11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008

Sediment Assessment of Stormwater Retention Ponds within the Urban Environment of Calgary, Canada

K. Vopicka1*

1 Strategic Planning and Policy, City of Calgary, P.O. Box 2100, Stn. M, LOC #433, T2P 2M5,

Calgary, AB, Canada

*Corresponding author, e-mail krista.vopicka@calgary.ca ABSTRACT The treatment of urban stormwater by retention ponds is known to be effective for water quality improvement as well as storm flow management and in the past two decades has become widely implemented. However, limited research has been conducted on the quality of the resulting sediment within ponds. This research focuses on contaminant concentrations within the sediment from stormwater ponds that have been created in Calgary, Canada. Electrical conductivity and the sodium adsorption ratio consistently exceeded CCME agricultural soil quality guidelines, indicating a city wide salt contamination issue. F3 hydrocarbon fractions, cadmium, chromium, copper, lead and zinc were also identified as parameters of concern. In particular 61 Ave SE Duck pond displayed the greatest diversity and severity of contaminants due to the industrial catchment area. Removal and disposal options were limited due to the characteristics of the sediment. Removal is anticipated to be mechanical as the solids concentrations were greater than the liquid limit of clay. In addition, the examination of the solids content illustrates that all the retention ponds will require the sediment to be dewatered prior to disposal. Disposal options were subsequently restricted to landfill disposal due to salt, metal and/or hydrocarbon parameters exceeding CCME soil guidelines. KEYWORDS Disposal; heavy metals; hydrocarbons; retention pond; salt; sediment. INTRODUCTION Water is rapidly becoming an important commodity and it is necessary that urban centres maintain high water quality to mitigate impact upon downstream communities. Subsequently urban centres need to take the initiative and be proactive in protecting priority watersheds affected by urban activities. Management practices have been established to reduce contaminants from entering the watershed via stormwater by the increasing utilization of retention ponds. These retention ponds are known to be effective for water quality improvement and storm flow management. However the resulting sediment in the ponds requires periodic maintenance to retain water treatment efficiency. Knowledge of retention pond sediment composition is limited within literature, however urban runoff generally contains contaminants which include sediment, nutrients, metals, salt, and hydrocarbons (The City of Calgary, 2000; EPA, 1993a). This is particularly important as the extent of contamination will directly affect the potential maintenance and disposal options of the sediment. The primary objective of this thesis was to provide a base of knowledge on the contaminant concentrations within the sediment in a variety of ponds receiving stormwater from differing

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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008 residential, commercial, industrial and highway land uses. Secondly, sediment removal and disposal were evaluated.

Regulatory legislation Water management is governed by both provincial and federal statutes. Federally, the government takes on a supervisory and enforcement role while provinces have the authority to legislate water supplies, pollution control, irrigation and recreation use (Environment Canada, 1987; BRBC, 2005). Alberta Environment has adopted the federally issued Canadian Council of Ministers of the Environment (CCME) water quality guidelines (CCME, 1999) to supplement provincial legislation. This provides actual parameter restrictions to delineate specific environmental goals for users discharging water. This regulates the quality of the water exiting retention ponds, however currently there are no guidelines that are directly applicable to the deposited sediment within. It should also be noted that CCME sediment guidelines exist but are applicable to natural wetlands with purpose to maintain wetland health. Retention ponds encompassed within this study are not designed to be pristine systems, replace removed wetlands or be maintained as natural ecosystems. Instead the retention ponds are maintained to mitigate water quantity and quality. Therefore CCME sediment criteria were not utilized. Moreover accumulation of sediment is expected to be an ongoing process, requiring periodic removal and disposal. Due to the required ex-situ disposal of sediment and the lack of applicable sediment specific criteria, any sediment removed from the retention ponds will hereafter be classified as a soil and subsequently regulated as such. Urban retention pond induction Surface flow retention ponds have been utilised by The City of Calgary since 1979 when Calgary constructed its first wet pond at 68th Street and 17th Avenue SE to moderate stormwater event volumes reaching the river systems. By 1988 retention ponds were designed as part of the storm drainage systems with a storage capacity to accommodate a 1 in 100 year precipitation event (The City of Calgary, 2006a). During this time it was also recognized that retention ponds demonstrated beneficial water quality improvements as they are efficient at pollutant removal, capable of addressing multiple contaminants, sustainable, require relatively low maintenance, have a high aesthetic appeal and are cost effective (Kadlec and Knight, 1996; Lin et al., 2002; Griffin and Upton, 1999; Mitsch and Gosselink, 1993; Magmedov et al., 1996). This has lead to all new residential subdivisions requiring the installation of retention ponds to treat the stormwater, prior to it discharging into the rivers. SITE SELECTION CRITERIA The retention ponds chosen as sampling sites for this study were selected from Calgary wet ponds and wetlands which have been receiving stormwater for an extensive period of time and subsequently have developed a distinct sediment layer. The intention was to encompass retention ponds that are reaching their water treatment capabilities and will require dredging shortly to maintain treatment efficiency. Furthermore sites were chosen to represent a variety of dominant land uses present within the catchment area, and represent degrees of ongoing development within Calgary. Based on these criteria the following five stormwater facilities were selected:

Deerfoot Trail & Highway 22X pond (Reid Crowther & Partners Ltd., 2000) was constructed in 2001 to treat runoff from a 63.7 ha of highway runoff. Pond design specifics consist of a surface area of 7950 m2, permanent water level (PWL) of 1031.5 m and a pond bottom of 1029.0 m.

2 Sediment Assessment of Stormwater Retention Ponds within the Urban Environment of Calgary, Canada

11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008

The 68 Street SE retention lake was constructed in 1979 and accommodates runoff from an exceptionally large catchment area of approximately 2925 ha (The City of Calgary, 2006b). The land use present within the catchment area consists of residential, parkland, commercial and light industrial. Pond design specifics available include the pond surface area of 20.03 ha, a pond bottom of 1047.62 m and the PWL of 1049.92 m.

The Edgemont wetland was completed in 1996 (IMC Consulting Group Inc., 1995) servicing a designated drainage area of 114.2 ha of residential and parkland land uses. The Edgemont wetland was designed with a permanent water level elevation of 1175.5 m, a pond bottom of 1173.5 m and total surface area of 17768 m2.

Harvest lake construction was completed in 1988. It was designed to treat a drainage area of 390 ha, consisting primarily of residential and parkland land use (The City of Calgary, 2006b). Pond specifics include a surface area of 44587 m2, a permanent water level of 1066.0 m and a set pond bottom of 1062.7 m.

61 Ave SE Duck Pond was constructed in 1985 and designed to treat stormwater originating from a 28 ha catchment area dominated by industrial land use (Westhoff Engineering Resources Inc., 1998). However due to growth of Calgary, the pond currently receives runoff from 1375 ha. Pond design specifics encompass a surface area of 5477 m2, pond bottom of 1032.0 m and a PWL of 1034.0 m.

SAMPLING EVENTS All samples were collected from February 24 to 26, 2004 during the winter freeze. Sediment samples were collected in mid-winter which allowed the samples to be more accurately obtained and mapped. Additionally, winter collection avoided disturbance of the sediments that might occur if accessed by boat (paddle or poling action) and avoided drifting that would occur when utilizing a boat. Discrete grab samples were collected at even intervals from the inlet to the outlet of the pond, following the main flow path, which was determined from the facility design plans. Grab samples were collected using an Eckman dredge, and appropriately preserved and kept on ice. METHODS All of the parameters were analysed using standard methods.

Total solids, fixed solids and volatile solids: Method 2540G (APHA, 1998) Particle size distribution by laser diffraction (Malvern Instruments, 1998) Heavy Metal Concentrations were digested using the Method 3050B (EPA, 1996a)

and analysed using ICP/MS and ICP/OES Total Kjeldahl Nitrogen was digested following the Method 351.2 (EPA, 1993b) and

subsequently analyzed by Semiautomated Colorimetry Total Phosphorus was digested using EPA Method 351.2 (EPA, 1993b) and

subsequently analysed by Semiautomated Colorimetry Petroleum Hydrocarbons by Gas Chromatography (CCME, 2001) Paint Filter Test: Method 9095A (EPA, 1996b) Electrical conductivity, pH and chloride were analysed for all samples using field

probes

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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008

RESULTS Solids The average total solids concentration of each pond was found to be 44.10 %, 30.34 %, 44.40 %, 41.83 % and 38.48 % for Deerfoot Trail & 22X pond, 68 Street SE retention lake, Edgemont wetland, Harvest lake and 61 Ave SE Duck pond respectively. The highest average volatile solids concentration determined was 4.5 % for 61 Ave SE Duck pond, which is well below both sediment and organic soil thresholds. Particle Size Distribution Deerfoot Trail & 22X pond, 68 Street SE retention lake, Harvest lake and 61 Ave SE Duck pond (Figures 1 A, B, D, E) all display a high proportion of sand at the inlet, with the exception of the Edgemont wetland (Figure 1 C).

0

10

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Distance from inlet (m)

Parti

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(%)

sand siltclay

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20 60 100 140 200 290 470 650 830 980 1040

Distance from inlet (m)

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sand siltclay

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7.5 26 55 140

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)sand siltclay

A: Deerfoot Trail & 22X pond B: 68 St SE retention pond C: Edgemont wetland

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30 50 70 90 120 150 180 210 240 270 300 330 360Distance from inlet (m)

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sand siltclay

D: Harvest lake E: 61 Ave SE Duck pond

Figure 1. Particle fraction (%) of each fraction for sand (> 50 microns), silt (50 2 microns) and clay (< 2 microns)

Metals The main summary of the analysed chemical constituents with their respective guidelines are displayed in Table 1. Chromium, copper and lead mean concentrations exceeded guidelines in 61 Ave SE Duck pond while cadmium and zinc mean concentrations exceed guidelines in both 61 Ave SE Duck pond and 68 St SE retention lake. Cadmium (F0.05,4,13 = 14.11), chromium (F0.05,4,13 = 6.65), copper (F0.05,4,13 = 13.17), lead (F0.05,4,13 = 45.82), and zinc (F0.05,4,13 = 15.67) concentrations were determined to be significantly higher in 61 Ave SE Duck pond compared to the remainder of the sites. Additionally, cadmium (F0.05,3,11 = 9.55) and zinc (F0.05,3,11 = 19.59) concentrations were determined to be significantly higher in 68 St SE retention lake.

4 Sediment Assessment of Stormwater Retention Ponds within the Urban Environment of Calgary, Canada

11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008

Table 1. Total chemical concentrations for compounds with soil quality guidelines per sampling location, bolded parameters indicate values that exceed fine-grained CCME agricultural soil criteria (CCME, 1999).

Sample site/ Chemical

concentration (mg/kg)

CCME Guidelines (agricultural)

(mg/kg)

Deerfoot Trail &

22X

68 St SE retention

lake

Edgemont wetland

Harvest lake

61 Ave SE Duck pond

Arsenic 12 Mean = 5 Max = 6 Mean = 7 Max = 8

Mean = 7 Max = 7

Mean = 5 Max = 9

Mean = 5 Max = 6

Barium 750 Mean = 227 Max = 250 Mean = 263 Max = 310

Mean = 315 Max = 330

Mean = 311 Max = 339

Mean = 310 Max = 375

Cadmium 1.4 Mean = 0.6 Max = 0.8 Mean = 1.6 Max = 2.1

Mean = 1.1 Max = 1.7

Mean = 0.8 Max = 1.0

Mean = 49 Max = 64

Chromium 64 Mean = 16 Max = 21 Mean =33 Max = 38

Mean = 27 Max = 31

Mean = 21 Max = 23

Mean = 205 Max = 352

Hexavalent Chromium 0.4

Mean = 0.01 Max = 0.02

Copper 63 Mean = 16 Max = 22 Mean = 41 Max = 48

Mean = 29 Max = 33

Mean = 22 Max = 27

Mean = 69 Max = 89

Lead 70 Mean = 11 Max = 14 Mean = 59 Max = 78

Mean = 20 Max = 25

Mean = 15 Max = 18

Mean = 96 Max = 106

Nickel 50 Mean = 21 Max = 31 Mean = 27 Max = 29

Mean = 32 Max = 33

Mean = 25 Max = 29

Mean = 31 Max = 38

Thallium 1 Mean = 0 Max = 0 Mean = 0 Max = 0

Mean = 0 Max = 0

Mean = 0 Max = 0

Mean =1 Max = 1

Vanadium 130 Mean = 23 Max = 29 Mean = 30 Max = 39

Mean = 31 Max = 32

Mean = 24 Max = 26

Mean = 29 Max = 34

Zinc 200 Mean = 85 Max = 118 Mean= 281 Max = 347

Mean = 178 Max = 233

Mean = 124 Max = 155

Mean = 945 Max = 1220

Nutrients With respect to nutrients, nitrogen and phosphorus were examined. Total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were measured (Table 2) as they are macronutrients which predominantly influence nutrient loading and limit biological activity. Table 2. Total Kjeldahl nitrogen and total phosphorus concentrations of dredge samples per sampling location

Sample ID Total Kjeldahl Nitrogen (mg/kg)

Total Phosphorus (mg/kg)

Deerfoot Trail & 22X 1680.14 1134.60 68 St SE retention lake 3332.27 1185.81

Edgemont Wetland 1717.50 1346.24 Harvest lake 1756.62 739.84

61 Ave SE Duck pond 1661.43 1648.63 Hydrocarbons The averages of F2 (C10-C16) and F3 (C16-C34) concentrations (mg/kg) of each pond were found to be 0.49, 140.75; 1.23, 1923.12; 0.68, 569.11; 0.22, 279.02 and 1.14, 1893.51 for Deerfoot Trail & 22X pond, 68 Street SE retention lake, Edgemont wetland, Harvest lake and 61 Ave SE Duck pond respectively. For all sites, the average concentration and ranges were well below the CCME agricultural soil guideline for the F2 hydrocarbon fraction of 900 mg/kg. With respect to the F3 fraction the average concentrations for 68 St SE retention pond and 61 Ave SE Duck pond exceed the allowable CCME F3 hydrocarbon concentration of 800

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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008 mg/kg. Furthermore the hydrocarbon content of 68 St SE retention pond and 61 Ave SE Duck pond were significantly higher (F0.05,4,10 = 11.64) than the remaining ponds. Additional Sediment Parameters With respect to the average pH values, all retention ponds are within the CCME soil quality guideline range of 6 to 8. The averages electrical conductivity (EC) (dS/m) and Sodium Adsorption Ratio (SAR) of each pond was found to be 2.31, 5.76; 5.84, 10.52; 5.79, 24.83; 2.29, 5.42 and 3.78, 11.65 for Deerfoot Trail & 22X pond, 68 Street SE retention lake, Edgemont wetland, Harvest lake and 61 Ave SE Duck pond respectively. All of the site averages exceeded agricultural soil guideline for EC and SAR of 2.0 dS/m and 5.0. Additionally the electrical conductivity varied significantly between sites (F0.05,4,48 = 6.11) with Edgemont wetland and 68 St SE retention lake being significantly greater compared to the remaining sites. Paint Filter Test Landfill criteria require that any material disposed of within a landfill cannot have any free liquids present. Paint filter test were conducted for all sites and after five minutes all sites failed the test. DISCUSSION The primary objective was to determine the presence and concentration of contaminants in order to understand the extent of contamination of accumulated sediment within the retention ponds. Consequently each parameter was evaluated against the CCME agricultural soil guideline as a baseline comparison, as well as evaluated against literature. The parameters that exceeded the CCME guidelines in every pond were EC and SAR. This indicates that all of the retention ponds within The City of Calgary have contamination problems with salinity and sodicity regardless of the catchment area differences. This is potentially due to the widespread usage of road salts (sodium chloride and calcium chloride) for winter road maintenance (The City of Calgary, 2006c). This illustrates that salt is the primary contaminant of concern for cold climate urban environments. In addition, the remaining parameters varied between retention ponds illustrating differences due to catchment area contributions. It was observed that of all the metals evaluated within this study only cadmium, chromium, copper, lead and zinc accumulated sufficiently to exceed the baseline levels. Moreover the contaminant of greatest concern within the ponds was cadmium. Literature reports of background soil levels (mg/kg) within Alberta are known to be 0.16, 0.01, 20, 12 and 74 for cadmium, chromium, copper lead and zinc respectively (Knight & Klassen, 2005) This illustrates anthropogenic sources are contributing to the contaminant loading of the sediment. Cadmium, chromium, copper, lead and zinc concentrations were subsequently compared to the studies including Kadlec and Knight, 1996; Heal, 1999; Yousef et al., 1994a,b; Vymazal and Krasa, 2003; Marsalek and Marsalek, 1997; Marsalek et al., 1999; Mallin et al., 2002 and Kamalakkannan et al., 2004. The metal concentrations in sediments from other urban retention pond studies have found concentrations (mg/kg) to range between 0.051-53.0 (cadmium), 0.97-128.0 (chromium), 0.45-1441 (copper), 1.5-1047 (lead) and 1.0-779 (zinc). These studies encompass a diverse urban environment including residential, parkland, commercial, roadways and light industrial similar to the urban land uses examined within this study. These concentrations illustrate two important points. Firstly all of the retention ponds within this study had comparable concentrations to those observed in other urban retention pond sediments, with the exception of 61 Ave SE Duck pond. Secondly the ranges found in

6 Sediment Assessment of Stormwater Retention Ponds within the Urban Environment of Calgary, Canada

11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008

literature emphasises the severity of the contamination observed within 61 Ave SE Duck pond. This is especially true for cadmium, chromium and zinc with respective average concentrations (mg/kg) of 49, 205 and 945 which illustrates that sediment from industrial land use is severely contaminated compared to urban retention ponds within other studies. TKN and TP concentrations are not regulated by the CCME soil quality guidelines. Literature reports levels of nitrogen-n in soil from Calgarys urban perimeter to be an average of 3859 mg/kg for an A horizon and 1245 mg/kg for a B horizon (Macmillan, 1987). Consequently all nitrogen concentrations within the retention ponds are similar to the natural soil levels as average TKN concentrations within the ponds were found to range between these natural concentrations. Hydrocarbons were anticipated to be present in urban areas due to fuel storage, automotive wear and maintenance. The two most prominent hydrocarbons fractions found were the F2 and F3 fractions. F3 hydrocarbon anthropogenic sources are related to the handling, transport, storage and disposal of heavy end fuel, oil and grease products within urbanised areas (Allcock et al., 1991; Heal, 1999) while F2 hydrocarbon originates from the subsequent handling, transport, storage and disposal of lighter end fuels. This could be because the light end hydrocarbons are very mobile, are easily volatilized and have a high microbial degradation potential (CCME, 2001; Allcock et al., 1991; Heal, 1999). Conversely, heavy end hydrocarbons such as oil and grease persist longer in the environment, have a stronger association to particulate matter and cannot be easily degraded (Allcock et al., 1991; Heal, 1999). With respect to the industrial sector, oil and greases are more prevalently used and subsequently have an increased potential of entering the environment in areas of high industrial activity (Allcock et al., 1991; Heal, 1999). To illustrate the internal dynamics, correlations were conducted between the contaminant parameters and sediment parameters. It was anticipated that once material enters the system there would be a close association between contaminants and clay particles (Horowitz, 1991). Within each pond only a few contaminants displayed a close affinity to clay particles but this relationship was neither consistent for the contaminant or retention pond. One exception was 61 Ave SE Duck pond, which illustrated a high positive association with the majority of the metal constituents as well as the F3 fraction to clay/silt particles and a negative correlation with sand. Phosphorus also illustrates this trend in the 61 Ave SE Duck pond, which has been observed in other industrial site studies investigated by Verstraeten and Poesen (2002). The only other pond which displayed a strong relationship to phosphorus and clay particles was Edgemont wetland. This is potentially due to the presence of a marsh area between the two cells, which appears to have reduced the phosphorus levels in the latter portion of the pond. With respect to phosphorus the concentrations present represent the phosphorus fraction most easily retained. Specifically soluble reactive phosphorus and phosphorus bound to particles are subject to the greatest mechanical settling (Nungesser and Chimney, 2001). This is reiterated by studies indicating nutrient concentrations are primarily influenced by catchment area erosion or sediment yield variability and to a far lesser degree to variations in input concentrations (Verstraeten and Poesen, 2002). Collectively for metals, hydrocarbons and nutrients correlations suggest that the association of contaminants to small particulates is stronger at high parameter concentrations. This positive relationship with silt and clay is reiterated in the retention ponds with observed high concentration of F3 hydrocarbon fractions present in 68 St SE retention lake and 61 Ave SE Duck pond. The associations are due to the charges of each particle, wherein clay particles have a higher negative charge in relation to surface area than sand with respect to bulk sediment volume. Consequently at higher concentrations contaminants preferentially adhere to the highly charged clay particles (Scholes et al., 1998; Horowitz, 1991).

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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008 The distribution of particles sizes combined with the association of contaminants to smaller particles illustrates an advantageous phenomenon particularly within retention ponds which have high contamination levels. Since sand typically accumulates at the inlet this particulate fraction forms the bulk of the sediment present at the inlet. Sand also has the lowest association to contaminants. This trend can be utilized to facilitate sediment disposal wherein the less contaminated inlet portion of retention ponds can be dredged and handled separately. Disposal With insight into the properties of sediment, removal and disposal options can be investigated. Considerations of each option will depend on the physical and chemical properties of the sediment as well as monetary considerations, regulatory viability, and public acceptance. To complete the disposal of sediment considerations it will be necessary to consider removal options and possible treatment requirements. Sediment volumes must be determined to assess the amount of sediment in the retention ponds requiring disposal. Sediment volumes were derived from measured surface areas and collected sediment depth taken along the main flow path. With respect to disposal, the approximate sediment volumes (m3) were 2284, 5221, 15192, 28447 and 172058 for 61 Ave SE Duck pond, Deerfoot Trail & 22X pond, Edgemont wetland, Harvest lake and 68 St SE retention pond, respectively. A limiting factor with respect to sediment removal is the solids content. Generally sediment behaves as either a solid, semisolid or liquid depending upon the solids content. These limits are defined as 30 % solids for the liquid limit, which is the transition point between liquid and semi solid, and 69 % solids for the plastic limit, which is the transition point between semi solids and solids. The average percent solids for the retention ponds range between 38 to 44 % with the exception of 68 St SE retention lake which approached the liquid limit of clay. Therefore it is recommended that the sediment be dredged mechanically. 68 St SE retention lake on the other hand will require hydraulic dredging if all sediment is intended to be removed as the latter half of the pond is well below the liquid limit. Landfills can accept a broad array of waste products but restrictions include: no free liquids, does not contain a restricted waste, waste contains concentrations less than the regulated limits, does not contain a substance that ignites or propagates combustion and has a pH less than 12.5 (Alberta Environment, 1995). Disposal into a landfill should only be considered once other disposal options are exhausted. This is typically the most expensive disposal option since material must be transferred to the landfill site, possibly dewatered to achieve a high solids content and has large associated tipping fees. To determine the disposal possibility of sediment within a landfill, metal concentrations, pH and solids content need to be addressed. Comparison of all metals regulated from each pond indicates that metal concentrations found were under the regulated criteria. pH was not a concern as it did not exceed the regulated limits and therefore does not restrict disposal. However all the sediment samples failed the standard paint filter test illustrating the presence of free liquids. Therefore all ponds could potentially be disposed of directly into a landfill site, based on these preliminary results, if dewatered. To estimate the landfill disposal costs it will be assumed that the material has an average weight of 1388 kg/m3. Consequently for every 1000 m3 of sediment there will be 1388 tonnes of sediment to dispose of. Normal landfill rates are $42/tonne for stabilised material (The City of Calgary, 2005). At this rate total tipping charges would therefore be $182,000; $10,000,000; $886,000; $1,660,000; and $133,000 for Deerfoot Trail & 22X pond, 68 St SE retention lake, Edgemont wetland, Harvest lake, and 61ave SE Duck pond, respectively. These costs do not include trucking, dewatering or removal costs illustrating that disposal of sediment from retention ponds will not be completed without very large associated costs.

8 Sediment Assessment of Stormwater Retention Ponds within the Urban Environment of Calgary, Canada

11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008

CONCLUSIONS All the retention ponds within the study were deemed to be contaminated as they

exceeded criteria for one or more of the following parameters: salt, cadmium, chromium, copper, lead, zinc, and/or F3 fraction hydrocarbons

A strong positive relationship was found between heavy metals, F3 fraction hydrocarbons and phosphorus when correlated to finer particulates. However this was only observed at higher contamination concentrations.

A primary sedimentation area or forebay displayed useful characteristics in sediment disposal. Although these would require more frequent maintenance, due to sediment volume, the sediment removed from these forebays would ultimately have a lower concentration of contamination. The lower concentration is due to the greater volume accumulations, higher proportion of large particulates and the lower contamination association with the large particulate sediment, which could potentially lower disposal costs.

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10 Sediment Assessment of Stormwater Retention Ponds within the Urban Environment of Calgary, Canada

Macmillan, R.A. (1987). Soil survey of the Calgary urban perimeter: Alberta soil survey report No.45. Edmonton: Terrain Science Department.

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ABSTRACTKEYWORDS INTRODUCTIONSITE SELECTION CRITERIASAMPLING EVENTS RESULTS Nutrients Hydrocarbons

DISCUSSIONCONCLUSIONSREFERENCES