Wake County Comprehensive Groundwater Investigation

1
Wake County Comprehensive Groundwater
Investigation Groundwater Study Advisory
Committee Meeting November 13, 2002
2
Project Schedule
3
Review of October GSAC Meeting
Update of Data Collection

• NCDENR Groundwater Section final report.
  Methodology for Compiling Ground-Water Recharge
  Maps in the Piedmont and Coastal Plain Provinces
  of the Southeastern US
• NCGS updated geologic mapping of Wake County
  (NCGS to ID Hydrogeologic Units).
• USGS Wake County water use estimates for year
  2000. Final Dec. 2002
• Source water assessment reports. Draft
  Nov. 2002, Final Mid/Late 2003(?)

Have Final Versions of
Awaiting Final Versions of
4
Water Budgets - Review
Review of October GSAC Meeting

• Accounting system for water
• Water In Water Out
• Provides information to
• assess current demand vs yield
• better understand local details of hydrologic
  cycle and movement of water within the County
• focus management efforts on most pressing issues

5
Water Budget
Review of October GSAC Meeting

• P WW/IND Rech EDR SW Disch
• ET RO SWW GWW EDW BF

P Average precipitation WW/IND Rech
Wastewater and industrial discharge to GW EDR
Estimated domestic recharge from private septic
systems SW Disch Discharge to streams (NPDES
discharges) ET Evapotranspiration RO Runoff
component of precipitation SWW Surface water
withdrawal from creeks GWW Groundwater
withdrawal from PWSs and Industrial wells EDW
Estimated withdrawal from domestic wells BF
Median Baseflow of streams
6
Hydrologic Cycle
Review of October GSAC Meeting
7
Distribution of Maximum Domestic Well Yield
Review of October GSAC Meeting
Triassic Basin
Maximum Well Yield (gals/min)
0 to 25 26 to 50 51 to 75 76 to 100 gt100
Coastal Plain Sediments
8
Distribution of Maximum PWS Well Yield
9
Upper Falls Lake
Water Budget Drainage Basins
Lower Falls Lake
Beaver Dam
Upper Neuse
Crabtree Creek
Little River
Walnut Creek
Jordan Lake
Lower Neuse
Swift Creek
Harris Lake
Middle Creek
Black Creek
Kenneth Creek
10
Water Budget
All values in inches per year
11
Water Budget
All values in inches per year
12
Stream Baseflow

• Assuming there are no long term changes in
  groundwater storage,
• baseflow groundwater recharge
• Baseflow separations analytical technique to
  separate baseflow from total streamflow
• Sliding Interval Method
• used here

Flow
Days
13
Stream Gage Locations
14
Stream Baseflow
15
Recharge Units and Rates
flood plains (0 in/yr) gentle slopes CP (12.2
in/yr) gentle slopes SB (5.1 in/yr) gentle slopes
TR (3.1 in/yr) gentle slopes other (11.0
in/yr) other slopes (7.9 in/yr) other slopes CP
(3.1 in/yr) other slopes SB (4.7 in/yr) other
slopes TR (2.4 in/yr) stream terraces (8.7
in/yr) undifferentiated (0 in/yr) upland
flats-mineral (13.8 in/yr) water (0 in/yr)
Harris Lake Drainage Basin

• H.E. Mew, Jr., D. Hirth, D. Van Lewis, R.B.
  Daniels and
• Keyworth. Methodology for Compiling Ground Water
  Recharge
• Maps in the Piedmont and Coastal Plain Provinces
  of North Carolina.
• Ground Water Bulletin No. 25, NCDENR Div. of
  Water Quality

16
Comparison of Baseflow Separation and Landscape
Model Recharge Estimates
17
Baseflow and Recharge

• Baseflow accounts for approximately 45 of total
  streamflow in Wake County Streams
• Middle Creek 55
• Crabtree Creek 45
• Walnut Creek 47
• Swift Creek 34
• On average, 15 of precipitation recharges the
  groundwater system in Wake County
• Jordan Lake 6
• Harris Lake 8
• Black Creek, Beaver Dam Lower Neuse 18
• Little River 19

18
Water Budget
Evapotranspiration
All values in inches per year
19
Evapotranspiration in the Piedmont
USGS Water Resources Investigation Report 96-4220
Ground-Water Recharge to the Regolith - Fractured
Crystalline Rock Aquifers System, Orange County,
NC
20
Evapotranspiration in the Piedmont

• Raleigh/Durham Area 30.6 in/yr
• (Tang, 1980)
• Piedmont 33.84 in/yr
• (Hardy and Hardy, 1975)

21
Water Budget
Public/Industrial/Commercial Groundwater
Withdrawal
All values in inches per year
22
Groundwater Withdrawals

• Year 2000 Billing Records from Heater Utilities
  and Carolina Water Service
• No good single source of information of water
  withdrawals from other (small) purveyors
• Account for these under EDW
• Estimate commercial use (e.g. car washes) ?

23
Water Budget
Estimated Domestic Withdrawal
All values in inches per year
24
Groundwater Demand from PWS Systems(Heater
Utilities, year 2000 and 2001 billing records)

• Population 2000
  Usage Usage Rate
• Basin Served per Basin 2000 2001
  
  (million gals) (gal/pers/day)
• Lower Falls Lk. 16,693 604.4 99 108
• Beaver Dam 74 2.6 95 86
• Upper Neuse 3,350 86.7 71 72
• Little River 284 7.0 68 70
• Middle Creek 10,001 236.1 65 68
• Lower Neuse 1,629 37.9 64 65
• Swift Creek 6,294 138.7 60 66
• Black Creek 100 2.1 59 54
• Walnut Creek 244 4.9 55 55
• Harris Lake 44 0.8 52 51
• Crabtree Creek 2,381 31.7 36 77
• TOTAL 41,094 1,153 77 85

HIGH
LOW
25
Up. Falls Lake Use average of Harris Lake
Determining EDW
52
Upper Falls Lake
Beaver Dam Use average of Little River
Usage Rate by Basin (gals/person/day)
Lower Falls Lake
99
Beaver Dam
Upper Neuse
Crabtree Creek
71
Jordan Lake
68
68
77
Jordan Lake Use average of Harris Lake
Little River
64
Walnut Creek
52
Lower Neuse
55
Swift Creek
60
Harris Lake
65
Middle Creek
52
59
Kenneth Creek Use average of Black Creek
59
Black Creek
Kenneth Creek
26
Water Budget
Estimated Domestic Recharge
All values in inches per year
27
Estimated Domestic Recharge

• Assume 22 consumptive use
• (DWR Water Supply Plan Updates, Wake Co.)
• Assume 10 lost to evapotranspiration in the
  leaching field
• Estimate needs to be based on non-growing season
  groundwater withdrawal (GWW) values

28
Determining EDR
2000/2001 Average Water Use for PWS 392373 (Lower
Falls Lake) Population Served 10,279
29
Determining EDR
2000/2001 Average Water Use for PWSs 392357,
392293, 392080 and 392335 (Middle Creek)
Population Served 2,115
30
Water Budget By Next Meeting
All values in inches per year
31
Water Quality PWS Data
Inorganics - All Wake County
32
Water Quality PWS Data
Nutrients - All Wake County
33
Water Quality PWS Data
Synthetic Organic Compounds - All Wake County
31 Compounds were not detected in any sample and
are not shown above
34
Water Quality PWS Data
Volatile Organic Compounds - All Wake County
38 Compounds were not detected in any sample and
are not shown above
35
Water Quality Next Steps

• Summarize by basin and water supply watershed
  areas
• Summarize raw water quality data (inorganics and
  SOCs) from domestic wells (State lab data)
• Trend analysis
• Summarize existing information on Radon

36
Project Schedule
37
Questions / Comments?