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<br />punch recorder. Ground-water levels were measured in
<br />the water-table wells on the east side ofthe river at each
<br />site (wells Henderson IA and Road 8 IA). The water-
<br />table wells were instrumented with a water-level
<br />potentiometer connected to an electronic data logger so
<br />that changes in ground-water levels could be recorded.
<br />All measurements were recorded every 15 minutes.
<br />The gaging station and water-table well at each site
<br />were sUlveyed to an arbitrary local datum so that river
<br />stage and ground-water levels could be directly com-
<br />pared.
<br />
<br />Water.Quallty Sampling
<br />
<br />Grab samples of surface water were collected
<br />from the McKay Road, Henderson, and Road 8 sites
<br />and analyzed for field properties, major ions, nutrient~,
<br />iron, and manganese (pI. I). Field properties were
<br />measured at the time of sample collection and included
<br />specific conductance, pH, water temperature (T), DO,
<br />and alkalinity. Major ions included calcium, magne-
<br />sium, sodium, potassium, sulfate, and chloride. Nutri-
<br />ent species included nitrite, nitrite plus nitrate,
<br />ammonium, ammonium plus organic nitrogen (all as
<br />nitrogen), phosphorus, and orthophosphate (all as
<br />phosphorus). Grab samples of surface water were col-
<br />lected next to temporary nested piezometers (discussed
<br />later in this section) so that comparisons could be made
<br />between surface-water and ground-water chemistry.
<br />Samples were collected from August 1992 through
<br />January 1993 and in May and July 1993,
<br />The specific conductance, pH, T, and DO of sur-
<br />face water also were measured at each of the 30 cross-
<br />section sites (pI. I). Measurements were made in the
<br />middle ofthe channel. Measurements were made from
<br />August 1992 through January 1993.
<br />All field measurements in surface water, exclud-
<br />ing alkalinity, were made using portable meters with
<br />the electrode suspended directly in the river. Measure-
<br />ments of alkalinity were made by incremental titration
<br />ofa 50-mL sample of filtered water using 1..6 Nonnal
<br />sulfuric acid. Prior to making a measurement, each
<br />meter and electrode were calibrated using standards
<br />obtained from the USGS Water-Quality Service Unit in
<br />Ocala, Florida. The conductivity electrode and meter
<br />were calibrated daily using conductivity standards that
<br />bracketed the expected range of conductivity values to
<br />be measured. The pH electrode and meter were cali-
<br />brated daily using pH 7 and 10 buffers. The DO elec.
<br />trode was calibrated daily in water-saturated air, and
<br />measurements were compared to theoretical values for
<br />the given water temperature and atmospheric pressure
<br />to check the high-concentration range of the DO elec-
<br />trode and meter. The low-concentration range of the
<br />
<br />DO electrode and meter was checked weekly using a
<br />zero-DO solution, The performance of the DO elec-
<br />trode and meter also was checked weekly against mod-
<br />ified Winkler DO titrations of replicate water samples.
<br />
<br />Surface-water samples collected for major-ion
<br />and nutrient analyses were filtered (0.45-~ pore size,
<br />5,6-in-diamcter membrane filter) immediately after
<br />collection, preserved if needed, and stored on ice until
<br />delivery to the laboratory at the end of the day. Sam-
<br />ples were filtered by pumping the sample with a peri-
<br />staltic pump through the filtration device (acrylic filter
<br />assembly). Samples analyzed for dissolved calcium,
<br />magnesium, sodium, potassium, iron, and manganese
<br />were preserved with nitric acid. Samples analyzed
<br />for dissolved nitrite, nitrite plus nitrate, ammonium, .
<br />and ammonium plus organic nitrogen were preserved
<br />with sulfuric acid. No preservative was added to
<br />samples analyzed for dissolved sulfate, chloride,
<br />phosphorus, and orthophosp~ate, Chemical analyses
<br />were perfonned by the MWRD laboratory following
<br />established U.S. Environmental Protection Agency
<br />guidelines, Analytical results for nitrogen-bearing
<br />nutrient species and phosphorus-bearing nutrient
<br />species were reported in milligrams per liter as nitro-
<br />gen and in milligrams per liter as phosphorus, respec-
<br />tively.
<br />
<br />Samples of ground water in the alluvial aquifer
<br />were collected from twelve 2-in-diameter PVC moni-
<br />toring wells located adjacent to the South Platte River
<br />(pI. I), Samples were collected from August 1992
<br />through January 1993 and in May and July 1993. Sam-
<br />ples were analyzed for specific conductance, pH, T,
<br />DO, alkalinity, major ions, nutrients, iron, and manga-
<br />nese. Four wells were installed at each of three loca-
<br />tions near: (I) McKay Road, 5.8 mi downstream from
<br />the MWRD plant; (2) Henderson, 11.1 mi downstream
<br />from the MWRD plant; and (3) Road 8, 22.1 mi down-
<br />stream from the MWRD plant The three locations
<br />were selected so that ground water could be sampled
<br />adjacent to the two segments of river in which DO sags
<br />occur (McKay Road and Road 8) and adjacent to a seg-
<br />ment of the river in which DO concentrations recover
<br />(Henderson). TWo wells were installed near the right
<br />bank of the river (wells designated IA and IB), and
<br />two wells were installed near the left bank of the river
<br />(wells designated 2A and 2B) at each of the three loca-
<br />tions. Each pair of wells consisted of a shallow well
<br />screened near the water table (wells designated A) and
<br />a deep well screened at the base of the alluvial aquifer
<br />(wells designated B). The wells were located about 15
<br />to 100 ft from the bank of the river. Construction
<br />details for the monitoring wells are listed in table 3.
<br />
<br />S QUlntl1y Ind QUlnly of Ground,Wlter Oll.hlrgl to'thl South Plltto RIYIl", OlnYlr to Fort Lupton, Colorldo,
<br />August 1992 Through July 1993
<br />
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