Petroleum Refinery Runoff Management

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Stalzer and McArdle [49] reported on a SOHIO Toledo refinery, 2 km2 (500 acre) area, storm-water runoff management study in which a nonsegregated oily sewer system collected both process wastewater and stormwater runoff. The handling of runoff at such a large petroleum refinery site requires adequate diversion and impounding capacity to store excessive storm flows for treatment after the runoff subsides. The paper presented the case history of upgrading the refinery's wastewater treatment system to efficiently manage the runoff while maximizing overall treatment efficiency. One of the primary objectives of the study was to estimate the peak flow rate and total impounding volume required for design storm events using the Illinois Urban Drainage Area Simulator (ILLUDAS) for stormwater runoff computer modeling. By establishing a hydraulic profile of the oily sewer at the wastewater treatment system, the diversion and impounding system, and primary wastewater treatment units, it was determined that the influent weir to the oil/water separator controlled the water level in the sewer for a considerable distance upstream. A water level sensor at a lift station downstream of the oil/ water separator was used to monitor changes in flows and determine the sequence for opening

Figure 17 Feedlot and treatment train (from Ref. 48).

Table 6 Water Quality Data for the Runoff Collecting Lagoons

Parameter concentration (mg/L)

Table 6 Water Quality Data for the Runoff Collecting Lagoons

Parameter concentration (mg/L)

Date

TDS

TSS

COD

BOD

T-P

10-1-70

1316

174

620

165

21.3

11-4-70

1122

107

314

15

17.0

12-2-70

1059

216

386

23

11.1

1-5-71

959

267

396

-

11.3

2-4-71

1128

174

403

65

13.6

2-24-71

1169

136

298

31

12.6

3-25-71

1046

292

569

80

7.9

Mean

1114

195

426

63

13.5

Source: Ref. 48.

the diversion valves. This was based on the lift pump having a maximum capacity of 0.5 m3/s (8000 gpm). For use as a design basis, the 25 year, 1 hour and 10 year, 24 hour storm events were chosen to establish the design peak flow rate (4.3 m3/s or 152 cfs) and total impounding volume (based on a peak rate of 1.93 m3/s or 68 cfs), respectively. To determine the required impounding capacity from the 10 year storm hydrograph, the amount of the runoff that can be treated during the storm was determined based on the maximum allowable wastewater treatment system flow rate and the dry weather flow rate. This flow rate was then subtracted from the hydrograph of the storm, with the area under the resultant hydrograph equal to the required impounding volume.

Because of the variability in dry flow rates, the base flow used to calculate the required impounding volume was not the average, but a 90% maximum dry weather flow based on four years of data to ensure some conservatism in the design. Even though the chance of a design storm actually occurring at the same time as the 90-percentile dry flow rate may have low probability, the additional cost for extra impounding volume must be weighed against the liabilities of not having sufficient volume. On the other hand, to enhance the conservative nature of the overall design, peak flows used in designing for diversion into the impounding basin and overflow from the basin under flood conditions were based on the 100 year storm. As flows

Table 7 Water Quality Data for the Farm Pond Discharge

Parameter concentration (mg/L) Date Days of operation TDS TSS COD BOD T-P T-N

Table 7 Water Quality Data for the Farm Pond Discharge

Parameter concentration (mg/L) Date Days of operation TDS TSS COD BOD T-P T-N

10-1-70

0

342

10

78

2

0.4

4.4

11-4-70

35

437

19

71

2

0.2

3.5

12-2-70

63

477

11

92

2

0.2

3.6

1-5-71

97

848

24

149

5

1.0

6.7

2-4-71

107

832

8

166

5

0.5

6.3

2-24-71

127

780

6

134

6

0.4

5.1

3-25-71

158

874

6

183

12

1.0

8.0

Mean

-

656

12

125

5

0.5

increase in the oily sewer due to stormwater runoff, a dam in the sewer with a flow meter and valve combination allows a preset maximum flow to the wastewater treatment system. As a result, the water level upstream of the dam increases until it begins spilling over a diversion weir into the impounding basin, thereby maintaining a constant optimum flow rate through the treatment system.

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