20 January 2014 KG

Transcription

1 2 January 24 KG2-85 Mike Hollebrands Meiners Oaks Water District 22 West El Roblar Drive Ojai, California 9323 Re: Well interference measurements and modeling Greetings Mike: The following discussion serves to summarize the results of our pumping evaluation and interference between several of the wells near MOWD Well Nos. 4 and 7. This work is conducted at your request and incorporates data from our March 22 testing and January 24 testing. The tests consisted of a series of pumping operations of the MOWD wells to obtain information regarding aquifer characteristics under different hydrologic conditions. Most notably, the conditions of testing during March 22 were during a period of higher static water levels (depths to water 33 feet in MOWD wells) compared to the January 24 testing where deeper static water levels were measured (66 feet to water). Among other utility, the depth to water is a measurement used to determine storage in the basin and unconfined aquifer thickness. These parameters directly relate to well production, aquifer transmissivity, and the degree of interference between wells pumping at different rates under the variable conditions. Ultimately, it appears that the aquifer yields less water to wells when water levels are low due to the decreased transmissivity (a product of aquifer thickness [b] and hydraulic conductivity [K] of the aquifer material [T=Kb]) and increased pumping lift (TDH) of fixed-frequency drive pumps. As contrasted to higher water level conditions, the cone of depression surrounding a pumping well during low water level conditions is deeper near the pumping well but not as wide. This is more typical of unconfined systems. nterestingly, at distance, the drawdown at high rates during high water levels is similar to the drawdown at low rates during low water levels. The following pages present our discussion of testing and measured interference between wells, modeled interference between wells, and a discussion of potential effects of the interference. KEAR GROUNDWATER P.O. BOX 26 SANTA BARBARA, CALFORNA 932 TELEPHONE: (85) JORDAN@KEARGROUNDWATER.COM CALFORNA REGSTERED PROFESSONAL GEOLOGST N. 696 CALFORNA CERTFED HYDROGEOLOGST N. 749

2 Testing and measured interferences During the testing periods, the MOWD Wells were tested at various rates and durations based on demand and well capacity. Typical durations were one day of pumping, which can be expected as normal operations. Well testing in March 22 was conducted under relatively wet conditions, with depths to water in the MOWD Wells of 33 feet below the reference points. Well testing in January 24 was conducted in the middle of a third consecutive year of deficient rainfall, just weeks before a Drought Emergency would be declared in California. Water levels at that time were 66 feet below the reference point in the MOWD Wells. During March 22, a distance-drawdown curve was prepared based on distance from pumping wells and drawdown observed in non-pumping wells. Graphical depictions of these observations are presented on the attached charts, with results in Table. Well Table Observed Drawdown - End of full day of pumping March 22: Well 4 Pumping at 82 GPM, Aquifer Thickness ft January 24: Well 7 Pumping at 35 GPM, Aquifer Thickness 67 feet MOWD ft 6.43 ft MOWD 7 2. ft 7.3 ft Gramkow South Gramkow North.92 ft ft.27 ft Raw data were adjusted for pressure and other corrections, and subjected to standard aquifer testing analyses to solve for transmissivity and storativity. AQTESOLV data sheets showing graphical Tartakovsky-Neuman solutions for these parameters are attached. These indicate an expected reduction in transmissivity with less water in storage and an increase in storativity as the aquifer behaves in an increasingly unconfined nature with lower water levels. Results are be summarized below: Drought conditions: Aquifer thickness, b = 67 feet Transmissivity, T = 52.6 ft 2 /min (567, gpd/ft) Storativity, S =.985 Wet conditions: Aquifer thickness, b = feet Transmissivity, T = 2.6 ft 2 /min (,3, gpd/ft) Storativity, S =.3723 KEAR GROUNDWATER P.O. BOX 26 SANTA BARBARA, CALFORNA 932 TELEPHONE: (85) JORDAN@KEARGROUNDWATER.COM CALFORNA REGSTERED PROFESSONAL GEOLOGST N. 696 CALFORNA CERTFED HYDROGEOLOGST N. 749

3 Model and calculations Using data from the testing and various hydrololigc conditions, KG modeled and caclulated various scenarios to estimate the effect of theoretical pumping of the Gramkow Wells on MOWD Wells 4 and 7 at various rates. Rates of 3 and 6 gpm were presented for both Gramkow Wells under both wet and drought conditions. Calculation tables are attached, with a summary of modeled interference presented below in Table 2. Table 2 Summary of Theoretical nterference Calculations Pumping Duration, Day Well, condition, rate MOWD 4 MOWD 7 Gramkow South, drought, 3 gpm Gramkow North, drought, 3 gpm Total Gramkow South, wet, 3 gpm.7.7 Gramkow North, wet, 3 gpm.2.2 Total Gramkow North, drought, 6 gpm Gramkow South, drought, 6 gpm.67.7 Total.4.4 Gramkow North, wet, 6 gpm Gramkow South, wet, 6 gpm Total KEAR GROUNDWATER P.O. BOX 26 SANTA BARBARA, CALFORNA 932 TELEPHONE: (85) JORDAN@KEARGROUNDWATER.COM CALFORNA REGSTERED PROFESSONAL GEOLOGST N. 696 CALFORNA CERTFED HYDROGEOLOGST N. 749

4 Discussion Based on the analysis described above, the area of MOWD Well Nos. 4 and 7 exhibits variable responses to pumping under various hydrologic conditions. nterference observed and modeled between actual and theoretical pumping wells indicates interference on the order of. ft individually and. ft cumulatively with the greatest affects being estimated when wells are pumped at high rates during drought conditions. Given the specific capacity of the MOWD Wells, the effect of the interference on production can be estimated. Hence, during drought periods when interference would be greatest, MOWD No. 7 exhibits a specific capacity of 47. gpm/ft drawdown (344 gpm/(75.7 ft pwl ft swl)). f an additional.4 ft of drawdown is induced by cumulative pumping of adjacent private wells, then the theoretical reduction in capacity is estimated at 53.7 gpm. f MOWD No. 4 exhibits a specific capacity of 6 gpm/ft and the.4 ft of drawdown is induced due to pumping of adjacent private wells, then the theoretical reduction in capacity is 68.4 gpm. Hence, the cumulative effect of pumping adjacent wells at high rates (6 gpm each) during drought conditions could be a reduction in MOWD groundwater production capacity of upwards of 22. gpm. Lower end estimates of interference effects could be as low as one tenth (a 2 gpm reduction) of the higher end estimates. Further testing can be conducted to calibrate these modeled values. We trust that this information will be of assistance in deliberations and working toward optimized management of a shared groundwater resource. Do not hesitate to contact me with any questions. Best Regards, Jordan Kear California Certified Hydrogeologist No. 749 (85) KEAR GROUNDWATER P.O. BOX 26 SANTA BARBARA, CALFORNA 932 TELEPHONE: (85) JORDAN@KEARGROUNDWATER.COM CALFORNA REGSTERED PROFESSONAL GEOLOGST N. 696 CALFORNA CERTFED HYDROGEOLOGST N. 749

5 r 54 t o::t c 52-3: o :e ::t :a.:-----~.~~ ; i48 Response to MOWD Well No.7 Pumping at 35 gpm 3-4 January -i- KG KEAR GROUNDWATER ,.- 5._ iqj t ~ 49.5 ~ ~~~;;~:::~:!il --- ] j :::::-:----._--f Uj ~ J </ LL _. ~ , , , o , y r--~-49 4 MOWD NO.4: 72 feet away. Gramkow North: 665 feet away

6 ~~----~------~----~------~-- --~------~----~.: ~ l~~ ~! c: ~ o "'C ~ e C (U U c: ro ;).- c g -; 3 QO C "Q. E ~----~----~ ~------~----~ a E '::. ~ ~ ii v{" ~ ~--lj--l- \~l_~_ c,, 'i"'l> +.- ~. <P... ~ t % - ~ _----_ _----_r~--~~----_r----_+.- o ~----~----_ _----_ _----_r----_4~---~l q a a N M.q ell) UMOpMeJQ

7 D i s P a c e m. e n t ( f t ). L----"---'--'-...L.li-~ ' L_L.l...l._'_LL..l._L_l. LLLl.l..J. L_._L_L_L_L.LLU... Time (min)..e+4 WELL4 TEST Data Set: C:\...\MOWD4 on Gramkow north.agt Date: /7/4 Time: 9:22:42 Company: KG Client: MOWD Project: KG2-89 Location: Ventura River Basin Test Well: MOWD Well 4 Test Date: 3/27/2 PROJECT NFORMATON -- AQUFER DATA Saturated Thickness:. ft Anisotropy Ratio {KzlKr}:. - WELL DATA Purnpinq Wells Observation Wells X (ft) Gramkow North Well Name X (ft) y (ft) Well Name MOWDWell y (ft) SOLUTON Aquifer Model: Unconfined Solution Method: Tartakovsky-Neuman T = 2.6 ft 2 /min S =.3723 ~v = n n7n~? K7/Kr = n nn

8 . - D i s. p a c e m. e n t Q] c~[ ~ M U,l" [ =. ''''' f- -, ~ -' - ( f t )..E-4... Time (min)..e+4 WELL 4 TEST Data Set: C:\...\MOWD7 on Gramkow north.aqt Date: /7/4 Time: 9:22:48 Company: KG Client: MOWD Project: KG2-89 Location: Ventura River Basin Test Well: MOWD Well 4 Test Date: 3/27/2 PROJECT NFORMATON AQUFER DATA Saturated Thickness: 67. ft Anisotropy Ratio (KzlKr):. - WELL DATA Pumping Wells Observation Wells X (ft) Gramkow North Well Name X (ft) Y (ft) Well Name MOWDWell Y (ft) SOLUTON Aquifer Model: Unconfined Solution Method: Tartakovsky-Neuman T = ft 2 /min S =.985 Sv = OO?:ifiq K7/Kr =

9 GRAMKOW NORTH WELL DSTANCE-DRAWDOWN CALCULATONS: MOWD south well field - Drought 67 ft aquifer thickness & Wet ft aquifer thickness WELL RATE T S TME Radius from u W(u) Drawdown STE (gpm) (gpd/ft) (days) pumping well GRAMKOWN MOWD E MOWD A7E GRAMKOWS r, E WELL RATE T S TME Radius from u W(u) Drawdown STE (gpm) (gpd/ft) (days) pumping well GRAMKOWN MOWD E MOWD E GRAMKOWS E WELL RATE T TME Radius from u W(u) Drawdown S STE (gpm) (gpd/ft) (days) pumping well GRAMKOWN MOWD E MOWD E GRAMKOWS E WELL RATE T S TME Radius from u W(u) Drawdown STE (gpm) (gpd/ft) (days) pumping well GRAMKOWN MOWD E MOWD A2E GRAMKOWS E

10 GRAMKOW SOUTHWELL DSTANCE-DRAWDOWN CALCULATONS: south well field - Drought 67 ft aquifer thickness & wet ft thickness WELL STE GRAMKOWS RATE (gpm) 3 S TME (days) Radius from pumping well W(u) Drawdown T (gpdlft) 567. MOWD E MOWD E GRAMKOWN E T (gpd/ft) 567 S W(u) Drawdown. MOWD E MOWD E GRAMKOWN E T (gpd/ft) 3 S W(u) Drawdown. MOWD E MOWD E GRAMKOWN E T (gpd/ft) 3 S W(u) Drawdown. MOWD E MOWD E GRAMKOWN E WELL STE GRAMKOWS WELL STE GRAMKOWS WELL STE GRAMKOWS RATE (gpm) 6 RATE (gpm) 3 RATE (gpm) 6 TME (days) Radius from pumping well TME (days) Radius from pumping well TME (days) Radius from pumping well u MOWD 7.5 u ~5. u 3.25 u 7.5