J. Ray Cox, PE | Highfill Infrastructure EngineeringEddie Smith, Wastewater Manager | Grand Strand Water and Sewer Authority

Proactive Pump Station Contingency Planning

Outline GSWSA overview

PS #1 overview

PS #1 contingency planning

Problem definition

Evaluation steps

Findings and recommendations

Grand Strand Water and Sewer Authority

(GSWSA)

• Major Water and Sewer Provider in Horry County

• Services in Marion, Georgetown, Dillon Counties in SC and Columbus County in NC

• Approximately 91,250 active customers

GSWSA

Major system components 13 Wastewater Treatment Plants (67 MGD capacity)

2 Surface Water Treatment Plants (90 MGD capacity)

4 Groundwater Systems (10 MGD capacity)

Water distribution (1,842 miles)

4 Ground Storage Tanks (13.5 MG capacity) and 22 Elevated Tanks (5.3 MG capacity)

Wastewater collection (869 miles gravity) and conveyance (868 miles forcemain)

671 pump stations and 4 regional pump stations

Regional Pump Stations

Pump Station

Number of Stations

Connected

Pump Station

Capacity (MGD)

Number of Customers

PS #1 46 5.0 8,374

PS #2 34 4.3 5,306

PS #3 30 2.0 4,870

PS #225 31 5.0 3,702

Pump Station #1

PS #1 service area

Pump Station #1 Densely populated service area in summer

Environmentally sensitive areas

42 major pump stations feed to PS #1

Forcemain system has interconnectivity

PS #1 FM: 24-in/30-in FM to Schwartz WWTP

PS #1 fail-over protection

Monitoring

Generator

Bypass pumping

What if we lose the ability to pump through the PS #1 FM for 24 hours

during July 4th weekend?

Eating the proverbial elephant Prioritize the 42 upstream pump stations

Evaluate diversion capabilities

Evaluate storage capabilities

Consider mitigative measures

Pump and haul

Temporary pumping and piping

Temporary flow reduction

Supplemental storage

Future diversion capabilities

Prioritizing 42 pump stations Prioritize to know where to focus first

Assess total risk of a spill occurring

Total risk = likelihood of failure X consequence of failure

Likelihood: what is the probability of a spill at this PS?

Consequence: how bad could it be?

Criteria Description Scoring MatrixRaw

ScoreWeight

Weighted Score (Raw Score x

Weight)

up to 6 hours 10 100 1000

more than 6 hours up to 12 hours 8 100 800

more than 12 hours up to 18 hours 5 100 500

more than 18 hours up to 24 hours 3 100 300

more than 24 hours 1 100 100

Permanent infrastructure to handle 0% - 24% of ADF 10 80 800

Permanent infrastructure to handle 25% - 49% of ADF 7 80 560

Permanent infrastructure to handle 50% - 74% of ADF 4 80 320

Permanent infrastructure to handle 74% -100% of ADF 0 80 0

more than 2 hours 10 6 60

less than 2 hours but more than 1 hour 5 6 30

less than 1 hour 0 6 0

Peak-Season Response Time

Probability of failure based on reponse time. Travel time measured from GSWSA Operations Center. Since travel

time during peak season can be challenging, this factor is scored seperately from off-season travel time. Pump

stations with the longest response time scored higher.

Pump Station No. 1 Contingency PlanLikelihood of Failure Scoring Criteria

Storage Time

Probability of failure based on estimated storage time at Max. Month (July) Average Daily Flow. Pump stations with less storage time are more vulnerable to SSO and scored

higher.

Ability to Divert FlowProbability of failure based on the ability to divert flow.

Pump stations with no permanent infrastructure in place to divert flow scored higher.

Criteria Description Scoring MatrixRaw

ScoreWeight

Weighted Score (Raw Score x

Weight)

ADF > 400,000 GPD 10 7 70

ADF of 300,000 GPD - 399,000 GPD 8 7 56

ADF of 200,000 GPD - 299,000 GPD 6 7 42

ADF of 100,000 GPD - 199,000 GPD 4 7 28

ADF < 100,000 GPD 0 7 0

< 100 feet to surface water or wetland 10 6 60

100 feet - 499 feet to surface water or wetland 5 6 30

500 feet or more to surface water or wetland 0 6 0

< 100 feet to surface water or wetland 10 5 50

100 feet - 499 feet to surface water or wetland 5 5 25

500 feet or more to surface water or wetland 0 5 0

Pump Station No. 1 Contingency PlanConsequence of Failure Scoring Criteria

Quantity of Flow

Flow estimates based on influent max. month (July) average daily flow (ADF). Pump stations with greater

incoming ADF have the potential for higher consequences and are scored higher.

Surface Water Impacts (Human Impact)

Pump stations located closest to swimming beaches or other recreational impact waters are scored higher than

those farthest from these surface waters.

Surface Water Impacts (Environmental Impact)

Pump stations located closest to stormwater ponds, fresh surface waters, or wetlands are scored higher than those

farthest from these surface waters.

Criteria Description Scoring MatrixRaw

ScoreWeight

Weighted Score (Raw Score x

Weight)

Hospital(s) or School(s) 10 4 40

Medical or Dental office(s) 8 4 32

Restaurant(s) 6 4 24

24-hour business(es) 10 3 30

> 10 businesses (excluding those above) 7 3 21

5 - 9 businesses (excluding those above) 4 3 12

1 - 5 businesses (excluding those above) 1 3 3

Service area includes Historic District, Public Park, or Tourist Area

5 2 10

Service area DOES NOT include Historic District, Public Park, or Tourist Area

0 2 0

1000 or more residential units 10 1 10

500 - 999 residential units 7 1 7

100 - 499 residential units 4 1 4

< 100 residential units 1 1 1

Pump Station No. 1 Contingency PlanConsequence of Failure Scoring Criteria

Cultural Resource ImpactsService areas with historic district, park, or tourist

attraction open to the public are scored higher than service areas without those cultural amenities.

Residential ImpactsService areas with a high number of residential units score higher than those with few residential parcels.

Potential Public Health Impacts

Pump station customer type. More critical customers served scored higher than less critical (from public health

perspective).

Economic Impacts

Service areas with a high number of commercial or business parcels score higher than those with few

commercial or business parcels. 24-hour businesses considered most critical.

PS ID Pump Station Name/LocationTotal

Likelihood Score

Total Consequence

Score

Total Risk Score

(Normal)

16 OCEAN LAKES 1855 145 268,975 17 OCEAN LAKES / LOVESTONE DR 1855 145 268,975 58 DEERFIELD / AZALEA DR 1855 142 263,410 171 FLORA VILLAS/SURFSIDE / 5TH N & DOGWOOD 1055 212 223,660 71 MB RESORT 1855 111 205,905 70 SPRINGMAID BEACH / OCEAN BLVD SOUTH 1855 101 187,355 5 PRESTWICK / MCMASTER DR 1855 100 185,500 37 OCEANSIDE VILLAGE / WACCAMAW DR 1055 172 181,460 4 PIRATELAND / CALICO TRAIL 1855 97 179,935

166 BEACH PARK / SPRINGMAID BEACH BLVD 1855 96 178,080 172 BALL PARK/SURFSIDE / 4TH S & DOGWOOD 855 199 170,145 57 DEERFIELD / HWY 17 BUS 1655 98 162,190 99 LAKEWOOD 1655 97 160,535 149 UPPER LONG BAY / WOODVIEW LN 1655 93 153,915 174 10TH AVE N & OCEAN BLVD SURFSIDE 855 176 150,480 103 LAKEWOOD 1855 69 127,995 38 OCEAN LAKES / CLAM DR 1655 69 114,195 102 LAKEWOOD 1655 69 114,195 90 DEERPARK GARDEN / GARDEN DR 1855 57 105,735 34 CRYSTAL LAKE / MOONLIGHT 1655 62 102,610 367 IRON GATE SALOON / HWY 17 BUS 1855 51 94,605 54 PIRATELAND / PIRATELAND TRAIL 1355 69 93,495

Diversion capabilities 17 of 42 stations divert to PS #2

Operate two valves

2.75 MGD diverted

PS ID Pump Station Name/Location July ADF (GPD)

171 FLORA VILLAS/SURFSIDE / 5TH N & DOGWOOD 658,800 172 BALL PARK/SURFSIDE / 4TH S & DOGWOOD 464,400 37 OCEANSIDE VILLAGE / WACCAMAW DR 388,800 58 DEERFIELD / AZALEA DR 357,000 174 10TH AVE N & OCEAN BLVD SURFSIDE 231,000 23 CAROPINES / SPANISH OAK DR 176,220 90 DEERPARK GARDEN / GARDEN DR 135,000 47 CAROPINES / PINE VALLEY 82,800 82 HARBOUR VILLAGE / WIND DRIFT CT 74,400 32 CAROPINES / CAROPINES DR 71,280 173 3RD & MYRTLE/SURFSIDE 43,320 396 BERMUDA BAY - HWY 17 BUS 25,500 448 TUPELO BAY GOLF VILLAS HWY 17 BUS 17,220 298 MALLARD LANDING VILLAGE 12,540 438 MURDOCK RD - GARDEN CITY 7,140 332 DINGO PARK / HWY 17 BUS 2,520 525 SPANISH OAK LN - CAROPINES 1,890

2,750,000 Total diverted ADF (GPD)

Storage capabilities 8 “receiver” or re-pump stations

4 divert to PS #2

Remaining 4 must be managed

Receiver PS Giver PSAnticipated Maximum Emergency

Shutoff Duration (hrs)4 12

54 1235 12

5 7.534 7.5109 24

GC 23 leave in operation16 3.5

36 23.338 9.9

99 11102 11103 4.3 (leave in operation)

Storage capabilities Considered wetwell and

system storage

Storage analysis caused us to reassess total risk

Only 3 stations had 24-hr storage capacity

Low storage capacity = low to no reaction time

Multiple larger stations had storage of 3 hours or less

PS ID Pump Station Name/LocationEstimated Storage

(Emergency Operation)

July ADF (GPD)

Total Risk Rank

(Emergency)

16 OCEAN LAKES 3.5 456,450 117 OCEAN LAKES / LOVESTONE DR 1.4 535,500 271 MB RESORT 1.5 226,800 370 SPRINGMAID BEACH / OCEAN BLVD SOUTH 1.1 319,440 4166 BEACH PARK / SPRINGMAID BEACH BLVD 2.9 14,040 55 PRESTWICK / MCMASTER DR 7.5 186,000 657 DEERFIELD / HWY 17 BUS 6.7 166,320 799 LAKEWOOD 11.0 183,600 8149 UPPER LONG BAY / WOODVIEW LN 10.6 13,440 94 PIRATELAND / CALICO TRAIL 12.5 189,000 10

103 LAKEWOOD 4.3 88,200 1138 OCEAN LAKES / CLAM DR 9.9 41,280 12102 LAKEWOOD 11.7 40,890 1334 CRYSTAL LAKE / MOONLIGHT 7.5 59,280 14367 IRON GATE SALOON / HWY 17 BUS 5.3 132 1554 PIRATELAND / PIRATELAND TRAIL 12.7 59,220 1635 PIRATELAND / PIRATELAND TRAIL 12.5 92,400 1736 OCEAN LAKES 23.3 47,880 18109 WINGS SOUTH / ACADEMY RD 24 3,600 196 BEACHWOOD / LAKESIDE DR 5.1 51,000 20

134 PRESTWICK / LINKS RD 17.1 73,920 2198 OCEAN LAKES COMMERCIAL VILLAGE 24 2,760 22515 BERMUDA GARDENS HWY 17 BUS 24 5,400 2360 STATE PARK / OVERFLOW SECTION 2.5 33,600 2461 STATE PARK /CAMPGROUND CIRCLE 2 11.6 40,800 25

Mitigative measures considered Temporary measures considered

Pump and haul Accessibility is problematic, particularly in peak season

Even considering only stations with < 6 hours of storage, must move 175,000 gallons each hour to avoid a spill

Logistically infeasible

Temporary pumping and piping May help a particular station within the basin, but is essentially “whack a mole” in this situation

Temporary flow reduction efforts (shut off water, PSAs, etc.) GSWSA does not control all water supplies in the service area

May buy some time, but not realistic for a 24-hour period in peak season

Mitigative measures considered Supplemental storage

Decentralized Space limitations

Not practical for many stations

Centralized Large basin/structure required (likely ≥ 2 MG)

Expensive contingency

Mitigative measures considered Planned future interconnect with Myrtle Beach FM

GSWSA preliminary analysis – 10 stations (~ 670,000 GPD) diverted

Interconnect is conceptual at this time

15 stations still need accommodation

PS ID Pump Station Name/LocationEstimated Storage

(Emergency Operation)

July ADF (GPD)

Total Risk Rank

(Emergency)70 SPRINGMAID BEACH / OCEAN BLVD SOUTH 1.1 319,440 460 STATE PARK / OVERFLOW SECTION 2.5 33,600 24166 BEACH PARK / SPRINGMAID BEACH BLVD 2.9 14,040 56 BEACHWOOD / LAKESIDE DR 5.1 51,000 20

367 IRON GATE SALOON / HWY 17 BUS 5.3 132 155 PRESTWICK / MCMASTER DR 7.5 186,000 6

149 UPPER LONG BAY / WOODVIEW LN 10.6 13,440 961 STATE PARK /CAMPGROUND CIRCLE 2 11.6 40,800 25109 WINGS SOUTH / ACADEMY RD 24 3,600 19515 BERMUDA GARDENS HWY 17 BUS 24 5,400 23

Total diverted (GPD) 667,452

Findings and Recommendations

Conclusions Insufficient storage exists to contain a 24-hour, peak season event

Existing interconnectivity, redundancy and fail-over protections work well for localized events but will not remedy a basin-wide event

Temporary efforts to store or transport wastewater to another basin are not practical for a basin-wide event of any significant duration

Any plan that does not convey most or all of the flow out of the basin will not ensure spill prevention and results in a complex emergency action plan

Potential holistic solutions include the following: Adding centralized supplemental storage

Adding a redundant PS and FM

Maximizing the planned interconnect with the Town of Myrtle Beach FM

Recommendations Install permanent generators or bypass pumps at stations with < 6 hours of storage

Maximize the diversion to PS #2 basin

Model the diversion to identify potential concerns

Conduct at least one test run during an off-peak “shoulder” month

Conduct additional test runs during higher flow periods as warranted for assessment and debugging

Divert the flow from the remaining stations to the Myrtle Beach FM

Model the system to determine the appropriate size and location of the interconnect

Install isolation valves and pumper connections required to facilitate the diversion

Eddie Smitheddie@gswsa.comRay Coxrcox@hiepc.com

Questions