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Water-Resources Investigations Report

Surface-Water, Water-Quality, and Ground-Water Assessment of the Municipio of Comerío, Puerto Rico, 1997-99

By Jesús Rodríguez-Martínez, Fernando Gómez-Gómez, Luis Santiago-Rivera, and Mario L. Oliveras-Feliciano


In cooperation with the


Water-Resources Investigations Report 01-4083


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To meet the increasing need for a safe and adequate supply of water in the municipio of Comerío, an integrated surface-water, water-quality, and ground-water assessment of the area was conducted. The major results of this study and other important hydrologic and water-quality features were compiled in a Geographic Information System, and are presented in two 1:30,000-scale map plates to facilitate interpretation and use of the diverse water-resource data.

Because the supply of safe drinking water was a critical issue during recent dry periods, the surface-water assessment portion of this study focused on analysis of low-flow characteristics in local streams and rivers. Low-flow characteristics were evaluated at one continuous-record gaging station based on graphical curve-fitting techniques and log-Pearson Type III frequency curves. Estimates of low-flow characteristics for 13 partial-record stations were generated using graphical-correlation techniques. Flow-duration characteristics for the continuous- and partial-record stations were estimated using the relation curves developed for the low-flow study. Stream low-flow statistics document the general hydrology under current land- and water-use conditions.

A sanitary quality survey of streams utilized 24 sampling stations to evaluate about 84 miles of stream channels with drainage to or within the municipio of Comerío. River and stream samples for fecal coliform and fecal streptococcus analyses were collected on two occasions at base-flow conditions to evaluate the sanitary quality of streams. Bacteriological analyses indicate that about 27 miles of stream reaches within the municipio of Comerío may have fecal coliform bacteria concentrations above the water-quality goal established by the Puerto Rico Environmental Quality Board (Junta de Calidad Ambiental de Puerto Rico) for inland surface waters. Sources of fecal contamination may include illegal discharge of sewage to storm-water drains, malfunction of sanitary sewer ejectors, clogged and leaking sewage pipes, septic tank leakage, unfenced livestock, runoff from livestock pens, and seepage from pits containing animal wastes. Long-term fecal coliform data at two sampling stations on the Río de la Plata indicate that since 1984, the geometric mean of five consecutive samples commonly has been at or below 2,000 colonies per 100 milliliters (established as the sanitary quality goal in Puerto Rico for Class SD type waters). At the sampling station upstream of Comerío, the geometric mean concentration has been near 500 colonies per 100 milliliters; downstream of the town of Comerío, the geometric mean concentration has been near 2,000 colonies per 100 milliliters concentration. The data at these stations also indicate that fecal coliform concentrations increase commonly above 2,000 colonies per 100 milliliters during storm-runoff events, ranging from 1,000 to 100,000 colonies per 100 milliliters at both stations.

Geologic, topographic, soil, hydrogeologic, and streamflow data were used to divide the municipio of Comerío into five hydrogeologic terranes. The integrated database was then used to evaluate the ground-water development potential of each hydrogeologic terrane. Analysis suggests that areas with slopes greater than 15 degrees have relatively low ground-water development potential. Fractures may be important locally in enhancing the water-bearing properties in the hydrogeologic terranes containing igneous rocks.

The integrated hydrogeologic approach used in this study can serve as an important tool for regulatory agencies of Puerto Rico and the municipio of Comerío to evaluate the ground-water resource development potential, examine ground- and surface-water interaction, and determine the effect of land-use practices on ground-water quantity and quality.

Stream low-flow statistics document the general hydrology under current land and water uses. Low-flow characteristics may substantially change as a result of streamflow diversions for public supply, increase in ground-water development, waste-water discharges, and flood-control measures; this current analysis provides baseline information to evaluate these impacts and develop water budgets.






Chapter A: Surface-Water Resources Assessment of the Municipio of Comerío, Puerto Rico, 1997-99

Purpose and Scope


Results and Interpretation

Low-Flow at Continuous-Record Gaging Stations

Low-Flow at Partial-Record Stations

Flow-Duration Characteristics

Drainage-Basin Area/Discharge Relation

Map Features

Reservoir Sites

Flood-Prone Areas

Public Water-Supply Filtration Plants and Waste-Water Treatment Facilities

Chapter B: Sanitary Quality of Surface Water During Base-Flow Conditions in the Municipio of Comerío,
Puerto Rico, 1997-99 Background

Purpose and Scope

Field-Data Collection

Analytical Techniques

Results and Interpretation

Chapter C: The Hydrogeologic Terranes and Ground-Water Resources in the Municipio of Comerío,
Puerto Rico, 1997-99
Purpose and Scope

Results and Interpretation

Summary and Conclusions




  1. Streamflow and bacteriological data collection sites, important hydrologic features, and sanitary classification of streams with drainage to or within the municipio of Comerío, Puerto Rico

  2. Hydrogeologic terranes, selected sub-basins, lineament traces, and well locations within the municipio of Comerío, Puerto Rico


Download the Report (PDF, 1.8 MB).


The citation for this report, in USGS format, is as follows:


Rodríguez-Martínez, Jesús, Gómez-Gómez, Fernando, Santiago-Rivera, Luis, Guzmán-Ríos, Senén, and Oliveras-Feliciano, M.L., 2001, Surface-water, water-quality, and ground-water assessment of the municipio of Comerío, Puerto Rico, 1997-99: U.S. Geological Survey Water-Resources Investigations Report 01-4083, 41 p., 2 pls.


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