Watershed Protection Plan - Lower Rio Grande Valley Development ...

POLLUTION IN THE ARROYO COLORADO
• 22% of the ammonia nitrogen
• 20% of the nitrate nitrogen
• 40% of the orthophosphate
• 1% of the sediment
In all, 18 municipal wastewater treatment facilities
account for more than 95% of all point source loading
of pollutants of concern entering the Arroyo Colorado
upstream of the Zone of Impairment. These eighteen
facilities are considered to be the “Principal Point
Source Contributors” of pollutants in the Arroyo
Colorado Watershed (Figure 23).
Wastewater facility
discharge amount from these aquaculture facilities is
150 million gallons per day (MGD). The discharge point
for these facilities is located approximately 15 miles
downstream of the Zone of Impairment. Additionally,
several industrial facilities discharge effl uent into the
Arroyo Colorado via municipal wastewater treatment
facilities operated by several municipalities in the
watershed.
The Phase I TMDL analysis of the Arroyo Colorado
concluded that between 1989 and 1999, municipal
wastewater facilities accounted for the following portion
of pollutant loads (TCEQ, 2003):
• 23% of the BOD
Colonias
Of the 1,200 colonias located along the US-Mexico
border, about 75 % are located in Lower Rio Grande
Valley (TWDB 1997). The most recent population
estimates show there are 199,529 residents living in
colonias in Hidalgo, Cameron and Willacy counties
(TWDB 2003b). However, the number of colonia
residents in the Rio Grande Valley is increasing.
Between 1996 and 2003, the colonia population in
these three counties increased by more than 20,000.
The TWDB estimates that in Hidalgo County alone,
73,000 residents live with inadequate wastewater
services (TWDB 2003b). Figure 24 shows the location
of known colonias in the Arroyo Colorado watershed.
Figure 22. Location of Wastewater Outfalls in the Arroyo Colorado Watershed
January 2007 57 Arroyo Colorado Watershed Protection Plan