 84 Discharge at Cuevitas repaired

6 Las Cachinches upstream WWTP outfall 20 54 26.17 100 46 35.56 5/9/13 12:04 11 No rain previous 72 hours


2 Las Cachinches above Bypass 1 pipe 20 54 47.5 100 46 01.84 6/9/13 13:40 8 No rain previous 72 hours

3 Las Cachinches below Bypass 1 pipe 20 54 45.56 100 46 05.13 6/9/13 13:28 33

4 Sewage canal above railroad crossing 20 54 45.29 100 46 4.06 6/9/13 12:55 96

2 Las Cachinches above Bypass 1 pipe 20 54 48.65 100 46 0.82 12/9/13 13:14 17 Little rain previous 24 hours


4 Sewage canal above railroad crossing 20 54 42-82 100 46 07-72 12/9/13 12:35 66

5 Sewage canal below railroad crossing 20 54 34.04 100 46 14.39 12/9/13 12:00 45

6 Las Cachinches upstream WWTP outfall 20 54 26.17 100 46 35.56 12/9/13 11:30 144


2 Las Cachinches above Bypass 1 pipe 20 54 48.65 100 46 0.82 19/9/13 11:35 76 Rain previous 12 hours


4 sewage canal above railroad crossing 20 54 42-82 100 46 07-72 19/9/13 11:15 56

5 sewage canal below railroad crossing 20 54 34.04 100 46 14.39 19/9/13 10:55 36



2 Las Cachinches above Bypass 1 pipe 20 54 48.65 100 46 0.82 27/9/13 9:40 294 Rain previous 12 hours


4 Sewage canal above railroad crossing 20 54 42-82 100 46 07-72 27/9/13 10:22 8



2 Las Cachinches above Bypass 1 pipe 20 54 48.65 100 46 0.82 10/10/13 11:30 65 No rain previous 72 hours




Documents

Evaluation of Wastewater inputs into the Presa …...1 Evaluation of Wastewater Inputs into the Presa Allende Janna Owens, Ph.D.; Terry Griffith, P.E. INTRODUCTION In 2012, the Chaac