Abstract:
As part of the curriculum for the 2000-2001 Environmental Analysis program at The Evergreen State College, a group project was undertaken to study the hydrologic systems in Grass Lake Park, Olympia, Washington. A topographic elevation survey of the area immediately surrounding the lake was conducted, and survey points were located using GPS technology. A benthic survey of lake bottom elevations was also conducted. Water samples were taken from several locations around the lake’s shore during the period from October 2000 through May 2001. These samples were tested for pH, dissolved oxygen, conductivity, and concentrations of major cations and anions. The intent of the study was to provide information relating to the water budget and ionic charge balance of the lake, for use by the City of Olympia and other interested parties.
Background:
Grass Lake Park is located in Township 18N, Range 2W, Sections 8, 9, 16, and 17, in Olympia, WA. The park covers an area of over 160 acres in the Green Cove drainage basin, and is bounded by Kaiser Rd. on the west, 14th Ave. on the north, Cooper Point Rd. on the east, and Mud Bay Rd. on the south. The lake’s inflow from the surrounding watershed, as well as its outflow, runs through culverts underneath these boundaries (Skeens et. al., 1995). The surrounding area is developed residential, and more development is underway.
Fig.
1: Location of the study site with
respect to the local area.
Grass Lake Park lies in northern Thurston County, and as such exhibits geology dominated near the surface by the Quaternary Vashon Recessional (Qvr) and Quaternary Vashon Till (Qvt) formations. These formations consist largely of sand and gravel, and exhibit good aquifer properties. Lying underneath these formations is the Kitsap formation, an aquitard of silt and clay (Noble and Wallace, 1966). It is reasonable to assume that the surface of Grass Lake is concurrent with the surrounding water table, and that the entire groundwater system near the surface in this area comprises a perched aquifer.
Purpose:
This investigation involved a water quality baseline study of the Grass Lake area and had four goals. The first goal was to survey and map the entire Grass Lake wetland area; second to create a three-dimensional map of the lakebed; and third, take water samples at various locations and use instrumentation for analysis of concentration of anions, cations, pH, alkalinity, dissolved oxygen and temperature. The final goal was to calculate the volume of the lake as well as inflow/outfall at different times throughout the rain year.
Methods:
Fig. 2: Sampling locations for surface water, ground water, and soil around Lake Louise.
Water sample sites were designated in October during the beginning of project work, and all samples were gathered from these sites (Fig. 2). Samples were collected directly from the lake, near the surface, into pre-washed and lake water rinsed 1000 mL polypropylene bottles. Bottles were filled to the top to limit trapped air. Samples were refrigerated on arrival at the lab.
Soil samples were taken at five sites around the edge of the lakebed (Fig. 2). The top layer of organic matter was brushed aside and a two and one half inch soil core was used to take a four-inch deep sample.
Ground
water was also sampled at the site. The
existing pieziometer at the site was too shallow (Fig. 2). A soil core was used to extend this
pieziometer down to eight feet, logging the soil conditions at half-foot
increments. (See Table 1 below.)
Table 1. Soil log of pieziometer
|
Depth of Soil |
Composition |
|
4in |
Organic mixture |
|
6 in |
Silty/sandy organic mix-damp |
|
10 in |
Tan/Brown sand-damp |
|
1 ft |
Coarser sand-damp |
|
1 ft 6 in |
Small pebbles and sand-damp |
|
1 ft 8 in |
Iron like deposits coarse sand |
|
2 ft |
Clumping coarse sand |
|
2 ft 1 in |
Small sand-gray in color |
|
2 ft 2 in |
Iron like color in sand larger pebbles 1 in-2 in. |
|
2 ft 6 in |
No gravel-sandy and gray in color |
|
3 ft |
Damp gray sand-Iron like color |
|
3 ft 3 in |
Sandy and more iron like color |
|
3 ft 6 in |
Sandy and iron like color |
|
4 ft |
Grayish sand less iron color |
|
4 ft 6 in |
Iron like color tan/gray sand |
|
5 ft |
Gray sand |
|
5 ft 6 in |
Small amount of clay iron like color |
|
6 ft |
Gray sand |
|
6 ft 6 in |
Sand-quite moist |
|
7 ft |
Water with sand-WATER TABLE |
|
7 ft 3 in |
Moist sand and silt |
|
7 ft 6 in |
Sand and silt |
|
8 ft |
Moist sand |
Titrations for surface water alkalinity were performed directly on unfiltered samples. The samples were vacuum filtered with 0.45-micron filter paper before analysis by the ion chromatograph (IC), atomic absorption spectrophotometer (AA), and inductively coupled plasma spectrometer (ICP).
The ground water sample was centrifuged to remove sediments and then processed by the same methods as the surface water samples. When soil samples were brought back to the lab they were dried in a 60 C oven until all moisture was removed. 10.0 grams of dried soil was weighed on an analytical scale and mixed with 100mL of deionized water. This solution was then placed on a shaker for 48 hours to extract soluble ions. After extraction, the sample was placed in a centrifuge for two hours to remove sediments. The centrifuged soil-extract was treated the same as surface water samples above.
Filtered samples were refrigerated in clean 125-to 250 mL polypropylene bottles.
Samples to be analyzed on the AA and ICP were stabilized by addition of 1-4 drops 6M HCl, unless run within 24 hours of collection.
Sample Analysis – Alkalinity Determination.
Alkalinity
in water samples was determined by acid titration to pH 4.5 using EPA method
number 310.1. The method was completed
using 0.0207 M HCl.
Sample Analysis – Ion Chromatography.
Filtered
samples were analyzed using a Dionex 2020i Ion Chromatograph. EPA method number 300.0 was followed for Ion
Chromatography. Mixed standards were
prepared by appropriate dilutions of 1000 ppm Cl-, NO3-
and 4000 ppm SO42-, H2PO4-
stock solution. Concentrations of
standards were as follows: Low standard
-- 0.200 ppm Cl-, NO3-; 0.800 ppm SO42-,
H2PO4-: Mid standard – 1.00 ppm Cl-,
NO3-; 4.00 ppm SO42-, H2PO4-:
High standard – 10.0 ppm Cl-, NO3-; 40.0 ppm
SO42-, H2PO4-. Standards and samples were run within 48
hours of sample collection, and were run on the same day. Standards were prepared fresh each day.
Sample
Analysis – Atomic Absorption Spectrophotometry.
Filtered samples were analyzed for
sodium and potassium using a Perkin-Elmer Model 305 Atomic Absorption Spectrophotometer.
Methods by J.M. Stroh for water analysis were followed to conduct analysis
on the AA. Standards for K+ and Na+
were stable over a period of weeks, and did not need to be made daily. Standards for K+ were 2.00, 6.00,
and 12.0 ppm; those for Na+ were 1.00, 3.00, and 6.00 ppm. 1000ppm
of Cesium was added to free up Na+ and K+ in all solutions.
Although sample concentration were above the linear response range for the
instrument, Perkin-Elmer’s curve fitting range extension method was used to
make measurements in this range (Perkin Elmer Corporation).
Sample
Analysis – Inductively Coupled Plasma Spectroscopy.
Filtered samples were analyzed for calcium and magnesium using an Atom Scan 16 Inductively Coupled Plasma Spectrophotometer.
Surveying and GPS Data Collection.
The elevation of the lake surface was determined using a stake at the water’s edge. Elevations for points below the surface of the lake were determined using a kayak, a meter stick, and a GPS unit for positions.
Position measurements were taken with a Geo-Explorer II and were collected only when the Pdop was below 6.00 to reduce error. When the Geo-explorer III became available the Pdop was lowered to under 3.0. The data gathered using the GPS units were downloaded into Pathfinder Office to do differential correction on the data. These corrected data points were then exported to ArcView to generate a map of the lakebed.
Results:
Figure 3, below, is the topographical map of the lakebed that was created. The dark areas represent the lower elevations areas of the lakebed. At the beginning of the study, Grass Lake was made up of four separate pond areas during October and part of November. During the month of November, the lake areas became interconnected into one body of water. The only current existing source of incoming water into Grass Lake is a culvert designed to drain water out of the lake at the West side. The culvert began to discharge a small amount of water into the lake during January and continued at a flow too low to measure through the end of our sampling in May. At no point during our study (Oct, 2000 to May, 2001) did water discharge from the lake.
A cation/anion charge balance for each sample site and date was calculated and presented in Table 2. Ion concentrations were also determined for two nearby wells located in Green Cove drainage basin. The Green Cove wells are at depths of 106 and 64 feet. The depth of our Piezometer is 7.5 feet (see soil log)(Thurston County GIS wells data).
Table
2: Shows the concentrations of the different elements
(by site and date) sampled for at our study site. This table also shows the charge balance of
the individual sample sites by date.
*Bold numbers and present are to show qualitative analysis of this sites only. The data was corrupted when ran on the IC but is still useful to show that soil and groundwater have NO3 and the surface water does not.
|
Location |
Alkalinity as CaCO3 ppm |
Cl ppm |
SO4 ppm |
K ppm |
Na ppm |
Mg ppm |
Ca ppm |
Charge Balance |
|
W |
7.83 ± 1.05 |
2.18± .50 |
1.68± .99 |
0.27± .06 |
1.27± .29 |
1.01± .17 |
2.62± .73 |
4.38 |
|
NW |
7.79± 2.28 |
2.22± .34 |
1.46± .35 |
0.29± .08 |
1.30± .31 |
1.11± .27 |
3.09± .89 |
10.9 |
|
E |
9.09± 4.41 |
2.08± .71 |
0.89± .53 |
0.20± .08 |
1.16± .32 |
0.71± .25 |
2.11± .5 |
-8.05 |
|
S |
9.35± 3.45 |
2.37± .86 |
1.02± 1.06 |
0.21± .06 |
1.21± .18 |
0.76± .31 |
2.32± .79 |
-7.39 |
|
N |
8.41± 1.69 |
2.51± .58 |
0.85± .78 |
0.25± .04 |
1.17± .26 |
0.89± .32 |
2.54± .75 |
0.116 |
Table
4. Elevation of the lakes water level in relation to
|
Date |
Staff gage elevation
(ft) |
Water level elevation
Height above sea level (ft) |
|
1/12/2001 |
2.32 |
129.04 |
|
4/6/2001 |
2.34 |
129.06 |
|
4/19/2001 |
2.36 |
129.08 |
|
5/5/2001 |
2.13 |
128.85 |
Discussion:
Upon completing a survey of the lakebed we created a topographic map of the site. This map has allowed us to visualizes the contours of the lake bottom and see what shape the lake will take at low and high water levels.
Rainfall was abnormally low this year so storm water runoff from areas outside of the lake basin was not a factor in the elevation and composition of the lake water. It only rained a total of 26.17 inches between October 2000 and May 2001. The previous year rainfall during the same period was 53.89 inches. This study provides a baseline for the concentrations of ions in the lake and the surrounding basin without interference from outside water sources. It would be interesting to compare these values to the concentrations in the lake when the lake serves as a catch basin. Storm water coming into this basin could either dilute the concentrations of the lake or could bring in more concentrated ions.
Table 3. shows that there is no significant difference in ion content between the different sample sites at the lake. Even when the lake was separated into four smaller ponds, the ion content was statistically the same
A qualitative look at the soil, surface water, and groundwater shows that all three have the same ions except for NO3-, which is present in only soil and groundwater. It is possible that NO3- is consumed by organisms when it enters the surface water, but further studies need to be done to determine the cause for the difference in nitrate content.
The elevation of the lake was determined using the staff gauge located next to the culvert, (Fig. 2). After determining the elevation of the lake we found the staff gauge to be 126.72 feet above sea level. So by adding 126.72 to the reading on the staff gauge, the elevation of the lake can be determined. Using the elevation map and the staff gauge, volumes of water can be calculated for the lake.