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Washington State Department of <br /> r. HEALTH <br /> Minimum Lot Sizes <br /> Minimum lot sizes have been increased by 500— 1000 sq ft, depending on soil type. <br /> 0- <br /> �U� Minimum Usable Land Area <br /> New lots being served by OSS must have a certain land area that is usable for septic system <br /> installation and repairs. This land cannot be underwater, paved, impacted by an easement, or <br /> otherwise unusable for the OSS. <br /> g Field Verification of Proprietary Treatment Products <br /> I1:�� <br /> Manufacturers of OSS using disinfecting and nitrogen-treating proprietary treatment components <br /> must verify the efficacy of their products in the field. This will entail collecting samples from 25 <br /> installations in Washington State to evaluate their performance under field conditions. <br /> 9�A <br /> Product Supply Chain <br /> Proprietary products may be retrofitted with components they were not tested with if there is a supply <br /> chain or other manufacturing disruption. The manufacturer must provide a statement from an <br /> engineer that the retrofit will not impact OSS performance or maintenance. <br /> Resilience <br /> Sea Level Rise — LHOs in Puget Sound counties are required to identify areas where sea level rise <br /> may impact horizontal setbacks to OSS resulting in an increased risk to public health. <br /> Phosphorus — LHOs in Puget Sound counties are required to identify areas where phosphorus has <br /> been found to be a contaminant of concern. They must identify measures to protect public health and <br /> water quality from phosphorus from new and repaired OSS in these areas. This is already an <br /> established requirement for areas where nitrogen is a contaminant of concern. <br /> Nitrogen-based minimum lot size for small lots — Lots may be allowed to be made smaller than the <br /> minimums if certain safety measures are met and nitrogen treatment is installed on the OSS. <br /> Page 2 of 2 <br /> 22 <br />