Location: Ministry Home > Publications > Technical Studies and Reports > 4022e4.pdf > HTML version

This is a HTML version of the original PDF document. The HTML version is being provided for reading purposes only and is not the official version of the document.

4. PREDICTIVE WATER AND SEDIMENT QUALITY MODEL

4.1 Objective

The objective of this component was to construct a water and sediment quality model to assess the level of cleanup required at the Deloro Mine Site for downstream arsenic, cobalt and nickel concentrations to reach, or fall below, provincial water and sediment quality objectives for the protection of aquatic life. In this exercise, the interim provincial water quality objective (PWQO of 5 µg/L (MOE 1999) was used for arsenic because the MOE has stated that one of the objectives of the final cleanup plan for the Deloro Mine Site is to meet this interim PWQO.

4.2 Scope

The Moira River Model (MRM) was built to simulate long-term water and sediment quality in the Moira River system between the Deloro Mine Site and the outlet of Stoco Lake. The model was based on average, long-term monthly water flows. The model incorporated sediment - water interaction and was calibrated to reflect general, long-term, water quality trends observed over the last 10 years. As such, the model may not adequately reflect the effects of short-term, sporadic events, such as flooding events, dry spells, or the effects of spring and fall turnover in lakes. However, the model included all of the most important processes that control long-term average metal concentrations in the Moira River system. The model was developed as a decision tool, and predictions are meant to serve as general indicators of the response of the Moira River system to future cleanup actions at the Deloro Mine Site.

4.3 Approach

The Moira River system between the Deloro Mine Site and the outlet of Stoco Lake was divided into nine model segments (Figure 4.3-1):

• Deloro Mine Site to Young's Creek;
• Young's Creek to half way to Bend Bay;
• Remaining distance to Bend Bay;
• Bend Bay;
• Bend Bay to West Moira Lake;.
• West Moira Lake;
• East Moira Lake;
• East Moira Lake to Stoco Lake; and
• Stoco Lake.

RIVER SEGMENTS FOR WATER AND SEDIMENT QUALITY MODEL

REFERENCE
BASE MAP PROVIDED BY GIS GOLDER MISSISSAUGA

SCHEMATIC ONLY NOT TO SCALE

The MRM was built using STELLA software (HPS 1997). Each model segment incorporates advective transport, chemical partitioning, sediment deposition and resuspension, sediment bioturbation and sediment burial (Figure 4.3-2). The MRM was calibrated using historical water flow and water quality data and results from recent sediment sampling (as described in Section 2.2). Calibration also included adapting partition, deposition, burial and resuspension rates taken from relevant, available literature. The calibrated MRM was then used to determine the level of cleanup required at the Deloro Mine Site for downstream arsenic, cobalt and nickel concentrations to reach, or fall below, provincial water quality objectives (PWQOs) for the protection of aquatic life.

Arsenic, cobalt and nickel were selected from the metals of concern discussed in Sections 2.1 and 2.2, because:

• arsenic and cobalt concentrations consistently exceeded PWQOs throughout the Moira River system; and,
• other heavy metals, including silver, copper and lead, will exhibit similar behavioural patterns as one of the chosen substances (i.e., in-stream concentrations will increase or decrease in the same fashion as predicted for one of the modelled substances).

Figure 4.3-2
Illustration of the Pathways Included in the Moira River Model

4.4 Model Construction and Calibration

The general set-up of the MRM is described in Section 4.4.1, followed by a discussion of how water flows and the movement of suspended sediments were incorporated into the MRM (Sections 4.4.2 and 4.4.3, respectively). Section 4.4.4 describes the chemical component of the MRM in greater detail and the general process used to calibrate the model for arsenic, cobalt and nickel.

4.4.1 Model Set-up

The physical dimensions of each of the nine model segments are summarized in Table 4.4-1. Each model segment was sub-divided into three compartments: water, surface sediment (the uppermost 10 cm of the sediment profile) and deep sediment (below a sediment depth of 10 cm). The water compartment in each model segment was assumed to be completely mixed, an assumption supported by the absence of thermal stratification in Moira and Stoco lakes (Section 2.1). Surface sediments were also assumed to be completely mixed to a depth of 10 cm to account for bioturbation by benthic invertebrates (Diamond 1995, Bosworth and Thibodeaux 1990). The deep sediments do not mix in the model; they act as a sink for buried sediment and associated heavy metals (Figure 4.3-2).

Table 4.4-1
The Physical Dimensions of Each Model Segment

Segment		Depth (m)	Width (m)	Surface Area (m2)	Volume (m3)	Source
Number	Name
1	Deloro to Young's Creek	1	30	114 000	114 000	Based on data from Section 2.3
2	Young's Creek to half way to Bend Bay	1	30	186 000	186 000	Based on datafrom Section 2.3
3	Remaining distance to Bend Bay	1	30	214 500	214 500	Based on data from Section 2.3
4	Bend Bay	1	-	210 000	210 000	Diamond (1995)
5	Bend Bay to West Moira Lake	1	30	102 000	102 000	Based on data from Section 2.3
6	West Moira Lake	3.5	-	2 160 000	7 560 000	Diamond (1995)
7	East Moira Lake (EML)	4	-	6 110 000	24 440 000	Diamond (1995)
8	EML to Stoco Lake	2	50	890 000	1 780 000	Based on data from Section 2.3
9	Stoco Lake	4	-	5 630 000	22 520 000	MOE (1972, 1974)

The concentration of arsenic, cobalt or nickel in the water compartment of a given model segment was calculated based on the following relationship:

concentration at time "t" = mass at time "t" / water volume at time "t"

where,

mass at time "t" = mass at time "t-1" + the change in mass from time "t-1" to time "t" (Δm)

and,

Δm = mass in - mass out - mass settled + mass resuspended + mass diffused

Similarly, arsenic, cobalt or nickel levels in the surface sediments of a given model segment were calculated based on the same relationship where:

concentration at time "t" = mass at time "t" / sediment volume at time "t"

and,

Δm = mass settled - mass resuspended - mass diffused - mass buried

The chemical mass moving in and out of each model segment was controlled by water flow. Sediment interactions (i.e., settling, resuspension and burial) were controlled, in part, by the rates at which sediments settled, became resuspended or were buried. Sediment settling, resuspension and burial rates operated independently from the chemical being modelled (i.e., they were the same for arsenic, cobalt and nickel).

4.4.2 Water Flows

Source Data

The sources of the water flow data used in the MRM are given in Table 4.4-2. Monthly precipitation data from 1925 to 1990 were taken from an Environment Canada monitoring station located in Tweed, Ontario (Environment Canada 1994). Estimates of monthly evapotranspiration rates were derived from MOE (1974). Average, monthly net precipitation rates used in the MRM are illustrated in Figure 4.4-1.

Table 4.4-2
Source of Water Flow Data Used to Build the Moira River Model

^a1 = Environment Canada (1999), 2 = WSC (2000) and 3 = CG&S (1999).

Figure 4.4-1
Average, Monthly Net Precipitation Rates Used in the Moira River Model

Water Balance

The long-term water balance for the Moira River system was constructed based on the assumption that the volume of water held within each model segment was constant over time. Therefore,

segment outflow = upstream inflow + tributary inflow + net precipitation

Tributaries included in the model were: the Black and Skootamatta rivers (discharging to the Moira River between Moira and Stoco lakes); the Clare River (discharging to Stoco Lake); Young's Creek (discharging to the Moira River downstream of Highway 7); and, Madoc Creek (discharging to West Moira Lake).

Long-term, average monthly flow rates were calculated for the Black, Skootamatta and Clare rivers and for the Moira River at Deloro. For Young's Creek, the average annual flow rate calculated by CG&S (1999) was equivalent to 0.2% of the long-term, average annual flow rate observed in the Moira River at Deloro, so monthly flows in Young's Creek were assumed to be equal to 0.2% of monthly flows observed in the Moira River at Deloro. Similarly, Diamond (1995) noted that flows in Madoc Creek, a small tributary to West Moira Lake, were approximately equal to 10% of the inflow from the Moira River, so monthly flows in Madoc Creek were assumed to be equal to 10% of monthly flows in the Moira River at the inlet to West Moira Lake.

Net precipitation, as defined in Figure 4.4-1, was included in the Bend Bay, West Moira Lake, East Moira Lake and Stoco Lake model segments, but it was not included (i.e., set to zero) in the five river segments. It was assumed that evaporation and precipitation would only be significant in large open water areas with relatively still waters. The gain or loss of water through evaporation and precipitation represented a small fraction of the water flowing through each lake segment (Table 4.4-3), and the inclusion of net precipitation in the river segments would not substantially alter the conclusions of this study.

To calibrate the water balance, monthly outflows from the Stoco Lake model segment were compared to average monthly flow rates recorded at the Thomasburg monitoring station. Only two years worth of data were available from the Thomasburg monitoring station (Table 4.4-2). To increase the amount of data available for comparison, data from the Foxboro monitoring site were transformed using the following relationship:

Q_Tx = Q_Fx * ((Q_Fa - Q_Ta) / Q_Fa)

where: Q_Tx = monthly flow at Thomasburg in Year "x" (m³/s)

Q_Fx = monthly flow at Foxboro in Year "x" (m³/s)

Q_Fa = average monthly flow at Foxboro between 1969 and 1970 (m³/s)

Q_Ta = average monthly flow at Thomasburg between 1969 and 1970 (m³/s)

Stream flows in Clare River were adjusted until the outflow from Stoco Lake matched with the average monthly flow record developed for Thomasburg. The resulting water balance is summarized in Table 4.4-3.

Table 4.4-3
Water Flow Through The Moira River Model

Model Segment	Parameter	Month
		Jan	Feb	Mar	April	May	June	July	Aug	Sept	Oct	Nov	Dec
Deloro to Young's Creek	Upstream inflow (m3/s)	3.5	3.0	7.7	14.3	5.2	1.7	0.6	0.3	0.6	1.3	3.5	4.2
	Outflow (m3/s)	3.5	3.0	7.7	14.3	5.2	1.7	0.6	0.3	0.6	1.3	3.5	4.2
	Retention time (day)	0.4	0.4	0.2	0.1	0.3	0.8	2.3	4.7	2.1	1.0	0.4	0.3
Young's Creek to half way to Bend Bay	Upstream inflow (m3/s)	3.5	3.0	7.7	14.3	5.2	1.7	0.6	0.3	0.6	1.3	3.5	4.2
	Young's Creek (m3/s)	0.007	0.006	0.016	0.029	0.011	0.004	0.001	0.001	0.001	0.003	0.007	0.009
	Outflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.8	0.6	0.3	0.6	1.3	3.5	4.2
	Retention time (day)	0.6	0.7	0.3	0.2	0.4	1.2	3.7	7.7	3.4	1.6	0.6	0.5
Remaining distance to Bend Bay	Upstream inflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.8	0.6	0.3	0.6	1.3	3.5	4.2
	Outflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.8	0.6	0.3	0.6	1.3	3.5	4.2
	Retention time (day)	0.7	0.8	0.3	0.2	0.5	1.4	4.3	8.8	3.9	1.9	0.7	0.6
BendBay	Upstream inflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.8	0.6	0.3	0.6	1.3	3.5	4.2
	Net precipitation (m3/s)	0.006	0.004	0.003	0.001	-0.001	-0.002	-0.004	-0.002	0.004	0.003	0.005	0.006
	Outflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.7	0.6	0.3	0.6	1.3	3.5	4.2
	Retention time (day)	0.7	0.8	0.3	0.2	0.5	1.4	4.3	8.7	3.8	1.8	0.7	0.6
Bend Bay to West Moira Lake	Upstream inflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.7	0.6	0.3	0.6	1.3	3.5	4.2
	Outflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.7	0.6	0.3	0.6	1.3	3.5	4.2
	Retention time (day)	0.3	0.4	0.2	0.1	0.2	0.7	2.1	4.2	1.8	0.9	0.3	0.3
West Moira Lake	Upstream inflow (m3/s)	3.5	3.0	7.7	14.3	5.3	1.7	0.6	0.3	0.6	1.3	3.5	4.2
	Madoc Creek (m3/s)	0.35	0.30	0.77	1.43	0.53	0.17	0.06	0.03	0.06	0.13	0.35	0.42
	Net precipitation (m3 /s)	0.06	0.05	0.03	0.01	-0.01	-0.02	-0.04	-0.03	0.04	0.03	0.06	0.06
	Outflow (m3/s)	4.0	3.4	8.6	15.7	5.8	1.9	0.6	0.3	0.7	1.5	3.9	4.7
	Retention time (day)	22	26	10	6	15	46	149	311	117	59	22	19
East Moira Lake (EML)	Upstream inflow (m3/s)	4.0	3.4	8.6	15.7	5.8	1.9	0.6	0.3	0.7	1.5	3.9	4.7
	Net precipitation (m3/s)	0.16	0.13	0.09	0.03	-0.03	-0.07	-0.11	-0.07	0.11	0.10	0.16	0.18
	Outflow (m3/s)	4.1	3.5	8.6	15.8	5.7	1.8	0.5	0.2	0.9	1.6	4.1	4.8
	Retention time (day)	69	81	33	18	49	154	599	1346	331	178	70	58
EML to Stoco Lake	Upstream inflow (m3/s)	4.1	3.5	8.6	15.8	5.7	1.8	0.5	0.2	0.9	1.6	4.1	4.8
	Black River (m3/s)	4.4	3.6	9.3	17.7	7.3	2.8	1.4	1.3	1.4	1.9	4.3	5.4
	Skootamatta River (m3/s)	7.6	7.0	15.3	30.0	12.5	4.1	1.5	1.0	1.5	3.1	6.9	9.1
	Outflow (m3/s)	16.1	14.0	33.3	63.4	25.5	8.7	3.4	2.5	3.8	6.6	15.2	19.4
	Retention time (day)	1.3	1.5	0.6	0.3	0.8	2.4	6.1	8.2	5.5	3.1	1.4	1.1
Stoco Lake	Upstream inflow (m3/s)	16.1	14.0	33.3	63.4	25.5	8.7	3.4	2.5	3.8	6.6	15.2	19.4
	Clare River (m3/s)	9.0	8.9	18.7	33.1	13.8	2.5	0.4	0.3	0.2	0.3	1.3	2.4
	Net precipitation (m3 /s)	0.15	0.12	0.08	0.03	-0.03	-0.06	-0.11	-0.07	0.10	0.09	0.15	0.17
	Outflow (m3/s)	25.3	23.1	52.1	96.6	39.3	11.1	3.7	2.7	4.0	7.0	16.7	21.9
	Retention time (day)	10	11	5	3	7	24	71	95	65	37	16	12

4.4.3 Suspended Solids

Source Data

The turbidity and total suspended solids (TSS) data used to calibrate the MRM were obtained from a series of water quality sample stations maintained by the Ontario Ministry of the Environment (see Section 2.1). TSS monitoring has been limited to occasional sampling since 1998. Turbidity measurements are available from 1967 to the end of 1998. Using the available TSS information, a turbidity to TSS relationship was developed (Figure 4.4-2). Long-term, average annual turbidity levels were transformed into TSS concentrations using this relationship (Table 4.4-4). The resulting annual average TSS concentration for West Moira Lake (i.e., 3.9 mg/L) matched the annual average TSS concentration reported by Diamond (1995).

Figure 4.4-2
Total Suspended Solids Concentrations in the Moira River System as a Function of Turbidity
as a Function of Turbidity

Table 4.4-4
Average Annual Total Suspended Solids and Turbidity Levels in the Moira River System

^a Derived based on the relationship illustrated in Figure 4.4-2.
- = no data.

Sediment Balance

A sediment mass balance for the Moira River system was constructed based on the assumption that sediment density, sediment porosity, the depth of the surface sediment layer and the amount of suspended sediment contained within each model segment were constant over time. Under these conditions,

outgoing sediment mass = total incoming sediment mass - buried sediment mass

or

Q_out* [TSS] = Q_in*[TSS]_in - V_b*A*(1-φ)*ρ*C

where: Q_out = outflow from model segment "x" (m³/s)

[TSS] = TSS concentration in model segment "x" (mg/L)

Q_in = inflow to model segment "x" (m³/s)

[TSS]_in= TSS concentration in segment "x" inflow (mg/L)

V_b= burial velocity (mm/yr)

A = active sediment area (m²)

φ = sediment porosity (unitless)

ρ = sediment density (kg/L)

C = unit conversion factor

Each parameter listed above was assigned a value based on available literature. The rate at which sediments were buried (V_b) and the initial TSS concentration in each segment ([TSS]) were then adjusted to achieve a balance. Values assigned to each parameter are listed in Table 4.4-5, and the resulting sediment balance is summarized in Table 4.4-6.

Table 4.4-5
Values Used to Achieve a Sediment Balance for the Moira River System

Model Segment	Sediment		TSS		Active Sediment Areaa(%)	Burial Velocity
	Density (kg/L)	Porosity (unitless)	Initial (mg/L)	Final (mg/L)		Initial mm/yr)	Final (mm/yr)
Deloro to Young's Creek	2.2b	0.98cd	3.6e	3.6	20f	0.236f	0.205
Young's Creek to half way to Bend Bay			3.6e	3.6	20f	0.236f	0.207
Remaining distance to Bend Bay			3.6f	3.6	20f	0.236f	0.218
Bend Bay			3.5b	3.5	80b	1.180f	1.314
Bend Bay to West Moira Lake			3.5f	3.5	20f	0.236f	0.202
West Moira Lake			3.9b	3.1	33b	2.360c	2.054
East Moira Lake (EML)			3.9b	2.0	33b	3.530d	1.618
EML to Stoco Lake			3.5e	3.0	25f	1.765f	1.811
Stoco Lake			4.8e	2.9	33f	3.530f	3.524

^aActive sediment area = fraction of bottom area where sediment accumulates.

^bBased on information from Diamond (1995).

^cBased on information from Mudroch and Capobianco (1980).

^dBased on information from Cornett et al. (1987).

^eBased on information in Table 4.4-4.

^fAssumed value based on the characteristics of the other model segments.

Sediment Settling and Resuspension

For sediment density, sediment porosity and the depth of the surface sediment layer to be constant over time within each model segment,

resuspended sediment mass = settled sediment mass – buried sediment mass

or,

V_r*A*(1- φ )*ρ = V_s*A*[TSS]*C - V_b*A*(1- φ)*ρ

where: V_r = resuspension velocity (mm/yr)

Table 4.4-6
Sediment Balance for the Moira River System

Model Segment	Parameter	Month (kg/month)
		Jan	Feb	Mar	April	May	June	July	Aug	Sept	Oct	Nov	Dec
Deloro to Young's Creek	Upstream sediment	34018	26411	74300	132694	50946	16468	5581	2715	5938	12705	32562	40213
	Buried sediment	16	12	35	63	24	8	3	1	3	6	15	19
	Outgoing sediment	34002	26399	74265	132631	50922	16460	5578	2714	5936	12699	32546	40194
Young's Creek to half way to Bend Bay	Upstream sediment	34002	26399	74265	132631	50922	16460	5578	2714	5936	12699	32546	40194
	Young's Creek	69	54	152	271	104	34	11	6	12	26	66	82
	Buried sediment	27	21	58	104	40	13	4	2	5	10	25	31
	Outgoing sediment	34045	26432	74359	132798	50986	16481	5585	2717	5943	12715	32587	40244
Remaining Bay distance to Bend	Upstream sediment	34045	26432	74359	132798	50986	16481	5585	2717	5943	12715	32587	40244
	Buried sediment	32	25	70	126	48	16	5	3	6	12	31	38
	Outgoing sediment	34012	26407	74289	132672	50938	16465	5580	2715	5937	12703	32557	40206
Bend Bay	Upstream sediment	34012	26407	74289	132672	50938	16465	5580	2715	5937	12703	32557	40206
	Buried sediment	724	566	1669	3023	1173	397	164	85	101	259	695	860
	Outgoing sediment	33288	25841	72620	129650	49765	16068	5415	2630	5836	12444	31862	39346
Bend Bay to West Moira Lake	Upstream sediment	33288	25841	72620	129650	49765	16068	5415	2630	5836	12444	31862	39346
	Buried sediment	14	11	31	55	21	7	2	1	2	5	14	17
	Outgoing sediment	33274	25830	72589	129594	49744	16062	5413	2629	5834	12438	31848	39329
West Moira Lake	Upstream sediment	33274	25830	72589	129594	49744	16062	5413	2629	5834	12438	31848	39329
	Madoc Creek sediment	4268	3313	9310	16622	6380	2060	694	337	748	1595	4085	5044
	Buried sediment	4721	3695	11083	20175	7854	2699	1181	620	597	1661	4528	5617
	Outgoing sediment	32821	25448	70816	126041	48270	15422	4926	2346	5985	12373	31405	38756
East Moira Lake (EML)	Upstream sediment	32821	25448	70816	126041	48270	15422	4926	2346	5985	12373	31405	38756
	Buried sediment	10768	8404	24644	44569	17269	5816	2360	1213	1549	3873	10321	12782
	Outgoing sediment	22053	17044	46173	81472	31000	9606	2566	1133	4437	8500	21083	25974
EML to Stoco Lake	Upstream sediment	22053	17044	46173	81472	31000	9606	2566	1133	4437	8500	21083	25974
	Black River sediment	37880	27944	79864	146463	62735	23341	11830	10974	11563	16069	35342	46703
	Skootamatta R. sediment	69300	58058	139232	263762	114505	36135	13950	9276	13230	28350	60752	82833
	Buried sediment	791	1085	955	4372	3956	1589	1370	1412	353	618	-2	1235
	Outgoing sediment	128442	101961	264313	487326	204285	67494	26976	19970	28878	52300	117179	154274
Stoco Lake	Upstream sediment	128442	101961	264313	487326	204285	67494	26976	19970	28878	52300	117179	154274
	Clare River sediment	98568	89187	204317	351150	153033	26817	4472	3359	1664	3695	14190	25843
	Buried sediment	27995	25416	59820	104062	45552	8735	2366	1668	-16	873	4085	7556
	Outgoing sediment	199014	165733	408809	734414	311766	85576	29082	21661	30558	55123	127285	172560

A = active sediment area (m²).

φ = sediment porosity (unitless)

ρ = sediment density (kg/L)

V_s = settling velocity (mm/yr)

[TSS] = TSS concentration (mg/L)

C = unit conversion factor

V_b = burial velocity (mm/yr)

All of these parameters, except for resuspension and settling velocity, have been defined by the sediment balance described above (Table 4.4-5). Settling velocities (V_s) were initially derived from sedimentation rates and TSS concentrations reported by Diamond (1995) using the following relationship:

settling velocity (m/yr) = sedimentation rate (g/m²/yr) / TSS concentration (g/m³)

The resulting values were then scaled to reflect the changes in burial velocity required to achieve a sediment balance (i.e., final settling velocity = initial settling velocity * final burial velocity / initial burial velocity) (Table 4.4-7). The new settling rates were plugged back into Equation (9) to produce the corresponding resuspension velocities listed in Table 4.4-7.

Table 4.4-7
Settling and Resuspension Rates in the Moira River System

^aAssumed value based on settling velocities in East and West Moira Lake.
^bBased on information from Diamond (1995).

4.4.4 Selected Metals of Concern

Model Equations

As stated in Section 4.4.1, the change in mass of arsenic, cobalt or nickel in the water compartment of a given model segment was calculated based on the following relationship:

Δm_water = mass in - mass out - mass settled + mass resuspended + mass diffused

or,

Δm_water = Q_in*[metal]_in - Q_out*[metal] - V_s*A*F_pw*[metal]*C + V_r*A*[metal]_sed*C +
V_D*A* (F_ds*[metal]_sed - F_dw*[metal])*C

where: Q_in = inflow to model segment "x" (m³/s)

[metal]_in = total concentration of metal "z" in inflow to model segment "x" (µg/L)

Q_out = outflow from model segment "x" (m³/s)

[metal] = total concentration of metal "z" in model segment "x"(µg/L)

V_s = settling velocity (mm/yr)

A = active sediment area (m²)

F_pw = fraction of metal "z" associated with suspended sediment (unitless)

V_r = resuspension velocity (mm/yr)

metal]_sed = total concentration of metal "z" in model segment "x" sediment (µg/L)

C = unit conversion factor

V_D = diffusion velocity (mm/yr)

F_ds = fraction of metal "z" dissolved in porewater (unitless)

F_dw = fraction of metal "z" dissolved in water (unitless)

Changes in the mass of arsenic, cobalt or nickel contained in surface sediments were calculated using a similar relationship:

Δmsed = mass settled - mass resuspended - mass diffused - mass buried

or,

Δmsed = V_s*A*F_pw*[metal] – V_r*A*[metal]_sed – V_D*A*(F_ds*[metal]_sed – F_dw*[metal])*C –
V_b*A*[metal]_sed

where: V_b = burial velocity (mm/yr)

Flow rates (Q), burial velocities (V_b), settling velocities (V_s), resuspension velocities (V_s) and active sediment areas (A) for each model segment have been defined through the water and sediment balances discussed in Sections 4.4.2 and 4.4.3, respectively. The remaining parameters were defined as follows:

Diffusion velocities (V_D) for arsenic, cobalt and nickel were derived using the following formula (Chapra 1997):

V_D = 69.35 * φ * MW_ion^2/3

where: φ = sediment porosity (unitless)

MW_ion = molecular weight of the dominant ion (g/mol)

The dominant ionic form for arsenic, cobalt and nickel were assumed to be H₂AsO₄ (Cornett et al. 1987), Co and Ni (Cornett et al. 1987), respectively.

The fraction of chemical dissolved in water (F_dw) was defined as:

F_dw = 1/ (1 + K_w* [TSS])

where: K_w = partition coefficient for water (L/mg)

[TSS] = concentration of total suspended solids (mg/L)

F_pw = 1 -F_dw

The fraction of chemical dissolved in sediment porewater (F_ds) was defined as:

F_ds = 1/ (1 + K_s* (1-φ) * ρ)

where: K_s = partition coefficient for sediment (L/g)

φ = sediment porosity (unitless)

ρ = sediment density (kg/L)

Tributary and Upstream Input

Young's Creek, Madoc Creek, the Black, Skootamatta and Clare rivers and the Moira River upstream of the Deloro Mine Site were assigned arsenic, cobalt and nickel concentrations based on average concentrations observed in each waterbody over the past 10 years (i.e., January 1990 to January 2000)

Table 4.4-8
Average Arsenic, Cobalt and Nickel Concentrations in Tributaries to the Moira River
and in the Moira River Upstream of the Deloro Mine Site (1990 to 2000)

^aSample locations are shown on Figure 2.1-1.

Loading from the Deloro Mine Site

The amount of arsenic, cobalt and nickel reaching the Moira River at or near the Deloro Mine Site was determined by examining water quality results from the following monitoring stations:

• W1 – at Malone upstream of Deloro;
• W2 – at Highway 7 bridge downstream of Deloro;
• DM7 – at Highway 7 bridge downstream of Deloro;
• DM1 – on Young's Creek near confluence with Moira River; and,
• DM8 – on Moira River immediately below confluence with Young's Creek.

Loading rates were calculated using mean annual concentrations for the past 10 years and average annual flow in Moira River recorded at Highway 7, as shown in Table 4.4-9.

Table 4.4-9
Loading Rates from the Deloro Mine Site to the Moira River

Parameter		Units	Arsenic	Cobalt	Nickel
Between Deloro and Highway 7 - Deloro Mine Site
Water flowa	Upstream of Deloro	m3/s	4.18
	Upstream of Young's Creek	m3/s	4.18
Concentration	Upstream of Deloro	µg/L	1.0	0.7	2.3
	Upstream of Young's Creek	µg/L	43.3	4.5	5.6
Loading rates	Upstream of Deoloro	kg/yr	132	93	304
	Upstream of Young's Creek	kg/yr	5713	594	739
	Deloro Mine Site	kg/yr	5581	501	435
Between Highway 7 and Downstream of Young's Creek - immediately below Deloro Mine Site
Water flowa	Upstream of confluence with Young's Creek	m3/s	4.18
	Young's Creek	m3/s	0.01
	Downstream of confluence with Young's Creek	m3/s	4.19
Concentration	Upstream of Young's Creek	µg/L	43.3	4.5	5.6
	Young's Creek	µg/L	163.9	95.0	32.8
	Downstream of confluence with Young's Creek	µg/L	52.1	29.6	8.7
Loading rates	Upstream of Young's Creek	kg/yr	5713	594	739
	Young's Creek	kg/yr	41	24	8
	Downstream of Young's Creek	kg/yr	6875	3906	1148
	Immediately below Deloro Mine Site	kg/yr	1121	3288	401

^aAssuming that a negligible amount of water comes off the Deloro Mine Site.

Total estimated loading rates for the following contributing areas are summarized in Table 4.4-10:

• upstream of the Deloro Mine Site
• from Deloro Mine Site to Highway 7;
• Golder Associates
• Young's Creek; and,
• from Highway 7 to below confluence with Young's Creek.

Estimated loading rates are similar to those calculated by CG&S (1999). As noted by CG&S (1999), there is a significant amount of arsenic, cobalt and nickel entering the Moira River between Highway 7 and the confluence of Young's Creek.

Table 4.4-10
Summary of Estimated Loading Rates (kg/yr) to the Moira River near the Deloro Mine Site

Calibration Procedure

Based on information from Diamond (1990, 1995) and Cornett and Chant (1986), partition coefficients (K_w) for arsenic, cobalt and nickel in water were developed using the following equation:

K_w = (1 - [d. metal] / [t. metal]_w) / ([d. metal] / [t. metal] _w * [TSS])

where: [d. metal] = concentration of metal "z" dissolved in water (µg/L)

[t. metal]_w = total concentration of metal "z" in water (µg/L)

[TSS] = concentration of total suspended solids (mg/L)

Sediment partition coefficients (K_s) were developed using information from Diamond (1990) and Azcue and Dixon (1994) in the equation:

K_s = (1 - [p.metal] / [t. metal]_s) / ([p. metal] / [t. metal]_s * (1-φ)* ρ)

where: [p. metal] = concentration of metal "z" in porewater (µg/L)

[t. metal]_s = total concentration of metal "z" in surface sediments (µg/g)

φ = sediment porosity (unitless)

ρ = sediment density (kg/L)

Partition coefficients, diffusion velocities and initial water and sediment concentrations were then adjusted to calibrate the MRM, so that arsenic, cobalt and nickel concentrations predicted by the MRM matched trends observed in the river over the last 10 years. The calibration was performed under steady state conditions. It was deemed complete when the modelled concentrations in water reasonably reflected historical levels, and sediment concentrations were constant over time. Final parameter values used to calibrate the MRM are summarized in Tables 4.4-11 and 4.4-12, and results of the calibration are shown in Figures VI-1 to VI-24 (Appendix VI).

For arsenic and nickel, a good calibration was generally obtained in all model segments (Appendix VI, Figures VI-1 to VI-8 and VI-17 to VI-24). With cobalt, a good calibration was achieved in the five model segments upstream of West Moira Lake. The MRM consistently overestimated cobalt concentrations during the open water season in the remaining four model segments, suggesting that there may be an additional sink for cobalt that is not included in the MRM (e.g., uptake by growing vegetation).

Table 4.4-11
Partition Coefficients and Diffusion Velocities Used to Calibrate the Moira River Model

^aFrom Upstream of Deloro to the inlet of West Moira Lake.

^bFrom West Moira Lake to the outlet of Stoco Lake.

Table 4.4-12
Initial Arsenic, Cobalt and Nickel Concentrations Used to Calibrate the Moira River Model

Model Segment	Arsenic		Cobalt		Nickel
	Water (µg/L)	Sediment (µg/L)	Water (µg/L)	Sediment (µg/L)	Water (µg/L)	Sediment (µg/L)
Deloro to Young's Creek	43.3	315	4.5	214	5.6	130
Young's Creek to half way to Bend Bay	52.1	380	10.3	490	8.7	210
Remaining distance to Bend Bay	52.1	390	10.3	505	8.7	220
Bend Bay	52.1	705	10.3	895	8.7	500
Bend Bay to West Moira Lake	52.1	370	10.3	490	8.7	200
West Moira Lake	53.0	650	9.8	490	8.1	490
East Moira Lake (EML)	76.0	375	13.3	300	10.5	225
EML to Stoco Lake	19.0	88	3.3	69	3.2	80
Stoco Lake	18.0	93	3.1	67	3.2	105

4.5 Model Implementation

Once calibrated, the MRM was used to: (1) predict arsenic, cobalt and nickel concentrations downstream of the Deloro Mine Site assuming that all loading from the Deloro Mine Site ceased; and, (2) determine the level of cleanup required on site for downstream arsenic, cobalt and nickel concentrations in water to reach, or fall below, PWQOs and provincial sediment quality guidelines (PSQGs) for the protection of aquatic life.

4.5.1 No Loading Scenarios

As a result of short retention times (Table 4.4-3), arsenic concentrations in the water column quickly dropped below the interim PWQO of 5 mg/L (MOE 1999) after all arsenic loading from the Deloro Mine Site, between Highway 7 and Young's Creek, and Young's Creek was eliminated (Table 4.4-13). The interim PWQO for arsenic of 5 µg/L was used for this component, because the MOE has stated that one of the objectives of the final cleanup plan for the Deloro Mine Site is to meet this interim PWQO. Arsenic concentrations in surface sediments remained above the Ontario sediment Severe Effect Level (SEL) guideline of 33 mg/g (MOE 1993) at all model segments for the first 10 years, then declined to less than the SEL in some portions of Moira Lake and Stoco Lake after 20 years

Table 4.4-13
Predicted Concentrations of Arsenic Downstream Assuming
No Arsenic Loading from Deloro Mine Site

Model Segment	Initial	After				Provincial Guidelinea
		5 yrs	10 yrs	20 yrs	30 yrs
Water (µgL)bc
Deloro to Young's Creek	43.3	1.0 - 1.1	1.0 - 1.1	1.0 - 1.0	1.0 - 1.0	5.0
Young's Creek to half way to Bend Bay	52.1	1.0 - 1.2	1.0 - 1.2	1.0 - 1.1	1.0 - 1.1
Remaining distance to Bend Bay	52.1	1.0 - 1.4	1.0 - 1.3	1.0 - 1.2	1.0 - 1.1
Bend Bay	52.1	1.2 - 2.2	1.1 - 1.7	1.0 - 1.3	1.0 - 1.2
Bend Bay to West Moira Lake	52.1	1.3 - 2.3	1.3 - 2.3	1.0 - 1.3	1.0 - 1.2
West Moira Lake	53.0	2.0 - 2.8	1.4 - 1.8	1.1 - 1.2	1.0 - 1.1
East Moira Lake (EML)	76.0	2.4 - 3.4	1.7 - 2.4	1.2 - 1.7	1.1 - 1.4
EML to Stoco Lake	19.0	0.8 - 1.2	0.7 - 1.0	0.6 - 0.8	0.6 - 0.7
Stoco Lake	18.0	0.9 - 1.2	0.8 - 1.0	0.7 - 0.8	0.7 - 0.7
Sediment (µg/g)cd
Deloro to Young's Creek	315	243	196	129	88	6.0 (LEL) 33 (SEL)
Young's Creek to half way to Bend Bay	380	293	236	154	105
Remaining distance to Bend Bay	390	299	239	154	105
Bend Bay	705	299	149	44	21
Bend Bay to West Moira Lake	370	287	233	153	106
West Moira Lake	650	226	98	27	16
East Moira Lake (EML)	375	290	230	144	96
EML to Stoco Lake	88	64	48	28	18
Stoco Lake	93	58	38	19	12

^aWater quality objective from MOE (1999); sediment quality guidelines from MOE (1993)

^bConcentrations in water reported as minimum to maximum levels observed in Year 5, 10, 20 or 30.

^cValues in bold exceed the PWQO or the Severe Effect Level (SEL) sediment guideline.

^dSediment concentrations at the end of Year 5, 10, 20 or 30.

Cobalt concentrations in the water column decreased rapidly after loading from the Deloro Mine Site, Young's Creek and between Highway 7 and Young's Creek ceased (Table 4.4-14). However, up to 30 years after all loading to the river ceased, cobalt levels in Bend Bay and Moira Lake remained above the PWQO of 0.9 µg/L for at least part of the year. Cobalt concentrations in surface sediments were below screening level concentrations (SLC) in Moira and Stoco lakes 10 years after all cobalt loading to the Moira River ceased (Table 4.4-14). Sediment cobalt concentrations in all model segments were less than the SLC of 296 µg/g after 20 years.

Initial nickel concentrations in water in all model segments were below the PWQO of 25 µg/L (MOE 1999). They decreased to background levels after all nickel discharges from the Deloro Mine Site and adjacent areas, including Young's Creek stopped (Table 4.4-15). Surficial sediments initially contained nickel concentrations in excess of the provincial SEL guideline of 75 mg/g (MOE 1993). Nickel levels in the surface sediment exceeded the SEL in all model segments, except East Moira Lake to Stoco Lake, 10 years after nickel loading ceased. Nickel levels declined below the SEL in the Deloro to Young's Creek and Stoco Lake model segments after 20 years. They remained above the SEL in Bend Bay and Moira Lake even after 30 years.

Table 4.4-14
Predicted Concentrations of Cobalt Downstream Assuming
No Cobalt Loading from Deloro Mine Site

Model Segment	Initial	After				Provincial Guidelinea
		5 yrs	10 yrs	20 yrs	30 yrs
Water (µgL)bc
Deloro to Young's Creek	4.5	0.7 – 0.7	0.7 - 0.7	0.7 - 0.7	0.7 - 0.7	0.9
Young's Creek to half way to Bend Bay	10.3	0.7 – 0.9	0.7 - 0.9	0.7 - 0.8	0.7 - 0.8
Remaining distance to Bend Bay	10.3	0.7 - 1.1	0.7 - 1.0	0.7 - 0.9	0.7 - 0.9
Bend Bay	10.3	1.0 - 2.1	0.8 - 1.5	0.7 - 1.1	0.7 - 1.0
Bend Bay to West Moira Lake	10.3	1.0 - 2.1	0.9 - 1.6	0.7 - 1.1	0.7 - 1.0
West Moira Lake	9.8	1.4 - 2.1	1.0 - 1.4	0.7 - 0.9	0.6 - 0.8
East Moira Lake (EML)	13.3	1.6 - 2.4	1.2 - 1.8	0.8 - 1.2	0.7 - 1.0
EML to Stoco Lake	3.3	0.2 - 0.6	0.2 - 0.5	0.1 - 0.3	0.1 - 0.3
Stoco Lake	3.1	0.3 - 0.6	0.2 - 0.4	0.1 - 0.3	0.1 - 0.2
Sediment (µg/g)cd
Deloro to Young's Creek	214	174	147	107	83	296 (SLC)
Young's Creek to half way to Bend Bay	490	388	321	222	162
Remaining distance to Bend Bay	505	398	328	225	163
Bend Bay	895	425	243	104	70
Bend Bay to West Moira Lake	490	394	329	230	169
West Moira Lake	490	220	121	53	38
East Moira Lake (EML)	300	247	205	141	102
EML to Stoco Lake	69	54	42	27	18
Stoco Lake	67	45	32	17	11

^a Water quality objective from MOE (1999); Screening Level Concentration (SLC) calculated according to MOE (1993).

^bConcentrations in water reported as minimum to maximum levels observed in Year 5, 10, 20 or 30.

^cValues in bold exceed he PWQO or the SLC.

^dSediment concentrations at the end of Year 5, 10, 20 or 30.

Table 4.4-15
Predicted Concentrations of Nickel Downstream Assuming
No Nickel Loading from Deloro Mine Site

Model Segment	Initial	After				Provincial Guidelinea
		5 yrs	10 yrs	20 yrs	30 yrs
Water (µg/L)b
Deloro to Young's Creek	5.6	2.3 - 2.4	2.3 - 2.3	2.3 - 2.3	2.3 - 2.3	25
Young's Creek to half way to Bend Bay	8.7	2.3 - 2.5	2.3 - 2.4	2.3 - 2.4	2.3 - 2.4
Remaining distance to Bend Bay	8.7	2.3 - 2.6	2.3 - 2.6	2.3 - 2.5	2.3 - 2.4
Bend Bay	8.7	2.4 - 3.6	2.3 - 3.2	2.3 - 2.9	2.3 - 2.8
Bend Bay to West Moira Lake	8.7	2.4 - 3.6	2.3 - 3.2	2.3 - 2.9	2.3 - 2.8
West Moira Lake	8.1	2.6 - 3.9	2.3 - 3.2	2.1 - 2.8	2.1 - 2.7
East Moira Lake (EML)	10.5	2.6 - 3.8	2.2 - 3.2	2.0 - 2.7	1.9 - 2.5
East Moira Lake (EML)	10.5	2.6 - 3.8	2.2 - 3.2	2.0 - 2.7	1.9 - 2.5
EML to Stoco Lake	3.2	1.0 - 1.6	1.0 - 1.4	1.0 - 1.3	0.9 - 1.2
Stoco Lake	3.2	1.5 - 1.6	1.4 - 1.5	1.3 - 1.5	1.3 - 1.4
Sediment (µ g/g)cd
Deloro to Young's Creek	130	105	90	72	63	16 (LEL) 75 (SEL)
Young's Creek to half way to Bend Bay	210	159	130	93	75
Remaining distance to Bend Bay	220	166	135	96	77
Bend Bay	500	268	188	137	126
Bend Bay to West Moira Lake	200	154	126	91	73
West Moira Lake	490	266	190	140	130
East Moira Lake (EML)	225	183	153	111	89
EML to Stoco Lake	80	68	60	49	45
Stoco Lake	105	91	82	73	69

^aWater quality objective from MOE (1999); sediment quality guidelines from MOE (1993).

^bConcentrations in water reported as minimum to maximum levels observed in Year 5, 10, 20 or 30.

^cValues in bold exceed the PWQO or the Severe Effect Level (SEL) sediment guidelines.

^dSediment concentrations at the end of Year 5, 10, 20 or 30.

4.5.2 Level of Cleanup of the Deloro Mine Site Required to Meet Cleanup Objectives

Should arsenic migration from the Deloro Mine Site be essentially eliminated (e.g., 99% reduction) the model results indicate that arsenic concentrations in the Moira River at Highway 7 (which is located in the first model segment – Deloro to Young's Creek) would meet the interim PWQO during periods of high flow only (Table 4.4-16). During periods of low flow, arsenic levels would continue to exceed the interim PWQO 30 years after Deloro Mine Site cleanup. This is because a relatively small amount of arsenic from the Deloro Mine Site, coupled with relatively high background concentrations in the Moira River upstream of the mine, would still be significant relative to the interim PWQO of 5 µg/L. The interim PWQO for arsenic would be met year round in and downstream of Moira Lake within 5 years of 99% reduction in loading (Table 4.4-16). The continual release of arsenic from sediments in the bottom of Moira Lake is expected to have slight effect on arsenic concentrations in lake water, but not to the extent that the interim PWQO would be exceeded.

Table 4.4-16
Predicted Arsenic Levels Downstream Assuming a 99% Reduction in the Amount of
Arsenic Released from the Deloro Mine Site

Model Segment	Initial	After				Provincial Guidelinea
		5 yrs	10 yrs	20 yrs	30 yrs
Water (µ g/L)bc
Deloro to Young's Creek	43.3	1.1 - 7.3	1.1 - 7.3	1.1 - 7.2	1.1 - 7.2	5.0
Young's Creek to half way to Bend Bay	52.1	1.2 - 8.5	1.2 - 8.4	1.2 - 8.4	1.2 - 8.4
Remaining distance to Bend Bay	52.1	1.2 - 8.1	1.2 - 8.0	1.2 - 7.9	1.2 - 7.9
Bend Bay	52.1	1.4 - 8.2	1.3 - 7.6	1.2 - 7.2	1.2 - 7.1
Bend Bay to West Moira Lake	52.1	1.4 - 7.8	1.3 - 7.3	1.2 - 6.8	1.2 - 6.7
West Moira Lake	53.0	2.2 - 4.7	1.6 - 3.7	1.2 - 3.1	1.2 - 3.0
East Moira Lake (EML)	76.0	2.6 - 4.0	1.9 - 3.1	1.5 - 2.4	1.3 - 2.2
EML to Stoco Lake	19.0	0.8 - 1.5	0.7 - 1.2	0.6 - 1.0	0.6 - 1.0
Stoco Lake	18.0	1.0 - 1.4	0.8 - 1.2	0.8 - 1.0	0.7 - 0.9
Sediment (µ g/g)cd
Deloro to Young's Creek	315	244	197	130	91	6.0 (LEL) 33 (SEL)
Young's Creek to half way to Bend Bay	380	294	237	156	108
Remaining distance to Bend Bay	390	300	241	157	108
Bend Bay	705	303	155	50	28
Bend Bay to West Moira Lake	370	288	234	155	108
West Moira Lake	650	231	104	33	22
East Moira Lake (EML)	375	290	231	147	99
EML to Stoco Lake	88	64	48	29	19
Stoco Lake	93	58	39	20	13

^aWater quality objective from MOE (1999); sediment quality guidelines from MOE (1993).

^bConcentrations in water reported as minimum to maximum levels observed in Year 5, 10, 20 or 30.

^cValues in bold exceed the PWQO or the SEL.

^dSediment concentrations at the end of Year 5, 10, 20 or 30.

Arsenic concentrations in surface sediments are projected to remain above the SEL for 10 years in all model segments after a 99% reduction in the amount released from the Deloro Mine Site and surrounding area (Table 4.4-16). After 30 years, arsenic would continue to exceed the SEL in all model segments, except in West Moira Lake, East Moira Lake to Stoco Lake and Stoco Lake.

The nickel PWQO of 25 µg/L is currently being met in all model segments on an annual average basis. However, exceedances occur in the section between the mine site and Bend Bay during periods of low flow (Appendix I). The PWQO would be met year-round after a 75% reduction in nickel loading (Table 4.4-17).

Nickel concentrations in surface sediments are projected to remain above the SEL in all model segments, except between East Moira Lake and Stoco Lake, 30 years after a 75% reduction in total nickel loading to Moira River (Table 4.4-17).

Model results indicate that cobalt concentrations will continue to exceed the PWQO of 0.9 µg/L as far downstream as the outlet of Moira Lake, even with the elimination of 95% of cobalt loadings from the Deloro Mine Site and adjacent area (Table 4.4-18). Below Moira Lake, cobalt concentrations would meet the PWQO within 5 years, because of the effects of dilution from the Black and Skootamatta rivers.

Following a 95% reduction in total cobalt loading from the Deloro Mine Site and surrounding area, cobalt levels in surface sediments in the Moira River between Young's Creek and Moira Lake would fall below the SLC of 296 µg/g within 20 years (Table 4.4-18). In the other model segments, sediment cobalt levels are either currently below the SLC or projected to drop below the SLC within 5 years.

Table 4.4-17
Predicted Nickel Levels Downstream Assuming a 75% Reduction in the Amount of Nickel
Released from the Deloro Mine Site

Model Segment	Initial	After				Provincial Guidelinea
		5 yrs	10 yrs	20 yrs	30 yrs
Water (µ g/L)bc
Deloro to Young's Creek	5.6	2.5 – 14	2.5 – 14	2.5 – 14	2.5 – 14	25
Young's Creek to half way to Bend Bay	8.7	2.8-25	2.8-25	2.8-25	2.8-25
Remaining distance to Bend Bay	8.7	2.8 – 24	2.8 – 24	2.8 – 24	2.8 – 24
Bend Bay	8.7	2.9 – 22	2.8 – 21	2.8 – 21	2.8 – 21
Bend Bay to West Moira Lake	8.7	2.9 – 21	2.8 – 20	2.8 – 20	2.8 – 20
West Moira Lake	8.1	3.1 – 9.4	2.8 – 8.9	2.7 – 8.5	2.7 – 8.5
East Moira Lake (EML)	10.5	3.1 – 5.8	2.9 – 5.4	2.7 – 5.0	2.6 – 4.9
EML to Stoco Lake	3.2	1.1 – 2.1	1.1 – 2.0	1.1 – 1.9	1.0 – 1.9
Stoco Lake	3.2	1.5 – 2.1	1.5 – 2.0	1.5 – 1.9	1.5 – 1.9
Sediment (µ g/g)
Deloro to Young's Creek	130	111	100	87	80	16 (LEL) 75 (SEL)
Young's Creek to half way to Bend Bay	210	172	150	122	109
Remaining distance to Bend Bay	220	179	156	126	112
Bend Bay	500	326	266	228	220
Bend Bay to West Moira Lake	200	166	145	119	106
West Moira Lake	490	322	264	227	220
East Moira Lake (EML)	225	194	172	141	125
EML to Stoco Lake	80	71	65	57	53
Stoco Lake	105	95	88	81	79

^aWater quality objective from MOE (1999); sediment quality guidelines from MOE (1993)

^bConcentrations in water reported as minimum to maximum levels observed in Year 5, 10, 20 or 30.

^c"Initial" nickel concentrations = nickel concentrations at the end of December; during summer low flows, nickel concentrations can increase beyond initial segment concentrations.

^dSediment concentrations at the end of Year 5, 10, 20 or 30.

^eValues in bold exceed the PWQO or the SEL.

Table 4.4-18
Predicted Cobalt Levels Downstream of the Deloro Mine Site Assuming a 95% Reduction in
the Amount of Cobalt Released from the Mine Site

Model Segment	Initial	After				Provincial Guidelinea
		5 yrs	10 yrs	20 yrs	30 yrs
Water (µ g/L)bc
Deloro to Young's Creek	4.5	0.8 -3.5	0.8 -3.5	0.8 -3.5	0.8 -3.5	0.9
Young's Creek to half way to Bend Bay	10.3	0.9 -7.7	0.9 -7.7	0.9 -7.6	0.9 -7.6
Remaining distance to Bend Bay	10.3	0.9 -7.5	0.9 -7.4	0.9 -7.3	0.9 -7.3
Bend Bay	10.3	1.1 - 7.4	1.0 - 6.9	0.9 -6.5	0.9 -6.4
Bend Bay to West Moira Lake	10.3	1.1 - 7.1	1.0 - 6.6	0.9 -6.2	0.9 -6.0
West Moira Lake	9.8	1.6 - 3.8	1.2 - 3.1	0.9 -2.6	0.8 -2.5
East Moira Lake (EML)	13.3	1.8 - 2.9	1.3 - 2.3	1.0 - 1.8	0.9 -1.6
EML to Stoco Lake	3.3	0.2 - 0.8	0.2 - 0.6	0.1 - 0.5	0.1 - 0.5
Stoco Lake	3.1	0.3 - 0.7	0.2 - 0.6	0.2 - 0.4	0.2 - 0.4
Sediment (µg/g)cd
Deloro to Young's Creek	214	176	150	113	90	296 (SLC)
Young's Creek to half way to Bend Bay	490	393	329	235	179
Remaining distance to Bend Bay	505	403	337	239	181
Bend Bay	895	449	275	144	112
Bend Bay to West Moira Lake	490	399	337	243	185
West Moira Lake	490	233	140	75	60
East Moira Lake (EML)	300	249	210	149	112
EML to Stoco Lake	69	54	44	29	21
Stoco Lake	67	46	34	19	13

^aWater quality objective from MOE (1999); Screening Level Concentration (SLC) calculated according to MOE (1993).

^bConcentrations in water reported as minimum to maximum levels observed in Year 5, 10, 20 or 30.

^cValues in bold exceed the PWQO or reference sediment concentrations

^dSediment concentrations at the end of Year 5, 10, 20 or 30.

4.6 Conclusions

Results from this modelling exercise indicate that:

• Total arsenic loading from the Deloro Mine Site and the surrounding area would have to be essentially eliminated (99% reduction) for arsenic concentrations in Moira Lake and downstream to be less than the interim PWQO of 5 µg/L during average summer low flows. Even with 99% reduction, arsenic will remain above theinterim PWQO between the Deloro Mine Site and Moira Lake at low flows.
• Total nickel loading rates from the Deloro Mine Site and the surrounding area would have to be reduced by 75% for nickel concentrations at Highway 7 and downstream to be equivalent to, or less than, the PWQO of 25 µg/L year round.
• Cobalt concentrations are projected to exceed the PWQO downstream of the Deloro Mine Site to East Moira Lake for the 30-year period of the model, even with 95% cleanup of the Deloro Mine Site and the surrounding area. If total cobalt loading rates were reduced by 95%, cobalt concentrations downstream of East Moira Lake are projected to drop below the PWQO following the addition of dilution water through the Black & Skootamatta rivers.
• Arsenic and nickel concentrations in surface sediments immediately downstream of the Deloro Mine Site are projected to remain above guideline levels for some time (i.e.,> 30 years), regardless of the level of on-site cleanup.
• Following a 95% reduction in total cobalt loading from the Deloro Mine Site and surrounding area, cobalt levels in surface sediments in the Moira River between Young's Creek and Moira Lake would fall below the SLC of 296 µg/g within 20 years. In the other model segments, downstream of Moira Lake, sediment cobalt levels are either currently below the SLC or projected to drop below the SLC within 5 years.
• Since Young's Creek contributes relatively small amounts of arsenic, nickel and cobalt to the Moira River in comparison to discharge released directly from the Deloro Mine Site, the greatest benefit will be from cleanup efforts focussed on the Deloro Mine Site. However, there is a concern about the Deloro Mine Site derived sediments currently being held back behind a series of beaver dams on Young's Creek (see Chapters 2.2 and 5.0). Were these dams to completely fail, a significant quantity of sediment could be released to the Moira River (see Appendix VIII for a description of the results of a partial beaver dam failure in June 2000).

References

Azcue, J. M and D.G. Dixon. 1994. Effects of past mining activities on the arsenic concentration in fish from Moira Lake, Ontario. J. Great Lakes Res. 20(4):717-724.

Bosworth, W.S. and L. J. Thibodeaux. 1990. Bioturbation: a facilitator of contaminant transport in bed sediment. Environmental Progress, 9(4): 211-217.

CG&S (CH2M Gore & Storrie Ltd.). 1999. Deloro Mine rehabilitation project, development of a sitewide water and load balance - final report. Prepared for the Ontario Ministry of the Environment. May 1999.

Chapra, S.C. 1997. Surface water-quality modeling. McGraw-Hill International Editions, Civil Engineering Series, Toronto, Canada.

Cornett, R.J. and L. Chant. 1986. Speciation of arsenic and nickel in sediments of Moira Lake. Prepared for the National Uranium Tailings Program, Canadian Centre for Mineral and Energy Technology, Energy, Mines and Resources Canada, Ottawa, Canada. DSS File No. O5Gs.23241-5-1716.

Cornett, R.J., B. Risto, and L. Chant. 1987. Kinetics of arsenic and nickel in sediments in Moira Lake. Prepared for the National Uranium Tailings Program, Canadian Centre for Mineral and Energy Technology, Energy, Mines and Resources Canada, Ottawa, Canada. DSS Contract No. 23317-6-1736/OI-SQ.

Diamond, M. L. 1990. Modelling the fate and transport of arsenic and other inorganic chemicals in lakes. Ph.D. Thesis, University of Toronto, Toronto, Canada.

Diamond, M. L. 1995. Application of a mass balance model to assess in-place arsenic pollution. Environ. Sci. Technol. 29:29-42.

Environment Canada. 1994. Canadian monthly climate data and 1961-1990 normals, 1994 release. Environment Canada, Ottawa, Canada.

Environment Canada. 1999. HYDAT, Version 96 - 1.05.8: Surface water and sediment data to 1996. Atmospheric Environment Service, Environment Canada, Ottawa, Canada.

HPS (High Performance System Inc.). 1997. STELLA software and technical documentation.

MOE (Ontario Ministry of the Environment). 1972. Report on water quality in Stoco Lake. Ontario Ministry of the Environment, Toronto, Canada.

MOE. 1974. Water Resources of the Moira River drainage basin. Ontario Ministry of the Environment, Toronto, Canada. MOE Water Resources Report 6.

MOE. 1993. Guidelines for the protection and management of aquatic sediment quality in Ontario. Ontario Ministry of the Environment, Toronto, Canada. August 1993.

MOE. 1999. Water management policies, guidelines and provincial water quality objectives of the Ministry of Environment and Energy. Ontario Ministry of the Environment, Toronto, Canada. February 1999.

Mudroch, A. and J.A. Capobianco. 1980. Impact of past mining activities on aquatic sediments in Moira River Basin, Ontario. J. Great Lakes Res., 6(2):121-128.

WSC (Water Survey of Canada). 2000. Monthly water flow data from 1997 to 1999 for the Moira River.