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<br />000276 - <br /> <br />Several other homes exist in the valley that rely on septic systems that either have been or will be <br />impacted by the rising groundwater trend in the Yuma Valley. <br /> <br />In the future, several newly constructed subdivisions, and several older subdivision in the Yuma <br />Valley could experience problems similar to those in Hacienda Estates if the trend of rising <br />groundwater levels in the Yuma Valley isn't reversed. <br /> <br />Current zoning plans allow for high density housing in the north eastern portion of the valley. <br />The rest ofthe valley is to be zoned for agriculture purposes. However, parcels as small as forty <br />acres would be allowed. Thus, severafhomes would be expected to be constructed throughout <br />the valley in the'.future. In addition, some businesses are locating in the valley. The new Super <br />K-Mart would be one example where special drainage had to be provided in order to allow the <br />facility to be constructed without potential damage to their parking lot, and to prevent subsidence <br />of the foundation for the store from occurring. <br /> <br />Question 3: Has there also been an increase in water usage, either through more acreage <br />dedicated to crops, conversion of lower-water use crops to higher-water use crops or more <br />acre-feet of water used per acre for other reasons? <br /> <br />Answer: Figure 1 is a plot of the volume of irrigation water applied to farms and total crop <br />evapotranspiration for Yuma Valley from 1970 through 1998. Also shown on the plot is the <br />maximum irrigation recharge to the groundwater system, which is taken as the difference <br />between water applied and crop evapotranspiration. Figure 2 is a similar plot for Yuma Mesa. <br /> <br />From Figure 1, irrigation recharge varies up and down from year to Year, with a maximum year- <br />to-year change during the period of 40,000 acre-feet. Overall, recharge in Yuma Valley has <br />increased slightly since 1970 due to a slight increase in water applied and a slight decline in crop <br />evapotranspiration. The best-fit line through the recharge data has a rising slope of about 1000 <br />acre-feet/year. <br /> <br />From Figure 2, irrigation recharge varies up and down from year to year on Yuma Mesa. The <br />maximum year-to-year change for the period was 46,000 acre-feet. Most of the year-to-year <br />change is due to variation in the amount of water applied. The crop evapotranspiration varies <br />much less from year to year. There is no clear, sustained trend in recharge for Yuma Mesa. If <br />anything, recharge has declined very slightly from 1970 through 1998. The slope of the best-fit <br />line through the data is about -130 acre-feet/year. <br /> <br />In general the Yuma Mesa's primary crop is citrus. Citrus normal maintains reasonably good <br />yields over a period of 20 to 30 years, thus the consistency in consumptive use on the mesa. <br />However, the citrus is planted on sandy soils and thus requires high irrigation application to <br />sustain the trees. Much of this additional water application percolates into the groundwater <br />underlying the Yuma Mesa. This has resulted in the buildup of a large groundwater mound on <br />the mesa over the years. This mound is considerably higher than the surrounding valley lands <br />which causes water to flow from the mound into the groundwater aquifer underlying the valley. <br />