FLOOD10357

• Document ID: 123
• County: Rio Grande
• Stream Name: Alamosa River
• Basin: Rio Grande
• Sub-Basin: Alamosa - Trinchera
• Water Division: 3
• Title: Alamosa River Watershed Project Literature and Watershed Assesment, Final EPA Report
• Date: 9/30/2003
• Prepared For: Valle del Sol Community Center
• Prepared By: US Environmental Protection Agency
• Watershed Pro - Doc Type: Project Report

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Water Resources. At this location the bankfull discharges of the Alamosa River is 656
cfs with bankfull dimensions of 49 feet in width, 2.9 feet in depth, a cross sectional area
of 140 square feet and mean velocity of 4.5 fUsee. There is also a gaging station 1 mile
above Terrace Reservoir (Gage number 08236000). CDPHE has several temporary
gaging stations to support the Summitville Mine Superfund Project. Figures 4 and 5
provide hydrographs for the Alamosa River above and below Terrace Reservoir (25).
Attachment 4 provides hydrographs for these two gaging stations for water years 1998,
1999 and 2000.

4.2 Groundwater

Basic Groundwater Quality Standards for the State of Colorado (Regulation 41) are
applicable to the groundwater conditions in the Alamosa River Watershed. The
groundwater use classifications in the state are as follows:

. Domestic Use
. Agricultural
· Surface Water Quality Protection
. Potentially Usable Quality
. Limited Use

The groundwater in the Alamosa River Watershed is of sufficient quality to support all of
the groundwater classifications listed above. No site-specific exemptions exist in the
watershed. Specific numeric and narrative standards for groundwater are provided in
Attachment 5 (26).

There are no known routine groundwater monitoring programs in the Alamosa River
Watershed. There are no public water supplies that come from groundwater sources
that would require routine monitoring and reporting to CDPHE. The watershed is
dominated by individual, private wells for domestic drinking and for agriculture.

The most extensive groundwater monitoring program performed in the Alamosa River
Watershed was part of the Summitville Mine Superfund Project by EPA and CDPHE. In
1993, a comprehensive study was performed by Ecology and Environment, Inc. for the
EPA to determine baseline conditions and if contamination from the mine had occurred
in the aquifer. Twenty-one domestic wells were sampled, three upstream and 18
downstream of Terrace Reservoir. The results of the 1993 groundwater sampling
showed that some wells contained metals sueh as copper, zinc and occasionally
arsenic; none of these concentrations exceeded the Maximum Concentration Level
(MCL) or secondary MCLs for drinking water established by EPA (27).

Similar metal concentrations in groundwater were found in 1998 after 24 wells in the
Alamosa River Watershed were sampled and tested. No drinking water MCLs were
exceeded in this study, but it was noted that two wells exceeded standards for iron and
manganese (secondary MCLs). High concentrations of iron and manganese cause
visual staining on clothes or fixtures and are not generally associated with human
toxicity. CDPHE initiated a groundwater monitoring study of 21 wells in June 1999.
Copper, an indicator of acid mine drainage, was not detected above MCLs in any

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