(plaintiff brought suit that agency’s letters regarding Clean Water Act and municipal water systems written to Senator were rulemaking in violation of Administrative Procedures Act (APA); court held plaintiff had sufficient standing to bring claim; court agreed with 9th Circuit precedents that no deference should be granted to agency when determining whether APA has been followed and de novo review should be given in determining whether agency action was legislative rulemaking imposing new rights or duties requiring notice and comment procedures versus interpretive rules which state what the agency thinks the statute means and reminds affected parties of existing duties; court held agency has no preexisting legal norm or lawfully promulgated legislative rule supplying the basis for the agency’s prohibition on bacteria mixing zones, which violated APA in bypassing notice and comment procedures; likewise the agency’s new blending rule was also in violation of APA for same reasons; court also granted plaintiff’s request to strike down agency’s blending rule as exceeding its statutory scope by imposing secondary treatment regulations on flows within facilities even if APA rulemaking followed; issue remanded to agency for further consideration).