2

The Town of Colonie entered into this research agreement with Rensselaer Polytechnic
Institute as part of its continuing efforts to revitalize the Mohawk River waterfront area.
The focus of that effort, as described in the Mohawk River Management Study (MRMS),
Draft Number Three (10/18/2006), is on improving river access. The major problems to be overcome include siltation (sediment accumulation) and unchecked growth of invasive species, particularly water chestnut ( Trapa natans ), in nearshore areas along the south bank of the Mohawk River. This project addresses several of tasks identified in the
MRMS.
The first author of this report has led a number of projects that involved collection of sediment samples from the Mohawk River. Of particular significance to this study, are samples that were collected from two specific areas –

Just upstream of the Crescent (Route 9) Bridge, in the water chestnut bed along the south (Town of Colonie) shore. Recent rates of net particle accumulation in cores from this area will be determined from the interpretation of radionuclide analyses.

A highly depositional area just upstream of lock 7 (Niskayuna). Samples from this site document inputs of particle-reactive radionuclides from the Knolls Atomic Power
Laboratory (Chillrud 1996). As described below, these radionuclide tracers provide important constraints on the rate of sediment accumulation in our study area which is the Mohawk River in the Town of Colonie.
Analyses of particle-reactive radionuclides provide a useful tool for studying rates of sediment accumulation in natural water systems and have been applied extensively in the
Hudson-Mohawk basin (Bopp et al., 2006).
A most straightforward application involves the collection of cores, often by simply pushing a plastic tube into the mud and retrieving a vertical column of sediment. The cores are typically sectioned at 1 to 4 cm intervals and the sections are analyzed for particular radionuclides with known input histories.
Among the most useful radionuclides to analyze are Cs-137 and Be-7. Both can be quantified using the relatively simple technique of gamma spectroscopy. The sample preparation and analytical procedure consists of drying, grinding, and setting the samples on a semi-conductor crystal for several hours to count the gamma rays that are assigned, based on characteristic energies, to particular nuclides (Olsen, 1979). In this report,
3

radionuclide concentrations are reported as activities in units of picocuries per dry kilogram of sediment (pCi/kg) decay corrected to the date of core collection. One picocurie is equivalent to 2.22 decays per minute. Activities are reported with error bars of one standard deviation (

1 σ) based on gamma counting statistics. By convention,
“detectable” activities are defined as those that are at least 2 σ greater than zero.
Cs-137 is an anthropogenic radionuclide supplied to natural water systems globally via fallout from the atmospheric testing of nuclear weapons. The principle time horizons associated with Cs-137 in sediments include the first (i.e. deepest) detection, corresponding to approximately 1954, the start of large-scale atmospheric testing, and the peak activity related to the maximum fallout delivery of 1963-4 (see Bopp et al., 2006).
Natural water systems adjacent to nuclear power or research reactors can also receive direct inputs of Cs-137. This is the case with the Mohawk River where effluent from the
Knolls Atomic Power Laboratory (KAPL) in Schenectady is a major contributor to Cs-
137 levels in sediments deposited downstream of the site (Chillrud, 1996; Bopp et al.,
2006).
From the perspective of Cs-137 based time horizons in the sediment column of our
Mohawk cores, inputs from KAPL do not present a major problem. The history of discharge to the river is fairly well documented and generally similar to the deposition of fallout Cs-137. Reported releases to the Mohawk River from KAPL decreased by more than two orders of magnitude following a peak in 1962-3 and the first (i.e. deepest) detection in cores would be associated with the start of operations at KAPL in 1946
(Chillrud 1996 and references therein).
Be-7 is a natural radionuclide produced in the atmosphere by cosmic ray spallation of nitrogen and oxygen. Because of its short half-life (53.4 days), it is confined to the upper layers of sediment. Detection of Be-7 indicates that the sample contains a significant fraction of particles deposited within about a year of core collection (see Bopp et al.,
2006).
Locations of our previous cores from the study area are shown on Figure 1. A summary of recent net sediment accumulation rates as indicated by the distribution of radionuclide tracers in these cores is given in Table 1. All cores are unambiguously identified by a unique control number that is used in all reports and publications from this laboratory.
The profiles of the Cs-137 activity with depth and Be-7 activity in near surface samples for each of the cores are included in Appendix 1.

Moh 4 – This core was collected in the summer of 1992 from the cove just downstream of the Route 9 Bridge as part of the Hudson River PCB Reassessment
RI/FS tributary sampling under Federal Superfund. Subsequent to 1992, NYSDEC public fishing access was established at the upstream end of this cove. Detectable
4

levels of Cs-137 were found in all sections of this 41 cm long push core. Using 1946
(the start of operations at KAPL) as the earliest possible date of Cs-137 accumulation and a total time of 46 years (1946 to 1992) yields a net accumulation rate of > 0.89 cm/yr (41 cm/ 46 yrs). Be-7 activity in the 0-2 cm section (210

160 pCi/kg) was between 1 and 2σ positive suggesting that accumulation over the year prior to core collection was less than 2 cm.

Moh 3 - This core was collected in the summer of 1992 from the cove just upstream of the Route 9 Bridge as part of the Hudson River PCB Reassessment RI/FS. Similar to Moh 4, it was a 41 cm push core with detectable activity of Cs-137 throughout its length. In contrast, Moh 3 had detectable activity of Be-7 in its 0-2 cm section (880

350 pCi/kg) indicating significant accumulation over the year prior to collection.
Consequently, all other archived cores in the study area were collected within ca. 20 meters the site of Moh 3, with the exception of Moh 16 which was taken ca. 80 meters to the east (shoreward).
Figure 1. Locations of sediment cores in the vicinity of the Route 9 Bridge across the
Mohawk River. Only Moh 19 was collected as part of this project. For scale, the river is
350 m wide at Route 9.
5

TABLE 1. Recent Accumulation Rates in Previous Cores from the Study Area.
Core ID Control # Date Collected Core length Cs-137 Net penetration accumulation
Downstream of the Rte 9 Bridge (Figure 1)
> 0.89 cm/yr Moh 4 CN2164 27-Aug-92 41 cm
Downstream of the island to the west of the Rte 9 Bridge (Figure 1)
Moh 3 CN2163 27-Aug-92 41 cm
Moh 5i
Moh 10V
Moh 10P
CN2193
R1100
R1099
5-Oct-92
6-Sep-96
6-Sep-96
70 cm
112 cm
58 cm
ND
2
41 cm
41 cm
60 cm
72 cm
44 (58) cm
1
Moh 12
Moh 16
R1147
R1372
10-Oct-97
29-May-01
ND
52 cm
Moh 10C1 R1558 14-Nov-05
52 cm
69 cm ND
> 0.89 cm/yr
1.3 cm/yr
1.5 cm/yr ca. 1 cm/yr ca. 1 cm/y
>0.95 cm/yr ca. 1 cm/yr
1
Cs-137 was not detected in the samples between 44 and 56 cm, but was more than two standard
deviations greater than zero in the bottom (56-58 cm) section.
2
Not Determined. Only the near-surface sections were saved and/or analyzed.

Moh 5i - This core was collected in the fall of 1992 from the cove just upstream of the Route 9 Bridge as part of the Hudson River PCB Reassessment RI/FS. It was a
70 cm push core with detectable Cs-137 to a depth of 60 cm which indicates a net accumulation rate of 1.3 cm/yr. Be-7 activity was just under 2σ positive (980

550 pCi/kg) in the 0-2 cm section. The Cs-137 profile (Appendix 1) is characteristic of cores from this site – a subsurface peak activity (in this core at the 52-56 cm section; in others between 40 and 68 cm) that drops to non-detectable levels below within one or two samples. Above the peak, Cs-137 activity decreases by more than two-thirds within two or three samples. This core does contain one anomalous section with respect to Cs-137, a high-activity, single-point “outlier” at 6-8 cm (Appendix 1) that has never been adequately explained.

Moh 10V – This was a vibracore collected in the summer of 1996 as part of our continuing monitoring of Hudson basin sediments as part of our collaboration with
NYSDEC. Vibracorers, as the name implies, impart electrically generated vibrations to the core tube during sampling to help overcome friction and enhance penetration.
The 112 cm long core had detectable Cs-137 activity to a depth of 72 cm indicating a net accumulation rate of 1.5 cm/yr. The depth profile was “characteristic for cores from this site” as explained in the description of Moh 5i, above. Near-surface
6

samples were not processed or analyzed in time to determine with any reasonable precision the activity of the short-lived Be-7.

Moh 10P – This was a piston core collected the same day as Moh 10V (above).
Piston coring is another technique than can often result in the collection of longer cores than push coring. The 58 cm core had peak Cs-137 activity in the 40-44 cm section. Cs-137 was not detected in the samples between 44 and 56 cm, but was more than two standard deviations greater than zero (210

50 pCi/kg) in the bottom (56-58 cm) section. Consequently, the net accumulation rate in this core since 1946 was on the order of 1 cm/yr. Be-7 activity in the 0-2 cm section was just under 2σ positive
(2150

1230 pCi/kg) with a large standard deviation reflecting a significantly longer than average time between collection and sample analysis.

Moh 12 – This push core was collected in the fall of 1997 in an effort to obtain Be-7 bearing sediment from this site deposited in the late 1990s. Consequently only the 0-
2 cm section of the core was saved for analysis. The measured Be-7 activity was just under 2σ positive (620 
330 pCi/kg), consistent with accumulation on the order of 1 cm over the year prior to collection.

Moh 16 – This was a push core collected in the spring of 2001. Cs-137 was detected throughout its 52 cm length indicating a net accumulation rate of greater than 0.95 cm/yr. The Cs-137 activity increased sharply in the deepest sample (see Appendix 1), suggesting that the depth profile was approaching what would be “characteristic for cores from this site,” as described above.

Moh 10C1 – This is our most recent core from this site, a 69 cm long push core collected in the fall of 2005. Only the upper six cm have been analyzed to date. A strong Be-7 signal was observed in the 0-2 cm section (1530

250 pCi/kg) of this core suggesting accumulation of 1 to 2 cm over the year prior to collection.
Overall, the radionuclide data from the cores described above is quite consistent and indicates a net accumulation rate on the order of 1 to 2 cm per year of fine grained (silt and clay sized) material. Some additional interpretation of the characteristic Cs-137 depth profile that was observed is possible with reference to our previous analyses of archived cores collected upstream of the current study area, but downstream of KAPL.
In the fall of 1993, three sediment cores were collected from a highly depositional area about a kilometer upstream of Lock 7 and about 1.8 kilometers downstream of KAPL in
Niskayuna (Figure 2). Moh 6 and Moh 7P (piston) were collected on October 15 and
Moh 9P, 10 days later. Based on field notes, the three cores were located within about twenty meters of each other.
7

Figure 2. Location of the sediment coring site upstream of Lock 7. For scale, the length of the dam between Goat Island and the southwest shore of the Mohawk River is 225 m.
The distribution of Cs-137 activity with depth in these cores (Appendix 1) has several distinct features indicating that the dominant source of this nuclide to these sediments is not global fallout, but rather discharges from historical nuclear reactor operations at
KAPL. These include –

Peak Cs-137 activity ranging from 12,000 (Moh 6) to 24,000 (Moh 7P) pCi/kg
(Figure 3). These values are not outside the range of peak fallout levels observed in sediments of lakes and other natural water systems with relatively low particle fluxes including sites in the upper Hudson Basin that drain forested areas of the Adirondacks
(Bopp and Simpson, 1989; Chillrud, 1996). They are, however, to my knowledge, unprecedented in river systems like the Mohawk where significant agricultural land use in the drainage basin produces a relatively high particle flux (Phillips and
Hanchar, 1996) that serves to “dilute” the fallout Cs-137 signal on accumulating
8

particles. Peak Cs-137 activities of a few thousand pCi/kg characterize such systems
(see Bopp et al., 2006).
Figure 3. The distribution of Cs-137 activity with depth in core Moh 7P.

A dramatic decline, by more than an order of magnitude, from peak levels to the Cs-
137 activities measured in more recently deposit sediments. This corresponds quite well to reported releases from KAPL which span the period from 1959 through 1971.
Cs-137 releases were highest between July 1962 and December 1963 and at least two orders of magnitude lower in all subsequent years (see Chillrud, 1996).
Furthermore, a rapid decline in the concentration of any particle-reactive tracer in sediment cores from a river is characteristic of direct inputs such as discharge from
9

KAPL to the Mohawk. The concentration of a particle-reactive tracer input primarily to drainage basin soils, such as Cs-137 derived from global fallout, would be expected to decrease much more slowly in sediments depositing in the river. In sediments of the Hudson basin, Cs-137 activity was observed to decrease from the
1963-4 fallout peak with half times of 6-8 years reflecting holdup in drainage basin soils (Bopp et al., 1982; Chillrud, 1996; Bopp et al., 2006).
 A “double maximum” in Cs-137 activity in one of the cores, Moh 7P (Figure 3). Of our three cores from the Lock 7 area, Moh 7 had the deepest penetration of detectable
Cs-137 activity (90 cm) and consequently the greatest temporal resolution. The observation of a double maximum is generally consistent with KAPL reports that show much lower levels of Cs-137 releases in the two years prior to the peak release of 1962-63, but increased releases in 1960 and 1959.
This analysis suggests that the Cs-137 actvity in sediment depositing downstream, and more specifically in the study area, should be influenced by releases from KAPL. Further interpretation of the depth profiles of Cs-137 activity in the archived cores from the vicinity of the Route 9 Bridge (Figure 1) includes the following observations and conclusions –

The rapid decline in Cs-137 activity in samples above the peak in our archived cores from the vicinity of the Route 9 Bridge (e.g. Moh 10V, Figure 4) is similar to what was observed in the cores from upstream of Lock 7 (Moh 7P, Figure 3). This suggests that the Cs-137 profiles in sediments from both areas reflect the influence of releases from KAPL.

Below the peak, the profiles of Cs-137 activity in the Route 9 Bridge area cores appear to be “truncated” relative to the profiles in the Lock 7 cores. As described above, and illustrated for Moh 10V in Figure 4, a characteristic of Cs-137 depth profiles in the Route 9 Bridge cores is that the peak Cs-137 activity “drops to nondetectable levels below within one or two samples.” This is consistent with a major removal of deposited sediment either with dredging or as the result of a major sediment scour and transport event and is certainly not evident in the cores from Lock
7. In Moh 7P (Figure 3), the thickness of sediment with very high Cs-137 activity is generally consistent with deposition from the start of operations at KAPL in 1946 through the peak reported discharge in 1962-3.

Further evidence for a dredging or scour event comes from the levels of peak Cs-137 activity in cores from the two sites. While some downstream attenuation of peak activities would be expected, note that the maximum in Moh 10V (2560

160 pCi/kg, Figure 4)) is almost an order of magnitude lower than in Moh 7P (24,200

1200 pCi/kg, Figure 3). This major reduction in peak Cs-137 activity would be consistent with a dredging or scour event sometime after 1963 in the Route 9 Bridge area.
10

One possibility would be dredging associated with operation of the recently closed
Marina on the south (Colonie) shore of the Mohawk just downstream of the Mohawk
10V site (Figure 1). Garrett O’Connor of the NYS Canal Corporation (personal communication) indicated that the agency would not have records of such activity since their focus was on channel maintenance.
Figure 4. The distribution of Cs-137 activity with depth in core Moh 10V.
USGS data on Mohawk River discharge at Cohoes were examined for evidence of a high flow event that could have produced sediment scour in the Route 9 Bridge area.
11

Table 2 is a list of all the average daily flows that exceeded 70,000 cfs in the record that spans the period from December 1, 1917 through September 30, 2007, the end of the 2007 water year. The event of March 14-15, 1977 was exceeded only by the event of March 18-19, 1936. It is possible that the 1977 event was responsible for sediment scour in the normally depositional Route 9 Bridge area. In a recent RPI
Master’s thesis, high discharge from the Batten Kill during this same event was cited as the probable cause of unusual scour observed at a site along the main stem of the upper Hudson (Dively, 2006). The March 1977 event will be discussed again in the section that follows on the interpretation of cores collected from the study area as part of this project
TABLE 2. Highest Mean Daily Discharge, Mohawk River at Cohoes.
USGS SITE 01357500 MOHAWK RIVER AT COHOES NY
PERIOD OF RECORD: 12/1/1917 THROUGH 9/30/2007
Rank Date discharge
(cfs)
Rank Date discharge
(cfs)
5
6
7
3
4
1
2
3/19/1936
3/14/1977
1/20/1996
9/22/1938
6/29/2006
3/18/1936
10/17/1955
112000
97800
92600
89800
89700
88900
87500
8
9
10
11
12
13
14
3/15/1977
1/9/1998
3/22/1980
4/3/2005
3/6/1964
4/5/1960
4/17/2007
85000
81800
79100
79000
77500
76100
75300
The Sponsored Research Agreement supporting this project was entered into on
September 6, 2007 and field work was planned for the fall, after the dieback of the water chestnuts that severely limited boat access to the study area. As a result of delays associated with preparing and submitting the application to the NYS Canal Corporation, our sampling permit was only received in mid November, just after the first ice covered the areas where core collection was planned. Safe access to the river was restricted until mid-March, close to the last possible time when cores could be collected and the samples processed and analyzed by the end date of the Agreement (June 1, 2008).
Three push cores were collected on March 13, 2008. Moh 19 was from a site downstream from the Route 9 Bridge (Figure 1) accessed in a 12 foot Jon boat launched from shore into open water just downstream and tethered to the edge of shore ice. A
12

proposed site, near the western end of the bike path and River Road, could not be accessed safely because of shore ice. Consequently, two cores, Moh 17 and 18, were collected from the cove downstream of the Twin Bridges adjacent to the Colonie Town
Park (Figure 5). Access for launching the Jon boat was graciously provided by park staff via the boat ramp. Breaking through the thin layer of ice that covered portions of the cove provided stable boat positioning during the collection of Moh 17. The more typical technique, holding on to a spike inserted into the sediment, was used with Moh 18.
Figure 5. Locations of sediment cores collected from the cove downstream of the Route
87 Twin Bridges adjacent to the Colonie Town Park.
A summary of recent net sediment accumulation rates as indicated by the distribution of radionuclide tracers in these cores is given in Table 3. The profiles of the Cs-137 activity with depth and Be-7 activity in near surface samples are shown in Figure 6 (Moh 7 and 8) and Figure 7 (Moh 9).
13

Core ID Control # Location
1
Core length Cs-137 Net penetration accumulation
Moh 17
Moh 18
Moh 19
R1640
R1641
R1642
N 42° 47.900'
W 73° 44.864'
N 42° 47.782'
W 73° 45.016'
N 42° 48.810'
W 73° 43.588'
78 cm
86 cm
52 cm
72 cm
72 cm
28 cm
1.2 cm/yr
1.2 cm/yr
0.45 cm/yr
1
Lat and Long were determined using a Garmin e trex 12 channel GPS. The accuracy indicated on the
instrument ranged from 14 to 25 feet.

Moh 17 – Detectable levels of Cs-137 were found to a depth of 72 cm out of a total length of 78 cm. Accumulation of 72 cm between the start of operations at KAPL in
1946 and core collection in 2008 yields a net rate of 1.2 cm/yr. Be-7 activity was between 1 and 2σ positive (320 
210 pCi/kg) in the 0-2 cm sample suggesting on the order of 0.5 cm of accumulation over the year prior to collection.

Moh 18 – Detectable levels of Cs-137 were found to a depth of 72 cm out of a total length of 86 cm. As in Moh 17, accumulation of 72 cm of Cs-137 bearing sediment yields a net rate of 1.2 cm/yr. A strong Be-7 signal (1120

230 pCi/kg) was observed in the 0-2 cm sample indicating that ca. 2 cm of sediment had accumulated over the year prior to collection.
These two cores had very similar distributions of Cs-137 activity with depth (Figure
6) that can be interpreted based on discussions presented above. As expected, above the peak in Cs-137 activity that occurs at about 60cm in these cores, there is a rapid decline in Cs-137 activity. This is similar to observations in both the Lock 7 and
Route 9 Bridge area cores and likely reflects the influence of Cs-137 discharges from
KAPL.
Below the peak activity the profiles of Cs-137 activity in Moh 17 and 18 do not appear to be “truncated” as in the Route 9 Bridge area cores, but decline more smoothly to non-detectable levels as in the Lock 7 cores. This indicates that the sediments of these sites have not experienced significant dredging since the 1940s or scour associated with the March 1977 high flow event.
Further evidence for uninterrupted accumulation in Moh 17 and 18 comes from the level of peak Cs-137 activity, 3700 (Moh 17) to 5000 (Moh 18) pCi/kg. Correcting for the decay of Cs-137, in 1993 (the year of collection of the Lock 7 area cores), peak activities would have been 5000 to 7000 pCi/kg, about a third of peak Cs-137
14

activity observed in the Lock 7 area cores. This represents a more reasonable attenuation of peak levels with distance from the KAPL source than the order of magnitude differences between the Lock 7 and Route 9 Bridge area cores discussed above.
Figure 6. The distributions of Cs-137 activity with depth in cores Moh 17 and Moh 18.

Moh 19 – Detectable levels of Cs-137 were found to a depth of 30 cm out of a total length of 52 cm yielding a net accumulation rate of about 0.45 cm/yr. Be-7 activity was between 1 and 2σ positive (290

210 pCi/kg) in the 0-2 cm sample suggesting on the order of 0.5 cm of accumulation over the year prior to collection.
The depth profile of Cs-137 in Moh 19 (Figure 7) is similar to those observed in our archived cores from the Route 9 Bridge area. Peak Cs-137 activity was only about
1300 pCi/kg (or about 1800 pCi/kg if decay corrected to 1993). Since the closest marina is more than half a kilometer upstream and there is no other obvious reason for dredging at this site, the abrupt drop to non-detectable levels of Cs-137 at depths below 28 cm is more likely related to scour associated with the March 1977 event.
15

Figure 7. The distributions of Cs-137 activity with depth in core Moh 19.
One obvious possible short-term remedy to address sediment accumulation/siltation in the nearshore areas of the Mohawk in the Town of Colonie is dredging. “Short-term” seems appropriate because the discussion above indicates that several areas that would be likely candidates for dredging accumulate sediment at rates of 1 to 2 cm per year. The rate of accumulation of new sediment could be significantly higher following dredging and deepening of such areas. Deepening can result in lower near-bottom energy and
16

enhanced accumulation rates. Longer-term accumulation rates in the study area will be addressed in Section IV of this report.
Another major consideration associated with dredging is the disposal of the dredge spoils.
Depending on the level of contamination, disposal options may range from “beneficial use” (e.g. as a soil conditioner or landfill cover), often a source of funds, to disposal in a secure landfill as dewatered contaminated sediment, an option costing on the order of fifty dollars per cubic yard. Consequently, information on contaminant levels in sediments of the study area would be most useful.
Six sections of core Moh 10V from the area upstream of the Route 9 Bridge (Figure 1) were analyzed for copper, lead, zinc, and cadmium as part of a Master’s project of Erika
Zamek at RPI, a graduate student of Richard Bopp. Three of those samples were analyzed for total mercury content by a commercial laboratory (Brooks Rand Ltd.). The results are shown in Table 4 along with typical “geological background” levels that would be expected in uncontaminated fine-grained sediments.
TABLE 4. Trace Metal Levels in Sections of Core Moh 10V.
depth
(cm)
Cu
(ppm)
Pb
(ppm)
Zn
(ppm)
Cd
(ppm)
Hg
(ppm)
0-2
20-24
44-48
64-68
64-68 dup
72-76
84-88
43
56
68
118
180
135
43
52
57
67
67
57
132
143
178
205
230
212
2.2
2.6
2.6
3.9
5.1
3.9
0.13
0.45
0.56
0.68
Background* 25 20 95 0.5
0.18
* Based on data compiled by H.J.M. Bowen in Environmental Chemistry of the Elements,
Academic Press, London, 1979.
As expected for recent sediments of an industrialized drainage basin, most values are significantly elevated above background (see Bopp et al., 2006). From a dredging and disposal perspective, the sediments would likely be considered “moderately contaminated,” a designation discussed further below.
17

These same samples plus the 0-2 cm section of Moh 12 (Figure 1) have been analyzed for polychlorinated biphenyls by commercial laboratories and three of the sections of Moh
10V were analyzed for pesticides. Of the persistent chlorinated pesticides, only DDTderived compounds and dieldrin were typically detected. The results (Table 5) again indicate that the sediments would be classified as “moderately contaminated” with respect to dredging and disposal. The levels of PCBs and pesticides at this site were discussed in basin-wide perspective in Bopp et al. (1998). Also noted were the generally low levels of dioxins and related compounds that were found.
TABLE 5. Levels of PCBs and Pesticides in Cores Moh 10V and Moh 12.
Core depth
(cm) total PCBs
1
(ppm) total DDT
2
(ppb) dieldrin
(ppb)
Moh 10V 0-2
20-24
44-48
64-68
72-76
84-88
0.15
0.43
0.60
1.20
0.43
0.14
4.8
28
16
0.14
0.61
<0.2
Moh 12 0-2
0-2 wet
3
0.13
0.08
1
Total PCBs were reported as the sum of the individual homolog groups (mono- through deca-).
2
Total DDT is the sum of the op'- and pp'- isomers of DDE, DDD, and DDT.
3
All other analyses were carried out on dried aliquots of the core sections.
All analyses were carried out by Axys Analytical Services Ltd. except for the PCB analyses on Moh 10V, 44-48 cm and 84-88 cm. These two sections were analyzed for PCBs by
Philip Analytical Services Inc.
General guidance on dredging, prepared specifically for marinas, but applicable to the water-chestnut infested areas of the Mohawk bordering the Town of Colonie, was published in 2005 by New York Sea Grant. The report entitled Hudson River Marina
Dredging: A Guide for Marina Operators was prepared by Nordica Holochuck, Hudson
Estuary Specialist, and based significantly on a study of existing Marina and ambient sediment contaminant data compiled and interpreted by an RPI graduate student, Michael
Wood, under the supervision of the first author of this report.
18

Should dredging of the Mohawk River adjacent to the Town of Colonie be proposed, several additional samples would have to be collected and analyzed for a more extensive suite of contaminants by a certified laboratory. The results reported above indicate that the sediments will be judged moderately contaminated and eligible for a case-specific beneficial use designation (BUD) that would need to be issued by NYSDEC (see 6
NYCRR Part 360-1.15(b)(7)). Based on the currently available contaminant data, it appears that any dredge spoils from the area should be appropriate for some beneficial use, perhaps as cover material at a landfill or fill at a brownfield site.
Public access to the Mohawk River along the water-chestnut infested areas in the Town of Colonie is limited by generally shallow water depths. As part of this study we conducted a search for information on historical depth soundings in the study area.
Navigation maps for the Hudson basin prepared by the National Oceanic and
Atmospheric Administration end at the Green Island Dam in Troy. No source of navigation maps for the lower Mohawk River was found. Garrett O’Connor of the NYS
Canal Corporation (personal communication) indicated that the agency records of depth soundings in the Mohawk adjacent to the Town of Colonie were confined to the main channel with the possible exception of a single measurement in the water chestnut infested area behind the island just upstream of the Route 9 Bridge.
Measurements of water depth undertaken as part of this study were carried out in two areas – just upstream of the Route 9 Bridge between the island and the east (Colonie) shore (see Figure 1), and in the cove downstream of the Route 87 Twin Bridges adjacent to the Colonie Town Park (see Figure 5). The measuring instrument consisted of an acrylic tube marked off in one inch increments and read to the nearest half-inch. Vertical reference was provided by Canal Corporation personnel at the Guard Gate upstream of
Lock 6 who were contacted by cell phone at the beginning, near the midpoint, and at the end of each survey (Table 6). Over the course of the first survey (Route 9; 5/14/08), stage in the pool varied by only 0.1 foot, from 184.6 to 184.7. It remained constant at
184.6 feet during our measurements in the cove adjacent to the Colonie Town Park
(5/20/08). Horizontal locations (latitude and longitude) were determined using a Garmin e trex 12 channel GPS. The accuracy indicated on the instrument ranged from 14 to 25 feet. The data collected is presented in tabular format in Appendix 2. A summary of the data can be found in Tables 6 and 7. Maps indicating water depths are presented as
Figures 8 and 9. These figures and data can also be supplied in Google Earth format as
.kmz files.
19

TABLE 6. Summary of Water Depth Readings, May 14, 2008.
Area:
Specific
Sites:
Elevation
Reference:
Accuracy:
Mean Depth:
Range:
0 to 1 foot:
1 to 2 feet:
2 to 3 feet:
3 to 4 feet:
Between the island just upstream of the Route 9 Bridge and the southeast (Colonie) shore of the Mohawk River (see Figures 8 and 9).
Fifty -one individual sites located to an accuracy of 14 to 25 feet a Garmin e trex 12 channel GPS.
Latitudes and longitudes and corresponding depths are reported in Appendix 2.
The stage of the pool during our survey was reported as 184.6 to 184.7 feet by New York State
Canal Corporation personnel at the Guard Gate near Lock 6.
Depths were recorded to the nearest 0.5 inches (ca. 0.04 feet).
29.6 inches
5.5 to 68 inches. Survey of areas less than 7 inches was limited by the draft of the boat.
9 sites
14 sites
9 sites
11 sites
Specific
Sites:
Elevation
Reference:
Accuracy:
Mean Depth:
Range:
0 to 1 foot:
1 to 2 feet:
2 to 3 feet:
3 to 4 feet:
>4 feet:
Pattern:
>4 feet: 8 sites
Pattern: Deeper sites, greater than ~3 feet, define a "channel" between the island and the shore.
Such sites are found significantly closer to the shore than to the island.
TABLE 7. Summary of Water Depth Readings, May 20, 2008.
Area: In the cove just upstream of the Town of Colonie Park (see Figures 10 and 11)..
Forty-three individual sites located to an accuracy of 14 to 30 feet a Garmin e trex 12 channel GPS.
Latitudes and longitudes and corresponding depths are reported in Appendix 2.
The stage of the pool was reported as 184.6 feet at the beginning, middle, and end of this survey by New York State Canal Corporation personnel at the Guard Gate near Lock 6.
Depths were recorded to the nearest 0.5 inches (ca. 0.04 feet).
23.2 inches
5 to 103 inches. Survey of areas less than 7 inches was limited by the draft of the boat.
13 sites
19 sites
4 sites
3 sites
4 sites
Deeper sites, greater than ~3 feet, were all located in two distinct areas - at the downstream end of the survey adjacent to the Town boat launch, and at the upstream end of the survey area near the marina.
20

Figure 8. Water depth measurements in the Route 9 Bridge area. Sites are color coded by depth as follows – yellow, 0-1 foot; light blue, 1-2 feet; green, 2-3 feet; dark blue, 3-4 feet; purple, > 4 feet.
21

Figure 9. Water depth measurements in the cove adjacent to the Colonie Town Park.
Sites are color coded by depth as in Figure 8.
22

Each measurement of water depth had a corresponding measurement of “thickness of easily penetrated sediment.” This was accomplished by inserting a copper rod into the sediment (Hilton and Lisle, 1993). The rod was marked off in inches and read to the nearest half-inch at the water’s surface. Sediment thickness was calculated by subtracting the water depth at the site. The data collected is presented in tabular format in Appendix 2. A summary of the data can be found in Table 8. Maps indicating the thickness of easily penetrated sediment are presented as Figures 10 and 11. These figures and data can also be supplied in Google Earth format as .kmz files.
TABLE 8. Summary of Easily-Penetrated Sediment Thickness.
Penetration
0-1 foot
1-2 feet
2-3 feet
3-4 feet
>4 feet
Route 9 Area
(n = 51)
Percent of Sites
Colonie Town Park
(n = 43)
35
18-22*
2
7-9
2-14
20-27
14-27
2-5
21-26
66-73
* A range of values reflects the fact that at some sites it was only possible to
determine a "greater than" estimate of penetration depth. This limitation
resulted from a combination of copper probe length and water depth.
23

Figure 10. Thickness of easily penetrated sediment in the Route 9 area. Values are color coded on the same scale as the depth measurements presented in Figures 8 and 9. At any site where a “greater than” estimate of thickness was obtained (see Table 8), purple (> 4 feet) color coding was used.
24

Figure 11. Thickness of easily penetrated sediment in the cove adjacent to the Colonie
Town Park. Values are color coded as in Figure 10.
25

The generally much thicker layer of fine sediment observed in the cove adjacent to the
Colonie Town Park (median > 4 feet) compared to the Route 9 area (median 1-2 feet) may be related to differences in sediment accumulation history at the two sites (see
Section II, Sediment Accumulation, above). Although cores from both areas had recent net accumulation rates on the order of one or two cm/year (Tables 1 and 3), those from the Route 9 area appeared to have lost a significant amount of sediment to erosion as a result of the 1977 high flow event (Table 2). Cores from the cove adjacent to the Colonie
Town Park showed a more continuous record of deposition back to at least the early
1950s, the limit of Cs-137 dating. Lower susceptibility to scour and erosion in this area is consistent with preservation of a generally thicker layer of fine sediment.
Fine-grained sediment accumulation in these areas may have begun as early as 1912 with the completion of Crescent Dams A, B, and C (http:\\findlakes.com). Changes in river morphology associated with the closing of the dams are recorded on historical USGS topographic maps based on surveys conducted in 1892 and 1925-6 (Figures 12 and 13).
Significant widening of the river and inundation of the floodplain is evident between the two surveys. Much less dramatic changes took place between the 1925-6 survey and the most recent USGS topographic maps which are based on aerial photos and last updated in the late 1970s.
Cores Moh 17 and Moh 18 collected from the cove adjacent to the Colonie Town Park
(Figure 5) were from sites with a total thickness of easily penetrated sediment of approximately 5 feet (Figure 11). Assuming continuous accumulation since 1912 yields a net rate of approximately 1.6 cm per year. This is in good agreement with the radionuclide based estimate of 1.2 cm per year between 1946 and 2008 (Table 3). The slightly higher longer term rate suggests that net accumulation may have slowed a bit as the cove filled in.
Hummel and Kiviatt (2004) reviewed the world literature on water chestnut in 2004.
Since that effort, the following articles dealing with water chestnut have appeared in the scientific literature:
Baldisserotto, C. et al. Responses of Trapa natans L. floating laminae to high concentrations of manganese. Protoplasma (2007) 231: 65–82.
Bolpagni, R. et al. Diurnal exchanges of CO
2
and CH
4
across the water–atmosphere interface in a water chestnut meadow ( Trapa natans L .). Aquatic Botany (2007) 87: 43–
48.
Boylen, C.W. et al. Use of Geographic Information Systems to monitor and predict nonnative aquatic plant dispersal through north-eastern North America. Hydrobiologia
(2006) 570: 243–248.
26

Figure 12a. 1898 USGS topographic map based on a survey conducted in 1892 showing the
Mohawk River in the area of the Route 9 Bridge.
Figure 12b. 1929 USGS topographic map based on a survey conducted in 1925-6. The area shown is approximately the same as in Figure
12a.
Figure 12c. Mid 1980s USGS topographic map based on aerial photos from 1952 and 1954 updated with aerial photos from the late 1970s.
The area shown is approximately the same as in
Figures 12a and b.
27

Figure 13a. 1898 USGS topographic map based on a survey conducted in 1892. Dunsbach Ferry is at the western end of what is currently the cove on the Mohawk River adjacent to the
Colonie Town Park.
Figure 13b. 1929 USGS topographic map based on a survey conducted in 1925-6. The area shown is approximately the same as in Figure
13a.
Figure 13c. Mid 1980s USGS topographic map based on aerial photos from 1952 and 1954 updated with aerial photos from the late 1970s.
The area shown is approximately the same as in
Figures 13a and b.
28

Ding, J. et al. Galerucella birmanica (Coleoptera: Chrysomelidae), a promising potential biological control agent of water chestnut, Trapa natans . Biological Control (2006) 36:
80-90.
Hummel, M. and E. Kiviat. Review of World Literature on Water Chestnut with
Implications for Management in North America. J. Aquat. Plant Manage. (2004) 42: 17-
28.
Hummel, M. and S. Findlay. Effects of water chestnut ( Trapa natans ) beds on water chemistry in the tidal freshwater Hudson River. Hydrobiologia (2006) 559: 169–181
Laba, M. et al. Mapping invasive wetland plants in the Hudson River National Estuarine
Research Reserve using quickbird satellite imagery. Remote Sensing of the Environment
(2008) 112: 286-300.
Marion, L. and J.-M. Paillisson. A mass balance assessment of the contribution of floating-leaved macrophytes in nutrient stocks in an eutrophic macrophyte-dominated lake. Aquatic Botany (2003) 75: 249–260.
Smyth, R.L., M.C. Watzin and R.E. Manning. Investigating public preferences for managing Lake Champlain using a choice experiment. Journal of Environmental
Management (2008) in press.
Strayer, D.L. et al. Invertebrate communities associated with a native ( Vallisneria americana ) and an alien ( Trapa natans ) macrophyte in a large river. Freshwater Biology
(2003) 48, 1938–1949.
Wu, J. and M. Wu. Feasibility study of effect of ultrasound on water chestnuts.
Ultrasound in Med. & Biol. (2006) 32: 595-601.
An understanding of the current science and the ability to evaluate new developments in the area of water chestnut control will support any future efforts to obtain funding from sources such as the NYSDEC Aquatic Invasive Species Eradication Grant Program
(http://www.dec.ny.gov/animals/32861.html).

Net accumulation rates of fine-grained sediment in the water chestnut infested areas of the Mohawk River bordering the Town of Colonie in the Route 9 area and in the cove adjacent to the Colonie Town Park are on the order of 1-2 cm per year.

The Route 9 area appears to have experienced significant erosion associated with the high flow event of 1977 while the cove adjacent to the Colonie Town Park appears to
29

have been depositional since the closure of the Crescent Dams in 1912. As a result, much greater thickness of fine grained sediment is found in the cove.

The available data on contaminant levels in recent sediments of these two areas has been compiled. For dredging purposes, it is most likely that the sediment will be deemed “moderately contaminated” and eligible for beneficial use designation
(BUD).

The first significant data on water levels in these two areas has been produced and presented on maps.

Scientific literature related to water chestnut control has been compiled.
Bopp, R.F., H.J. Simpson, C.R. Olsen, R.M. Trier and N. Kostyk, Chlorinated
Hydrocarbons and Radionuclide Chronologies in Sediments of the Hudson River and
Estuary, New York, Environ. Sci. Technol., 16 , 666-676, 1982.
Bopp, R.F. and H.J. Simpson, Contamination of the Hudson River: The Sediment
Record, In : Contaminated Marine Sediments Assessment and Remediation, pp 401-416,
National Research Council, NAS, Washington, D.C., 1989.
Bopp, R.F., S.N. Chillrud, E.L. Shuster, and H.J. Simpson, Contaminant Chronologies from Hudson River Sedimentary Records. In, The Hudson River Estuary, J. Levinton and J. Waldman eds., Chapter 26, 383-397, Cambridge University Press, January 2006.
Chillrud, S.N. 1996. Transport and fate of particle associated contaminants in the Hudson
River Basin. Ph.D. Thesis. Columbia University, New York. 277 pp.
Dively, C. 2006. Trace Metals in the Upper Hudson: Extending Knowledge on Sources and Tributary Dilution. M.S. Thesis. Rensselaer Polytechnic Institute, Troy, NY. 83pp.
Hilton, S. and T.E. Lisle, 1993. Measuring the Fraction of Pool Volume Filled with Fine Sediment. Res. Note PSW-RN-414. Albany, CA: Pacific Southwest Research
Station, Forest Service, U.S. Department of Agriculture; 11 p.
Olsen, C.R. 1979. Radionuclides, Sedimentation and the Accumulation of Pollutants in the Hudson Estuary. Chillrud, S.N. 1996. Transport and fate of particle associated contaminants in the Hudson River Basin. Ph.D. Thesis. Columbia University, New York.
343 pp.
30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

32
33
34
35
36
28
29
30
31
23
24
25
26
27
19
20
21
22
14
15
16
17
18
10
11
12
13
7
8
5
6
9
3
4
1
2
46
47
48
49
50
51
41
42
43
44
45
37
38
39
40
Depth Soundings, 5/14/2008, Route 9 Bridge Area.
Site #
42.818778
42.817667
42.817639
42.817500
42.817333
42.817222
42.817167
42.817083
42.816611
42.816667
42.816722
42.816722
42.816250
42.816250
42.816139
42.815806
42.815667
42.815583
Latitude
(degrees)
42.819111
42.819056
42.818917
42.818833
42.818972
42.818222
42.818306
42.818389
42.818583
42.818167
42.817556
42.817139
42.818722
42.815500
42.815000
42.815083
42.815167
42.814750
42.814583
42.814417
42.814333
42.813472
42.813417
42.813389
42.812528
42.812194
42.812000
42.811361
42.811028
42.810861
42.810250
42.809944
42.809778
-73.735417
-73.733472
-73.733250
-73.732889
-73.733778
-73.733444
-73.733139
-73.732889
-73.733167
-73.733472
-73.733806
-73.734083
-73.734056
-73.733778
-73.733389
-73.734222
-73.734000
-73.733833
Longitude
(degrees)
-73.734167
-73.733806
-73.733111
-73.732750
-73.732278
-73.732778
-73.733194
-73.733667
-73.734361
-73.734722
-73.735111
-73.735306
-73.735333
-73.733611
-73.734000
-73.734278
-73.734611
-73.734944
-73.734694
-73.734472
-73.734250
-73.734694
-73.735028
-73.735500
-73.736056
-73.735778
-73.735556
-73.736639
-73.736417
-73.736222
-73.737389
-73.737278
-73.737167
65
24
13
12
43
64
12
47
55.5
32.5
19
58.5
27
5.5
45
40
13
44
Water depth
(inches)
25.5
37
36.5
30.5
15
25
41.5
17
27
20.5
13
11
15.5
10
56
21
7
47
13
6
54
68
32.5
15.5
22
39
49.5
11
6
21.5
42.5
29.5
25
Sediment Thickness
(inches)
60.5
49
8.5
5
8
2
3.5
0
59
43
29.5
27.5
1
4
2
0
7.5
21
62
38
15
43
1.5
18
4
7
41.5
23
0
19
8
53
30
19
53
39
47
44
32
18
53.5
22.5
21
0
36.5
14
37
35.5
16
10.5
40
68
14
47
63
86
86
51
27
86
34
37
62.5
34
47
68
40
32
52
Probe depth
(inches)
86
86
45
35.5
23
27
45
17
86
63.5
42.5
38.5
16.5
63
86
40
60
86
60
50
86
86
86
38
43
39
86
25
43
57
58.5
40
65
47

32
33
34
35
36
28
29
30
31
23
24
25
26
27
19
20
21
22
37
38
39
40
41
42
43
14
15
16
17
18
10
11
12
13
7
8
5
6
9
3
4
1
2
Depth Soundings, 5/20/2008, Cove Adjacent to Colonie Town Park.
Site #
42.796361
42.796500
42.796667
42.796806
42.797278
42.797222
42.797028
42.796833
42.797528
42.797694
42.797889
42.798028
42.798222
42.798361
42.798167
42.798139
42.798444
42.798556
Latitude
(degrees)
42.793556
42.794222
42.794806
42.795333
42.795889
42.795500
42.795000
42.794722
42.796111
42.796028
42.795694
42.795611
42.795444
42.798750
42.798917
42.799167
42.799444
42.799528
42.799583
42.799278
42.799139
42.798972
42.798750
42.798444
42.798556
-73.750194
-73.750417
-73.750694
-73.750889
-73.750444
-73.750361
-73.749722
-73.749139
-73.748639
-73.748861
-73.749278
-73.749528
-73.749306
-73.748667
-73.748194
-73.747806
-73.747444
-73.748056
Longitude
(degrees)
-73.753472
-73.753972
-73.754694
-73.755194
-73.754083
-73.753556
-73.752833
-73.752444
-73.753472
-73.753056
-73.752333
-73.751500
-73.750917
-73.748556
-73.748833
-73.748111
-73.748694
-73.749083
-73.749389
-73.749556
-73.749361
-73.749250
-73.749722
-73.733472
-73.733861
22
21
18
23
23
11
6
6
14
10
24
13
19
26
23
11
5
6
Water depth
(inches)
37
53
54
103
5
9
17
18
29
16
22
28
17
71
40
23
12
12
8
24
19
41
15
8
35
86
93
28
85
81
58
21
50
83
69
79
26
39
85
90
70
37
50
Probe depth
(inches)
115
115
115
115
108
68
78
65
72
65
50
57
68
68
67
80
95
90
115
95
95
55
55
50
95 bold italic = greater than measurement listed (limited by length of probe)
Stage
5/14/2008
5/20/2008
Initial
184.7'
184.6'
Mid*
184.7'
184.6'
Final
184.6'
184.6'
* Mid stage was taken after site 17 on 5/14 and after site 24 on 5/20.
Sediment Thichness
(inches)
78
62
61
12
60
41
40
50
79
52
56
37
55
64
72
10
62
58
47
15
44
69
59
55
13
20
59
67
59
32
44
44
55
72
43
56
59
56
76
49
40
42
60
48