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34816 Dewatering Calcs Tables Table 1A: Dewatering Calculations for Installation of Underground Storage Tanks Facility Name: 7-Eleven Store No. 34816 Facility Address: 3701 Santa Barbara Blvd, Naples, Collier Co, FL 34104 FDEP ID: 11/9063983 aquifer thickness water table drop (b) in feet in feet H=total head of aquifer 50 13 H= 15.2 m h=total head of dewatered aquifer 37 h= 11.3 m K in ft/day K=hydraulic conductivity 6.97 Ro = Radius of Influence K= 2.46E-05 m/s Re = Equivalent Radius of Influence Ro in feet Ro + Re in Feet Ro=3000(H-h)sqrtK L in ft W in ft 193.4 217.8 Ro= 58.9 m 52 36 ab Re=radius of influence (equivalent) 15.8 11.0 Re= 7.4 m # well points q= 7.84335E-05 m^3 / sec 50 q= 1.2 gpm per well point Total pump rate 62 (gpm) 89,452 (gpd) NOTE: 1. Please see enclosed the Broward County Environmental Protection Department Exhibit III: Calculation Methods for Radius of Influence and Dewatering Flow Rate from Aquifer Test Data. 2. Aquifer values are from subject site assessment data. Table 1B: Dewatering Calculations for Installation of Fuel Dispenser Sumps, Product Piping, and Canopy Footers Facility Name: 7-Eleven Store No. 34816 Facility Address: 3701 Santa Barbara Blvd, Naples, Collier Co, FL 34104 FDEP ID: 11/9063983 aquifer thickness water table drop (b) in feet in feet H=total head of aquifer 50 3 H= 15.2 m h=total head of dewatered aquifer 47 h= 14.3 m K in ft/day K=hydraulic conductivity 6.97 Ro = Radius of Influence K= 2.46E-05 m/s Re = Equivalent Radius of Influence Ro in feet Ro + Re in Feet Ro=3000(H-h)sqrtK L in ft W in ft 44.6 81.3 Ro= 13.6 m 132 32 ab Re=radius of influence (equivalent) 40.2 9.8 Re= 11.2 m # well points q= 0.000212597 m^3 / sec 50 q= 3.4 gpm per well point Total pump rate 168 (gpm) 242,463 (gpd) NOTE: 1. Please see enclosed the Broward County Environmental Protection Department Exhibit III: Calculation Methods for Radius of Influence and Dewatering Flow Rate from Aquifer Test Data. 2. Aquifer values are from assessment data of nearby contaminated site (FDEP ID 41/9103607). Environmental Protection and Growth Management Department POLLUTION PREVENTION, REMEDIATION AND AIR QUALITY DIVISION One North University Drive, Suite 203, Plantation, Florida 33324 954-519-1260 • FAX 954-765-4804 EXHIBIT III CALCULATION METHODS FOR RADIUS OF INFLUENCE AND DEWATERING FLOW RATE FROM AQUIFER TEST DATA Radius of Influence The most accurate method of estimating Radius of Influence (Ro) is to perform an aquifer test at the same flow rate at which dewatering will occur; however, an aquifer test conducted at such a high flow rate may itself cause a contaminant plume to migrate. Therefore, the dewatering flow rate required to achieve the necessary drawdown and the associated value of Ro must be estimated from an empirical relationship developed by Sichardt (Powers, 1992). Using values of hydraulic conductivity calculated directly from a site-specific aquifer test or from the EAR aquifer test database (see SOP Section II.C.1.), the Ro for an unconfined aquifer can be readily calculated using the following equation: RHhKo =−3000() where Ro and (H - h) are in meters and K is in meters per second (m/s). Note that in calculating hydraulic conductivity (K) from aquifer test data, the Division utilizes the base of the Biscayne Aquifer as depicted in Figure A-11 of SFWMD’s A Three Dimensional Finite Difference Groundwater Flow Model of the Surficial Aquifer System, Broward County, Florida (1992), as the saturated thickness (H). When Ro from Sichardt’s equation is added to the effective radius of the wellpoint configuration, and if the resulting value is less than the distance of the dewatering perimeter to the edge of the nearest contaminant plume, then it is reasonable to assume that the proposed dewatering will not cause the contaminant plume to migrate. If the resulting value is greater than the distance to the nearest contaminant plume, then further information is required for approval. The Dewatering Plan may be modified to include further hydraulic control, and analysis may be performed using a three-dimensional computer model. Dewatering Flow Rate A direct calculation of flow rate may be derived from the following equation: n ⋅ q H 2 − h 2 = (ln R − ln r ) π ⋅ k o e where n = the number of wellpoints, q = flow rate per wellpoint in m3/sec, re = effective radius of dewatering in m, H = the total head of the water table aquifer in m, h = the total head of the dewatered aquifer in m, Ro = radius of influence in m, calculated via Sichardt’s equation, and k = hydraulic conductivity, in m/s This equation is particularly useful to determine not only the total flow rate from all points (the value nq) but also the flow rate from each point (q). To correctly calculate Ro, equations generally assume that water is withdrawn from a circular area. Most dewatering activities, however, are from rectangular areas. Therefore, an equivalent radius of influence (re) must be calculated to make rectangular projects applicable: Broward County Board of County Commissioners Sue Gunzburger • Kristin D. Jacobs • Albert C. Jones • Ken Keechl • Ilene Lieberman • Stacy Ritter • John E. Rodstrom, Jr. • Diana Wasserman-Rubin • Lois Wexler www.broward.org Broward County Dewatering SOP Exhibit III Page 2 of 2 b re ab a re = π Example: Dewatering is required at a site in Broward County where Figure A-11 of SFWMD’s report indicates a total saturated aquifer thickness of 150ft (45.7m). The closest contaminant plume is identified at 1000ft (304.8m) away. It is proposed to depress the water table 15ft (4.6m) to excavate an area 100 feet (30.5m) long by 50 feet (15.2m) wide. The groundwater table is to be lowered to the base of the excavation using a pattern of wells along the rectangular perimeter. A total of 26 wells, each connected to the pumping system, are to be used. The hydraulic conductivity of the aquifer is 100ft/day (3.528 x 10-4m/s). From Sichardt’s equation, the resulting radius of influence would be: h = 45.7m – 4.6m = 41.1m Rmmxms=−3000 457... 411 3528 10 −4 / () Rmft==259 850 o To calculate the effective radius of the dewatering wellpoint configuration: ()()305..mm 15 2 re = π rmft==121. 40 e . When added to Ro, the total radius of influence is 890ft from the center of the dewatered area. Because the radius of influence is less than 1000ft (the distance to the nearest contaminant plume), the dewatering plan may be submitted to the Division for approval. And using 22nq Hh−=()lnRroe − ln , πk nq ()()45..7mm22−=411 ()()ln ()259mm −ln( 12.1 π 3./528xms 10−4 () m3 ft 3 gal nq ==0144.,, 439 313 = 2 282 s d min For n = 26 (i.e., 26 wells), the pump rate per well must be: ft 3 439, 313 3 ft gal q ===d 16,. 397 87 8 26 d min Broward County Board of County Commissioners Sue Gunzburger • Kristin D. Jacobs • Albert C. Jones • Ken Keechl • Ilene Lieberman • Stacy Ritter • John E. Rodstrom, Jr. • Diana Wasserman-Rubin • Lois Wexler www.broward.org TABLE 2 - Infiltration Gallery Design Facility Name: 7-Eleven Store No. 34816 Facility Address: 3701 Santa Barbara Blvd, Naples, Collier Co, FL 34104 FDEP ID: 11/9063983 Aquifer Characteristics Proposed Gallery Sizing K= 6.97 ft/day Surface Area (SA)=WxL b= 50 ft Depth= 4 ft T= 348.5 ft2/day Width= 30 ft SY= 0.25 Length= 215 ft DTW= 5 ft bls SA= 6450 ft2 Design Flow Rate (Qd) (gpm)= 62 11,959 ft3d Recharge Rate (RR)= Qd/SA 1.85 ft/day Gallery Length Confirmation and Safety Factor Using the formula from the SFWMD/s 2014 ERP Information Manual to calculate the gallery length required given the proposed depth and width: V ____________________ L= K*(H2*W+2H2*Du-Du2+2H2*Ds)+(1.39x10-4)*W*Du where: L=Length of trench required in feet Input Data V=Volume treated in acre-inches V= 3.3 acre-in. =assumed to be total flow for one day W= 30 feet W=Proposed trench width in feet K= 0.00008 ft/sec K=Hydraulic conductivity in ft/sec H2= 5 feet H2=Depth to water table in feet Du= 4 feet Du=Non-saturated trench depth in feet Ds= 0 feet Ds=Saturated trench depth in feet Length= 107 feet SA= 3217 ft2 Safety Factor= Length Used/Calculated Length =2.00 At an estimated flow rate of 62 gpm and depth-to-water of approximately 5 feet below land surface, an excavation area of approximately 3,217 square feet would be required for on-site discharge of groundwater from the UST area, and 6450 square feet would be needed to meet the safety factor requirement of 2. As such, there is no onsite retainage of storm water and due to construction activities on the small parcel, it is not feasible to install a temporary drainage feature that meets the required safety factor. PUMPAGE CALCULATIONS Facility Name: 7-Eleven Store No. 34816 Facility Address: 3701 Santa Barbara Blvd, Naples, Collier Co, FL 34104 FDEP ID: 11/9063983 USTs Daily pumpage (from Table 1) = 89,452 gpd = 0.08945 mgd Total pumpage = 10 days x 0.08945 mgd = 0.8945 million gallons Product Piping, Dispenser Sumps, and Canopy Footers Daily pumpage (from Table 1) = 242,463 gpd = 0.24246 mgd Total pumpage = 20 days x 0.24246 mgd = 4.8493 million gallons Total Project Pumpage = 5.7438 million gallons.
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